Passive Pitching Motion Research Articles

Maneuvering Characteristics of Bilateral Amplitude-Asymmetric Flapping Motion Based on a Bat-Inspired Flexible Wing.

Flapping-wing micro air vehicles (FWMAVs) have gained much attention from researchers due to their exceptional performance at low Reynolds numbers. However, the limited understanding of active aerodynamic modulation in flying creatures has hindered their maneuverability from reaching that of their biological counterparts. In this article, experimental investigations were conducted to examine the effect of the bilateral amplitude asymmetry of flexible flapping wings. A reduced bionic model featuring bat-like wings is built, and a dimensionless number ΔΦ* is introduced to scale the degree of bilateral amplitude asymmetry in flapping motion. The experimental results suggest that the bilateral amplitude-asymmetric flapping motion primarily induces maneuvering control forces of coupling roll moment and yaw moment. Also, roll moment and yaw moment have a good linear relationship. To achieve more efficient maneuvers based on this asymmetric motion, it is advisable to maintain ΔΦ* within the range of 0 to 0.4. The magnitude of passive pitching deformation during the downstroke is significantly greater than that during the upstroke. The phase of the peak of the passive pitching angle advances with the increase in flapping amplitude, while the valleys lag. And the proportion of pronation and supination in passive pitching motion cannot be adjusted by changing the flapping amplitude. These findings have important practical relevance for regulating turning maneuvers based on amplitude asymmetry and help to understand the active aerodynamic modulation mechanism through asymmetric wing kinematics.

Optimization of semi-active hydrofoil propulsion performance based on CFD Taguchi method and neural network

In order to improve the propulsive performance of the existing pure heaving motion hydrofoil, the effect of varying stiffness ratio K*, damping ratio C* and inertia ratio J* on the propulsive efficiency of the semi-active NACA 0012 hydrofoil is systematically investigated by using the combination of CFD, Taguchi method and neural network. The results show that the passive pitching motion can significantly affect the propulsive performance of the hydrofoil. Compared to the pure heaving hydrofoil, the propulsive efficiency of the optimized semi-active hydrofoil can be improved by up to 20.97%. Further analysis reveals that the passive pitching motion can weaken the strength of the vortex around the hydrofoil, thus reducing the thrust and lift force on the hydrofoil, which results less power consumed by the active heaving motion of the hydrofoil. Although the thrust coefficient is reduced, the energy consumed by the passive pitching hydrofoil is reduced more, which leads a higher propulsive efficiency of the semi-active hydrofoil.

Fluid-structure interaction for aerodynamic performance evaluation of flapping wing with passive pitching motion

The aim of this study is to investigate the impact of locust-like wing flexibility which is modelled with Mylar and carbon fibre pultruded rods on aerodynamic performance. An in-house 3D Navier Stokes solver coupled with a structure solver has been used to evaluate passive pitching motion and aerodynamic performance. The study has focused on two effects which are variations in the diameter of root and spar distribution. All wings have been analysed for a prescribed flapping motion in a horizontal plane, with a peak-to-peak stroke amplitude of 120°, flapping frequency of 25 Hz, and Reynolds number of 13,500. The flow has been assumed to be laminar, viscous, and incompressible. The diameter of the wing root segment attached to the leading edge has been varied to control the extent of the passive pitching motion. The effect of spar distribution on the aerodynamic performance of the flexible flapping wing has also been investigated. The results revealed that careful selection of wing root parameters and spars distribution can achieve a passive pitch angle with an amplitude of 45° and the highest power economy of 1.26. Moreover, a comparison of the flexible wing with its rigid counterpart suggested that flexible wings modelled with a simple passive pitching mechanism can be an efficient solution for bio-inspired flapping-wing micro aerial vehicles.

Aerodynamic Performance of the Three-Dimensional Lumped Flexibility Wing Under Wind Fluctuating Condition

Understanding the effect of fluctuating wind on the aerodynamic performance of the wing is important for designing practical using flapping-wing micro air vehicles (FMAV). This paper aims at providing a systematic synthesis on the fluctuating wind influence on the performance of the three dimensional lumped flexibility wing based on the numerical analysis approach. The fluctuating wind is simplified as a sine type function, and the flexibility of the wing is modeled as the passive pitching motion by connecting a rigid wing to a torsional spring at the root of the wing. The interaction between the fluctuating wind and the lumped flexibility wing is performed on a high-resolution computational grid. The evaluation is based on validation with published experiment data. The results indicate that the fluctuating wind cannot enhance the flexible wings’ propulsive and lifting performance simultaneously, however, it influences the aerodynamic characteristics of the wing greatly. Comparing to the rigid wing, the suppress leading edge vortex and trailing edge vortex are observed of the flexible wing under appropriate fluctuating wind, which leads the flexible wing to not only have better propulsive and lifting performance, but also flight stability performance.

Kinematics, Deformation, and Aerodynamics of a Flexible Flapping Rotary Wing in Hovering Flight

The Flapping Rotary Wing (FRW) is a micro air vehicle wing layout coupling flapping, pitching, and rotating motions. It can gain benefits in high lift from a fast passive rotating motion, which is tightly related to the passive pitching motion directly caused by wing flexible deformation. Therefore, flexible deformation is crucial for the wing kinematics and aerodynamic performance of an FRW. In this paper, we explored the effect of flexibility on wing kinematics and aerodynamics on the basis of a mechanical FRW model. A photogrammetric method was adopted to capture motion images according to which wing orientations and deformations were reconstructed. Corresponding aerodynamic force was computed using computational fluid dynamic method, and wing kinematics and deformations were used as simulation inputs. The experimental measurements presented the real orientation and deformation pattern of a real FRW. The wing passive deformation of a high-intensity FRW was found to be mainly caused by inertial force, and a linear positive spanwise twist was observed in the FRW. The effects of wing deformation on aerodynamic force production and the underlying mechanism were addressed. Results showed that lift augment, rotating moment enhancement, and power efficiency improvement can be achieved when a wing becomes flexible. Wing spanwise twist mainly accounts for these changes in aerodynamics, and increment in spanwise twist could further contributes to aerodynamic improvement.

Effects of tunable stiffness on the hydrodynamics and flow features of a passive pitching panel

Three-dimensional numerical simulations are carried out to study the hydrodynamic performance and flow features of a bio-inspired underwater propulsor. The propulsor is constituted by a passive pitching panel. The leading edge of the panel is prescribed under a periodic heaving motion while the panel pitches passively due to the employing of a stiffness-lumped torsional spring at the leading edge. Effects of the torsional spring stiffness have been put emphases on. A real-time tunable stiffness strategy is presented and employed in the study. We first study the passive pitching effects on the hydrodynamics and flow features of the panel using a series of constant stiffness and then we study the tunable stiffness effects using cosinusoidal curve based waveforms, in which the effects of phase difference (φ) between the stiffness profile and the oscillation motion and as well as the effects of stiffness fluctuation amplitude (Gk) are investigated, respectively. The stiffness profile beneficial for propulsion efficiency is further applied to cases with different oscillation amplitudes. A high-fidelity immersed boundary method based direct numerical simulation (DNS) solver is employed to acquire the fluid dynamics and to simulate the flow. The panel passive pitching motion is solved by coupling the DNS flow solver and the Euler rigid body dynamic equation. Results show that for the constant stiffness cases, the panel generates sinusoidal-like pitching motion, and in certain stiffness range, flexibility could benefit efficiency while holding some extent of stiffness could enhance the thrust. For the tunable stiffness cases, it is found that both the mean thrust and propulsive efficiency improved when the stiffness change is in-phase with the heaving motion (φ=0°). The largest mean thrust is found at φ=120°. The wake profile shows that in the constant stiffness cases and φ=120° case, the panel in each cycle generates a pair of elongated and twisted vortex tubes, the vortex tubes in each pair interconnected with each other and induces unprofitable interactions. While in the φ=0° case the panel generates a pair of round and closed vortex loops in each cycle and the vortex loops separated directly after they have been detached from the panel and thus avoided the unprofitable vortex interactions. The stiffness fluctuation amplitude (Gk) effects study (all employing the in-phase stiffness profile) shows that all the three tested cases (Gk=0.25G0,0.5G0,0.75G0) acquired thrust and efficiency enhancement while the Gk=0.5G0 case acquired the largest efficiency benefit and the Gk=0.75G0 case had the largest thrust. Wake profiles show entire vortex loops may not be formed when Gk is small while larger Gk may affect the arrangement of the vortex loops thus may generate unprofitable vortex interactions. The results of cases with motions with variable oscillating amplitudes (A∗) show employing the real-time altering stiffness profile (φ=0°,Gk=0.5G0) improves the propulsion performance in a certain range of A∗ (0.4≤A∗≤0.8). Results from this paper demonstrated the potential of using real-time tunable stiffness in the design of passive pitching propulsors of underwater vehicles that pursue higher performance.

Computational Study of Fluid-Structure Interaction on Flapping Wing under Passive Pitching Motion

AbstractDuring the past few decades, various fluid–structure interaction (FSI) analysis approaches have been developed and applied to understand the physical processes related to a flexible flappin...

Optimal pitching axis location of flapping wings for efficient hovering flight

Flapping wings can pitch passively about their pitching axes due to their flexibility, inertia, and aerodynamic loads. A shift in the pitching axis location can dynamically alter the aerodynamic loads, which in turn changes the passive pitching motion and the flight efficiency. Therefore, it is of great interest to investigate the optimal pitching axis for flapping wings to maximize the power efficiency during hovering flight. In this study, flapping wings are modeled as rigid plates with non-uniform mass distribution. The wing flexibility is represented by a linearly torsional spring at the wing root. A predictive quasi-steady aerodynamic model is used to evaluate the lift generated by such wings. Two extreme power consumption scenarios are modeled for hovering flight, i.e. the power consumed by a drive system with and without the capacity of kinetic energy recovery. For wings with different shapes, the optimal pitching axis location is found such that the cycle-averaged power consumption during hovering flight is minimized. Optimization results show that the optimal pitching axis is located between the leading edge and the mid-chord line, which shows close resemblance to insect wings. An optimal pitching axis can save up to 33% of power during hovering flight when compared to traditional wings used by most of flapping wing micro air vehicles (FWMAVs). Traditional wings typically use the straight leading edge as the pitching axis. With the optimized pitching axis, flapping wings show higher pitching amplitudes and start the pitching reversals in advance of the sweeping reversals. These phenomena lead to higher lift-to-drag ratios and, thus, explain the lower power consumption. In addition, the optimized pitching axis provides the drive system higher potential to recycle energy during the deceleration phases as compared to their counterparts. This observation underlines the particular importance of the wing pitching axis location for energy-efficient FWMAVs when using kinetic energy recovery drive systems.

A predictive quasi-steady model of aerodynamic loads on flapping wings

Quasi-steady aerodynamic models play an important role in evaluating aerodynamic performance and conducting design and optimization of flapping wings. The kinematics of flapping wings is generally a resultant motion of wing translation (yaw) and rotation (pitch and roll). Most quasi-steady models are aimed at predicting the lift and thrust generation of flapping wings with prescribed kinematics. Nevertheless, it is insufficient to limit flapping wings to prescribed kinematics only since passive pitching motion is widely observed in natural flapping flights and preferred for the wing design of flapping wing micro air vehicles (FWMAVs). In addition to the aerodynamic forces, an accurate estimation of the aerodynamic torque about the pitching axis is required to study the passive pitching motion of flapping flights. The unsteadiness arising from the wing’s rotation complicates the estimation of the centre of pressure (CP) and the aerodynamic torque within the context of quasi-steady analysis. Although there are a few attempts in literature to model the torque analytically, the involved problems are still not completely solved. In this work, we present an analytical quasi-steady model by including four aerodynamic loading terms. The loads result from the wings translation, rotation, their coupling as well as the added-mass effect. The necessity of including all the four terms in a quasi-steady model in order to predict both the aerodynamic force and torque is demonstrated. Validations indicate a good accuracy of predicting the CP, the aerodynamic loads and the passive pitching motion for various Reynolds numbers. Moreover, compared to the existing quasi-steady models, the presented model does not rely on any empirical parameters and thus is more predictive, which enables application to the shape and kinematics optimization of flapping wings.

昆虫翼の受動的ピッチング運動に対する周波数比の影響

昆虫翼の受動的ピッチング運動に対する周波数比の影響

258 昆虫羽ばたき翼の受動的ピッチングに対する流体構造連成解析

258 昆虫羽ばたき翼の受動的ピッチングに対する流体構造連成解析

OS1-5 Fluid-structure interaction analysis for the aerodynamic contribution to the passive pitching motion of dipteran flapping wings(OS1: Bio-inspired Flight System Biomechanics I)

OS1-5 Fluid-structure interaction analysis for the aerodynamic contribution to the passive pitching motion of dipteran flapping wings(OS1: Bio-inspired Flight System Biomechanics I)

An experimental and three-dimensional computational study on the aerodynamic contribution to the passive pitching motion of flapping wings in hovering flies

The relative importance of the wing’s inertial and aerodynamic forces is the key to revealing how the kinematical characteristics of the passive pitching motion of insect flapping wings are generated, which is still unclear irrespective of its importance in the design of insect-like micro air vehicles. Therefore, we investigate three species of flies in order to reveal this, using a novel fluid-structure interaction analysis that consists of a dynamically scaled experiment and a three-dimensional finite element analysis. In the experiment, the dynamic similarity between the lumped torsional flexibility model as a first approximation of the dipteran wing and the actual insect is measured by the Reynolds number Re, the Strouhal number St, the mass ratio M, and the Cauchy number Ch. In the computation, the three-dimension is important in order to simulate the stable leading edge vortex and lift force in the present Re regime over 254. The drawback of the present experiment is the difficulty in satisfying the condition of M due to the limitation of available solid materials. The novelty of the present analysis is to complement this drawback using the computation. We analyze the following two cases: (a) The equilibrium between the wing’s elastic and fluid forces is dynamically similar to that of the actual insect, while the wing’s inertial force can be ignored. (b) All forces are dynamically similar to those of the actual insect. From the comparison between the results of cases (a) and (b), we evaluate the contributions of the equilibrium between the aerodynamic and the wing’s elastic forces and the wing’s inertial force to the passive pitching motion as 80–90% and 10–20%, respectively. It follows from these results that the dipteran passive pitching motion will be based on the equilibrium between the wing’s elastic and aerodynamic forces, while it will be enhanced by the wing’s inertial force.

The Effect of Supraspinatus Tears on Glenohumeral Translations in Passive Pitching Motion

Background: Supraspinatus tears are common in pitchers. However, the effect of these tears on glenohumeral (GH) mechanics is incompletely understood. Purpose/Hypothesis: To describe the effect of supraspinatus tears and repairs on GH kinematics during an abbreviated throwing motion using the intact shoulder girdle. The hypothesis was that supraspinatus tears would lead to an increase of GH translation in the coronal plane and supraspinatus repairs would restore GH kinematics. Study Design: Controlled laboratory study. Methods: Six shoulders from 3 fresh-frozen cadavers were tested in a novel 7 degrees of freedom robotic testing system. Torsos were mounted and the wrist was pinned to an actuator mounted on an upper frame. After the deltoid was removed, the shoulders were studied during an abbreviated throwing motion (ATM) from maximum external rotation to the midcoronal plane to establish a baseline. The ATM was repeated after creation of a 1-cm supraspinatus tear, after creation of a 3-cm supraspinatus tear, and after repair with a transosseous equivalent (TOE) technique. Retroreflective bone markers and high-speed infrared cameras were used to measure GH kinematics and calculate the center of rotation of the GH joint (CORGH) instantaneously. Results: The 1- and 3-cm supraspinatus tears did not significantly alter GH translation. The TOE repair shifted the CORGH posteriorly, as evidenced by a significant decrease in the overall GH translation in all 3 planes (P = .003, .019, and .026, for x-y, y-z, and x-z planes, respectively). Conclusion: In contrast to a TOE repair of the supraspinatus tendon, isolated supraspinatus tears did not perturb GH kinematics in this cadaveric model of the throwing shoulder. Clinical Relevance: In throwing athletes, treatment of rotator cuff tears should be addressed with caution to avoid an unintended alteration in GH kinematics due to overtightening of the tendon.

J0220401 昆虫羽ばたき翼の受動的ピッチング運動における空気減衰の数値的検討([J022-04]生物規範メカニクス・システム:生物の運動、力学及びミメティクスセッション(4))

J0220401 昆虫羽ばたき翼の受動的ピッチング運動における空気減衰の数値的検討([J022-04]生物規範メカニクス・システム:生物の運動、力学及びミメティクスセッション(4))

Evaluation Using Dynamically Scaled Experiment of Dipteran Passive Pitching Motion Caused by Fluid-Structure Interaction

In this study, we evaluated the dipteran passive pitching motions caused by the fluid-structure interaction using the dynamically scaled experiments. Since the model wing and the surrounding fluid interact with each other, the dynamic similarity between the model and the actual dipteran flights was measured using not only the Reynolds and Strouhal numbers but also the mass and Cauchy numbers. Using these four numbers, the data of the flapping flights of Tipula obsolete, Tipula paludosa, Eristalis tenax, Calliphora vicina were dynamically scaled and applied to the model wing flights. In all tested insect flights the characteristic pitching motions were well simulated, i.e. the model wing maintained the high angle of attack in the middle of each half stroke and rotated during the stroke reversals. The simulated pitch amplitudes were equivalent to those of observations in the actual insect flights and the generated lift was sufficient to support the insect weight. As a consequence the dipteran pitching motion is fundamentally caused by the fluid-structure interaction.

Numerical Study of Flexible Flapping Wing Propulsion

In this study, a strong-coupling approach is applied to simulate highly flexible flapping wings interacting with fluid flows. Here, the fluid motion, solid motion, and their interaction are solved together by a single set of equations of motion on a fixed Eulerian mesh, with the elastic stress being solved on a Lagrangian mesh and projected back to the Eulerian mesh. To provide necessary flapping mechanism, control cells are implemented in solid area (i.e., the wing) as skeleton. The moving trajectory of the skeleton is therefore prescribed by a conventional direct-forcing type of immersed boundary method, while the rest of the wing moves passively through elasticity and fluid-structure interaction. This combined algorithm is then used to study the propulsion characteristics of flexible flapping wings with different elastic moduli and at different flapping frequencies and amplitudes. A two-dimensional NACA0012 airfoil is chosen as a model wing, and it is under active plunging defined by control cells and corresponding passive pitching motion. With different input parameters, very different wake structures can be observed. As a result, the coupled plunging-pitching motion can be either drag-producing or thrust-producing. Finally, passive pitching angle θ and nominal angle of attack α for flexible wings are defined to characterize the flapping motion. It is found that θ needs to be greater than 0.26 and α needs to be greater than 0.3 to generate thrust instead of drag for the flapping motion within the current parametric matrix.

1610 昆虫羽ばたき飛行の受動的ピッチング運動と揚力の動力学的スケール拡大モデルを用いた評価(OS16-3 生物・生体工学に関する流れ,オーガナイズドセッション)

In this study, we evaluated the passive pitching motion and lift force during the insect flapping flight using the dynamically scaled model. Since the wing and the surrounding fluid interact with each other, the dynamic similarity between the model and the insect flights was measured using not only Reynolds and Strouhal numbers but also the mass and Cauchy numbers. Our model includes the plate spring to simulate the low torsional stiffness of the insect wing. Our model wing simulated the pitching motion similar to the actual insect and generated the enough force to lift the insect.

A two-dimensional computational study on the fluid–structure interaction cause of wing pitch changes in dipteran flapping flight

In this study, the passive pitching due to wing torsional flexibility and its lift generation in dipteran flight were investigated using (a) the non-linear finite element method for the fluid-structure interaction, which analyzes the precise motions of the passive pitching of the wing interacting with the surrounding fluid flow, (b) the fluid-structure interaction similarity law, which characterizes insect flight, (c) the lumped torsional flexibility model as a simplified dipteran wing, and (d) the analytical wing model, which explains the characteristics of the passive pitching motion in the simulation. Given sinusoidal flapping with a frequency below the natural frequency of the wing torsion, the resulting passive pitching in the steady state, under fluid damping, is approximately sinusoidal with the advanced phase shift. We demonstrate that the generated lift can support the weight of some Diptera.