Influence of pitch rate on freely translating perching airfoils

Jardin, Thierry; Doué, Nicolas

doi:10.1017/jfm.2019.421

Cited by 8 publications

(11 citation statements)

References 22 publications

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“…The numerical method is further detailed in the works by 17 and 18 . It has been previously validated over a relatively large spectrum of low Reynolds number applications including axisymmetric bluff bodies 19 , revolving wings 20 and perching airfoils 21 .…”

Section: Methodsmentioning

confidence: 99%

Numerical investigation of three-dimensional asymmetric hovering flapping flight

et al. 2021

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Direct numerical simulations are performed to assess the aerodynamic performance of three-dimensional wings undergoing asymmetric hovering flapping flight. A large number of flapping kinematics is investigated, varying the pitch rate and the upstroke and downstroke angles of attack. We show that, for all cases, time-average performance is driven, to leading order, by the mean angle of attack over a flapping period despite the increased contribution of drag to vertical force with increased stroke plane angle. We hence suggest that asymmetric hovering is not intrinsically more efficient than normal hovering, conversely to what has been previously reported in the literature. This may explain the underrepresentation of this flight mode in nature.

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Section: Methodsmentioning

confidence: 99%

Numerical investigation of three-dimensional asymmetric hovering flapping flight

et al. 2021

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“…The numerical method used to solve the Navier-Stokes equations is further detailed in the works by [36,37]. It has been previously validated over a relatively large range of low Reynolds number applications including axisymmetric bluff bodies [38], revolving wings [39] and perching airfoils [40].…”

Section: Numerical Simulationsmentioning

confidence: 99%

Experiments and numerical simulations on hovering three-dimensional flexible flapping wings

Díaz-Arriba¹,

Jardin²,

Gourdain³

et al. 2022

Bioinspir. Biomim.

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In this paper, the applicability and accuracy of high-fidelity experimental and numerical approaches in the analysis of three-dimensional flapping (revolving and pitching) wings operating under hovering flight conditions, i.e. where unsteady and three-dimensional rotational effects are strong, are assessed.Numerical simulations are then used to explore the role of mass and frequency ratios on aerodynamic performance, wing dynamics and flow physics. It is shown that time-averaged lift increases with frequency ratio, up to a certain limit that depends on mass ratio and beyond which upward wing bending and flexibility induced phase lag between revolving an pitching motions at stroke reversal become strong and contribute to phases of negative lift that counterbalances the initial lift increase. This wing dynamics, which is dominated by spanwise bending, also affects wing-wake interactions and, in turn, leading edge vortex formation.

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“…They found that the significant lift and drag force on a wing during perching is mainly caused by the added mass effect and the formation of strong vortices at the leading and trailing edge of the wing. Jardin & Doué (2019) also performed a numerical study on a perching airfoil and concluded that a minimum kinetic energy could be achieved on the airfoil at the end of the perching manoeuvre at a higher pitch rate or the lift and drag force on the airfoil can be enhanced by increasing the pitch rate. Similarly, Fernando & Rival (2017) examined low-aspect-ratio plates undergoing deceleration and pitch-up motion.…”

Section: Introductionmentioning

confidence: 99%

Rapidly pitching plates in decelerating motion near the ground

Adhikari,

Bhattacharya

2024

J. Fluid Mech.

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Birds employ rapid pitch-up motions close to the ground for different purposes: perching birds use this motion to decelerate and come to a complete stop while hunting birds, such as bald eagles, employ it to catch prey and swiftly fly away. Motivated by these observations, our study investigates how natural flyers accomplish diverse flying objectives by rapidly pitching their wings while decelerating near ground. We conducted experimental and analytical investigations focusing on rapidly pitching plates during deceleration in close proximity to the ground to explore the impact of ground proximity on the unsteady dynamics. Initially, we executed synchronous pitch-up motion, where both pitching and deceleration have the same motion duration, at different ground heights. Experimental results demonstrate that as the pitching wing approaches the ground, the instantaneous lift increases by approximately $38\,\%$ compared with a far-from-ground case, while the initial peak drag force remains relatively unchanged. Our analytical model conforms to this trend, predicting an increase in lift force as the wing approaches the ground, indicating enhanced added mass and circulatory lift force due to the ground effect. Next, we examined asynchronous pitch-up motion cases, where rapid pitching motions were initiated at different stages of deceleration. The results reveal that initiating the wing pitch early in the deceleration leads to the formation of larger counter-rotating vortices at the early stage of the manoeuvre. These vortices generate stronger dipole jets that orient backward in the later stages of the manoeuvre after impinging with the ground surface, which hunting birds utilize to accelerate after catching prey. Conversely, when the wing pitch is delayed, smaller vortices form, but their growth is postponed until late in the manoeuvre. This delayed vortex growth produces lift and drag force at the end phase of the manoeuvre that facilitates a smooth landing or perching. Thus, through strategic tuning of a rapid pitch-up motion with deceleration, natural flyers, such as birds, achieve diverse flying objectives.

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Influence of pitch rate on freely translating perching airfoils

Cited by 8 publications

References 22 publications

Numerical investigation of three-dimensional asymmetric hovering flapping flight

Numerical investigation of three-dimensional asymmetric hovering flapping flight

Experiments and numerical simulations on hovering three-dimensional flexible flapping wings

Rapidly pitching plates in decelerating motion near the ground

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