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

#1 
New Member
Valentin Mayer
Join Date: Jul 2009
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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
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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
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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 
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Henrik Rusche
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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 
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Valentin Mayer
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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 
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Henrik Rusche
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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 
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Valentin Mayer
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Hello Hendrik,
thanks a lot.Have a nice evening (in German). Bye Valentin 

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

#10 
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Nima Samkhaniani
Join Date: Sep 2009
Location: Tehran, Iran
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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) .... ) 

December 4, 2015, 14:51 
Bulk temperature

#11 
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Mohammad Reza
Join Date: Sep 2015
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Hi nima sam and Bruno
I need the answer to this question, my case is an axisymetric heated pipe too, I need to calculate bulk temperature at each cross section ,tbulk = integration(U*T*dA) / integration(U*dA) to compute nusselt number.additionally it is needed for fully developed condition of T at the outlet of pipe!! any help or hint would be appreciated! Thanks in advance 

December 7, 2015, 03:59 

#12 
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Nima Samkhaniani
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you should write some pieces of code to gather cells in each section and then return the value of them for calculation, above structure give you hints how to go forward.
__________________
Telegram channel (https://telegram.me/openfoam4Iranian) My Weblog in Persian(http://openfoam.blogfa.com/) My Personal Website (http://nimasamkhaniani.ir/) 

December 7, 2015, 14:18 

#13 
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Mohammad Reza
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Dear Nima Sam
Thanks for your reply, your code was very inspiring for me but why it didn't get anticipated 2d array? maybe "size()" member function returns the number of neighbour cells for a cell but in this case we need to access patches which are normal to each wall patch.Is it the problem or anything else? bests, MohammadReza 

July 30, 2016, 16:59 

#14  
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Milad Setareh
Join Date: Oct 2012
Location: Tehran, Iran
Posts: 35
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Quote:
the above code have been written by nimasam is very good but must be corrected till it works well. for reformation, if clause must be written as following: Quote:
Best regards, Milad 

November 3, 2016, 13:50 

#15  
Member
Mirage
Join Date: Jul 2012
Posts: 42
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Quote:
I would like to use the code to compute my Tbulk. But It is for me not clear, how does this code compute Tbulk and Where should I write the code? Thanks for your help 

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