2017-10-22 00:11 BST

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IDProjectCategoryView StatusLast Update
0002722OpenFOAMFeaturepublic2017-10-15 10:22
Reporteratulkjoy 
Assigned To 
PrioritynormalSeverityminorReproducibilityalways
StatusnewResolutionopen 
PlatformCentos OSCentos 7.0OS VersionCentos 7.0
Product Versiondev 
Target VersionFixed in Version 
Summary0002722: Wall Heat Flux function object
Description/OpenFOAM-dev/src/functionObjects/field/wallHeatFlux/wallHeatFlux.C
Total heat flux should be cumulative of convective heat flux and radiative heat flux at boundary. At wall boundary lower temperature then next adjacent cell due to gradient or snGrad convectibe heat flux will be negative.

wallHeatFluxBf[patchi] = heatFluxBf[patchi]; // ln 78 Col 45

This results in substracation not addition

wallHeatFluxBf[patchi] += radHeatFluxBf[patchi]; // Ln 90 col 61
Steps To ReproducewallHeatFluxBf[patchi] = -heatFluxBf[patchi]; //sign has been changed to make it +ve due to which or better make it +ve always if it is negative to see the effect
TagsfunctionObject
Attached Files

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-Notes

~0008863

henry (manager)

Can you provide a simple case or is there a tutorial case which demonstrates the need for this change?

~0008864

StephanG (reporter)

I don't quite understand what you are getting at. The heat flux can be negative. This is not an error. The sign tells you if the heat is flowing into the domain or if it is leaving it. For CHT one side is always negative and the other positive.

~0008874

wyldckat (updater)

@atulkjoy: Please provide more details for this bug report, as requested on the rules page: https://bugs.openfoam.org/rules.php

I know that you asked about this on this thread: https://www.cfd-online.com/Forums/openfoam-post-processing/192658-wall-heat-flux-utulity.html

But in this report here, please also provide the evidences of what you initially discovered and how you reached the conclusion regarding what should be the correct sign. I know that you provided the plots and results on that thread, but it's not accessible to the public unless people log in there, so please post the images here as well.

----

@Henry and @StephanG: Just in case atulkjoy doesn't answer in the meantime, here is a partial quote of what I wrote regarding this topic on that thread:

   In OpenFOAM 4.x and older, the calculation is done as:

       convective_term - radiative_term

   While in OpenFOAM 5.x and newer, the calculation is done as:

       convective_term + radiative_term

   I haven't managed to figure out which one is correct, because I haven't managed to figure out what is the sign convention for Qr and for the convective heat flux.
   At a first glance, it seemed like Qr was always positive ("q = Boltzman * T^4 * Area"), which doesn't make much sense in this context, since it should be a subtraction of the two or more temperature[/radiation] sources, imposed on the wall.
+Notes

-Issue History
Date Modified Username Field Change
2017-10-12 11:29 atulkjoy New Issue
2017-10-12 11:29 atulkjoy File Added: wallHeatFlux.C
2017-10-12 11:29 atulkjoy Tag Attached: functionObject
2017-10-12 15:45 henry Note Added: 0008863
2017-10-13 09:21 StephanG Note Added: 0008864
2017-10-15 10:22 wyldckat Note Added: 0008874
+Issue History