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Andrew August 13, 2008 04:44

turbulent initial condition

I am modelling a buoyancy driven flow in a horizontal concentric cylinder at high rayleigh number. After doing some research, i have narrowed down my turbulence model to either the SST k-w or the Reynolds stress BSL k-w model. However, i am finding it difficult to get a converged solution. I've sent the convergence criteria to 10^-5. I only used automatic initial conditions given in CFX. Does anyone know what initial values i should use? How can i check if my solution is correct?

John S. August 13, 2008 09:46

Re: turbulent initial condition
Which transport equations specifically are you having difficulty converging?

In general the SST model is more stable than the Reynolds Stress models. You might try to get an initial solution using the BSL model and then restart it with SST.

Also, CFX uses the first order upwind differencing scheme as default for the calculation of the Reynolds Stress and turbulence parameters (this is true even if you specify the high resolution scheme over all). You might try to run them high res to see if that helps. You'll have to manually change that in the CCL, though.

You could also try setting the expert parameters turbulence diffusion scheme = 2, turbulence posdef option = 1 and varying their values.

Andrew August 15, 2008 05:48

Re: turbulent initial condition
The navier stokes and heat transfer equation are not converging....both of them a fluctuating at 10^-4.

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