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

Buoancy

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

Reply
 
LinkBack Thread Tools Display Modes
Old   May 26, 2008, 10:53
Default Hi, I am currently developi
  #1
Member
 
Flavio Galeazzo
Join Date: Mar 2009
Location: Karlsruhe, Germany
Posts: 30
Rep Power: 8
flavio_galeazzo is on a distinguished road
Hi,

I am currently developing a solver for incompressible (but with variable density), multicomponent, steady state flow based on simpleFoam. It solves a equation for the concentration, which is used to calculate the density of the mixture. I want now to add the effects of buoyancy, due to density gradients created by the mixture, and I found two ways of doing it:

1. Modifying the pressure equation, as in buoyantSimpleFoam;
2. Adding the "weight" rho*g in the equation of velocity, as in reactingFoam.

With the first approach I don't get convergence. With the second one it converges, but to a wrong solution.

My questions are: What is the difference between these two approaches? There is one that is more suitable to my problem?
flavio_galeazzo is offline   Reply With Quote

Old   May 27, 2008, 03:58
Default Hi, buoyantSimpleFoam is ba
  #2
Member
 
sradl's Avatar
 
Stefan Radl
Join Date: Mar 2009
Location: Graz, Austria
Posts: 82
Rep Power: 9
sradl is on a distinguished road
Hi,

buoyantSimpleFoam is based on a compressible fluid solver. Hence, you have to be very careful when using this as you might get problems with stability due to the additional equation for the density!

What I can suggest is to throw away the equation for the density and compute it locally from temperature (and your mixture fraction). Then couple this with a standard incompressible solver and underrelax the density calculation - you should have no problems with convergence.

Second, your wrong result described under 2. maybe due to the fact that the boussinesq approximation you are using does not hold (
http://en.wikipedia.org/wiki/Boussin...%28buoyancy%29

, i.e., you temperature differences are too big.

cheers
Stefan
sradl is offline   Reply With Quote

Old   May 27, 2008, 04:41
Default Thanks for the reply, Stefan!
  #3
Member
 
Flavio Galeazzo
Join Date: Mar 2009
Location: Karlsruhe, Germany
Posts: 30
Rep Power: 8
flavio_galeazzo is on a distinguished road
Thanks for the reply, Stefan!

You are right, my maximum density difference is about 7:1, what is too large for the Boussinesq approximation.

I will follow your advice and use the approach from buoyantSimpleFoam. I will post my impressions here, as soon as get good results with it.

Flavio
flavio_galeazzo is offline   Reply With Quote

Old   May 19, 2010, 17:41
Default
  #4
Member
 
Alan Russell
Join Date: Aug 2009
Location: Boise, Idaho USA
Posts: 61
Rep Power: 7
AlanR is on a distinguished road
You could also look at buoyantBoussinesqSimpleFoam, which is an incompressible solver.

Alan
AlanR 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



All times are GMT -4. The time now is 15:45.