진동하는 날개의 Tip Vortex Roll-up 에 관한 실험적 연구 I : 평균 속도장

Abstract

An experimental study was carried out to examine quantitatively the tip vortex roll-up in the near-field of an oscillating wing. A NACA 0012 rectangular planform wing with an aspect ratio of 4.0 was mounted on the floor of the wind tunnel test section, and the wing was sinusoidally pitched about the quarter chord. Both the mean incidence angle and the amplitude of oscillation were set at 1T, which made the angle of attack vary from 0` to 3 0`. The flow visualization and measurements were made for the case of K=0.09, and RN=3.4 × 104 Masurements by using the triple hot-film probe were carried out at two downstream stations : X/C=0.5 and 1.5. The streamwise flows for the pitch-up motion remained attached and resulted in well-defined circular vortex cores, while those for the pitch-down motion were separated to yield irregular and turbulent cores. The phase-averaged mean velocity profiles were distinctly different from each other at the same instantaneous angle of attack for pitch-up and pitch-down motions. The flow field of pitch-down motion was strongly influenced by massive separation, and hence the differences among various flow quantities for pitch-up motion and those for potch~down motion were severer. The phase-averaged velocity fields in the wing tip vortex region are presented and variations with respect to the instantaneous angle of attack are discussed.