Controlling the utility of wake capture in hovering flapping flight: An experimental investigation

Flapping insect wings flip their direction of motion at stroke reversals, encountering the wake left behind from the previous half-stroke, which leads to changes in the instantaneous flow field and aerodynamic force production. This study identifies how to control the utility of this wing-wake interaction aerodynamic mechanism, also known as wake capture, by experimentally measuring the aerodynamic force coefficients of insect-like wings employing representative “normal hovering” kinematics. Dynamically similar model wings were driven by a custom-designed robotic manipulator to realise sinusoidal and semi-triangular flapping kinematic waveforms within a water tank. Forces were measured for wing planform shapes with different aspect ratio and radial area centroid location at a Reynolds number of 3000. Our experimental results show that for all wing planform shapes considered, a sinusoidal flapping waveform always leads to lower average wake capture lift and drag coefficients values than those produced from a semi-triangular flapping waveform. On the other hand, for the different wing planforms considered in this study, the wake capture force production increases with the increase of aspect ratio but decreases with the increase of radial centroid location.