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Old   December 30, 2004, 08:05
Default Pressure computation on inlet
Diego Nogueira
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Greetings everyone,

I have a doubt on pressure boundary condition on inlet. I'm trying to simulate smtg as simple as an incompressible flow on a flat pipe, for instance.

I've seen this:

Pi = Pn - 2(Vn-Vi)/(dx*Re)

Pi -> pressure @ inlet. Pn -> pressure @ neighbor cell, Vn -> y-component of air velocity @ inlet

The problem with this is that since Pn depends on Pi and vice-versa, at some point on my computations these values explode while I was expecting them to reach a stable value at some point.

Could you help this poor CS guy? Are there any other options?
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Old   January 3, 2005, 03:31
Default Re: Pressure computation on inlet
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Try this:

1)Make sure your discretization is correct for the viscous term.

2) In your pressure solver (I assume you are solving a poisson equation) do not solve for Pi. i.e. solve only upto Pn. Now, you need to supply a boundary condition for your poisson equation at Pn. For this, use the following neumann condition, namely (Pn-Pi)/dx = 2(Vn-Vi)/(dx*dx*Re)

3) Once you get the pressure solution at all internal points including Pn, use Pi = Pn - 2(Vn-Vi)/(dx*Re) to compute Pi.
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