Pressure instabilities when running RANS on mixed grid type ( Case from DPW7)

[fomistul-cfd]

Hi all, I encounter a problem when running a case for grid convergence from dpw7
The case is :

When inspecting the solution on the surface section the contour plot is showing instabilities that are not influenced by convective scheme , MUSCL reconstruction or limiter.

This was run on a grid generated by me, so to see if it's a grid problem I run also a simulation with comitee grid from dpw7 workshop ( DLR grid with mixed elements)
https://dpw.larc.nasa.gov/DPW7/DLR_Grids.REV00/

When converged the plot showed the same instabilities but on the wing tip where I observed they are appearing on a specific grid topology.
The pressure instabilities:

The grid topology:

We can see that the instabilities appear when a topology of this type is appearing in the grid:

Here is a config file example.

config.txt

I also tried to inspect residuals and orthogonality of the mesh to see if it's a warping/quality problem but the output for quality show zero for all volume cells( it can be me doing something wrong, if someone could help me with that will be great). In term of residuals they were low -8 in logarithmic scale.

Is there something I can do to get rid of these instabilities or is it a bug/ numerical error related problem?

Thank you.

L. E. : In term of force coefficients the results are really good.

[pcarruscag]

Have you tried using Green-Gauss gradient instead of weighted least squares?

[fomistul-cfd]

Hi, yes, I tried both GG and WLS for the gradient.
For convective schemes, I tried SLAU2, Roe, and JST.
For upwind, I switched MUSCL on and off, but it didn’t help.
I changed the turbulence order to 1 and used the simple SA formulation, but nothing worked.
I tried multiple limiters: Van Albada Edge, Nishikawa R5, Barth-Jespersen, Venkatakrishnan, and Venkatakrishnan-Wang.
I also tried modifying the k factor from 0.05 to 0.1 to 0.3.
I thought it could be a problem due to MPI partitioning (I sometimes get instabilities like this when reading a decomposed case from OpenFOAM), but running on a single core did not make the instabilities go away.
My guess is that the fluxes are not being computed correctly, but it’s just a guess.
Tomorrow, I will try to make a flat plate with the surface pattern that is causing the instability and see if non-warped faces have the same problem.

[pcarruscag]

mpi issues usually lead to divergence, or the artifacts follow the MPI partition lines.
If you can make this happen on a smaller case it will be very helpful.
What exact version of SU2 are you using?
Do you see these patterns in any other variables? Temperature, shear stress

[fomistul-cfd]

Density and yplus also had this instabilities, those are the variables that I'm sure about, I will check other ones tomorrow . I have the latest version 8.3, the problem was present also in 8.2. And by mpi problem I meant artifact across partion line (as you said) due to postprocessing, but unfortunately it's not the case here.