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-   -   Vortex Shedding (http://www.cfd-online.com/Forums/cfx/20668-vortex-shedding.html)

Morenike September 24, 2004 08:32

Vortex Shedding
 
Hello All, I am sure this question has been answered before. Perhaps Neale or Glen, at the time I paid no attention (Sorry !) I am trying to create vortex shedding around a rectangle, I tried using transient analysis with SST at about 0.001 secs over 2 secs,but I am unsucessful. I read that I may need to a create a pertubation at the inlet to get things going. I have no idea how to do it. I have a 1-D interpolation velocity profile measured in a wind tunnel at the inlet. I have access to bot CFX5.6 & 5.7

Neale September 24, 2004 12:13

Re: Vortex Shedding
 
Hello,

If you let it run long enough vortex shedding should start on it's own, eventually. Problem is that this relies on perturbations from the truncation, roundoff and possibly model errors. So, generating vortex shedding could take forever or may never happen at all if the turbulent viscosity is high enough to damp these sources of perturbations out.

So, as a result, you may need to add a perturbation to your initial conditions (as opposed to your inlet boundary condition), i.e. something that is non-uniform in the transverse direction. For example, you might start out with a a non-uniform initial condition for velocity. Eg, initialised your domain with a shear layer or a step velocity profile. You will need to run long enough to transport out the effects of the perturbation and if it's strong enough you should be able to generate vortex shedding.

Also, for transient runs, make sure the solver is converging to something reasonable within a timestep.

Neale



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