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June 18, 2018, 06:23 |
Define turbulent Prandtl Number
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#1 |
New Member
Andi
Join Date: Jun 2018
Posts: 13
Rep Power: 7 |
Where can i define the turbulent Prandtl number? What is the default value?
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June 18, 2018, 09:38 |
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#2 |
Senior Member
Join Date: Jun 2012
Location: Germany, Bochum
Posts: 230
Rep Power: 15 |
You need to define it in transportProperties. There are several threads in this forum which discuss this issue. For syntax etc. please search the forum.
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June 18, 2018, 09:59 |
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#3 |
New Member
Andi
Join Date: Jun 2018
Posts: 13
Rep Power: 7 |
sorry i couldn`t find anithing about this topic.
actually i found a solution outside of the forum where you define the Prandtl number in the boundary conditions. |
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June 19, 2018, 08:57 |
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#4 |
Senior Member
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Hi,
There is, in fact, two default values for turbulent Prandtl number. Code:
$ cd $FOAM_SRC $ ack Prt TurbulenceModels/compressible/EddyDiffusivity/EddyDiffusivity.C ... 74: Prt_("Prt", dimless, 1.0), ... TurbulenceModels/compressible/turbulentFluidThermoModels/derivedFvPatchFields/wallFunctions/alphatWallFunctions/alphatJayatillekeWallFunction/alphatJayatillekeWallFunctionFvPatchScalarField.C 142: Prt_(0.85), ... 175: Prt_(dict.lookupOrDefault<scalar>("Prt", 0.85)), ... TurbulenceModels/compressible/turbulentFluidThermoModels/derivedFvPatchFields/wallFunctions/alphatWallFunctions/alphatWallFunction/alphatWallFunctionFvPatchScalarField.C 48: Prt_(0.85) ... 73: Prt_(dict.lookupOrDefault<scalar>("Prt", 0.85)) ... TurbulenceModels/incompressible/turbulentTransportModels/derivedFvPatchFields/wallFunctions/alphatWallFunctions/alphatJayatillekeWallFunction/alphatJayatillekeWallFunctionFvPatchScalarField.C 143: Prt_(0.85), ... functionObjects/solvers/energyTransport/energyTransport.C 252: Prt_(dict.lookupOrDefault("Prt", dimensionedScalar("Prt", dimless, 1))), regionModels/surfaceFilmModels/derivedFvPatchFields/wallFunctions/alphatFilmWallFunction/alphatFilmWallFunctionFvPatchScalarField.C ... 99: Prt_(dict.lookupOrDefault("Prt", 0.85)) |
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June 19, 2018, 09:20 |
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#5 |
New Member
Andi
Join Date: Jun 2018
Posts: 13
Rep Power: 7 |
ok. actually i am simulating a heatsink so i use the chtmultiregion solver.
with the adaption of the Prt i want wo fit the simulation results to my experiment. the simulation overpredicts the temperature at the heatsink. i see this result in all my heatsink simulations in a low reynoldsnumber regime (RE=2000-12000) i currently use SSTkomega turbulence model. in the past i have tried different turbulence models without any success. in the future i want to try LES simulation to see if i get better results. i also tried to refine the boundary mesh to fare beyond yplus 1. the result gehts closer to the experiment but is also 10% different (Tsim is hotter than Texperiment) The heatsink is cooled with an axial fan(impingement setup) (120mm diameter) |
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June 19, 2018, 17:23 |
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#6 |
Senior Member
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Hi,
Did you try to check if your results depend on turbulent Prandtl number at all? I can imagine if your mesh is not quite OK, and flow is highly turbulent, heat diffusivity can be overestimated near walls and heat removal is also overestimated. BUT I would start with convergence check and then with a check of BC. |
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April 19, 2019, 07:18 |
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#7 |
Senior Member
Jianrui Zeng
Join Date: May 2018
Location: China
Posts: 157
Rep Power: 7 |
So if I want to redefine Prt. I should just change the Prt number in nutWallFunciton/ nutLowReWallFunciton/....? So I needn't change code?
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April 19, 2019, 16:20 |
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#8 |
Senior Member
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Hi,
You want to redefine turbulent Prandtl number for what? Neither nutWallFunction, nor nutLowReWallFunction use Prt. |
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April 19, 2019, 22:49 |
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#9 | |
Senior Member
Jianrui Zeng
Join Date: May 2018
Location: China
Posts: 157
Rep Power: 7 |
Quote:
If I use turbulence models to simulate, there are some terms related to Prt in equations. So I want to change the default value of it. |
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April 20, 2019, 12:04 |
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#10 |
Senior Member
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You can change turbulent Prandtl number, used in alphatWallFunction by putting Ptr in boundary field dictionary. There are lots of examples in tutorials:
Code:
$ pwd $WM_PROJECT_DIR/tutorials $ grep -r Prt * combustion/PDRFoam/flamePropagationWithObstacles/0/alphat.orig: Prt 0.85; combustion/PDRFoam/flamePropagationWithObstacles/0/alphat.orig: Prt 0.85; combustion/PDRFoam/flamePropagationWithObstacles/0/alphat.orig: Prt 0.85; combustion/XiEngineFoam/kivaTest/-180/alphat: Prt 0.85; combustion/XiEngineFoam/kivaTest/-180/alphat: Prt 0.85; combustion/XiEngineFoam/kivaTest/-180/alphat: Prt 0.85; combustion/coldEngineFoam/freePiston/0/include/boundaryConditions: Prt 0.85; combustion/fireFoam/LES/flameSpreadWaterSuppressionPanel/constant/turbulenceProperties: Prt 1; combustion/fireFoam/LES/oppositeBurningPanels/constant/turbulenceProperties: Prt 1; combustion/reactingFoam/RAS/DLR_A_LTS/0/alphat: Prt 0.85; combustion/reactingFoam/RAS/DLR_A_LTS/0/alphat: Prt 0.85; combustion/reactingFoam/RAS/DLR_A_LTS/0/alphat: Prt 0.85; combustion/reactingFoam/RAS/DLR_A_LTS/constant/turbulenceProperties: Prt 0.85; combustion/reactingFoam/RAS/SandiaD_LTS/0/alphat: Prt 0.85; combustion/reactingFoam/RAS/SandiaD_LTS/0/alphat: Prt 0.85; combustion/reactingFoam/RAS/membrane/0/alphat: Prt 0.85; compressible/rhoPimpleFoam/RAS/annularThermalMixer/constant/boundaryConditions: Prt 0.85; compressible/rhoPimpleFoam/RAS/cavity/0/alphat: Prt 0.85; compressible/rhoPimpleFoam/RAS/cavity/0/alphat: Prt 0.85; compressible/rhoPimpleFoam/RAS/mixerVessel2D/0/alphat: Prt 0.85; compressible/rhoPimpleFoam/RAS/mixerVessel2D/0/alphat: Prt 0.85; compressible/rhoPimpleFoam/RAS/squareBendLiq/0/alphat: Prt 0.85; compressible/rhoSimpleFoam/squareBend/0/alphat: Prt 0.85; compressible/rhoSimpleFoam/squareBendLiq/0/alphat: Prt 0.85; compressible/sonicFoam/RAS/nacaAirfoil/0/alphat: Prt 0.85; heatTransfer/buoyantBoussinesqPimpleFoam/BernardCells/0/alphat: Prt 0.85; heatTransfer/buoyantBoussinesqPimpleFoam/BernardCells/constant/transportProperties:Prt [0 0 0 0 0 0 0] 1.0; heatTransfer/buoyantBoussinesqPimpleFoam/hotRoom/0/alphat: Prt 0.85; heatTransfer/buoyantBoussinesqPimpleFoam/hotRoom/0/alphat: Prt 0.85; heatTransfer/buoyantBoussinesqPimpleFoam/hotRoom/0/alphat: Prt 0.85; heatTransfer/buoyantBoussinesqPimpleFoam/hotRoom/constant/transportProperties:Prt [0 0 0 0 0 0 0] 0.85; heatTransfer/buoyantBoussinesqSimpleFoam/hotRoom/0/alphat: Prt 0.85; heatTransfer/buoyantBoussinesqSimpleFoam/hotRoom/0/alphat: Prt 0.85; heatTransfer/buoyantBoussinesqSimpleFoam/hotRoom/0/alphat: Prt 0.85; heatTransfer/buoyantBoussinesqSimpleFoam/hotRoom/constant/transportProperties:Prt [0 0 0 0 0 0 0] 0.85; heatTransfer/buoyantBoussinesqSimpleFoam/iglooWithFridges/0/alphat: Prt 0.85; heatTransfer/buoyantBoussinesqSimpleFoam/iglooWithFridges/constant/transportProperties:Prt [0 0 0 0 0 0 0] 0.85; heatTransfer/buoyantSimpleFoam/buoyantCavity/0/alphat: Prt 0.85; heatTransfer/buoyantSimpleFoam/buoyantCavity/0/alphat: Prt 0.85; heatTransfer/buoyantSimpleFoam/buoyantCavity/0/alphat: Prt 0.85; heatTransfer/buoyantSimpleFoam/buoyantCavity/0/alphat: Prt 0.85; heatTransfer/buoyantSimpleFoam/circuitBoardCooling/0.orig/alphat: Prt 0.85; heatTransfer/buoyantSimpleFoam/circuitBoardCooling/0.orig/alphat: Prt 0.85; heatTransfer/buoyantSimpleFoam/externalCoupledCavity/0/alphat: Prt 0.85; heatTransfer/buoyantSimpleFoam/externalCoupledCavity/0/alphat: Prt 0.85; heatTransfer/buoyantSimpleFoam/externalCoupledCavity/0/alphat: Prt 0.85; heatTransfer/buoyantSimpleFoam/externalCoupledCavity/0/alphat: Prt 0.85; heatTransfer/buoyantSimpleFoam/hotRadiationRoomFvDOM/0/alphat: Prt 0.85; heatTransfer/buoyantSimpleFoam/hotRadiationRoomFvDOM/0/alphat: Prt 0.85; heatTransfer/buoyantSimpleFoam/hotRadiationRoomFvDOM/0/alphat: Prt 0.85; heatTransfer/buoyantSimpleFoam/hotRadiationRoomFvDOM/0/alphat: Prt 0.85; lagrangian/reactingParcelFoam/hotBoxes/0.orig/alphat: Prt 0.85; lagrangian/reactingParcelFoam/hotBoxes/0.orig/alphat: Prt 0.85; lagrangian/reactingParcelFoam/verticalChannel/0/alphat: Prt 0.85; lagrangian/reactingParcelFoam/verticalChannelLTS/0/alphat: Prt 0.85; lagrangian/simpleReactingParcelFoam/verticalChannel/0/alphat: Prt 0.85; mesh/snappyHexMesh/iglooWithFridges/0/alphat: Prt 0.85; mesh/snappyHexMesh/iglooWithFridges/constant/transportProperties:Prt [0 0 0 0 0 0 0] 0.85; multiphase/reactingMultiphaseEulerFoam/RAS/wallBoiling1D_2phase/0/alphat.gas: Prt 0.85; multiphase/reactingMultiphaseEulerFoam/RAS/wallBoiling1D_2phase/0/alphat.gas: Prt 0.85; multiphase/reactingMultiphaseEulerFoam/RAS/wallBoiling1D_2phase/0/alphat.liquid: Prt 0.85; multiphase/reactingMultiphaseEulerFoam/RAS/wallBoiling1D_2phase/0/alphat.liquid: Prt 0.85; multiphase/reactingMultiphaseEulerFoam/RAS/wallBoiling1D_3phase/0/alphat.gas: Prt 0.85; multiphase/reactingMultiphaseEulerFoam/RAS/wallBoiling1D_3phase/0/alphat.gas: Prt 0.85; multiphase/reactingMultiphaseEulerFoam/RAS/wallBoiling1D_3phase/0/alphat.gas2: Prt 0.85; multiphase/reactingMultiphaseEulerFoam/RAS/wallBoiling1D_3phase/0/alphat.gas2: Prt 0.85; multiphase/reactingMultiphaseEulerFoam/RAS/wallBoiling1D_3phase/0/alphat.liquid: Prt 0.85; multiphase/reactingMultiphaseEulerFoam/RAS/wallBoiling1D_3phase/0/alphat.liquid: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/LES/bubbleColumn/0/alphat.air: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/LES/bubbleColumn/0/alphat.water: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/LBend/0/alphat.gas: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/bubbleColumn/0/alphat.air: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/bubbleColumn/0/alphat.water: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/bubbleColumnEvaporatingReacting/0/alphat.gas: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/bubbleColumnPolydisperse/0/alphat.air: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/bubbleColumnPolydisperse/0/alphat.water: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/fluidisedBed/0/alphat.air: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoiling/0/alphat.gas: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoiling/0/alphat.gas: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoiling/0/alphat.liquid: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoiling/0/alphat.liquid: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoiling1D/0/alphat.gas: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoiling1D/0/alphat.gas: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoiling1D/0/alphat.liquid: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoiling1D/0/alphat.liquid: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoilingIATE/0/alphat.gas: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoilingIATE/0/alphat.gas: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoilingIATE/0/alphat.liquid: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoilingIATE/0/alphat.liquid: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoilingPolyDisperse/0/alphat.gas: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoilingPolyDisperse/0/alphat.gas: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoilingPolyDisperse/0/alphat.liquid: Prt 0.85; multiphase/reactingTwoPhaseEulerFoam/RAS/wallBoilingPolyDisperse/0/alphat.liquid: Prt 0.85; multiphase/twoPhaseEulerFoam/LES/bubbleColumn/0/alphat.air: Prt 0.85; multiphase/twoPhaseEulerFoam/LES/bubbleColumn/0/alphat.water: Prt 0.85; multiphase/twoPhaseEulerFoam/RAS/bubbleColumn/0/alphat.air: Prt 0.85; multiphase/twoPhaseEulerFoam/RAS/bubbleColumn/0/alphat.water: Prt 0.85; multiphase/twoPhaseEulerFoam/RAS/fluidisedBed/0/alphat.air: Prt 0.85; |
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February 27, 2023, 22:41 |
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#11 |
Senior Member
Desh
Join Date: Mar 2021
Location: Sydney
Posts: 108
Rep Power: 5 |
Hi Foamers,
I do not want to start a different tread because my issue is very related, apologies for hijacking though. I am running a model with significant pressure drops in the system. with the pressure drops, fluid properties, particularly the thermal conductivity changes. I am updating my thermophysical properties on the run using NIST data. All was good so far ( even the results ) until I wanted to try turbulence in RAS model. my first question is, do the thermophysical properties ( say conductivity ) defined in 'thermophysicalProperties' files get washed out by the 'turbulent Prt number' defined in 'alphat' ? If yes, is there anyway forcing the model to read property data from 'thermophysicalProperties' whilst the turbulence is on ? Is the Prt used only at boundary layers and the rest of the fluid region assigned with properties from thermophysicalProperties ? Thank you in advance. Dasith |
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February 28, 2023, 19:15 |
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#12 | |
Senior Member
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Quote:
Turbulent Prandtl number Prt is used as alphat = turbulence->nut()/Prt. Effective thermal diffusivity alphaEff is obtained from alphaEff = turbulence->nu()/Pr + turbulence->nut()/Prt. Contribution of turbulence is added to laminar one (turbulence->nu()/Pr) . https://develop.openfoam.com/Develop...pleFoam/TEqn.H |
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March 1, 2023, 18:39 |
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#13 | |
Senior Member
Desh
Join Date: Mar 2021
Location: Sydney
Posts: 108
Rep Power: 5 |
Quote:
Thank you Last edited by dasith0001; March 5, 2023 at 22:32. |
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