Flow - Steady and Unsteady Flows


What is a Steady Flow?

A Steady flow is a condition in which the quantity of liquid flowing per unit time is constant.

In steady flow, the velocity, pressure and density at a given point are constant.

Mathematically, for steady flow

where P is any quantity such as velocity, density or pressure.

What is an Unsteady flow ?

An Unsteady flow is one in which the quantity is not constant but varying.  In unsteady flow, the characteristics of the liquid such as velocity, density or pressure are not constant.

All flows are unsteady while starting.  They may become steady later.  For instance, the flow from a tap may be unsteady when opened and it may become steady later.