Computational Fluid Dynamics Study on Flapping Wing Aerodynamics

Abstract

Birds, Insects and butterflies adopt several mechanisms for propulsion like asymmetric flapping, delayed stall along with wing rotation, clap and fling mechanism, wake capturing etc. Flyers perpetuate their very tethered flight by suddenly changing their wingbeat frequency and stroke amplitude. Present study focuses on the fluid dynamics associated with the flapping motion of the finite thickness elliptical wings. For numerical simulation, an in-house code - based on novel Level Set Immersed Boundary Method - developed by Shrivastava et al. (2013) is adopted. Code has been validated for wing performing fling half stroke with published results. Two dimensional, finite thickness, elliptical wings performing flapping motion is numerically modelled in the present work and coupled with an in-house code. Effect of the two governing parameter (trailing edge separation distance (δ) and initial opening angle (θ1)) is investigated at a Reynolds number (Re) of 500. To study the effect of parametric variation, simulations were carried out with three different trailing edge separation distance i.e. 0.2, 0.3 and 0.4 and three different initial opening angle i.e. 00, 22.50 and 450. Wing-wing interaction effect investigated by considering single-winged and double-winged flapping motion. Presence of another wing downstream of the single wing increases the pressure difference across the wings resulting in rise in instantaneous lift coefficients. Trailing edge separation distance (δ) has a minor effect on average lift and drag coefficients. However, Initial opening angle (θ1) has a strong influence on the average lift and drag coefficients. It is found that wings performing flapping motion with initial opening angle θ1 = 00 (results in maximum angular displacement of 1350) and minimum separation distance δ =0.2, experience maximum lift.