A translating tornado simulator for engineering tests: comparison of radar, numerical model, and simulator winds

A tornado simulator that allows a large translating vortex has been developed to study the interaction of a tornado-like vortex with the built environment. The simulator was designed taking into account the role that intense convergence from a rear-flank downdraft descending to the ground and encircling a strong updraft may play in tornadogenesis. The simulator uses a downdraft occurring in a circle of 18 ft diameter to create a tornado whose diameter can reach 4 ft. Although the primary purpose of the simulator is to test the pressures imparted on engineered structures, validation of the simulated tornado is being performed using Doppler on Wheels radar data from the Spencer, South Dakota tornado of 1998 and numerical simulations performed with Fluent software. 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 60 m and 100 m above ground, and remains relatively constant above that level. Numerical model data based on a smaller laboratory prototype show both differences and similarities compared to the radar observations. Preliminary pressure measurements taken within the simulated large translating vortex agree well with observations made within an F4 tornado in Manchester, South Dakota in 2003. More comprehensive measurements from within the large translating vortex simulator will be taken in the coming months and compared to radar and numerical simulations in the extended abstract.