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Compressibility corrections options in Turulence Model

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Old   February 1, 2022, 05:31
Default Compressibility corrections options in Turulence Model
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Shahid Khan
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I am running a 3-D axisymmetric, fully turbulent case using SA model at high mach no=2.5. In my reference paper a compressibility correction option is given based on Catris and Aupoix 'Density corrections for turbulence models'. I tried looking for these compressibility correction options in SU2 but was not able to get anything about them.

Can anyone explain more about these and if these options are available in SU2?
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Old   February 1, 2022, 13:37
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Hi! For SA, we only have this compressiblity correction to improve results in a compressible mixing layer:


https://turbmodels.larc.nasa.gov/spalart.html#sacomp


You could implement the model based on the nasa page and its references, but there are several versions of the model. What kind of problem are you interested in?
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Old   February 2, 2022, 02:20
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Quote:
Originally Posted by bigfootedrockmidget View Post
Hi! For SA, we only have this compressiblity correction to improve results in a compressible mixing layer:


https://turbmodels.larc.nasa.gov/spalart.html#sacomp


You could implement the model based on the nasa page and its references, but there are several versions of the model. What kind of problem are you interested in?

My problem is related to interaction between shock-wave and the turbulent boundary layer in an axisymmetric geometry.

One model- SA_E_COMP is also available in SU2 I believe.
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Old   February 2, 2022, 17:32
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Hi!



Yes, you are right, there are 2 compressible SA models, but they have the same correction term.
Also note that the axisymmetry boundary condition for 2D flows has not been implemented for SA, so axially symmetric problems have to be simulated using a 3D mesh with some cells in the circumferential direction.


I do not know what the performance for your case will be with the current SA model. Do you have some idea if these corrections will be necessary for your case?
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Old   February 2, 2022, 21:58
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Quote:
Originally Posted by bigfootedrockmidget View Post
Hi!



Yes, you are right, there are 2 compressible SA models, but they have the same correction term.
Also note that the axisymmetry boundary condition for 2D flows has not been implemented for SA, so axially symmetric problems have to be simulated using a 3D mesh with some cells in the circumferential direction.


I do not know what the performance for your case will be with the current SA model. Do you have some idea if these corrections will be necessary for your case?



For my case, initially for some iterations solution is converging but then it starts to diverge. I am using just SA model yet not SA_COMP or SA_COMP_E. I am using second order flux reconstruction scheme.
I am not sure about these corrections (I am new to CFD). The reference paper which I am following has mentioned the compressibility correction hence I wanted to know and use it. They used corrections based on this paper 'Density Corrections for Turbulence Models'.



I am attaching the figure of my domain for you to have a look. Both are not same but it might give you some idea about the domain.
Attached Images
File Type: jpg h_I grid.JPG (50.9 KB, 6 views)
File Type: jpg dom.JPG (19.2 KB, 8 views)
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Old   February 3, 2022, 01:30
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Convergence issues can usually be solved by modifying numerical settings, so I would focus on getting your case converged for the current SA model. Have you based your setup on an existing tutorial or test case?

The first thing to check is always the mesh quality: does your mesh have low skewness and low aspect ratio cells?

The next thing to check is the CFL number: lower CFL is more stable but slower convergence. If your CFL is high, you could try CFL=1.

After this, we'll have to look at your config file to see which other settings are used.
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Old   February 3, 2022, 02:51
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Quote:
Originally Posted by bigfootedrockmidget View Post
Convergence issues can usually be solved by modifying numerical settings, so I would focus on getting your case converged for the current SA model. Have you based your setup on an existing tutorial or test case?

The first thing to check is always the mesh quality: does your mesh have low skewness and low aspect ratio cells?

The next thing to check is the CFL number: lower CFL is more stable but slower convergence. If your CFL is high, you could try CFL=1.

After this, we'll have to look at your config file to see which other settings are used.

I am using Turbulent ONERA M6 compressible flow tutorial as reference. I modified .cfg file from this case according to my needs as mentioned in my reference paper.



1. Mesh looks alright. I have checked. Although not 100% confident. If no other way works out I will do meshing again but first I need to know whether issue is with mesh or in .config file.


2. CFL=0.25 for my case with CFL_ADAPT_PARAM=(1.0, 1.1, 0.25, 5.0)


I am attaching my .cfg file with this. Please have a look.


Note- my initial residual start in order of 10^-6 drops till 16^-6.8 then starts to increase.
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File Type: txt extrude_normal_SA.txt (9.5 KB, 4 views)
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