The aim of this investigation is to provide an experimental volumetric visualization of the near wake topology of the vortex structures generated by a flapping-wing Micro Air Vehicle (MAV) by means of large-scale Robotic PIV. This novel technique implements coaxial illumination and imaging in combination with the use of Helium Filled Soap Bubbles (HFSB) as tracing particles to achieve large measurement volumes of the order of 10 liters. Information of different phases throughout the flapping cycle is obtained by means of a phase-locked averaging procedure. The MAV used for this study is called DelFly II. It is a platform composed a two pairs of wings attached to a slip body with horizontal and vertical tailplanes for stability and maneuverability. Measurements are performed at regular free-flight scenarios within the DelFly flying envelope. The configurations selected have different reduces frequencies which allows to analyze the effect of this important parameter. Same configurations are also measured with and without the presence of the tails to see their influence of the wake topology. In addition, experiments in both tethered and free-flight conditions have been performed, yielding an unprecedented comparison between the aerodynamics of the two conditions.
The significance of the proposed project lies on the ability of assess the complete three-dimensional wake of the DelFly II. This is the first experimental study performed that can achieve such measuring volumes for any flapping-wing platform, to the knowledge of the present author. Another major benefit of this study is the use of standard flight configuration to observe the wake structures when the MAV is able to sustain level flight. Therefore, the proposed work is expected to be a relevant addition to the understanding of the flapping-wing mechanism.