Pollutant transfer across the cavity region behind a two-dimensional fence

Abstract

The objectives of the present study are to construct a simple mathematical expression capable of predicting a pollutant flux across the cavity region or separation bubble behind a two-dimensional fence from knowledge of the fence height, the separation bubble length, the free-stream mean wind velocity, and the concentrations inside and outside the separation bubble. The separation bubble length is defined as the distance from the fence to the ground-level stagnation point where the mean wind direction changes from towards to away from the fence. In a practical application, the stagnation point can be determined easily by using cigarette smoke or a light-weight flag. An analytical expression for the pollutant flux has been obtained from the solution of the partial differential equations of momentum and pollutant transfer, using assumptions derived from experimental results. In order to determine the values of the constants in the analytical solution and to verify some of the assumptions, heat is used as a tracer representing the pollutant in wind-tunnel experiments conducted with various combinations offence height, heat input, and free-stream mean wind velocity. The wind tunnel results also show that excess temperature profiles behind the fence are similar if the excess temperature is scaled by the product of a reference excess temperature and the heat input, the vertical coordinate is scaled by the fence height, and the downstream distance from the fence is scaled by the separation bubble length. Show more