Aeroelastic Study of Leading Edge Minitabs for Gust Load Alleviation

Abstract

This thesis investigates the aeroelastic behaviour of a flexible wing with minitabs and their effectiveness in alleviating the peak gust loads. Minitabs, which are small deployable surfaces located on the upper surface of the wing, were examined through a series of static and dynamic Fluid-Structure Interaction (FSI) simulations, which evaluated the aerodynamic and structural responses when deployed and stowed. The transient response of deployment of the minitabs indicated a greater load reduction capability compared to their steady-state performance. Notably, the peak alleviation of the minitabs is achieved when the gust peak lies within the aerodynamic reaction time of the minitab. Evaluating the deployment of minitabs for various gust profiles further demonstrates that minitabs performed better in response to sharp, high-amplitude gusts, while their efficacy diminishes with longer gust lengths. When deployed at the ideal moment, the minitabs were found to reduce peak gust loads by an average of 5%. As a consequence of the mid-flight deployment and stowing of the minitabs, simulations revealed significant aeroelastic effects, characterized primarily by first bending mode oscillations at approximately 1 Hz. A sweep analysis of the deployment and stowing times revealed that delaying the actuation of the minitab beyond the ideal deployment or stowing time leads to an increased amplitude oscillations and extended recovery time to steady state conditions. The study evaluated the performance of the minitabs in response to various gust profiles characterized by different gust lengths. The minitabs demonstrated improved performance in alleviating the gust peak loads from short, sharp gusts. However, the effectiveness in reducing the peak loads diminished for gusts of longer gust length and subsequent longer recovery time. The study also identified gusts with frequencies close to the natural first bending frequency of the wing structure as critical cases, where resonant behaviour emerges, leading to large amplitude oscillations and prolonged recovery times. While minitabs effectively reduce peak lift and bending moments induced by gusts, they also introduce lower amplitude oscillations in the bending and torsion moments that persist over multiple cycles. While the peak moments do not exceed a magnitude that would raise a concern to the structural integrity, the subsequent prolonged multi-cycle oscillations in the moments raises concerns about potential fatigue life issues for the internal structure. In conclusion, while this research confirms the potential of minitabs as a viable load alleviation method, it emphasizes the need for further investigation. Comprehensive aeroelastic studies on various minitab configurations, geometries and placements over the wing will provide a complete understanding of the aeroelastic effects of the minitabs and determine an ideal configuration to maximize the load alleviation capability. Additionally, the original actuation method of the minitab involves the rotating them from a vortex generator position to the minitab position. This thesis simplified the actuation to a ON/OFF procedure. Further research is required to incorporate this motion to evaluate any aeroelastic effects resulting from this actuation motion.