ON FORWARD-IN-TIME DIFFERENCING FOR FLUIDS - STOPPING CRITERIA FOR ITERATIVE SOLUTIONS OF ANELASTIC PRESSURE EQUATIONS

In this note, the authors address the practical issue of selecting app ropriate stopping criteria for iterative solutions to the elliptic pre ssure equation arising in nonoscillatory, forward-in-time Eulerian and semi-Lagrangian anelastic fluid models. Using the simple computationa l example of 2D thermal convection in a neutrally stratified Boussines q fluid, it is shown that (a) converging to the machine precision is n ot necessary for the overall accuracy and stability of the model, and adversely affects the overall model efficiency; and (b) the semi-Lagra ngian model algorithm admits fairly liberal stopping criteria compared to the Eulerian flux-form model, unless the latter is formulated in t erms of field perturbations.