a b s t r a c tHigh-order accurate numerical simulations are performed to investigate the effects of wavy leading edges (WLEs) on aerofoil-gust interaction (AGI) noise. The present study is based on periodic velocity disturbances predominantly in streamwise and vertical directions that are mainly responsible for the surface pressure fluctuation of an aerofoil. In general, the present results show that WLEs lead to reduced AGI noise. It is found that the ratio of the wavy leading-edge peak-to-peak amplitude (LEA) to the longitudinal wavelength of the incident gust (λ g ) is the most important factor for the reduction of AGI noise. It is observed that there exists a tendency that the reduction of AGI noise increases with LEA=λ g and the noise reduction is significant for LEA=λ g ≥0:3. The present results also suggest that any two different cases with the same LEA=λ g lead to a strong similarity in their profiles of noise reduction relative to the straight leading-edge case. The wavelength of wavy leading edges (LEW), however, shows minor influence on the reduction of AGI noise under the present gust profiles used. Nevertheless, the present results show that a meaningful improvement in noise reduction may be achieved when 1:0 ≤LEW=λ g ≤1:5. In addition, it is found that the beneficial effects of WLEs are maintained for various flow incidence angles and aerofoil thicknesses. Also, the WLEs remain effective for gust profiles containing multiple frequency components. It is discovered in this paper that WLEs result in incoherent response time to the incident gust across the span, which results in a decreased level of surface pressure fluctuations, hence a reduced level of AGI noise.

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Gliding arboreal lizards in the genus Draco possess a pair of patagia, which are thin wing membranes supported by highly-elongated thoracic ribs and can be actively folded and unfolded. The uniqueness of Draco gliding flight is that the forelimbs of Draco can move freely independent of the patagia which are the main lifting surfaces. During the main glide phase, the entire forelimbs are straightened, abducted from the body and held very close to the patagial leading edges. The reasons for adopting this abducted pose have not been investigated before, especially from the perspective of fluid physics. In this study, wind tunnel experiments and computational simulations are conducted to compare the aerodynamic performances of the abducted pose with two other poses, which have the forelimbs held away from the patagial leading edges. The results show that the abducted pose leads to the highest maximum lift coefficient. This aerodynamic advantage is caused by the larger leading-edge radius due to the abducted forelimbs and small gaps between the abducted forelimbs and the patagial leading edges. Furthermore, it is found that the low aspect ratio of the patagium (0.985) allows the wingtip vortex to energise the flow over the top patagial surface at high angles of attack which leads to a gentle stall characteristic. The current results also show the existence of distinct leading-edge vortices up to moderate angles of attack. Overall, this work deepens our understanding of the gliding flight aerodynamics of Draco lizards, and is useful for future artificial flying machine applications.

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