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-   -   Wall Heat Flux utulity (https://www.cfd-online.com/Forums/openfoam-post-processing/192658-wall-heat-flux-utulity.html)

atulkjoy September 8, 2017 08:43

Wall Heat Flux utulity
 
3 Attachment(s)
Hi,
The Vertical wall fire case where WallHeatFlux has been calculated on Vertical Isothermal Wall at 300k 722 mm high , Radiation model used is fvDOM.
The flow is natural convective and buoyancy driven mostly similar to buoyant hot plume after 200 mm. Meshing is simply block Mesh.

I have use two versions of OpenFoam , OpenFOAM-4.x and OpenFOAM-plus utility for post Processing wallHeatFlux.
OpenFOAM-4.x gives convective Wall Heat Flux and Total Wall Heat Flux,
while OpenFOAM-plus give only wallHeatFlux using fireFoam -postProcess -func wallHeatFlux.

There is significant difference between this two during summation of Qr and Convective HeatFlux and any one can be right.

Which version calculation is right

student666 September 9, 2017 22:28

Hi,

it's hard to say what is the problem as anybody can't understand what you're doing.
What are you simulating? What solver? Mesh? etc...
You should give more details in order to get help.

Quote:

There is significant difference between this two during summation of Qr and Convective HeatFlux and any one can be right.
I suppose that you're running your final case or you're running it without some preliminary hand-calculations, as the case needs a CFD calculation.

I suggest to stop and use a simple case taken from your text book where you can be confident of the results and use it as an OF case to get same results.
You should take one where you can test:
  • radiative only
  • convective only
  • both of them
This way I think you can get to a conclusion by yourself.

Regards

atulkjoy September 10, 2017 08:28

reply with images
 
2 Attachment(s)
Hi,
Thanks For quick reply it is Vertical fire case where WallHeatFlux has been calculated on Vertical Isothermal Wall at 300k 722 mm high , Radiation model used is fvDOM.
The flow is natural convective and buoyancy driven mostly similar to buoyant hot plume after 200 mm.

wyldckat September 10, 2017 20:10

Greetings to all!

Quote:

Originally Posted by atulkjoy (Post 663645)
I have use two versions of OpenFoam , OpenFOAM-4.x and OpenFOAM-plus utility for post Processing wallHeatFlux.
OpenFOAM-4.x gives convective Wall Heat Flux and Total Wall Heat Flux,
while OpenFOAM-plus give only wallHeatFlux using fireFoam -postProcess -func wallHeatFlux.

There is significant difference between this two during summation of Qr and Convective HeatFlux and any one can be right.

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

convective_term - radiative_term
While in OpenFOAM 5.x and OpenFOAM v1612+ and newer, the calculation is done as:
Code:

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 sources, imposed on the wall.

The only way to verify this is to do as student666 indicated: it is necessary to isolate and conquer. In other words, it is necessary to create small+simple test cases that allow us to check how the signs work for each term.

The problem is I don't have the time necessary right now to check this myself. So I will have to leave this to someone else here on the forum.

Best regards,
Bruno

atulkjoy September 30, 2017 15:40

Hi bruno
Thanks for your blogs I have corrected it. Now solver is validated.

Thanks and Regards.
Atul K Joshi


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