Time step size sensitivity of piso algorithm

TypeR · January 29, 2017, 16:18

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!

Tobi · February 1, 2017, 17:00

Hey,

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)

January 29, 2017, 16:18	Time step size sensitivity of piso algorithm	#1
TypeR New Member soichiro Join Date: Jun 2015 Posts: 6 Rep Power: 12	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!

February 1, 2017, 17:00		#2
Tobi Super Moderator Tobias Holzmann Join Date: Oct 2010 Location: Bad Wörishofen Posts: 2,716 Blog Entries: 6 Rep Power: 53	Hey, 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) __________________ Keep foaming, Tobias Holzmann

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