Periodic Behavior of Cavitation Cloud Shedding in Submerged Water Jets Issuing from a Sheathed Pipe Nozzle

Peng, Guoyi; Wakui, Ayaka; Oguma, Yasuyuki; Shimizu, Seiji; Ji, Hong

doi:10.4236/jfcmv.2018.61002

Cited by 13 publications

(3 citation statements)

References 24 publications

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“…The average gray level of a focused cylindrical area of 𝑅𝑅/𝑑𝑑 = 10 taken from the sheath exit to 𝑋𝑋′/𝑑𝑑 = 20 is evaluated and the temporal variation of the average grey level is investigated. Then, the dominant frequency 𝑓𝑓 of the average grey level variation is calculated by FFT transformation (Peng et al, 2018). As a dimensionless index for the unsteady periodicity Strouhal number St is defined by the following formula.…”

Section: Periodic Characteristics Of Air Layer Pulsationmentioning

confidence: 99%

Experimental investigation of two-phase flow evolution in a high-speed submerged water jet with air ventilation

Peng

MUKAIYAMA

CAO

et al. 2023

JFST

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In order to improve the submerged cutting performance of water abrasive suspension jet an experimental investigation on the two-phase flow structure of submerged water jet with semi-coaxial air ventilation is conducted by the method of high-speed camera observation under the condition of flow dynamic similarity, and its unsteady behavior under different conditions is evaluated by analyzing of sequence images. Experiment results show that the flow pattern of air-ventilated jet depends upon the ventilation flow rate. It may be classified into bubbly flow surrounded jet, continuous air-layer covered jet and cavity-bubble flow surrounded jet. In the case of non-ventilation, high-speed water jet into water is accompanied by intensive cavitation and the flow field appears to be a narrow jet surrounded by cavitation bubble clouds. By ventilating to the cavitating jet, air-bubbles become bigger gradually and a cavity area is formed at the exit of nozzle head. When the ventilation flow ratio reaches to the level of 5 a large cavity covering the jet is formed and a continuous air-layer covered jet is then generated. Image analysis demonstrates that the continuous air-layer covering the liquid jet pulsates and sheds downstream periodically. The Strouhal number defined by the dominant frequency of jet pulsation decreases quickly with the increase of ventilation flow rate in the range of 𝐶 5. At a suitable ventilation flow ratio (𝐶 6 ~ 8) a relative long stable continuous air-layer covering the jet is generated at high time ratio, which will dramatically enhance the processing ability of submerged water jets. Cutting tests demonstrates that the cutting ability of air ventilated jet depends on the ventilation flow ratio. The relation of processing ability with the flow structure of air ventilated jet is clarified.

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Section: Periodic Characteristics Of Air Layer Pulsationmentioning

confidence: 99%

Experimental investigation of two-phase flow evolution in a high-speed submerged water jet with air ventilation

Peng

MUKAIYAMA

CAO

et al. 2023

JFST

Self Cite

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“…Keiichi Sato et al [27] carried out a high-speed photographic study on the cavitation jet of a contraction expansion nozzle, and also obtained the low-frequency and high-frequency signals corresponding to the pressure fluctuation of the piston pump and the shedding of the cavitation group through the statistics of the change in cavity length over time. Peng G et al [28][29][30] used acrylic resin to make a transparent contraction nozzle, took a high-speed video of the cavitation distribution inside the nozzle and at the exit, and extracted the gray value of the image to obtain high-frequency and low-frequency signals respectively. By comparison, it was found that the low-frequency signal was consistent with the pulsation of the piston pump, while the high-frequency signal corresponded to the shedding frequency of the cavitation mass.…”

Section: Introductionmentioning

confidence: 99%

Effect of Nozzle Outlet Shape on Cavitation Behavior of Submerged High-Pressure Jet

et al. 2021

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A submerged high-pressure water jet is usually accompanied by severe cavitation phenomenon. An organ pipe nozzle can greatly improve the cavitation performance of the jet, making use of the self-excited oscillation of the flow. In order to study the effect of organ pipe nozzles of different nozzle outlet shapes on cavitation behavior of submerged high-pressure jet, in this paper we build a high-pressure cavitation jet experiment system and carried out a high-speed photography experiment to study cavitation cloud characteristics of a high-pressure submerged jet. Two organ pipe nozzles with and without a whistle were compared. The dynamic characteristics of the cavitation cloud was extracted through the POD method, it was found that the result effectively reflect the dynamic characteristics of the cavitation jet. The reconstruction coefficients of mode-1 obtained by the POD can better reflect the periodic time-frequency characteristics of cavitation development. The effect of the nozzle outlet shape on the cavitation behavior of organ pipe nozzle was analyzed based on unsteady numerical simulation, and it was found that the jet generated by the nozzle with a divergent whistle had a larger vorticity in the shear layer near the outlet. Further, stronger small-scale vortex and much severe cavitation occurred from the nozzle with a divergent whistle.

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“…A transparent shrink-type nozzle using acrylic resin is used to observe the internal cavitation of the high-pressure jet nozzle, and high-frequency and low-frequency signals are obtained from the image grayscale of the high-speed photography [25]. By comparison, it is found that the low-frequency signal is consistent with the pulsation of the plunger pump, and the high-frequency signal is related to the frequency of the cavity shedding.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on the Unsteady Characteristics and the Impact Performance of a High-Pressure Submerged Cavitation Jet

Yang

Shi

et al. 2020

Shock and Vibration

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High-pressure submerged cavitation jet is widely used in the fields of material peening, petroleum drilling, and ocean engineering. The impact performance of the jet with intensive cavitation is related to the factors such as working condition and the nozzle geometry. To reveal the relationship between the nozzle divergent angle and the jet pressure on the unsteady characteristics of the jet, high-speed photography with frame rate of 20000 fps is used to record the image of the cavitation clouds. Grayscale analysis algorithm developed in MATLAB is used to study the effects of injecting condition on the special structure, unsteady characteristics, and shedding frequency of the cavitation bubbles. The impact load characteristics of the cavitation jet with different cavitation numbers and stand-off distances are recorded using a high-response pressure transducer. It is found that the cavitation number is the main factor affecting the cavitation morphology of the submerged jet. The lower the cavitation number is, the more intense the cavitation occurs. The outlet divergent angle of the convergent-divergent nozzle also has a significant influence on the development of the cavitation clouds. In the three nozzles with the outlet divergent angles of 40°, 80°, and 120°, the highest bubble concentration is formed usinga nozzle with a divergent angle of 40°, but the high-concentration cavitating bubbles are only distributed in a very small range of the nozzle outlet. The cavities generated by using the nozzle with a divergent angle of 80° can achieve good results in terms of concentration and distribution range, while the nozzle with divergent angle of 120° has lower cavitation performance due to the lack of the constraint at the outlet which intensifies the shear stress of the jet. According to the result of frame difference method (FDM) analysis, the jet cavitation is mainly formed in the vortex structure generated by the shearing layer at the nozzle exit, and the most severe region in the collapse stage is the rear end of the downstream segment after the bubble cloud sheds off. The impact load of the cavitation jet is mainly affected by the stand-off distance of the nozzle from the impinged target, while the nozzle outlet geometry also has an effect on the impact performance. Optimizing the stand-off distance and the outlet geometry of the nozzles is found to be a good way to improve the performance of the cavitation jet.

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Periodic Behavior of Cavitation Cloud Shedding in Submerged Water Jets Issuing from a Sheathed Pipe Nozzle

Cited by 13 publications

References 24 publications

Experimental investigation of two-phase flow evolution in a high-speed submerged water jet with air ventilation

Experimental investigation of two-phase flow evolution in a high-speed submerged water jet with air ventilation

Effect of Nozzle Outlet Shape on Cavitation Behavior of Submerged High-Pressure Jet

Experimental Study on the Unsteady Characteristics and the Impact Performance of a High-Pressure Submerged Cavitation Jet

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