CFD Online Logo CFD Online URL
Home > Forums > OpenFOAM Running, Solving & CFD

convergence of pressure-adjusting icoFoam solver

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

LinkBack Thread Tools Display Modes
Old   December 10, 2012, 11:52
Default convergence of pressure-adjusting icoFoam solver
Join Date: Jul 2012
Posts: 31
Rep Power: 5
kpax is on a distinguished road
Hi everybody,

i am currently trying to solve the flow of fluid in a simple geometry with one velocity inlet and two pressure outlets. I want to implement a modified icoFoam solver that adjusts the pressure values at the outlets based on certain criteria (e.g., to achieve a certain predescribed flow split).
My main problem is that PISO seems to converge terribly slow. E.g., if I use a constant inlet velocity and constant pressure values at the outlets (i.e., steady-state), a relatively steady state is reached after around ten time steps, but both inlet pressure and outlet fluxes do not reach a constant value even after 100 time steps, although the changes are small in the end. Unfortunately, it seems that that many time steps are necessary whenever I change the outlet pressures.
So here are my questions:
- why does it take so long to converge? is there a way to accelerate this? I used timestep = 0.001; piso corrector steps did not have a significant effect.
Is it allowed to use PISO in this way?

Anyone who has something to chip in, please feel free!

thx in advance

Last edited by kpax; December 13, 2012 at 12:10.
kpax is offline   Reply With Quote

Old   December 13, 2012, 12:13
Join Date: Jul 2012
Posts: 31
Rep Power: 5
kpax is on a distinguished road
just a small update: i also tried timestep = 0.0001s and constant inlet velocity. the inlet pressure converged to a constant value after around 1000 time steps!! this cant be right.

edit: the result of checkMesh:
Checking geometry...
Overall domain bounding box (-0.00500013 0.0737801 0.0766678) (0.0261582 0.0874276 0.0917605)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (-9.2092e-17 -2.65308e-16 -5.09871e-17) OK.
Max cell openness = 2.76457e-16 OK.
Max aspect ratio = 6.53503 OK.
Minumum face area = 1.51201e-09. Maximum face area = 5.16808e-08. Face area magnitudes OK.
Min volume = 2.2457e-13. Max volume = 5.80311e-12. Total volume = 3.88672e-07. Cell volumes OK.
Mesh non-orthogonality Max: 59.2528 average: 17.1145
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 1.52552 OK.
Coupled point location match (average 0) OK.

seems alright doesnt it? maybe non-orthogonality could be a problem?

Last edited by kpax; December 14, 2012 at 06:14.
kpax is offline   Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Calculation of the Governing Equations Mihail CFX 7 September 7, 2014 06:27
Pressure Outlet Guage pressure Mohsin FLUENT 34 January 12, 2012 06:45
Help! Divergence detected in AMG solver: pressure correction user0314 FLUENT 3 September 2, 2011 16:12
Gas pressure question Dan Moskal Main CFD Forum 0 October 24, 2002 22:02
Hydrostatic pressure in 2-phase flow modeling (long) DS & HB Main CFD Forum 0 January 8, 2000 16:00

All times are GMT -4. The time now is 16:34.