On modelling angular momentum and vorticity in compressible fluid flow

The conservation of angular momentum and the preservation of vorticity are examined in particle-in cell and finite difference solutions to the equations for viscous, compressible flow. Both methods are found to conserve angular momentum in the solution of the Lagrangian equations of motion to O(Δt2). In the modeling of convection, however, the finite difference method has computational diffusion that is absent in the particle-in-cell method. In numerical experiments, the effect of computational diffusion is shown to be greater as the number of grid points is decreased.