Define turbulent Prandtl Number
Where can i define the turbulent Prandtl number? What is the default value?
|
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.
|
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. |
Hi,
There is, in fact, two default values for turbulent Prandtl number. Code:
$ cd $FOAM_SRC |
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) |
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. |
So if I want to redefine Prt. I should just change the Prt number in nutWallFunciton/ nutLowReWallFunciton/....? So I needn't change code?
|
Hi,
You want to redefine turbulent Prandtl number for what? Neither nutWallFunction, nor nutLowReWallFunction use Prt. |
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. |
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 |
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 |
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 |
Quote:
Thank you |
All times are GMT -4. The time now is 17:03. |