# Outflow boundary condition for transonic Nasa 37 in CFX

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 December 24, 2014, 00:03 Outflow boundary condition for transonic Nasa 37 in CFX #1 New Member   saleh Join Date: Nov 2014 Posts: 16 Rep Power: 3 Dear All What is the best outlet boundary condition for transonic(subsonic inlet and outlet but transonic passage) compressor and in general transonic turbomachines? why? I would like to have specified inlet mass flow rate. I use total pressure(because of more stable and better convergence behavior than inlet mass flow rate) at inlet but by applying static pressure at outlet, desired mass flow rate is not be obtained. short length of outlet is a problem that does not allow to select desired boundary condition. smahdavi likes this.

 December 24, 2014, 00:15 #2 New Member   saman Join Date: Dec 2014 Posts: 1 Rep Power: 0 Dear sfallah I also have this problem. If you found a solution let me know.

 December 24, 2014, 04:49 #3 New Member   vashista ademane Join Date: Apr 2014 Posts: 4 Rep Power: 4 Dear sfallah If you are solving for the case of compressor blade you can mention the static pressure for the out flow boundary condition but you need to specify the relative pressure. Normally for the case of compressor blade outlet pressure will be your desired pressure. You try by specifying the relative pressure and do replay on the result. sfallah likes this.

 December 25, 2014, 04:50 #4 New Member   saleh Join Date: Nov 2014 Posts: 16 Rep Power: 3 All right. which one of the cfx static pressure must be used? average static pressure, radial equilibrium averaged static pressure or circumferential averaged static pressure? Note that outlet length is short and I have pressure gradient in outlet. As a result, using sst turbulence model, fault result is obtained.

 December 31, 2014, 03:28 #5 New Member   Saleh Join Date: Jul 2012 Posts: 2 Rep Power: 0 Dear all; please help me, My latest question has no response: Which one of the cfx static pressure must be used? average static pressure, radial equilibrium averaged static pressure or circumferential averaged static pressure? Note that outlet length is short and I have pressure gradient in outlet. As a result, using sst turbulence model, fault result is obtained. Last edited by s.fallah; December 31, 2014 at 08:53.

 January 1, 2015, 01:18 #6 New Member   vashista ademane Join Date: Apr 2014 Posts: 4 Rep Power: 4 Dear Sfallah I don't know exactly which static pressure can be used. But you can try with avg. static pressure. Regarding turbulence model better use low Renold's no. k-epsilon turbulence models like Chien. May be your problem lies in the transition range so you also try using Re-theta and intermittency transition model by Mentor.

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