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turbulent modelling.... help needed

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Old   June 23, 2006, 12:53
Default turbulent modelling.... help needed
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hello all i m trying to model flow over a cylinder. the reynolds number is 20000. i m using the unsteady solver and k epsilon model. i have two questions: 1. how to specify the turbulent speciafications.. i mean what values shud i use for turbulent intensity and the dissipation rate. i have gone thru the documentation but cudnt find a satisfactory answer. 2. how to decide the time step size? i m expecting unsteady vortex shedding, but the results doesnt show anything like that. wud be glad if anyone of u help me. thanks very much.
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Old   June 24, 2006, 23:41
Default Re: turbulent modelling.... help needed
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For example in wind tunnels you have a value of 0.01 to 0.05 for k. Epsilon you have to estimate by viscosity ratio.

epsilon ~ C_mu * (k^2/viscosity)*(viscosity/viscosity_turbulent)

where (viscosity/viscosity_turbulent)= 1/10 ... 1/50.

But note that those values depend on the specific case.

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