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

Eddy viscosity VS Turbulent viscosity

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

Like Tree1Likes
  • 1 Post By LuckyTran

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 26, 2019, 21:24
Default Eddy viscosity VS Turbulent viscosity
  #1
New Member
 
Naveed
Join Date: Dec 2016
Location: Saitama, Japan
Posts: 11
Rep Power: 5
Shayankhan is on a distinguished road
Greetings members,
I want to investigate eddy viscosity (m2/s) in Fluent. But, I can find the turbulent viscosity in Fluent with units "kg/m-s".
Is the turbulent viscosity similar to that of eddy viscosity ?? Or should I convert it using the density of fluid ?? Please help. Thank you.
Shayankhan is offline   Reply With Quote

Old   February 27, 2019, 09:53
Default
  #2
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 4,013
Rep Power: 48
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Turbulent and eddy viscosity are the same thing. In your case, it's clear that you need to divide the turbulent viscosity from Fluent by the density to get the thingy that you want. I wouldn't call this the eddy viscosity (because it doesn't have units of viscosity) but eddy diffusivity (having the same units as diffusivity). Anyway, what you decide to call it is up to you.
Shayankhan likes this.
LuckyTran is offline   Reply With Quote

Old   February 27, 2019, 20:52
Default
  #3
New Member
 
Naveed
Join Date: Dec 2016
Location: Saitama, Japan
Posts: 11
Rep Power: 5
Shayankhan is on a distinguished road
Quote:
Originally Posted by LuckyTran View Post
Turbulent and eddy viscosity are the same thing. In your case, it's clear that you need to divide the turbulent viscosity from Fluent by the density to get the thingy that you want. I wouldn't call this the eddy viscosity (because it doesn't have units of viscosity) but eddy diffusivity (having the same units as diffusivity). Anyway, what you decide to call it is up to you.
Thank you for the kind response.
Shayankhan is offline   Reply With Quote

Old   February 20, 2020, 10:37
Default
  #4
Senior Member
 
Santiago Lopez Castano
Join Date: Nov 2012
Posts: 282
Rep Power: 10
Santiago is on a distinguished road
Quote:
Originally Posted by LuckyTran View Post
Turbulent and eddy viscosity are the same thing. In your case, it's clear that you need to divide the turbulent viscosity from Fluent by the density to get the thingy that you want. I wouldn't call this the eddy viscosity (because it doesn't have units of viscosity) but eddy diffusivity (having the same units as diffusivity). Anyway, what you decide to call it is up to you.
What you say is not true! Eddy Difussivity refers to scalar turbulence. Eddy viscosity in the Incompressible world is presented as m2/s, corresponding to the kinematic viscosity, which is \nu = \mu/\rho

FLUENT looves putting particular names for things, just to add confusion.
Santiago is offline   Reply With Quote

Old   February 20, 2020, 10:44
Default
  #5
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 4,013
Rep Power: 48
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Everything in incompressible world is presented in per rho units. Even mass flux. It's just a preference. It's not Fluent's fault, everybody has their own way of doing things.


Again, eddy viscosity having units of m2/s doesn't have units of viscosity, just like mass flux doesn't have units of mass flux in incompressible world.
LuckyTran is offline   Reply With Quote

Old   February 20, 2020, 11:50
Default Viscosity
  #6
Senior Member
 
vinerm's Avatar
 
Vinerm
Join Date: Jun 2009
Location: Nederland
Posts: 2,948
Blog Entries: 1
Rep Power: 31
vinerm will become famous soon enough
Eddy viscosity models are, well, models. And the way these models model the turbulence (instead of simulate, which is done by LES and DNS) is by adding an extra diffusion due to the turbulence, which is significantly higher (within the turbulent region) than the molecular diffusion. So, the apparent viscosity of a fluid in a turbulent flow is higher than its molecular viscosity. A fluid behaves as a highly viscous fluid when turbulent, hence, requiring extra energy to flow.

Now, eddy viscosity is just a number that quantifies the diffusion of a field, such as, momentum or thermal energy or a component, due to the turbulence. And unit for a diffusion coefficient is same for all fields.
__________________
Regards,
Vinerm

PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.
vinerm is offline   Reply With Quote

Reply

Tags
eddy viscosity, turbulent viscosity

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Problem with divergence TDK FLUENT 13 December 14, 2018 06:00
What is linear eddy viscosity toboto Main CFD Forum 2 January 12, 2018 18:30
turbulent viscosity limited to viscosity ratio Alex_B FLUENT 16 September 12, 2012 13:17
Too low temperature at combustor outlet romekr FLUENT 2 February 6, 2012 10:02
Problem of Turbulent Viscosity Ratio Limited David Yang FLUENT 3 June 3, 2002 06:13


All times are GMT -4. The time now is 00:38.