FSI-Courant number

mortazavi · August 25, 2016, 10:44

Hi,
In my transient fsi simulation, the RMS courant number is about 20. In the paper which i am trying to reproduce the results, it is mentioned that the courant number should be aorund 1. but my simulation does not converge if i reduce the time step. any suggestion please?
thanks

ghorrocks · August 25, 2016, 18:56

The CFX fluid solver is implicit so is not restricted to Courant number = 1. An explicit solver is, they go unstable for Courant number >1.

But I do not know how implicit or explicit the FSI link between fluids and solids is. If it has significant explicit properties then it will impose a time step restriction which may be tighter than the fluids one alone.

I would have a look at the allowable time step on the fluids simulation alone and the solid simulation alone. Obviously you will need to use the smallest one, and probably even a fraction of that.

August 25, 2016, 10:44	FSI-Courant number	#1
mortazavi Member SMN Join Date: Jun 2009 Location: CANADA Posts: 71 Rep Power: 16	Hi, In my transient fsi simulation, the RMS courant number is about 20. In the paper which i am trying to reproduce the results, it is mentioned that the courant number should be aorund 1. but my simulation does not converge if i reduce the time step. any suggestion please? thanks

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August 25, 2016, 18:56		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,705 Rep Power: 143	The CFX fluid solver is implicit so is not restricted to Courant number = 1. An explicit solver is, they go unstable for Courant number >1. But I do not know how implicit or explicit the FSI link between fluids and solids is. If it has significant explicit properties then it will impose a time step restriction which may be tighter than the fluids one alone. I would have a look at the allowable time step on the fluids simulation alone and the solid simulation alone. Obviously you will need to use the smallest one, and probably even a fraction of that.