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An experimental investigation was performed to observe the effects of Reynolds number and stroke amplitude (number of degrees swept over a half stroke) on the leading-edge vortex (LEV) of an insect-like flapping wing in hover. This was performed with application to flapping-wing micro air vehicles (FMAVs) in mind. Experiments were accomplished with...
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Context 1
... motion of an insect's wing can be broken down into four parts: downstroke, supination, upstroke and prona- tion ( Figure 1). Starting with the downstroke, this is the translation of the wing at a relatively constant angle of attack from its most aft and dorsal position to its most for- ward and ventral position. At the end of the downstroke supination occurs, which is when the wing rapidly comes to a stop and reverses its direction and angle of attack so that the wing's underside becomes the topside for the sub- sequent half stroke. The wing then translates with a rel- atively constant angle of attack back to its most aft and dorsal position, which is referred to as the upstroke. Fi- nally, at the end of the upstroke, the wing pronates, which is where it again rapidly comes to a stop and reverses its direction and angle-of-attack. The flapping frequency ( f ) of insect wings ranges from 5 − 200Hz, and the path that the wingtip traces takes the form of irregular, self inter- secting shapes typically resembling a ...
Context 2
... insect's wing motion is composed of three separate motions: sweeping (fore and aft), plunging (up and down) and pitching (angle-of-attack variation). The position of the wing at any given moment is defined relative to the stroke plane (Figure 1). After Willmott & Ellington [6], the angle from the Z (lateral) axis to the projection of the wing's longitudinal axis (pitch axis) onto the stroke plane is the stroke angle φ, the angle between the minimum and maximum stroke angles is the stroke amplitude Φ, and the plunge angle θ is the position of the wing's longitudinal axis out of the stroke plane. In addition, the angle be- tween the minimum and maximum plunge angles is the plunge amplitude Θ and the wing's geometric angle of at- tack relative to the stroke plane is the pitch angle α, with α mid referring to the angle of attack at mid-stroke. An- other kinematic parameter that should be mentioned is ro- tation phase τ rp , which describes the timing of pitch re- versal with stroke reversal. Here it is defined as a per- centage of the flapping period T , where a positive sign implies that pitching begins early whereas a negative sign indicates that pitching is delayed. For example, at a 20Hz flapping frequency, a rotation phase of 5% means that the wing begins pitching early so that it reaches a 90 • angle of attack 2.5ms before reaching the end of the ...
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Flapping-wing micro air vehicles are not confined to undergoing the normal-hovering motion implemented by flying insects. In this study, the water-treading motion, which originates from aquatic propulsion, is studied in terms of its feasibility as an alternative wing motion for micro air vehicles. Experimental measurements and numerical simulations...
Citations
... Their results showed that, for the wing planform considered, lift is highest at a stroke amplitude of 180 • and angle of attack of 50 • . Later, Phillips and Knowles [28] also used a robotic flapping apparatus to study the effect of Reynolds number and stroke amplitude on the LEV structures of a model Drosophila wing using PIV. However, they found that for all Reynolds numbers investigated (Re = 3850-18,210), the LEV breaks down at a constant stroke amplitude of approximately 132 • , whereas for smaller stroke amplitudes, the breakdown of the LEV is suppressed. ...
In this paper, the effects of stroke amplitude and wing planform on the aerodynamics of hovering flapping wings are considered by numerically solving the incompressible Navier–Stokes equations. The wing planform geometry is represented using a beta-function distribution for an aspect ratio range of 3–6 and a dimensionless radial centroid location range of 0.4–0.6. Typical normal hovering kinematics has been employed while allowing both translational and rotational durations to be equally represented. The combined effects of stroke amplitude with wing aspect ratio and radial centroid location on the aerodynamic force coefficients and flow structures are studied at a Reynolds number of 100. It is shown that increasing the stroke amplitude increases the translational lift for either small aspect ratio or large radial centroid location wings. However, for high aspect ratio or low radial centroid location wings, increasing the stroke amplitude leads to higher lift coefficients during the translational phase only up to a stroke amplitude of 160°. Further increase in stroke amplitude results in reduced translational lift due to the increased wingtip stall effect. For all the cases considered, the lift and drag coefficients of the rotational phase decrease with the increase of stroke amplitude leading to decreased cycle-averaged force coefficients. Furthermore, it is found that the significant reduction in the rotational drag as the stroke amplitude increases leads to a consistently increasing aerodynamic efficiency against stroke amplitude for all aspect ratio and radial centroid location cases.
... Wing kinematics and aerodynamics of (a) hummingbird (reprinted from [71] with permission from Elsevier) and (b) insect flight (adapted from [72]). ...
... The flight characteristics are modeled in terms of aerodynamics and wing kinematic models. In the existing literature, two main strategies have been extensively studied for the development of the aerodynamic models (i.e., blade element Wing kinematics and aerodynamics of (a) hummingbird (reprinted from [71] with permission from Elsevier) and (b) insect flight (adapted from [72]). ...
This paper presents a thorough review on the system identification techniques applied to flapping wing micro air vehicles (FWMAVs). The main advantage of this work is to provide a solid background and domain knowledge of system identification for further investigations in the field of FWMAVs. In the system identification context, the flapping wing systems are first categorized into tailed and tailless MAVs. The most recent developments related to such systems are reported. The system identification techniques used for FWMAVs can be classified into time-response based identification, frequency-response based identification, and the computational fluid-dynamics based computation. In the system identification scenario, least mean square estimation is used for a beetle mimicking system recognition. In the end, this review work is concluded and some recommendations for the researchers working in this area are presented.
