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

Slow convergence in steadystate incompressible simpleFoam suggestions

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 3, 2006, 05:57
Default I've recently been doing some
  #1
brooksmoses
Guest
 
Posts: n/a
I've recently been doing some calculations in a simpleFoam-based solver (incompressible flow, Newtonian viscosity, steady-state), on a 2D flow around a circular cylinder with a 200x200-cell polar mesh.

The problem I'm having is that this is very slow to converge; after 1000 timesteps, it's still not especially well-converged. If I look at the intermediate results, it's fairly clear why -- the wake behind the cylinder is slowly developing, much as it would in a time-accurate simulation, and it takes on the order of a couple of hundred timesteps just for the flow disturbance to reach the downstream end of the domain.

Compare this to a multigrid solver which I've been using, in which the flow disturbance reaches the downstream end of the domain after five or ten timesteps, and a few hundred timesteps is sufficient to converge to machine-order accuracy.

I suspect the reasons for this are no more than the obvious: The simpleFoam solver is iterating the velocity equation in an explicit manner on a relatively fine grid, and so there the velocity information can only propogate across the grid at a fairly slow rate of one or two cells per iteration. My multigrid solver, on the other hand, propogates the velocity equation on grids of a wide range of sizes, which gets around this limitation even though it also is using explicit iterations.

I suppose I could achieve a similar result by doing a simpleFoam calculation on a coarse grid, and then repeatedly transferring the results by hand to a finer grid and repeating the calculation until I get to the fine grid that I want. This requires a lot of manual intervention, however....

Thus, my question: Is there any way, in OpenFOAM's standard suite of solvers or with straightforward modifications to them, to obtain a something equivalent to a multigrid iteration of the velocity equation, so that my calculations will converge faster? (For instance, I know that the pressure poisson-equation solver uses an algebraic-multigrid method; can this be leveraged to handle the velocity equation as well, perhaps by doing a method with an implicit velocity equation?)

Alternately, any suggestions on how to automatically do the process of calculating the flow on a coarse grid, and then going through a chain of interpolating onto progressively finer grids and re-solving?

Thanks much!
  Reply With Quote

Reply

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
Solver incompressible oil steadystate heat transfer in walls alki OpenFOAM Running, Solving & CFD 0 March 13, 2009 08:57
Steady incompressible laminar flow using simpleFoam yongshenglian OpenFOAM Running, Solving & CFD 0 October 29, 2008 16:28
Steadystate Incompressible Flow with Heat Transfer johanzietsman OpenFOAM Running, Solving & CFD 2 September 4, 2006 00:31
Steadystate incompressible laminar Newtonianfluids solver anja OpenFOAM Pre-Processing 10 March 23, 2006 06:43
Suggestions for convergence David CFX 4 November 12, 2002 02:50


All times are GMT -4. The time now is 05:55.