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Old   June 20, 2012, 03:11
Question Vortex shedding in sphere
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I'm trying to simulate vortex shedding in a sphere at Re 600, but without success. I am using PISO pressure velocity coupling.

Also, i tried providing an initial perturbation to the flow by putting in a patch with a certain velocity in some part of the flow domain, but it seems to work only in the case of a 2D cylinder and not for a sphere.

I've been stuck with this problem for 2 weeks. Please help!
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Old   June 20, 2012, 03:34
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Hi,

What error do you have? How is your domain?? Do you have a fine mesh? What are your boundary conditions?
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Old   June 21, 2012, 11:04
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hey, thanks for replying.

It just converges after a few iterations and the value of Cd and Cl becomes constant. I have a cuboidal flow domain with a very fine mesh near the surface of the sphere and a coarse mesh farther away.

The boundary conditions i'm using are velocity_inlet, pressure_outlet and symmetry.

Hope that answers your questions.
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Old   June 22, 2012, 06:42
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but if your problem converges, what is the problem you have? Otherwise, it is a good idea to make a fine mesh back to the sphere too, since fluent will solve better the sphere trail.
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Old   June 22, 2012, 08:37
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Ok havent got info on this till I look at one of my books but is vortex shedding not first observed at a higher Re number of 800. This is just off hand my thinking but havent got any literature on me to confirm.
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Old   June 22, 2012, 14:51
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For a case where vortex shedding occurs, the solution should not converge and the value of Cd and Cl should oscillate. I tried this for a cylinder and that is what happened.

Also, most sources report that vortex shedding in a sphere begins at < Re 250.
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Old   June 23, 2012, 17:52
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hi
i worked in this problem before. you can use this article:
" Simulation of Flow Past a Sphere using the Fluent Code" copy this in google and download. hehe
i couldn't reach vortex shedding at that time and i leaved that. so if you can reach the good result please inform me.
best regards
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Old   June 24, 2012, 01:21
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I have already gone through it and got no vortex shedding using the exact methodology that they have suggested.

Even the vortex shedding i obtained for a cylinder was accomplished using PISO instead of the SIMPLE that they've recommended.
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Old   June 25, 2012, 12:30
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yes PISO is more efficient for transient simulations. i will work on sphere next week again and if i reach good result then i will tell u
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