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Old   August 13, 2008, 22:55
Default increasing drag coefficient
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Alex
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hi, i'm modelling turbulent flow past a cylinder and when calculating the drag coefficient it just keeps increasing in value and doesn't level off, even thou the solution converges every time step
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Old   August 14, 2008, 00:52
Default Re: increasing drag coefficient
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Rudresh
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At the inlet you have to impose the proper values for the Turbulence parameters.Calculate the Turbulent kinetic for the given inlet boundary condition and Impose the same. And dissipation rate should be imposed as zero at the inlet.

This gives a better CFD prediction for Drag.This has given drag values close to theoritical values for ship hull hydrodynamics.
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Old   August 14, 2008, 21:18
Default Re: increasing drag coefficient
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Alex
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Do you mean for k-e viscous model i input my calculated value for turbulence kinetic energy under TKE and 0 for TDR. Do you calculate the TKE value using the equation k = 1.5*(UI)^2? It would be great if you could clarify this for me.

Thanks
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Old   August 20, 2008, 08:25
Default Re: increasing drag coefficient
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Ravi Shankar
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Always for External flows, make sure to check this.

1. Reference values for Drag component. 2. Boundary conditions - Neumann, Dirichlet and Mixed. 3. Inlet - velocity, Outlet - pressure, Walls - Zero wall shear.

Best Regards.
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