Flow-induced oscillations of pitching swept wings: stability boundary, vortex dynamics and force partitioning

We study experimentally the aeroelastic instability boundaries and three-dimensional vortex dynamics of pitching swept wings, with the sweep angle ranging from 0$^\circ$ to 25$^\circ$. The structural dynamics of the wings are simulated using a cyber-physical control system. With a constant flow spee...

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Bibliographic Details
Published in:Journal of fluid mechanics 2023-12, Vol.977, Article A1
Main Authors: Zhu, Yuanhang, Breuer, Kenneth
Format: Article
Language:English
Subjects:
Aeroelastic stability
Aeroelasticity
Control systems
Damping
Dynamic stability
Dynamic structural analysis
Energy
Flow stability
Flow structures
Frequency dependence
Frequency response
Hopf bifurcation
Inertia
JFM Papers
Limit cycle oscillations
Multilayers
Oscillation modes
Oscillations
Particle image velocimetry
Partitioning
Physical control
Physics
Pitching
Power transfer
Reynolds number
Static characteristics
Structural dynamics
Sweep angle
Swept wings
Swimming
Systems stability
Three dimensional flow
Unsteady aerodynamics
Vortices
Wings
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Summary:We study experimentally the aeroelastic instability boundaries and three-dimensional vortex dynamics of pitching swept wings, with the sweep angle ranging from 0$^\circ$ to 25$^\circ$. The structural dynamics of the wings are simulated using a cyber-physical control system. With a constant flow speed, a prescribed high inertia and a small structural damping, we show that the system undergoes a subcritical Hopf bifurcation to large-amplitude limit-cycle oscillations (LCOs) for all the sweep angles. The onset of LCOs depends largely on the static characteristics of the wing. The saddle-node point is found to change non-monotonically with the sweep angle, which we attribute to the non-monotonic power transfer between the ambient fluid and the elastic mount. An optimal sweep angle is observed to enhance the power extraction performance and thus promote LCOs and destabilize the aeroelastic system. The frequency response of the system reveals a structural-hydrodynamic oscillation mode for wings with relatively high sweep angles. Force, moment and three-dimensional flow structures measured using multi-layer stereoscopic particle image velocimetry are analysed to explain the differences in power extraction for different swept wings. Finally, we employ a physics-based force and moment partitioning method to correlate quantitatively the three-dimensional vortex dynamics with the resultant unsteady aerodynamic moment.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2023.925