Difference between compressible and incompressible flow

[mahaesh]

Hi all
I am really confused with what is the actual meaning of compressible and incompressible flow?

[FredGarvin]

In a nutshell: Does density of the media change significantly?

[tiny-tim]

Hi mahaesh! :smile:

Incompressible flow is flow whose density is constant along any streamline.

For details see http://en.wikipedia.org/wiki/Compressible_flow :smile:

[mahaesh]

Hi tiny-tim
Thanks for your reply but i am confusing because combustion is a compressible flow due to variation in density but in Computational Fluid dynamics analysis combustion treated as incompressible flow Why?

[FredGarvin]

I am not familiar with what exactly you are doing, but in a constant flow process, like in a jet engine, there is actually a very small pressure drop across the burner (in a well designed burner). I wonder if that doesn't have something to do with what you are looking at.

[Topher925]

Hi tiny-tim
Thanks for your reply but i am confusing because combustion is a compressible flow due to variation in density but in Computational Fluid dynamics analysis combustion treated as incompressible flow Why?

I don't know why, since it obviously isn't an incompressible substance and I would assume any CFD model that assumed incompressible flow would be very inaccurate. The only exception would be if you are considering something like flame dispersion in the combustion chamber over a small period of time and are assuming the piston to have such small travel in that period that the change in volume can be neglected.