Tornado papers Numerical Simulations of High Intensity Winds. Downburst Simulations Horia Hangan Department of Civil and Environmental Engineering University of Western Ontario, London, Canada July 2002 ICLR Research Paper Series – No. 19
Based on unpublished recent reports by Applied Research Associates more than 66% of all high intensity wind events in North Eastern United States involving damaging effects on buildings and structures are associated with thunderstorms. Also recent analysis of extreme wind speeds in Australia “indicate that thunderstorm downbursts are the extreme wind type at 10 metres height.” In a presentation given 25 years ago to the Norwegian Institute of Technology, Alan G. Davenport inferred the main downburst characteristics: “These storms produce high intensity winds of short duration. The mean wind profile during these storms is often quite different” from straight boundary layer winds. “The region of strong winds may be confined to much shallower layers and maximum wind speeds are encountered below 500m.”
However, given the above non-uniformity and localization of thunderstorms in both time and space these high intensity winds are difficult to physically simulate in conventional wind tunnels. Most of the current wind engineering tests and codes of practice are based on the effects of straight, boundary layer (synoptic) winds.
Computational Fluid Dynamics (CFD) has recently made significant progress in simulating the effects of wind on structures and has the potential to model the thunderstorm related high intensity winds such as downbursts or tornadoes.
This study is concerned with numerical simulations of downbursts and tornadoes using state of art CFD. Up to now mean and fluctuating velocity fields for downburst flows have been simulated to be used: (i) for further Finite Element Method (FEM) simulation of loading on structures and (ii) to calibrate simplified analytical models for structural codes implementation.
Funding from Manitoba Hydro and the Institute of Catastrophic Loss Reduction (ICLR) sponsors this work.