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Old   February 19, 2003, 07:37
Default I have problem...
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Hi all !!

I want to use STAR-CD for axial fan problem. My model has inlet b.c and outlet b.c. cyclic b.c. Outlet is problem. it is not converged and has many problem. What is differnece between outlet and press b.c. What is reference pressure cell means?? Reference pressure cell is one of the outlet cell. Reference pressure is 1.0e5 Pa. If I have pressure B.C, the Reference pressure is 0 ?

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Old   February 19, 2003, 11:26
Default Re: I have problem...
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I did an axial fan case once. I don't think you can use inlet or outlet b/c's because you don't know the flow rate yet, and that's determined by your fan's rotation speed and geometry.

My model only had pressure, periodic, and wall b/c's. I used the Multiple Reference Frames method with just one periodic sector slice of the fan. MRF methods then to be hard to converge. Try starting from a low RPM value and slowly ramp up to your ultimate RPM value -this will require many restarts.

Outlet b/c only permits flow going out and properties there are extrapolated from the domain interior. You may have problems if somehow the flow recirculates back at a outlet b/c. Pressure b/c permits both flows going in or out, as long as the the flow conforms to a fixed pressure there. To be valid, pressure b/c's are usually placed far from the main flow field to represent the quiescent 'ambient'.

You can read the FAQ ( about reference pressure and reference pressure cells. I don't do anything extraordinary so I usually stick with the defaults and arbitrarily choose a reference cell. I think the ref cell is only relevant if you don't have pressure b/c's. These other links may help you: (^ Good to find out how others do it...)

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