Rotor Stator Instability
 

Hi! Everyone, I am quite new to CFX. For those who are playing with turbomachineries, can anyone tell me if there is a way to avoid the transient effects which cause the residuals to fluctuate after converved to a certain value (magnitude of 1e-4s). I am trying to avoid transient simulation because I am only intereted in the overall performance of the pair. But even if I use transient simulation, the residuals dont go down far enough to make me happy, they will stay almost flat. Also, If i have to use transient simulations, How am I going to average the the quantities over a period? Thanks

Re: Rotor Stator Instability
 

Hi! is me again. Also I like to ask: if I got message as follwed in the process of iteration, is that normal? Is this the source of residual fluctuations?

"A wall has been placed at portion(s) of an OUTLET boundary condition (at 23.6% of the faces, 2.9% of the area) to prevent fluid from flowing into the domain. The boundary condition name is: S1 Outlet. The fluid name is: Air Ideal Gas. If this situation persists, consider switching to an Opening type boundary condition instead."

Thanks

Re: Rotor Stator Instability
 

Your BCs are of an inappropriate type and/or position.

Re: Rotor Stator Instability
 

Can you put your outlet further downstream?

Re: Rotor Stator Instability
 

Hi! Thank you very much for the help. So what is the next strategy after discovering extending the outlet does not help much? Do you think SST model will be better than k-e turbulent model in high speed turbomachines? Thanks