SIMPLE scheme and Boundary conditions

yhoarau · April 1, 2009, 18:13

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.

yhoarau · April 5, 2009, 15:17

Nobody have any ideas?

NewtonKF · April 5, 2009, 20:45

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...

yhoarau · April 6, 2009, 04:06

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'

NewtonKF · April 6, 2009, 10:32

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???

mb.pejvak · November 24, 2011, 00:11

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

April 1, 2009, 18:13	SIMPLE scheme and Boundary conditions	#1
yhoarau New Member Hoarau Yannick Join Date: Mar 2009 Posts: 24 Rep Power: 17	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.

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April 5, 2009, 15:17		#2
yhoarau New Member Hoarau Yannick Join Date: Mar 2009 Posts: 24 Rep Power: 17	Nobody have any ideas?

April 5, 2009, 20:45		#3
NewtonKF Member Newton KF Join Date: Mar 2009 Posts: 36 Rep Power: 17	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, 04:06		#4
yhoarau New Member Hoarau Yannick Join Date: Mar 2009 Posts: 24 Rep Power: 17	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, 10:32		#5
NewtonKF Member Newton KF Join Date: Mar 2009 Posts: 36 Rep Power: 17	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
mb.pejvak Senior Member Mehdi Babamehdi Join Date: Jan 2011 Posts: 158 Rep Power: 15	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