# Turbulent viscosity

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 April 9, 2010, 18:12 Turbulent viscosity #1 New Member   Santhosh Join Date: Oct 2009 Posts: 14 Rep Power: 7 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?

 April 9, 2010, 23:40 #2 Senior Member   Hamid Zoka Join Date: Nov 2009 Posts: 164 Rep Power: 8 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

 April 10, 2010, 17:41 #3 New Member   Santhosh Join Date: Oct 2009 Posts: 14 Rep Power: 7 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.

 April 11, 2010, 23:29 #4 Senior Member   Hamid Zoka Join Date: Nov 2009 Posts: 164 Rep Power: 8 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

 April 11, 2010, 23:37 #5 New Member   Santhosh Join Date: Oct 2009 Posts: 14 Rep Power: 7 Yes, thanks alot..

 Tags physics, turbulence, viscosity

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