Date

2019-10-20

Author

Yazdanpanah, Mahdi
Hazaveh, Hooman Amiri
Perçin, Mustafa
Van De Meerendonk, Remco
Van Oudheusden, Bas W.

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This study explores the effects of rotational mechanisms on the characteristics of the leading edge vortex (LEV) by comparing translating and revolving flexible wings that are started from rest. Tomographic particle image velocimetry (tomographic-PIV) technique was employed to acquire three-dimensional flow fields for the revolving wings, while planar flow fields for the case of translating wings were acquired via 2D2C-PIV measurements. The comparison of flow fields between the two motion kinematics reveals similar behavior of the vortical structures yet the LEV circulation in the translating wings has higher values. The LEV centroid in the revolving cases stays above the leading edge, while in the translating wings, it always remains at a lower position. The effect of high flexibility results in the retention of LEV closer to the wing surface for both cases. INTRODUCTION The design and development of aerial vehicles have been inspired by nature for centuries. Recently, with the advent of micro air vehicles (MAVs), the flapping flight of biological flyers has been explored by many researchers at the typical low Reynolds number (Re) due to having better aerodynamic performance compared to fixed and rotary wings [Pines and Bohorquez, 2006]. The flow around the flapping wings is unsteady, where the generation of a stable leading edge vortex (LEV) has shown to be one of the most prominent force generation mechanisms [Sane, 2003]. The flapping wing motion can be decomposed into three motion kinematics: sweeping, plunging and pitching. In the literature, the sweeping motion is simulated by either a rectilinear translation (i.e., infinite Rossby number) or revolving motion (finite Rossby number). In 2-D translational motion, the flow separates at the wing leading edge, forming a LEV. If the wing travels more, the trailing edge vortex (TEV) sheds to the wing wake. This is followed by the growth of LEV. The LEV cannot remain attached, and it sheds to the wake. In contrast to translating motion, a stable LEV presents during the revolving motion [Sane, 2003]. Figure 1 represents a comparison between the flow around a wing in translating and revolving motions. Numerous studies and different hypotheses support the idea of presence of stable LEV in revolving motion such as spanwise

URI

https://hdl.handle.net/11511/85436

Collections

Department of Aerospace Engineering, Conference / Seminar