# SIMPLE scheme and Boundary conditions

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 April 1, 2009, 17:13 SIMPLE scheme and Boundary conditions #1 New Member   Hoarau Yannick Join Date: Mar 2009 Posts: 21 Rep Power: 8 Hi, I've written a multi-bloc incompressible scheme on collocated grids (Rhie and Chow correction) and i have some problems. 1) I have fixed the pressure at the outlet : it's working for steady flows but for not for unsteady (cylinder at Reynolds 100). I've seen that some use zero second derivative of the pressure but in this case the the pressure deviates. Is there a trick? 2) Concerning the pressure correction on multibloc, what is the condition on the interface? I've tried dp'/dn=0 but in this case i have discontinuities on the pressure at the interfaces so i use p'=0. Is that correct? 3) Finally i have some difficulties with the SIMPLEC scheme, the correction is : (Ap)e minus the sum of Ap of the neighbors. (Ap)e is an averaged value. What is used for the neighbors? I explain myself : we have AP + AN + AS + AE + AW = 0 in 2D so in SIMPLEC does the correction resume to the under-relaxation? Many thanks.

 April 5, 2009, 14:17 #2 New Member   Hoarau Yannick Join Date: Mar 2009 Posts: 21 Rep Power: 8 Nobody have any ideas?

 April 5, 2009, 19:45 #3 Member   Newton KF Join Date: Mar 2009 Posts: 36 Rep Power: 8 What are the other BCs??? Have you used Neumann or Dirichlet??? What about the inlet??? You should not have problems when changing from steady to unsteady cases... in this kind of analysis... Good luck...

 April 6, 2009, 03:06 #4 New Member   Hoarau Yannick Join Date: Mar 2009 Posts: 21 Rep Power: 8 The other BC are : - for the inlet Dirichlet for the velocities and Neumann for the pressure and pressure correction - Block connection ; Dirichlet for velocitie, P and p' - Outlet : Neumann for velocities, dirichlet for P and p'

 April 6, 2009, 09:32 #5 Member   Newton KF Join Date: Mar 2009 Posts: 36 Rep Power: 8 Have you ever tried with only one block???? like a poiseuille flow??? does it works??? what about the lateral bcs??? neumann also??? like the outlet???

 November 24, 2011, 00:11 #6 Senior Member   Mehdi Join Date: Jan 2011 Location: Iran Posts: 130 Rep Power: 6 Hi I see you apply dirichlet boundary condition for pressure in outlet for collocated arrangment. iI have problem with applying that. In simpler method we don't need amount of pressure for faces but in applying this boundary condition we have constant pressure for face of boundary cell. I don't know how to make it. can you please tell me what should I do? thanks a lot

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