Gust and Flapping Flight

Abstract

This work examines the effect of unsteady flow environment on flapping flights. The small size of the fixed wing devices make them quite susceptible to wind fluctuations. Such works have not been extended to flapping wing devices applications largely. To some extent it is known that flapping type devices can alleviate the effect of unsteady wind environment and are able to stabilize the loads. This translates to less time fluctuations in the aerodynamic loads than the input fluctuations in the wind. The present work reviews the earlier works on different unsteady wind models  on stationary and flapping devices. Next, some canonical gust models have been formulated and their effect on a hovering flight are simulated. The main focus is to investigate the load enhancement capabilities of the gust models for the chosen kinematics. The gust models include horizontal and vertical gusts with various waveforms. Qualitative and quantitative comparison of the loads are done for different gust models. Almost all gust models show aerodynamic load enhancement compared to the no gust situation. Hence unsteady wind, suitably synchronized with the flapping kinematics becomes a means of higher lift. The flow-field under various gust models is examined in terms of the leading edge separation, Kramer effect, leading and trailing edge vortex interaction, rotational effects at the start of the strokes. For a quantitative comparison, mean loads and the specific power consumption are calculated.