axial flow compressor influence on fluid at inlet

rohit_turbo · February 1, 2016, 05:35

Hello,
I am working on a transonic axial compressor project in CFX, but I need help on a particular note which I am not sure off.
Can anybody please explain upto what length upstream of the rotor should I be taking as rotating domain since i am not sure till what axial distance does the compressor influence the fluid at inlet ??
If at all anybody would enlighten me on this it would be really helpful!
Thanks,
Rohit

D.B · February 1, 2016, 22:25

Quote:

Originally Posted by rohit_turbo

Hello,
I am working on a transonic axial compressor project in CFX, but I need help on a particular note which I am not sure off.
Can anybody please explain upto what length upstream of the rotor should I be taking as rotating domain since i am not sure till what axial distance does the compressor influence the fluid at inlet ??
If at all anybody would enlighten me on this it would be really helpful!
Thanks,
Rohit

Can you explain , what your domain is? Since it is a transonic compressor, I would assume that it is either in a rig or a gas turbine engine. Also I am assuming that you have no guide vanes/stators upstream of the compressor since you haven't mentioned that explicitly. So in that case you should only have a rotating domain atleast upstream of the compressor. In that case it would be ideal to do a domain independence study. You can start with C or 2C distance upstream of the compressor, with C being the maximum chord length.

rohit_turbo · February 2, 2016, 00:16

Dear D.B,
Thanks for your reply.
My domain is a single stage transonic compressor.
yes you are exactly right, no IGVs have been taken into consideration upstream of the rotor and yes it is a test rig. I have tried doing a study in which I have taken 2C length.
A domain upstream rotor with 2C length rotating and non-rotating comparison I have done.
But, a doubt arose in my mind that whatever may be the case If I keep the inlet domain at 2C rotating, the fluid undergoes a pre-whirl and then enters the compressor rotor. I thought there might be a thumb rule or so to keep a particular distance upstream of the rotor.I should try a different distance as u say and try giving it a rotation. May be I can establish something on this!!.
Thank you

turbo · February 2, 2016, 10:05

Take a far upstream ahead of the rotor like 2C or 3C, 4C ..., but you can set a rotating hub wall in the Pre which will be the same as your real machine. The rest will be set as a non-rotating hub.

February 1, 2016, 05:35	axial flow compressor influence on fluid at inlet	#1
rohit_turbo New Member Rohit S Iyer Join Date: Oct 2015 Posts: 16 Rep Power: 10	Hello, I am working on a transonic axial compressor project in CFX, but I need help on a particular note which I am not sure off. Can anybody please explain upto what length upstream of the rotor should I be taking as rotating domain since i am not sure till what axial distance does the compressor influence the fluid at inlet ?? If at all anybody would enlighten me on this it would be really helpful! Thanks, Rohit

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February 2, 2016, 00:16		#3
rohit_turbo New Member Rohit S Iyer Join Date: Oct 2015 Posts: 16 Rep Power: 10	Dear D.B, Thanks for your reply. My domain is a single stage transonic compressor. yes you are exactly right, no IGVs have been taken into consideration upstream of the rotor and yes it is a test rig. I have tried doing a study in which I have taken 2C length. A domain upstream rotor with 2C length rotating and non-rotating comparison I have done. But, a doubt arose in my mind that whatever may be the case If I keep the inlet domain at 2C rotating, the fluid undergoes a pre-whirl and then enters the compressor rotor. I thought there might be a thumb rule or so to keep a particular distance upstream of the rotor.I should try a different distance as u say and try giving it a rotation. May be I can establish something on this!!. Thank you

February 2, 2016, 10:05		#4
turbo Senior Member Join Date: Jun 2009 Posts: 174 Rep Power: 16	Take a far upstream ahead of the rotor like 2C or 3C, 4C ..., but you can set a rotating hub wall in the Pre which will be the same as your real machine. The rest will be set as a non-rotating hub.