Revised moment propagation method for scalar transport.

The moment propagation (MP) method was used to study the transport of a passive scalar by a turbulent fluid. Numerical results show that the MP method does not accurately capture the evolution of a scalar field at moderate Reynolds numbers. A theoretical analysis proves that the diffusivity derived from the MP model depends on fluid velocity, which limits the range of Péclet number. We describe an improved MP model (MP2) which eliminates the velocity-dependent diffusion, leading to more accurate predictions of scalar transport in high-velocity flows; at low velocities both methods give similar results. We test the model for a variety of simple flows and find that accurate results can be obtained at grid Péclet numbers in excess of 10.