A Laboratory Tornado Simulator: Comparison of Laboratory, Numerical and Full-Scale Measurements

Abstract eng:
A laboratory tornado simulator that can generate a translating vortex has been built for the purpose of studying the interaction of a tornado-like vortex with the built environment such as individual buildings or suburban and urban complexes. The simulator, mounted on a crane to impart translation, operates like a closed-return wind tunnel with an open test section. It has two concentric ducts to circulate the flow between the inside duct that houses the 1.83-m diameter fan and the outside duct with 5.5 m outer diameter and 4.88 m inside diameter to create a tornado-like vortex whose diameter can reach 1.22 m and tangential velocity can reach 33 m/s. Since the primary purpose of the simulator is to assess the windinduced loads on engineered structures, it is important to validate the wind field of the simulated tornado with full-scale data. Doppler on Wheels radar data from the Spencer, South Dakota tornado of 1998 was used for this purpose. Numerical simulations were also performed with Fluent software for assessing the near-ground flow field (less than 50 m) since the Doppler radar data may not be very accurate at those heights. Analyses of the radar data show peak tangential winds occurring at the lowest scan, roughly 20 m above ground level, with a vortex whose core radius increases between 120 m and 200 m above ground, and remains relatively constant above that level. Numerical model data based on the dimensions of the laboratory simulator and laboratory inflow data are generally consistent with the laboratory and radar observations despite some differences.

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