Ricerc@Sapienza

This work presents laboratory estimates of the turbulent Schmidt number (Sct) above an idealized three-dimensional urban canopy. To do this, a neutral atmospheric boundary layer has been reproduced in the water channel and a staggered array of cubic obstacles of equal heights placed on the channel bottom has been used to simulate the canopy. A point source emitted a passive tracer at a constant rate above the cube array. Simultaneous measurements of pollutant concentration and velocity permitted the estimation of the vertical fluxes of mass and momentum and, therefore, of Sct.

We present results from water-channel experiments on neutrally-stable turbulent flows over staggered arrays of cubical obstacles modelling idealised urban canopies. Attention is concentrated on the vertical profiles of the Eulerian (TE) and Lagrangian (TL) time scales of the turbulence above three canopies with different plan area fractions (λP = 0.1, 0.25 and 0.4). The results show that both the streamwise and vertical components of TL increase approximately linearly with height above the obstacles, supporting Raupach’s linear law.

We present turbulent Schmidt number (Sct) estimations above three-dimensional urban canopies, where Sct is a property of the flow defined as the ratio of the eddy diffusivity of momentum (KM) to the eddy diffusivity of mass (Dt). Despite the fact that Sct modelling is of great interest, inter alia, for pollutant dispersion simulations conducted via computational fluid dynamics, no universal value is known.