Optimizing Parapets for Rooftop Wind Safety Using CFD Simulations and Sensitivity Analysis

The complex rooftop wind environment, dominated by flow separation at building edges, presents safety challenges for rooftop activities such as roof gardens and urban air mobility (UAM) operations. This study investigates the wind sheltering performance of rooftop parapets on a 40 m-high isolated building using computational fluid dynamics (CFD) simulations, with the wind direction perpendicular to the windward building face. A total of 729 simulations are conducted, systematically varying the parapet height (0-4 m in 1m intervals) and porosity (solid or 40%) across the upwind, two sides, and downwind edges. Configurations of the two side parapets are kept identical across all cases. CFD results for solid parapets are validated against wind tunnel measurements at a 1:200 scale, showing good agreement. Wind conditions are evaluated using volume-averaged statistics within the 0-2 m height range above the rooftop surface, corresponding to the typical occupied zone during rooftop use. Results reveal that different parapet configurations can cause rooftop wind speed (WS) to vary between a 50% reduction and a 12% increase, turbulent kinetic energy (TKE) between a 72% reduction and a 2% increase, and total kinetic energy (total KE) between a 65% reduction and a 6% increase. Global sensitivity analysis using the Sobol method identifies the upwind and downwind parapet heights as the dominant parameters affecting WS, while the height and porosity of the upwind parapet primarily influence TKE and total KE. Specifically, a porous upwind parapet with height ≤ 2 m combined with solid side parapets proves most effective to reduce WS. A tall solid upwind parapet (≥ 3 m) paired with solid side parapets is recommended to minimize TKE and total KE. These findings offer guidance for optimizing rooftop parapet design to enhance wind safety in rooftop usage scenarios.