HEAT FLUXES AND EDDY DIFFUSITIVIES FROM LARGE-EDDY SIMULATIONS OF TURBULENT EPISODES IN THE STABLE BOUNDARY LAYER

摘要

The stable boundary layer (SBL) is of considerable interest because it is often the 'worst ~* case' scenario for air pollution studies and health effect assessments associated with the accidental release of toxic material. Traditional modeling approaches used in such studies do not simulate the non-steady character of the velocity field, and hence often overpredict concentrations while underpredicting spatial coverage of potentially harmful concentrations of airborne material. In addition, eddy diffusivity prescriptions for the SBL can underestimate the turbulent fluxes during episodes of enhanced turbulence that have been observed in the SBL (i.e. Coulter, 1990). The large-eddy simulation (LES) approach with its subgrid-scale (SGS) turbulence model does a better job of capturing the temporally and spatially varying features of the SBL than do Reynolds-averaging models. Thus, the LES approach is used to simulate the SBL and obtain turbulent fluxes and mean gradients from which eddy diffusivities can be estimated. These are then compared to values from algorithms used in simpler models.