CFD Online Logo CFD Online URL
Home > Forums > Main CFD Forum

Pressure outlet in two-phase flow in horizontal 2D channel

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

LinkBack Thread Tools Display Modes
Old   November 17, 2010, 08:32
Default Pressure outlet in two-phase flow in horizontal 2D channel
Senior Member
Robert Sawko
Join Date: Mar 2009
Posts: 117
Rep Power: 13
AlmostSurelyRob will become famous soon enough
Dear All,

I have recently encountered an issue whilst trying to model simple 2D case of a channel flow and I was wondering if you could give me some insights about it.

The minimal example illustrating my point is the following:
2D geometry
Left, Top and Bottom boundaries are Walls. Right boundary is a pressure boundary.
Transient simulation
Initial condition Velocity = 0

I have tried three different initialisations for two phase flow:
1) Full air
2) Full water
3) 50/50 water/air stratified (air at the top).

I have run these cases in a number of codes (Fluent, openFoam, STAR-CD) and all of them give a bit strange results.

In case 1) and 2) I expect a no flow solution. Fluent and openFoam meet my expectations. STAR-CD results seem to be affected by a choice of reference density. It's probably because hydrostatic pressure at the outlet is calculated with the use of reference density.

With 3) the situation is less obvious to me.

All the codes give me some sort of backflow. It usually looks a little bit like a dam break problem but occurring on a pressure boundary. So either water seems to be 'sloshing down' or the air gets pushed away by a fluid moving from outside the domain.

My conclusion for now is that with two-phase flow the outlet conditions matter. So it generally depends on a particular application.

But is there any other way to model outlet? How would you implement/model the outlet conditions with two phase flow. I am aiming at modelling long channels and ideally I would like to minimize the effect of outlet. Is there any expedient way of doing it?

STAR-CD offers a mean pressure boundary. So only the mean pressure is specified and the cell values are adjusted to fit it. This seems to be solving my problem, but there is still a small back-flow occurring in the above example.
AlmostSurelyRob is offline   Reply With Quote


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
Outlet pressure for compressible flow Michelle CFX 12 September 1, 2015 18:38
reversed flow in xxxx faces on pressure outlet franzdrs FLUENT 6 March 19, 2014 04:16
Outlet condition for open channel flow? gareth__it_power OpenFOAM Running, Solving & CFD 1 July 17, 2011 03:44
reverse flow at the pressure outlet bapu FLUENT 2 November 29, 2005 07:58
flow simulation across a small fan jane luo Main CFD Forum 15 April 12, 2004 17:49

All times are GMT -4. The time now is 22:26.