| Summary: | 학위논문 (박사)-- 서울대학교 대학원 : 공과대학 기계항공공학부(멀티스케일 기계설계전공), 2019. 2. 최해천. Leading-edge tubercles on a humpback whale flipper are known to enhance its hydrodynamic performance at post-stall angles of attack (Miklosovic et al 2004). We investigate vortical structures above a three-dimensional wing with tubercles using surface-oil-flow visualization and particle image velocimetry measurement. Two wing models with and without tubercles, previously studied by Miklosovic et al (2004), are considered at the Reynolds number of 180,000 based on the free-stream velocity and mean chord length. At this Reynolds number, tubercles delay the stall angle by 7° and increase the maximum lift coefficient by about 22%. At a low angle of attack, flow separation first occurs near the tip region for both wing models. While flow separation rapidly progresses inboard (toward the wing root) for the model without tubercles with increasing angle of attack, tubercles produce two types of vortical motions and block the inboard progression of flow separation, resulting in delayed stall from α = 8° to 15°. One of these two vortical structures is pairs of counter-rotating streamwise vortices evolving from hemi-spherical separation bubbles near the leading edge troughs at pre-, near-, and post-stall angles of attack, and the other is asymmetric pairs of streamwise vortices evolving from separated flow regions after the mid-chord region at near-stall angle of attack. At a post-stall angle of attack (α = 16°), strong clockwise and counter-clockwise streamwise vortices are generated from foci at the root and tip near the trailing edge, respectively, and delay flow separation in the mid-span, resulting in a higher lift coefficient than that without tubercles. Leading-edge tubercles are applied to the quadrotor blade(Phantom4, DJI) to improve performance in forward flight condition. The new blade has ten tubercles with amplitude of 6% and wavelength of 50% of the mean chord length of the blade without tubercles. The rotating speed is varied from 3,500 RPM ...
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