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

DSMC Grid

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

Like Tree1Likes
  • 1 Post By TomS

Reply
 
LinkBack Thread Tools Display Modes
Old   October 20, 2010, 03:41
Default DSMC Grid
  #1
New Member
 
Andre van der Walt
Join Date: Jun 2010
Posts: 5
Rep Power: 7
Andre van der Walt is on a distinguished road
HI all, does anyone know the subcell division of dsmcFoam works? Is the subcells divided automatically so that the correct number of molecules per subcell is obtained. IS the grid that is initially specified only for sampling purposes? IS the time step varied over the domain, so that the time step is smaller at regions of high number densities? It is not clear how all this works, the selection of the number of equivalent dsmc molecules, the specification of the grid, and the specification of the timesteps.
I would appreciate it if anyone could point mein the right direction.
Andre
Andre van der Walt is offline   Reply With Quote

Old   October 20, 2010, 12:45
Default DSMC Grid
  #2
New Member
 
Join Date: Oct 2010
Posts: 5
Rep Power: 6
TomS is on a distinguished road
Hi Andre,

I believe the sub-cell division is carried out automatically in every sampling cell in order to promote nearest-neighbour collisions. The cell centroid acts as a locator to split any cell into 8 quadrants (sub-cells). The initial, un-divided grid is used for sampling.

The "correct" number of dsmc simulators per sub-cell is difficult to achieve and will change as the solution progresses. Good dsmc practice suggests an initial number of 10-20 particles per sampling cell. Particle number sensitivity studies should always be conducted in any case. The parameter nEquivalentParticles should be set to produce the initial 10-20 particles at the beginning of a solution using the utility dsmcInitialise.

The time-step is fixed (normally based on the mean free time or likely particle residence time). The grid is also non-adaptive and fixed (cell size based on mean free path) but this is not normally a restrictive issue.

Regards,
Tom
jessyastronasa likes this.
TomS is offline   Reply With Quote

Old   November 2, 2010, 12:25
Default
  #3
New Member
 
Join Date: Oct 2010
Posts: 5
Rep Power: 6
TomS is on a distinguished road
A review of the validation of dsmcFoam can be found at:

Scanlon, Roohi, White, Darbandi and Reese, " An open-source, parallel, DSMC code for rarefied gas flows in arbitrary geometries", Computers and Fluids, 39, 2078-2089, 2010.

Regards,
Tom
TomS 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
MapFields to New Grid For Extreme Grid Deformations due to Body Motion albcem OpenFOAM 0 May 5, 2009 14:17
Grid Adaptation Suresh FLUENT 0 October 15, 2003 13:18
GRID TO GRID INTERPOLATION in FLUENT calogero FLUENT 3 June 4, 2003 08:32
Combustion Convergence problems Art Stretton Phoenics 5 April 2, 2002 05:59
Troubles modelling flow through a grid Hans Klaufus CFX 1 June 28, 2000 16:43


All times are GMT -4. The time now is 10:49.