Influence of swirl ratio and radial Reynolds number on wind characteristics of multi-vortex tornadoes

Abstract

In this study, systematic numerical simulations are conducted to investigate how swirl ratio and radial Reynolds number affect the wind characteristics of multi-vortex tornadoes. By properly controlling boundary conditions, multi-vortex tornadoes are produced in a cylindrical computational domain. Six cases with different swirl ratios are studied to examine the influence of swirl ratio, while five cases with different radial Reynolds number are studied to investigate the influence of radial Reynolds number. To facilitate the characterization, the core size and rotational speed of subvortices, as well as the relative distance between the subvortex and the core radius of the main vortex, are defined. The results demonstrate that the increase in swirl ratio leads to the increase in the number of subvortices. For the overall vortex, the increase in swirl ratio decreases the maximum tangential velocity but increases the core radius of the overall flow. For subvortices, for the case where four subvortices are produced, the increase in swirl ratio increases the core size of subvortices but decreases the rotational speed of subvortices. While the increase in radial Reynolds number does not change the number of subvortices produced, it decreases the core size of subvortices, but increases the rotational speed of each subvortex.