Beating phenomenon in frequency lock-in 2DOF stall flutter

A particular behaviour is observed in the pitch-heave stall flutter of a NACA0012 airfoil at transitional chord-based Reynolds numbers during lock-in. When the air speeds is such that the airfoil oscillates at the pitch structural natural frequency, and the structural natural frequencies of the two...

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Bibliographic Details
Published in:Journal of fluids and structures 2021-01, Vol.100, p.103176, Article 103176
Main Authors: Benaissa, A., Biskri, S., Goyaniuk, L., Poirel, D., Bouda, N. Nait
Format: Article
Language:English
Subjects:
2DOF limit cycle oscillation
Beating phenomenon
Lock-in
Stall flutter
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Summary:A particular behaviour is observed in the pitch-heave stall flutter of a NACA0012 airfoil at transitional chord-based Reynolds numbers during lock-in. When the air speeds is such that the airfoil oscillates at the pitch structural natural frequency, and the structural natural frequencies of the two motions are close and their ratio ω̄ (= fh∕fθ) is smaller than 1, the system exhibits a beating phenomenon in both pitching and heaving motions. The modulated amplitude of the two motions presents a phase shift allowing a feedback energy transfer alternatively from pitch to heave and from heave to pitch. Through this energy exchange, the limit cycle oscillation (LCO) is maintained with two frequencies. This phenomenon fades when the ratio ω̄ become greater than one. •Study of interaction between two degree of freedom (2DOFs) airfoil in pitch and heave.•Lock-in between the 2DOFs.•Observation of beating phenomenon under specific conditions.•Use of wavelet analysis to characterise the unsteady nature of the beating.
ISSN:0889-9746
1095-8622
DOI:10.1016/j.jfluidstructs.2020.103176