SimScale CAE Forum

Set diffusion coefficient

Hello,

I noticed that I need to set a diffusion coefficient in the incompressible model. I wondered if this should be the molecular diffusion coefficient or the turbulent diffusion coefficient. I think that it should be the molecular diffusion coefficient (which is a property of materials and does not depend on the flow field.) And turbulent diffusion coefficient is something that is associated with my turbulent closure. I know that many other models allow you to set a background turbulent diffusivity in case your turbulent closure produces a very low diffusivity value, and I wondered is there any places in SIMSCALE that we can set the background turbulent diffusion coefficient. Thank you so much!

Hey,

It’s only necessary to set a diffusion coefficient when modeling passive scalars:

The diffusion coefficient is for the binary of substances (e.g. carbon dioxide in excess of air). Some combinations can be found here.

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Hi, Thank you so much for answering this question!

Now I got it that the diffusion coefficient here is the molecular diffusivity which depends on the substances.

And I wondered if there is any place that I can set the background turbulent diffusivity.

Thanks!