# Helicopter Rotor in Hover - Pressure Farfield Boundary Conditions

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 April 8, 2013, 16:13 Helicopter Rotor in Hover - Pressure Farfield Boundary Conditions #1 New Member   Join Date: Jun 2012 Posts: 18 Rep Power: 14 I am trying to replicate one of the cases from the Caradonna & Tung paper. I have a symmetric mesh similar to this paper with a semi-cylndrical far-field and am using a density based solver in Fluent 14. I think the velocity at the far-field boundaries should be zero, however I am confused about the gauge and operating pressures. I imagine the top, bottom and cylindrical far-field should all be set as pressure-far-field and the pressure there should be equal to the atmospheric pressure. Does this mean I should have a zero operating pressure and gauge pressure as 101325, or the other way around? I have tried a stationary reference frame with the blade rotating and also with a rotating reference frame but neither seems to give any reasonable results. Any help would be much appreciated.

 April 8, 2013, 23:53 #2 New Member   Colin Fiola Join Date: Jul 2012 Posts: 19 Rep Power: 13 Are you considering compressible flow? Assuming that the blade tips at the rotor can reach speeds nearing Mach 1 you should include compressibility. Gauge pressure and operating pressure are used to calculate density through the Mach number. Either the Fluent theory guide or user manual states for Mach > .1 (I think) to use '0' as an operating pressure, thus making the gauge pressure what ever you are assuming for atmosphere, as well as initial gauge pressure on your BC. You may want to use 'Pressure Inlet' instead of 'Pressure Far-Field' for your BC... ari003 likes this.

 April 9, 2013, 03:54 #3 New Member   Join Date: Jun 2012 Posts: 18 Rep Power: 14 Thanks for your help. I am using an ideal gas with sutherland law due to compressibility and pressures as you suggest. I will try using a pressure inlet and see how it goes.

 Tags fluent, helicopter, rotating