Characterization of the cavitating flow in converging-diverging nozzle based on experimental investigations

Rudolf, Pavel; Hudec, Martin; Gríger, Milan; Štefan, David

doi:10.1051/epjconf/20146702101

Cited by 19 publications

(18 citation statements)

References 6 publications

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“…Due to the complex mix of unsteadiness, twophase flow dynamics, turbulence and fluid-structure interactions, this is a very complicated research field. In previous research usually three different test geometries are used to visualize this cloud shedding: (1) hydrofoils ( Callenaere et al, 2001;Danlos et al, 2014;De Lange and De Bruin, 1997;Foeth et al, 2008;Long et al, 2018 ), (2) planar converging-diverging nozzles with a rectangular cross-section ("wedges") ( Chen et al, 2015;Ganesh et al, 2016;Jana et al, 2016;Croci et al, 2016 ) and (3) converging-diverging axisymmetric nozzles ("venturis") ( Rudolf et al, 2014;Hayashi and Sato, 2014;Tomov et al, 2016;Long et al, 2017 ). Although in all geometries periodic cloud shedding can be observed, due to the specific shape of each of the geometries, they all have their own characteristic flow dynamics.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of partial cavitation in an axisymmetric converging-diverging nozzle

Jahangir

Hogendoorn

Poelma

2018

International Journal of Multiphase Flow

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Partial cavitation dynamics in an axisymmetric converging-diverging nozzle are investigated experimentally. Shadowgraphy is used to visualize and analyze different cavitation regimes. These regimes are generated by changing the global static pressure and flow velocity independently. Cloud cavitation is the most interesting and complex regime, because the shedding of vapor clouds is caused by two different mechanisms: the re-entrant jet mechanism and the bubbly shock mechanism. The dynamics are investigated using a position-time diagram. Using such a diagram we show that for cavitation number σ > 0.95 the cavity shedding is caused by the re-entrant jet mechanism, and for σ < 0.75 the mechanism responsible for periodic cavity shedding is the bubbly shock mechanism. Both mechanisms are observed in the transition region, 0.75 < σ < 0.95. The shedding frequencies, expressed as Strouhal numbers, collapse on a single curve when plotted against the cavitation number, except for the transition region. The re-entrant jet mechanism is a pressure gradient driven phenomenon, which is caused by a temporary stagnation point at the cavity front. This leads to stick-slip behavior of the cavity. In the bubbly shock regime, a shock wave is induced by a collapse of the previously shedded vapor bubbles downstream of the venturi, which triggers the initiation of the detachment of the growing cavity. The propagation velocity of the shock wave is quantified both in the liquid and the mixture phase by means of the position-time diagram.

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Section: Introductionmentioning

confidence: 99%

Dynamics of partial cavitation in an axisymmetric converging-diverging nozzle

Jahangir

Hogendoorn

Poelma

2018

International Journal of Multiphase Flow

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“…Standard orifices have one circular hole with prescribed thickness/diameter ratio and shape of the orifice edge. In our previous research [3,4], it was found out that pressure amplitudes downstream of both one-hole and multihole orifices are lower than those generated by Venturi tube.…”

Section: Introductionmentioning

confidence: 87%

Cavitation in Fractal Geometry Orifices

Rudolf¹,

Kubina²,

Hudec³

et al. 2018

Proceedings of the 10th International Symposium on Cavitation (CAV2018)

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An experimental research of three types of orifices was carried out in a hydraulic circuit. One-hole orifice and two fractal-shaped orifices (von Koch snowflake, Apollonian gasket) were tested. Fractalshaped orifices had lower pressure loss in non-cavitating regime. For cavitating conditions, von Koch snowflake orifice maintained the reduced pressure loss, while pressure loss curve within Apollonian gasket orifice gradually aligned with that of one-hole orifice. Dynamics of the cavitating flow behind the orifices featured distinct peak for one-hole orifice connected with shedding of one strong coherent vortical structure, while pressure amplitudes for fractal-shaped orifices (especially von Koch snowflake orifice) were significantly lower. This conclusion is attributed to multiscale behavior of the flow behind the fractal-shaped orifices.

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“…In case of Kunz cavitation model, the source terms Re and Rc are computed using the formulas (4) and (5).…”

Section: ∂(αρ L )mentioning

confidence: 99%

“…For this purpose, cavitation and its dynamics within the Venturi tube have been investigated and results were discussed in several contributions. [5][6] [7] Introduction of swirl using the swirl generator represents the further step of this investigation. The cavitation patterns downstream the throat of the nozzle have been highly modified by the presence of the swirl.…”

Section: Introductionmentioning

confidence: 99%

Numerical and Experimental Investigation of the Cavitating Flow Within Venturi Tube

Kozák

Rudolf

Hudec

et al. 2018

Journal of Fluids Engineering

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Hydrodynamic cavitation represents complex physical phenomenon undesirably affecting operation as well as lifespan of many hydraulic machines from small valves to the large hydro power plants. On the other hand, the same phenomenon and its concomitants such as pressure pulsations can be exploited in many positive ways. One of them which seems to be very promising and perspective is the cavitation utilization for reduction of the microorganisms such as cyanobacteria within large bulks of water. Mutual effect of the swirl induced by the upstream mounted generator and flow constriction in converging–diverging nozzle has been experimentally investigated. The analysis of the hydraulic losses in the wide range of the cavitation regimes has been done as well as the investigation of the pipe wall acceleration induced by the fluctuations of the cavitating structures. The dynamics of the cavitation was studied using the proper orthogonal decomposition (POD) of the captured video records. The main scope of this paper is numerical investigation complementing the experimental results. The multiphase simulations were carried out using the OpenFOAM 1606+ and its interPhaseChangeFoam solver. The present study focuses on computational fluid dynamics results of the cavitating velocity field within the nozzle and analysis of the loss coefficient within the nozzle. The results of the numerical analysis were utilized for the further discussion of the experimental results.

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Characterization of the cavitating flow in converging-diverging nozzle based on experimental investigations

Cited by 19 publications

References 6 publications

Dynamics of partial cavitation in an axisymmetric converging-diverging nozzle

Dynamics of partial cavitation in an axisymmetric converging-diverging nozzle

Cavitation in Fractal Geometry Orifices

Numerical and Experimental Investigation of the Cavitating Flow Within Venturi Tube

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