Experimental investigation of some aspects of insect-like flapping flight aerodynamics for application to micro air vehicles

Abstract

Insect-like flapping flight offers a power-efficient and highly-manoeuvrable basis for micro air vehicles for indoor applications. Some aspects of the aerodynamics associated with the sweeping phase of insect wing kinematics are examined by making particle image velocimetry measurements on a rotating onebladed propeller immersed in a tank of seeded water. The work is motivated by the paucity of data with quantified error on insect-like flapping flight, and aims to fill this gap by providing a detailed description of the experimental setup, quantifying the uncertainties in the measurements and explaining the results. The experiments are carried out at two Reynolds numbers-500 and 15000-accounting for scales pertaining to insects and flapping-wing micro air vehicles, respectively. Results from the experiments are used to describe prominent flow features, and Reynolds number-related differences are highlighted. In particular, the behaviour of the leading-edge vortex at these Reynolds numbers is studied and the presence of Kelvin-Helmholtz instability observed at the higher Reynolds number in computational fluid dynamics calculations is also verified. Keywords low Reynolds number flow • insect flight • flapping wing • micro air vehicles • particle image velocimetry • leading-edge vortex • Kelvin-Helmholtz instability

Vortex flow structures and interactions for the optimum thrust efficiency of a heaving airfoil at different mean angles of attack

“…[2][3][4][5] But the interest in the unsteady aerodynamics of flapping flight has significantly grown in recent years in relation to the design of Micro-Aerial Vehicles (MAVs) that take advantage of the accumulated knowledge on animal flight. [6][7][8][9][10] Here, we focus on the thrust generation by an oscillating airfoil at low Reynolds numbers, particularly on the characterization of the vortical flow structures responsible for the maximum thrust efficiency at selected non-dimensional frequencies and amplitudes of the oscillations. We consider the two-dimensional (2D) and incompressible viscous flow around a plunging airfoil at different mean angles of attack.…”

Positive and Negative Spanwise Flow Development on an Insect-Like Rotating Wing

“…This issue was investigated in a previous study by Ansari et al [8], in which the conclusions drawn also apply here because the same rig was used in both cases. In their study, the flow velocities following a wing rotation were measured to observe how the fluid settled, which is illustrated in Fig.…”

“…It was found that this induced flow velocity was essentially zero, and therefore, the seeding response error was assumed to be negligible. This evaluation of the seeding response error is described in greater detail in [8].…”

“…This approach led to measurement uncertainties of 0.0247 and 0.00138 m∕s for the Re 15; 000 and 500 cases, respectively. For further details on the calculation of PIVerrors in this study, the reader is referred to [8].…”

“…Here, the Reynolds number is the product of the mean chord length and the mean wingtip speed divided by the kinematic viscosity of the fluid. It is generally observed that the peak spanwise velocity is comparable to the mean wingtip speed [5][6][7][8], but it has been reported to be as high as two times this velocity [9]. In studies at lower Reynolds numbers (Re 160) by Birch and Dickinson, using a mechanical model of a fruit fly wing, it was observed that there was very little spanwise flow and that placing fences on the wing to limit spanwise flow had little effect on the structure of the LEV [10].…”