HTC - turbulence model

Jiricbeng · July 22, 2014, 08:07

Hi there,

I try to receive HTC values in a conical pipe in which air flows. I ve already tried out many combinations of setting and I ve found out that k-epsilon gives much smaller values (cca twice smaller) of HTC than other turbulence models (SST, k - omega, k-epsilon EARSM etc..).
However the results given by k-epsilon fit better to analytical solution.. Do you have any recommendation about turbulence models for HTC ?
My y+ is about 10-15 and even smaller y+ gives actually the same results.

ghorrocks · July 22, 2014, 19:08

What reference temperature have you used for your HTC? Most engineering calculations use a far-field temperature for this (eg free stream temperature), but by default CFX does not use this. If you are comparing to experimental results you should make sure your reference temperature is the same by setting the expert parameter.

So before you look at accuracy or other turbulence models make sure your reference temperature is correct.

Jiricbeng · July 23, 2014, 02:06

Thanks for your reply,

I am not sure where to set up reference temperature, cause in the domain I can just set reference pressure. Is it an expert parameter?

Ludvik · July 23, 2014, 02:37

Try:
FLOW: Flow Analysis 1 &replace EXPERT PARAMETERS:
tbulk for htc = 300.0
END
END

July 22, 2014, 08:07	HTC - turbulence model	#1
Jiricbeng Senior Member Jiri Join Date: Mar 2014 Posts: 218 Rep Power: 13	Hi there, I try to receive HTC values in a conical pipe in which air flows. I ve already tried out many combinations of setting and I ve found out that k-epsilon gives much smaller values (cca twice smaller) of HTC than other turbulence models (SST, k - omega, k-epsilon EARSM etc..). However the results given by k-epsilon fit better to analytical solution.. Do you have any recommendation about turbulence models for HTC ? My y+ is about 10-15 and even smaller y+ gives actually the same results.

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July 22, 2014, 19:08		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	What reference temperature have you used for your HTC? Most engineering calculations use a far-field temperature for this (eg free stream temperature), but by default CFX does not use this. If you are comparing to experimental results you should make sure your reference temperature is the same by setting the expert parameter. So before you look at accuracy or other turbulence models make sure your reference temperature is correct.

July 23, 2014, 02:06		#3
Jiricbeng Senior Member Jiri Join Date: Mar 2014 Posts: 218 Rep Power: 13	Thanks for your reply, I am not sure where to set up reference temperature, cause in the domain I can just set reference pressure. Is it an expert parameter?

July 23, 2014, 02:37		#4
Ludvik Member Join Date: Apr 2009 Location: Czech Republic Posts: 65 Rep Power: 18	Try: FLOW: Flow Analysis 1 &replace EXPERT PARAMETERS: tbulk for htc = 300.0 END END