Post by Alberto Passalacqua on Dec 18, 2019 10:53:05 GMT -6
the moment transport equations are always solved in their unsteady form: the fvm:ddt term is always present in the first part of the code. The subtraction of fvc::ddt(m) is done if the realizable ODE solver is used to solve for the source terms. The solution proceeds in two steps: first advection, diffusion and implicitly discretized source terms (if any) are accounted for. This changes m. Then, if the realizable ODE is used, the result of the integration from the ODE is included. Subtracting fvc::ddt(m) is necesssary because if not done, the change in the first step of the integration would not be included in the integration.