CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

free air/water surface with Euler/Euler

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 25, 2000, 07:04
Default free air/water surface with Euler/Euler
  #1
Paal Chr.
Guest
 
Posts: n/a
Hi everyone,

I'm working with a 3D bubble column where the gas amount is so significant that I have to use the Euler-Euler method. My problem is the sudden change in gas fractions at the surface, which causes numerical unstabilities.

As a test case I fill half the column with water, and the rest with air. As long as the gravity is turned off everything looks nice, with a sharp cut for the surface. Turning on the gravity causes the surface to grow thick, and in a few iterations the case will diverge.

I have tried using higher order schemes, increased number of sweeps and decreased the underrelaxation with the same results. I have also tried to set the gravity to only 0.1 to decrease the shock on the system, but it does not help.

I have also written my own code using the well known 1. order upwind scheme. Here I solved this problem by using harmonic averaging instead of arithmetic. This made it possible to get nice, smooth surfaces even for heavily stirred tank reactors.

My questions are:

1. Is it possible to implement something like this in Fluent 4.5?

2. Have anyone any experience on how to best simulate such surfaces? (I want to have the outlet boundary in the gas phase, not in the two-phase area).

Regards, PC
  Reply With Quote

Old   January 28, 2000, 05:58
Default Re: free air/water surface with Euler/Euler
  #2
Detlef Schulze
Guest
 
Posts: n/a
Hi, unfortunatly you don't give enough information on the things you do. Therefore, some of my hints might be obsolete: - you perform an unsteady simulation and hence you should use the scheme geometric reconstruction to get a sharp interface. - what is your time step. My experience is to decrease it to 0.001 s or even smaller. - use the first-order time stepping.

I hope this helps a bit. I would be interested in any success or failure.

Greetings Detlef
  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
Thermocapillary free surface flow zakifoam OpenFOAM Running, Solving & CFD 6 August 24, 2014 03:24
Free surface is below than expected..results are not good mechovator CFX 24 April 8, 2011 00:41
Submarine Free Surface samwh CFX 7 August 30, 2009 07:14
Multiphase flow. Dispersed and free surface model Luis CFX 8 May 29, 2007 18:13
Modeling Free Surface Flows Elliot Schwartz Main CFD Forum 5 August 25, 1998 21:03


All times are GMT -4. The time now is 07:13.