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

This article focuses on a computational fluid dynamics (CFD) study investigating how swirl ratio and radial Reynolds number influence the wind characteristics of multi-vortex tornadoes, which contain multiple smaller vortices called subvortices. The study systematically simulates tornadoes within a cylindrical domain, varying swirl ratio and radial Reynolds number to analyze their effects on subvortex properties such as rotational speed, core size, and relative location within the overall vortex. Results indicate that increasing swirl ratio raises the number of subvortices (from three to four), enlarges their core sizes, and decreases their rotational speeds when four subvortices are present, while increasing radial Reynolds number enhances subvortex rotational speeds but reduces their core sizes without changing their number. Force balance analysis reveals that, unlike single-vortex tornadoes where pressure gradient and centrifugal forces dominate and balance each other, multi-vortex tornadoes exhibit significant transient radial velocity variations and complex pressure gradients concentrated around subvortex cores rather than the overall vortex center.