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.

Wake Behavior Around Flapping Wings of Model Hawkmoth Moving Sideways

2019 ◽  
Author(s):  
Jong-Seob Han ◽  
Jae-Hung Han
Keyword(s):  
Particle Image ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Digital Particle Image Velocimetry ◽  
Flapping Wings ◽  
Windward Side ◽  
Leeward Side ◽  
Image Velocimetry ◽  
Wake Interaction ◽  
Edge Vortex

Abstract This study investigated nearwake behaviors around flapping wings moving sideways. A dynamically scaled-up flapping manipulator was installed on a servo-driven towing carriage to give the sideways movement. In the single wing configuration, the wing in the windward side did not encounter any noticeable effects on the aerodynamic characteristics. The wing in the leeward side, on the other hand, experienced a substantial lift augmentation. We found a stretched leading-edge vortex (LEV) on the wing in the leeward side, implying the additional feeding flux into the LEV. In this case, the moving sideways gave a continuous lateral wind, which became the source to maintain the lift augmentation with the less downward component. We also found that the moving sideways rather intensified the interaction between the wake of the wing in the windward side and the contralateral wing, i.e., the wing-wake interaction. Accordingly, the lift augmentation on the wing in the leeward side practically disappeared by the wing-wake interaction. A digital particle image velocimetry for nearwake behaviors found the less developed trailing-edge shear layer and wingroot vortex traces. This implied that the massive downwash induced by the wing in the windward side was the main source to neutralize the lift augmentation on the contralateral wing.

Influence of aspect ratio on wing–wake interaction for flapping wing in hover

2019 ◽  
Vol 60 (11) ◽  
Author(s):  
Reynolds Addo-Akoto ◽  
Jong-Seob Han ◽  
Jae-Hung Han
Keyword(s):  
Aspect Ratio ◽  
Flapping Wing ◽  
Wake Interaction

scholarly journals The experimental study of aerodynamic characteristics with wing flexibility for hawkmoth-like wings in hovering flight

2021 ◽  
Author(s):  
YeongGyun Ryu
Keyword(s):  
Experimental Study ◽  
High Speed ◽  
Aerodynamic Force ◽  
Aerodynamic Characteristics ◽  
Flow Structures ◽  
Water Tank ◽  
Hovering Flight ◽  
Flexible Wings ◽  
Image Velocimetry ◽  
Rigid Wing

An experimental study on flapping wing flexibility in hovering flight has been conducted to investigate the wing flexibility for insect-inspired flapping Micro Aerial Vehicles (MAVs). Hawkmoth-like wing models, derived from Manduca sexta, were made of Polycarbonate (PC) sheet with a spanwise length of 200 mm and an aspect ratio of 6.18. For the distributions of wing flexibility, the wing thickness was selected as the design variable: rigid wing (3 mm-thick) and flexible wings (2, 1, 0.8, 0.5, 0.35, 0.2, and 0.1 mm-thick). In the experiment, the wing models were constrained to the symmetrical and sinusoidal flapping motions with sweeping and rotating amplitudes of 120° and 90° in water tank with size of 3.5 m×1.0 m×1.1 m. Aerodynamic force and flow structures for flapping the wing were measured using a six-axis force/torque sensor and a high speed camera with a laser using Digital Particle Image Velocimetry (DPIV). To compare the flow structures of flexible wings with rigid wing, they were captured at the same chordwise cross-section as the rigid wing, 50% of wing length. Based on the experimental results, vortices and aerodynamic force. Consequently, the wing with thickness of 0.8 mm has better aerodynamic characteristics than other wings in hovering flight. This finding will be instrumental in identifying the range of wing flexibilities that improves the aerodynamic efficiency for the development of insect-inspired flapping MAVs.

Towing Tank Experiments for Flapping-Wing Aerodynamics

2017 ◽  
Author(s):  
Jong-Seob Han ◽  
Jong-Wan Lee ◽  
Jae-Hung Han
Keyword(s):  
Cross Sections ◽  
Aerodynamic Force ◽  
Scale Up ◽  
Aerodynamic Characteristics ◽  
Flapping Wing ◽  
Test Results ◽  
Towing Tank ◽  
Image Velocimetry ◽  
Towing Tank Experiment ◽  
Wing Aerodynamics

This paper presents an empirical approach for flapping-wing aerodynamics using a servo-driven towing tank and a dynamically scale-up robotic manipulator. Time-varying aerodynamic force and moment were measured, and digital particle image velocimetry in multiple cross-sections were conducted. Three case studies showed that the towing tank experiment could be an effective way to investigate the aerodynamic characteristics in detail, which are difficult to be predicted by other conventional approaches. The force and moment measurements clarified that an advance ratio has significant role in governing the LEV behavior and consequent aerodynamic performance of flapping wings. Results for moving sideways showed the effects of the wing-wing and wing-body interaction, and the usefulness of the towing tank experiments for analyzing the flight dynamic characteristics. It was also shown that the towing tank experiments can be applicable to realistic wing motions; test results using the wing kinematics of a living insect in forward flight were well compatible with the trim condition of the insect.

scholarly journals The experimental study of aerodynamic characteristics with wing flexibility for hawkmoth-like wings in hovering flight

2021 ◽  
Author(s):  
YeongGyun Ryu
Keyword(s):  
Experimental Study ◽  
High Speed ◽  
Aerodynamic Force ◽  
Aerodynamic Characteristics ◽  
Flow Structures ◽  
Water Tank ◽  
Hovering Flight ◽  
Flexible Wings ◽  
Image Velocimetry ◽  
Rigid Wing

An experimental study on flapping wing flexibility in hovering flight has been conducted to investigate the wing flexibility for insect-inspired flapping Micro Aerial Vehicles (MAVs). Hawkmoth-like wing models, derived from Manduca sexta, were made of Polycarbonate (PC) sheet with a spanwise length of 200 mm and an aspect ratio of 6.18. For the distributions of wing flexibility, the wing thickness was selected as the design variable: rigid wing (3 mm-thick) and flexible wings (2, 1, 0.8, 0.5, 0.35, 0.2, and 0.1 mm-thick). In the experiment, the wing models were constrained to the symmetrical and sinusoidal flapping motions with sweeping and rotating amplitudes of 120° and 90° in water tank with size of 3.5 m×1.0 m×1.1 m. Aerodynamic force and flow structures for flapping the wing were measured using a six-axis force/torque sensor and a high speed camera with a laser using Digital Particle Image Velocimetry (DPIV). To compare the flow structures of flexible wings with rigid wing, they were captured at the same chordwise cross-section as the rigid wing, 50% of wing length. Based on the experimental results, vortices and aerodynamic force. Consequently, the wing with thickness of 0.8 mm has better aerodynamic characteristics than other wings in hovering flight. This finding will be instrumental in identifying the range of wing flexibilities that improves the aerodynamic efficiency for the development of insect-inspired flapping MAVs.

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 Turbulent drag in a rotating frame

2016 ◽  
Vol 794 ◽  
Author(s):  
Antoine Campagne ◽  
Nathanaël Machicoane ◽  
Basile Gallet ◽  
Pierre-Philippe Cortet ◽  
Frédéric Moisy
Keyword(s):  
Large Scale ◽  
Scaling Law ◽  
Stereoscopic Particle Image Velocimetry ◽  
Turbulence Theory ◽  
Water Tank ◽  
Wave Interactions ◽  
Turbulent Drag ◽  
Image Velocimetry ◽  
Weak Turbulence Theory ◽  
Large Scale Flow

What is the turbulent drag force experienced by an object moving in a rotating fluid? This open and fundamental question can be addressed by measuring the torque needed to drive an impeller at a constant angular velocity ${\it\omega}$ in a water tank mounted on a platform rotating at a rate ${\it\Omega}$. We report a dramatic reduction in drag as ${\it\Omega}$ increases, down to values as low as 12 % of the non-rotating drag. At small Rossby number $Ro={\it\omega}/{\it\Omega}$, the decrease in the drag coefficient $K$ follows the approximate scaling law $K\sim Ro$, which is predicted in the framework of nonlinear inertial-wave interactions and weak-turbulence theory. However, stereoscopic particle image velocimetry measurements indicate that this drag reduction instead originates from a weakening of the turbulence intensity in line with the two-dimensionalization of the large-scale flow.

Experimental and Numerical Study on the Flow Field Around a Parallel-Foil Turbine

2020 ◽  
Author(s):  
Yulu Wang ◽  
Di Zhang ◽  
Yonghui Xie
Keyword(s):  
Flow Field ◽  
Aerodynamic Force ◽  
Numerical Study ◽  
Energy Extraction ◽  
Reduced Frequency ◽  
Image Velocimetry ◽  
Efficiency Increase ◽  
Oscillation Process ◽  
Effective Angle ◽  
Extraction Performance

Abstract An experiment facility of parallel-foil turbine is proposed in this study. The flow field around foils at different reduced frequency, pitching amplitude and plunging amplitude is measured by 2D Particle Image Velocimetry (PIV) system. And the energy extraction performance at different motion parameters is analyzed numerically. The comparison between experimental and numerical flow field is conducted at different reduced frequency. The evolution of flow field and the aerodynamic force with different pitching amplitude and plunging amplitude are discussed. The effect of pitching amplitude and plunging amplitude on energy extraction performance is obtained. Results indicate that the pitching amplitude can increase the range and the strength of acceleration area by varying the pitching velocity and the effective angle of attack. The optimal extraction performance appears at 70°. Due to the increase in plunging amplitude, the energy extraction performance and efficiency increase gradually. The optimal plunging amplitude is 1.0. The pitching amplitude and the plunging amplitude influence the power output by affecting the vortex shedding and the flow reattachment in oscillation process.

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