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-   -   overspecified or sufficiently specified ? (https://www.cfd-online.com/Forums/phoenics/52162-overspecified-sufficiently-specified.html)

 Noel March 26, 2007 13:34

overspecified or sufficiently specified ?

I have 2 questions. The first is basically aimed at any CFD solution process, whilst the second is for Phoenics.

I have a domain with some objects within it. At the left and right end I set an inlet and an outlet, both of the same size. I want to solve an incompressible steady state fluid flow.

If I set these following conditions : 1. The pressure at the inlet (Pin) and at outlet (Pout) are fixed. 2. The velocity at the inlet (Vin) and at outlet (Vout) are the same (Vin = Vout). I don't fix the value, I just want the convergent velocity will give me the condition Vin = Vout.

Question-1 : Is this problem feasible to solve in Phoenics ? Algebraically speaking, we have some available equations : 1. momentum equation 2. continuity equation 3. Pin = fixed 4. Pout = fixed 5. Vin = Vout

Is this sufficiently specified or overspecified ?

Question-2 : Can you suggest me how to set this kind of problem in Phoenics ? I don't know exactly how to set a periodic boundary condition Vin = Vout in Phoenics.

 Mike April 3, 2007 07:29

Re: overspecified or sufficiently specified ?

In PHOENICS, periodicity can be enforced in the x-direction only. This is done by setting XCYCLE=T. This facility might be used for periodic fully-developed flows whereby the solution domain is restricted to a single geometrical module which repeats itself in identical fashion in the actual geometry. In this single geometrical module which repeats itself in identical fashion in the actual geometry. The pressure in fully-developed periodic flow can be decomposed into two components, the periodic pressure p' and the mean axial pressure gradient along the periodic element of the duct in the axial direction. Alternatively, the user can adopt the approach of repeatedly transferring the downstream exit values of all variables, except pressure, to the inlet plane at IZ=1; as demonstrated with PHOENICS by the papers of Beale [1990] and Chang and Mills [1991].

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