CONFIRMED: EAS Doctoral Proposal Defense by Mostafa KhazaeeKuhpar
Topic: Experimental Study on Fluid-Structure Interactions of Highly Flexible High Aspect Ratio Wings Location: SENG 110 (Materials Science Lab) Abstract: High aspect-ratio wings have garnered substantial interest due to their aerodynamic benefits, particularly their ability to reduce undesirable tip vortex effects, thereby achieving a superior lift-to-drag ratio compared to lower aspect-ratio wings. However, this structural configuration inherently results in increased flexibility, which can lead to aeroelastic instabilities such as flutter, divergence, and control reversal. Flutter instability, in particular, poses a critical design challenge due to its potential to cause catastrophic failure. While extensive research has addressed both linear and nonlinear dynamics related to the onset of flutter in high aspect-ratio wings, few studies have systematically investigated the post-flutter behavior. Understanding this post-flutter response is essential for predicting and managing complex flutter phenomena, thereby enhancing design safety and resilience. The objective of this study is to fill the gap by conducting a thorough experimental study of the interaction between fluid and structure in highly flexible wings during the post-critical phase. When studying the performance of high aspect-ratio wings, it's crucial to recognize the Fluid-Structure Interaction (FSI) at play. This involves a full coupling between the fluid dynamics and structural mechanics. Therefore, a comprehensive understanding demands a simultaneous exploration of both the structural and flow aspects, allowing for a full understanding of the interaction dynamics. The majority of studies focusing on flow visualization around airfoils have been conducted on either stationary airfoils or those with limited degrees of freedom. While the study of flow around rigid airfoils has contributed to our fundamental understanding, the dynamics of flow around rigid wings differ significantly from the complex, three-dimensional dynamics seen in flexible wings. Recent efforts have offered insights into how wing flexibility influences surrounding flow; however, the complexity of 3-D flow physics and its interaction with flexible wing structures remains unexplored, and this gap is further compounded by a shortage of integrated studies that concurrently examine both structural and fluid dynamics. Additionally, the lack of comprehensive experimental data limits the ability of numerical models to accurately capture the three-dimensional flow behavior around flexible wings. This research presents a detailed experimental investigation of the flow-induced vibration characteristics of a highly flexible wing, focusing on parameters such as vibration amplitude, dominant frequencies, mode shapes, and mean deflection, with special attention to the post-flutter phase. A modal analysis-based method, along with digital image correlation (DIC) technique, was employed to measure the wings structural response. Concurrently, flow behavior around the wing was analyzed quantitatively using time-resolved volumetric particle tracking velocimetry (TR-PTV) and two-dimensional particle image velocimetry (TR-2D-PIV) techniques. The study examines a wide range of angles of attack and flow velocities to provide a comprehensive view of fluid-structure interactions in high aspect-ratio wings under varied operational conditions. Our preliminary results show that changes in the angle of attack significantly affect the onset of limit cycle oscillations, as well as the dominant oscillation frequencies and mode shapes. At higher flow velocities and angles of attack, a significant increase in tip deflection was observed, while minimal deflection occurred at lower or zero angles of attack. By employing the Q-criterion, we identified and visualized the coherent structure of vortices, uncovering the substantial influence of angle of attack and flow velocity on their behavior. At lower angles of attack, the leading edge and trailing edge vortices were almost vertical, with minimal interaction with the tip vortex. As the angle of attack increased, these vortices tilted to follow the wing's curvature and became larger and stronger, interacting more with the tip vortex. Our results show that at low-amplitude oscillations, the vortices dissipated quickly, whereas at high-amplitude oscillations, they were able to sustain their coherence for a longer duration, influencing the downstream flow pattern. ADVISOR(S): Dr. Banafsheh Seyed-aghazadeh, Department of Mechanical Engineering (b.aghazadeh@umassd.edu) COMMITTEE MEMBERS: Dr. Mehdi Raessi, Department of Mechanical Engineering and Dr. Hangjian Ling, Department of Mechanical Engineering and Dr. Geoffrey Cowles, SMAST Department of Fisheries Oceanography All EAS Students are ENCOURAGED to attend.
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Engineering and Applied Sciences
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