Unsteady flow calculation

wzf603709 · January 2, 2024, 03:17

Is it normal for the parameter fluctuation period obtained from unsteady calculations to be greater than the rotation period? What is the reason for it?

ghorrocks · January 2, 2024, 03:34

Are you doing a rotating machinery simulation? What are you modelling? What parameter are you looking at?

But talking about it in general:
This could be physical: for example the flow is dominated by other factors than the rotation and that is causing the parameter fluctuation, like the pipe downstream of the rotating machinery has a resonant frequency which is larger than the rotational period with a compressible fluid.

This could be numerical: (that is, a simulation error) - your simulation has not converged, is numerically inaccurate or has not achieved a repeatable periodic flow yet.

January 2, 2024, 03:17	Unsteady flow calculation	#1
wzf603709 New Member Wang Zhenfei Join Date: Aug 2023 Posts: 1 Rep Power: 0	Is it normal for the parameter fluctuation period obtained from unsteady calculations to be greater than the rotation period? What is the reason for it?

January 2, 2024, 03:34		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,705 Rep Power: 143	Are you doing a rotating machinery simulation? What are you modelling? What parameter are you looking at? But talking about it in general: This could be physical: for example the flow is dominated by other factors than the rotation and that is causing the parameter fluctuation, like the pipe downstream of the rotating machinery has a resonant frequency which is larger than the rotational period with a compressible fluid. This could be numerical: (that is, a simulation error) - your simulation has not converged, is numerically inaccurate or has not achieved a repeatable periodic flow yet. Opaque likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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