Geometry-Driven Variations of the Horseshoe Vortex and Its Impact on Windward Wall Loads of Low-Rise Buildings

This paper examines how geometric parameters influence windward-wall pressures of low-rise buildings by analyzing the effects of the mean roof height-to-breadth ratio ( h / B ) and roof slope ( θ ) on the horseshoe vortex system under atmospheric boundary layer wind fields. Wind-tunnel tests on rigid building models were conducted. Surface-pressure measurements on the ground plane and windward wall were used to infer time-averaged horseshoe vortex features and their connection to fluctuating pressures and windward wall design loads. Specifically, the locations of the primary separation point from the ground plane and primary vortex core were inferred from the pressure statistics, and an effective collapse of these time-averaged features across flat and gable roof-shaped configurations was achieved using the normalization hB . Based on examining the horseshoe vortex footprint on the ground plane and the windward wall, the HSV transitions from a single coherent vortex at higher h / B values to a branched configuration at lower h / B values, producing larger mean suction and showing aerodynamic admittance functions greater than one at point pressures near the wall edges. This transition is associated with lower spatial pressure correlations, resulting in lower windward wall loads. In contrast, a more coherent vortex structure for larger h / B yields increased windward wall loads. Increasing the θ shifts the stagnation streamline upward, thereby slightly increasing the vertical extent of the side edges influenced by the horseshoe vortex. This expanded region of unsteady interaction leads to decreased spatial correlation of pressure fluctuations and, consequently, a reduction in the gust effect factor. These findings provide a physical basis for the geometry-dependent behavior of windward-wall design loads, linking them to the variable topology and coherence of the horseshoe vortex system as a function of the wall aspect ratio.