Unsteady aerodynamic analysis and effectiveness of bio-inspired flapping wings in V-formation flight

Abstract

Several bird species have been observed to fly in V-formation, an arrangement which exploits aerodynamic features to allow the group to conserve energy when migrating over long distances without stopping and feeding. The use of such grouping arrangement and organized pattern has demonstrated longer endurance and less power consumption in comparison with single flights. In this work, a computationally efficient potential flow solver based on the unsteady vortex lattice method (UVLM) is employed to assess the aerodynamic performance of flapping wings in forward flight in terms of lift and thrust generation along with the propulsive efficiency. The UVLM has the capability to simulate incompressible and inviscid flows over moving thin wings where the separation lines are known a priori. A bio-inspired, albatross wing shape is considered and its aerodynamic performance in formation flights is compared against conventional elliptical and rectangular wing shapes. The aerodynamic analysis is carried out for different wing arrangements of 3-body and 5-body V-formations to determine the optimal spacing parameters leading to maximum propulsive efficiency. The simulation results reveal that, at the optimal formation angle and separation distance, the albatross-inspired wing shape produces the most lift over the flapping cycle, while the rectangular wing shape generates the most thrust over the flapping cycle. Furthermore, the optimal configuration in terms of propulsive efficiency is found to be a 5-body V-formation utilizing the albatross wing shape with a separation distance set to one-third of the span and a formation angle set to 139°. The present study provides guidance for the design of multi-flapping wing air vehicles based on the expected flight mission. The albatross wing shape is found to have superior capability in producing lift, while the elliptical wing shape is observed to consume less power. The rectangular wing shape is found to produce higher thrust and then can achieve faster forward motion.

Generating high-efficiency swimming kinematics using hydrodynamic eigenmode decomposition

“…Both 2D and 3D VLMs have been used extensively for first-order estimates of steady and unsteady airfoil loading, in a variety of applications such as wind and tidal energy 48,49 , boat propellers 50 , and aircraft wing modelling 51 . More recently, they have seen extensive use in the study of oscillating airfoils, propulsive kinematics and fluid-structure interaction 39,[52][53][54] . VLM in the format used in this paper gives results identical to classical inviscid airfoil theory such as the Theodorsen and Sears functions, for both steady and unsteady flow 50,55 , and also performs well compared to high-order CFD simulations as long as separated flow effects are not dominant 49,51 .…”