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Wind and Structures
  Volume 26, Number 3, March 2018 , pages 115-128

Numerical investigation of effects of rotating downdraft on tornado-like-vortex characteristics
Shuyang Cao, Mengen Wang, Jinwei Zhu, Jinxin Cao, Tetsuro Tamura and Qingshan Yang

    Appropriate modeling of a tornado-like vortex is a prerequisite when studying the near-ground wind characteristics of a tornado and tornado-induced wind loads on structures. Both Ward- and ISU-type tornado simulators employ guide vanes to induce angular momentum to converge flow in order to generate tornado-like vortices. But in the Ward-type simulator, the guide vanes are mounted near the ground while in the ISU-type they are located at a high position to allow vertical circulation of flow that creates a rotating downdraft to generate a tornado-like vortex. In this study, numerical simulations were performed to reproduce tornado-like vortices using both Ward-type and ISU-type tornado simulators, from which the effects of rotating downdraft on the vortex characteristics were clarified. Particular attention was devoted to the wander of tornado-like vortices, and their dependences on swirl ratio and fetch length were investigated. The present study showed that the dynamic vortex structure depends significantly on the vortex-generating mechanism, although the time- averaged structure remains similar. This feature should be taken into consideration when tornado-like-vortex simulators are utilized to investigate tornado-induced wind forces on structures.
Key Words
    Tornado-like vortex; large-eddy simulation; vortex wander; rotating downdraft
Shuyang Cao and Jinxin Cao: State Key Lab of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China
Mengen Wang: College of Civil Engineering, Tongji University, Shanghai 200092, China
Jinwei Zhu: hanghai Urban Construction Design & Research Institute Shanghai, China
Tetsuro Tamura: Tokyo Institute of Technology, Japan
Qingshan Yang: Chongqing University, China

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