Reason for asymmetry in symmetric geometries

doubtsincfd · June 10, 2010, 03:20

say I have a symmetric geometry like a circular cylinder. the grid is perfectly symmetric around the cylinder and the inlet profile is also symmetric. still why do we get alternate vortex shedding? what is the numerical reason?

in real life scenario there is some asymmetry in the inlet flow which might trigger the asymmetric vortex shedding. but why does this happen in a perfect cfd simulation?

agd · June 10, 2010, 09:13

It is true that in real life there may be some asymmetry that can trigger an asymmetry in a flow, which might not happen in a "perfectly" symmetric CFD simulation. But no CFD simulation is perfectly symmetric, due to such things as round-off error. Also, you are failing to consider the possibility that the Navier-Stokes equations can support solutions that are time-varying and only symmetric in a time-averaged sense.

June 10, 2010, 03:20	Reason for asymmetry in symmetric geometries	#1
doubtsincfd Senior Member Join Date: Nov 2009 Location: Michigan Posts: 135 Rep Power: 17	say I have a symmetric geometry like a circular cylinder. the grid is perfectly symmetric around the cylinder and the inlet profile is also symmetric. still why do we get alternate vortex shedding? what is the numerical reason? in real life scenario there is some asymmetry in the inlet flow which might trigger the asymmetric vortex shedding. but why does this happen in a perfect cfd simulation?

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June 10, 2010, 09:13		#2
agd Senior Member Join Date: Jul 2009 Posts: 358 Rep Power: 19	It is true that in real life there may be some asymmetry that can trigger an asymmetry in a flow, which might not happen in a "perfectly" symmetric CFD simulation. But no CFD simulation is perfectly symmetric, due to such things as round-off error. Also, you are failing to consider the possibility that the Navier-Stokes equations can support solutions that are time-varying and only symmetric in a time-averaged sense.