NavierStokes solution and tracers
Hello:
I have an embarrassingly basic question to ask. As far as I understand it, solving the NavierStokes equations furnishes a velocity field for the considered domain subject to the imposed assumptions. If this is indeed the case, my question is, say I wanted to describe the spread of an inert tracer (for example) in that domain, do I only need to know this velocity field? Alternatively, do I also need to consider mixing coefficients or are they already incorporated in the velocity field during the solution of the NavierStokes equations? Thanks in advance! :) 
Thanks for the reply, SergeAS! In that equation, does the diffusion term reflect molecular diffusion or diffusive mixing? That is to say, should D be the mixing coefficient that features in the NavierStokes equations or the molecular diffusion coefficient? (Also, I'm a bit confused by the term "binary diffusion coefficient". Why binary?)

Molecular diffusion and diffusion term in the Navier  Stokes equations are of the same nature.
Diffusion is a physical process that occurs in a flow of gas in which some property is transported by the random motion of the molecules of the gas. Diffusion is related to the stress tensor and to the viscosity of the gas. In your case (single inert tracer) we have binary diffusion (In the process involves only two components) 
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