Parametric excitations and lock-in of flexible hydrofoils in two-phase flows

The influence of fluid–structure interaction on cloud cavitation about a stiff hydrofoil. Part 1.

“…The lock-in phenomenon occurs when a structure is being excited by an instability the frequency of which modulates to be near a structural natural frequency, resulting in amplification of the structural response. This has previously been observed in hydrofoils experiencing cloud cavitation Pearce et al 2017;Harwood et al 2019Harwood et al , 2020 with Akcabay & Young (2015) showing that parametric excitations cause frequency modulation in the vibration response. This is due to changes in the fluid mixture density causing fluctuations in effective fluid added mass.…”

“…However, the influence of compliance was only significant when the cavity length was near the trailing edge. The unsteady two-phase flow has effect on the spectral content of a compliant hydrofoil compared to a relatively stiff one, causing frequency modulation (Akcabay & Young 2015), broadening of the frequency content FSI of cloud cavitation about a hydrofoil 896 A1-3 and leading to phenomena such as lock-in that lead to significant amplification of vibrations (Kato, Dan & Matsudaira 2006;Akcabay & Young 2015).…”

The hydroelastic response of a surface-piercing hydrofoil in multiphase flows. Part 2. Modal parameters and generalized fluid forces

“…The frequency of modulation or one of its sub-harmonics can excite the natural frequency of the flexible body. Akcabay & Young (2015) derived a SDOF model of parametric excitation and lock in using a van der Pol oscillator to model the modulation of system parameters with the cavity shedding frequency.…”

“…Notable exceptions include foundational papers by Kaplan & Lehman (1966), Song & Almo (1967) and Song (1969), which focused on the interactions of cavitation with 2-degree-of-freedom flutter and by Besch & Liu (1971), Besch & Liu (1973) and Besch & Liu (1974), which dealt with the same on three-dimensional (3-D) geometries. More recent experimental work has explored the steady or unsteady FSI of two-phase (cavitating) flows as well (Ducoin, Young & Sigrist 2010;Ducoin, Andre & Sigrist 2012;Rodriguez 2012;Akcabay & Young 2015;Chae et al 2016;Pearce et al 2017;Young et al 2018a,b).…”

“…Recording durations were as follows. FW flow: 520 s. FV flow: 1900 s. PC flow: 930 s.shown to induce temporal modulations of the fluid mass, damping and stiffness matricesAkcabay & Young 2015;Lelong, Guiffant & Astolfi 2017)…”