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-   -   Turbulent viscosity in Laminar Flow (http://www.cfd-online.com/Forums/main/5887-turbulent-viscosity-laminar-flow.html)

 Mike March 24, 2003 09:45

Turbulent viscosity in Laminar Flow

Hi,

I would like to know if a laminar flow (not potential flow), has got the turbulent or eddy viscosity? If the answer is yes, in which way I can compute it?

Thank you

Mike

 ag March 24, 2003 09:52

Re: Turbulent viscosity in Laminar Flow

No. By definition a laminar flow has no turbulence. Eddy viscosity is a model for how turbulence works, and is computed using turbulence models, developed to simulate turbulent flows.

 Mike March 24, 2003 09:57

Re: Turbulent viscosity in Laminar Flow

Thank you!

Another question: is the eddy viscosity proportional with an another (non turbulent) quantity? I.e., the kinematic viscosity?

 Steve March 24, 2003 10:40

Re: Turbulent viscosity in Laminar Flow

Have a look at pages 6-7 of the following link.

ftp://ftp.nist.gov/pub/bfrl/mcgratta...S/techman3.pdf

Steve

 san.pirate April 10, 2010 17:48

Steve,

th link given by you is nt working anymore.

Can you post an updated one.

 agd April 12, 2010 08:56

You do realize that the thread you resurrected is 7 years old, and Steve may not inhabit these fora anymore, don't you?

 sydney_tekam April 12, 2010 09:04

Quote:
 Originally Posted by Mike ;23761 Thank you! Another question: is the eddy viscosity proportional with an another (non turbulent) quantity? I.e., the kinematic viscosity?
Steve, eddy and turbulent viscosity are properties of the flow.
Kinematic viscosity is a property of the flui. It remains constant in every area of most common flow.

 san.pirate April 12, 2010 09:21

ooops..

I didnt realize, I thought the qn was still relevant today..!

 PGodon April 12, 2010 11:40

turbulent flows

Eventhough the original post is 7 years old... I thought maybe someone might still be interested in that topics.. or for all others who might be interested... In a turbulent flow the size of the Eddies L can be as large as the size of the domain and the velocity of the eddies is as large as the change in the velocity over a distance L, so Vturb ~ V(x+L)-V(x) , such that the viscosity of the turubulence can be written

viscosity from tubulence ~ Vturb L

Usually supersonic eddies dissipate quickly by shocks such that
Vturb < Vsound .

In the limit of small L, one can write

Vturb = V(x+L)-V(x) = (dV/dx) L
such that
turbulent viscosity ~ L^2 (dV/dx)

the turbulent viscosiity is proportional to the shear dV/dx

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