Aerodynamic performance of low aspect-ratio flapping wing with active wing-chord adjustment

Cong, Longfei, Teng, Bin, Chen, Lifen, Bai, Wei ORCID: https://orcid.org/0000-0002-3537-207X, Jin, Ruijia and Chen, Biaosong (2023) Aerodynamic performance of low aspect-ratio flapping wing with active wing-chord adjustment. Journal of Fluids and Structures, 122. p. 103964. ISSN 0889-9746

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Abstract

In daily life, excellent aerodynamic performance of birds and bats has been widely observed during their flying and propulsion. In the present research, a low aspect-ratio wing flapping in uniform flow with a combined heaving-pitching motion has been adopted to mimic such aerodynamic process of flapping-wing-based propulsors. Inspired by the changeable skeleton of natural bio-livings, a bio-inspired flow controlling strategy based on active wing-chord adjustment has been raised to achieve aerodynamic enhancement. Adopting an Immersed Boundary-Lattice Boltzmann Method (IB-LBM) to resolve relating fluid flow with moving boundary, the effects of stretching pattern, i.e., the amplitude and the phase of the wing-chord adjustment, on the aerodynamic performance of the wing, and the role of Aspect-Ratio ( ) have been confirmed and investigated in detail. With the Direct Numerical Simulation to achieve the vortical flow identification, detachment delaying of Leading Edge Vortex (LEV) and enhancement of Trailing Edge Vortex (TEV) have been observed for cases with in-phase active controlling, and it has been revealed that such phenomenons correlate well with the aerodynamic enhancement of the wing. On the other hand, it has been observed that, the out-phase wing-chord adjustment dominates the LEV detachment, and further the flow separation around the leading edge of the wing. It is believed that such flow detachment, together with the TEV weakening caused by the anti-phase wing-chord controlling, leads to the performance deterioration of the wing, compared with the in-phase case. Meanwhile, the present numerical results show that, with the increase of stretching ratio, the aerodynamic performance of the flapping wing becomes susceptible with respect to the stretching phase of wing-chord. Compared with the bounded thrust enhancement caused by the LEV bursting, the lifting enhancement of the flapping wing during the reinforced wing-chord adjustment shows consistent dependency on the stretching ratio.