A recycling method for the large-eddy simulation of plumes in the atmospheric boundary layer

A method for the large-eddy simulation (LES) of dispersion and mixing of passive scalars is developed and evaluated. The new method addresses the requirements of tracking the evolution of plumes for large distances from their sources while attaining a low computational cost. To reduce computational cost, the velocity and thermodynamic fields are solved on a doubly periodic domain in the horizontal directions. In contrast, when the plume reaches the downstream end of the computational domain, it is reintroduced at the upstream plane but as a different scalar field. The same procedure is repeated when the new scalar field reaches the downstream boundary. By using several scalar fields to describe the evolution of a single plume, the simulation is computationally cheaper since the same velocity and thermodynamic fields are reused, or recycled, when computing the plume evolution. The recycling method is verified by showing that low-order plume statistics are identical to a single-domain LES. Three cases of dispersion and mixing from a point ground source in diverse boundary layer conditions (stable, convectively unstable, and shallow cumulus convection) are considered. Moreover, the LES results are compared with the predictions a Gaussian plume model, which is found to perform satisfactorily in all cases when accurate information about the state of the boundary layer is provided.