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why this boundary condition works?

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Old   November 25, 2005, 00:03
Default why this boundary condition works?
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manish
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I have read manual that when we apply mass flow or velocity at inlet and pressure at outlet then it will more robust.but when we apply pressure at inlet and velocity at outlet it will diverge the solution.The later is applicable only to compressible flow.Can anybody tell me why this is happening? the outlet mass flow is applicable to fully developed flow.so what is fully developed flow? and why it is robust for outer mass flow? Thanx

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Old   November 30, 2005, 06:20
Default Re: why this boundary condition works?
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mike
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The solution algorithm is more stable numerically when the pressure is fixed at the outlet, and the mass inflow rate is prescribed at the inlet. If the boundary conditions are reversed as you describe, then I do not think that divergence will necessarily result. It should be possible to acheieve convergence, although the prescription of a uniform mass outflow rate may not necessarily be realistic on physical grounds.

I don't really understand the comment "The later is applicable only to compressible flow.", and hence the remainder of your questions are rather unclear. If you can say where this statement appears, and in which manual, I may be able to provide some explanation.
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