The influence of wing-wake interactions on the production of aerodynamic forces in flapping flight
TLDR
The wake capture force represents a truly unsteady phenomenon dependent on temporal changes in the distribution and magnitude of vorticity during stroke reversal and is well explained by a quasi-steady model.Abstract:
We used two-dimensional digital particle image velocimetry (DPIV) to visualize flow patterns around the flapping wing of a dynamically scaled robot for a series of reciprocating strokes starting from rest. The base of the wing was equipped with strain gauges so that the pattern of fluid motion could be directly compared with the time history of force production. The results show that the development and shedding of vortices throughout each stroke are highly stereotyped and influence force generation in subsequent strokes. When a wing starts from rest, it generates a transient force as the leading edge vortex (LEV) grows. This early peak, previously attributed to added-mass acceleration, is not amenable to quasi-steady models but corresponds well to calculations based on the time derivative of the first moment of vorticity within a sectional slice of fluid. Forces decay to a stable level as the LEV reaches a constant size and remains attached throughout most of the stroke. The LEV grows as the wing supinates prior to stroke reversal, accompanied by an increase in total force. At stroke reversal, both the LEV and a rotational starting vortex (RSV) are shed into the wake, forming a counter-rotating pair that directs a jet of fluid towards the underside of the wing at the start of the next stroke. We isolated the aerodynamic influence of the wake by subtracting forces and flow fields generated in the first stroke, when the wake is just developing, from those produced during the fourth stroke, when the pattern of both the forces and wake dynamics has reached a limit cycle. This technique identified two effects of the wake on force production by the wing: an early augmentation followed by a small attenuation. The later decrease in force is consistent with the influence of a decreased aerodynamic angle of attack on translational forces caused by downwash within the wake and is well explained by a quasi-steady model. The early effect of the wake is not well approximated by a quasi-steady model, even when the magnitude and orientation of the instantaneous velocity field are taken into account. Thus, the wake capture force represents a truly unsteady phenomenon dependent on temporal changes in the distribution and magnitude of vorticity during stroke reversal.read more
Citations
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Journal ArticleDOI
Recent progress in flapping wing aerodynamics and aeroelasticity
Wei Shyy,Hikaru Aono,Satish Kumar Chimakurthi,Pat Trizila,Chang-Kwon Kang,Carlos E. S. Cesnik,Hao Liu +6 more
TL;DR: In this article, a review of the recent progress in flapping wing aerodynamics and aeroelasticity is presented, where it is realized that a variation of the Reynolds number (wing sizing, flapping frequency, etc.) leads to a change in the leading edge vortex (LEV) and spanwise flow structures, which impacts the aerodynamic force generation.
Journal ArticleDOI
Dissecting insect flight
TL;DR: The results obtained by “taking the insects apart” helped to resolve previous puzzles about the force estimates in hovering insects, to ellucidate basic mechanisms essential to flapping flight, and to gain insights about the efficieny of flight.
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A hybrid Cartesian/immersed boundary method for simulating flows with 3D, geometrically complex, moving bodies
TL;DR: In this paper, a numerical method is developed for solving the Navier-Stokes equations in Cartesian domains containing immersed boundaries of arbitrary geometrical complexity moving with prescribed kinematics.
Journal ArticleDOI
Unsteady forces and flows in low Reynolds number hovering flight:two-dimensional computations vs robotic wing experiments
TL;DR: Comparing computational, experimental and quasi-steady forces in a generic hovering wing undergoing sinusoidal motion along a horizontal stroke plane investigates unsteady effects and compares two-dimensional computations and three-dimensional experiments in several qualitatively different kinematic patterns.
References
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TL;DR: In this paper, the authors present a practical guide for the planning, performance and understanding of experiments employing the PIV technique, which is primarily intended for engineers, scientists and students, who already have some basic knowledge of fluid mechanics and nonintrusive optical measurement techniques.
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TL;DR: In this paper, the authors show that the enhanced aerodynamic performance of insects results from an interaction of three distinct yet interactive mechanisms: delayed stall, rotational circulation, and wake capture.
Wing rotation and the aerodynamic basis of insect flight
TL;DR: A comprehensive theory incorporating both translational and rotational mechanisms may explain the diverse patterns of wing motion displayed by different species of insects.
Journal ArticleDOI
Leading-edge vortices in insect flight
Charles P. Ellington,Coen van den Berg,Coen van den Berg,Alexander P. Willmott,Adrian L. R. Thomas,Adrian L. R. Thomas +5 more
TL;DR: In this article, the authors visualized the airflow around the wings of the hawkmoth Manduca sexta and a 'hovering' large mechanical model, and found an intense leading-edge vortex was found on the downstroke, of sufficient strength to explain the high-lift forces.
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