SimScale CAE Forum

Magic numerics to get TETforCFD meshes to converge quicker (sometimes 1/11th real time and 1/6th core hours), to more stable CFD results


#1

That is a big bold topic title but here is the project that seems to back it up.

EDIT: Yes they converge great to stable results but are giving me accuracy headaches in a NACA0012 verification project that I am working on. Stay tuned for updated numerics soon if I can more closely verify the NACA0012

PLEASE try these out and report back here on your difficult TETforCFD mesh, CFD convergence problems :wink:

EDIT: I just thought the topic was necessary to quickly put ‘out there’ as I do not want people getting discouraged when trying TETforCFD meshes with DEFAULT numerics. (I almost gave up and I have a lot of perseverance :wink: )


Simulation Error
DalesStuff: My Topics and Projects that I need quick access to :wink:
#2

Hi Dale,

Just some advise, on these numerics.

Firstly for stability, I agree with you numerics, in terms of divergence schemes. Additionally, if any poor cells are present in the mesh, limited schemes to 0.33 or 0.5 will help for laplacian schemes. Also, for tet meshes, I add 2 non-orthogonal correctors. and that is my robust set of numerics for tet meshes.

However :slight_smile: Although this produces fantastic stability, it comes at a cost to accuracy, because the divergence schemes are first-order accurate (bounded gauss upwind is 1st order accurate) and for velocity and possibly the turbulence divergence schemes it’s better for accuracy if you used Gauss linear upwind (limited gradU or limited gradient) and are 2nd order accurate and in some industries where velocity gradients are critical to accuracy (such as aerospace) this might be the difference between invalid and valid results.

That’s just my penny for them, hope it helps.

Best,
Darren


#3

LOL, I am just coming to similar conclusions, not by knowledge but by iteration and perseverance…

I am trying to verify NACA0012 with TETforCFD mesh and my magic numerics are close on CL but I am not there yet on CD, but I know I will get there, even without knowledge :wink:

I will be updating this magic numerics topic soon to talk about the reduced result accuracy and perhaps show even better numerics if I can verify NACA0012…

EDIT: I just thought the topic was necessary to quickly put ‘out there’ as I did not want people getting discouraged when trying TETforCFD meshes with DEFAULT numerics. (I almost gave up and I have a lot of perseverance, as you know :wink: )

Thanks…


#4

Awesome work Dale, yes agreed.

The divergence sceheme for U using Gauss Linear Limited gradU was my ah ha moment for 0012 :slight_smile:

Best,
Darren


#5

COOL, I will have more comments in that area soon in your great NACA 0012 Verification project :wink: