# Airfoil Average Nusselt Number calculation

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 March 2, 2011, 23:46 Airfoil Average Nusselt Number calculation #1 New Member   Join Date: Mar 2011 Posts: 4 Rep Power: 7 Hi everyone my current version of ANSYS Fluent is 12.1 The type of flow I am using is a Spalart Allarmaras Model Please correct me if I am wrong Now, I wantwant to calculate an average nusselt number from the Solution so do I just simply click "monitor" -> " Surface Monitor" Report Type: Integral Field Variable: Wall Fluxes, Surface Nusselt Number?? and also how do I calculate the Reynolds number of the flow as well ? Thanks =)

 March 3, 2011, 01:25 #2 New Member   Join Date: Mar 2011 Posts: 4 Rep Power: 7 I have the Nusselt Number Distribution around the airfoil does the Nu Distribution look like that ? and how do I average them ? just add them all and divide by the number of point, n ??? ps: this airfoil is a unit length airfoil Thanks

 March 3, 2011, 03:41 #3 Senior Member     Amir Join Date: May 2009 Location: Montreal, QC Posts: 739 Blog Entries: 1 Rep Power: 15 Hi, before computing Nu No., be sure that your reference values are correct.(report->reference values) I think for evaluating average Nu No., you can compute total heat transfer from airfoil and then obtain an equivalent h(heat transfer coefficient) and then compute Nu.(just a suggestion)

March 3, 2011, 04:47
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 Originally Posted by Amir Hi, before computing Nu No., be sure that your reference values are correct.(report->reference values) I think for evaluating average Nu No., you can compute total heat transfer from airfoil and then obtain an equivalent h(heat transfer coefficient) and then compute Nu.(just a suggestion)
Yes I've checked the reference value are the correct for air properties

as far as obtaining equivalent h from total heat transfer...
what delta temperature should I use ?? ( Temperature varies along the chord length too)

Thanks,

March 3, 2011, 05:21
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Amir
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 Originally Posted by y2k_o__o Yes I've checked the reference value are the correct for air properties as far as obtaining equivalent h from total heat transfer... what delta temperature should I use ?? ( Temperature varies along the chord length too) Thanks,
I think it's a good idea to use dT=(Tave-Tinf). you can obtain Tave from report->surface integral->average facet. isn't it?

March 3, 2011, 06:45
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 Originally Posted by Amir I think it's a good idea to use dT=(Tave-Tinf). you can obtain Tave from report->surface integral->average facet. isn't it?
so what you're saying is:

h_avg = overall_heat_transfer_rate / ( T_avg - T_fluid )

Nu_avg = h_avg * chord_length / k_fluid

correct me if I am wrong

March 3, 2011, 08:37
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Amir
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 Originally Posted by y2k_o__o so what you're saying is: h_avg = overall_heat_transfer_rate / ( T_avg - T_fluid ) Nu_avg = h_avg * chord_length / k_fluid correct me if I am wrong
yes, it's right if T_fluid & k_fluid remain constant during solution.

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