Wind Effects Induced by Multivortex Tornadoes on a Low-Rise Building

Multivortex tornadoes contain two or more subvortices that orbit within a parent vortex and can generate highly intermittent and localized near-ground wind fields. This study investigates how tornado flow structure affects wind effects on a low-rise building using large-eddy simulations. One single-vortex tornado and three multivortex tornadoes with different subvortex configurations are examined by systematically varying swirl ratio. Tornado translation is modeled using a relative-motion framework in which the building traverses the vortex field. Aerodynamic force and moment coefficients are evaluated along the traversing path. Additional stationary simulations are conducted to examine repeated load amplification associated with subvortex passages. Compared with the single-vortex case, multivortex tornadoes produce substantially larger uplift and more complex temporal responses, characterized by multiple peak groups linked to sequential interactions with orbiting subvortices. Surface pressure analysis indicates a transition from wind-speed-driven suction to dominance of localized pressure deficits within subvortex cores. The results suggest the need to explicitly account for multivortex tornado dynamics when characterizing tornado-induced wind effects.