Does a revolving wing stall at low Reynolds numbers?

DOI Web Site 17 References Open Access
  • GUO Xiaoqian
    Shanghai Jiao Tong University and Chiba University International Cooperative Research Center (SJTU-CU ICRC)
  • CHEN Di
    Shanghai Jiao Tong University and Chiba University International Cooperative Research Center (SJTU-CU ICRC)
  • LIU Hao
    Shanghai Jiao Tong University and Chiba University International Cooperative Research Center (SJTU-CU ICRC) Graduate School of Engineering, Chiba University

Abstract

Motivated by the dynamic, i.e., “delayed” stall mechanism in bio-inspired flapping wing aerodynamics that can achieve high lift production at high angles of attack (AoA) we utilize a simplified revolving wing model to explore the novel mechanisms in concert with stall phenomenon at low Reynolds numbers. The dynamic stall-based leading-edge vortex structure recognized as the primary reason for lift augment in insect flapping flight is also observed in revolving wings in low Reynolds (Re) number regime. However, it is still unclear why this “delayed” stall at low Res performs remarkably distinguished from that at high Res. In this study, we built a hawkmoth wing-like geometric model and a revolving kinematic model with an impulsive accelerated start as the quasi-steady model of flapping wings. We carried out a systematic parametric study on stall characteristics in terms of Res effects over a wide range from 100 up to 5.4×105. Our results show that in the low Res regime where most insects fly, the revolving wing likely does not stall in a conventional sense: there is no trend that lift turns to reduce at some critical AoA but keeps increasing with increasing AoAs. Moreover, the Reynolds number effect on aerodynamic forces augment is mostly pronounced at Res less than 5400 during both unsteady acceleration and steady rotation phases. Our results imply that micro air vehicles (MAV) with rotary wings will suffer a rapid drop in aerodynamic performance probably at operating Res less than 5,400, which may point to the importance of the employment of flapping wings for insect-sized MAV design.

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