Impact of Wind Direction on Flow and Turbulent Statistics Over a Realistic Urban Area: A Large-Eddy Simulation Study

We conducted high resolution large eddy simulations of the atmospheric boundary layer over the Zona Universitària Pedralbes district in Barcelona to investigate the impact of wind direction on flow and turbulence statistics within a realistic urban canopy. The computational mesh employs fourth-order spectral elements, yielding pedestrian level resolutions of approximately 1 m and total grid sizes about 500 million degrees of freedom. Sixteen wind directions uniformly distributed over 360$^\circ$ are simulated to capture the full directional response of the urban fabric. At pedestrian level, the flow exhibits extreme directional sensitivity where moderate rotation of the incoming wind reorganises the dominant flow pathways, shifting from continuous accelerated corridors when winds align with major street axes to fragmented cellular patterns under oblique inflows. These directionally activated channeling corridors govern local ventilation and sheltering. Yet, despite this pronounced local variability, double averaged vertical profiles of mean velocity and turbulence intensity collapse remarkably across all wind directions. Two distinct inflection points are consistently identified in the mean velocity profiles: one located slightly below the average building height, confirming the persistence of a shear driven mixing layer regime even in highly heterogeneous urban morphology, and a second, deeper inflection point near pedestrian level ($z/H_{avg} = 0.08-0.10$)that marks the transition between recirculating near ground flow and more connected intra canopy transport. Turbulence intensity maxima are systematically located between the mean and maximum building heights, implicating the tallest structures as the dominant generators of turbulent kinetic energy through wake shedding and roof edge shear. It is shown that urban aerodynamic response is simultaneously robust at the neighbourhood scale, behaving quasi isotropically in the double averaged sense, and strongly directional at the local scale, where the activation of preferential ventilation pathways dictates the spatial distribution of momentum and turbulence.