Setting the Under-Relaxation Factor for the Slip Velocity
You should begin the mixture calculation with a low under-relaxation factor for the slip velocity. A value of 0.2 or less is recommended. If the solution shows good convergence behavior, you can increase this value gradually.
Calculating an Initial Solution
For some cases (e.g., cyclone separation), you may be able to obtain a solution more quickly if you compute an initial solution without solving the volume fraction and slip velocity equations. Once you have set up the mixture model, you can temporarily disable these equations and compute an initial solution.
Solve Controls Solution...
In the Solution Controls panel, deselect Volume Fraction and Slip Velocity in the Equations list. You can then compute the initial flow field. Once a converged flow field is obtained, turn the Volume Fraction and Slip Velocity equations back on again, and compute the mixture solution.