# Pressure computation on inlet

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 December 30, 2004, 08:05 Pressure computation on inlet #1 Diego Nogueira Guest   Posts: n/a 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?

 January 3, 2005, 03:31 Re: Pressure computation on inlet #2 agg Guest   Posts: n/a 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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