CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM

Convergence problems with rho*Foam

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 12, 2010, 10:53
Default Convergence problems with rho*Foam
  #1
New Member
 
Join Date: Apr 2009
Posts: 26
Rep Power: 8
askjak is on a distinguished road
I am having great difficulties getting rhoSimpleFoam, rhoPisoFoam and rhoPimpleFoam to converge.

At low speeds the solvers converges to a nice solution, but at increasing speeds (but still with max Mach number less than 0.3-0.4 - no shocks!) the solver blows up. I am interested in Mach numbers between 0.1 and approximately 1.

The mesh is fine according to checkMesh and the solution easily converges using incompressible solvers (simpleFoam, pisoFoam). On exactly the same mesh in CCM+ the compressible solver converges with no problems in both the coupled/segregated solver case.

I have tried the following without success.

1) played with relaxation parameters.
2) started with a converged solutions from potentialFoam and simpleFoam.
3) very slowly tried to ramp up the inlet velocity (from 1 to 20 m/s over 40000 steps) using the BC timeVaryingUniformFixedValue.
4) Tried various boundary conditions on inlet and outlet.
5) Slowly ramped up unsteady solvers like rhoPisoFoam and rhoPimpleFoam, but they become unstable at some point.

I have noticed people claiming that rho*Foam are missing density corrections: see Pressure instability with rhoSimpleFoam and RhoSimpleFoam negative pressure. Recently a density predictor was added to rhoPimpleFoam (see git log for 1.6.x). Apparently did not help. Should this predictor not be added to rhoSimpleFoam?

I really hope somebody can help me so I don't have to solve the problem in commercial codes since we need to analyze a very large number of geometries. Maybe somebody can explain why these solvers are so "fragile".

Specific to rhoSimpleFoam: There is no tutorial for this and it needs a scheme for div(U,p) (see hEqn.H). What should I use?

Best regards, Ask
askjak is offline   Reply With Quote

Old   March 17, 2010, 22:49
Default
  #2
Senior Member
 
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,894
Rep Power: 26
alberto will become famous soon enoughalberto will become famous soon enough
You did not provide any detail about your case. It's impossible to answer to your question
__________________
Alberto Passalacqua

GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image.
OpenQBMM - An open-source implementation of quadrature-based moment methods
alberto is offline   Reply With Quote

Reply

Tags
rhosimplefoam rhopisofoam

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
Problems with convergence with an easy system franzdrs Main CFD Forum 0 June 15, 2009 18:17
convergence in unstedy problems hedge FLUENT 0 November 27, 2007 10:24
convergence problems using SBF=1 Fonzie CFX 1 March 23, 2007 09:46
Convergence problems Chetan FLUENT 3 April 15, 2004 19:13
Convergence problems Emilien FLUENT 3 May 3, 2002 08:43


All times are GMT -4. The time now is 15:51.