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-   -   SIMPLE algorithm, P and u at inlet (http://www.cfd-online.com/Forums/main/66630-simple-algorithm-p-u-inlet.html)

 mauz July 20, 2009 12:06

SIMPLE algorithm, P and u at inlet

Hello everybody,

I'm solving the N-S equations using the SIMPLE algorithm.
It converge fine and quite fast when I set dirichlet boundary conditions for the velocity at inlet and outlet of the channel, but I have problems when I want to set dirichlet B.C. for both pressure and velocity at the channel inlet.
I'm solving the u-momentum equation at the main control volume interfaces, and the pressure correction equation at the central nodes. how should I set the pressure value on the first node, in order to fulfill the inlet pressure condition? I think the problem is there.

Mauri

 majesty February 13, 2014 10:00

Hello Mauri,

I am having the same problem. My code works almost perfect for velocity inlet but I have problems when I try pressure BCs. Were you able to come up with a solution to set pressure inlet & outlet to your boundary?

 leflix March 2, 2014 18:06

Quote:
 Originally Posted by mauz (Post 223342) when I set dirichlet boundary conditions for the velocity at inlet and outlet of the channel
How do you know the velocity magnitude at the outlet?
Imposing a neumann BC for velocity at the outlet is a better option.

Quote:
 but I have problems when I want to set dirichlet B.C. for both pressure and velocity at the channel inlet.
what you do at inlet is not consistent.
If you want to impose a dirichlet BC for pressure at inlet then use neumann BC for velocity.

 samurai_01 March 3, 2014 11:04

Hi!

1. The inflow conditions will be u=u_inlet, v=0, dp/dx = 0. and for outlet, we can use fully developed outflow BC, (by making few assumptions).
Fully outflow BC is du/dx = 0, dv/dx = 0 and drichlette BC on pressure, ie P=0.

2.The boundaries are always given at physical domain. I believe you are familiar with concept of fictitious cell method for imposing BCs(ref. veerstag & malasekra, or milovan Peric's CFD book). if U or V lies on the "PHYSICAL BOUNDARY" of domain, leave it as it is. If the value lies at fictitious cell, then impose P_boundary = (P_fictitious+P_internal)/2 and make P_b = 0.