Experimental Investigation of the Beating Phenomenon in the Aerodynamic Lift Coefficient of a Hovering Wing with Elliptical Cross Section

Hovering enables natural flyers and swimmers to generate lift that balances their weight in still air against gravity. Understanding the kinematics of hovering and the corresponding lift coefficient (C_L) is vital for the design of flapping-wing-based vehicles. In this experimental investigation, an elliptical cross-sectional wing with a chord length (c) of 0.04 m and a span length (b) of 0.4 m was set to heave and pitch sinusoidally in a quiescent fluid. Experiments were conducted at normalized heaving amplitudes (h₀/c) of 0.375 and 0.750. The pitching amplitudes (θ₀) were set to 15°, 30°, and 45°. The Reynolds number (Re), calculated based on h₀/c and the hovering frequency (f), was set to 3016 and 6032. Analysis of the experimentally measured C_L demonstrated the presence of a beating phenomenon for several combinations of h₀/c and θ₀. The spectrum plot of C_L in each case shows that beating occurs due to the presence of two closely spaced C_L signals near the hovering frequency of the respective case. Nevertheless, the beating frequency in all identified cases was found to vary between 0.021 and 0.042. The underlying flow structures responsible for this behaviour will be discussed during the presentation.