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Alex August 13, 2008 22:55

increasing drag coefficient
 
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

Rudresh August 14, 2008 00:52

Re: increasing drag coefficient
 
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.

Alex August 14, 2008 21:18

Re: increasing drag coefficient
 
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

Ravi Shankar August 20, 2008 08:25

Re: increasing drag coefficient
 
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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