Experimental Study on Effects of Ground Roughness on Flow Characteristics of Tornado-Like Vortices
The three-dimensional wind velocity and dynamic pressure for stationary tornado-like vortices that developed over ground of different roughness categories were investigated to clarify the effects of ground roughness. Measurements were performed for various roughness categories and two swirl ratios. Variations of the vertical and horizontal distributions of velocity and pressure with roughness are presented, with the results showing that the tangential, radial, and axial velocity components increase inside the vortex core near the ground under rough surface conditions. Meanwhile, clearly decreased tangential components are found outside the core radius at low elevations. The high axial velocity inside the vortex core over rough ground surface indicates that roughness produces an effect similar to a reduced swirl ratio. In addition, the pressure drop accompanying a tornado is more significant at elevations closer to the ground under rough compared with smooth surface conditions. We show that the variations of the flow characteristics with roughness are dependent on the vortex-generating mechanism, indicating the need for appropriate modelling of tornado-like vortices.
KeywordsSurface roughness Swirl ratio Tornado-like vortices Wind profiles
The authors would like to thank the reviewers, whose constructive comments led to an improved paper. This research was funded in part by Natural Science Foundation of China (NSFC) grant no. 51478358 and Research Foundation of State Key Laboratory of Disaster Reduction in Civil Engineering grant no. SLDRCE14-A-01. The first author greatly appreciates the Double-PhD Degree Program between Tongji University in China and Clemson University in the USA.
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