The Effects of Wakes on Aerodynamic Characteristics of Flapping Wings in Clap-and-Fling Motion at Re of ~104

2018 ◽  
Author(s):  
Jong-Seob Han ◽  
Jae-Hung Han
Keyword(s):  
Aerodynamic Force ◽  
Force Production ◽  
Micro Air Vehicles ◽  
Aerodynamic Characteristics ◽  
Flapping Wing ◽  
Flapping Wings ◽  
Water Tank ◽  
Cross Sectional ◽  
Robotic Arms ◽  
Tip Vortices

In this paper, aerodynamic characteristics of two flapping wings in clap-and-fling motion at Re of ∼104, which corresponds to the flight regime of flapping-wing micro air vehicles, was investigated. The test employing dynamically scaled-up robotic arms installed on a water tank revealed that the wingbeat motion at such high Re in1duced the fully developed wake within two wingbeat cycles. This wake widely influenced the lift production covering the entire wingbeat period; the wings earned the additional lift during the entire downstroke, and lost the lift during the upstroke. Chordwise cross-sectional DPIV showed the massive downwash with enlarged tip vortices, when the wake was fully developed. The wake blew down the headwind and reduced the effective angles of attack. In the case of the clap-and-fling motion, the wake was leaned toward the dorsal part, in which the wings created the clap-and-fling motion, causing the global fluctuation of the aerodynamic force production.

scholarly journals Experimental Study on Flexible Deformation of a Flapping Wing with a Rectangular Planform

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Wenqing Yang ◽  
Jianlin Xuan ◽  
Bifeng Song
Keyword(s):  
High Speed ◽  
Aerodynamic Force ◽  
Inertial Force ◽  
Aerodynamic Characteristics ◽  
Flapping Wing ◽  
Image Correlation ◽  
Flapping Wings ◽  
Aerodynamic Forces ◽  
Cyclic Movements ◽  
Flexible Deformation

A flexible flapping wing with a rectangular planform was designed to investigate the influence of flexible deformation. This planform is more convenient and easier to define and analyzed its deforming properties in the direction of spanwise and chordwise. The flapping wings were created from carbon fiber skeleton and polyester membrane with similar size to medium birds. Their flexibility of deformations was tested using a pair of high-speed cameras, and the 3D deformations were reconstructed using the digital image correlation technology. To obtain the relationship between the flexible deformation and aerodynamic forces, a force/torque sensor with 6 components was used to test the corresponding aerodynamic forces. Experimental results indicated that the flexible deformations demonstrate apparent cyclic features, in accordance with the flapping cyclic movements. The deformations in spanwise and chordwise are coupled together; a change of chordwise rib stiffness can cause more change in spanwise deformation. A certain lag in phase was observed between the deformation and the flapping movements. This was because the deformation was caused by both the aerodynamic force and the inertial force. The stiffness had a significant effect on the deformation, which in turn, affected the aerodynamic and power characteristics. In the scope of this study, the wing with medium stiffness consumed the least power. The purpose of this research is to explore some fundamental characteristics, as well as the experimental setup is described in detail, which is helpful to understand the basic aerodynamic characteristics of flapping wings. The results of this study can provide an inspiration to further understand and design flapping-wing micro air vehicles with better performance.

Wing-Wake Interaction of Insect-Like Flapping Wing in Hover: Effect of Aspect Ratio and Kinematics at Re~104

2019 ◽  
Author(s):  
Reynolds Addo-Akoto ◽  
Jong-Seob Han ◽  
Jae-Hung Han
Keyword(s):  
Aspect Ratio ◽  
Time Course ◽  
Aerodynamic Force ◽  
Flapping Wing ◽  
Windward Side ◽  
Water Tank ◽  
Image Velocimetry ◽  
Wake Interaction ◽  
Entire Flow ◽  
Accelerated Flow

Abstract In this paper, the effect of wing aspect ratio and kinematics on wing-wake interaction at Re∼104, which matched the flight regime of flapping-wing micro air vehicle (FWMAV), was investigated. The dynamically scaled-up robotic model submerged in a water tank environment revealed that the wing-wake interaction augmented lift across a decrease in both aspect ratio and wing pitching duration. At such high Re, a time-course digital particle image velocimetry (DPIV) measurement showed the entire flow was strongly dominated by trailing-edge vortices (TEV). A pair of counter-rotating TEV was found to induce a jetlike flow towards the windward side of the wing at stroke reversal. The transfer of momentum from the accelerated flow to the wing caused the enhanced lift. The size of the pair vortex decreased for an increase in both aspect ratio and wing pitching duration. The size of the TEV pair was the key feature found to generate the observed aerodynamic force characteristics.

Deformable Blade Element and Unsteady Vortex Lattice Fluid-Structure Interaction Modeling of a 2D Flapping Wing

2020 ◽  
Author(s):  
Joseph Reade ◽  
Mark A. Jankauski
Keyword(s):  
Vortex Lattice ◽  
Normal Force ◽  
Aerodynamic Force ◽  
Fluid Structure Interaction ◽  
Force Production ◽  
Flapping Wing ◽  
Energetic Efficiency ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Blade Element

Abstract Flapping insect wings experience appreciable deformation due to aerodynamic and inertial forces. This deformation is believed to benefit the insect’s aerodynamic force production as well as energetic efficiency. However, the fluid-structure interaction (FSI) models used to estimate wing deformations are often computationally demanding and are therefore challenged by parametric studies. Here, we develop a simple FSI model of a flapping wing idealized as a two-dimensional pitching-plunging airfoil. Using the Lagrangian formulation, we derive the reduced-order structural framework governing wing’s elastic deformation. We consider two fluid models: quasi-steady Deformable Blade Element Theory (DBET) and Unsteady Vortex Lattice Method (UVLM). DBET is computationally economical but does not provide insight into the flow structure surrounding the wing, whereas UVLM approximates flows but requires more time to solve. For simple flapping kinematics, DBET and UVLM produce similar estimates of the aerodynamic force normal to the surface of a rigid wing. More importantly, when the wing is permitted to deform, DBET and UVLM agree well in predicting wingtip deflection and aerodynamic normal force. The most notable difference between the model predictions is a roughly 20° phase difference in normal force. DBET estimates wing deformation and force production approximately 15 times faster than UVLM for the parameters considered, and both models solve in under a minute when considering 15 flapping periods. Moving forward, we will benchmark both low-order models with respect to high fidelity computational fluid dynamics coupled to finite element analysis, and assess the agreement between DBET and UVLM over a broader range of flapping kinematics.

Four-Bar Linkage Mechanism for Insectlike Flapping Wings in Hover: Concept and an Outline of Its Realization

2005 ◽  
Vol 127 (4) ◽  
pp. 817-824 ◽  
Author(s):  
Rafał Z˙bikowski ◽  
Cezary Galin´ski ◽  
Christopher B. Pedersen
Keyword(s):  
Insect Flight ◽  
Micro Air Vehicles ◽  
Flapping Wing ◽  
Flapping Wings ◽  
Test Bed ◽  
Linkage Mechanism ◽  
Actual Design ◽  
Straight Line Mechanism ◽  
Four Bar Linkage ◽  
Air Vehicles

This paper describes the concept of a four-bar linkage mechanism for flapping wing micro air vehicles and outlines its design, implementation, and testing. Micro air vehicles (MAVs) are defined as flying vehicles ca. 150 mm in size (handheld), weighing 50–100 g, and are developed to reconnoiter in confined spaces (inside buildings, tunnels, etc.). For this application, insectlike flapping wings are an attractive solution and, hence, the need to realize the functionality of insect flight by engineering means. Insects fly by oscillating (plunging) and rotating (pitching) their wings through large angles, while sweeping them forward and backward. During this motion, the wing tip approximately traces a figure eight and the wing changes the angle of attack (pitching) significantly. The aim of the work described here was to design and build an insectlike flapping mechanism on a 150 mm scale. The main purpose was not only to construct a test bed for aeromechanical research on hover in this mode of flight, but also to provide a precursor design for a future flapping-wing MAV. The mechanical realization was to be based on a four-bar linkage combined with a spatial articulation. Two instances of idealized figure eights were considered: (i) Bernoulli’s lemniscate and (ii) Watt’s sextic. The former was found theoretically attractive, but impractical, while the latter was both theoretically and practically feasible. This led to a combination of Watt’s straight-line mechanism with a drive train utilizing a Geneva wheel and a spatial articulation. The actual design, implementation, and testing of this concept are briefly described at the end of the paper.

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

2016 ◽  
Vol 800 ◽  
pp. 688-719 ◽  
Author(s):  
Q. Wang ◽  
J. F. L. Goosen ◽  
F. van Keulen
Keyword(s):  
Aerodynamic Force ◽  
Micro Air Vehicles ◽  
Mass Effect ◽  
Reynolds Numbers ◽  
Flapping Wings ◽  
Accurate Estimation ◽  
Pitching Motion ◽  
Aerodynamic Loads ◽  
Design And Optimization ◽  
Aerodynamic Torque

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.

Optimal Compliant Flapping Mechanism Topologies With Multiple Load Cases

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Bret Stanford ◽  
Philip Beran
Keyword(s):  
Aerodynamic Force ◽  
Compliant Mechanism ◽  
Micro Air Vehicles ◽  
Flapping Wing ◽  
Gradual Transition ◽  
Multiple Load Cases ◽  
Thrust Generation ◽  
Force Moment ◽  
Turning Maneuver ◽  
Multiple Load

The conceptual design of effective actuation mechanisms for flapping wing micro air vehicles presents considerable challenges, with competing weight, power, authority, and life cycle requirements. This work utilizes topology optimization to obtain compliant flapping mechanisms; this is a well-known tool, but the method is rarely extended to incorporate unsteady nonlinear aeroelastic physics, which must be accounted for in the design of flapping wing vehicles. Compliant mechanism topologies are specifically desired to perform two tasks: (1) propulsive thrust generation (symmetric motions of a left and a right wing) and (2) lateral roll moment generation (asymmetric motions). From an optimization standpoint, these two tasks are considered multiple load cases, implemented by scheduling the actuation applied to the mechanism’s design domain. Mechanism topologies obtained with various actuation-scheduling assumptions are provided, along with the resulting flapping wing motions and aerodynamic force/moment generation. Furthermore, it is demonstrated that both load cases may be used simultaneously for future vehicle control studies: gradual transition from forward flight into a turning maneuver, for example.

scholarly journals Towards Bio-Inspiration, Development, and Manufacturing of a Flapping-Wing Micro Air Vehicle

Drones ◽  
2020 ◽  
Vol 4 (3) ◽  
pp. 39
Author(s):  
P. Lane ◽  
G. Throneberry ◽  
I. Fernandez ◽  
M. Hassanalian ◽  
R. Vasconcellos ◽  
...  
Keyword(s):  
Aerodynamic Force ◽  
Force Production ◽  
Flight Test ◽  
Flapping Wing ◽  
Micro Air Vehicle ◽  
Air Vehicle ◽  
Successful Design ◽  
The Stability ◽  
And Control ◽  
The Impact

Throughout the last decade, there has been an increased demand for intricate flapping-wing drones with different capabilities than larger drones. The design of flapping-wing drones is focused on endurance and stability, as these are two of the main challenges of these systems. Researchers have recently been turning towards bioinspiration as a way to enhance aerodynamic performance. In this work, the propulsion system of a flapping-wing micro air vehicle is investigated to identify the limitations and drawbacks of specific designs. Each system has a tandem wing configuration inspired by a dragonfly, with wing shapes inspired by a bumblebee. For the design of this flapping-wing, a sizing process is carried out. A number of actuation mechanisms are considered, and two different mechanisms are designed and integrated into a flapping-wing system and compared to one another. The second system is tested using a thrust stand to investigate the impact of wing configurations on aerodynamic force production and the trend of force production from varying flapping frequency. Results present the optimal wing configuration of those tested and that an angle of attack of two degrees yields the greatest force production. A tethered flight test is conducted to examine the stability and aerodynamic capabilities of the drone, and challenges of flapping-wing systems and solutions that can lead to successful flight are presented. Key challenges to the successful design of these systems are weight management, force production, and stability and control.

scholarly journals Aerodynamic Performance of a Passive Pitching Model on Bionic Flapping Wing Micro Air Vehicles

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Jinjing Hao ◽  
Jianghao Wu ◽  
Yanlai Zhang
Keyword(s):  
High Efficiency ◽  
Aerodynamic Force ◽  
Leading Edge ◽  
Micro Air Vehicles ◽  
Flapping Wing ◽  
Torsional Stiffness ◽  
Important Goal ◽  
Edge Vortex ◽  
Yaw Moment ◽  
Air Vehicles

Reducing weight and increasing lift have been an important goal of using flapping wing micro air vehicles (FWMAVs). However, FWMAVs with mechanisms to limit the angle of attack (α) artificially by active force cannot meet specific requirements. This study applies a bioinspired model that passively imitates insects’ pitching wings to resolve this problem. In this bionic passive pitching model, the wing root is equivalent to a torsional spring. α obtained by solving the coupled dynamic equation is similar to that of insects and exhibits a unique characteristic with two oscillated peaks during the middle of the upstroke/downstroke under the interaction of aerodynamic, torsional, and inertial moments. Excess rigidity or flexibility deteriorates the aerodynamic force and efficiency of the passive pitching wing. With appropriate torsional stiffness, passive pitching can maintain a high efficiency while enhancing the average lift by 10% than active pitching. This observation corresponds to a clear enhancement in instantaneous force and a more concentrated leading edge vortex. This phenomenon can be attributed to a vorticity moment whose component in the lift direction grows at a rapid speed. A novel bionic control strategy of this model is also proposed. Similar to the rest angle in insects, the rest angle of the model is adjusted to generate a yaw moment around the wing root without losing lift, which can assist to change the attitude and trajectory of a FWMAV during flight. These findings may guide us to deal with various conditions and requirements of FWMAV designs and applications.

scholarly journals Characterizing and modeling the enhancement of lift and payload capacity resulting from thrust augmentation in a propeller-assisted flapping wing air vehicle

2017 ◽  
Vol 10 (1) ◽  
pp. 50-69 ◽  
Author(s):  
Alex E Holness ◽  
Hugh A Bruck ◽  
Satyandra K Gupta
Keyword(s):  
Mixed Mode ◽  
Aerodynamic Force ◽  
Force Production ◽  
Flight Time ◽  
Flapping Wing ◽  
Operating Conditions ◽  
Biologically Inspired ◽  
Air Vehicle ◽  
Payload Capacity ◽  
Aerodynamic Lift

Biologically-inspired flapping wing flight is attractive at low Reynolds numbers and at high angles of attack, where fixed wing flight performance declines precipitously. While the merits of flapping propulsion have been intensely investigated, enhancing flapping propulsion has proven challenging because of hardware constraints and the complexity of the design space. For example, increasing the size of wings generates aerodynamic forces that exceed the limits of actuators used to drive the wings, reducing flapping amplitude at higher frequencies and causing thrust to taper off. Therefore, augmentation of aerodynamic force production from alternative propulsion modes can potentially enhance biologically-inspired flight. In this paper, we explore the use of auxiliary propellers on Robo Raven, an existing flapping wing air vehicle (FWAV), to augment thrust without altering wing design or flapping mechanics. Designing such a platform poses two major challenges. First, potential for negative interaction between the flapping and propeller airflow reducing thrust generation. Second, adding propellers to an existing platform increases platform weight and requires additional power from heavier energy sources for comparable flight time. In this paper, three major findings are reported addressing these challenges. First, locating the propellers behind the flapping wings (i.e. in the wake) exhibits minimal coupling without positional sensitivity for the propeller placement at or below the platform centerline. Second, the additional thrust generated by the platform does increase aerodynamic lift. Third, the increase in aerodynamic lift offsets the higher weight of the platform, significantly improving payload capacity. The effect of varying operational payload and flight time for different mixed mode operating conditions was predicted, and the trade-off between the operational payload and operating conditions for mixed mode propulsion was characterized. Flight tests revealed the improved agility of the platform when used with static placement of the wings for various aerobatic maneuvers, such as gliding, diving, or loops.

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