Turbulence Structure and Implications for Dispersion: Insights from Large-Eddy Simulations

Large eddy simulations have been used to obtain an improved understanding of the character of turbulence in stratified flows over wavy and flat boundaries. Fine scale time- and space-varying features of the flow fields produced by LES are not captured by traditional RANS turbulence models. The wavy flow has been simulated on the laboratory-scale for a variety of hill heights and degrees of stratification. The nature of turbulence varies strongly both with position and with time. This has important implications for the transport and dispersion of releases from various regions of the flow with unique turbulence characteristics. Massless marker particles are released in the recirculation zone, the shear layer, the upslope region, and the outer flow. The effects of hill height and strength of stratification are assessed. Atmospheric-scale flows have been simulated for the evolving stable boundary layer (SBL). An advanced SGS turbulence model, similar to that used in the LES of laboratory-scale flows, allows backscatter of SGS energy. This has led to simulated SBLs that have intermittently occuring periods of enhanced turbulence. Due to the strong vertical shear of wind speed and direction in the SBL, the enhanced turbulence alters the dispersion of plumes simulated by marker particles. Our results have implications for assessment of health impacts from the airborne release of hazardous materials.