Nonlinear aeroelastic limit-cycle oscillations (LCOs) have become an area of interest due to both detrimental effects on flying vehicles and use in renewable energy harvesting. Initial studies on the interaction between aeroelastic systems and incoming flow disturbances have shown that disturbances can have significant effects on LCO amplitude, with some cases resulting in spontaneous annihilation of the LCO. This paper explores this interaction through wind-tunnel experiments using a variable-frequency disturbance generator to produce flow disturbances at frequencies near the inherent LCO frequency of an aeroelastic system with pitching and heaving degrees of freedom. The results show that incoming disturbances produced at frequencies approaching the LCO frequency from below produce a cyclic growth-decay in LCO amplitude that resembles interference between multiple sine waves with slightly varying frequencies. An aeroelastic inverse technique is applied to the results to study the transfer of energy between the pitching and heaving degrees of freedom as well as the aerodynamic power moving into and out of the system. Finally, the growth-decay cycles are shown to both excite LCOs in an initially stationary wing and annihilate preexisting LCOs in the same wing by appropriately timing the initiation and termination of disturbance generator motion.
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Toward on-demand modulation and annihilation of aeroelastic limit cycle oscillations with dynamic upstream disturbance generator
Periodic upstream flow disturbances from a bluff body have recently been shown to be able to modulate and annihilate limit cycle oscillations (LCOs) in a downstream aeroelastic wing section under certain conditions. To further investigate these phenomena, we have implemented a controllable wind tunnel disturbance generator to enable quantification of the parameter ranges under which these nonlinear interactions can occur. This disturbance generator, consisting of a pitch-actuated cylinder with an attached splitter plate, can be oscillated to produce a von Karman type wake with vortex shedding frequency equal to the oscillation frequency over a range of frequencies around the natural shedding frequency of the cylinder alone. At vortex shedding frequencies away from the LCO frequency of the wing, forced oscillations were observed in the wing, but the wing did not enter self-sustaining LCOs. However, when disturbances were introduced near the LCO frequency, the initially static downstream wing entered self-sustaining oscillations in the presence of the incoming vortices, and these LCOs persisted when the disturbance generator was stopped. Annihilation of the wing LCOs was also observed disturbance vortices were introduced upstream of the wing in LCO.
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- Award ID(s):
- 2015983
- NSF-PAR ID:
- 10333340
- Date Published:
- Journal Name:
- Proceedings of the Online Symposium on Aeroelasticity, Fluid-Structure Interaction, and Vibrations
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The interaction between upstream flow disturbance generators and downstream aeroelastic structures has been the focus of several recent studies at North Carolina State University. Building on this work, which observed the modulation of limit cycle oscillations (LCOs) in the presence of vortex wakes, this study examines the design and validation of a novel disturbance generator consisting of an oscillating cylinder with an attached splitter plate. Analytical design of the bluff body was performed based on specific flow conditions which produced LCO annihilation in previous studies. Computational fluid dynamics simulations and experimental wind tunnel tests were used to validate the ability of the new disturbance generator to produce the desired wake region. Future work will see the implementation of this novel design in conjunction with aeroelastic structures in an effort to modulate and control LCOs, including the excitation and annihilation thereof.more » « less
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