03.4 - Applied Aerodynamics
ASPECT RATIO AND ADVANCE RATIO EFFECTS ON AERODYNAMIC CHARACTERISTICS OF FLEXIBLE FLAPPING WINGS
R. Addo-Akoto¹, S.-G. Lee¹, J.-S. Han, Chungnam National University, South Korea; J.-H. Han¹; ¹KAIST, South Korea
In this study, experiments are conducted to examine the aspect ratio AR and advance ratio J effects on the aerodynamic characteristics of flexible flapping wings. Three aspect ratios and five J cases are considered in this study. The study reveals that flexible wings can generate non-negative (? 0) transient lift in the upstroke for higher J cases, which is in contrast to the negative lift reported in literature for rigid wings. An increase in J decreases both the cycle-average aerodynamic lift and power irrespective of AR. Hence, a negative exponential relation is found to exist between the cycle-average lift and J, and cycle-average power and J. The AR = 1.5 and 6.0 wings are found to produce almost the same amount of lift for each change in J. However, the AR = 3.0 wing produced the best aerodynamic performance in terms of maximum lift generation and balance in efficiency. To maximize lift at mid-downstroke, the study reveals the existence of an optimum combination of J and AR. Furthermore, the resultant effect of AR and J on the forward force and pitching moment on the virtual body of the flapping flier is examined. The study reveals the tendency of low AR wings (= 1.5 and 3.0) to restore the body to its neutral position; convergence with increasing J. In addition, the low AR wings produce higher forward force than the high AR (= 6.0) wing, emphasizing the dominance and benefits of adopting a low AR wing in flapping flight applications.