cylinder and Kármán vortex street

sarav · December 23, 2009, 09:27

Hi,
I'm studying the problem of a turbulent flow over a circular cylinder and I'm trying to display the vortices in the wake of the bluff body.

Unfortunately I'm not getting the expected achievements, since I obtain only a kind of steady wake but not the typical alternating vortices.

Where can be the problem?

I've setted the "implicit unsteady" as time physical model, I'v chosen a reasonable (I hope

) time step using the relationship about the frequency of vortex shedding in a circular cylinder [0.05s (D=0.1m,V=5m/s)] and an arbitrary number of inner iterations (25).

Thanks!
bye

abdul099 · July 6, 2010, 11:49

The frequency of the vortex shedding is approx. 10Hz. A time step of 0.05 seconds is only half the vortex shedding frequency.
I would assume, you should decrease your time step.

If your simulation is set up correct, you can use less than 25 inner iterations. Maybe around 10, this will speed up the simulation.

Best regards

December 23, 2009, 09:27	cylinder and Kármán vortex street	#1
sarav New Member Join Date: Jul 2009 Posts: 25 Rep Power: 16	Hi, I'm studying the problem of a turbulent flow over a circular cylinder and I'm trying to display the vortices in the wake of the bluff body. Unfortunately I'm not getting the expected achievements, since I obtain only a kind of steady wake but not the typical alternating vortices. Where can be the problem? I've setted the "implicit unsteady" as time physical model, I'v chosen a reasonable (I hope ) time step using the relationship about the frequency of vortex shedding in a circular cylinder [0.05s (D=0.1m,V=5m/s)] and an arbitrary number of inner iterations (25). Thanks! bye

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July 6, 2010, 11:49		#2
abdul099 Senior Member Join Date: Oct 2009 Location: Germany Posts: 636 Rep Power: 21	The frequency of the vortex shedding is approx. 10Hz. A time step of 0.05 seconds is only half the vortex shedding frequency. I would assume, you should decrease your time step. If your simulation is set up correct, you can use less than 25 inner iterations. Maybe around 10, this will speed up the simulation. Best regards