Application of a Perturbation Recycling Method in the Large-Eddy Simulation of a Mesoscale Convective Internal Boundary Layer

Abstract

An arrangement of boundary conditions is described and demonstrated that facilitates the large-eddy simulation (LES) of inhomogeneous boundary layers such as internal boundary layers. In addition to the domain where the internal boundary layer develops, the method requires a section of domain over the upwind surface that is of the order of 10 boundary layer thicknesses and thus similar in size to that needed for the LES of the upwind boundary layer. In addition to periodic lateral, closed upstream, and open downstream boundary conditions, a simple and efficient perturbation recycling technique, which follows from one of Lund, Wu, and Squires, is used to generate a steady supply of fully developed turbulence from the inflow boundary. The arrangement is used to simulate a convective internal boundary layer during a cold-air outbreak over water. Results show the method consistently produces a solution that is homogeneous over the upwind surface and inhomogeneous over the downwind surface, and that the statistics are stationary after spinup. The sensitivity to the placement of the outflow boundary is tested, and examples of instantaneous and mean fields generated by the simulations are shown.