Axial turbine simulation - BC setup problem
 

Hi to all,
I am new to turbo machinary simulation.I am doing an axial turbine multistage cfd analysis.At first i am doing 1st stage only

1) In this i setup run initially using CFX turbo mode.Interface type I kept Stage Rotor and I kept all other BC's as default.For this i am getting good converged results(1e-5).

2) Later in 1st case i found that, Rotor shroud wall BC is counter rotating .In 2nd case, i changed it (rotor shroud wall) to rotating wall BC .Now i am getting oscillating behavior (periodic) in solver.

In both cases stator is stationary and rotor is rotating.All other BC's are same.

could anybody explain me which one is right and why the oscillating behavior in 2nd case.

Thanks in advance

FAQ: http://www.cfd-online.com/Wiki/Ansys...gence_criteria

Looks like your change in BC moved the simulation into a more numerically or physically unstable regime.

Thanks ghorrocks
What you told i understood.

1) What i am not getting is which direction is right one?

2) And another query is I am getting about 10% more mass flow at Rotor outlet (Stage1) with good converged results.Is it correct behaviour for the turbine?

Can you post an image of what you are modelling and where the boundaries are?

Thanks ghorrocks

Sorry I can't post images as it is official document (Confidential).

But i understand the things.Actually i mean to say whether Rotor shroud wall velocity (influence on flow) should be uncheked in cfx pre, if it doesn't have clearance.Now i am clear.

Thanks for your reply.