Turbulence closure schemes suitable for air pollution and wind engineering

Abstract

Computationally efficient turbulence closure schemes are formulated and evaluated. Fully explicit algebraic expressions for Reynolds stresses and turbulent scalar fluxes are derived in the weak-equilibrium assumptions from the transport equation for these functions. The two-equation Eulerian turbulent diffusion model is used for describing evolution of the concentration field of contaminant emitted from a ground source in the turbulent boundary layer in the absence of buoyancy forces. Results of modelling passive scalar propagation from a continuous line finite-size source located on the underlying surface of the boundary layer with using the non-local two-parameteric turbulence model and the transport equation of mean concentration are presented. In proposed diffusion model the turbulent diffusion coefficient changes not only with the vertical coordinate but also with the distance downstream from the source according to the laboratory experiments data. The results of modelling reproduce well the measurements data for structural features of the concentration field transformation. Using the differential transport equation model for turbulent matter flux and the low Reynolds number corrections for normal Reynolds stresses approximation gives the same results and somewhat more exact reproduction of fine features of diffusion field both near the source and near rigid surfaces. Diffusion of passive contaminant from a line source in a flow behind a backward-facing step is investigated.