A Comparative Study of Asymmetrically Flapping Single and Tandem Finite Wings with 2D Airfoils*

The study compares the aerodynamic performance of a 2D NACA0012 airfoil with that of a finite rectangular single wing with an aspect ratio (AR) of 1.85 through numerical simulations. This comparison is done at a flow Reynolds number (Re) of 5000, with the upstroke accounting for 70% of the total asymmetric flapping cycle time of 1.14s. Differences in aerodynamic performance observed between the wings are linked to changes in vortex dynamics. In addition, 3D tandem wing simulations are performed on a previously identified optimal arrangement of asymmetrically flapping finite wings with identical dimensions. Here, the rear wing motion leads the front wing by a phase difference of 10⁰. Comparisons between this optimal configuration and a pair of identical rectangular wings with the same motion show that the former performs better with a total lift coefficient of 1.59 compared to the latter's 1.30. Efforts are made to minimise adverse 3D aerodynamic effects such as spanwise flow and leading-edge vortex disruption. This involves designing new finite wings with a higher aspect ratio (AR of 3.7) for both single and tandem wing cases which enhances the aerodynamic performance, bringing results closer to the 2D cases. Details on the flow physics will be covered in the presentation.