Numerical study of flow characteristics of tornado-like vortices considering both swirl ratio and aspect ratio: Fid-Bau Portal

Numerical study of flow characteristics of tornado-like vortices considering both swirl ratio and aspect ratio

Zhang, Dongqin / Liu, Zhenqing / Jiang, Xinye / Jiang, Wenjun / Gao, Huanxiang / Li, Chao / Xiao, Yiqing / Hu, Gang

Abstract Flow characteristics of tornado-like vortices are primarily influenced by the swirl ratio and aspect ratio. This study systematically investigates effects of these two essential parameters on vortex visualization, mean flow fields, and fluctuations by large eddy simulations (LES). The geometric dimensions of a tornado-like vortex simulator are characterized by the inner cylinder radius and floor height. The former affects the core radii where maximum tangential velocities occur, as well as the vortex type which is used to separate flow structures while the latter influences the vortex type. Furthermore, the ratios of flow characteristics of tornado-like vortices, such as radial distances where the maximum tangential and radial velocities occur, to the inner cylinder radius ( $R_{V . \max} / r_{0}$ ; $R_{U . \max} / r_{0}$ , $R_{c} / r_{0}$ ) have a high correlation with the swirl ratio. The ratios of heights where the maximum tangential and radial velocities occur to the floor heights ( $Z_{V . \max} / H_{0}$ ; $Z_{U . \max} / H_{0}$ ) are mainly related to the aspect ratio. These parameters can be expressed by the swirl ratio and aspect ratio with high R-squared values of 0.941, 0.794, 0.984, 0.964, 0.958. Finally, vortex types can be modeled as a function of both swirl ratio and aspect ratio. This study reveals the relationship between the simulator geometry and generated vortices.

Highlights • Flow characteristics of tornado-like vortices are essentially affected by the swirl ratio and aspect ratio. • The ratios of vortex core radii to the inner cylinder radius have high correlations with the swirl ratio. • The ratios of heights of the maximum velocities to the floor height have exponential relationships with the aspect ratio. • The vortex types should be evaluated by the internal swirl ratio and aspect ratio simultaneously.