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

On the pimpleFoam solution algorithm

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

Reply
 
LinkBack Thread Tools Display Modes
Old   February 1, 2011, 06:56
Default On the pimpleFoam solution algorithm
  #1
Senior Member
 
Vesselin Krastev
Join Date: Jan 2010
Location: University of Tor Vergata, Rome
Posts: 361
Rep Power: 10
vkrastev is on a distinguished road
Hi all, I'm trying to go deeper into the solution algorithm implemented in the pimpleFoam transient solver, especially for what concerns URANS incompressible applications. This is what I have understood about the solver till now (please, correct me if I'm wrong)

1) At the beginning of the time step, the solver applies the PISO algorithm for pressure-velocity coupling (with a given number of PISO loops, tipically 2) and then solves the transport equations for the turbulent quantities

2) If the outer loops parameter (nOuterCorrectors) is set > 1, the solver turns back and performs an additional integration (formally identical to the procedure described in point (1) ), but this time using as initial values the final values (eventually under-relaxed) obtained after the previous time integration.

3) Point 2 is repeted a number of times depending on the nOuterCorrectors value

First question: if all of those statements are correct, this means that with nOuterCorrectors set to 1 the whole procedure reduces to the classical PISO algorithm, is it right?

Second question: using the outer loops (and under-relaxation) allows to increase a lot the Courant number without loosing stability of the solution. However, what is the dependency between the number of the outer loops and the max Co allowed? I mean, using only one additional loop (thus performing two complete integrations per time step) is enough for pushing the max Co above 2 (maybe 4-5)?

Third question: what about the time accuracy? Of course the time resolution is far less critical in the URANS approach than in the LES one, but how will be affected the solution by a very large time step (assuming that the outer correction still preserves from instability)?

Any opinion and/or suggestion will be really appreciated

Thank you all

V.
vkrastev is offline   Reply With Quote

Old   February 1, 2011, 09:25
Default
  #2
Senior Member
 
Vesselin Krastev
Join Date: Jan 2010
Location: University of Tor Vergata, Rome
Posts: 361
Rep Power: 10
vkrastev is on a distinguished road
I've shifted the tread here On the pimpleFoam solution algorithm

V.
vkrastev is offline   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
grid dependancy gueynard a. Main CFD Forum 19 June 27, 2014 21:22
Exact solution of Burgers equation mcaro Main CFD Forum 3 January 25, 2011 07:46
How to get the solution of last time step? lzgwhy Fluent UDF and Scheme Programming 0 September 15, 2010 22:23
Integration along a line during solution DaRumpel CFX 16 September 2, 2010 11:17
Energy Equation Solution Algorithm Chandra Main CFD Forum 6 June 23, 2006 08:05


All times are GMT -4. The time now is 17:34.