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

low velocity but high mach number? it is true!

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 2, 2008, 19:52
Default low velocity but high mach number? it is true!
  #1
frank
Guest
 
Posts: n/a
hi all,

I am modeling a electro-chemical reaction flow in cfx11.0 with velocity about 1.0~2.0 m/s, but the density will change (2~3 times) along the flow channel.

When I solve this problem with normal incompressible N-S equation. The solver will stop with error message "the current mach number is **",which is much more than 1.0.

How to deal with this problem? Any comment will be appreciate! Thanks.

frank
  Reply With Quote

Old   October 3, 2008, 11:21
Default Re: low velocity but high mach number? it is true!
  #2
John S
Guest
 
Posts: n/a
This is a fairly common error message and could be caused by a number of things: poor initial guess, poor boundary conditions, poor quality grid. I would start by examining all of those first. You could also try setting the expert parameter "max continuity loops = 2" but I've had issues with energy imbalance in the past using this.
  Reply With Quote

Old   October 3, 2008, 16:24
Default Re: low velocity but high mach number? it is true!
  #3
CycLone
Guest
 
Posts: n/a
Check you scales. Is the geometry/grid the right size? What about the units on your boundary conditions?
  Reply With Quote

Old   October 3, 2008, 21:20
Default Re: low velocity but high mach number? it is true!
  #4
frank
Guest
 
Posts: n/a
Thanks for John S and CycLone.

Do the scales and size really effect the this problem, CycLone? The flow channel is solid oxide fuel cell flow channel.The geometry and grid are in 'mm' unit(1.5mm x 1.5mm) and the inlet velocity is 'm' unit(1~2m/s).

  Reply With Quote

Old   October 23, 2008, 05:46
Default Re: low velocity but high mach number? it is true!
  #5
pratik mehta
Guest
 
Posts: n/a
you have to estimate your Re number and also put on the ideal gas option ON
  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
Low Mach Number for Combustion sahm OpenFOAM 10 October 11, 2013 20:43
Mesh Refinement Luiz Eduardo Bittencourt Sampaio (Sampaio) OpenFOAM Mesh Utilities 41 January 17, 2013 03:43
The Far-field Pressure Boundary & Low Mach Number Saif-Deen Akanni FLUENT 1 March 5, 2007 06:05
compressible at low Mach number with uniteration ricklee Main CFD Forum 2 October 20, 2005 23:15
Trimmed cell and embedded refinement mesh conversion issues michele OpenFOAM Other Meshers: ICEM, Star, Ansys, Pointwise, GridPro, Ansa, ... 2 July 15, 2005 04:15


All times are GMT -4. The time now is 00:25.