Vortex characteristics of a large-scale Ward-type tornado simulator at Central South University
Haiquan Jing, Shiqin Zeng, Xuhui He, Dongqin Zhang, Bo Li
Abstract
Recently, a new large-scale Ward-type tornado simulator has been built at Central South University, CSU-TW5. Three-dimensional (3-D) velocity and surface pressure on the ground were measured to investigate the vortex characteristics under different fan speeds and swirl ratios. The measured vortices were compared with those of real tornado vortices and numerical models proposed by previous researchers to check the performance of the simulator. The results showed that CSU-TW5 successfully reproduced the main characteristics of tornado-like vortices as other simulators, such as WindEEE, VorTECH, and ISU simulator. The fan speed only affects the magnitude of wind speed and has little effect on the vortex structures. The swirl ratio has a significant influence on the vortex structures as reported by previous researchers. The simulated results of velocity and surface pressure are similar to those of real tornadoes. The vortex structure apparently transforms from a narrow one-celled vortex to a two-celled vortex when the swirl ratio rises from 0.18 to 0.87. A downdraft appears at the upper vortex core when the swirl ratio is 0.42 and moves downward when the swirl ratio increases. It reaches the location near the ground as the swirl ratio increases to 0.87. For the tornado-like vortex of CSU-TW5, the distribution of tangential velocity at the height of the maximum value is relatively closer to the Burgers-Rott and Sullivan models; the distribution of radial velocity at the height of the maximum value is generally closer to the Baker model, and it becomes closer to the Kuo-Wen model inside the core region when the swirl ratio is 0.87; the axial velocity at the height of the maximum value matches well with the Baker model under the smallest swirl ratio. However, as the swirl ratio increases, the downdraft region gradually becomes larger, causing an obvious difference in the velocity distribution between the experimental results and the numerical models. The experimental data in the present study has been freely available on GitHub and can be found at: https://github.com/CSUtornado/Experimental-data .