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-   -   How to compute values of Navier Stokes terms (https://www.cfd-online.com/Forums/cfx/67098-how-compute-values-navier-stokes-terms.html)

mixer August 3, 2009 21:25

How to compute values of Navier Stokes terms
 
Can I get the values of individual terms in Navier Stokes, like convection, accumulation, diffusion, or in case of k-epsilon, production term. I would like to see relative contribution of each term in the flow field. I have been told that in Fluent it is possible. Is it possible in CFX 12 to obtain the value of these term. I think one will require to compute mean velocity gradients on the run. Is it possible to be obtained using Fortran or Junction box routine. Has anyone attempted this and share the information. Thank you, very much.

ghorrocks August 4, 2009 01:40

Hi,

This can be done (I think) in post-processing in CFD-Post. Create variables for the various components. It could also be done during a simulation but it would really slow things down and generate huge datafiles.

Glenn Horrocks

mixer August 4, 2009 19:41

Hi Glenn

One needs to obtain components like,say 'gradient' of 'mean axial velocity gradient in x direction'. Such components are not available in Post or by transStat. So, one has to obtain for each time step the 'mean axial velocity gradient in x direction', and update the gradient and mean value at each time. Any ideas if someone has done this, does one uses the Get_Var function and computing mean on the fly. thanks.

ghorrocks August 5, 2009 00:01

Hi,

Can't you do what you want using the Velocity u/v/w.Gradient X/Y/Z variables? These variables are also available for pressure. These variables are in the res file by default so you can see them in CFD-Post.

Glenn Horrocks

mixer August 5, 2009 01:41

Thanks Glen for your response, yes, they are available in Post, but i need to find the "Time Average or Mean" of these vel gradient terms, in order to compute terms of Navier Stokes . These gradient variables (du-Velocity-dx or du-Velocity-dy) are not available for selection in 'transstat', so in the Post one does not get its Mean. Any idea on how to obtain gradients of mean variables (du-Velocity-dx) or how to call them..do i have to use GETVAR. Thank you.


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