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 AndrĂ© Gaathaug July 11, 2007 08:19

Pressure correction BC using SIMPLE

Hi I just started a course in CFD at my masters education. I am working on my own CFD solver, but I found a bit of a problem defining the BC of the pressure-correction when using the SIMPLE algorithm. It's especially wall-BC for the pressure-correction I find hard, but also outlet-BC for pressure-correction. I find pressure-correction BC hard to figure out since they give no physical meaning to me at all. Please reply if you have a hint to the BC or know where I can find a hint.

For visualization of velocities I just wonder about wether to use mean values for the x- and y-velocity, since I am using the backwards staggered grid and then no velocity is stored on the same place. Do I mean the values and place them in the centers as all the scalars?

 dontknow July 11, 2007 16:07

Re: Pressure correction BC using SIMPLE

Hi!

Incompressible SIMPLE:

-Inlet, Wall: massflux through boundary is given: massflux correction is zero, so pressure correction gradient is zero there and you have a Neumann Boundary-Condition -Outlet: Usually velocity is extrapolated and will be corrected to satisfy continuity. These corrected velocities are then considered to be fixed for the current iteration and so the massflux there is considered to be given.

So you have Neumann Boundary conditions on all boundaries, the pc becomes singular and you have to fixe the pressure at one point to get a solution.

For the compressible extension of SIMPLE all becomes a bit more complicated, look in the book by Ferziger and Peric!

Good Luck...

 sekarapandian August 3, 2007 01:38

Re: Pressure correction BC using SIMPLE

dear Andre,

First make sure that u-velocity and v-velocity points coincide with physical vertical and horizontal boundaries respectively. Accordingly, other boundary nodes lie outside the physical boundaries. This is the place where beginners struggle. For excellent explanation of implementation of boundary conditions, i suggest you to refer CFD book by Malalasekara & Versteeg. hope it helps..

Sekar...

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