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

Problem, adding passive scalar transport for turbulent, compressible flow

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

Reply
 
LinkBack Thread Tools Display Modes
Old   February 26, 2013, 10:01
Question Problem, adding passive scalar transport for turbulent, compressible flow
  #1
New Member
 
Daniel
Join Date: Nov 2012
Posts: 5
Rep Power: 4
cryple is on a distinguished road
Hey everybody,

I'm currently trying to implement passive salar transport for visualization of concentrations in my turbulent, compressible jet in crossflow simulation with rhoCentralFoam and the komegaSST model.

I read a lot about passive scalar transport for incompressible cases and also for turbulent cases, but it is the compressible thing that makes me a headake... :-/

I implemented alphaNEqn.H with alphaN, being the dimensionless concentration as follows:

Code:
fvScalarMatrix alphaNEqn
(
fvm::ddt(rho,alphaN)
+ fvm::div(phi, alphaN)
- fvm::laplacian(DalphaN, alphaN)
);
DalphaN, being the diffusion coefficient with units [m^2/s].

Obviously, the units of the unsteady and convective term on the left do not correspont to the units of the diffusion term on the right. I think that rho has to be added to the diffusion term aswell, but I don't know how to do that.

Dividing the whole equation by rho is also not possible, because it is compressible.

So... does anybody have an idea, what I should do in this case?

By the way... DalphaN is computed using

Code:
dimensionedScalar myMi
  ("myMi",dimensionSet(1,0,0,0,-1,0,0),scalar(28.9652e-3));
dimensionedScalar myd
  ("myd",dimensionSet(0,1,0,0,0,0,0),scalar(2e-10));
dimensionedScalar mykB
  ("mykB",dimensionSet(1,2,-2,-1,0,0,0),scalar(1.3806488e-23));
dimensionedScalar myN
   ("myNa",dimensionSet(0,0,0,0,-1,0,0),scalar(6.02214129e23));
dimensionedScalar myPI
  ("myPI",dimless,scalar(3.14159265359));
 
volScalarField DalphaN
(
"DalphaN",
2/3/rho*myMi/myd/myd*sqrt(mykB*T/myPI/myPI/myPI/myMi/myNa)
);
I know it is not the most elegant way, but I wanted to be sure using the right units and honestly, I don't know how to get the constants from within the code... ;-)

Thanks in advance...
Daniel
cryple is offline   Reply With Quote

Old   February 26, 2013, 12:42
Default
  #2
New Member
 
Daniel
Join Date: Nov 2012
Posts: 5
Rep Power: 4
cryple is on a distinguished road
After some trys, I realized that adding rho to the diffusive term like here

Code:
 
fvm::ddt(rho, alphaN)
+ fvm::div(phi, alphaN)
- fvm::laplacian(DalphaN*rho, alphaN)
really solves the dimension problem. BUT I'm not sure if this is allowed in respect to the underlying physics of the problem.

Can anybody say something about that?

In addition, the now calculated alphaN, which is initialized as 1 in the jet flow and 0 in the crossflow increases slightly above 1 (< 1.09) in regions of high density gradients and in other regions it also decreases slightly below 0 (> 0.9999). That should not be possible for how I wanted alphaN to be.

Does anybody know why that happens? The overall picture of the alphaN field looks allright. Could the mesh be the problem? It is still pretty coarse for testing reasons. Or should I devide alphaNEqn by density though?

Daniel
cryple is offline   Reply With Quote

Old   March 25, 2013, 12:00
Default Hi Thanks
  #3
New Member
 
bhushan
Join Date: Feb 2011
Location: Erlangen, Gremany
Posts: 7
Rep Power: 6
bhushanvelis is on a distinguished road
Thanks it worked for me too
bhushanvelis 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
dieselFoam problem!! trying to introduce a new heat transfer model vivek070176 OpenFOAM Programming & Development 10 December 24, 2014 00:48
Newbie to compressible, viscous flow. Advice on approach to problem? bzz77 Main CFD Forum 4 December 4, 2012 08:59
compressible scalar transport euqation Chrisi1984 OpenFOAM Programming & Development 1 October 18, 2010 05:17
Need help with a compressible flow problem JP FLUENT 0 August 19, 2008 13:11
fluid flow fundas ram Main CFD Forum 5 June 17, 2000 21:31


All times are GMT -4. The time now is 08:26.