Turbulent Schmidt Number Measurements Over Three-Dimensional Cubic Arrays

We present turbulent Schmidt number ([Formula: see text]) estimations above three-dimensional urban canopies, where [Formula: see text] is a property of the flow defined as the ratio of the eddy diffusivity of momentum ([Formula: see text]) to the eddy diffusivity of mass ([Formula: see text]). Despite the fact that [Formula: see text] modelling is of great interest, inter alia, for pollutant dispersion simulations conducted via computational fluid dynamics, no universal value is known. Simultaneous measurements of fluid velocity and mass concentration are carried out in a water channel for three staggered arrays of cubical obstacles corresponding to isolated flow, wake-interference, and skimming-flow regimes. A passive tracer is released from a continuous point source located at a height [Formula: see text] where H is the obstacle height. The results show an increase of [Formula: see text] with height above the canopy for all three arrays, with values at [Formula: see text] ([Formula: see text]) about double compared to that at [Formula: see text]. The observed [Formula: see text] agrees well with that modelled by using a simple formulation for [Formula: see text] based on expressions for [Formula: see text] and [Formula: see text] published in previous studies. Comparisons with other [Formula: see text] models found in the literature are also presented and discussed.