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July 5, 2009, 12:05 
bulk temperature about a Area

#1 
New Member
Valentin Mayer
Join Date: Jul 2009
Posts: 5
Rep Power: 8 
Hello
I new in OpenFoam user and I try to get the bulk temperautre about a area. the theory: my problem tbulk = integration(U*T*dA) / integration(U*dA) the nummerical: I'm not really sure how to sovle this problem. Postprocessing or ? I think that you need a summation about the area,like: sum = sum + T(n)*U(n)*dy (Fortran 2D) How can i fixed this problem? Have somebody a idea? Thanks valentin 

July 6, 2009, 04:32 

#2 
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Henrik Rusche
Join Date: Mar 2009
Location: Braunschweig, Niedersachsen, Germany
Posts: 275
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Dear Valentin,
There are two issues. How to define the area and how to parallelise. I would also advise you to use the flux rather than the velocity since it is guaranteed to be conservative. Neglecting parallelisation issues and assuming that you want to work with patch (iP) the following will the job: Code:
heatFlux = sum(T.boundaryField()[iP]*phi.boundaryField()[iP])/sum(phi.boundaryField()[iP]); 

July 6, 2009, 12:30 

#3 
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Valentin Mayer
Join Date: Jul 2009
Posts: 5
Rep Power: 8 
Hi Henrik,
sorry for this Question. But i'm not in used to work with openFoam. what means [ip] ? It is for direction, like [x]. I'm not sure if i get you wrong: Your equation mean: q=sum(t*flux)/sum(flux)=sum(t*rho*U)/sum((rho*U)) ? Is there no multiply wirh dy and dx? Thanks Valentin 

July 6, 2009, 14:51 

#4  
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Bernhard Gschaider
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Quote:
Bernhard 

July 7, 2009, 08:34 

#5 
Senior Member
Henrik Rusche
Join Date: Mar 2009
Location: Braunschweig, Niedersachsen, Germany
Posts: 275
Rep Power: 9 
Dear Valentin,
thanks for your private message (in German). I hope you don't mind if I repeat what I understand is what you are trying to do. Valentin is seeking to evaluate the local Nusselt number and needs the bulk temperature to do so. The local Nusselt number would be per wall face (additional averaging may apply) and the bulk temperature is a function of the axial position in the pipe (xcoordinate in his case). The problem is now to evaluate the bulk temperature for a given axial position. Is this correct? Henrik 

July 7, 2009, 10:23 

#6 
New Member
Valentin Mayer
Join Date: Jul 2009
Posts: 5
Rep Power: 8 
Hello Hendriks,
that's right. I search for a summation (lilke (sum(sum( T.yz*U.yz*dy)dz)each Cells) about an area (yz).And every summation should go every cells in x> direction. Perhaps somebody has an idea. Thanks Valentin 

July 7, 2009, 11:22 

#7 
Senior Member
Henrik Rusche
Join Date: Mar 2009
Location: Braunschweig, Niedersachsen, Germany
Posts: 275
Rep Power: 9 
Dear Valentin,
Okay. I would try the following. Create a lookup table for T_bulk as a function of x. To do so, you need a function that maps x into an index. Code:
scalarField vol(nCellsx, 0.0); scalarField Tbulk(nCellsx, 0.0); forAll(T, cellI) { if ( inBulkRegion(mesh.C()[cellI]) ) { label index = floor(mesh.C()[cellI].x()/length*nCellsx); vol[index] += mesh.V()[cellI]; Tbulkl[index] += T[cellI]*mesh.V()[cellI]; } } Tbulk /= vol; This is by no means elegant, it will not parallelise easily and there are better ways of doing this. However, this will get you a long way. Henrik 

July 7, 2009, 12:19 

#8 
New Member
Valentin Mayer
Join Date: Jul 2009
Posts: 5
Rep Power: 8 
Hello Hendrik,
thanks a lot.Have a nice evening (in German). Bye Valentin 

August 13, 2011, 15:46 
bulk Temperature + cell selection

#10 
Senior Member

Code:
label patchii = mesh.boundaryMesh().findPatchID("fixedWall"); const Foam::fvsPatchField<Foam::Vector<double> > Cpatches = mesh.Cf().boundaryField()[patchii]; scalar nCellsx = Cpatches.size(); labelListList inBulkRegionList (nCellsx); forAll(Cpatches, cellj) { label nSelectedCell = 1; forAll(mesh.C(), celli) { if ( (Cpatches[cellj]).z() == (mesh.C()[celli]).z()) { inBulkRegionList[cellj].setSize(nSelectedCell,celli); nSelectedCell ++; } } } hi dear foamer i have a pipe! its axismyetric and it is 40*160! i want to have the cells in each cross section means the cells with the same highth! so i should have a list, this list has 160 sublist, each sublist contains the cell IDs of in each highth! so it should be 40! i wrote above code to make a list of list!!! it compiles well but the result is some how strange and it dose not return all cell selections in each height i expected it returns 40 cells in each height but you can see the results.can anybody tell me why? labelListList: 160 ( 19 // it should be 40 cells! ( 2 6 7 9 10 11 13 14 16 18 19 20 21 23 24 27 33 35 37 ) 18 ( 43 47 50 51 52 53 57 58 59 63 64 66 68 69 70 73 74 79 ) 5(84 85 87 117 119) 11 ( 123 125 129 130 136 139 140 141 143 149 152 ) 20 ( 160 161 166 167 169 170 172 173 176 177 178 180 181 182 185 190 195 196 197 199 ) 13 ( 200 201 205 209 210 217 221 222 224 229 232 235 238 ) 8(244 246 247 262 265 266 275 278) .... ) 

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