http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
수직 하강 비행 시 로터-로터 상호작용이 UAV의 후류 구조에 미치는 영향
채석봉(Seokbong Chae),이승철(Seungcheol Lee),김주하(Jooha Kim) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
In the present study, we experimentally investigate the effect of rotor-rotor interaction on the rotor wake structure in axial descent. A twin rotor configuration system with various rotor separation distances were installed in the closed-circuited wind tunnel to observe wake structures of rotors in axial descent. Velocity fields around twin rotors were measured by using DPIV(digital particle image velocimetry). At a range of descent rate of V<SUB>d</SUB>/V<SUB>h</SUB> = 1.08 – 1.52 and a high rotor separation distance (s/R = 2.5), the flow around rotor enters VRS(vortex ring state), which form a large recirculation zone near the rotor tip. However, a decrease in s/R induces a stronger effect of rotor-rotor interaction on the rotor wake, resulting in the change in the location of a vortex ring core. At a very low s/R of 0.25, rotor-rotor interactions disrupt the vortex ring structure and make synthetic jets with the adjacent rotor wake. At various rotor separation distances, the frequency of vortex ring state was analyzed through the correlation analysis. At V<SUB>d</SUB>/V<SUB>h</SUB> = 1.08, the frequency of vortex ring decreases gradually as the rotor separation distance decreases and reach less than half at s/R = 1.5.
축 방향으로 나열된 관통홀을 구비한 원형 실린더 주위 유동
김지희,채석봉,김주하,Kim, Jihee,Chae, Seokbong,Kim, Jooha 한국가시화정보학회 2020 한국가시화정보학회지 Vol.18 No.1
In the present study, we experimentally investigated the flow around a circular cylinder with axially arranged holes (AAH). The wind-tunnel experiment was performed at Re = 3.2 × 10<sup>4</sup> while varying the angle of attack (α) from 0° to 90°. At low α, the passive jet from the AAH pushes near wake to the downstream, increasing the wake formation length. On the other hand, at high α, blowing and suction through AAH occurs alternatively, rather decreasing the wake formation length. The passive jet generated by AAH can effectively control not only the wake where AAH is located, but also the wake between holes. As a result, the AAH reduce the drag on the cylinder up to 23.8% at low α but rather increase the drag at high α, as compared to that on a smooth cylinder.
선단 돌기가 적용된 패러글라이더 캐노피의 공력성능에 대한 실험적 연구
신정한(J. Shin),채석봉(S. Chae),신이수(Y. Shin),황성윤(S. Hwang),박정목(J. Park),송진석(G. Song),김주하(J. Kim) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
The stall frequently occurs during the paraglider flight because the paraglider has wide range of angle of attacks due to repetition of ascending and descending flights. In this study, we apply the tubercle structure the leading edge of a paraglider canopy model dynamically similar to Boomerang 11 (Gin gliders). The tubercle structure is from a humpback whale flipper, which is known to delay the stall. The aerodynamic performances of the canopy with and without the leading-edge tubercles are experimentally measured by load cell at Re = 3.3×10<SUP>5</SUP>, where Re is the Reynolds number based on the mean chord length and the free-stream velocity. The leading-edge tubercles delay the stall and increase the lift coefficient on low angle of attack. Based on the above result, a role of the leading-edge tubercles will be explained with flow visualization data in the presentation.
홍슬기(Seulki Hong),채석봉(Seokbong Chae),김주하(Jooha Kim) 한국가시화정보학회 2017 한국가시화정보학회지 Vol.15 No.2
In the present study, the characteristics of kinematics and dynamics in the fluttering motion of free-falling plates are investigated at Reynolds number of 105. We record quasi-two-dimensional trajectories of free-falling plates with and without superhydrophobic coating using high-speed camera, and compute the drag and lift forces by trajectory analysis. Translational and angular velocities are modeled as harmonic functions with specific phase differences. In particular, periodic mass elevations near turning points are explained using the suggested models. At each turning point, a sudden drop in lift and a rapid increase in drag occur simultaneously due to fast increase in angle of attack. However, the lift is increased over the buoyancy-corrected weight of plate during gliding flight, resulting in periodic mass elevations near turning points. Superhydrophobicity is shown to increase lift but to reduce drag on a fluttering plate, resulting in the decrease of mean descent speed.