Learning Forum

[Federico]

Second, Under relaxation factors will allow you to effectively tune the convergence rate of your solution. A low URF (near zero) will make convergence slower but make your solution more stable, and vice versa for URF closer to 1. 

There could be several reasons specific to your case which would explain why your solution sees negative volume cells with URF of 0.2, which is on the low side. Some of these reasons could be:

• use of incompressible fluid
• bad Dynamic Mesh settings
• time step size too large (if transient case)