A Numerical Study on the Effects of Wing Spacing on the Thrust Performance of the Two-Dimensional Tandem Flapping Wings for Different Rear Wing Sizes

Abstract

In this numerical investigation, the effects of wing spacing (distance between wings) on the thrust performance of two flapping elliptic wings in tandem orientation is analysed for the rear wings of different sizes. The wing spacing (R) is varied from 0.25C1 to 2.00C1 at an interval of 0.25C1. The chord length of the rear wing (C2) is varied from 0.50C1 to 1.50C1 at an interval of 0.25C1. Here, C1 is the chord length of the fore wing that is kept constant. The Reynolds number and Strouhal number based on the chord length of the front wing are set as 5000 and 0.32, respectively. In addition, the aspect ratio (i.e. the ratio of the chord length and thickness of the wing) of both front and rear wings is fixed as 8. The starting phase angle between the two wings is maintained at zero degrees to maintain in-phase flapping. It is observed that the thrust performance of the rear wing is significantly affected by the change in the wing size ratio and the distance between them when placed in tandem arrangement. At the smallest wing spacing (i.e. R = 0.25C1), the rear wing with the largest size ratio generates the highest time-averaged thrust. As the distance between the wings is increased, smaller-sized wings are found more effective in terms of thrust performance. When wings are placed furthest apart (i.e. R=2.00C1), the smallest wing has the highest transient peak and cyclic-averaged thrust values. These results could be considered while designing any bio-inspired device having flapping wings in tandem arrangement.