Problems with residuals??

Peter Kolb

Hi CFD-users,

I'm a FLUENT 5.4.- user and I try to simulate the flow inside a stirred tank. For the motion of the stirrer I use the MRF-Model. The viscous model is the standard k-epsilon. I begin my calculations with very low rotational speed and after reaching a destined convergence, I increase the speed. When I postulate small scale residuals it's no problem for the x-velocity, y-velocity, z-velocity, k and epsilon to get a small value. At 10^-7 they all reach a kind of "steady state" where no changes could be recognized; but the continuity reach a stedy state at 10^-6. When I now increase the rotational speed step by step, all residulas will find "this steady state" at the value 10^-7 again except for the continuity. The residual for the continuity is increasing while I increase the speed. To my questions: 1)Is this normal that the residual for the continuity is increasing while I increase the speed? 2)What adjustments do I have to change to solve this problem?

Solve Control Solution:

Under-relaxation factors Pressure 0.3 Momentum 0.7 Turbulence Kinetic Energy 0.8 Turbulence Dissipation Rate 0.8 Viscosity 1.0 Density 1.0 Body Forces 1.0

Discretization Pressure PRESTO! Momentum First Order Upwind Pressure-Velocity Coupling SIMPLE Turbulence Kinetic Energy First Order Upwind Turbulence Dissipation Rate First Order Upwind

Thanks Peter