Fluid-structure interaction of a tornado-like vortex with low-rise structures
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A laboratory tornado simulator was developed to obtain physical insight into the fluid-structure interaction of a tornado-like vortex and scaled-models of external structures. Based on the Ward-type tornado simulator, the TTU simulator uses sixteen slotted jets to impart angular momentum to the incoming flow. Use of the slotted jets allowed access to the confluence and convergence zones so that scaled models could be moved through the vortex. Generic scaled models a cube and a cylinder, both with flat roofs, were used to investigate the fluid-structure interaction in simulator. Both stationary and moving pressure distributions were tested as a function of position to the vortex core. Results showed the cube and the cylinder had very different roof responses when interacting with the vortex. The roof of the cylinder encountered more suction than the roof of the cube. For instance, the pressure coefficient Cp on the leading edge of roof for the cube was from -2.5 to 0.5; however, the pressure coefficient Cp on the leading edge of roof for the cylinder was from -4 to -1 when the aspect ratio equaled 1 and the swirl ratio equaled 0.5. After comparing the stationary and the moving pressure distributions of each model, the averaged pressure results did not show much difference between them; however, the pressure fluctuated by as much as 150% in comparison to the reported averages for the moving test. Helium bubbles and a "smoke" were used to visualize the flow. A single-celled vortex and a two-celled vortex were identified in the center of the simulator. As the swirl ratio increased, the size of the vortex became larger. It is not readily apparent as to whether vortex-breakdown occurred in the convergence region.