Help For Turbulence Modeling,please!

Yapoo · August 12, 2011, 10:40

Hello Freinds!

I'm working on a problem of Catamaran hydrodynamic analysis in fluent.
i have a problem with a Turbulent intensity and turbulence viscosity ratio in k-e model. i try this values:

Turbulent intensity= 0.1%
Turbulence viscosity ratio= 1.01

but this erro was appear:
"turbulent viscosity limited to viscosity ratio of 1.000000e+005 in 10 cells "

what am i doing to solve this problem?
Thanks!

nikhil · August 13, 2011, 21:24

I think you are providing inappropriate boundary conditions as long as turbulence boundaries are considered.
May be should play around with the turbulence intensity and related parameters and ensure that these are close to actual flow conditions

mrdumpa · August 14, 2011, 13:58

1. In your problem you selected K-E model which is generally used for high
turbulent flows(Re).
2. Turbulent Intensity depend on Reynolds number ie.
Only for low turbulent Re that value will be less then 1% ( in this case)
So by varying that value check the solution once that may help you.
Ex: for Re of 5e4 the Turbulent intensity value is 4%
3. Similarly Turbulent Viscosity ratio ie
For High Turbulent(Re) flow that value range 100-1000.
For Low Turbulent flows generally that values lies 1 to 10.
So by varying that value check the solution once that may help you.

..As my understanding from fluent userguide...If it is not useful just ignore this

mrji8011 · August 14, 2011, 23:51

As I know it can be related to size of the cells close to wall. it means you need to decrease the dimention which is parallel to the walls

Yapoo · August 15, 2011, 15:09

Quote:

Originally Posted by mrji8011

as i know it can be related to size of the cells close to wall. It means you need to decrease the dimention which is parallel to the walls

نه دوست عزیز با تغییر در پارامترهای توربولانس این مشکل حل شد ممنونم

shaoda169 · August 17, 2011, 06:41

if you are sure there exist low reynolds zone inside the domian, maybe the standard k-e model is not suitable for your problem, because it is developed for fully developed turbulent flows. But anyhow you can select other variations of k-e model for your problem, like RNG or Realized k-e.

Hope this can help u!

August 12, 2011, 10:40	Help For Turbulence Modeling,please!	#1
Yapoo New Member Pooya Join Date: May 2010 Posts: 26 Rep Power: 15	Hello Freinds! I'm working on a problem of Catamaran hydrodynamic analysis in fluent. i have a problem with a Turbulent intensity and turbulence viscosity ratio in k-e model. i try this values: Turbulent intensity= 0.1% Turbulence viscosity ratio= 1.01 but this erro was appear: "turbulent viscosity limited to viscosity ratio of 1.000000e+005 in 10 cells " what am i doing to solve this problem? Thanks!

August 13, 2011, 21:24		#2
nikhil New Member Nik Join Date: Mar 2010 Location: Michigan Posts: 25 Rep Power: 16	I think you are providing inappropriate boundary conditions as long as turbulence boundaries are considered. May be should play around with the turbulence intensity and related parameters and ensure that these are close to actual flow conditions Yapoo likes this.

August 14, 2011, 13:58		#3
mrdumpa New Member mahendra Join Date: Aug 2011 Posts: 6 Rep Power: 14	1. In your problem you selected K-E model which is generally used for high turbulent flows(Re). 2. Turbulent Intensity depend on Reynolds number ie. Only for low turbulent Re that value will be less then 1% ( in this case) So by varying that value check the solution once that may help you. Ex: for Re of 5e4 the Turbulent intensity value is 4% 3. Similarly Turbulent Viscosity ratio ie For High Turbulent(Re) flow that value range 100-1000. For Low Turbulent flows generally that values lies 1 to 10. So by varying that value check the solution once that may help you. ..As my understanding from fluent userguide...If it is not useful just ignore this ramakant and Yapoo like this.

August 14, 2011, 23:51		#4
mrji8011 New Member mj Join Date: Apr 2011 Posts: 24 Rep Power: 14	As I know it can be related to size of the cells close to wall. it means you need to decrease the dimention which is parallel to the walls Yapoo likes this.

August 17, 2011, 06:41		#6
shaoda169 New Member Join Date: Nov 2009 Posts: 13 Rep Power: 16	if you are sure there exist low reynolds zone inside the domian, maybe the standard k-e model is not suitable for your problem, because it is developed for fully developed turbulent flows. But anyhow you can select other variations of k-e model for your problem, like RNG or Realized k-e. Hope this can help u! Yapoo likes this.