Axial turbine simulation - BC setup problem

bharath · November 27, 2013, 11:04

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

ghorrocks · November 27, 2013, 16:36

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.

bharath · November 28, 2013, 00:14

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?

ghorrocks · November 28, 2013, 00:49

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

bharath · November 28, 2013, 06:07

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.

November 27, 2013, 11:04	Axial turbine simulation - BC setup problem	#1
bharath Senior Member Bharath kumar Join Date: Apr 2009 Posts: 169 Rep Power: 17	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

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November 27, 2013, 16:36		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	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.

November 28, 2013, 00:14		#3
bharath Senior Member Bharath kumar Join Date: Apr 2009 Posts: 169 Rep Power: 17	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?

November 28, 2013, 00:49		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Can you post an image of what you are modelling and where the boundaries are?

November 28, 2013, 06:07		#5
bharath Senior Member Bharath kumar Join Date: Apr 2009 Posts: 169 Rep Power: 17	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.