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- - **BC's for compressor cascade flow**
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BC's for compressor cascade flowHi Folks,
i try to analize the flow over an compressor cascade, using fluent 14.5 . As usual, i want to have a look at the behaviour of the deflection of the cascade in dependence on different inflow angles, at prescribed flow velocity. i set up the case with the following BC's: incomressible operating pressure = 103520 PA inlet: velocity inlet, with the given flow velocity and an angle of attack outlet: pressure outlet , gauge pressure = 0 periodic conditions on the two remaining channel sides. Well, that worked quit well. But i realized that due to the high inlet velocity, the local flow velocity above the cascade became really high in several local spots, so the Ma is >0,2 (max. Ma = 0,54) . Now i want to investigate a compressible case, due to high Ma numbers. In the manual of fluent, its said that velocity inlet conditions shouldnt be used for compressible flow. i changed the inlet BC to pressure inlet, but heres the problem. How can i setup the BC's that the inlet velocity will reach the desired, prescribed value? i tried it like this: the incompressible case for a certain inflow angle delivered a dynamic pressure at the outlet. i tried to use this value for the compressible calculation. operating pressure = 0 inlet: pressure inlet, with desired direction, Total Gauge pressure = 103520 Pa outlet: pressure outlet, Gauge Pressure = 103520 - dynamic pressure from compressible calculation Well, the calculated inlet velocity by fluent is as half as big as in the incompressible case. And Ma is <0,2 in the whole flow area, what makes an compressible calculation unnecessary. Is there a possibilty, to set up the BC's in a way, that a desired inlet velocity can be reached? any advice? thanks in advance greeting Muffin |

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