Numerical and Experimental Study of a Covert-Inspired Passively Deployable Flap for Aerodynamic Lift Enhancement

Othman, Ahmed K.; Nair, Nirmal J.; Sandeep, Anushka; Goza, Andres; Wissa, Aimy

doi:10.2514/6.2022-3980

Cited by 3 publications

(10 citation statements)

References 18 publications

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“…For example, most post-stall lift improvement happens at the trailing edge flap location (i.e. x s ⩾ 65%), which is consistent with the literature [14,26].…”

Section: Liftsupporting

confidence: 88%

Covert-inspired flaps: an experimental study to understand the interactions between upperwing and underwing covert feathers

et al. 2023

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Birds are agile flyers that can maintain flight at high angles of attack (AoA). Such maneuverability is partially enabled by the articulation of wing feathers. Coverts are one of the feather systems that has been observed to deploy simultaneously on both the upper and lower wing sides during flight. This study uses a feather-inspired flap system to investigate the effect of upper and lower side coverts on the aerodynamic forces and moments, as well as examine the interactions between both types of flaps. Results from wind tunnel experiments show that the covert-inspired flaps can modulate lift, drag, and pitching moment. Moreover, simultaneously deflecting covert-inspired flaps on the upper and lower sides of the airfoil exhibit larger force and moment modulation ranges compared to a single-sided flap alone. Data-driven models indicate significant interactions between the upper and lower side flaps, especially during the pre-stall regime for the lift and drag response. The findings from this study are also biologically relevant to the observations of covert feathers deployment during bird flight. Thus, the methods and results summarized here can be used to formulate new hypotheses about the coverts role in bird flight and develop a framework to design covert-inspired flow and flight control devices for engineered vehicles.

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“…For example, most post-stall lift improvement happens at the trailing edge flap location (i.e. x s ⩾ 65%), which is consistent with the literature [14,26].…”

Section: Liftsupporting

confidence: 88%

Covert-inspired flaps: an experimental study to understand the interactions between upperwing and underwing covert feathers

et al. 2023

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“…The average value is indicated by the solid line, while the shaded region indicates the range of timeaveraged lift values measured for all flap configurations. The mean lift values results confirm findings of prior studies that covert-inspired flaps are post-stall lift enhancement devices [1,6,11,20,22,24,28]. On average, the flap improves lift at post-stall angles of attack (α > 16 • ), while at pre-stall angles (α < 16 • ), the flap is either detrimental or has no effect on lift, depending on the flap parameters.…”

Section: Overviewsupporting

confidence: 87%

Feather-inspired flow control device across flight regimes

Othman,

Nair,

Goza

et al. 2023

Bioinspir. Biomim.

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Bio-inspired ﬂow control strategies can provide a new paradigm of eﬃciency and adaptability to overcome the operational limitations of traditional ﬂow control. This is particularly useful to small-scale uncrewed aerial vehicles since their mission requirements are rapidly expanding, but they are still limited in terms of agility and adaptability when compared to their biological counterparts, birds. One of the ﬂow control strategies that birds implement is the deployment of covert feathers. In this study, we investigate the performance characteristics and ﬂow physics of torsionally hinged covert-inspired ﬂaps mounted on the suction side of a NACA2414 airfoil across diﬀerent Reynolds numbers, speciﬁcally 200,000 and 1,000. These two Reynolds numbers are representative of diﬀerent avian ﬂight regimes where covert feathers have been observed to deploy during ﬂight, namely cruising and landing/perching. We performed experiments and simulations where we varied the ﬂap location, the hinge stiﬀness, and the moment of inertia of the ﬂap to investigate the aerodynamic performance and describe the eﬀects of the structural parameters of the ﬂap on the aerodynamic lift improvements. Results of the study show up to 12% lift improvement post-stall for the ﬂapped cases when compared to the ﬂapless baseline. The post-stall lift improvement is sensitive to the ﬂap’s structural properties and location. For instance, the hinge stiﬀness controls the mean deﬂection angle of the ﬂap, which governs the resulting time-averaged lift improvements. The ﬂap moment of inertia, on the other hand, controls the ﬂap dynamics, which in turn controls the ﬂap’s lift-enhancing mechanism and how the ﬂap aﬀects the instantaneous lift. By examining the time-averaged and instantaneous lift measurement, we uncover the mechanisms by which the covert-inspired ﬂap improves lift and highlights similarities and diﬀerences across Reynolds numbers. This article highlights the feasibility of using covert-inspired ﬂaps as ﬂow control across ﬂight missions and speeds.

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“…Moreover, the implementation of covertinspired devices in engineering studies ranges from real feathers and hair-like flaps to rigid plastic and metal flaps with various geometries [21][22][23][24] . Furthermore, flaps with various mobility have also been studied, starting from simple static flaps at a fixed angle, to freely moving flaps, to torsionally-hinged flaps with adjustable stiffness [25][26][27][28][29][30] . Despite the different structural and mobility forms of the covert-inspired flaps, most studies confirmed that upperwing coverts act as a lift enhancement flow control device at post-stall conditions.…”

Section: Avian Flow Controlmentioning

confidence: 99%

“…Duan and Wissa 25 showed that rigid static covert-inspired flaps placed between 40% and 80% of the chord from the leading edge can improve post-stall lift up to 23% at a Re ~(10 5 ). Several studies 26,27,29,31 also examined the effects of freely moving upperwing flaps at Re ~(10 5 −10 6 ). Bechert et al 27,28 , and Meyer et al 31 examined the effects of a freely moving flap on two different airfoils using both wind tunnel testing and numerical simulations and observed lift improvement of more than 10% and stall delay in both studies.…”

Section: Avian Flow Controlmentioning

confidence: 99%

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Aerial and aquatic biological and bioinspired flow control strategies

et al. 2023

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Flow control is the attempt to favorably modify a flow field’s characteristics compared to how the flow would have developed naturally along the surface. Natural flyers and swimmers exploit flow control to maintain maneuverability and efficiency under different flight and environmental conditions. Here, we review flow control strategies in birds, insects, and aquatic animals, as well as the engineered systems inspired by them. We focus mainly on passive and local flow control devices which have utility for application in small uncrewed aerial and aquatic vehicles (sUAVs) with benefits such as simplicity and reduced power consumption. We also identify research gaps related to the physics of the biological flow control and opportunities for device development and implementation on engineered vehicles.

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Numerical and Experimental Study of a Covert-Inspired Passively Deployable Flap for Aerodynamic Lift Enhancement

Cited by 3 publications

References 18 publications

Covert-inspired flaps: an experimental study to understand the interactions between upperwing and underwing covert feathers

Covert-inspired flaps: an experimental study to understand the interactions between upperwing and underwing covert feathers

Feather-inspired flow control device across flight regimes

Aerial and aquatic biological and bioinspired flow control strategies

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