Large eddy simulations of strong wind mechanisms at pedestrian level around square-section buildings with same aspect ratios and different sizes

Physical mechanisms of high pedestrian-level winds around buildings are known as downwash effect and Venturi effect. Downwash effect is more significant than Venturi effect for isolated buildings. Two types of variations of downwash effect with building configurations were conjectured in Tamura et al. (2019): Type 1, due to flow pattern change between 2D (two dimensional) and 3D (three dimensional) and Type 2, due to wind speed change near the front stagnation height. Large Eddy Simulations were performed for buildings with the same aspect ratios (ARs) and different sizes in boundary layer flow (BLF) and uniform turbulence flow (UTF) to verify the type 2 variation of downwash effect and investigate its influence on wind speeds around buildings. The results confirmed that, for buildings with the same ARs and different sizes in the same BLF, the same downwash flow patterns can be assumed, and that pedestrian-level winds are mainly related to wind speed change near the front stagnation level in BLF, and a quantitative relationship between them is identified. The difference between downwash flow patterns for buildings with different ARs in BLF, and flow patterns around buildings in UTF are also discussed in detail for better understanding of the downwash effect on pedestrian-level winds.