Huge Heat Transfer Coefficient with SST turbulence model

andoss · September 14, 2009, 04:13

Hello!

I am modelling conjugate heat transfer at a pipe - the pipe is cooled by air, which flows through the pipe. Therefor I use the SST turbulence model. The y+ value is y+ <1 (around 0.5) The number of nodes in the boundary layer is about 15. The value for the wall heat transfer coefficient which i got from the simulation is very high with 26105,7 W/m²K (From analytical calculations I got a value around 650 W/m²K)

Does someone know what the reason could be?

Thank you in advance,
Andy

denizen · September 14, 2009, 05:10

try to check reference temperature for calculation of HTC

andoss · September 15, 2009, 09:23

The temperatures are ok. I did the simulation also with the k epsilon turbulence model (with scaleable wall functions) and then I got much better results than with the sst model. So I dont understand why the results with use of the sst turbulence modell are so high.

ghorrocks · September 15, 2009, 18:29

I don't think you have understood denizen's point. HTC is by default referenced to a local temperature which is another variable available for viewing in CFD-Post called "Wall Adjacent Temperature". This variable is often miles away from the reference temperature an engineer would use in the bulk flow.

andoss · January 9, 2010, 07:40

Thank you! This was very helpful!

September 14, 2009, 04:13	Huge Heat Transfer Coefficient with SST turbulence model	#1
andoss New Member Andi Join Date: Aug 2009 Location: Austria/Graz Posts: 5 Rep Power: 17	Hello! I am modelling conjugate heat transfer at a pipe - the pipe is cooled by air, which flows through the pipe. Therefor I use the SST turbulence model. The y+ value is y+ <1 (around 0.5) The number of nodes in the boundary layer is about 15. The value for the wall heat transfer coefficient which i got from the simulation is very high with 26105,7 W/m²K (From analytical calculations I got a value around 650 W/m²K) Does someone know what the reason could be? Thank you in advance, Andy

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September 14, 2009, 05:10		#2
denizen New Member Join Date: Mar 2009 Posts: 25 Rep Power: 0	try to check reference temperature for calculation of HTC

September 15, 2009, 09:23		#3
andoss New Member Andi Join Date: Aug 2009 Location: Austria/Graz Posts: 5 Rep Power: 17	The temperatures are ok. I did the simulation also with the k epsilon turbulence model (with scaleable wall functions) and then I got much better results than with the sst model. So I dont understand why the results with use of the sst turbulence modell are so high.

September 15, 2009, 18:29		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,943 Rep Power: 145	I don't think you have understood denizen's point. HTC is by default referenced to a local temperature which is another variable available for viewing in CFD-Post called "Wall Adjacent Temperature". This variable is often miles away from the reference temperature an engineer would use in the bulk flow.

January 9, 2010, 07:40		#5
andoss New Member Andi Join Date: Aug 2009 Location: Austria/Graz Posts: 5 Rep Power: 17	Thank you! This was very helpful!