Measurements of Core Radii and Peak Velocities in Modeled Atmospheric Vortices

Abstract

Measurements in a tornado simulator have yielded quantitative data on certain aspects of the mean flow of a variety of modeled vortices. The radius of maximum velocity in the vortex core has been measured using a hot-film anemometer for swirl ratio values from zero to 6. A simple model of the turbulent core radius as a function of swirl ratio shows good agreement with the experimental data. The magnitude of the mean total velocity vector at the core radius has also been determined for the same range of swirl ratios and for a range of Reynolds numbers. The measurements indicate that for laminar vortices the peak velocity is strongly dependent on swirl ratio, whereas for turbulent vortices the swirl ratio dependence is weak. For both laminar and turbulent vortices, peak velocities are directly proportional to the mean vertical velocity in the updraft region. The application of the experimental measurements to the estimation of actual tornadic velocities is demonstrated.