Abstract
We investigated the three-dimensional vorticity dynamics of the flows generated by revolving wings using a volumetric 3-component velocimetry system. The three-dimensional velocity and vorticity fields were represented with respect to the base axes of rotating Cartesian reference frames, and the second invariant of the velocity gradient was evaluated and used as a criterion to identify two core vortex structures. The first structure was a composite of leading, trailing, and tip-edge vortices attached to the wing edges, whereas the second structure was a strong tip vortex tilted from leading-edge vortices and shed into the wake together with the vorticity generated at the tip edge. Using the fundamental vorticity equation, we evaluated the convection, stretching, and tilting of vorticity in the rotating wing frame to understand the generation and evolution of vorticity. Based on these data, we propose that the vorticity generated at the leading edge is carried away by strong tangential flow into the wake and travels downwards with the induced downwash. The convection by spanwise flow is comparatively negligible. The three-dimensional flow in the wake also exhibits considerable vortex tilting and stretching. Together these data underscore the complex and interconnected vortical structures and dynamics generated by revolving wings.
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Acknowledgments
We thank former graduate student Zheng Hu for assistance with the V3V experiments, and Spencer Frank for the discussion on the experimental results.
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Cheng, B., Sane, S.P., Barbera, G. et al. Three-dimensional flow visualization and vorticity dynamics in revolving wings. Exp Fluids 54, 1423 (2013). https://doi.org/10.1007/s00348-012-1423-0
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DOI: https://doi.org/10.1007/s00348-012-1423-0