Define turbulent Prandtl Number

meshingpumpkins · June 18, 2018, 06:23

Where can i define the turbulent Prandtl number? What is the default value?

Bazinga · June 18, 2018, 09:38

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.

meshingpumpkins · June 18, 2018, 09:59

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.

alexeym · June 19, 2018, 08:57

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))

meshingpumpkins · June 19, 2018, 09:20

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)

alexeym · June 19, 2018, 17:23

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.

calf.Z · April 19, 2019, 07:18

So if I want to redefine Prt. I should just change the Prt number in nutWallFunciton/ nutLowReWallFunciton/....? So I needn't change code?

alexeym · April 19, 2019, 16:20

Hi,

You want to redefine turbulent Prandtl number for what? Neither nutWallFunction, nor nutLowReWallFunction use Prt.

calf.Z · April 19, 2019, 22:49

Quote:

Originally Posted by alexeym

Hi,

You want to redefine turbulent Prandtl number for what? Neither nutWallFunction, nor nutLowReWallFunction use Prt.

Sorry I made a mistake. It should be alphatWallFunction.

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.

alexeym · April 20, 2019, 12:04

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;

dasith0001 · February 27, 2023, 22:41

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

snak · February 28, 2023, 19:15

Quote:

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' ?

No.

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

dasith0001 · March 1, 2023, 18:39

Quote:

Originally Posted by snak

No.

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

Thank you for the response.

Thank you

June 18, 2018, 06:23	Define turbulent Prandtl Number	#1
meshingpumpkins 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		#2
Bazinga 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.

June 18, 2018, 09:59		#3
meshingpumpkins 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.

June 19, 2018, 09:20		#5
meshingpumpkins 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)

June 19, 2018, 17:23		#6
alexeym Senior Member Alexey Matveichev Join Date: Aug 2011 Location: Nancy, France Posts: 1,930 Rep Power: 38	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.

April 19, 2019, 07:18		#7
calf.Z 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?

April 19, 2019, 16:20		#8
alexeym Senior Member Alexey Matveichev Join Date: Aug 2011 Location: Nancy, France Posts: 1,930 Rep Power: 38	Hi, You want to redefine turbulent Prandtl number for what? Neither nutWallFunction, nor nutLowReWallFunction use Prt.

February 27, 2023, 22:41		#11
dasith0001 Senior Member Desh Join Date: Mar 2021 Location: Sydney Posts: 107 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