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-   -   Alphat file in heat transfer case (https://www.cfd-online.com/Forums/openfoam-solving/117887-alphat-file-heat-transfer-case.html)

xiyuqiu May 16, 2013 16:53

Alphat file in heat transfer case
 
Hello all,

I am trying to run a turbulent heat transfer in a pipe with k-epsilon model using buoyantBuossieqSimpleFoam. I use the hotroom example to set up my case. I don't know what the Alphat file in the 0 folder from the tutorial. I don't see it got calculated from the fvSolution or fvSchemes files. Would someone help? thank you.

best,

yu

elegant_v June 8, 2017 17:39

Hi Yu, this is an old question, but I encountered the same one. I'll share the information I found as it might help others.

As mentioned in this thread, you can find the code for alphat calculations in the appropriate file in \src\TurbulenceModels\compressible\turbulentFluidT hermoModels\derivedFvPatchFields\wallFunctions\alp hatWallFunctions.

For in the alphatWallFunction, you'll see something like alphat = rho*nut/Prt, where rho is density, nut is the turbulent kinematic viscosity and Prt is the turbulent Prandtl number.

Relations with conventional variables:
Pr = nu/alpha = (viscous diffusion rate/thermal diffusion rate) = (mu/rho)/alpha
and nu = mu/rho

alpha is conventionally defined as the thermal diffusivity, and from these relations it follows that rho*nu/Pr = rho*alpha. In the model, alphat is then defined as the density*thermal diffusivity.

A unit analysis of this train of thought matches the units in the parameter files where alphat [1 -1 -1 0 0 0 0] and mut [0 2 -1 0 0 0 0].


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