POLLUTANT DISPERSION BY A TURBULENT WIND FLOW NEAR A LOW HILL

Abstract eng:
A methodology is developed to study the pollutant concentration distribution in a turbulent shear flow over a two dimensional hill with small slope. As in a typical boundary layer problem, the flow domain is divided into an inner and an outer region: the inviscid outer region is subdivided into an upper and a middle layer, while the viscous inner region consists of a shear stress and an inner surface layer. With the velocities obtained from the Navier-Stokes and continuity equations, the diffusion equation for the pollutant concentration is readily solved. A variational method with adjustments to the streamline coordinate system is used in order to obtain an accurate solution of the concentration in the downwind region. Closed form analytical solutions of the pollutant dispersion patterns and concentration distributions are determined. It is shown that when there is an upwind source located at the upper layer, the concentrations decrease with distance along the upwind side of the hill and tend to be a constant rapidly near the hilltop. As the eddy diffusivity increases, the concentrations become saturated at an earlier position. This diffusion model can be applied to any realistic flow field once the streamlines can be specified through the velocities.

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