Some characteristics of the wind flow in the lower Urban Boundary Layer

The characteristics of the wind flow at low levels in the urban environment (Roughness Sublayer (RS)) are quite different from, and to some extent independent of the characteristics of the flow in the upper part of the Urban Boundary Layer. In the RS, in fact, the flow is influenced more by the local geometry, than by a homogeneous energy transfer between horizontal layers. In this paper, the results of wind tunnel flow measurements in and above a regular urban geometry pattern, with street canyons parallel and orthogonal to the oncoming wind, are reported. The statistics and the spectral characteristics of the flow in the RS are discussed. The influence of the oncoming turbulence on the RS flow is analysed, and the differences between the flow in transversal and longitudinal street canyons are evidenced.