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Research Papers: Multiphase Flows

Study of the Cavitating Instability on a Grooved Venturi Profile

[+] Author and Article Information
Amélie Danlos

Associate Professor
Laboratoire du Génie des
Procédés pour l'Energie,
l'Environnement et la Santé (LGP2ES), EA 21,
Conservatoire National des Arts et Métiers,
292 Rue Saint Martin,
Paris 75003, France
e-mail: amelie.danlos@cnam.fr

Jean-Elie Méhal

DynFluid Laboratory, EA 92,
Arts et Métiers ParisTech,
151 Boulevard de l'Hôpital,
Paris 75013, France

Florent Ravelet

Associate Professor
DynFluid Laboratory, EA 92,
Arts et Métiers ParisTech,
151 Boulevard de l'Hôpital,
Paris 75013, France
e-mail: florent.ravelet@ensam.eu

Olivier Coutier-Delgosha

Professor
Laboratoire de Mécanique de Lille, UMR 8107,
Arts et Métiers ParisTech,
8 Boulevard Louis XIV,
Lille 59046, France
e-mail: olivier.coutier@ensam.eu

Farid Bakir

Professor
DynFluid Laboratory, EA 92,
Arts et Métiers ParisTech,
151 Boulevard de l'Hôpital,
Paris 92290, France
e-mail: farid.bakir@ensam.eu

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received May 3, 2013; final manuscript received April 16, 2014; published online July 24, 2014. Assoc. Editor: Edward M. Bennett.

J. Fluids Eng 136(10), 101302 (Jul 24, 2014) (10 pages) Paper No: FE-13-1291; doi: 10.1115/1.4027472 History: Received May 03, 2013; Revised April 16, 2014

Instabilities of a partial cavity developed on a hydrofoil, a converging-diverging step, or in an interblade channel have already been investigated in many previous works. The aim of this study is to evaluate a passive control method of the sheet cavity. According to operating conditions, cavitation can be described by two different regimes: an unstable regime with a cloud cavitation shedding and a stable regime with only a pulsating sheet cavity. Avoiding cloud cavitation can limit structure damage since this regime is less aggressive. The surface condition of a converging-diverging step is here studied as a solution to control the cavitation regime. This study discusses the effect of longitudinal grooves on the developed sheet cavity. Analyzes conducted with laser Doppler velocimetry, visualizations, and pressure measurements show that the grooves geometry, and especially the groove depth act on the sheet cavity dynamics and can even suppress the cloud cavitation shedding.

Copyright © 2014 by ASME
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References

Figures

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Fig. 1

Test section of the experimental device using a Venturi profile (the origin of the Cartesian coordinate system is located at the throat, in the middle of the test section wide, α = 8 deg is the angle for the LDV measurements system xy'z' and Hthroat = 67 mm is the reference length)

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Fig. 2

Characterization of the flow in the test section inlet: (a) nondimensional longitudinal velocity profile vy* = vy/vref (the line represents the mean value of the velocity vref = 5.56 m .s-1) and (b) the profile of the turbulence intensity RMS(vy)/〈vy〉, where 〈vy〉 is the time-averaged velocity, y*≃-4.5 and x* = 0 (results come from LDV measurements, presented in the Sec. 4.1)

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Fig. 3

Venturi components: (a) venturi basis with C1 to C7 pressure sensors on the basis surface, (b) junction between the Venturi basis and a plate, and (c) zoom of a grooved plate with the definition of the grooves geometric parameters (d and h are, respectively, the grooves diameter and depth, e is the width of the ridge, and λ is the grooves wavelength).

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Fig. 4

Pressure sensors on the Venturi suction side

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Fig. 5

Characteristics of the studied plates used on the Venturi suction side (N is the number of grooves) and description of symbols used in following graphics

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Fig. 6

Images processing for the sheet cavity length measurements: (a) normalized instantaneous image, (b) image binarization with different threshold levels 0.5, 0.4 or 0.3, and (c) median filter applied on the binarized image.

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Fig. 7

Sheet cavity on the smooth plate 0 for σ = 1.18: (a) normalized average image, (b) root mean square of normalized images (the line represents the nondimensional sheet cavity length L* = L/Hthroat≃1.62), and (c) a profile of the root mean square of normalized images RMS (I) plotted in z* = 0.

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Fig. 8

Nondimensional sheet cavity length L* = L/Hthroat according to the cavitation number σ: ×: plate 0, ★: plate 1, △: plate 2, ▲: plate 3, +: plate 4, ★: plate 5, +: plate 6, ◇: plate 7, ◻: plate 8

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Fig. 9

Nondimensional sheet cavity mean height H* = H/Hthroat according to the nondimensional sheet cavity mean length L* = L/Hthroat: ×: plate 0, ★: plate 1, △: plate 2, ⋆: plate 3, +: plate 4, ★: plate 5, +: plate 6, ◇: plate 7, ◻: plate 8

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Fig. 10

Aspect ratio H/L according to the cavitation number σ: ×: plate 0, ★: plate 1, △: plate 2, ⋆: plate 3, +: plate 4, ★: plate 5, +: plate 6, star: plate 7, ◻: plate 8

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Fig. 11

Pressure fluctuations RMS(P) on the Venturi bottom wall according to the cavitation number σ, at different distances from the Venturi throat: (a) for plate 0, (b) for plate 2, (c) for plate 6, (d) for plate 7, and (e) for plate 8. ▲: C1, •: C2, ◻: C4, ×: C6 (see positions of sensors in Fig. 5).

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Fig. 12

Frequency of the sheet cavity length oscillation fL according to the nondimensional sheet cavity mean length L*: ×: plate 0, ★: plate 1, △: plate 2, ⋆: plate 3, +: plate 4, ★: plate 5, +: plate 6, ◇: plate 7, ◻: plate 8

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Fig. 13

Frequency spectrum of the variation of the gray level in the closure of the sheet cavity, on the plate 0: (a) for σ = 1.17 and (b) for σ = 1.44

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Fig. 14

Frequency spectrum of the variation of the gray level in the closure of the sheet cavity, for σ = 1.17 for: (a) the plate 7 and (b) the plate 8

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Fig. 15

Strouhal number StL = LfL/v according to the cavitation number σ: ×: plate 0, ★: plate 1, △: plate 2, ⋆: plate 3, +: plate 4, ★: plate 5, +: plate 6, ◇: plate 7, ◻: plate 8

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Fig. 16

Visualization of (a-j) the cloud cavitation shedding for the smooth plate 0 and (a‘-j’) the sheet cavity pulsation for the plate 8, when σ = 1.17 (Δt = 2 ms between two images)

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Fig. 17

Longitudinal nondimensional velocity profile v' y*/v' y∞ of the noncavitant flow, at (a) y* = 0, (b) y* = 0.5, (c) y* = 1, and (d) y* = 2. ×: plate 0, ◇: plate 2, +: plate 6, ◇: plate 7, □: plate 8

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Fig. 18

Longitudinal nondimensional velocity profile v' y*/v' y∞ of the noncavitating flow, at y* = 0.5, for (a) the grooved sheet 6 and (b) the grooved sheet 2. •: x* = 0, Δ: x* = λ/2

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