Multiple buoyancy tracers

[raphael-ouillon]

Hi all, I am trying to set up simulations where multiple tracers contribute to the buoyancy. This is fairly common in particle-driven flows where multiple tracers that all contribute to buoyancy are used to represent sediment suspensions of different particle sizes (and thus settling velocities).

I am curious to hear people's thoughts on adding a MultipleBuoyancyTracer model to Oceananigans. An approach would be to have the buoyancy term be calculated as the sum of the contributions from other tracers, but this limits the number of applications. I am thinking in particular of particle-driven double diffusive convection, which can involves T, S and multiple sediment concentration tracers. A more general approach would be to have a MultipleBuoyancyTracer model with a custom equation of state, something along the lines of b = α(T-T₀)+ β(S-S₀) + ∑γᵢcᵢ. Curious to hear if people think this should exist in Oceananigans or in a separate package!

[glwagner]

I think this is a great idea!

I wonder if it makes sense to first generalize LinearEquationOfState to any list of tracers + coefficients γᵢ. We can rename the existing equation of state LinearSeawaterEquationOfState if we want to keep it.

Then it would be fun to have a MultipleBuoyancies analogous to MultipleForcings. Or, just a tuple (like we have closure tuples) might work too.