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September 26, 2016, 04:41 |
Validation of passive scalar transport
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#1 |
New Member
Patrick Kastner
Join Date: Apr 2016
Posts: 10
Rep Power: 10 |
Hi everyone,
I am trying to validate a passive scalar transport case. The idea is to model the emission of simplified by people in a room with a certain air change rate. My goal is to obtain the average concentration in ppm in that domain. My current issue is that I cannot correctly reproduce average concentrations compared to mass balances calculated on paper. A simple mass balance can be done like this: http://www.engineeringtoolbox.com/po...oms-d_692.html As test cases I tried the simpleFoam solver as well as the passiveScalarsimpleFoam by Yan Wang. In order to keep it simple, lets start with simpleFoam. --- Steps I took: 1. The domain is a cuboid with (30*10*2.5) m, which yields 750 . Both inlet and outlet spans one full boundary (25 ) 2. The source term is triggered by a (volumetric) source at breathing height within the room of about 40 (10*4*1) m 3. For the source term I use a field called TS with an entry in ./0/ and dimensions of . Apart from the inlet, I set all the BCs(TS) to zeroGradient. The inlet concentration should be 400 ppm (vol-based). yields 7.22 E-04 for the inlet. Then, the following entry in controlDict: Code:
TS { type scalarTransport; active true; resetOnStartUp false; autoSchemes false; fvOptions { TS-01 { active true; type scalarSemiImplicitSource; scalarSemiImplicitSourceCoeffs { cellSet volumeCell; selectionMode cellSet; volumeMode absolute; // absolute <quantity>; specific <quantity>/m^3 injectionRateSuSp { TS 0.000528; //kg/s/ accounts for 64 people (number of people * density(CO2) * 15 l/h CO2 /3600s) } } } } } 5. Now, I obtain the following visual result which looks reasonable to me (inlet is on the left): An evaluation with swak4Foam yields an average value of ~1000 ppm for those conditions which is acceptable. Now, if I test this setup for different occupancies, the results get significantly worse (rel. error > 10 %), as can be seen in the following plots: http://postimg.org/gallery/icavz4dy/ The only sub-case that goes along with the static calculation, coincidentally, is the 64 people emission case. On both ends of the spectrum the results deviate significantly. In my opinion, if I change the number of people, which scales the emission linearly, the relative error should not change at all. Interestingly enough, the option specific/absolute doesn't change the result to a large extent, which is not what I would expect. In fact, the absolute option yields better results. --- With that being said, I have some questions regarding my method:
Any hint is appreciated! Kind regards, Patrick Last edited by kostnermo; September 26, 2016 at 06:29. |
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September 28, 2016, 06:47 |
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#2 |
Member
Naresh Yathuru
Join Date: Feb 2015
Posts: 66
Rep Power: 11 |
Hi patrick,
I have the same problem and same questions. were you able to find answers for your questions? |
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October 6, 2016, 05:37 |
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#3 |
New Member
Patrick Kastner
Join Date: Apr 2016
Posts: 10
Rep Power: 10 |
Hi Naresh,
I did receive some remarks as PMs but none that solve the issue. How about you share your current findings and we work it out together? Best, Patrick |
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December 18, 2016, 16:25 |
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#4 |
Senior Member
abdikerim kurbanaliev
Join Date: Jun 2010
Location: Kyrgyzstan, Osh
Posts: 121
Rep Power: 16 |
Hi,
Could some of you please share the case setup for openfoam? Best regards |
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Tags |
gas, passive scalar, scalar, scalartransport, tracer |
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