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Time step size sensitivity of piso algorithm

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Old   January 29, 2017, 16:18
Default Time step size sensitivity of piso algorithm
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Hello, for a simple circular cylinder case with Re=64k I have completely different vortex shedding frequency and force history using deltaT=4e-6s and deltaT=4e-7s. Both time steps are several magnitudes lower than shedding period, the larger time step actually compares better with experimental result.

I'm using 2nd order backward time scheme, I also tried Crank Nicolson and got another two different results, I don't know the segregated approach of the PISO algorithm is the cause, and I also tried adding an extra outer loop(PIMPLE algorithm) and the result is the same as the PISO. Please help, thanks!
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Old   February 1, 2017, 17:00
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I have no idea at the moment but maybe (really maybe) it is related to that one: Wrong treatment of time derivatives in matrices (Jasak Presentation)
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