CFD Online Discussion Forums

CFD Online Discussion Forums (
-   CFX (
-   -   bouyancy driven flow (

adrienne December 16, 2002 04:21

bouyancy driven flow
Hi, i have problem about the setting for the bouyancy driven flow, how would know the simulation should neglect the bouyancy effect or not? Is the value of the y-axis acceleration is -9.81ms^2 at most of the time? how to determine the x- or z-axis acceleration? what should i put for the density reference?? is that the density of the fluid that i used in simulation? is there got anymore details tutorial about the bouyancy driven heat transfer?? thanks guys.... have a nice day!!!

Holidays December 16, 2002 08:04

Re: bouyancy driven flow
In CFX it should apply to multiphase situations. If you look in the manual there should be recomendations so as how to set this up (both in CFX-4 and 5 manuals). If you are dealing with dispersed flows (bubbles) the ref density should be that of the dispersed phase; otherwise in FS cases, it should be that of the lighter fluid.

Bob December 16, 2002 09:05

Re: bouyancy driven flow
Hi what I think you need to do, and if anyone else would like to confirm this it would be great as I'm not 100%, you will need to define the acceleration due to gravity in only your y axis (if i understand what you have said?). Then define the buoyancy reference density 9assuming you are using the Thermal energy model) by looking at your ambient density and your max or min density, then adopting a reference density at about half way between the two. also have a look at the Help manual on advice on modelling, there is a section in the that may help (Page 469).

Holidays December 17, 2002 12:21

Re: bouyancy driven flow
Sorry I read too fast and missed the 'heat' bit, and of course answered for the wrong scenarii. Follow Bob's advice in your case indeed; please note however that all the info/hints Bob and I gave are in the manual I believe.

Atit Koonsrisuk December 17, 2002 14:12

Re: bouyancy driven flow
I am the newcomer of CFX. Surprisedly that I am trying to solve the problem that is bouyancy driven also. I think that there are something different to set the condition to solve bouyancy driven flow between CFX4 and CFX5.There is the tutorial about your question. It is tutorial No.6. And try to search for the word "bouyancy" or "Boussinesq" in the help, then you will get the good explanation on this. Hope this help.


Sascha Becker January 6, 2003 09:55

Re: bouyancy driven flow
You haveonly to inlcude the gravity vector as 0;0;-9.81 m/s^-2 if the accelaterion is perpendicular to z-axis. The buoyancy option shall be included in Command language otherwise it is neglected !

All times are GMT -4. The time now is 22:18.