# outlet boundary condition for compressor modeling

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 August 6, 2009, 11:07 outlet boundary condition for compressor modeling #1 New Member   mazda Join Date: Jul 2009 Posts: 7 Rep Power: 16 hi friends, i have several questions. i want to solve a 3D blade of a compressor with LES of FLUENT. boundary condition I useed is "VELOCITY INLET" for inlet . is it correct? for the outlet, which bounadry condition I must use? is "PRESSURE OUTLET" correct? for using "PRESSURE OUTLET", is minimum distance from outlet plane and trailing edge necessary? and how "gauge pressure" set? i am so thankful for your attention.

 August 6, 2009, 11:38 #2 New Member   Ryan Join Date: Jul 2009 Location: Windsor Posts: 9 Rep Power: 16 Hello, From my knowledge, you should not use pressure outlet with velocity inlet. I believe that you should be using the pressure inlet boundary condition. When using the pressure inlet condition, you would need to define the temperature as well for the compressible flow. I read in the Fluent manual that when using velocity inlet condition, it should be used with the outflow condition and this would be well suited for incompressible flow. I assume you would want your model to incorporate compressibility effects considering you are modeling a compressor, is this correct? Gauge pressure is defined as: p_absolute = p_gauge + p_operating So you should define the gauge pressure accordingly to this equation If this does not help you try looking in the Manual for more information... Sincerely, Ryan

 August 8, 2009, 03:29 #3 New Member   mazda Join Date: Jul 2009 Posts: 7 Rep Power: 16 thanks ruyguy. i am thankful for your attention. a have another question about this. is there any restriction for the distance of outlet plane from trailing edge and distance of inlet plane from leadin edge?

 August 8, 2009, 05:55 #4 New Member   Join Date: Jul 2009 Posts: 4 Rep Power: 16 For the in-duct compressed flow problems, pressure inlet and pressure outlet is suitable. Anyway others also possible. for example, massflow inlet and pout. But it will be more difficult to reach convergence. If the problem is to solve airfoil, pressure far field condition is also reasonable. But Vin and Pout is just for compressed flow? Noway....