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Old   March 24, 2008, 14:13
Default rotating domain - pressure rise
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Hi all, This supposed to be a simple problem but i am not getting it. And i am new to CFX.

I have a centrifugal compressor impeller kind geometry where my flow region is solid and blades are empty spaces as it is generally done. I just want to know how much pressure rise can i get out of this impeller when i rotate this with air as working fluid. I dont have any diffuser, volutes or igv. It is just the impeller. Also, i want to know how much the pr. ratio changes with diameter.

Now, in order to set the boundary conditions, ideally i don't know mass flow rate in or out, i don't know pressure condt. at inlet and outlet. how to solve? Even if i choose a mass flow rate, i still don't know the pressure conditions.

I tried putting mass flow in and out and it gives me creepy static pressure like -15 psi at inlet and 10 psi at outlet.

2) Also, is there something called "opening" boundary condition?. If so what is that? I see this term in the solver window where it says Ansys is putting "WALLS" in some place. Can you please explain what is this.

Thank you for your answers and help. Peter P.

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Old   April 5, 2008, 06:57
Default Re: rotating domain - pressure rise
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hiu ok your problam i am understading but static prassure why negative prassure given nagative prassure means vaccum prassure know your results also coming negative values your fluid is steam or water.and 2)
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Old   April 5, 2008, 07:03
Default Re: rotating domain - pressure rise
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Inlets and Outlets are exclusive; they only allow flow in or out and the solver puts up walls if the flow tries to go in the wrong direction. This is done primarily to help convergence, but can also be used to simulate the action of a valve. The only exception to this is a velocity specified inlet, whereby the velocity direction is respected regardless of whether flow goes out of the domain.

An opening, on the other hand allows flow to move in or out of the domain. This is similar to a pressure boundary in many other codes (though most other codes do not have exclusive inlet/outlet boundary conditions as CFX does). If the flow direction is not known, then an opening may be appropriate. For details on the options I recommend reviewing the CFX documentation.
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