Fix slidingmesh for SA

[maxaehle]

Proposed Changes

CSlidingInterface::GetDonor_Variable needs to access the Primitive of flow variables and the Solution of turbulent variables. Which one is the case, is currently decided by checking donor_solution->GetnPrimVar() == 2 (true->turbulent, false->flow). If the SA turbulence model is used, the non-overidden "virtual placeholder" CVariable::GetPrimitive(unsigned long,unsigned long) const returning zero is incorrectly called.

We propose to fix this by additionally checking for donor_solution->GetnPrimVar() == 1.

Related Work

@maxaehle, @mcmorelli, @BeckettZhou, @EduardoMolina

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[maxaehle]

I followed @pcarruscag 's request in commit 12974ab.
BTW it's very confusing that the SA/SST turbulent solvers have nPrimVar==1,2 but GetPrimitive is not overridden and thus returns zero. So another fix to the bug considered in this PR would be to override GetPrimitive on the turbulent solvers such that it forwards to GetSolution?

[pcarruscag]

Thanks Max, I missed the solution v primitive part of the problem.

[pcarruscag]

I don't think forwarding GetPrimitive to GetSolution by default is a good option, a "Slinding state" layer could be appropriate but that does not need to be fixed right now.

[maxaehle]

By "Sliding State layer", do you mean a virtual CVariable::GetSlidingMeshDonorVariable that returns 0 by default, but forwards to GetSolution on the flow and GetPrimitive on the turb variables?

[pcarruscag]

I would add that layer to the solver so that the interpolation does not have to bypass it by going straight to the nodes.

[maxaehle]

Ok thanks Pedro!

[TobiKattmann]

Thanks @maxaehle 💐

Not sure how this will interact with scalar solvers (species transport) to come ... but in case someone there wants to work with sliding interfaces then I guess one has to test that a priori