[Proxima]

Hi, i want to get the divergence of velocity field, and i have calculated the gradient of velocity on tecplot. When using equation DuDx+DvDy+DwDz to get divergence i find it is not equal 0 in incompressible fluid. can Anyone help me?
Thank you!

[FMDenaro]

There are a lot of possible reasons. Provide more details about the source of your velocity field. Consider that in a numerical code it is also possible that you do not satisfy exactly the div v =0 constraint. But if you want to assess, you must use the same discrete operators used in the code.

[Proxima]

I am using ansys fluent to do my sumulation, second order upwind discrete on v and p. div v equal 0.5，1 or even smaller in almost domain, but it equal 50 in somewhere.

[FMDenaro]

Originally Posted by Proxima

I am using ansys fluent to do my sumulation, second order upwind discrete on v and p. div v equal 0.5，1 or even smaller in almost domain, but it equal 50 in somewhere.

What you have to do is the check in Fluent, computing the div v field in Tecplot without using the same scheme used in Fluent makes no sense.
First of all, you have to assess if Fluent provide the correct divergence-free field.

[sbaffini]

Also, as Fluent uses the Rhie-Chow approach for colocated meshes, your divergence free field will also nees a pressure part.

Your best shot is directly exporting the mass fluxes on the faces.