# Mass Flow Problem

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

November 21, 2011, 14:45
Mass Flow Problem
#1
New Member

Student_87
Join Date: Nov 2011
Posts: 6
Rep Power: 5
Good evening

I am creating mass in my model, and I get very high velocities in the air phase. Anybody that have an idea where the mistake/s could be?

Geometry data: Length of model = 10m, width=1m,
Inlet area and outlet area = 1.25m^2, height step =0,25m.

The geometry is set to be 70% filled with water.

Set-up:

- Pressure-based, velocity formulation absolute, transient, gravity=-9.81
- VOF, implicit, open channel flow, implicit body force,
- k-epsilon, relizable, standard wall functions
- Primary phase = air (constant density) and secondary phase = water
- Inlet boundary: Multiphase, free surface level -2.14,bottom level -3.015.
Air, mass flow rate = 0.045 kg/s
Water, mass flow rate = 87,5 kg/s
- Outlet boundary: Outflow, flow rate weighting = 1
- Reference values: v=0.1m/s
- Solution method: PISO

Any help would be appreciated
Attached Images
 mass flow problem.jpg (58.7 KB, 40 views)

 November 22, 2011, 12:51 #2 Member     Laurent B Join Date: Jun 2009 Location: Lille, FRANCE Posts: 70 Rep Power: 8 Hi, What's about your residuals ? Did you achieve convergence ?

November 22, 2011, 15:07
#3
New Member

Student_87
Join Date: Nov 2011
Posts: 6
Rep Power: 5
Quote:
 Originally Posted by laurentb Hi, What's about your residuals ? Did you achieve convergence ?
After 800 iterations it has still not converged. The residual for the continuity is 10^-2.

Under relaxation factors was set up:
Pressure = 0.3
Density = 1
Body Forces = 1
Momentum = 0.5
Volume Fraction = 0.5
Turbulent Kinetic Energy = 0.8
Turbulent Viscosity =1

Thank you for trying to help me

 November 23, 2011, 04:08 #4 Member     Laurent B Join Date: Jun 2009 Location: Lille, FRANCE Posts: 70 Rep Power: 8 You must obtain convergence before checking mass imbalance. Try to iterate more until you obtain convergence

November 23, 2011, 04:44
#5
New Member

Student_87
Join Date: Nov 2011
Posts: 6
Rep Power: 5
Quote:
 Originally Posted by laurentb You must obtain convergence before checking mass imbalance. Try to iterate more until you obtain convergence
Thanks. I will do some more iteration to try to get convergence, but do you think the under relaxation factors seems reasonable? Is it corect to set this up as a transient problem, or should it have been steady state?

 November 23, 2011, 04:57 #6 Member     Laurent B Join Date: Jun 2009 Location: Lille, FRANCE Posts: 70 Rep Power: 8 The choice between steady and transient depends on what you want to do, what's the aim of your work ? don't matter about under relaxation factors before you are not sure of what you want to do exactly...

 November 23, 2011, 08:48 #7 New Member   Student_87 Join Date: Nov 2011 Posts: 6 Rep Power: 5 I want to see the effect the step has on the flow pattern.

 November 23, 2011, 09:21 #8 Member     Laurent B Join Date: Jun 2009 Location: Lille, FRANCE Posts: 70 Rep Power: 8 try to use steady state formulation wilhelms likes this.

 November 24, 2011, 02:13 #9 Senior Member   Join Date: Mar 2009 Location: Indiana, US Posts: 185 Rep Power: 8 If it's an open channel flow, the top wall of your model should have a pressure BC of atmosphere

November 24, 2011, 04:54
#10
New Member

Student_87
Join Date: Nov 2011
Posts: 6
Rep Power: 5
Quote:
 Originally Posted by delaneyluke If it's an open channel flow, the top wall of your model should have a pressure BC of atmosphere
Thank you. That sounds like a good advise

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post mcnair CFX 9 March 22, 2011 15:06 pilou FLUENT 0 January 31, 2011 09:19 Zhihua Xie CFX 0 September 3, 2007 09:49 philippe FLUENT 8 May 5, 2003 11:43 ram Main CFD Forum 5 June 17, 2000 21:31

All times are GMT -4. The time now is 04:20.