# SIMPLE algorithm, P and u at inlet

 Register Blogs Members List Search Today's Posts Mark Forums Read

 July 20, 2009, 12:06 SIMPLE algorithm, P and u at inlet #1 New Member   Join Date: May 2009 Posts: 6 Rep Power: 17 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. thanks in advance Mauri

 February 13, 2014, 09:00 #2 New Member   Join Date: Jul 2013 Posts: 2 Rep Power: 0 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?

March 2, 2014, 17:06
#3
Senior Member

Join Date: Aug 2011
Posts: 272
Rep Power: 15
Quote:
 Originally Posted by mauz 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.

 March 3, 2014, 10:04 #4 Member   Join Date: Oct 2012 Posts: 46 Rep Power: 13 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. Hope this helps. In case of doubts, please reply back

 Tags channel flux, n-s, simple