Help???

Kiran

Hi all, I'm working on the unsteady flow in a rocket nozzle.I'm trying to use the Spalart-Allmaras model for viscosity.I've used a value of 1 for the turbulent viscosity ratio for the inlet and a value of 8 for the backflow TVR.But,for some reason,the solution crashes and I'm not able to proceed further.Can somebody who has worked on similar problems tell me what the turbulent viscosity ratio is and what are the factors that affect it?Also,what do we calculate TVR from?Any help would be greatly appreciated. Thanks in advance, -Kiran