C N
Ansys Employee

Hello,

Incompressible flow

In Incompressible flow the density is constant and it obeys the ideal gas law for gases typically air. There is nothing purely incompressible it is a theoretical concept most of the liquids undergo infinitesimal volume change which changes the density slightly due to pressure and temperature change so they are considered to be incompressible. In fluent the pressure based solver is used for incompressible fluids. 

Compressible flow

In compressible flow the density is not constant and the variation is considerable . Most of the real gases are compressible flow. In ansys fluent the density based solver is used for compressible flow. In material settings there is option to choose compressible density property for the fluids. 

Hope this helps you in understanding the difference .

Thanks