Three-dimensional and clap-and-fling effects on a pair of flapping wings used for thrust generation

TL;DR

This study explores how three-dimensional flow effects influence thrust generation in flapping wings with clap-and-fling motion, showing that aspect ratio and wing proximity can minimize efficiency loss.

Contribution

It provides new insights into three-dimensional effects on flapping wing performance, highlighting the role of wing aspect ratio and clap-and-fling interactions in efficiency.

Findings

Three-dimensional effects reduce efficiency by up to 5.59% with aspect ratio 8.

Wing proximity in clap-and-fling interactions mitigates adverse 3D effects.

Efficiency loss is limited at higher aspect ratios and close wing configurations.

Abstract

This research investigates the three-dimensional effects of flow around a pair of flapping wings undergoing clap-and-fling interactions through harmonic in-plane motions combining pitching, heaving, and deviation. Both wings mirror each other in their movements. Baseline parameters were selected based on efficient configurations from a previous two-dimensional study. Simulations at a Reynolds number of 800 were conducted on wings in a thrust configuration utilizing the clap-and-fling mechanism. Rectangular flat-plate wings with various aspect ratios were evaluated to assess the impact of three-dimensional effects on performance. Results were compared with equivalent two-dimensional computations. It was found that the relative decrease in cycle-averaged efficiency due to three-dimensional effects can be limited to approximately 5.59% by using wings with an aspect ratio of 8, the largest considered in this work. Moreover, wing proximity inherent to clap-and-fling kinematics helps mitigate adverse three-dimensional effects.