Experiments on flapping flight under hovering condition

Abstract

In the recent past, we have begun to recognize many of the benefits that Micro Air Vehicles (MAV’s) may have. The important ones being, their small size and high manoeuvrability, which makes them suitable for reconnaissance, exploration, and even, targeted payload delivery. In this backdrop, unsteady flight has received considerable attention. Many unsteady mechanisms have been proposed that can be used for generating sustained lift. One such mechanism that could be used for MAV application is asymmetric flapping. Asymmetric flapping is a simple wing kinematics in which downward stroke is faster than the upward stoke. This thesis aims to understand the role of asymmetric flapping in hovering flight. A one degree of freedom flapping model is designed and asymmetry is introduced by making the downstroke faster than the upstroke, while keeping the total flapping time-period constant. Work done in our group previously using two-dimensional numerical simulations and flow visualization experiments, has found an optimum asymmetry ratio, for which maximum lift is obtained. With a view to quantify these findings with experiments, a range of asymmetry ratios (ratio of downstroke time to upstroke time) is studied using twodimensional PIV. For this, a mechanical model is used with a fixed aspect ratio, flapping amplitude and velocity profile. Typical Reynolds number used in the present study is about three hundred.