Diffusion number in chtMultiRegionFoam

Heyheymymy · October 20, 2015, 11:30

Hello OpenFoam Community,

I am using the chtMultiRegionFoam solver to simulate the heat transfer between two solid layers with different materials properties (no fluid).

I have a question concerning the Diffusion number definition and its use to control the time step adjustment in the chtMultiRegionSolver.

Looking at the source file, I found that unlike the Courant number, the Diffusion Number has dimension. It has a length dimension and is defined as DiNum = thermal diffusivity * timeStep / Length

As a consequence, I am a bit confused when trying to give a target value for this number for the adjustTimeStep option.
In the tutorials the maximum value (maxDi) is set to 10. Is this valid for any case ? Does it depends on the mesh size?

Thank you very much for your help regarding this matter,

Adrien

Artur.Ant · April 17, 2020, 09:37

I think it depends on the case.
In laminar simulation (of a small heat sink), considering natural convection I didn't notice any difference in using maxDi=10 or maxDi=60 with maxCo =0.3.
After the same number of iterations the solution in both cases converged to the same result.

October 20, 2015, 11:30	Diffusion number in chtMultiRegionFoam	#1
Heyheymymy New Member Adrien Join Date: Apr 2013 Posts: 2 Rep Power: 0	Hello OpenFoam Community, I am using the chtMultiRegionFoam solver to simulate the heat transfer between two solid layers with different materials properties (no fluid). I have a question concerning the Diffusion number definition and its use to control the time step adjustment in the chtMultiRegionSolver. Looking at the source file, I found that unlike the Courant number, the Diffusion Number has dimension. It has a length dimension and is defined as DiNum = thermal diffusivity * timeStep / Length As a consequence, I am a bit confused when trying to give a target value for this number for the adjustTimeStep option. In the tutorials the maximum value (maxDi) is set to 10. Is this valid for any case ? Does it depends on the mesh size? Thank you very much for your help regarding this matter, Adrien Artur.Ant, Kummi and Bobby02 like this.

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April 17, 2020, 09:37		#2
Artur.Ant Member Arthur Join Date: Aug 2014 Location: Italy Posts: 47 Rep Power: 12	I think it depends on the case. In laminar simulation (of a small heat sink), considering natural convection I didn't notice any difference in using maxDi=10 or maxDi=60 with maxCo =0.3. After the same number of iterations the solution in both cases converged to the same result.