I am working on an open channel problem. Multi-phase (water+air) VOF, and k-epsilon turbulence model are utilized. I want to study the turbulent characteristics (for example k and epsilon) of the converged solution. In Ansys-Fluent, under the "Solution Controls" menu, there is an option to select the governing equations to be solved. For example, in my problem this option is as shown in the attached figure.
Now my question is can I only select the turbulence equation to be solved (to reduce computational costs)? Will the solutions be reliable ?
If you have strong shear at the phasic interface between air and water, than for the corresponding wave formation the k-epsilon model might not be the best model to use. I would recommend SST or another k-omega-based turbulence model with activated turbulence damping terms on the free surface. Otherwise you end up with rather unrealistically high turbulence values directly at the free surface separating the phases. This would correspond to rather large characteristic eddy length scale in the vicinity of the free surface, which could not be realized (physically realistic) in practice. This is the reason for the introduction of these turbulence damping terms in free surface flow modeling.
And yes, of course than all the governing equations have to be solved, since turbulence properties depend to a large extend on velocity gradients. Damping terms depend on phase distribution in space.
Regards,
Dr. Th. Frank.
Dear Nima,
For a open channel turbulent flow problem using VOF method, all these questions must be solved. However, if your water level is relatively flat you can use rigid-lid boundary condition which in return significantly reduce the computational power, since you are dealing with a single-phase problem.
Regards,
Shervin
If you have strong shear at the phasic interface between air and water, than for the corresponding wave formation the k-epsilon model might not be the best model to use. I would recommend SST or another k-omega-based turbulence model with activated turbulence damping terms on the free surface. Otherwise you end up with rather unrealistically high turbulence values directly at the free surface separating the phases. This would correspond to rather large characteristic eddy length scale in the vicinity of the free surface, which could not be realized (physically realistic) in practice. This is the reason for the introduction of these turbulence damping terms in free surface flow modeling.
And yes, of course than all the governing equations have to be solved, since turbulence properties depend to a large extend on velocity gradients. Damping terms depend on phase distribution in space.
Regards,
Dr. Th. Frank.
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