Three-dimensional numerical simulations are performed to examine the effects of dynamic wing morphing of a hummingbird-inspired flexible Flapping wing on its aerodynamic performance in hovering flight. The range analysis and variation analysis in the orthogonal experiment are conducted to assess the significance level of various deformations observed in the hummingbird wings on wing aerodynamic performance. It has been found that both camber and twist significantly can affect lift, and twist has an even higher significant impact on lift efficiency. Spanwise bending, whether out-of-stroke-plane or in-stroke-plane, has a negligible impact on lift and efficiency, and the in-stroke-plane bending can cause lift to decrease to an extent. Optimal parameters for determining the wing deformations are selected and tested to validate the conclusions drawn in the analysis for the results in orthogonal experiment. Through a comparison study between the optimized wings and the rigid wing, it is found that although the wing flexibility can cause the net force to decrease, the flexible wing used less energy to bring the net force closer to the vertical direction, thereby improving the lift efficiency. This study provides an aerodynamics understanding of the efficiency improvement of the hummingbird-inspired flexible Flapping wing.

Effect of constrained flow is investigated experimentally for a Flapping foil power-generator. The flow structures around and in the near wake of a flat plate placed between two side walls are captured via PIV technique with simultaneous direct force measurements in uniform flow at Re=10 000. The rectangular flat plate oscillates with periodic non-sinusoidal pitching and plunging motions about its 0.44 chord position with stroke reversal times (D TR) of 0.1 (rapid reversal) to 0.5 (sinusoidal reversal), phase angles of f=90o and 110o, plunge amplitude of 1.05 chords and pitch amplitude of 73° at a constant reduced frequency of k=0.8. The non-dimensional distances between the side walls and the oscillating flat plate aredw=0.1, 0.5 and 1.0. Airfoil rotation speed dictates the strength, evolution and timing of shedding of leading and trailing edge vortices; as the stroke reversal time is decreased, earlier shedding of stronger vortices are observed. Increasing the phase angle between the pitching and plunging motions decreases the power generation efficiency for all cases. The highest power extraction coefficient is acquired for the non-sinusoidal case ofD TR=0.4 in free flow. Optimum choice of side-wall distance improves power generation of Flapping foils compared to free flow performance, up to 6.52% increase in efficiency is observed for the non-sinusoidal caseD TR=0.4 with dw=0.5, with remarkable enhancements for the sinusoidal case; 27.85% increase is observed with dw=0.5 and 43.50% increase with dw=1.0 where both cases outperform the highest power generation efficiency of the finite flat plate with non-sinusoidal Flapping motion.

To evaluate the propulsion system capabilities of a Flapping Micro Air Vehicle (FMAV), a new aeroelastic model of a typical flexible FMAV is developed, utilizing the EulerBernoulli torsion beam and quasi steady aerodynamic model. The new model accounts for all existing complex interactions between the mass, inertia, elastic properties, aerodynamic loading, Flapping amplitude and frequency of the FMAV, as well as the effects of several geometric and design parameters. To validate the proposed theoretical model, a typical FMAV, as well as an instrumented test stand for the online measurement of forces, Flapping angle and power consumption, has been constructed. The experimental results are initially utilized to validate the flight dynamic model, and several appropriate conclusions are drawn. The model is subsequently used to demonstrate the Flapping propulsion characteristics of the FMAV via simulation. Using dimensionless parameters, a set of new aeroelastic coordinates are introduced. In this reduced design space, new generalized performance curves have been deduced. The results indicate that by proper adjustment of the wing stiffness parameter, as a function of reduced frequency, the FMAV will attain its optimum propulsive efficiency. This fact raises additional ideas of utilizing intelligent variable stiffness materials and/or an active morphing technology for the sustained flight of FMAVs.

Flapping-wing robotic insects are small, highly maneuverable flying robots inspired by biological insects and useful for a wide range of tasks, including exploration, environmental monitoring, search and rescue, and surveillance. Recently, robotic insects driven by piezoelectric actuators have achieved the important goal of taking off with external power; however, fully autonomous operation requires an ultralight power supply capable of generating high-voltage drive signals from low-voltage energy sources. This paper describes high-voltage switching circuit topologies and control methods suitable for driving piezoelectric actuators in Flapping-wing robotic insects and discusses the physical implementation of these topologies, including the fabrication of custom magnetic components by laser micromachining and other weight minimization echniques. The performance of laser micromachined magnetics and custom-wound commercial magnetics is compared through the experimental realization of a tapped inductor boost converter capable of stepping up a 3.7V Li-poly cell input to 200V. The potential of laser micromachined magnetics is further shown by implementing a similar converter weighing 20mg (not including control functionality) and capable of up to 70mW output at 200V and up to 100mW at 100V.