Boundary Condition

pks126 · September 19, 2012, 02:32

Hello
I have given BC at inlet of a compressor as velocity profile and total T
And at outlet BC as mass flow rate but it did not run, showing error that P is not mention at any boundary.I wanted to know is it necessary to give Pressure as a BC in case of compressor at any one of the boundary.

If my compressor outlet is going into the atmosphere then what could be the pressure(total/static) boundary condition at outlet plane.

Thanks
Prashant

Maged_CFD · September 22, 2012, 20:01

Hello Prashant,

You need to set the boundary condition at the outlet as:
P_static = atmospheric pressure

Note that your outlet plane should be far enough from the compressor blades.

pks126 · September 24, 2012, 01:18

Thanks Maged_CFD
I did same thing and give outlet static P 101325Pa and after completion in cfx also shows outlet static P as 101334Pa which ony 9pa higher i think this BC is ok.
thanks once again

vicarious · October 31, 2012, 05:15

You need to set both inlet and outlet boundary conditions as pressure. You calculate the inlet velocity from the compressor flow coefficient (phi) and dynamic pressure (Pv) as well. Then you calculate the inlet static pressure (Ps=Pt-Pv). Pt as total pressure and Ps as static pressure. the outlet static pressure can be calculated by the compressor head coefficeint (si). By in entering these BCs your solver will be able to calculate the velocity and pressure field.

Best regards.

September 19, 2012, 02:32	Boundary Condition	#1
pks126 New Member Prashant Kumar Singh Join Date: Jun 2012 Location: IIT Bombay Posts: 19 Rep Power: 13	Hello I have given BC at inlet of a compressor as velocity profile and total T And at outlet BC as mass flow rate but it did not run, showing error that P is not mention at any boundary.I wanted to know is it necessary to give Pressure as a BC in case of compressor at any one of the boundary. If my compressor outlet is going into the atmosphere then what could be the pressure(total/static) boundary condition at outlet plane. Thanks Prashant

September 22, 2012, 20:01	Re: Boundary Condition	#2
Maged_CFD New Member Maged Join Date: Sep 2012 Posts: 7 Rep Power: 13	Hello Prashant, You need to set the boundary condition at the outlet as: P_static = atmospheric pressure Note that your outlet plane should be far enough from the compressor blades. khalid khedir likes this.

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September 24, 2012, 01:18		#3
pks126 New Member Prashant Kumar Singh Join Date: Jun 2012 Location: IIT Bombay Posts: 19 Rep Power: 13	Thanks Maged_CFD I did same thing and give outlet static P 101325Pa and after completion in cfx also shows outlet static P as 101334Pa which ony 9pa higher i think this BC is ok. thanks once again

October 31, 2012, 05:15		#4
vicarious Member Pedram Mojtabavi Join Date: Apr 2011 Location: Iran Posts: 66 Rep Power: 15	You need to set both inlet and outlet boundary conditions as pressure. You calculate the inlet velocity from the compressor flow coefficient (phi) and dynamic pressure (Pv) as well. Then you calculate the inlet static pressure (Ps=Pt-Pv). Pt as total pressure and Ps as static pressure. the outlet static pressure can be calculated by the compressor head coefficeint (si). By in entering these BCs your solver will be able to calculate the velocity and pressure field. Best regards.