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Old   October 29, 2003, 07:24
Default pressure outlet problem
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I have a swirl inducing pipe and I'm simulating a 1.5m/s water flow through this pipe (100mm length pipe). I find that I'm getting a sudden change in pressure and tangential velocity at the exit where I've specified press. outlet BC with zero pressure. The tangential velocity which is high upto 1mm before the outlet suddenly drops and the press. drop also suddenly increases.

I read somewhere that when you have swirling flow through an outlet, if you specify a constant pressure, the results won't be good because a change in pressure across the cross-section is required to provide the necessary centrifugal forces for the swirling flow. Is this the reason for the discrepancy?

Does anyone know how I could fix this? At the moment I've simply extended the pipe beyond the point where I require results so that this affects somewhere I'm not concerned with.

thanks in advance!
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Old   October 31, 2003, 02:57
Default Re: pressure outlet problem
Conny Larsson
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With a swirling flow you have a pressure gradient in radial direction in the pipe. When you enforce a constant pressure at the outlet the flow must adapt to this by decreasing the tangential velocity. You can try to use the "radial equilibrium pressure distribution" option for the pressure outlet. This should solve the problem.

Conny L
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Old   November 5, 2003, 07:59
Default Re: pressure outlet problem
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Thanks for the suggestion. I've tried this and it doesn't help. I still have the same problems. I guess I'll stick to extending the length for now!

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