Thesis by Songzhi Yang*

Numerous technological applications requiring the use of numerical simulation involve complex two-phase flows, as is the case with the engine injection context. Most calculation software in the field of fluid mechanics can simulate single phase (liquid or gas) flows, potentially in a supercritical regimea, or two-phase flows (liquid-gas) in a subcritical regime. This research proposes a complete modeling approach to simulate both cases, including the transcritical regimeb, as well as any phase transition (evaporation or condensation). For this, a totally compressible, diffuse interface two phase flow model was developed, based on a Eulerian-Eulerian approachc with real fluids assuming liquid-vapor equilibrium(1).

It made it possible to simulate transcritical injection in the Spray A reference injector of the ECNd (2). It also proved capable of predicting the cavitation phenomenonin a three-dimensional nozzle, thereby highlighting the importance of taking into account dissolved gases in injection modeling(3). In particular, its use has provided a greater understanding of the phenomenon of bubble nucleation, as a function of the quantity of non-condensable dissolved gases.

Transcritical injection simulation on the Spray-A injector (temperature field at 112 μs).

Numerous other applications incorporating complex two-phase flows can now be simulated more realistically, such as gas turbines and cryogenic rocket engines, or coolant boiling for electric powertrain power electronics or computing centers.

*Thesis entitled "Modeling of Diesel injection in subcritical and supercritical conditions"

a - State of a pure body when its pressure P>Pc or its temperature T>Tc. In the opposite case, the fluid is in a subcritical state
b - Condition generated when a subcritical fluid is injected into a supercritical fluid
c - Eulerian approach for both the liquid and gas
d - Engine Combustion Network (https://ecn.sandia.gov/workshop/ECN1/intro.pdf)
e - Formation of gas or vapor bubbles in a liquid subject to a pressure drop

(1) P. Yi, S. Yang, C. Habchi, R. Lugo, 2019. Phys. Fluids 31, 026102.

(2) S. Yang, P. Yi, C. Habchi, 2020. Int. J. Multiph. Flow 103145.

(3) S. Yang, C. Habchi, 2020. Phys. Fluids 32, 032102.

Scientific contact: chawki.habchi@ifpen.fr