The influence of fluid–structure interaction on cloud cavitation about a flexible hydrofoil. Part 2.

Smith, S.M.; Venning, James A.; Pearce, BW; Young, Yin Lu; Brandner, PA

doi:10.1017/jfm.2020.323

Cited by 42 publications

(17 citation statements)

References 25 publications

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“…The fundamental shedding mode for the abundant case is reduced to the low-frequency mode for all cavitation numbers investigated. The frequency of this is relatively independent of the cavitation number, which is comparable to the so-called Type I shedding mode observed by Smith et al (2020b) at low cavitation numbers.…”

Section: Shedding Phenomena In Nuclei-abundant Flowsupporting

confidence: 67%

Nucleation effects on cloud cavitation about a hydrofoil

2022

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The dynamics of cloud cavitation about a three-dimensional hydrofoil are investigated experimentally in a cavitation tunnel with depleted, sparse and abundant free-stream nuclei populations. A rectangular planform, NACA 0015 hydrofoil was tested at a Reynolds number of $1.4\times 10^{6}$ , an incidence of $6^{\circ }$ and a range of cavitation numbers from single-phase flow to supercavitation. High-speed photographs of cavitation shedding phenomena were acquired simultaneously with unsteady force measurement to enable identification of cavity shedding modes corresponding to force spectral peaks. The shedding modes were analysed through spectral decomposition of the high-speed movies, revealing different shedding instabilities according to the nuclei content. With no active nuclei, the fundamental shedding mode occurs at a Strouhal number of 0.28 and is defined by large-scale re-entrant jet formation during the growth phase, but shockwave propagation for the collapse phase of the cycle. Harmonic and subharmonic modes also occur due to local tip shedding. For the abundant case, the fundamental shedding is again large-scale but with a much slower growth phase resulting in a frequency of $St=0.15$ . A harmonic mode forms in this case due to the propagation of two shockwaves; an initial slow propagating wave followed by a second faster wave. The passage of the first wave causes partial condensation leading to lower void fraction and consequent increase in the speed of the second wave along with larger-scale condensation. For a sparsely seeded flow, coherent fluctuations are reduced due to intermittent, disperse nuclei activation and cavity breakup resulting in an optimal condition with maximum reduction in unsteady lift.

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Section: Shedding Phenomena In Nuclei-abundant Flowsupporting

confidence: 67%

Nucleation effects on cloud cavitation about a hydrofoil

2022

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“…Hence, the structural dynamics of the hydrofoil has minimal effect on the loading and cavity dynamics. Part 2 (Smith et al 2020) investigates the influence of FSI by utilising a compliant hydrofoil with observations informed by those made on the relatively stiff reference in Part 1.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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“…The partial cavities can display unsteady periodic growth-collapse cycles, with cavity cloud shedding from the trailing end of the cavity [11,21]. The mechanism of collapse can vary depending on the cavitation number, with re-entrant jets and bubbly shock waves as two identified methods [25,26,27,28].…”

Section: Cavitating Flow Over Hydrofoilsmentioning

confidence: 99%

“…Increased trailing edge displacements during cavitation were in turn observed to amplify the vortex strength as well as promote cavitation inception at higher cavitation numbers. Smith et al [28] experimentally compared the influence of FSI on cloud cavitation about a flexible and rigid hydrofoil. The transition between cavitation regimes was observed to be accelerated for the flexible hydrofoil indicating a significant influence of the structural dynamics on the cavity.…”

Section: Cavitation With Flow-induced Vibrations (Fiv)mentioning

confidence: 99%

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Unsteady cavitation dynamics and frequency lock-in of a freely vibrating hydrofoil at high Reynolds number

Kashyap¹,

Jaiman²

2022

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In the current work, we investigate the influence of unsteady partial cavitation on the fluid-structure interaction of a freely vibrating hydrofoil section at high Reynolds numbers. We consider an elastically-mounted NACA66 hydrofoil section that is free to vibrate in the transverse flow direction. Cavitating flow dynamics coupled with the transverse vibration are studied at low angles of attack. For this numerical study, we employ a recently developed unified variational fluid-structure interaction framework based on homogeneous mixture-based cavitation with a hybrid URANS-LES turbulence modeling. We first validate the numerical implementation against the experimental data for turbulent cavitating flow at high Reynolds numbers. For the freely oscillating hydrofoil, we observe large-amplitude vibrations during unsteady partial cavitating conditions that are absent in the non-cavitating flow configuration. We identify a frequency lock-in phenomenon as the main source of sustained large-amplitude vibration whereby the unsteady lift forces lock into a sub-harmonic of the hydrofoil natural frequency. During the cavity collapse and shedding, we find a periodic generation of clockwise vorticity, leading to the unsteady lift generation. We determine the origin of this flow unsteadiness at the vicinity of the trailing edge of the hydrofoil through the interplay between the growing cavity with the adverse pressure gradient. The flow-induced structural vibration is also observed to have a consequent impact on the cavity dynamics. In the frequency lock-in regime, large coherent cavitating structures are seen over the hydrofoil suction surface undergoing a full cavity growth-detachment-collapse cycle. For the post-lock-in regime, the cavity length is shorter and the attached cavity length is observed to undergo high frequency spatially localized oscillations. In this regime, cavity shedding is primarily limited to the cavity trailing end and the frequency of a complete cavity detachment and shedding event is reduced. This work has a practical relevance to the cavitation-induced vibration of marine propellers with the target of noise mitigation by active or passive control mechanisms.

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The influence of fluid–structure interaction on cloud cavitation about a flexible hydrofoil. Part 2.

Cited by 42 publications

References 25 publications

Nucleation effects on cloud cavitation about a hydrofoil

Nucleation effects on cloud cavitation about a hydrofoil

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

Unsteady cavitation dynamics and frequency lock-in of a freely vibrating hydrofoil at high Reynolds number

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