Wind tunnel measurements of the urban boundary layer development over a historical district in Italy

This paper presents the results of an experimental study aimed at investigating the urban boundary layer in a district of Livorno city, in Tuscany. The wind flow over this area has been measured in the wind tunnel of the University of Genova using a physical model in scale 1:300. Two sets of measurements have been carried out, aimed at measuring the urban canopy layer inside the main curved street canyon and the evolution with fetch of the urban boundary layer above the model. The development of the urban boundary layer and its variability with fetch is analysed in terms of spatial evolution of friction velocity, roughness length and zero-plane displacement of the vertical velocity profiles. It is shown that, at the transition from sea to urban area, friction velocity and roughness length grow quite rapidly to higher values. After the transition, the skin friction coefficient and the roughness length decrease, while the zero-plane displacement slightly increases with the same order of magnitude of the height of the buildings. The results are also intended to become a benchmark for further experimental and numerical investigations of a real neighbourhood with architectural characteristics typical of historical cities.