CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > FLUENT

strange phenomenon for compressible gas in closed volume

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

LinkBack Thread Tools Search this Thread Display Modes
Old   April 17, 2015, 08:17
Default strange phenomenon for compressible gas in closed volume
New Member
Karnauhov Valery
Join Date: Dec 2013
Posts: 20
Rep Power: 12
kveki is on a distinguished road
Before sorry for my bad english.

Dear colleagues, I need help for relatively simple task on Fluent 15.0.

There is closed 2d-volume with gas. Gas is compressible (ideal gas or Redlich-Kwong, it doesn't matter). Gravity operates on y-direction. As Fluent requires for compressible gases with buoyancy, I set reference operate density as 0. The task is transient. No heat transfer, no velocities, no sources, only gas in state of rest. Coupled scheme is used as Solution Method.

Further I encounter very strange phenomenon.

Velocity vectors appears on bottom cells in the volume (see fig). They directs down on gravity direction. For different turbulence models (I have seen laminar, k-e standart and SST) the behavior very different. For k-e model velocity is small (about 1.6 m/s) and stable during calculation process. For laminar model velocities is most great and increase during calculation. Therewith temperature and density in bottom cells also change. SST model gives intermediate results with other models.

If set operating density to average density in the volume, the vectors disappears and velocity in the volume becomes 0. If I increase operating density, the vectors changes its direct to reverse direction.

As I understand, operating density (reference density) appears in term (rho-rho_op)*g and its value (which I impose) affects on convergence (see fig) but it is not to affect on field variables. I fail to see what reason in addition can account for this phenomenon.

I'd be glad any help.
Attached Images
File Type: jpg 01.jpg (53.7 KB, 12 views)
File Type: jpg 02.jpg (69.4 KB, 10 views)
File Type: jpg 03.jpg (67.9 KB, 9 views)
kveki is offline   Reply With Quote

Old   April 19, 2015, 02:30
New Member
Karnauhov Valery
Join Date: Dec 2013
Posts: 20
Rep Power: 12
kveki is on a distinguished road
I have solved this problem having established Body Force Weighted for Pressure Spatial Discretization in Solution Methods tab.

Anybody can explain me how this method operate?
kveki is offline   Reply With Quote


compressible gas, fluent 15.0, operating density

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
snappyhexmesh remove blockmesh geometry philipp1 OpenFOAM Running, Solving & CFD 2 December 12, 2014 10:58
Calculation of the Governing Equations Mihail CFX 7 September 7, 2014 06:27
Two-Phase Buoyant Flow Issue Miguel Baritto CFX 4 August 31, 2006 12:02
help:pumping gas into a closed domain frank FLUENT 4 April 11, 2006 09:27
Gas pressure question Dan Moskal Main CFD Forum 0 October 24, 2002 22:02

All times are GMT -4. The time now is 23:07.