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

Viscosity Ratio

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 27, 2008, 17:18
Default Viscosity Ratio
  #1
Adam
Guest
 
Posts: n/a
I was wondering what the physical meaning of the viscosity ratio which is specified at the inlet. Can anyone point me in the right direction.

Cheers

Adam
  Reply With Quote

Old   March 27, 2008, 17:24
Default Re: Viscosity Ratio
  #2
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

It is the ratio of the turbulent viscosity to the molecular viscosity. For further information, read the CFX documentation or a turbulence textbook - Turbulence modelling for CFD by Wilcox is a good one.

Glenn Horrocks
  Reply With Quote

Old   March 28, 2008, 10:25
Default Re: Viscosity Ratio
  #3
CycLone
Guest
 
Posts: n/a
Hi Adam,

Turbulence is a transient, unsteady phenomenon. To make steady-state turbulent solutions possible, CFD codes "model" turbulence by representing the transient mixing effects of turbulent eddies as a "turbulent viscosity" relative to the mean or average flow. The turbulent viscosity is added to the dynamic viscosity to obtain an "effective" viscosity which varies throughout the flow field.

The Eddy Viscosity Ratio is simply the ratio of the Turbulent Eddy Viscosity to the Dynamic Viscosity. If the flow is indeed turbulent, the Eddy Viscosity Ratio should be at least 100.

Although this is an option at an inlet, I don't recommend using it. You would typically know the turbulent intensity (ratio of turbulent fluctuations to the steady velocity) better than the viscosity ratio.

-CycLone
  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
pressure eq. "converges" after few time steps maddalena OpenFOAM Running, Solving & CFD 69 July 21, 2011 07:42
Turbulent viscosity limited to viscosity ratio... Cyril FLUENT 8 February 7, 2006 20:34
On limiting to turbulent viscosity ratio! varghese FLUENT 2 November 15, 2003 08:56
Problem of Turbulent Viscosity Ratio Limited David Yang FLUENT 3 June 3, 2002 06:13
significance of viscosity ratio phil FLUENT 15 January 30, 2002 05:39


All times are GMT -4. The time now is 12:07.