Sensitivity test of different inflow conditions for CFD simulations of wind flow in urban areas

The common practice for defining inflow conditions for wind tunnel tests (WT) and Computational Fluid Dynamics (CFD) simulations of wind flow in urban areas consists to fitting an analytical formulation to the wind profiles using on-site measurements as input, when available. Currently cup and ultrasonic anemometric stations represent the most common instruments used to measure the wind velocity at a single point above the ground. Irrespective of the accuracy of the wind measurements, extrapolation based on single point data can cause large uncertainties in the mean wind velocity profile, especially over complex terrain and with stratified flow. This uncertainty can be reduced, in principle, by using instruments able to directly measure the vertical wind velocity profile such as Sonic (SoDAR) or Light Detection and Ranging (LiDAR) wind profilers. The aim of this study is to quantify this uncertainty through comparison with full-scale anemometric measurements and WT tests using a small district of Livorno city (Italy), called Quartiere La Venezia, as a case study. This area is placed very close to the Port of Livorno where a sophisticated anemometric monitoring network composed of seven ultrasonic anemometric stations and one LiDAR are installed. CFD simulations of wind flow over this area have been performed for two wind directions, i.e. 240° and 270°, using two different inflow conditions. For the first set of simulations the wind velocity profile at the inlet was obtained by extrapolating measured single point anemometric data with a logarithmic profile. The same CFD simulations have then been performed using inflow conditions based on wind profiles measured by the LiDAR. Finally, the wind flows inside the urban canopy and above it of both CFD cases have been compared with each other and with WT test results using validation metrics (i.e. Bias, NMSE, Correlation (R) and FAC1.3). Correlation of 77% and FAC1.3 equal to 89% were found between the first set of simulations and the WT results for the incoming wind direction 240°. In contrast, unsatisfactory agreement between the first set of simulations and WT results was found for the incoming wind direction 270° (R = 66% and FAC1.3 = 56%). CFD simulations concerning to the inflow conditions based on wind profiles measured by the LiDAR are still running. Further results will be presented in the full-paper version.