[Athos_e]

Hello everyone,
I have been trying to run a 3D simulation of a rotating cylinder in a hypersonic flow M=7. While I manage to get the simulation setup and running, the output results have me questioning whether I do something wrong.
I have initially run steady state cases for pitch angles 0-90 degrees and validated the results with another research paper. Now I wanted to see the effect of different angular velocities along the pitch axis has on the aerodynamic coefficients (Cl,Cd). I use RANS solver and SA turbulence model and multizone approach to prescribe different angular velocities for the cylinder. The problem is that my results even though I am running an unsteady case, seem to get close to the steady state ones with increasing the inner_iterations. In my understanding, increasing the inner iterations will just reduce the error from one physical step to the next but the unsteady nature should remain. I am not quite sure what is the issue here. I am using a time step of 1e-3 and DUAL_TIME_STEPPING-2ND_ORDER. Does anyone have any advice regarding such simulations? I can also supply the cfg file if needed.

Thanks in advance
Athos

[bigfootedrockmidget]

We have some pitching examples here:
https://github.com/su2code/SU2/tree/...Cases/unsteady
Do these cases work for you?

[Athos_e]

Hello, thanks for the quick reply. Just had a look at these and they seem to be similar to what I'm trying to achieve. However I have a few questions if you can help me out.

First of all I was trying to use the multizone approach, having 2 zones. One is the overall domain and another smaller sphere encapsulating my cylinder. I then prescribe a constant rotation in pitch on this second zone. Is this another correct approach? I know that multizone tends to be more computationally expensive but the results don't seem to be as correct as the approach you suggested.

If I understood correctly I can just prescribe a rotation along an axis by using ROTATION_RATE variable and I can neglect the pitching omega and pitching amplitude as in the tutorials right? In this way there will be a constant rotation around pitch.

I have also played around with the tutorial and saw that increasing the Mach number from subsonic to hypersonic (M=7) tends to give wrong results (in some steps Mach number reaches 50.) I would guess this would come from the mesh and also step size and CFL number correct? Since M=7 is hypersonic I should adjust accordingly these variables to get meaningful results.

Finally, using this method if I want to have a 3 dimensional simulation, is it only the mesh that needs to be changed or are there also extra variables that need to be included in the cfg file?

Thanks a lot for the help,
Athos