I have simulated a two phase flume using the MFiX. The results were not good at all. So I started to come back to a simple case of single phase flow in a 2d channel. Using the Laminar flow both the Slip and No slip BCs in single phase give good results. But using K-epsilon model, the free slip BC creates velocity gradient on the wall!!! In the figure below the bottom wall is no slip while the upper is free slip, but both of them have created velocity gradient.
I have also checked the available tutorials, may be all of them and those of the previous versions… None of them has used the FSW boundary condition of fluid with the k-epsilon model. Can we use them together???
k-epsilon turbulence model uses wall function, which assumes a viscous sub-layer. If you want to eliminate the wall friction, you need to set the viscosity to zero, while this conflicts with k-epsilon model because the dimensionless distance from the wall becomes infinity large.
