Piezoelectric Wing Research Articles

A lumped-parameter coupled electro-piezo-aeroelastic model for flapping wings

Induced-strain actuated flapping wings and fins, achieved by surface-mounted piezoelectric actuators, do not need conventional motors and mechanisms, potentially reducing system weight, energy consumption, and mechanical complexity compared to conventional systems. A piezocomposite flapping wing or an underwater oscillating fin with induced-strain actuation can interact with the ambient fluid to yield flow vectoring, control, and lift or thrust generation. In this article, an electro-piezo-aeroelastic coupled lumped-parameter model is developed to predict the dynamic behavior of strain actuated flapping wings, and obtain insight into coupling mechanisms such as bend-twist coupling, fluid-structure interaction, and electro-piezo coupling. The piezoelectric wing is modeled as a laminated orthotropic plate. Using the Rayleigh-Ritz method, the distributed wing motion can be represented by lumped wing heave, chordwise curvature, and pitch displacements by assuming prescribed deformation shapes. The assumed shapes are compatible with the fluid effects interpreted as translational and torsional added mass and damping to the structure. The aeroelastic model is then coupled to the circuit model via electro-piezo coupling. The mechanical model is validated using the finite element method. It is found that four wing tip parameters, including first and second order heave motion, pitch, and chordwise curvature are sufficient to represent the wing motion. The lumped parameter wing model is then used to investigate the system optimal parameters for maximizing desired aero- and/or hydro-dynamic responses. System properties such as structural parameters, excitation frequency ratio, etc., are under investigation. The lumped parameter model is computationally efficient, and suitable for trade studies and multi-disciplinary design optimization. Also, the lumped parameter model serves as a foundation for flapping flight analysis, e.g., analyzing lift force, leading-edge vortex stabilization, and tip vortex shedding.

Piezoelectric Energy Harvesting for Flapping Wing Micro Air Vehicle and Flapping Wing Sensing Based on Flexible Polyvinylidene Fluoride

The flapping wing micro air vehicle (FWMAV) has been attracting lots of interest since the 1990s and is one of the research hotspots in microminiaturization design. However, along with the miniaturization of FWMAV development, flight endurance becomes the bottleneck that significantly impedes the rapid development for these aircrafts because of the critical limit in energy supply due to the limited overall size and weight. In this paper, energy recovery technology was developed for FWMAV with the new type polyvinylidene fluoride (PVDF) piezoelectric wing which could generate the electric potential energy caused by the wing deformation due to the characteristics of the PVDF material. A single crank double rocker mechanism flapping platform was designed to test the deformation energy collection effect and aerodynamic lift. The PVDF wing surface was divided into 16 grid areas to be measured respectively. The lift, output voltage and output power variations for the different flapping frequency was successfully obtained in tests. By analyzing test data, if could be found that the output power could reflect the flutter condition without equipping other sensors and adding extra weight to the aircraft. Moreover, when the flapping frequency was accelerated to 12 Hz, the output power and root mean square (RMS) voltage could increase to 21 μW and 6 V respectively, which is enough to power micro electronic devices such as LED lights.

Observer-based sliding mode control for piezoelectric wing bending-torsion coupling flutter involving delayed output

An observer-based sliding mode control scheme is proposed for suppressing bending-torsion coupling flutter motions of a wing aeroelastic system with delayed output by using the piezoelectric patch actuators. The wing structure is modeled as a thin-walled beam, and the aerodynamics on the wing are computed by the strip theory. For the implementation of the control algorithm, the piezoelectric patch is bonded on the top surface of the beam to act as the actuator. Ignoring the effect of piezoelectric actuators on structural dynamics, only considering the bending moments induced by piezoelectric effects, the corresponding dynamic motion equation is established by using the Lagrange method with the assumed mode method. The flutter speed and frequency of the closed-loop system with time delay are obtained by solving a polynomial eigenvalue problem. An observer-based controller that does not dependent on time delay is developed for suppressing the flutter, and the corresponding gain matrices are obtained by solving linear matrix inequalities. The sufficient condition for the asymptotic stability of the closed-loop system is derived in terms of linear matrix inequalities. The simulation results demonstrate that the proposed control strategy based on the piezoelectric actuator is effective in wing bending-torsion coupling flutter system with a delayed output.

Flutter suppression for highly flexible wings using passive and active piezoelectric effects

This paper addresses both active and passive flutter suppressions for highly flexible wings using piezoelectric transduction. An active aeroelastic formulation is used in the studies, featuring a geometrically nonlinear beam formulation coupled with 2-D unsteady aerodynamic equations. The piezoelectric effect is involved in the dynamic nonlinear beam equations, allowing for the aeroelastic studies on multifunctional wings for both piezoelectric energy harvesting and active actuation. In this study, the active piezoelectric actuation is applied as the primary approach for the flutter suppression, with the energy harvesting, as a secondary passive approach, concurrently working to provide an additional damping effect on the wing vibration. The multifunctional system may also convert wing vibration energy to electric energy as an additional function. Moreover, a Linear Quadratic Gaussian controller is developed for the active control of wing limit-cycle oscillations due to the flutter instability. In the numerical studies, both the active and passive flutter suppression approaches are enabled for a highly flexible wing. The impact of the piezoelectric actuator and energy harvester placement on the wing flutter characteristic is explored. This paper presents a comprehensive approach to effectively suppress the aeroelastic instability of highly flexible piezoelectric wings, while allowing to harvest the residual vibration energy. The active multifunctional wing technology that is explored in the paper has the potential to improve the aircraft performance from both aeroelastic stability and energy consumption aspects.

Parametric analysis of a fluttering piezoelectric wing

Purpose The purpose of the research activity is to identify the best configuration of piezoelectric (PZT) elements for a typical condition of wing aeroelastic instability. The attention is mainly focused on the flutter behavior of the structure. However, the model can be extended with low-impact adjustments to other loading conditions.

Energy harvesting from the discrete gust response of a piezoaeroelastic wing: Modeling and performance evaluation

The objective of this paper is to investigate energy harvesting from the unfavorable gust response of a piezoelectric wing. An aeroelectroelastic model is built for the evaluation and improvement of the harvesting performance. The structural model is built based on the Euler–Bernoulli beam theory. The unsteady aerodynamics, combined with 1-cosine gust load, are obtained from Jones׳ approximation of the Wagner function. The state-space equation of the aeroelectroelastic model is derived and solved numerically. The energy conversion efficiency and output density are defined to evaluate the harvesting performance. The effects of the sizes and location of the piezoelectric transducers, the load resistance in the external circuit, and the locations of the elastic axis and gravity center axis of the wing are studied, respectively. The results show that, under a given width of the transducers in chordwise direction, there are one thickness of the transducers corresponding to highest conversion efficiency and one smaller optimal value for the output density. The conversion efficiency has an approximate linear relationship with the width. As the transducers are placed at the wing root, a maximum conversion efficiency is reached under a certain length in the spanwise direction, whereas a smaller length helps reaching a larger output density. One optimal resistance is found to maximize the conversion efficiency. The rearward shift of either the elastic axis or gravity center axis improves the energy output while reducing the conversion efficiency.

An experimental study of the unsteady vortex structures in the wake of a root-fixed flapping wing

An experimental study was conducted to characterize the evolution of the unsteady vortex structures in the wake of a root-fixed flapping wing with the wing size, stroke amplitude, and flapping frequency within the range of insect characteristics for the development of novel insect-sized nano-air-vehicles (NAVs). The experiments were conducted in a low-speed wing tunnel with a miniaturized piezoelectric wing (i.e., chord length, C = 12.7 mm) flapping at a frequency of 60 Hz (i.e., f = 60 Hz). The non-dimensional parameters of the flapping wing are chord Reynolds number of Re = 1,200, reduced frequency of k = 3.5, and non-dimensional flapping amplitude at wingtip h = A/C = 1.35. The corresponding Strouhal number (Str) is 0.33, which is well within the optimal range of 0.2 < Str < 0.4 used by flying insects and birds and swimming fishes for locomotion. A digital particle image velocimetry (PIV) system was used to achieve phased-locked and time-averaged flow field measurements to quantify the transient behavior of the wake vortices in relation to the positions of the flapping wing during the upstroke and down stroke flapping cycles. The characteristics of the wake vortex structures in the chordwise cross planes at different wingspan locations were compared quantitatively to elucidate underlying physics for a better understanding of the unsteady aerodynamics of flapping flight and to explore/optimize design paradigms for the development of novel insect-sized, flapping-wing-based NAVs.