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how does it affect????????

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Old   January 14, 2008, 00:22
Default how does it affect????????
  #1
jamal
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i am solving a laminar flow across a cylinder.i am interested in getting a good vortex shedding in unsteady flow. i want to know how this time step size,no. of time steps and no. of iterations per time step affect this phenomenon....

thanks a lot friends
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Old   January 14, 2008, 05:57
Default Re: how does it affect????????
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kris
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you should consider physical time scale

if incompressible flow, you should consider a turbulent time scale which is probably smallest time scale.

if compressible flow, you should consider a speed of sound for non-reacting flow due to smallest time scale

if reacting flow, you should consider chemical time scale, maybe 10^-6 or more

you should need no. 100 samples for 1-period.

good luck
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Old   January 14, 2008, 08:30
Default Re: how does it affect????????
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Sham
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To get a good vortex shedding you need to make sure that your mesh is fine enough and also your time step is small enough. To do this, you need to do some mesh dependence studies and also time step convergence study. I always keep the CFL number less than 1 to make sure your time step is small enough. If you keep your time step size small enough, you need not to worry about no. of time steps and no. of iterations per time step.

Sham.
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Old   January 16, 2008, 00:05
Default Re: how does it affect????????
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jamal
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thanks a lot friends..
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