Wind flow characteristics of multi-vortex tornadoes and their wind effects on residential houses

Tornadoes strike the USA very frequently, with an average of 1200 reports per year, and the average annual tornado-induced property loss has reached $10B. The devastation from recent tornadoes have prompted a renewed interest in better understanding tornado dynamics, their interactions with the built environment, and the performance of civil structures during tornadoes. In the past, the wind effects caused by single-vortex tornadoes have been widely studied, while the multi-vortex tornadoes were rarely considered. In fact, many previous deadly, costly tornadoes involved multiple vortices. Therefore, it is important to understand the wind flow characteristics of multi-vortex tornadoes in order to understand their actions on civil structures. To achieve this, Computational Fluid Dynamics (CFD) simulations are adopted to simulate tornadoes and tornado-structure interaction. First, an approach to derive the vertical velocity of tornadoes from the tangential and radial velocities (extracted from the radar measured velocities) is developed in order to simulate tornadoes in a more precise manner. Second, a multi-vortex tornado is simulated, and its wind flow characteristics are investigated and compared with a single vortex tornado. Third, a parametric study is conducted to examine the influence of swirl ratio and radial Reynolds number on multi-vortex tornadoes, to produce different types of multi-vortex tornadoes. Forth, the wind effects induced by multi-vortex tornadoes are studied and their unique features are identified. Last, the understanding of tornado-structure interaction is expanded to manufactured or mobile homes, which are more vulnerable during tornado striking compared to permanent homes, to bridge a knowledge gap --Abstract, page iv