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-   -   Turbulent viscosity (http://www.cfd-online.com/Forums/fluent/67566-turbulent-viscosity.html)

eng.nassim August 19, 2009 08:50

Turbulent viscosity
 
hi every body
I'm working on modeling of V.A.W.T for my thesis the problem is that the wake is too much small and every iter I have this message "Turbulent viscosity is limited to Turbulent viscosity in xxxxxxx cells " what this message means and what its effect on the solution and also how can resolve it.
if any body have an idea
thanks

tstorm August 19, 2009 11:04

The turbulent viscosity ratio is the turbulent viscosity / laminar viscosity (mu_t/mu_l).

The problem COULD be a number of things. Usually, it's either a poor mesh (skewed cells, large changes in cell size, or cells are too big,) or bad boundary conditions. If the boundary conditions are correct, try refining the grid in the region where the TVR is limited (go to adapt, then gradient.)

Ryun August 19, 2009 11:18

To change the property of limit
 
I encoutered similar problem of yours, actually in my case, I faced

"Temperature is limited~~~" message.

In FLUENT menual - I can`t exactly recall the section regarding this

matter, In this case, FLUENT may lead inaccuracy result.



In conclusion, I solved it by changing the value of Tab of

SOLVER > LIMITS > TEMPERATURE> 5000



initial temp limit is 5000, but I changed it up to 500000000

There is no serious estimation but just increasing the range of FLUENT

computation upper limit.

So that, FLUENT can use more higher temperature value to calculate.


So, similarly, I recommend you to change the initial value of TURBULENCE

LIMITATION

at the SOLVER > LIMIT > turb - initial value

BUT, THIS IT JUST MY THINGKING.

Hope this helped you~^^

tstorm August 19, 2009 11:26

Ryun,
I don't know what material you're working with, but the temperature limit exists to keep your solutions feasible. Temperatures on the order of 500000000 are not realistic for CFD, so increasing the limit to allow temperatures this high will not yield physically accurate results.

There's been discussion before about the correct limit for the turbulent viscosity ratio though, and a limit like 1e6 is certainly realistic. That may help if you're dealing with high Reynolds number flows there the TVR may actually reach a million, but usually the TVR limit (and probably temperature limit) are due to BCs or grid issues.

Ryun August 19, 2009 11:41

Yes. you`re right.
 
Dear TSTORM.

Thank you for your correction. and I learned that one in this time.

I didn`t consider the grid, or BC condition factor.

When I`m writing the reply hardly in english, your reply is updated earier.^^

Then, I look your advice, it is more hard fact.

So, probably my solution may be also possible to fail.


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