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Old   January 18, 2011, 13:23
Default Purchasing a new desktop for CFD
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Robert
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I am looking to buy a new desktop for OpenFOAM simulations.
I would like to quickly run successive simulations with ~80k cells using kOmegaSST turbulence model and GGI. Any suggestions? I am going to buy from Dell.

On a i5 (3.2Ghz, quad core) computer with 8gb of RAM the above case for a .25-second-long simulation (max courant 1.0) takes about 7-9 hours. Is this reasonable?
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Old   January 26, 2011, 06:45
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7-9 hours seems a little long for only 80k cells and 0.25 seconds even with a moving mesh. Have you checked your numerical settings are reasonable (ie a reasonable number of sweeps)?
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Old   January 26, 2011, 10:06
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The rotor is turning at 5000 rpm, which I thought was the cause of the long runtime because small timesteps are needed. I set tolerances in fvSolution to 1e-4 and max courant to 1. About 50k of the 80k cells are in the rotor.
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Old   January 26, 2011, 15:40
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Oh, ok, with 5000 rpm that works out to about 21 rotations in that quarter second, quite a bit more mesh updating is required and much much smaller time steps than I would have expected. I don't have experience with simulations of that type so I can't really give a good estimate of how long they should take. That being said you may have difficulty speeding up the simulation by dividing it onto more processors since there is a certain point where dividing the problem up further and further has a diminishing return or negative effect. I think if you had to choose between a high end quad core (by this I mean 4 process threads/ 2 physical cores if intel or 4 physical cores without hyperthreading) and an a less high end 8 core, the quad (with each core being better) would be the way to go. That being said if you want to do larger simulations then 80k cell, more cores will start to help you more overall. I have seen i7 2600 series for as low as $300 (newegg) if you don't mind it not being the very top of the line i7. If you can find a comparison/benchmark between your current processor and other models you can get some idea of the performance increase you will see.
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