Large-eddy simulation of turbulent flow and coherent structures over rotated random-height building arrays

Urban canopy flows exhibit complex interactions between geometric heterogeneity and turbulent organization, posing challenges for air-quality, ventilation, and low-altitude urban-flow prediction. While canonical studies have characterized idealized building arrays, realistic urban morphologies often involve building-height variability (H/3≤h≤H) and variable orientations relative to prevailing winds, whose combined effects remain insufficiently characterized. This study investigates turbulent flow over rotated building arrays with randomly sampled heights at 0°, 15°, 30°, and 45° using large-eddy simulations, with single-cube validation and array-level grid-refinement checks. A balanced rotation–height matrix retains the same sampled height layouts across orientations, allowing trends associated with the rotation-induced projected-blockage change to be distinguished from realization-dependent variability. Mean velocity and wake-deficit fields show that local height contrast influences passage acceleration and channeling flows between buildings, whereas array rotation induces wake deflection, skewness, and wake-deficit organization. Across the 16 rotation–height cases, array rotation increases projected frontal blockage, domain-averaged turbulent kinetic energy (TKE), and low-to-intermediate spanwise spectral energy. The transition from θ = 30° to 45° separates wake-deficit and turbulence responses: wake-deficit metrics decrease or saturate in several realizations, whereas TKE and transport-related quantities continue to increase. A projected-blockage-adjusted comparison relates the remaining TKE response to the spanwise gradient of turbulent streamwise-momentum transport. Local analyses show that height realization modulates wake asymmetry and turbulence redistribution. These results support a multiscale interpretation in which the rotation-induced projected-blockage response is associated with canopy-scale wake organization and turbulence response, whereas height arrangement and spanwise exchange remain important for local recovery.