Partial cavity shedding on a hydrofoil resulting from re-entrant flow and bubbly shock waves

Bhatt, Anubhav; Ganesh, Harish; Ceccio, Steven L.

doi:10.1017/jfm.2022.999

Cited by 14 publications

(10 citation statements)

References 32 publications

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“…However, at high , a strong re-entrant jet below the vapour cavity pinches the cavity before the new cavity starts growing. It is confirmed in our study that the likelihood of the re-entrant jet causing cavity shedding increases with the increase in , as also shown recently by Bhatt, Ganesh & Ceccio (2023). Pressure waves due to cloud implosions are present at all (Gawandalkar & Poelma 2022).…”

Section: Resultssupporting

confidence: 92%

The characteristics of bubbly shock waves in a cavitating axisymmetric venturi via time-resolved X-ray densitometry

Gawandalkar,

Poelma

2024

J. Fluid Mech.

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The bubbly shock-driven partial cavitation in an axisymmetric venturi is studied with time-resolved two-dimensional X-ray densitometry. The bubbly shock waves are characterised using the vapour fraction and pressure changes across it, propagation velocity, and Mach number. The sharp changes in vapour fraction measured with X-ray densitometry, combined with high-frequency dynamic pressure measurements, reveal that the interaction of the pressure wave with the vapour cavity dictates the shedding dynamics. At the lowest cavitation number ( $\sigma \sim 0.47$ ), the condensation shock front is the predominant shedding mechanism. However, as $\sigma$ increases ( $\sigma \sim 0.78$ ), we observe an upstream travelling pressure discontinuity that changes into a condensation shock as it approaches the venturi throat. This coincides with the increasing strength of the bubbly shock wave as it propagates upstream, manifested by the increasing velocity of the shock front and the pressure rise across it. Consequently, the Mach number of the shock front increases and surpasses the critical value 1, favouring condensation shocks. Further, at higher $\sigma$ ( ${\sim }0.84\unicode{x2013}0.9$ ), both the re-entrant jet and pressure wave can cause cavity detachment. However, at such $\sigma$ , the pressure wave likely remains subsonic. Hence cavity condensation is not favoured readily. This leads to the re-entrant jet causing the cavity detachment at higher $\sigma$ . The shock front is accelerated as it propagates upstream through the variable cross-section of the venturi. This enhances its strength, favouring cavity condensation and eventual shedding. These observations explain the existence of shock fronts in an axisymmetric venturi for a large range of $\sigma$ .

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Section: Resultssupporting

confidence: 92%

The characteristics of bubbly shock waves in a cavitating axisymmetric venturi via time-resolved X-ray densitometry

Gawandalkar,

Poelma

2024

J. Fluid Mech.

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“…Although the models under investigation did not take into account the compressibility effect, they still showed good agreement with the experimental data. This serves as a starting point for further research on the impact of second mechanism governing the dynamics of unsteady cloud cavitation, as discussed in reference [19].…”

Section: Discussionmentioning

confidence: 99%

“…As a result, the integrity of the attached cavity is disrupted and the gas-vapor mixture becomes discontinuous. It is worth noting that, despite the abundance of research on cavitation around generic symmetric foils [7,[16][17][18][19], which even cover subtle spatial distributions of mean and turbulence characteristics, there remains a limited amount of comparative data for realistic shapes of machine and equipment elements, such as guide vanes and rotor blades. In particular, further investigations are required when the test body represents a foil shaped to replicate a 2D vane or a 3D blade, even in scaled-down models of real full-scale hydraulic machinery.…”

Section: Introductionmentioning

confidence: 99%

Unsteady Cloud Cavitation on a 2D Hydrofoil: Quasi-Periodic Loads and Phase-Averaged Flow Characteristics

Ivashchenko,

Hrebtov,

Timoshevskiy

et al. 2023

Energies

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We perform large-eddy simulations to study a cavitating flow over a two-dimensional hydrofoil section—a scaled-down profile (1:13.26) of guide vanes of a Francis turbine—using the Schnerr–Sauer cavitation model with an adaptive mesh refinement in intensive phase transition flow areas. In the test case, the guide vane is tilted at an angle of attack of 9° to the direction of the flow, in which the Reynolds number, based on the hydrofoil chord length, equals 1.32×106, thus providing a strong adverse pressure gradient along the surface. The calculated time-averaged turbulence characteristics are compared with those measured by particle image velocimetry to verify that the flow is correctly reproduced in numerical simulations using the procedure of conditional averaging proposed and tested in our previous investigation. A re-entrant jet is identified as the primary source of vapor cloud shedding, and a spectral analysis of the cavitating flow over the profile midsection is conducted. Two characteristic frequencies corresponding to the cases, when an attached cavity detaches completely (as a whole) and two partially from the hydrofoil, are found in the flow. The study reveals that the natural frequency of partial cavity shedding is three times higher than that of full detachments. The examined regime exhibits an oscillatory system with two oscillation zones related to cavitation surge instability and unsteady cloud cavitation resulting from the re-entrant jet. Conditional averaging correlates cavitation structures with pressure distributions, forces, and torque on the guide vane. This modeling approach captures the fine details of quasi-periodic cavitation dynamics, providing insights into unsteady sheet/cloud cavitation and offering a method for developing control strategies.

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“…In the investigation of the cavitation cloud by X-rays, the void fraction of cloud cavitation around the Venturi [48] , [49] , [50] and hydrofoil [51] , [52] , [53] , [54] , [55] , [56] were evaluated. Vapor bubbles in the Venturi tube profile were detected at 3,000 frames per second using synchrotron radiation at the XOR 32-ID beamline of the Advanced Photon Source (APS), Argonne National Laboratory (ANL) [57] .…”

Section: Introductionmentioning

confidence: 99%

Revealing the origins of vortex cavitation in a Venturi tube by high speed X-ray imaging

Soyama,

Liang,

Yashiro

et al. 2023

Ultrasonics Sonochemistry

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Partial cavity shedding on a hydrofoil resulting from re-entrant flow and bubbly shock waves

Cited by 14 publications

References 32 publications

The characteristics of bubbly shock waves in a cavitating axisymmetric venturi via time-resolved X-ray densitometry

The characteristics of bubbly shock waves in a cavitating axisymmetric venturi via time-resolved X-ray densitometry

Unsteady Cloud Cavitation on a 2D Hydrofoil: Quasi-Periodic Loads and Phase-Averaged Flow Characteristics

Revealing the origins of vortex cavitation in a Venturi tube by high speed X-ray imaging

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