Scalars Prolongation and Restriction

[saisandeepdammati]

Howdy!

I am currently using scalar implementation in Athena++ for combustion applications with multiple species. Each primitive scalar (r_n) represents the species mass fraction (Y_n) of nth species. Then, we need to satisfy the following constraint in each computational cell:

sum(r_n) = sum(Y_n) = 1.0 (or) sum(s_n) = sum(rho*Y_n) = rho

where, conserved scalar s_n = rho*Y_n i.e. species mass density of nth species.

My question is, if at time t=0, I initialize the scalars on each meshblock such that the above constraint is satisfied on a cell to cell basis, will the scalars still satisfy the above constraint after prolongation or restriction? Or do we have to enforce it manually?

Thank you very much.

[c-white]

Currently there is no enforcement of this constraint, in order to allow passive scalars to represent non-constrained variables (e.g. entropy). So this would need to be enforced manually. The most straightforward way would be to use the EnrollUserExplicitSourceFunction interface. The last argument to user source functions is a modifiable array of s_n values after the flux divergence update has occurred.