# Turbulence viscocity

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1. Jul 15, 2015

### lingesh

whats turbulent viscocity?How it different from viscocity?Also i read that viscocity is fluid property.So has flow condition like laminar or turbulent has any effect on viscocity?

2. Jul 15, 2015

### SteamKing

Staff Emeritus
Beats me. Exactly where did you come across this term? BTW, it's "viscosity".

It is.

Just the opposite.

3. Jul 15, 2015

### lingesh

My senior doing CFD Analysis of a rain water filter..In the report she has given this plot of turbulence viscosity..I dont understand how its different from visosity?

4. Jul 15, 2015

### SteamKing

Staff Emeritus

5. Jul 15, 2015

Turbulent viscosity, or eddy viscosity, arises in the field of turbulence modeling. When you start with the Navier-Stokes equations and perform what is typically called Reynolds averaging, you get a new equation describing the mean velocity profile of a turbulent flow. This new equation looks identical to the standard Navier-Stokes equations except for the addition of a new term with the units of stress, typically called the Reynolds stress.

The Reynolds stresses essentially represent the effect of velocity fluctuations, and therefore turbulent mixing, on the stress in the flow. Boussinesq proposed modeling the Reynolds stress with a new viscosity term that takes the same form as the normal viscous term in the equation so that the Reynolds stress term would be replaced by something a little more intuitive like a new viscosity coefficient that could be combined with the more usual viscosity.

6. Jul 15, 2015

### Staff: Mentor

To add to what Boneh3ad said, unlike the ordinary viscosity, the turbulent viscosity is not a physical property of the fluid. It depends on the intensity of the turbulent fluctuations in the fluid (i.e., the flow).

Chet