Clap-and-fling mechanism in a hovering insect-like two-winged flapping-wing micro air vehicle

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  • Clap-and-fling mechanism in a hovering insect-like two-winged flapping-wing micro air vehicle

Abstract

This study used numerical and experimental approaches to investigate the role played by the clap-and-fling mechanism in enhancing force generation in hovering insect-like two-winged flapping-wing micro air vehicle (FW-MAV). The flapping mechanism was designed to symmetrically flap wings at a high flapping amplitude of approximately 192°. The clap-and-fling mechanisms were thereby implemented at both dorsal and ventral stroke reversals. A computational fluid dynamic (CFD) model was constructed based on three-dimensional wing kinematics to estimate the force generation, which was validated by the measured forces using a 6-axis load cell. The computed forces proved that the CFD model provided reasonable estimation with differences less than 8%, when compared with the measured forces. The measurement indicated that the clap and flings at both the stroke reversals augmented the average vertical force by 16.2% when compared with the force without the clap-and-fling effect. In the CFD simulation, the clap and flings enhanced the vertical force by 11.5% and horizontal drag force by 18.4%. The observations indicated that both the fling and the clap contributed to the augmented vertical force by 62.6% and 37.4%, respectively, and to the augmented horizontal drag force by 71.7% and 28.3%, respectively. The flow structures suggested that a strong downwash was expelled from the opening gap between the trailing edges during the fling as well as the clap at each stroke reversal. In addition to the fling phases, the influx of air into the low-pressure region between the wings from the leading edges also significantly contributed to augmentation of the vertical force. The study conducted for high Reynolds numbers also confirmed that the effect of the clap and fling was insignificant when the minimum distance between the two wings exceeded 1.2c (c = wing chord). Thus, the clap and flings were successfully implemented in the FW-MAV, and there was a significant improvement in the vertical force.

1. Introduction

The flight of insects is a source of inspiration for several researchers in robotics because of their potential application in the development of flapping-wing micro air https://www.hookupdate.net/nl/xdating-overzicht vehicles (FW-MAVs) [1–6]. Various studies on insect wings explored the basic principles of complex and unsteady force generation mechanisms during flight such as the clap-and-fling [7–12] effect, leading edge vortex (LEV) generation [9,10,13–15], delayed stall of the LEV, and wake capture and rotational circulation [15,16]. In contrast with the other mechanisms, the clap-and-fling effect is not considered as a typical method of lift generation in insect flight. The clap and fling occurs due to the interaction between two flapping wings at dorsal stroke reversal, and functions to improve the lift generation. It was first discovered by Weis-Fogh based on the captured hovering wing kinematics of the tiny Encarsia formosa wasp. The clap is placed when the leading edges of the left and right wings approach each other, prior to when the trailing edges of the wings approach each other at the end of upstroke. Following the clap, the wings commence the fling phase consisting of the next downstroke motions by rotating the wings about their trailing edges and moving the leading edges apart from each other . Most tiny insects such as wasps [7,12], diptera [17,18], lacewings , whiteflies [20,21] and thrips [22,23] use the clap-and-fling mechanism frequently during flight. However, this mechanism is not frequently used in larger insect species except during take-off, or when carrying a load or performing power intensive manoeuvres . In insects with flexible wings, the clap and fling is referred to as a clap-and-peel mechanism because the fling and the clap function in a manner similar to a peel and a reverse peel, respectively . This can be observed in Drosophila , butterflies [27–29], bush cricket, mantis [30,31] and locusts . Additionally, observations on white butterflies (Pieris barssicae), bluebottles (Calliphora vicina) and flour moths (Ephista) revealed that their left and right wings approach each other partially without touching the wings at the dorsal stroke reversal and this presents a near-clap-and-fling pattern [17,18,32].