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Flow Control of Flexible Structures

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Technical Report,24 Sep 2014,31 May 2017

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University of Colorado Boulder

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The kinematics and flow field development of two wing sections undergoing stall flutter limit cycle oscillations was thoroughly investigated with the goal of elucidating future pathways for successfully implementing aerodynamic flow control on flexible wing structures. A cyberphysical system was implemented with each wing section to prescribe and tune, in-situ, the torsional dynamics of the wing structure. Thefirst wing section studied was a flexible, semi-span, rectangular wing section composed of a NACA 0018 profile and having a semi-span aspect ratio of six. When tuned appropriately, the wing was able to maintain repeatable stall flutter limit cycle oscillations, which were dominated by primarily torsional motions. The torsional and bending kinematics were found to be accurately represented the first three eigenmodes of a fixed-free beam in free vibration. When analyzing the flowfield it was found that a coherent dynamic stall vortex was not produced in contrast to prior work on rigid wings. Instead the wing stall and flow separation was dominated by the growth and collapse of a small parabolic region of flow separation centered around 75 span location and at the wing trailing edge. The second wing section studied was a rigid, full-span, rectangular wing section composed of a NACA 0018 profile and having an aspect ration of 4. Instead of undergoing a twisting deformation this wing was constrained to a rigid body pitching motion in the wind tunnel and was used to identify the differences between prescribed sinusoidal pitching motion and passively sustained stall flutter. Specifically, it was found that stall flutter displays a slower pitch-up rate as compared to classically prescribed sinusoidal motions. This slower pitch-up rate reduced the maximum magnitude of the induced pitching moment and the coherence of the primary dynamic stall vortex that was formed.

Subject Categories:

  • Structural Engineering and Building Technology

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