中田 敏是

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA . All rights reserved.The NATO RTO AVT-202 task group was a collaborative effort to study the fundamental unsteady low Reynolds number aerodynamics of lift production in highly separated flows. Experimental and numerical results are presented here, compiled from four different research groups, to describe the evolution of the flow around a rotating wing experiencing unsteady motion in either pitch or surge and the resulting unsteady lift force. There is excellent agreement, both qualitatively and quantitatively, between the research groups. It was found that wing pitch was the dominant contributor to lift production, and that the magnitude of wing acceleration in surge had relatively little effect. Notably, the introduction of rotational acceleration (as compared to strictly translational motion) did not have a significant effect on the force history. It did, however, result in a different flow topology, namely an attached leading-edge vortex.

Inspired by novel mechanisms in insect and bird flights, in particular, the clap-and-fling mechanism associated with the aerodynamic force enhancement owing to the wing-wing interaction, we developed a prototype flapping micro air vehicle (fMAV), which is weighted 2.4 - 3.0 g, equipped with a X-type wing and a wingspan of 12 -15 cm. In this study, we carried out an integrated study of flexible wing aerodynamics and passive dynamic flight stability of the MAV by a combination of flexible wing kinematics and force measurements and computational approaches. We designed a high-speed camera filming system to measure the flexible wing kinematics and deformations and constructed the computational wing kinematic model. Together with the force measurements we investigated the wing stiffness effects on the force generation associated with the flexible wing deformation. We further used a biology-inspired, dynamic flight simulator to evaluate the aerodynamic performance of the flexible wing MAV. This simulator, by integrating the modeling of realistic wing-body morphology and realistic flapping-wing and body kinematics, provided an evaluation of the MAV's unsteady aerodynamics in terms of vortex and wake structures and their relationship with aerodynamic force generation. Our results show that the clap-and-fling mechanism is indeed realized by the prototype four-winged MAV and the flexible wing deformation even further enhance its effects. Furthermore, we employed a computational approach to analyze the passive dynamic flight stability of the MAV's forward flight. Results based on a linear theory indicated that the MAV is very likely of dynamical stability even with no active feedback control system. © 2012 IEEE.

In this study we investigated the effect of wing deformation on numerical simulation of aerodynamics of ornithopters. The ornithopter we used had a pair of wings and a tail wing, and is capable to perform forward flight. The wing consisted of a rigid leading edge bars and a polymer film membrane. We measured the wing deformation with three high-speed video cameras in three different conditions: free flight, tethered flight, and "semi-tethered flight" in which the ornithopter was mounted on a linear actuator and moved forward constantly. Then, measured wing deformations were applied to a CFD (Computational Fluid Dynamics)-based simulation in which the ornithopter was fixed in a steady flow. As a result, the wing deformation measured in the free flight and the semi-tethered cases caused larger vertical force than that with the wing deformation of the tethered case. It was also found that the wing deformation of the free flight case resulted in smaller horizontal force than that of the the other cases at the latter half of downstroke. On the contrary, at the middle of upstroke, the wing deformation of the free flight case caused larger drag than that of the other cases. These results suggest that it is desirable to use a free flight model when time variation of aerodynamic forces is considered.

Research and development of Micro air vehicles (MAVs) with a maximal dimension less than 15 cm have been a very hot topic in the last decade. MAVs are desired to be capable of performing missions such as environmental monitoring, surveillance, and assessment in dangerous environments. Currently most Bio-inspired MAVs have four wings, while many insects and birds can fly by two wings. In this study, especially focusing on the wing structure and in-flight deformation of flapping wings, we evaluated the aerodynamic performance of single flapping wing which has a semi-elliptic planform and is made of a polyethylene film, a carbon rod at leading edge and aluminum rod at wing base. The mean thrust forces by the flapping wings were measured by attaching the wings onto the newly developed measurement system. The aerodynamic performances of the flapping wings in terms of flexible wing kinematics and vortex structures and their relationship with aerodynamic force generation were further investigated by combining the reconstruction of three-dimensional wing kinematics and the computational fluid dynamic (CFD) method. The flexible wing kinematics, and the force generation by flexible flapping wings accordingly, was found to be strongly affected by the flapping frequency, wing beat amplitude and wing structure which suggest that the optimum wing structure for flapping MAV is dependent on the wing kinematics at wing base.

Aiming at establishing an effective computational framework to accurately predict free-flying dynamics and aerodynamics we here present a comprehensive investigation on some issues associated with the modelling of free flight. Free flight modelling/simulation is essential for some types of flights e.g. falling leaves or auto-rotating seeds for plants; unsteady manoeuvres such as take-off, turning, or landing for animals. In addition to acquiring the deeper understanding of the flight biomechanics of those natural organisms, revealing the sophisticated aerodynamic force generation mechanisms employed by them may be useful in designing man-made flying-machines such as rotary or flapping micro air vehicles (MAVs). The simulations have been conducted using the coupling of computational fluid dynamics (CFD) and rigid body dynamics, thus achieving the free flight. The flow field is computed with a three-dimensional unsteady incompressible Navier-Stokes solver using pseudo-compressibility and overset gird technique. The aerodynamic forces acting on the flyer are calculated by integrating the forces on the surfaces. Similarly, the aerodynamic torque around the flyer's centre of mass is obtained. The forces and moments are then introduced into a six degrees-of-freedom rigid body dynamics solver which utilises unit quaternions for attitude description in order to avoid singular attitude. Results are presented of a single body model and some insect-like multi-body models with flapping wings, which point to the importance of free-flight modelling in systematic analyses of flying aerodynamics and manoeuvrability. Furthermore, a comprehensive investigation indicates that the framework is capable to predict the aerodynamic performance of free-flying or even free-swimming animals in an intermediate range of Reynolds numbers (< 105). Copyright © 2011 by ASME.

Research and development of Micro Air Vehicles (MAVs) aiming at the investigation and the information gathering in the hazard area is now an active field. Flapping flight of insects and birds that are capable to perform precise hovering flight and to make rapid turn and maneuver steadily in sudden gust has been attracting specific attentions in the last decades. In this study, in order to validate a biology-inspired dynamic flight simulator that is designed to model realistic flapping-wing flights and to evaluate novel mechanisms in bio-flights, we conducted measurements and analysis of low Reynolds number unsetady flows around a flapping-wing robot "MOTH-1" by utilizing PIV techniques in a wind tunnel (JAXA). Our PIV results have thereby confirmed the strong leading-edge vortices and the vortex rings as predicted in our previous simulation study.

This paper describes the evaluation of aerodynamic performance of insect-inspired flapping wings for MAVs design. The insect-inspired wings are made of stiff leading edges and flexible membranes so as to employ the passive wing deformations due to inertial and aerodynamic forces in terms of feathering and camber. In this study, the effect of wing stiffness on the aerodynamic performance of flapping micro air vehicle is investigated. The wing stiffness is realized by attaching ribs on the wing surface and tape on the trailing edge of the wings. The wings are attached to a prototype MAV, which is designed to employ the "clap and fling" mechanism with four wings cross between. The thrust force on the flapping wings is further measured to evaluate the aerodynamic performance of the MAV. The experimental results indicate that the wing stiffness to achieve the maximum thrust depends on the flapping frequency. When the flapping frequency is high, the thrust force increase with the wing stiffness. In experimental range of this study, the wings that have higher stiffness showed high performance at more than 18Hz. This result shows that the stiffness of flapping wing is an important factor for the design of MAV.

This paper describes fabrication and characterization of high performance, that is, large deformation and high output force type active laminate using elastomer. The conventional and single active laminate was made by hot-pressing of an aluminum plate as a high CTE material, a unidirectional CFRP prepreg as a low CTE/electric resistance heating material and an epoxy adhesive film as an insulating material. The high performance type active laminate was made by sandwiching a sheet of elastomer between two conventional and single active laminates. The effect of hardness and partial removal of the elastomer on their shape, deformation and output force characteristics were investigated. It was found that the high performance type active laminate doubled the output force of the single active laminate without reducing its actuation capability by laminating a sheet of elastomer of which hardness is very soft or which is partially removed between two conventional and single active laminates.