Hey friends, welcome back to theCUBE's live coverage of AWS re-invent 2022 in Sin City. We are so excited to be here with tens of thousands of people. This is our third day of coverage, really the second full day of the show, but we started Monday night. You're going to get wall-to-wall coverage on theCUBE.  I'm Lisa Martin and I'm here with Paul Galen. Paul, this is great. We have had such great conversations. We've been talking a lot about data. Every company is a data company. It has to be a data company. We've been talking about developers, the developer experience and how that's so influential in business decisions for businesses in every industry. And it's a key element of what's going on here on the floor at re-invent is developers, the theme of developers just permeates the show. Lots and lots of boots here devoted to DevOps and Agile approaches. And certainly that is one of the things that the cloud enables is your team to rethink the way they develop software. And that's what we're going to talk about next. We have two guests from Split. Split.io is the URL if you want to check it out. Chris DeMars joins us, developer advocate. Chris, great to have you. And Pierre Mass, VP of engineering. Guys, thank you so much for joining us on the program. Thanks for having us. Thanks for having us. Talk to us, Pierre. We'll start with you. What, for the audience that might not know Split, what does the company do? What's the value in it for customers? What are you all about? Sure. So in very simple terms, for those who are familiar, we do feature flags, feature management. And experimentation. And essentially that two essential features of the Agile transformation, as you were mentioning, and elements that really helps getting as much as we can from the team in terms of productivity and in terms of impact. And we basically help with those elements. So that's a very short story. Excellent. Very nice. Chris, you were saying before we went live, you do a lot of speaking at conferences.  And in front of large audiences as the developer advocate, what are some of the key requirements you're hearing from the developer community that organizations need to be encompassing? I think community is key. Like community is at the forefront of developer advocacy and developer relations. Like you want to go where the developers are and developers want to hear those stories in those personalized pieces of the puzzle. And when you're able to talk about modern web and software technology and loop in product with that and still keep talking about those things and bring that to them, like that is on top of the list when it comes to developer advocacy and being embedded within the developer community. Tell us about feature flags because I would assume that for our viewers who are not developers, who are not familiar with Agile technology, the Agile approaches, that might be a new term. What are feature flags? How do you use them? Sure. I can start with that. So feature flag is a tool that you embed in your code that allows you to control the activation of your code, essentially. And that allows you to really validate things in a much better and sort way and also attach measurement to it. So when you're writing your new feature, you just put essentially a new statement around it. If my feature flag is on, then I actually do all those things with softs and I don't do any of those things. And then within our platform, then you can control the activation. Do you want to turn it on for yourself just to try it out? Do you want your QA team to start validating it? Do you want 5% of your users 10% and start seeing how they're interacting with the product? That's what feature flag is. It's an amazing piece of any part of the stack, right? Because I'm a web accessibility and UI specialist and being able to control the UI with a feature flag and being able to turn on and off those features based on percentage, locale, all of those things, it's very, very powerful. What are some of the scenarios which you would use feature flags? You have a testing? Yeah, yeah, we actually, you can imagine, we use it for pretty much everything. So as Chris was saying, in the front end, everything you want to change, you basically can validate and attach measurement so you can do AB testing so you can see the impact, you can see if there is a change in performance. We use it also for a lot of backend services and changes and a lot of even infrastructure changes where we can control the traffic and where it goes so we can validate that things are operating the way that they should before we fully turn them on forever. It can be as small as having a checkout button here and then writing an AB test and running an experiment and moving that checkout button somewhere else because then you can get conversion rates and see which one performed better to a certain amount of people. And whatever performed better, that's the feature you would go with. Chris, talk about the value, the impact in feature flags for the developer from a developer experience perspective, a productivity perspective. So I think that having that feature and being able to write that UI, let's say that you have a checkout button and there's specific content, there's verbiage on that checkout button and then let's say that another team within the organization wants to change that because the conversion is different. You can make those changes, still have it in production and then have it tested so you don't have to cut specific branches like test URLs to give to QA. You can do all of that behind that flag and then once everything is good to go, push it out there and then based on those metrics and that data, see which one performs better and then that's the one that you would go with. One of the things with feature flag and it goes to like our main theme of what a relief is that it gives autonomy to the teams and to the developers, enables them to move independently from others so their deployment can go but their code is not activated until they decide to and so they are not impeding anybody else. It makes releases a lot safer, a lot simpler and it gives a lot more speed to everybody because when you do releases with five teams, 10 teams pushing the code all at the same time, you have such a high risk of breaking something that it's a huge effort and it requires a lot of attention from a lot of people. If anything happens, all those teams need to investigate. When you decouple all those things, the deployments are essentially not doing anything per se until every individual team activates those things independently so if anything goes wrong, only them are affected and they don't have to depend on anybody else to get their thing out so it really helps them making their life a lot safer and gives them a lot more speed because they have autonomy. So why come to reinvent? What do you get with this audience that you don't get elsewhere? Why? To reinvent, I think like reinvent in the cloud and the WS is a lot about getting speed to companies to build better product and faster and essentially like the tool we provide and the technology and the platform we provide is really at the heart of that team in itself and so that's why we feel we have really great conversation with all the people on the floor. The people here have the right mindset to adopt who you are. It's very much, for me, it's very much community and networking. I love developer community and just community in general is my lifeblood. That's why I travel so much and I talk about these things and I'm with people and if it's not about the product, it's the story and the story is what gets people and that's why I love being here and being with my team and it's amazing. And what is that story? If you had an elevator pitch to give, what would you tell me? Oh, if you were in a late release or deploy at night, I've been there. I'm sure you've been there. It doesn't matter what you're doing. We don't want to be up till two, three in the morning doing those things, right? Our product helps alleviate those stresses and I'm talking about accessibility.  Well, stress and anxiety go hand in hand and you want to alleviate that all across the board for everybody involved. As you see organizations shift agile technologies and to parallel development and continuous release cycles, what are some of the biggest barriers they encounter in changing that mindset? Oh, what do you think? It depends on where they are in the organization. The agile transformation is a journey and it's also a change of mindset. It's a change of process. So depending on where they are, and they might have some areas where they need a little bit more effort in those directions, what we see is that feature flag just the control of the layout. It's usually something that's fairly easily adopted. Thinking about measurement and attaching measurement to it is often something that requires a little bit more thinking. Like engineers are not really used to thinking about A.B. testing. It feels like more of a product management thing, but A.B. testing is important also for performance information. Like errors and all those things. There is a lot of risk management to be done. We do that through monitoring with APMs, but with feature flag and with split, you can do that at a feature level and it really gives a great insight. And that's usually something that takes a little bit more digestion from the developers to really get their mind around it and get to it, but there's a lot of value to it. I'm looking at the split.io website and I like the tagline. Shorten time from code to customer. As customers in any industry, as consumers, we have this expectation that we can get whatever we want anytime 24 by seven and it's going to be a relevant experience. So it sounds to me like from a speed perspective, there's a lot of business impact that split can help organizations make from getting releases faster, getting cut faster time to market, delivering what customers expect because we all expect real time these days. Nobody wants to wait. That's right. Yeah. I think that has to do with going back to the decoupling of things, not having to go through so many teams to have it tested and getting away from all the meetings about meetings to review the metrics, right? We all love meetings about meetings. No. Right, exactly, exactly. So having, being able to take that away and being able to push all of that stuff into production, getting it tested while it's in production and then being able to turn those features on, it's already there without having to do another deployment. And I think that's really powerful, to me at least. Does your solution have value at the security level as well? Yes, so that's one of the particularities on the way we do things is like the way you control the feature flag, you have kind of two ways of doing it. Either the piece of code, the SDKs that we provide the library, we provide you that you put in your code, could come back to your platform and check. The way we do it is we send the rules back to the SDK. So the whole evaluation is local, the evaluation is extremely fast and it's very secure because it's all happening within your environment. You never have to share any information, no PIA whatsoever, contrary to some of the other tools that you might find on the market. So the theme of the booth is what a release, what a relief. What are some of the things that you're hearing as you're engaging folks on the show floor this week? What is aura photography and can I take a picture? I think just a lot of stresses of the release cycle and having to go through so many teams, like I feel like that's a common theme that I've heard of. Yeah, we see a number of teams, organizations that still have really big deployments with a lot of teams basically coming together, pushing their code together and there's a lot of pain in it. It's a huge effort by huge teams. You get 10, 20 people that have to have watched over it at always weird hours and I think there is a lot of pain to that and that resonates a lot with people. Then when we talk about monitoring at a feature level, that also helps a lot. I was part of organizations before where we had a dedicated staff engineer to just monitor and fix performance on a daily basis because it's such a huge problem and it affects so much the performance of the company and so essentially you have this person that has to look at the performance being degraded today with the deployment up yesterday and what went out yesterday and you have so many things that went out, it's so hard to control. With what we provide, we tell you exactly which feature flag is responsible for degradation and so you don't need that person to focus on that anymore and you can focus on delivering value a lot better. I think it also might take away the need for extensive release notebooks and playbooks. When you do bring all those teams together, it's certain people that are in that meeting and there's a PDF saying, all right, we check this off the list, we check this off the list. I think that might alleviate some of that overhead as well. Streamlining processes, process efficiencies, workforce productivity improvements, big impact. And that gets code quicker to the user. You talk about decoupling deploy from release. What do you mean by that? What's the value? So the deployment in my definition is essentially getting the code out to production. The release is activating the code in production. And often people do both of those things at the same time. But there's a huge risk when you do that because if anything goes wrong, now you need to revert everything which is not a short operation often and takes a lot of effort. So now if you can basically push your code to production but separate the activation of it, the release of it, then it goes a lot faster. You have a lot of autonomy and decoupling and if anything goes wrong, it's the click of a button at the top. So like there's a lot of safety that comes with it. And we know that any outages has a high cost for all the companies. So it's like if you can reduce the outage to like five seconds, right? It's a lot better than basically several hours. Can you talk about the value out of split versus DIY and where are most of your customers in this process?  The one thing I hear a lot is we rolled our own A-B testing and feature flagging system. But some of the issues I've seen and I've heard of that, they don't have all those metrics or they have to work with a specific data team to get those metrics. And then you go back to having those meetings about meetings where you have a data team that's putting together a report that is then presented to you and then that's got to be presented to a stakeholder. And then that stakeholder makes a decision whether to turn on feature A or feature B, right? Our product, from my understanding, is we have those metrics already built in and you can have that at your disposal. The other thing I would add to that is like, we see a number of people, they start on the feature flag journey just because they have a high risk thing that they need to put out. So they do the minimal thing to basically control it somehow, but it works only in one part of the stack. They can't basically leverage it anywhere else. And it's very limited in capability so that it just serves the purpose that was needed at that time. They don't have a dedicated team to manage it. So it's just there that is very constrained and it's not supported effectively. The other thing is like for those companies is like they have a question to us themselves. It's like, do they want to invest resources in managing that kind of tool? Or is it not so close to their business that they want essentially to have vendor deal with it at a much lower price and they would have to invest resources for them to support it? It sounds like feature flags are kind of a team building. And we have a team building dimension to them. Yeah. It takes a team for sure. Yeah, and then once you add like AB testing and the feature flag, it's the collaboration between product management and engineering. It can go even further like to executives like to basically this, you know, view the impact, understand the impact. So it goes from the control to the risk management to the product and to the impact and measuring the flow of delivery and the communication around it. Here we are at re-invent. So many thousands of people, as I mentioned, we're on the second full day of the event. What have you heard from AWS that really excites you about being in their ecosystem? Any news in particular that jumps out at you that really speaks to improving that developer experience? Because we've heard a lot of focus on the developer. Yeah. I haven't heard much. Have you? So I arrived yesterday. I haven't followed yet all the announcement. I'm just like running on the news. Yeah, yeah. So I'm thinking on the booth at the same time. I stopped counting at 15 during the keynote this morning. Yeah. I can't keep up. There's so much happening at one time. So much. This event is a canon of content. A canon of news. Exactly. Re-invented is hard. But yesterday they've spent so much time talking about data and how, and I always think every company today has to be a data company. It'd be a software company.  And sometimes I'll talk with retailers that think of themselves as technology companies that do retail. And I love that. But that's what companies have to enable these days is companies to become technology companies, deliver code faster to customer because the customer's demanding it. We're not going to want less stuff slower. Yeah. I mean, it's so essential I think for me. Like I joined Split because of that premise. It's like every company now is a software company. And every company has really to compete in innovation. You know, all those banks, Capital One, like we see it a lot in the financial industry where our message resonate extremely strongly is really in a high competitive environment and they have to be innovative. And innovation comes when people have speed and autonomy. And if you basically provide that to teams and the tools to basically get some signals and some quick feedback loop, that's how you get innovation. Like you go and decide what to build, but you can basically provide the tools to enable them to think about. You can experiment more flexibly, faster. And developers have to be empowered, right? I think that's probably one of the number one messages I've heard at all the shows we've done this year. How influential the developer is in the direction of the business. Autonomy and empowerment are two main factors. Because I'm a front end developer at heart and I want to work on cool stuff. And we're doing cool stuff. Like we are doing cool stuff. Now we can't talk about all of it, right? But I think we're doing a lot of cool things at Split. And I'm really stoked to be a part of the team and grow developer relations, grow developer advocacy and be along for the journey. Yeah, I love that. Last question for both of you. Same question. If you had a bumper sticker, you were going to put it on a fancy shiny new car, car of your choice. About Split, what would it say? P.A., start with you, then Chris. Bumper sticker. On the spot question. On the spot question.  I think that the first step for teams is like, you can have a message that's very, like even further, you know, the actual transformation is a journey. And I basically tell people, you know, you need to first crawl, walk and run. And I think that what a release, what a relief is a good step to like getting to the walking. And I think like that would be the first bumper sticker before I get to the further one about AB testing and, you know, innovative. Love it. Chris, what would your bumper sticker say? It would say split software, feature flags for the masses. Heart stop. Mic drop. Done. Awesome. Thank you so much for joining Pallami on the program. It's been outstanding. Introducing split to our audience, what you do, how you're impacting the developer experience and ultimately the business and the end customer on the back end who just wants things to work. We appreciate your insights. We appreciate your time. Thank you so much for having us. Our pleasure. For our guests on Paul Gillan. I'm Lisa Martin. You're watching the queue, which you know is a the leader in live enterprise and emerging tech coverage.


Kaleb here with Layton Sports Cards next up tonight. Tumki H going with box 12 of the Sports Card Almanac volume number two personal box edition. Here we go. What's up, Zee? You're only a few boxes late, man. Thanks again so much, box number 12. Tumki H, I appreciate it. Poor cut-shot of slicing the side first. Yeah, gotta change up my knife blade. It appears for the rest of them. We'll switch it up in a minute. Empty, guys. Thanks again before I slice off my finger. Using that dull blade. Lucky number 12. Of course, this was grabbed up right away. Oh, that's sick. That is sick. From iMac. Ooh, rookie, patch, autograph, Jamar Chase. 52 of 99. That is awesome. Pasty. Tumki H, congratulations, box number 12.  Nice iMac on card auto, Jamar Chase. Beauty there. Beauty 1099. Facts, JB. I'm familiar with those. So it's 600 a spot, Paul. And thanks again so much. Really appreciate that there. We'll have them all protected up and right out to you.


Welcome to drinks made easy we recently launched a new series called pop-up pub and for our first guest We have the brilliant comedian Greg proofs take a look. Welcome to pop-up pub the mobile speak easy Where we talk with interesting people you also you're known for Star Wars for doing one of the two voices Yes, of the enough so how did how did that come about they're getting ready to shoot the phantom menace Which as you know, it's the finest of all the Star Wars movies when you didn't I remember for Christmas Did you did you have an interaction with Tim Burton? No, I was a I was a monsters and monster voices in it. Yeah, and I sang believe it or not For the episode we created a new drink for Greg called the Greg proofs Maui Wally and here's how you can make it To build your great proofs Maui while you start by adding one and a half ounces of Tito's vodka Next you'll add one ounce of fresh pineapple juice or we recommend dole if you don't have fresh pineapple juice and One tablespoon of cocoa Lopez Next you'll add half an ounce of half and half and You'll cap that off into a shaker tin full of ice and give it a good shake Strain your cocktail into a martini glass and then you'll garnish with some chocolate shavings And there you have the Greg proofs Maui Wally cocktail Thanks so much for watching and please remember to always drink responsibly because everybody likes to make friends But no one likes to make them in a prison shower. We're gonna need to do another one of that. That was perfect. No, it wasn't


And I'll tell you one of the biggest secrets to dressing well is to not care at all what a woman thinks about the way you dress, because if you think about it, so much of what your clothing communicates is what your social status is within your tribe. And we'll talk about tribe a little bit further down, but the value of men within the tribe is always, always, always, or at least almost always, but mostly always determined by the other men within the tribe. It's not by the women. Women will reinforce that, but it's not determined by the women. And the problem that most men have, whether it comes to pick up and just trying to define their self-worth by how many women they can bed, or trying to dress in a way that's attractive to women, is that we're allowing our value to be determined rather than be reinforced by a relationship with women. When it should be something that's reinforced by the tribe. For me, that's my God, that's my country, that's my family. Those are other variables, but it's your tribe, not just, who's this hot person and what does she think of me and does she like what I'm wearing? Does that make sense? Okay. So I'm going to show you some ways that we can actually see the difference here. What's your reaction to a photo like this? See a dude putting on makeup, right? Little bit kind of uncomfortable. Maybe you shouldn't feel uncomfortable because we live in a progressive world and I don't know what to think about this and blah, blah, blah. But viscerally, you're just, that just doesn't look right, right? Because he's accentuating things that are visually appealing. By making his eyes look bigger, he looks more innocent. He's got soft skin tones. It's not indicative of hard work. He doesn't look like he's willing to embrace any sort of physical risk. There's nothing there about a protector or a provider. And you see a woman putting makeup on and it looks fine. It looks great. Okay, let's take it one step further and you see an older gentleman who's getting a little bit of makeup put on and you see this in the context of, okay, he's probably a broadcaster, maybe he's a politician who's going on national news. It's not that big of a deal. You can start to see a little bit of the context of it. This is kind of a neutral, right? It's neither good nor bad. It's just making sure that things are good. All right, what do you think about these guys? That's makeup, right? That's a whole ton of makeup. But that is a whole different story that they're telling. Is that appeal or is that power that they're communicating? That's power, right? You think you'd want to go into war against those guys?  Right? No, that's a whole different story that they're telling because of what they're doing with the same objective content. That's the power of style. That's the power of understanding the difference between visual power and visual appeal. These guys are masculine, dominant, intimidating men as opposed to the guy before that was neutral, the one before that who was effeminate. So that's one of the big differences. All right, let's go a little bit further with this. What do you think? Power or appeal? Appeal, okay. I would say there are a few things in this that are indicative of appeal. You've got all the lacing, right? He's got the tights on, he's got the white gloves, he's got the powdered wig, the mole. This guy does not look like he has ever been anywhere near a day of hard labor, right? Not even close. And even then when this was culturally appropriate, you think of like the scarlet Pimpernel as kind of the good balance between this refined dandy versus the rugged individualist who was actually going out and doing things. Even then, this was still kind of a weird way to communicate masculinity, but take this similar outfit to the next level. What do you think? Power or appeal? Yeah, but he's wearing lace. He's wearing skinny pants. He's got a powdered wig on. Why is it power instead of appeal? Colors, okay? Cool. Go ahead. Yeah, the environment. Part of it is that you know who he is and what he's done, right? Part of it is that you know the context of what this man has done and the environment in which he finds himself versus this gentleman over here. But that's the great thing about style is that it can either reinforce all of these other variables that help you communicate your masculinity to the rest of the world or it can provide a contrast to them and downplay it. What you wanna do, especially in a world that doesn't value traditional masculinity, especially in a world that tries to tell you there's only one way that you can actually aesthetically express that masculinity, is you wanna figure out the best way that you can do it and then leverage it as much as you can because the contrast between you and the sissy, limp-risted hipsters of the rest of the world is gonna be so much stronger and it's never been easier to dress better than it is now. So you can thank the baby boomers for ruining the idea of masculine aesthetics, right? So, huge difference between those two. How many of you guys have seen this image before? Right, okay, a little bit. Have you ever thought about this? To me, this is the perfect summation of the difference between visual appeal and visual power because if you think about it, a well-tailored suit doesn't really show a whole lot of skin, right? It's not showing anything that's actually gonna be turning a woman on from an appeal standpoint. You have no idea what kind of shape a guy is in. I mean, yeah, you have some general context but you don't know for sure. You have no idea about anything from an appeal standpoint but it tells a whole story about his power. It tells you about his financial situation. It tells you about his social status. It tells you about his social dominance. It tells you about his attention to detail and his level of discipline. And so it gives you an entire story and those are the things that women are primarily attracted to and so those are the kinds of things that you can signal by dressing well. Does a well-tailored suit do that? Absolutely. Is it the only thing it does it? Absolutely not. Otherwise, a well-tailored suit objectively across all time and across all cultures would have been the pinnacle of men's style and it certainly hasn't been. That's something relatively new and relatively recent. So what does this mean for you guys?


This is classical genetics. Some people wonder what is the difference between classical genetics and molecular genetics? Is it a historical difference? Well, yes. Classical genetics was developed by Gregor Mendel in the late 19th century and, of course, molecular genetics involves everything that we know about the DNA molecule after its structure was understood by Watson and Crick. But in addition to the historical differences, there's also kind of a hierarchical difference. Classical genetics focuses on everything at the level of the chromosome and above, things that we can see through the microscope and with our naked eyes, this physical structure of chromosomes. You know, chromosomes are supercoiled strings of DNA that have a very complex structure. They open for expression. There are many of them in a cell. We can lose chromosomes and that can cause problems. When chromosomes bang into each other at the beginning of meiosis, they can even exchange their tips, generating lots of variation. Now we'll be tracing this variation in genes and, of course, in the traits that they confer across the generations by looking at pedigrees. Pedigrees help us understand the inheritance of disease-causing genes throughout human families, but they also inform our plant and animal breeding programs. We'll be focusing a little bit on one of my favorite plant breeders, Norma Borlaug, who won the Nobel Prize in the few decades ago for developing varieties of wheat that doubled and tripled grain productions across Asia, forestalling a real starvation crisis for our global civilization. We'll also be focusing on population genetics. And population genetics is when you track the inheritance of genes and traits across, not just across the generations, like in a family, but within a population. And this is really the mathematical foundation for our modern understanding of evolution. And we'll be tracing the evolution of species and of genes within that species in some of our favorite animals, like humans. Well, anyway, I'm really looking forward to the class and I hope you'll enjoy it as well.


Hey guys, it's Nate, aka the Foot Accountant. Welcome back to the channel. You guys know what we got today. We got the new upgrades in FIFA 19 Ultimate Team. We got the three. They didn't give us just one or two. They gave us three different variations of upgrade SBCs during footies. Now we finally got these. The first batch is only in packs for a couple more days at the time that I'm recording this. And I'm gonna talk a little bit about these packs since they're out for a week. They are out for an entire week. And that means you can use them for the first batch and you'll be able to open them during the second batch as well. We're gonna talk a little bit about that in a bit. But I wanna take a look at each SBC really quick since you guys probably already know what's going on here. And then we're gonna get into opening the packs. I have five of each. It's not a ton, but it's just a few. I just rinsed my club and we were able to do five of each. So the first 81 to 86 upgrade looks really good. You only need four players. The rest you can use silvers and bronzes for. So this SBC is really, really cheap to do. And this is perfect for icon crafting and crafting SBCs that could be out in the store like the Firmino SBC and stuff like that. And I wanna mention one thing about this SBC, 81 to 86 upgrade, if somebody has a base card like a Sterling right now. Sterling has a special card in packs like the Champions League UCL Final Card, a Rogue to the Final Card. He has an 85 rated base card. So you could technically pack that card out of this pack since the base rating is from 81 to 86. So that's kind of the bee's knees with this one.  According to Footbin, it costs you 4,000 coins to do that pack. 82 plus rated guarantee gives you one player that is 82 plus rated base card or special card. All you need is gold players, five rares, 30 chem. That one's okay. It costs about 9,000 coins to complete. Then the 81 plus double upgrade is 11 gold, 11 rare players, 40 chemistry, but you do get those two players. So the 82 plus and the 81 double upgrade, I'm kind of like eh on. They're just okay. But the 81 to 86 is the real crafter's dream. Because honestly for that 81 to 86 upgrade pack, you can just do bronze pack method BPM and you can actually, if you do enough bronze packs, you're gonna make enough coins that you can use those bronze that don't sell in this SBC and you can also sell the bronzes and use those coins. Like if you get a squad fitness, that enables you to buy two gold cards that you need to put in that SBC. And you need four gold cards and the rest can be whatever rating, whatever type. So the 81 to 86's are really good. But obviously if these packs don't have good pack weight, they're not gonna be any good to do unless you do tons and tons and tons of them. So I wanna start off as it goes in order here. We're gonna go to the 82 plus packs first, then we'll go to the 81 double upgrade and then to the 81 to 86. So these are the 82 plus packs. First one, we get an 82 rated card and that is Sigurdsen. So not the best start. So again, I am doing five of these packs, five of each pack just to kind of compare them and see how we do. I know it's not a huge sample size. It would have been nicer to do 10 of each, but five of each is a decent start and I wanna just be able to show you guys this because these upgrades are gonna be very, very good for us in this next week. And that's what I wanna make the point of, I'm probably not gonna open too many before Wednesday when the second batch of cards comes out. I'm gonna be saving most of my packs for these upgrade packs until after that batch two comes out because that batch has a lot more promise than the cards in this first batch do. We finally get a board on our third 82 plus and it's going to be Luis Gustavo 83 rated. So the 82 plus are not looking so hot right now. That's for sure. I'm kinda interested to see how the 81 plus double upgrade compares to the 82 plus because you get two cards. Here we go, a walk out on our fourth 82 plus. This looks like a road to the final. Spanish center back, Nacho Fernandez. All right, so an 82 plus, we get an 87 rated road to the final, Nacho Fernandez. We'll take it, you know? 87 rated card, I already had PK in the club so I was really hoping not to see that PK walk out because that would be an untradable duplicate. I don't want that, but that is a nice pack pull. That's our first walk out and our first special card. Very good for SBCs. He's gonna go right into the Maldini SBC which is what I'm working on at the moment. All right, so last 82 plus out of five are we gonna get two walk outs or not? Will we get another board? Okay, so we got five packs, we got one walk out, two boards and 84 and 83 and two other 82s. So, you know, that's just okay. If you're averaging one walk out per five packs, that's honestly not terrible, but that's nothing too spectacular as well. They didn't surprise me that much, but we'll see what these other ones get to. These are 81 plus double upgrade. First one's a walk out. Looks like another road to the final. Oh, just kidding, wants to watch? Who's this? Who's this? Gretzgra? Let's go, man! 81 plus double upgrade. The first one we get wants to watch Gretzgra. That's a big time pull. Coming on the Spurs kit as well, we'll take that. That's a pretty solid pull, anything else? 81 rated Skirtle. The first 81 plus, we do get a pretty solid pull in wants to watch Gretzgra. So, off the bat, I'm liking these 81 plus double upgrades. That's for sure. We get boards in our second double upgrade. Can we get like an 85? We get a French center tack in mid. It's gonna be Paillette. That's an 84. So, right away, we're off to a pretty solid start. One walk out, one special card and an 84 from the 81 plus packs. We're gonna get in pack number three. It's not a walk out. Man, I can see that walk out symbol a couple times.  Another French player, goalkeeper Mandanda. All right, that's an 83. I'm really excited to span these upgrades though after the batch number two comes out. Two 83s actually in that pack, not bad. I'm really excited to see what comes out in batch two. I think there should be tots. There should be headliners. I mean, I feel like EA should have no holding back on this because it's the end of the year, right? It is the end of the year and what are they gonna lose? They're just gonna have people enjoy their game more if they put all of those cards back into packs. We're gonna get a duplicate Juan Mata. Please tell me this is tradable. It is. We'll throw him on the transfer list. So, we got two Manchester United players in that pack right there. Last 81 plus because so far, these have been comparable to the 82s. Very comparable to the 82 plus. It is a board as well. It wasn't gonna be French. That's our third French board in a row. Kingsley Coman. Ooh, rivery. We'll take that. 85 rate of rivery. Not too bad. So, we got an 85 and 84. The Gretzgra and a couple other 82s. So, right now I'd say the 81 pluses are winning over the 82 pluses. Let's get into the 81 to 86, which are, in theory, the least, you have the least amount of chance to get a high level or a high rated card from these unless you hit a special. And we hit Lucas Lieva in the first 81 to 86, which isn't too bad, 83 rated. We will take that. We will send him to the club. Four to go. And these are the perfect ones again. I mentioned this before. These are the perfect SBCs for crafting. If you're gonna do crafting, if you're gonna craft icons, or if you wanna craft a Firmino, or maybe one of the footies winners, this is gonna allow you to do it for a lot cheaper because you can spam a ton of these packs. You can do 100 of these packs for around 400,000 coins if they cost you 4K a piece. That's ridiculous. 100 packs for 400,000 coins. It's pretty nuts when it comes to upgrades. You know, 400 packs out of some of the other upgrades that we've had this year. Like if you did 100 of the 81 plus packs, that would run you about a million coins because they're 10,000 coins a piece. If you did 100 of them, that would be pretty crazy. That would be pretty crazy. All right, we have two 81 to 86 rated plus players left, packs left, excuse me. Nothing too big out of these, but that's kind of what you're gonna expect. If you're doing the 81 to 86, you're gonna spam these. And I could have told you that it was gonna come down to the 81 double upgrade and the 82. It was gonna be between those two packs personally. But you know, we gotta try out the 81 to 86 as well and test our luck. We do get another board. This is our second board. Portugal CDM, is it gonna be Pereira? It is the Nilo Pereira, 83 rated. So two boards out of the five 81 to 86 upgrades. Not terrible. If you're crafting again, that's decent, all right? Here's my thinking on this. We'll go over to footprint for this one. Show you the SBCs again. 10,000 coins for the double upgrade. 4,000 coins for the 81 to 86 and 9K for the 82 plus. I really think that this one, you're gonna get the most consistent. If you're looking for special cards and big polls, I think your 81 plus double upgrade is gonna be the way to go because you get two cards and they're both 81 plus. Yes, it does cost you 10,000 coins, but that's gonna get you your best chance at a special card, in my opinion. Getting walkouts, getting special cards, that's gonna be your best chance for that. If you're looking to craft purely craft SBCs or whatever SBC you wanna go for, like this Firmino, the 81 to 86 is the best bang for your buck. Now, especially as we get into this next set of cards, I feel like in this first set of batch one, there are more cards that are in that 81 to 86 rating. In this second set, we might see a few of them that are actually above that rating, so you might get more golds out of this than you would special cards, but this is still gonna be great for crafting. You're gonna get 84s, 85s, 86s that are perfect for SBCs. And then if you're doing a lot of these, you're gonna get some 81s. And from those 81s, you can either put them into the team of the week SBC or you can put them into like an 81 plus double upgrade and use those there, but that is really nice. Again, you can use a lot of these cards that you get from the 81 to 86. If you don't want to craft icons or players, throw them into a tradable 84 plus team of the week because these are also out for eight more days. So these are actually gonna be in the store when these upgrades go away. So you can use these upgrades to craft just about anything that is in the SBC section right now at the moment. So again, if we're looking for a clear cut winner on this, it really all just depends on what you're going for. The 81 plus double upgrade is gonna give you the best opportunity at packing big time players, special cards that are in packs and all that kind of stuff. And the 81 to 86 upgrade is gonna give you the best opportunity at packing a gold card for grinding out the SBCs and stuff like that. But again, a lot of this is really based upon what happens with batch two and those cards are gonna be coming out here in the next day. So I'm excited for that. I'm gonna be stacking a lot of packs. You're probably not gonna see me do too many more of these 81 to 86 or other upgrade SBCs. We'll do a few. But I'm gonna save most of these SBCs for the next batch of players because I think it could be something special. I think it could be pretty good. And I'm really crossing my fingers that we do get something good from the batch too. But again, GGCEA for putting out this content today. Firmino was a solid SBC. It's about half the price, a little bit over half, but still a big time drop in what it was when it was first out a couple of weeks ago during team of season, maybe about a month ago when that came out. So that's a big time deal from them. GGCEA and then GGCEA for giving us three different upgrade SBCs. Like, thank you. I was expecting one, maybe two. And we got three different ones. So foot economist, Zaro, Corey, whoever is responsible for this. I think foot economist, I think he's watching these videos. He hears me. That's just my take. Nah, I'm just kidding. But hey, whoever was responsible for it. Thank you very much for putting these out. GGCEA is the end of the game and you're allowing us to have fun. We really, really appreciate that. Yeah, it's gonna be really fun the next couple of weeks. Hopefully those upgrade packs get refreshed maybe towards the end of batch two into batch three a little bit because each batch has impacts for two weeks. So hopefully we get upgrade packs again at the end on batch three for one last time we can do upgrades if we really want to. I think a lot of people would be looking forward to that. But again, if you enjoyed this video, smash the thumbs up on it, comment down below if you have any questions and subscribe to the channel. If you're new, it's been Nate, Foot Accountant. Catch you guys later. Peace out.


Hello, and welcome to lecture number 11 of this lecture series on turbo machinery aerodynamics. And today we are on the 11th lecture of lecture series. And we are going to discuss a very important aspect of axial flow compressors today. And in today's class, we are going to talk about performance characteristics of single and multi stage axial compressors. And the reason why I said it is very important is because performance characteristics are extremely important information that are required by designers. And obviously, for the engine designers as a whole, because it is the compressor performance which determines the limits of operation of the engine itself, that is something which we are going to discuss in today's class. Which means that the limit of operation of an entire aero engine will in some sense be dictated by the compressor performance itself, that is beyond certain levels the compressor cannot operate. And that puts a limit on the engine operation itself. I am hoping that in the previous few lectures, 7 or 8 odd lectures which you have undergone so far, you must have had a fairly good amount of information about 2 dimensional as well as 3 dimensional aspects of flow through axial compressors. So today's lecture is kind of an overview of the whole thing. We thought of course looking at what is happening on the blade at individual stage level, but trying to find out how a certain compressor which has been designed is going to perform when the operating conditions change. So as the operating conditions of the compressor changes, how does the compressor react to such change in operating condition. So that is the aspect of discussion which we are going to take up in today's class. So we are going to talk about 2 distinct aspects which are related to performance characteristics of axial compressors. We will begin with the discussion on a single stage axial compressor performance and we will extend that to a multi stage axial compressor. The basic trends are identical for both of them, but the distinct differences between what happens in a single stage axial compressor as compared to a multi stage axial compressor. So these are 2 aspects of compressors performance that we are going to discuss in today's class. We will start with a single stage axial compressor. Now you might be aware that a stage of an axial compressor is constituted of a rotor and a stator. So rotor precedes the stator. So a rotor and stator combination together put together is what is known as a stage of an axial compressor and it is this that we are going to analyze in today's lecture on how we can estimate the performance of a single stage and how the single stage performance varies as the operating conditions change. So in today's class we will basically be talking about single and multi stage axial compressor characteristics. Let us start with the single stage axial compressor. So I mentioned that a combination of a rotor and a stator put together is a stage. So this is these 2 put together constitute a stage of an axial compressor and this is what we shall analyze and see how the performance changes as the operating conditions of this particular stage changes. So to understand that better let us construct the velocity triangles. Now this is the inlet velocity triangle for the rotor. The air is entering at an angle of C 1 absolute velocity. Relative velocity is V 1 which enters this blade at a tangential direction. Blade rotates at a peripheral speed of U. This is the velocity triangle at the inlet of the rotor and this is the velocity triangle at the exit of the rotor. Here velocity leaves the rotor at a velocity of V 2 which is again tangential to the rotor. C 2 is the absolute velocity leaving the rotor. U is the blade speed and C 2 is going to be the velocity with which the flow enters the stator. So the velocity leaving the stator is C 3. There is no relative component for the stator because the stator is stationary. Relative component is true only for rotating components like a rotor and that is why we have relative velocities at the inlet and exit of the rotor. So this is a typical axial compressor stage comprising of rotor and stator and we will see how we can estimate the performance or what are the parameters on which the performance of this single stage axial compressor would depend upon and for which we will need to analyze the velocity triangles a little more carefully. So if you look at the velocity triangles little closely and also mark the various velocity components on the velocity triangle, we get velocity triangle combination like this. So this is the velocity triangle at the inlet and exit put together. Since the blade speed is common for both the rotor entry and rotor exit that is the common point here. This is the inlet velocity triangle comprising of C 1 V 1 and angles alpha 1 and beta 1. At the exit we have C 2 V 2 and angles alpha 2 and beta 2. The corresponding velocity components are C w 1 which is the tangential component of C 1. C w 2 is the tangential component of C 2. V w 1 is tangential component of V 1. V w 2 is the tangential component of V 2. C a is the axial component of absolute velocity and delta C w is the difference between C w 2 and C w 1. Delta C w is important as we have seen earlier because the power required to drive the compressor primarily depends upon delta C w. So since the power required depends primarily on delta C w that is why in the analysis that will the change in tangential component will play a significant role. Now from these velocity triangles what we can see is the at the exit C w 2 should be equal to u minus C a tan beta 2 and C w 1 is C a tan alpha 1. Let us take a look at the velocity triangle. C w 2 is this component. C w 2 is u minus C a times tan beta 2 and similarly C w 1 which is this component is basically equal to C a tan alpha 1. And since the net change in enthalpy that is delta H naught is equal to u times delta C w.  So what we see here is that we get a parameter which is in terms of the delta C w to the velocity ratio which is a function of certain angles which come from the velocity triangle tan alpha 1 and tan beta 1 the axial velocity and the peripheral speed. So these are certain parameters which will kind of influence this parameter of delta C w by u. The significance of which is what we will discuss very soon that how this ratio delta C w by u will play any role in the performance characteristics. So what we see from this equation that we have now derived is that the performance of a single stage axial compressor will depend upon certain set of parameters. One of them of course becomes is the axial velocity the blade speed and the angles. So this means that any change in the design mass flow rate obviously will affect axial velocity C a and change in rotor speed obviously affects u. So change in either C a or u will change the inlet angle beta 1. Let us go back to the velocity triangle here. So if either C a or u changes it will cause a change in beta 1 and that means that the blade performance is strongly a function of this ratio C a by u that is this ratio of axial velocity to the blade speed will significantly affect the blade compressor performance. And it can be deduced that the stage performance is a function of 3 parameters the loading coefficient psi the flow coefficient phi and the efficiency. That is there are 3 parameters which of course will also include the flow coefficient which is C a by u. Besides C a by u the performance will depend upon the loading coefficient and also it will depend upon the efficiency of the compressor. So there are 3 parameters significant parameters on which a single stage axial compressor performance will depend loading coefficient which is denoted by psi flow coefficient which is C a by u and the efficiency eta. So these are 3 parameters on which a single stage performance will depend. Now when you go to a multi stage as we will see later on there are a host of other parameters which will also be playing a significant role in the performance which of course we will discuss in later slides. Now if I were to plot the loading coefficient which was delta C w by u with reference to the flow coefficient and also the efficiency with reference to flow coefficient. Let us now look at how that affects the performance. Before I go to that let me also emphasize this particular point that the flow coefficient C a by u is in some sense a measure of the mass flow rate. Because mass flow rate is directly a function of the axial velocity C a and rotational speed of course being fixed the mass flow rate is directly proportional or flow coefficient is directly proportional to the mass flow rate. So as the compressor is throttled or mass flow rate is changed it changes the flow coefficient. Similarly for the same mass flow rate as its speed is changed that also changes the flow coefficient or C a by u. Similarly the loading coefficient will depend upon how this mass flow rate is changing. So there is a dependence of the loading coefficient delta C w by u on the flow coefficient. There is also a dependence of the compressor efficiency on the flow coefficient. So let us now take a look at how these two parameters change as flow coefficient changes. So if I were to plot let us take a look at loading coefficient first. So I have loading stage loading on the y axis which is delta H naught by u square which is also equal to delta C w by u. On the x axis we have C a by u which is the flow coefficient and we have already seen this expression we have derived this delta C w by u is equal to delta H naught by u square is 1 minus C a by u into tan alpha 1 plus tan beta 1. So there is a direct correlation between the loading coefficient and the flow coefficient. If you were to plot this variation you should expect it to be a linear line that is what is given by this dotted line here. One would have expected a linear variation of C w by delta C w by u with the flow coefficient. Of course in an actual practice what is shown here is given by the solid line that is the measured performance. You can see the measured performance is not necessarily a linear variation. It is equal to the design point at which the compressor has been designed which is C a by u design at which both the measured and the actual is the ideal are the same. At any other point you can see that the performance is different from what it has it is supposed to be. And if you were to draw at tangent or basically the actual performance the slope of this line is basically given by this angle tan alpha 1 plus tan beta 2 at the design point. So this is basically giving us the slope which comes from this equation here. So what is to be noted here is that as the flow coefficient changes from the design point it also affects the loading coefficient correspondingly. So there is a change in loading coefficient there is a deviation of the loading coefficient from the design as the mass flow rate or the flow coefficient changes. Now if we similarly look at the stage efficiency the stage efficiency also has a similar variation with reference to the ideal performance. Stage efficiency would have approached an efficiency of 1 for a C a by u design and since when it is actually operating the stage efficiency deviates from the design point and there is a variation in stage efficiency as compared to the design point variation. So there is also a difference of the stage efficiency or dependence of stage efficiency on the flow coefficient. Similarly there is a strong dependence of the loading coefficient on the flow coefficient. So here there are 3 parameters as we have seen which kind of dictates the single stage performance. The first parameter is the stage loading coefficient which also has a dependence on the flow coefficient phi. Then we also have the efficiency which again depends upon phi in some sense that as phi varies that affects the efficiency as well. So these are parameters which drastically affect a single stage performance. Let us now look at what happens as we change the mass flow rate or as the ratio C a by u deviates from the design point at the blade level how does it affect the performance. What happens to the rotor performance as C a by u changes from its design point. So for that we have the velocity triangles for 3 different cases which have been shown. One is a design condition and 2 off design conditions. In the design condition which is normal operation we have C a by u is equal to C a by u design. This is the rotor blade and we have flow entering the rotor at an angle of v 1 which is relative velocity at an angle of beta 1. So this is the velocity triangle at the inlet v 1 at an angle beta 1 to axial direction C 1 at an angle of alpha 1 and a blade speed of u. So this is when the flow coefficient is equal to flow coefficient at design condition. Now if let us say for a constant speed the mass flow rate is reduced then this means that this ratio C a by u also reduces and this is necessarily an off design condition. When C a by u is less than C a by u design that is axial velocity is now decreases for same u. So keeping u fixed if we reduce axial velocity because mass flow rate is reduced it leads to an increase in beta 1 and as beta 1 increases beyond a certain angle it leads to what is known as positive incidence flow separation. So there could be flow separation taking place on the suction surface of the rotor blade. So this is the suction surface of the rotor blade there will be flow separation from the suction surface when beta 1 is greater than beta 1 design which occurs when flow coefficient is less than flow coefficient design. The other a counterpart of this off design condition is the negative incident separation which will occur when C a by u exceeds the C a by u design that is when C a is greater than C a design for constant u beta 1 becomes very low and as beta 1 decreases there could be chances of flow separation from the pressure surface of the blade of the rotor blade you can see that flow has separated from the pressure surface of the rotor blade and this is basically a negative incidence flow separation. So both these cases of flow separation can occur either positive incidence or negative incidence separation when you know the flow coefficient is different from its design value when flow coefficient is lower than design value it leads to what is known as positive incidence separation when flow coefficient is greater than the design value it may lead to negative incidence flow separation. So this is how the performance of a single stage compressor can vary you have dependence on three parameters the loading coefficient the flow coefficient and the efficiency and as flow coefficient changes we have seen how it affects the performance of a rotor and there are two extreme cases possible you may have a positive incidence separation when the flow coefficient is much lower than the design value leading to flow separation from the suction surface of the rotor and negative incidence separation which occurs when the flow coefficient is greater than the design flow coefficient leading to flow separation from the pressure surface of the rotor blades and these are two different possibilities wherein the performance of the compressor can be drastically affected. You also seen how phi versus psi and loading coefficient versus flow coefficient changes and how efficiency changes with the flow coefficient. Now having understood the single stage performance characteristics we will now proceed towards a multi stage axial compressor and see how a multi stage axial compressor performance changes or varies as the operating conditions change or what are the parameters on which a multi stage axial compressor performance will depend upon. So multi stage compressor as we know consists of a series of stages of axial compressor which means you will have several combinations of rotor stator and if you put all of them together that constitutes a multi stage axial compressor and what we are going to do is that we will denote the inlet station of a multi stage compressor by station 1 and exit of the compressor by stator as station 2. Therefore, the overall pressure ratio of the compressor we will denote as p 0 2 by p 0 1 where p 0 2 is the compressor outlet pressure and p 0 1 is the compressor inlet pressure. So, the compressor outlet pressure p 0 2 and the efficiency will depend upon several physical parameters of variables. So, we are going to look at what are these different parameters of variables on which the performance will depend. So, we will list all these different parameters on which the performance of a compressor is going to depend. So, let us list all these parameters and what we see is that p 0 2 which is exit stagnation pressure and efficiency is a function of these many parameters and what are these parameters? We have mass flow rate, inlet stagnation pressure, inlet stagnation temperature, rotational speed omega, the ratio of specific heats gamma, the gas constant r, the viscosity of the air then the design itself and the diameter d. So, these are the different parameters on which the pressure ratio will depend and so now if we non-dimensionalize these parameters we can do that using Buckingham pi theorem or you probably have learned about pi theorem earlier on. So, if you non-dimensionalize this and express these parameters in terms of non-dimensional clusters then we have p 0 2 by p 0 1 and efficiency both of which are functions of these many non-dimensional parameters which is one of them is mass flow rate times square root of gamma r t 0 1 divided by p 0 1 d square then we have omega d divided by square root of gamma r t 0 1 then omega d square by nu then gamma and design. So, these are anyway non-dimensionalized. So, the other non-dimensional parameters are these three. Now, for a particular design we can safely assume that gamma and nu do not affect the performance significantly. Similarly, d and gas constant are fixed. So, since d is fixed gas constant r is fixed design is fixed nu is fixed and gamma are fixed these non-dimensional parameters can be simplified and expressed as p 0 2 by p 0 1 and efficiency are functions of m dot root t 0 1 by p 0 1 and speed as n by root t 0 1. So, here we have the pressure ratio and efficiency expressed in terms of two distinct parameters I will still not call them non-dimensional because if you look at the dimensional if you look at the dimensions of these two parameters they are strictly not non-dimensional that is because we have taken off other parameters which would have indeed made it non-dimensional p 0 2 by p 0 1 pressure ratio and efficiency are functions of two parameters one is mass flow rate times square root of t 0 1 by p 0 1 the other is speed divided by square root of t 0 1. And so that means that there is one parameter which is a function of mass flow rate other parameter which is a function of speed. So, pressure ratio and efficiency are functions of mass flow rate and the rotational speed we will further simplify this and see how the performance changes we will take a look at how the pressure ratio changes as mass flow rate changes and speed changes how efficiency changes as mass flow rate and speed changes. But the bottom line is that the performance of axial compressors multi stage axial compressor in terms of pressure ratio and efficiency can be expressed as functions of two distinct groups one is to do with mass flow rate that is m dot root p 0 1 t 0 1 by p 0 1. And the second parameter is n by root t 0 1 which does not make it non-dimensional because there were other parameters which we have neglected for a given design like the diameter d gas constant and so on. Now let us simplify this expression further what is normally done is that the temperature and pressures are expressed in terms of standard day pressure and temperature we will non-dimensionalize temperatures and pressure with reference to standard day conditions. Therefore, p 0 2 by p 0 1 and efficiency can be expressed as functions of m dot root theta by delta and n by root delta theta. Here theta should be equal to t 0 1 by t 0 1 standard day and delta is stagnation pressure divided by stagnation pressure of a standard day. So, here theta and delta refer to temperature and pressure ratios for a standard day. I will explain the significance of why this non-dimensionalization is also required for temperature and pressure basically because when we are designing a compressor for a particular condition what normally designs it for a certain ambient condition. But this compressor may be operating in an engine which is used in an ambient condition which is entirely different from what it has been designed for. So, what is the guarantee that this compressor is going to perform the same way as it has been designed for a different condition. So, the way to account for this is to express the pressure and temperature in a non-dimensionalized form and so usually this is also referred to as corrected pressure and corrected corrected mass flow rate and corrected speeds because mass flow rate has been corrected for the standard day pressure and temperature. So, even if let us say the engine is operating at a temperature and pressure which is drastically different from what it has been designed for because of this correction it can partly take care of this variation in pressure and temperature. So, with this background that we have had so far on how we can express the performance of multi stage compressors. We will now proceed towards looking at how the variation of a compressor performance itself is expressed. So, basically a compressor performance variation is also referred to as a performance map. So, compressor performance is expressed in the form of a map and performance map forms a significant part of very very significant role in the design of an aero engine or for that matter any gas turbine engine because as I mentioned a compressor performance puts limit on limits on the whole engine performance as a whole because there are certain limits of operation for a compressor beyond which it cannot operate or there are instabilities which are introduced. Therefore, an engine will not be able to operate satisfactorily beyond these operating ranges and that is why a compressor map forms a very significant input for an engine designer who will need to know what are these limits between which this compressor is going to operate. That is if I am designing an engine and I will need to know that this compressor has certain limits in terms of mass flow rate and pressure ratio. So, this is the amount of limit that I have during which between which the engine has to operate because beyond that the compressor cannot operate and therefore, the engine as a whole will not operate at all. And therefore, compressor performance map will form a significant input for an engine designer who will need to know what are these limits. So, compressor performance is expressed in terms of two parameters as a function of the mass flow rate. So, one of the parameters which we are interested is what is the pressure ratio developed by the compressor. So, the pressure ratio p 0 2 by p 0 1 expressed as a function of mass flow rate m dot root theta by delta. And similarly, what is this variation with different speeds as speed changes that is n by root delta or n by root theta how the performance changes. This is one of the parameters which we are interested in. The other parameter is the variation of efficiency with the non-dimensional mass flow rate and the non-dimensional speed how the efficiency changes. So, I will now show you one typical compressor map which basically tells us how this variation can be tracked. Now, if you look at what is shown here I have a typical compressor map which is shown here on the y axis we have p 0 2 by p 0 1 and efficiency x axis we have mass flow rate which is expressed in terms of m dot root theta by delta where this is the temperature standard day ratio and this is the pressure ratio standard day with reference to standard day. And there are series of curves which you will see and each of these lines correspond to constant speed line and the speeds are expressed in terms of n by root theta. And that is as the speed changes as you change the speed of the compressor from very low speed where this ratio will be close to 0 and as you keep increasing that and it approaches the actual speed the design speed which is 1. You can see that initially the speed lines are flatter. So, as you look at compressor performance at lower speeds very low speeds one would see a flat variation rather flat variation of the pressure ratio with mass flow rate that is as mass flow rate changes pressure ratio also changes, but that is over a wide range. But as the speed increases as we go towards higher and higher speeds the speed curves become sharper and sharper. For example, if you look at the speed curve at n by root theta is equal to 1 you can see that the speed curve is extremely sharp. And therefore, the pressure ratio varies drastically with mass flow rate, but that is over a very narrow range of mass flow rate beyond which there is certain line which is shown here a daughter line. Of course, there is a curve beyond this also, but that is a curve which a designer would never want his engine to operate on. I will explain what that curve is a little later. Now, what you notice is that as the speed increases from very low speeds and as we proceed towards higher and higher speeds the performance curve which was initially flat starts becoming sharper and sharper to the extent that at very high speeds that is the design speed of 1 the curve becomes very sharp which means that there is a very narrow range of operation of the compressor here. And the sharp curve here basically means that mass flow rate does not really influence or for the pressure ratio versus mass flow rate is kind of a constant here. And this basically refers to what is known as the choking point where you are trying to pass the maximum mass flow rate which this compressor can generate. So, beyond which mass flow rate does not change much and there is a significant drop in efficiency which I will come to a little later. So, what this line here means is that under this operating condition even if we change the mass flow rate substantially there is the variation in pressure ratio is very drastic for a very narrow change in mass flow rate beyond which the pressure ratio drops as you try to operate the compressor for mass flow rates beyond that because mass flow rate is fixed. You might recall the concept of choking which you would have learnt in your gas dynamics or in fluid mechanics that under certain operating conditions mass flow rate attains a peak level and mass flow rate becomes maximum. This is exactly the case that is happening here that maximum mass flow rate has taken place and no further mass flow rate can be passed through by this compressor. And if you try to pass more and more mass flow what will happen is that it will affect two parameters one is the pressure ratio which drops and also the efficiency which drops drastically. So, the curves which are shown here are the efficiency curves for the corresponding speeds. So, for lower speeds as expected one would see a flatter efficiency curve and as the speeds approach one the efficiency curves also becomes sharp just like the pressure ratio curves and you can see that the change in efficiency is very drastic and very narrow as the speeds approach the design speed. Now, on this each design line or in on each speed line you can see multiple points which have been shown here. These are the different operating points of the compressor. So, compressor may be operating on any of these points or in between these points and so when a designer embarks upon designing a compressor what he does is that he tries to design it for a particular operating condition and then one would also need to evaluate what happens when the compressor is going to operate in conditions which are different from what it has been designed for or what are known as off design conditions. For an aero engine for example, the design the operating conditions can vary so drastically that the designer has to ensure that even if the off design condition is it is extreme the compressor still operates safely because as you have seen here in the curve on the left hand side there is a dotted line which has been shown on the pressure ratio versus mass flow rate. There is a dotted line which is shown and it is indicated as surge line. Now, what is surge is something we will discuss in detail in a later lecture, but let me tell you that compressor operation is affected drastically affected by two instabilities which are likely to occur. One is known as a rotating stall and the other is known as surge. Both of these are instabilities which can drastically affect the performance of the compressor to the extent that if surge occurs the compressor may fail and lead to flame blow out in the combustion chamber and the engine may shut down if the compressor is surging. So, the left the dotted line shown on the left hand side of the pressure ratio versus mass flow rate curve is sort of a limit for operation of the compressor that is though if you extend that line you will still see a line on the left hand side, but that is a line on which you just cannot operate the compressor because that is a region of instability for the compressor. The compressor cannot operate in a stable manner if it is on the left hand side of what is known as the surge line. So, if compressor tries to operate on the left hand side it would undergo what is known as surge during which the entire operation of the compressor breaks down and engine as a whole gets affected drastically and it might lead to failure of the compressor and engine shut down. So, surge is a phenomenon which can affect the performance of a compressor drastically. So, let me take a closer take you to a closer look of what is the surge line and how it affects the performance. Now, the same performance curve that you saw here pressure ratio versus mass flow rate is being shown in a better way here. Now, here we have the speed lines which are these different lines which are shown the surge line is shown here and what is also shown is the engine operating line. Now, engine operating line is the line which is something that the designer would like to use and how does one at arrive at the operating line operating line is the line through which the engine is accelerated from 0 speed all the way to design speed. Operating line would ideally have to be a line where the efficiency is maximum because you would always like to operate the compressor in a condition where it has maximum efficiency. So, if you join all those points ideally if you join all the points of maximum efficiency you can get the ideal operating line, but it may so happen that many a times the maximum efficiency is very close to the surge line which is a risky affair because if you are operating very close to the surge line any off design operation might push your engine into surge that is a risk which the designers are not willing to take will not obviously be willing to take because that is too high a risk to be taken to operate the engine very close to the surge line. So, the engine designer always wants to keep a certain margin between the operating line and the surge line this is known as the surge margin. Surge margin is a certain margin or buffer which the designer wants to put for the engine to ensure that even if the engine undergoes an off design operation a transient operation the engine still does not touch the surge line because if the engine were to indeed go towards the surge and touch the surge line that can lead to catastrophic effects which are something which the designer will always want to avoid. So, surge margin is something which is kind of a protection for the engine provided by the designer to ensure that the engine does not reach the surge condition even if there is an off design operation of the engine and most of the modern day engines have inbuilt surge warning systems and mechanisms which will prevent a pilot from accidentally operating the engine in such a way that it can surge. So, the modern day computer which operates an engine which is also known as the FADEC that is the full authority digital engine control basically has inbuilt functions which will prevent a pilot from making such mistakes that will lead to surge of an engine and even if there is a possibility the surge warning sensors which will give a warning to the pilot saying that there is a possibility that the engine can surge if you operate it so and so. So, in this operating multi stage compressor performance map there are two distinct lines that we should be familiar with one is of course, the surge line the other is the operating line operating line is the line on which the engine is designed to be operating for. There is also another line which may not be that significant that is on the right hand side right most side you may also join all those points on the right hand side to achieve what is known as the choking line. Choking line is not really significant for a compressor, but it may be significant for a turbine which we will see later on because turbines usually operate under choked condition. So, that we will discuss a little later when we take up the turbines for a compressor the choking line is not really a matter of that concern, but there could still be a line which represents choking in an axial compressor. So, surge line and operating line two distinct parameters or lines that we need to be aware of. Now, based on these parameters that we have discussed we will now look at how the performance changes as let us say the mass flow rate changes which we have also seen for a single stage compressor. We have seen that as the flow coefficient changes from the design condition it drastically affects the performance of a stage. Let us also look at how flow coefficient changes can affect the performance of a multi stage axial compressor. Now, in multi stage axial compressor the problem is that a small departure from the design point in the first stage can cause progressively increasing departures from the design from the first stage onwards. That is a small reduction in the ratio C A by U at the design point at the first stage could lead to positive incident separation at the last stage. Similarly, a small increase in C A by U design could lead to negative incident separation in the last stage and the most extreme mismatching of these front and rear stages occurs during starting. Now, during starting what happens is that the compressor has just about begun rotating. So, as that rotation begins the net change in density across the compressor is not very significant. So, change in density from the first stage to the last stage is insignificant. So, there is hardly any change in the densities. So, what happens as a result of that is that as the density changes are not very high whatever changes occurs at the inlet can have a very significant effect on what is happening at the exit. So, there is a very significant effect of the flow from the inlet all the way to the exit and this is especially true during starting when the density development has not really taken place. This is the pressure ratio and the density changes have not really been initiated because the compressor has just about started. So, we will take a look at what happens during starting what happens to the flow conditions or velocity triangles for the inlet or the first stages and what happens to the flow velocity triangles at the exit or the last stages. So, I have two sets of velocity triangles here one corresponding to the first stages and one set corresponding to the last stages. What is shown here by the dotted line correspond to the design velocity triangle. So, these dotted lines are supposed to be the so called design velocity triangles and what happens is that in the first stages axial velocity to then the ratio of C a by u is lower than what it should be for design condition. And what happens in the last stages is that C a by u ratio is higher than what it is for the design condition because mass flow rate is fixed. Now, mass flow rate being fixed the area is fixed and axial velocity is the only parameter which can change because density is also fixed during starting. So, from the inlet to the exit if you have seen an axial compressor geometry the area progressively reduces right. From the inlet you have the inlet you have a large area and that area progressively reduces and you have a smaller and smaller area at the exit. Since the area is reducing density is fixed for a constant mass flow axial velocity has to increase and that is what is happening during starting. Now, once it starts and the compressor operates the density increases and this problem does not take place once the compressor as is fully operational. So, this is basically a problem which occurs during transient operation during starting of the compressor. So, what happens in this case is that there are few stages in the beginning where C a by u ratio is lower than the design ratio which means it first few stages may encounter positive incident separation and towards the last stages C a by u is greater than C a by u design and it may lead to negative incident separation in the last stages. So, there is a huge mismatch between the initial stages and the later stages and that happens just during starting. So, how can we overcome this problem? So, there are different ways of overcoming this problem and what basically happens is that a decreased C a with alpha 1 and beta 2 constant results in increased alpha 2 and beta 1 and similarly it leads to an increased loading in both rotor and stator. Similarly case of increased C a it leads to an opposite defect. So, there are different ways in which designers have configured for self starting of compressors. One of the ways is to use bleed valves which will allow some of the incoming air to escape. So, this is the most common way one of the common ways of elevating this problem that is use a bleed valve somewhere midway between the multi stage compressor that will allow some of the mass flow rate to escape. So, as the mass flow rate escapes later stages will have lower mass flow and therefore, it will have C a by u ratios which are closer to the design value and therefore, the problem of extreme mismatch between the initial stage and the later stage does not really happen. Other way of course, is to use variable guide vanes which can change the inlet angles flow angles to ensure that the flow is matched to the design C a by u values and the third option is of course, to use multi spooling which is probably the most common thing which is used now that is you split the compressor into different stages. So, that the later stages operates at different speeds as compared to the initial stages which is why most of the modern day engines have multiple spools it could be twin spool or a three spool engines and therefore, you have initial fan followed by a low pressure compressor and then a high pressure compressor which are driven correspondingly by different stages of turbines. So, these are different ways of trying to ensure that the compressor operation especially during starting is also taken care of and there are no extreme mismatches taking place between the first few stages and the last stages of a multi stage axial compressor. Now, besides this I mentioned that there are two distinct problems or instabilities which can affect a compressor performance one is known as rotating stall as I mentioned and the other is known as surge. Now, we will discuss in detail about rotating stall and surge in a later lecture. Let me just give you a quick introduction to what is meant by rotating stall and rotating and surge. Rotating stall is basically a non axisymmetric phenomenon and it is a periodic. So, it is not a periodic phenomenon surge on the other hand is axisymmetric which means it affects the entire annulus of the compressor and it is periodic. Rotating stall is basically a progression around the blade annulus of a stall pattern in which one or more adjacent blade passages are instantaneously stalled and then cleared for unstalled flow as the stall cell progresses. Rotating stall obviously causes alternate loading and unloading of blades may be leading to a fatigue failure, but it is not fatal. Surge on the other hand is a low frequency oscillation of the entire annular flow and it is periodic, but it leads to it is a kind of a fatal phenomenon for the engine because onset of surge can almost always lead to engine failure and therefore, surge is much more severe phenomenon as compared to rotating stall. Now, let me just go to the pressure ratio versus mass flow characteristic to explain this little bit more. Now, in this pressure ratio versus mass flow characteristic on the left hand side that you see here is what is meant by surge. Even though theoretically there is a curve which extends if you draw this curve on the left hand side will still extend that way, but practical limitations in terms of initiation of surge will prevent compressor from operating on this side of the curve and that is why this is known as the surge line and it is important that we be clearly demarcate between the surge line and the engine operating line and so that is why there is a clear difference between engine operating line and the surge. Rotating stall is often considered to be a precursor to surge that is as the engine approaches the surge line there is a possibility that rotating stall initiates and rotating stall when allowed to proceed further and propagate further can evolve into surge and the engine can eventually lead to surge, but rotating stall is something which can be prevented and controlled, but surge once initiated is very difficult to control and that is some that is why designers would also always want to avoid that the engine when approaches surge. So, surge is something that will need to be avoided and under all circumstances and that is why it is important that is designer understands the surge margin variable. We will discuss details of surge and stall that is instabilities in detail in one of the later lectures. So, let me conclude today's lecture where we have discussed about very important aspect of performance characteristics of axial compressors. We began our lecture today with discussion on the performance of single stage characteristics and extended that to multi stage characteristics. We have seen that pressure ratio for single stage it is the loading coefficient versus the flow coefficient and efficiency versus flow coefficient that one would be interested in. In a multi stage characteristic we have pressure ratio versus mass flow rate non dimensional mass flow rate as a function of different speeds which is also non dimensionalized with the temperature and efficiency versus mass flow rate at different speeds. So, these are different parameters based on which one can construct the performance characteristics or performance map of multi stage axial flow compressors. So, these were the topics that we have discussed in today's lecture. So, I hope you have been able to grasp some of the effects of aspects of performance characteristics and what is the significance of performance map of an axial flow compressor. So, these were topics which we had discussed in today's lecture and we will continue discussion on instabilities and inflow conditions and their effect on performance of axial compressors in future lectures.