CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > OpenFOAM

DSMC: simulating flow into vacuum

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

Like Tree1Likes
  • 1 Post By Brinx

LinkBack Thread Tools Search this Thread Display Modes
Old   October 15, 2010, 08:43
Default DSMC: simulating flow into vacuum
New Member
Christiaan Brinkerink
Join Date: Oct 2010
Posts: 2
Rep Power: 0
Brinx is on a distinguished road
Hello all,

I've been trying to use dsmcFoam to simulate the flow of gas from a duct into a vacuum, in order to study the free expansion plume. The situation is axisymmetric (the gas emerges from a circular opening), so I've defined a wedge-shaped region on one side of the symmetry axis to conserve computational resources (as is done in the incompressible->pimpleDyMFoam->movingCone FOAM tutorial).

After reading several threads on this forum about other people trying similar things, I've managed to make one particle emitter at the duct opening, and I've managed to make the other domain boundaries act as particle sinks by setting their temperature to a value close to zero.

However, I encountered a problem: I couldn't find any way to set the initial conditions to specify a vacuum. Regardless of how I defined the RhoN and RhoM fields (type calculated, value 0 seemed a sensible way to do it), the domain was always seeded with about 20,000 particles at the start of the simulation. I tried to resolve this by simply editing the files holding particle information at zero time (in the folder "0/lagrangian/dsmc/" ) and removing all particle entries by hand.

This indeed made the domain empty at t=0, and running the simulation shows particles being inserted from the emitter into the domain. However, the rate at which particles are introduced is very low indeed: about one particle per ten time steps. This doesn't seem to agree with the densities I have set, and it also results in particles simply following straight trajectories because they never get close enough to interact with one another.

As a free expansion plume should in principle show particles interacting and performing work in expanding the flow longitudinally, I'm wondering how I should change the settings to allow this to happen. Below I have included a screenshot of the result so far (after a short run), the top edge of the domain is the symmetry axis. The plotted quantity is the kinetic energy density (linearKEMean) divided by the density (rhoNMean). The thickness of the wedge (which is not visible in the picture) increases from zero at the top to about 1 cm at the bottom. The width of the domain is 2 metres, and the number of cells is 200 (x) by 100 (y) by 1 (z). In the picture you can see the effects of particles that were in the domain before the jet particles came through: straight lines influencing the average kinetic energy per particle in various cells.

So, any ideas on what I should change to make the emitter emit more particles per unit of time? Maybe change the number of molecules represented by one DSMC particle?

jiaoxiaolei likes this.
Brinx is offline   Reply With Quote

Old   April 18, 2013, 05:22
New Member
Join Date: Dec 2012
Posts: 14
Rep Power: 13
jiaoxiaolei is on a distinguished road
HI,Brinx,have you succeed on this simulate?
jiaoxiaolei is offline   Reply With Quote


dsmc, jet, plume, vacuum, wedge

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Simulating flow past airfoil with different AOA ramin FLUENT 4 April 22, 2015 14:09
Modeling sudden flow in Vacuum chamber Sandilya Garimella FLUENT 0 February 8, 2008 16:04
Can 'shock waves' occur in viscous fluid flows? diaw Main CFD Forum 104 February 16, 2006 06:44
Simulating flow past airfoil with different AOA Quarkz Main CFD Forum 2 January 6, 2006 11:56
Simulating NACA0012 for inviscid flow. Stan Main CFD Forum 2 May 13, 2005 15:22

All times are GMT -4. The time now is 12:13.