Partial Cavities: Global Behavior and Mean Pressure Distribution

Le, Qichi; Franc, Jean-Pierre; Michel, Jean-Marie

doi:10.1115/1.2910131

Cited by 179 publications

(113 citation statements)

References 4 publications

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“…The largest impulses occur near transducer #2, close to the cavity closure region; however, as o is decreased to 0.85 the values at #3 increase as the cavitation collapse extends to that location. Le et al (1993) also noted that the largest pulses on their stationary foil occurred near cavity closure. When the foil is oscillating, the global impulses produced are also very sensitive to changes in cavitation number with the largest global impulses occurring in the middle of the cavitation number range.…”

Section: Comparison Sf Observed Structures On Two Hydrofoilsmentioning

confidence: 99%

“…The radiated noise produced by cloud cavitation is characterized by pressure pulses of very short duration and large magnitude. These pressure pulses were measured by Bark (1985), Bark & van Berlekom (1978), Le et al (1993), and Shen & Peterson (1978, 1980. More recently, McKenney & Brennen (1994) qualitatively related the acoustic signature of a cavitating cloud to the dynarnics of the unsteady cavitation on an oscillating hydrofoil.…”

Section: Introductionmentioning

confidence: 99%

“…Numerous investigators (Wade & Acosta 1966;Bark & van Berlekom 1978;Shen & Peterson 1978, 1980Blake, Wolpert & Geib 1977;Bark 1985;Franc & Michel 1988;Hart, Brennen & Acosta 1990;Kubola et al 1989;Kubota, Kato & Yamaguchi 1992;Le, Franc & Michel 1993;de Lange, de Bruin & van Wijngaarden 1994) have studied the complicated flow patterns involved in the production arid collapse of cloud cavitation on a hydrofoil. As early as 1964, Jakobsen suggested that a static bubbly condensation shock occurs in the bubbly closure region of a large attached cavity and provides the basic mechanism for cavity closure.…”

Section: Introductionmentioning

confidence: 99%

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Observations of shock waves in cloud cavitation

1998

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This paper describes an investigation o l the dynamics and acoustics of cloud cavitation, the structures which are often formed by the periodic breakup and collapse of a sheet or vortex cavity. This form of cavitation frequently causes severe noise and damage, though the precise mechanism responsible for the enhancement of these adverse effects is not fully understood. In this paper. we investigate the large impulsive surface pressures generated by this type of cavitation and correlate these with the images from high-speed motion pictures. This reveals that several types of propagating structures (shock waves) are formed in a collapsing cloud and dictate the dynamics and acoustics of collapse. One type of shock wave structure is associated with the coherent collapse of a well-defined and separate cloud when it is convected into a region of higher pressure. This type of global structure causes the largest impulsive pressures and radiated noise. But two other types of structure, termed 'crescent-shaped regions' and 'leading-edge structures' occur during the less-coherent collapse of clouds. These local events are smaller and therefore produce less radiated noise but the interior pressure pulse magnitudes are almost as large as those produced by the global events.The ubiquity and severity of these propagating shock wave structures provides a new perspective on the mechanisms reponsible for noise and damage in cavitating flows involving clouds of bubbles. It would appear that shock wave dynamics rather than the collapse dynamics of single bubbles determine the damage and noise in many cavitating flows.

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Section: Comparison Sf Observed Structures On Two Hydrofoilsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Observations of shock waves in cloud cavitation

1998

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“…Lush & Skipp (1986) also attributed the occurrence of periodic shedding to re-entrant jets. Visualization of re-entrant jets on cavitating flows has also been reported by Le, Franc & Michel (1993) using dye injection on a plano-convex hydrofoil and by de Lange (1996) using a transparent two-dimensional hydrofoil model. The presence of the re-entrant jet, and its role in cloud shedding on a two-dimensional hydrofoil, was verified in a study by Kawanami et al (1997).…”

mentioning

confidence: 95%

“…They suggested the importance of the flow in the closure of the cavity and its role in dictating the phase transfer and the development of the re-entrant jet. Le et al (1993) measured the pressure distribution in a partial cavity on a plano-convex foil, at different attack angle and cavitation number combinations, for constant cavity lengths. They found that the pressure distribution for cavities with re-entrant flow and shedding was different from non-shedding open cavities, with the maximum pressure having much lower values.…”

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confidence: 99%

Bubbly shock propagation as a mechanism for sheet-to-cloud transition of partial cavities

2016

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Partial cavitation in the separated region forming from the apex of a wedge is examined to reveal the flow mechanism responsible for the transition from stable sheet cavity to periodically shedding cloud cavitation. High-speed visualization and time-resolved X-ray densitometry measurements are used to examine the cavity dynamics, including the time-resolved void-fraction fields within the cavity. The experimentally observed time-averaged void-fraction profiles are compared to an analytical model employing free-streamline theory. From the instantaneous void-fraction flow fields, two distinct shedding mechanisms are identified. The classically described re-entrant flow in the cavity closure is confirmed as a mechanism for vapour entrainment and detachment that leads to intermittent shedding of smaller-scale cavities. But, with a sufficient reduction in cavitation number, large-scale periodic cloud shedding is associated with the formation and propagation of a bubbly shock within the high void-fraction bubbly mixture in the separated cavity flow. When the shock front impinges on flow at the wedge apex, a large cloud is pinched off. For periodic shedding, the speed of the front in the laboratory frame is of the order of half the free-stream speed. The features of the observed condensation shocks are related to the average and dynamic pressure and void fraction using classical one-dimensional jump conditions. The sound speed of the bubbly mixture is estimated to determine the Mach number of the cavity flow. The transition from intermittent to transitional to strongly periodic shedding occurs when the average Mach number of the cavity flow exceeds that required for the generation of strong shocks.

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Numerical simulation of cavitating flow in 2D and 3D inducer geometries

Coutier-Delgosha¹,

Patella²,

Reboud³

et al. 2005

Int. J. Numer. Meth. Fluids

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SUMMARYA computational method is proposed to simulate 3D unsteady cavitating ows in spatial turbopump inducers. It is based on the code FineTurbo, adapted to take into account two-phase ow phenomena. The initial model is a time-marching algorithm devoted to compressible ow, associated with a lowspeed preconditioner to treat low Mach number ows. The presented work covers the 3D implementation of a physical model developed in LEGI for several years to simulate 2D unsteady cavitating ows. It is based on a barotropic state law that relates the uid density to the pressure variations. A modiÿcation of the preconditioner is proposed to treat e ciently as well highly compressible two-phase ow areas as weakly compressible single-phase ow conditions. The numerical model is applied to time-accurate simulations of cavitating ow in spatial turbopump inducers. The ÿrst geometry is a 2D Venturi type section designed to simulate an inducer blade suction side. Results obtained with this simple test case, including the study of its general cavitating behaviour, numerical tests, and precise comparisons with previous experimental measurements inside the cavity, lead to a satisfactory validation of the model. A complete three-dimensional rotating inducer geometry is then considered, and its quasi-static behaviour in cavitating conditions is investigated. Numerical results are compared to experimental measurements and visualizations, and a promising agreement is obtained.

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Partial Cavities: Global Behavior and Mean Pressure Distribution

Abstract: International audienc

Cited by 179 publications

References 4 publications

Observations of shock waves in cloud cavitation

Observations of shock waves in cloud cavitation

Bubbly shock propagation as a mechanism for sheet-to-cloud transition of partial cavities

Numerical simulation of cavitating flow in 2D and 3D inducer geometries

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