Large-eddy simulation (LES) is a very useful tool in computational fluid dynamics. The LES model allows one to solve a filtered set of the Navier-Stokes equations, thereby explicitly resolving scales of motion larger than the discretization or grid size. Those motions smaller than the grid size are parameterized using a so-called subgrid scale model.; In this series of papers, we will use the TASS LES model, originally a cloud model, which has been modified to simulate planetary boundary layer turbulence. We will first introduce the LES model and a new grid-nesting method for the LES. Then we will present simulations of the convective planetary boundary layer, and then use the LES to study the decay of convective planetary boundary layer turbulence to a stably stratified state.; The LES model has been modified to include a grid nesting capability. Grid meshes of higher resolution may be embedded within the LES enabling one to resolve smaller scales of motion (turbulence) than would be possible by using a single grid mesh. The grid nesting methodology is described in detail in Chapter 2.; In Chapter 3, the nested-grid LES will be applied to the simulation of the convective planetary boundary layer. We will use a total of three grid meshes to increase the resolution in the surface layer, allowing a detailed analysis of the turbulence near the surface of the earth.; In Chapter 4 we will focus on applying Rayleigh Benard convection criteria, using a linearized perturbation method, to the surface layer of a CBL produced by large-eddy simulation. Similarities and differences will be discussed between the LES produced surface layer and classical Rayleigh-Benard convection theory.; In Chapter 5, using a large-eddy simulation model, we will examine in detail the turbulent kinetic energy (TKE) budget during the evening transition. The simulation will be performed in order to compare to observations gathered at the Dallas-Fort Worth International Airport, Fort-Worth, TX during September and October 1997.; In Chapter 6 the decay of planetary boundary layer turbulence during the evening transition will be studied. In previous studies of the decay of turbulence, the effects of mean winds and shears due to pressure gradient on the turbulence decay was not considered. We propose to examine the effects of increasing geostrophic wind on the convective boundary layer and its transition or decay to a stable condition. Finally, the overall conclusions of each chapter will be presented.
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