The influence of ventilated cavitation on vortex shedding behind a bluff body

Wang, Zhiying; Zhang, Mindi; Kong, Decai; Huang, Biao; Wang, Guoyu; Wang, Chenxi

doi:10.1016/j.expthermflusci.2018.05.029

Cited by 18 publications

(3 citation statements)

References 43 publications

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“…38 An increasing interest in ventilated cavitation has been drawn due to the drag reduction effect, i.e., underwater vehicles that are partially or fully enveloped in a large gas cavity. [39][40] In this paper, an uncontrollable and harmful ventilated cavitation, originating from the small leakage of the pipeline during the negative pressure conveying, is presented, which has not been well studied in literature.…”

Section: Dramatic Changes In Cavitation Performance With Free-gas Entrainmentmentioning

confidence: 99%

Effect of cavitation and free-gas entrainment on the hydraulic performance of a centrifugal pump

Wang

Zhang

Zhu

et al. 2020

Proceedings of the Institution of Mechanical Engineers, Part A:

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An experimental study on gas–liquid two-phase flow characteristics in a low-specific-speed centrifugal pump is presented via employing multiple investigation techniques, such as visualization observation, measurements of acoustic emission and vibration, etc. Specially, three different flow conditions were inspected, namely gas locking initiation, critical cavitation with/without free-gas presence, etc. For gas locking, the drastic deterioration of the pump performance and the disrupted balance of shaft were observed. Especially, at low rotational speeds, the gas locking accompanied with intermittent or churn flow can be triggered by even lower inlet gas volumetric fractions. When it came to the cavitation flow, a small amount of gas entrainment could induce the rapid deterioration of cavitation and stimulate much higher amplitude in low-frequency band of shaft rotation. The relationship between the gas bubble trajectory and the vibration level under the backflow is discussed. The results reveal that the combined effect of the free-gas entrainment and cavitation on the pump instability is much stronger than that under natural cavitation or free-gas entrainment flow, whose fault diagnosis can be determined by the data manifested in different spectral segments.

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Section: Dramatic Changes In Cavitation Performance With Free-gas Entrainmentmentioning

confidence: 99%

Effect of cavitation and free-gas entrainment on the hydraulic performance of a centrifugal pump

Wang

Zhang

Zhu

et al. 2020

Proceedings of the Institution of Mechanical Engineers, Part A:

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show abstract

“…Moreover, several previous studies have revealed that coherent flow structures play important roles in the turbulence dynamics of ventilated cavitation (e.g. Dittakavi, Chunekar & Frankel 2010;Wang et al 2018;Wu et al 2021). However, we still lack an understanding about how the coherent structures near the closure part of the ventilated cavity are linked to the turbulence dynamics, and what roles these coherent structures play during the air leakage and vortex shedding processes.…”

Section: Introductionmentioning

confidence: 99%

Simulation-based study of low-Reynolds-number flow around a ventilated cavity

2023

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Ventilated cavitating flows are investigated via direct numerical simulations, using a coupled level set and volume of fluid method to capture the interface between the air and water phases. A ventilated disk cavitator is used to create the cavity and is modelled by a sharp-interface immersed boundary method. The simulation data provide a comprehensive description of the two-phase flow and the air leakage and vortex shedding processes in the cavitating flow. The mean velocity of the air phase suggests the existence of three characteristic flow structures, namely the shear layer (SL), recirculating area (RA) and jet layer (JL). The turbulent kinetic energy (TKE) is concentrated in the JL in the closure region, and streamwise turbulent fluctuations dominate transverse fluctuations in both SL and JL. Budget analyses of the TKE show that the production term causes the TKE to increase in the SL due to the high velocity gradients, and decrease in the JL due to streamwise stretching effects. Air leakage and vortex shedding occur periodically in the closure region, and the one-to-one correspondence between these two processes is confirmed by the velocity and volume fluid spectra results, and the autocorrelation function of the air volume fraction. Moreover, the coherent flow structures are analysed using the spectral proper orthogonal decomposition method. We identify several fine coherent structures, including $SL_{KH}$ induced by the Kelvin–Helmholtz instability, $SL_{out}$ associated with large-scale vortex shedding, $SL_{in}$ associated with small-scale vortex shedding, and $SL_{r}$ associated with upstream turbulent convection. The present study complements previous research by providing detailed descriptions of the turbulent motions associated with the violent mixing of air and water, and the complex interactions between different characteristic structures in cavitating flows.

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“…Liu et al [10] analyzed a cavitation flow field using proper orthogonal decomposition and successfully captured the relationship between structural vibrations and cavitation shedding. Wang et al [11] examined the vortex shedding in the cavitation wake region around a bluff body using PCA and found that the energy of the large-scale vortex structure decreased as the ventilation coefficient increased.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study of Low-Specific-Speed Centrifugal Pump Based on Principal Component Analysis

Wei,

Zhu,

Fan

et al. 2024

Water

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The characteristics of pressure pulsations in centrifugal pumps have attracted considerable attention. In this study, principal component analysis is used to discuss the pressure pulsations in a centrifugal pump with a low specific speed, and the primary causes for these pressure pulsations are analyzed in conjunction with experimental results. The results indicate that principal component analysis effectively separates the primary modes that influence the flow field characteristics. An excessive wrap angle results in the formation of a backflow vortex on the working face of the blade. Obvious stratification of the zero-order modal pressure indicates that the geometric structure of the impeller is rational and that the transient flow field is stable. The second- and third-order modes are conjugates, and their dominant frequency coincides with the dominant rotating frequency of the impeller, indicating that the pulsations of a single channel are the primary component of the pressure pulsations. The primary frequency (148.54 Hz) of the pressure pulsations at monitoring points distributed across the volute is three times the rotational frequency (49.51 Hz) of the impeller. The different positions and sub-frequencies of the monitoring points mean that the principal component analysis can effectively identify the impeller-induced sub-frequency difference.

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The influence of ventilated cavitation on vortex shedding behind a bluff body

Cited by 18 publications

References 43 publications

Effect of cavitation and free-gas entrainment on the hydraulic performance of a centrifugal pump

Effect of cavitation and free-gas entrainment on the hydraulic performance of a centrifugal pump

Simulation-based study of low-Reynolds-number flow around a ventilated cavity

Numerical Study of Low-Specific-Speed Centrifugal Pump Based on Principal Component Analysis

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