# Buoyancy in gas turbine rotor

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 May 28, 2012, 09:20 Buoyancy in gas turbine rotor #1 New Member   Join Date: May 2012 Posts: 5 Rep Power: 5 Good day for everyone! I am investigate a question of heat transfer and flow through a rotor of axial compressor, like shown on a picture: rotor.jpg Red arrow in the left - it is an inlet into the domain. In the right - outlet. Arrows on the top - the heat flow from the gas in the compressor. Black lines- supposed flow direction inside the rotor. In my opinion I must observe strong buoyancy effect of heated from the disc air, which must transport to the axis, mix with cool air and go back to the "top" in rotating domain. In help i've found that: "For steady-state rotating domain simulations involving buoyancy, the gravity vector must be aligned with the axis of rotation." But i'm confused, because did not understand which number of gravity component must be specified in the appropriate window in bouyancy domain option. With disabled buoyancy option - there are now this effect off course. Can anyone help me to solve this problem in CFX? Thank you.

 May 28, 2012, 18:41 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 10,665 Rep Power: 84 If this device is rotating then isn't the only sensible thing to do to model the whole thing? I cannot see how modelling a small slice is going to work.

 May 29, 2012, 01:31 #3 New Member   Join Date: May 2012 Posts: 5 Rep Power: 5 Sorry. I didn't said, that i'am modelling a sector with periodic interface: sector.jpg Is it enough?

 May 29, 2012, 06:38 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 10,665 Rep Power: 84 If buoyancy is important then no, it is not enough. If buoyancy is significant then the flow will go from the bottom of the rotor to the top. This flow is not periodic. It might be symmetric - with only a single symmetry plane through the middle of the device. And in this case, guess what? The symmetry plane is parallel to the gravity vector like the original error message said.

 May 29, 2012, 06:44 #5 New Member   Join Date: May 2012 Posts: 5 Rep Power: 5 But what value of gravity must be specified if i'm talking about gravity of rotating region which acceleration equals: sqr(Angular Velocity)*radius ?

 May 29, 2012, 06:48 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 10,665 Rep Power: 84 You are not talking about gravity. You are talking about centrifugal forces. If you want to model centrifugal forces then use a rotating frame of reference, and just define a gravity vector pointing anywhere. Point it along the rotation axis to keep the solver happy.

 May 29, 2012, 07:10 #7 New Member   Join Date: May 2012 Posts: 5 Rep Power: 5 I'll try it. Thank you so much

 May 29, 2012, 07:23 #8 New Member   Join Date: May 2012 Posts: 5 Rep Power: 5 I'm sorry, but does it means that i must just enable rotating option in DOMAIN MOTION and Buoyancy model in additional coordinate frame? And what about buoyancy turbulence model? Last edited by snusmumrick; May 29, 2012 at 07:52.

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