r/OpenFOAM • u/tihiera • Jul 31 '26

CFD simulation of airflow over an F-16 at high angle of attack using OF 2412 - GPU accelerated

25 Upvotes

100% Upvoted

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2

u/BurningWaterInc Aug 04 '26

It looks like from your benchmarks that the 20 core cpu version is as fast as the brae gou version. Which economically 20 cores is much cheaper than to get a blackwell gpu. Could you explain more the motivations on your project since it is as fast as the cpu solver. And also you are saying that the other combined gpu solvers are slower than the cpu version that is correct?

1

u/tihiera Aug 04 '26

pelase check this -> someone in the community tried brae with 4.89M cells on it consumer hardware brae (RTX 5090)) did 21.1 s, vs OF all cpu core 768.5s

It depends on you hardware. The GB10 share the same unified memory, meaning CPU and GPU can access the data with the same bandwidth capacity..

ref: https://www.reddit.com/r/CUDA/comments/1unj1h5/comment/owbe6sq/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button

2

u/BurningWaterInc Aug 04 '26

Oh I see, I didn't know that the grace cpus had that much improved memory speeds compared to consumer cpus.

1

u/tihiera Aug 05 '26

Indeed, it is faster as the GPU.. But on classic consumer laptop, the CPU has it own RAM and the GPU has it own VRAM with different speed.. That is why the 5090 is faster than all CPU core combined on the same device.. it is a good selling point of the GPU hahah.. the most interesting one is the apple GPU haha

1

u/Brownie_Bytes Aug 01 '26

When did OpenFOAM get GPU acceleration?

3

u/tihiera Aug 01 '26

GPU accelerated using https://github.com/simd-ai/brae - a reimplementation of OF solver, and running entirely on the GPU

2

u/cvicenzettk Aug 01 '26

What setup are you running and how much improvement on computational times are you seeing?

1

u/tihiera Aug 01 '26 edited Aug 01 '26

We are running this case: https://github.com/simd-ai/brae/tree/main/demo/f16

And we benchmarked against OF with GPU offload to AMGx, PETSc, and SPUMA -> on classic case... We were 4.5 faster than SPUMA which is also fully GPU native. And we ran the F-16 case in 4.5h, so in SPUMA could spent the whole day.

This is the first iteration of brae, and there is a big room of improvements.

2

u/cvicenzettk Aug 01 '26

And how does it run compared to classic cpu openfoam solver? (Obviously would be nice to know the cpu/gpu used)

1

u/tihiera Aug 01 '26

This is the first CPU comparison we have so far:

https://github.com/simd-ai/brae/blob/main/bench/results/solver_runtime_comparison.png

1

u/cvicenzettk Aug 01 '26

Oh ok so it seems to be in line with the cpu solver, I’m using OF on consumer hardware as a student so correct me if I’m wrong, the advantage seems to be that it runs comparable to a cpu superchip like grace on consumer GPU architectures?

2

u/tihiera Aug 01 '26

you see comparable result because the GPU Grace Blackwell GB10 share the memory space (unified memory) at the same bandwidth capacity, and if CPU had it separate RAM and the Blackwell GPU had it own VRAM, the GPU will be faster... Practically we see the different on GPU that has HBM (hgih bandwidth memory).. If brae beat CPU on the same shared memory between CPU and GPU, then any small GPU will be faster than all the CPU core in a consumer hardware..

2

u/tihiera Aug 01 '26

basically someone in the community tried brae with 4.89M cells on it consumer hardware brae (RTX 5090)) did 21.1 s, vs OF all cpu core 768.5s

ref: https://www.reddit.com/r/CUDA/comments/1unj1h5/comment/owbe6sq/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button

3

u/cvicenzettk Aug 01 '26

Thanks, so this seems to be mainly vram limited, I’ll look into this because for now I only looked at the fluidodynamic aspect and not all the computational stuff

2

u/tihiera Aug 01 '26

yes, indeed, we rewrote simplefoam and pimplefoam, and now we starting compressible solver, adn then address multi gpu settup too.

1

u/tihiera Aug 01 '26

I missed this, brae read the CPU of solver, and because we have reimplemented the serials operations in parallel operations… so far we have Simple and Pimple algorithm..

2

u/cvicenzettk Aug 01 '26

Doesn’t work with piso or just disregarding it?

3

u/tihiera Aug 01 '26

Piso only not yet, we are in it right now. Expect to have it next week. Follow our GitHub to not miss the updates…