• Wind and Structures
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• 제34권3호
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• pp.303-312
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• 2022

As wind turbine rotors increase, the overall loads and dynamic response become an important issue. This problem is augmented by the exposure of wind turbines to severe atmospheric events with unconventional flows such as tornadoes, which need specific designs not included in standards and codes at present. An experimental study was conducted to analyze the loads induced by a tornado-like vortex (TLV) on horizontal-axis wind turbines (HAWT). A large-scale tornado simulation developed in The Wind Engineering, Energy and Environment (WindEEE) Dome at Western University in Canada, the so-called Mode B Tornado, was employed as the TLV flow acting on a rigid wind turbine model under two rotor operational conditions (idling and parked) for five radial distances. It was observed that the overall forces and moments depend on the location and orientation of the wind turbine system with respect to the tornado vortex centre, as TLV are three-dimensional flows with velocity gradients in the radial, vertical, and tangential direction. The mean bending moment at the tower base was the most important in terms of magnitude and variation in relation to the position of the HAWT with respect to the core radius of the tornado, and it was highly dependent on the rotor Tip Speed Ratio (TSR).

• Wind and Structures
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• 제26권3호
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• pp.179-190
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• 2018

Translation of tornadoes is an important feature in replicating the near-ground tornado flow field which has been simulated in previous studies based on Ward-type tornado simulators using relative motion of the ground plane. In this laboratory investigation, effects of translation on the near-ground tornado flow field were studied using the ISU Tornado Simulator that can physically translate over a ground plane. Two translation speeds, 0.15 m/s and 0.50 m/s, that scale up to those corresponding to slowly-moving tornadoes in the field were selected for this study. Compared with the flow field of a stationary tornado, the simulated tornado with translation had an influence on the spatial distribution and magnitude of the horizontal velocities, early reversal of the radial inflow, and expansion of the core radius. Maximum horizontal velocities were observed to occur behind the center of the translating tornado and on the right side of its mean path. An increase in translation speed, resulted in reduction of maximum horizontal velocities at all heights. Comparison of the results with previous studies that used relative motion of the ground plane for simulating translating tornadoes, showed that translation has similar effects on the flow field at smaller radial distances (~2 core radius), but different effects at larger radial distances (~4 core radius). Further, it showed that the effect of translation on velocity profiles is noticeable at and above an elevation of ~0.6 core radius, unlike those in studies based on the relative motion of the ground plane.

• 대한기계학회논문집B
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• 제25권1호
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• pp.71-77
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• 2001

A flow visualization study using the oil film method and the smoke-laser light sheet arrangement is carried out to investigate the three-dimensional flow pattern around the free end surface region of a finite circular cylinder (aspect ratios of 1.25 and 4.25) mounted on a flat plate. The experiment is performed for the cases of two Reynolds numbers: 5.92${\times}$10$^3$and 1.48${\times}$10(sup)5. Various kinds of singular points on the free-end surface are disclosed from the oil surface flow visualization. The smoke-laser light sheet visualization, to aid in understanding the oil streak-line patterns, clearly demonstrates that a pair of tornado-like vortices marched along the downstream together with a pair of side tip vortices. A topological sketch to characterize the surface flow and the four vortices emanating from the top surface is included.