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

Turbulent viscosity

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 9, 2010, 18:12
Default Turbulent viscosity
  #1
New Member
 
Santhosh
Join Date: Oct 2009
Posts: 14
Rep Power: 7
san.pirate is on a distinguished road
What exactly is the turbulent viscosity in a physical sense? How is it related to the velocity, like local velocity, resultant velocity?

How does it affect heat transfer?
san.pirate is offline   Reply With Quote

Old   April 9, 2010, 23:40
Default
  #2
Senior Member
 
Hamid Zoka
Join Date: Nov 2009
Posts: 164
Rep Power: 8
Hamidzoka is on a distinguished road
Dear San.Pirate
when flow is laminar, diffusion mechanism within the flow is only performed by molecular motions.viscosity,as a dissufion coefficient, is the parameter to quantify this phenomenon.
But when the flow becomes turbulent, diffusion mechanism is not only performed by molecular motions, but also it is going to be highly intensified by eddies motions. therefore when modeling the turbulence using eddy viscosity models, we need to intensify diffusion coefficient by adding turbulent viscosity to the molecular one. this coefficient will be applied to both momentum and heat transfer equations.
does it help?

regards
Hamidzoka is offline   Reply With Quote

Old   April 10, 2010, 17:41
Default
  #3
New Member
 
Santhosh
Join Date: Oct 2009
Posts: 14
Rep Power: 7
san.pirate is on a distinguished road
Thanks for the reply,

I understand the need to use it in the eddy viscosity models. And the reason that the eddies formed during turbulence increases its value.

But how does the magnitude of turbulent viscosity affect the heat transfer and velocity in a vague physical sense? (For the sake of understanding)

Just like flow friction causes the viscosity, and thereby increase the shear rate, what is the role of turb. viscosity.
san.pirate is offline   Reply With Quote

Old   April 11, 2010, 23:29
Default
  #4
Senior Member
 
Hamid Zoka
Join Date: Nov 2009
Posts: 164
Rep Power: 8
Hamidzoka is on a distinguished road
Dear San.Pirate
as i told you before, this term is added to molecular viscosity in momentum and energy equations and intenify diffusion mechanism in these equations. therefore turbulent viscosity increases the shear rate and affect the velocity and heat transfer.
turbulent viscosity is not a physical concept. it is a virtual viscosity. it is a just a model to predict turbulent flow characteristics.
does it help?

regards
Hamidzoka is offline   Reply With Quote

Old   April 11, 2010, 23:37
Default
  #5
New Member
 
Santhosh
Join Date: Oct 2009
Posts: 14
Rep Power: 7
san.pirate is on a distinguished road
Yes, thanks alot..
san.pirate is offline   Reply With Quote

Reply

Tags
physics, turbulence, viscosity

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
reversed flow at pressure inlet and turbulent viscosity is limited.... cfdiscool FLUENT 10 June 10, 2015 06:15
Link between eddy viscosity and subgrid-scale turbulent viscosity in LES Marvin Main CFD Forum 6 December 4, 2009 12:08
setting value of turbulent intensity and turbulent viscosity ratio in wind tunnel nuimlabib Main CFD Forum 0 August 4, 2009 00:05
effective? turbulent? laminar? viscosity MIssNancy FLUENT 3 December 3, 2002 00:53
Problem of Turbulent Viscosity Ratio Limited David Yang FLUENT 3 June 3, 2002 06:13


All times are GMT -4. The time now is 17:07.