Centrifugal fan modelling

GU

Does anybody know what the following means:

Error: > (greater-than): invalid argument [2]: wrong type [not a number] Error Object: nan

This is what Fluent spits out after a few iterations when i try to run a turbulent simulation of a centrifugal impeller in a volute using the K-epsilon model.

The impeller alone works fine and converges quickly in both the steady and transient cases but when i model with the volute, the turbulent viscosity is limited constantly by the viscosity ratio settings and the residuals don't converge.

does anybody have any suggestions as to what i'm doing wrong here???

Thanks