Call Dorothy! Researchers identify how a tornado’s ‘swirl ratio’ affects its structure and motion

Tornadoes cause extensive damage, economic loss, and casualties. Understanding how vortex structures develop and transport debris is essential for hazard mitigation and risk-informed design.

Kang et al. investigated the dynamics of small-scale tornado-like vortices, comparing experimental measurements and numerical simulations. They focused on the role of the swirl ratio — the ratio of tangential to radial momentum — in the structural evolution of the vortex.

“Experiments and simulations offer complementary advantages in the study of tornado dynamics,” said author Leonardo Chamorro. “Experiments are critical for capturing physical effects introduced by boundary conditions and environmental disturbances, while simulations allow for precise control of input parameters and the ability to resolve complex flow features in three dimensions.”

The researchers constructed a laboratory-scale vortex simulator, which combined bottom-mounted fans to impart rotation, vanes to guide radial inflow, and a top-mounted suction fan to drive axial flow. They seeded the air with green-dyed water droplets to track and visualize the flow and conducted complementary simulations under geometrically matched conditions for cross-validation.

They found the swirl ratio a key parameter for tornado-like flows. Lower swirl ratios were associated with greater vertical expansion of the vortex core and increased turbulence levels near the center. Transitions from single- to double-celled vortex structures were also linked to specific ranges of swirl ratios.

They plan to next incorporate suspended particles into experimental and computational approaches to study particle transport, dispersion, and deposition. This work has applications in meteorological contexts and in industrial and environmental applications.

“The insights from this research extend beyond tornadoes, with implications for engineering systems such as cyclonic separators and rotating plume transport in atmospheric and oceanic settings,” said author Yulia Peet.

Source: “Influence of swirl ratio on the structure and dynamics of tornado-like vortices,” by Soohyeon Kang, Rajesh Ramesh, Yulia T. Peet, and Leonardo P. Chamorro, Physics of Fluids (2025). The article can be accessed at https://doi.org/10.1063/5.0270056 .