# Talk:Turbulence modeling

### From CFD-Wiki

(low-re models and heat trasfer coefficients) |
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+ | Hi | ||

+ | I'm working on oil distribution analysis. My flow model consists on small passages (diam. 4 mm) | ||

+ | and I have to run a steady-state analysis with a commercial Code. Re number is about 12000. Flow enters | ||

+ | from a circular tube (Inlet b.cond.) and exit from two ducts (Pressure b. cond) | ||

+ | 1) I cannot use k-eps high-Re with wall function because I should use a 0.8-1 mm cell at wall | ||

+ | in order to have correct y+ (30-100). | ||

+ | 2) Then I tried to use both two layer models and k-eps low-Re/Hybrid Wall Function with a proper fine | ||

+ | mesh at wall (15 layers with y+ less than 1). | ||

+ | I do not know if the second way is correct or not. I can only say that by using the last two turbulence models | ||

+ | 3) I found some strange values for heat transfer coefficients at wall, about 24000-30000 W/m2 K while proper | ||

+ | values should be 4000-5000 W/m2 K | ||

+ | Could anyone tell me why I found so high heat trasfer coefficients and if low-Re models are correct or not | ||

+ | for such calculations? | ||

+ | |||

+ | Thanks in advance. | ||

+ | |||

+ | Massimo |

## Revision as of 16:06, 20 December 2005

Hi I'm working on oil distribution analysis. My flow model consists on small passages (diam. 4 mm) and I have to run a steady-state analysis with a commercial Code. Re number is about 12000. Flow enters from a circular tube (Inlet b.cond.) and exit from two ducts (Pressure b. cond) 1) I cannot use k-eps high-Re with wall function because I should use a 0.8-1 mm cell at wall in order to have correct y+ (30-100). 2) Then I tried to use both two layer models and k-eps low-Re/Hybrid Wall Function with a proper fine mesh at wall (15 layers with y+ less than 1). I do not know if the second way is correct or not. I can only say that by using the last two turbulence models 3) I found some strange values for heat transfer coefficients at wall, about 24000-30000 W/m2 K while proper values should be 4000-5000 W/m2 K

Could anyone tell me why I found so high heat trasfer coefficients and if low-Re models are correct or not for such calculations?

Thanks in advance.

Massimo