Measurement of nuclei seeding in hydrodynamic test facilities

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The dynamics of cloud cavitation about a 3D hydrofoil are investigated experimentally in a cavitation tunnel with deplete, sparse and abundant freestream nuclei populations. The rectangular-planform, NACA 0015 hydrofoil was tested at a Reynolds number of 1.4 × 10 6 , an incidence of 6 • and a cavitation number of 0.55. High-speed photography of cavitation shedding phenomena was acquired simultaneously with unsteady force measurement to enable identification of cavity shedding modes corresponding with force spectral peaks. Nuclei populations were varied through the injection of polydisperse microbubbles. Both the deplete and abundant cases were characterised by large-scale cloud cavitation. For a sparsely seeded flow, however, coherent fluctuations are significantly reduced due to random nuclei activation and cavity breakup resulting in minimum relative unsteady lift.

Section: Methodsmentioning

confidence: 99%

Control of Cloud Cavitation through Microbubbles

Venning¹,

Pearce²,

Brandner³

2020

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“…At peak operation, generators produce a poly-disperse plume of micro-bubbles 2-200 µm in diameter [9]. While generator parameters are coupled to the tunnel pressure and velocity -through the pressure in the plenum -a study of the bubble populations produced in the test section show that only minor changes are found when a constant generator-cavitation number of σ = 0.25 is maintained [10]. To achieve this the saturation vessel pressure was raised in conjunction with the tunnel pressure, with adequate time between data sampling to allow for en-gassing of the saturation vessel to take place.…”

Section: Methodsmentioning

confidence: 99%

Nucleation Effects on Tip-Gap Cavitation

Russell¹,

Barbaca²,

Venning³

et al. 2020

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Cavitation in tip leakage flows have been investigated in a water tunnel for different concentrations of free-stream cavitation nuclei. High-resolution still photography exhibits similar cavitation topology overall. However, hydro-acoustic measurements reveal stark differences in the desinent extinction of cavitation when different levels of active nuclei are present. Results quantify the anticipated challenges in designing enclosed propulsors and turbo-machinery that operate in flows with varying susceptibility to cavitation.

“…An injected polydisperse microbubble population (hereinafter termed 'polydisperse') with a range of bubble diameters was generated using the cavitation of supersaturated water fed through an array of injectors mounted in the plenum [11,19]. They are typically arranged in a triangular grid, 80 mm apart (an equivalent spacing of 30 mm in the test section), mounted across three columns of a supporting strut.…”

Section: Free and Dissolved Gas Contentmentioning

confidence: 99%

“…The injected nuclei populations were measured using Mie Scattering Imaging (MSI) [19,20]. They are presented as histograms of nuclei concentration against bubble diameter in figure 3.…”

Section: Free and Dissolved Gas Contentmentioning

confidence: 99%

Nucleation Effects on Tip Vortex Cavitation Inception Location

Khoo¹,

Venning²,

Pearce³

et al. 2020

Nuclei, or microbubble, populations are inextricably linked to tip vortex cavitation (TVC) inception and dynamics. In order to gain a better quantitative understanding of this relationship, high-speed video measurements were taken in a cavitation tunnel of TVC inception locations about an elliptical hydrofoil in flows with mono-and polydisperse injected nuclei populations.Sample sizes of O(1000) were acquired. For both populations, inception occurred between 0.02 chord lengths upstream of the hydrofoil tip and about 2.1 chord lengths downstream along the cavity trajectory. However, inception location distribution varied significantly with nuclei population. This is explained by the higher concentrations of weaker nuclei in the monodisperse case, which increases the distance along the vortex within which nuclei are susceptible to cavitation. These results provide the foundation for studies on TVC dynamics and acoustics.