The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Hitoshi Soyama - One of the best experts on this subject based on the ideXlab platform.
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Luminescence intensity of vortex Cavitation in a Venturi tube changing with Cavitation Number.
Ultrasonics sonochemistry, 2020Co-Authors: Hitoshi SoyamaAbstract:Hydrodynamic Cavitation in a Venturi tube produces luminescence, and the luminescence intensity reaches a maximum at a certain Cavitation Number, which is defined by upstream pressure, downstream pressure, and vapor pressure. The luminescence intensity of hydrodynamic Cavitation can be enhanced by optimizing the downstream pressure at a constant upstream pressure condition. However, the reason why the luminescence intensity increases and then decreases with an increase in the downstream pressure remains unclear. In the present study, to clarify the mechanism of the change in the luminescence intensity with Cavitation Number, the luminescence produced by the hydrodynamic Cavitation in a Venturi tube was measured, and the hydrodynamic Cavitation was precisely observed using high-speed photography. The sound velocity in the cavitating flow field, which affects the aggressive intensity of the Cavitation, was evaluated. The collapse of vortex Cavitation was found to be closely related to the luminescence intensity of the hydrodynamic Cavitation. A method to estimate the luminescence intensity of the hydrodynamic Cavitation considering the sound velocity was developed, and it was demonstrated that the estimated luminescence intensity agrees well with the measured luminescence intensity.
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Effect of Cavitation Number on the Improvement of Fatigue Strength of Carburized Steel Using Cavitation Shotless Peening
Key Engineering Materials, 2004Co-Authors: Dan O. Macodiyo, Hitoshi Soyama, Masumi SakaAbstract:Peening can be used to produce a layer of compressive residual stress at the surface of components which are subject to fatigue or stress corrosion, thereby retarding crack initiation and/or impeding the development of new cracks and hence improving their fatigue life. We have developed a new peening method, Cavitation Shotless Peening (CSP), which makes use of Cavitation impacts induced by the collapse of the Cavitation bubbles to produce compressive residual stress and work hardening on the material surface. CSP is a surface enhancement technique which differs with shot peening in that shots are not used. CSP uses a submerged high-speed water jet with Cavitation, herein referred to as a cavitating jet, whose intensity and occurring region can be controlled by parameters such as upstream pressure and nozzle size. Cavitation Number , which is defined by the ratio of upstream pressure to downstream pressure, is the main parameter of the cavitating jet. In this paper, the pit distribution on the specimen was observed with cavitating Numbers = 0.0057 and = 0.0142. The improvement of fatigue strength and introduction of residual stress were investigated for both conditions using carburized alloy steel (JIS SCM415). It was evident from a comparison between non-peened and Cavitation shotless peened specimens that the Cavitation Number has influence on the fatigue strength of metallic materials. Comparison of shot peened and CSP specimens has also been discussed.
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Useful Correlations for Cavitating Water Jet
THE REVIEW OF HIGH PRESSURE SCIENCE AND TECHNOLOGY, 1998Co-Authors: Hitoshi Soyama, A. LichtarowiczAbstract:In order to use a submerged water jet accompanied with Cavitation for practical applications, a cavitating jet was investigated experimentally. The static pressure on the impinging surface was measured to make clear the structure of the cavitating jet. The erosion tests were also carried out to measure the Cavitation intensity. The optimum standoff distance at different Cavitation condition was correlated by the Cavitation Number at the nozzle and the local Cavitation Number on the target. The relation between the Cavitation intensity and the hydraulic parameters was also revealed.
Xinping Long - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of the global Cavitation dynamic behavior in a venturi tube with special emphasis on the cavity length variation
International Journal of Multiphase Flow, 2017Co-Authors: Xinping Long, Junqiang Zhang, Jiong Wang, Qiao LyuAbstract:Abstract Experiments were conducted to investigate the global Cavitation behavior in a venturi tube. Images of various Cavitation stages were captured and analyzed to study the development characteristics of the cavity length and the factors influencing the cavity growth. The results show that once Cavitation occurs, the flow rate remains almost constant regardless of the outlet pressures variations, and the pressure ratio and Cavitation Number are linearly related. Cavitation occurs each time regardless of the inlet or outlet pressure at the same critical pressure ratio of 0.89, which corresponds to a critical Cavitation Number of 0.99. The cavity length is only the function of the pressure ratio or the Cavitation Number independent of the inlet pressures. The development tendency of the Cavitation structure and the cavity length can be divided into two sections by a transition pressure ratio of 0.47 (corresponding to a transition Cavitation Number of 0.51). When the pressure ratio is greater than the transition value, the upper and lower parts of the cavity cloud do not touch each other yet and the cavity length increases relatively slowly as the pressure ratio decreases. Below the transition value, the upper and the lower parts of the cavity cloud meet along the centerline and the Cavitation becomes more sensitive to the decreasing outlet pressure resulting in the cavity length increasing faster. However, the cavity lengths in the both parts are linearly related to the pressure ratios or Cavitation Numbers.
Seung Jin Song - One of the best experts on this subject based on the ideXlab platform.
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Measurement of thermal parameter and Reynolds Number effects on Cavitation instability onset in a turbopump inducer
Journal of the Global Power and Propulsion Society, 2017Co-Authors: Junho Kim, Seung Jin SongAbstract:AbstractThis study experimentally examines how the non-dimensional thermal parameter and Reynolds Number affect Cavitation instability onset in a turbopump inducer using water. Based on the time-resolved static pressure measured at the inlet of the turbopump inducer, the onset Cavitation Number of rotating Cavitation has been determined for varying Reynolds Number and non-dimensional thermal parameter values. Increasing non-dimensional thermal parameter suppresses rotating Cavitation and causes a monotonic decrease in the rotating Cavitation onset Cavitation Number. At low non-dimensional thermal parameter values (e.g., 0.0125), the onset Cavitation Number is independent of the Reynolds Number. However, at higher values of the non-dimensional thermal parameter (e.g., higher than 0.0537), the onset Cavitation Number increases with increasing Reynolds Number. Thus, the Reynolds Number promotes rotating Cavitation onset. This study provides the first assessment of the independent effects of the non-dimensional thermal parameter and Reynolds Number.
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Measurements of the Non-dimensional Thermal Parameter Effects on Cavitation in a Turbopump Inducer
2016Co-Authors: Junho Kim, Han Ho Song, Seung Jin SongAbstract:Cavitation is sensitive to liquid temperature. Hence, temperature effects on Cavitation in turbopump is an important issue. To quantify the temperature effects, the non-dimensional thermal parameter (Σ*) has been proposed. In this study, effects of non-dimensional thermal parameter on Cavitation performance and rotating Cavitation onset in a turbopump inducer have been experimentally investigated in water. Distinct from previous research, experiments have been performed at various temperatures and rotational speeds while maintaining a constant Reynolds Number. Static pressure upstream and downstream of the inducer have been measured to determine Cavitation performance, and unsteady pressures transducers and high speed camera have been used to identify Cavitation instabilities. Two types of Cavitation instabilities have been identified – rotating Cavitation and asymmetric attached Cavitation. Increasing non-dimensional thermal parameter lowers the critical Cavitation Number and the breakdown Cavitation Number at all values of non-dimensional thermal parameters. The onset Cavitation Number of rotating Cavitation is decreased as the non-dimensional thermal parameter increases.
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Measurement of Temperature Effects on Cavitation in a Turbopump Inducer
Journal of Fluids Engineering, 2015Co-Authors: Junho Kim, Seung Jin SongAbstract:Temperature effects on the critical Cavitation Number and rotating Cavitation in a turbopump inducer have been experimentally investigated in water. Static pressures upstream and downstream of the inducer have been measured to determine the Cavitation performance, and Cavitation instabilities have been detected using unsteady pressure sensors and a high-speed camera. Two kinds of Cavitation instabilities have been identified—rotating Cavitation and asymmetric attached Cavitation. To quantify temperature effects, nondimensional thermal parameter has been adopted. Increasing water temperature, or increasing nondimensional thermal parameter, lowers the critical Cavitation Number. Increasing nondimensional thermal parameter also shifts the onset of rotating Cavitation to a lower Cavitation Number and reduces the intensity of rotating Cavitation. However, for values larger than 0.540 (340 K, 5000 rpm), the critical Cavitation Number and the rotating Cavitation onset Cavitation Number become independent of the nondimensional thermal parameter. The onset of the head coefficient degradation correlates with the onset of rotating Cavitation regardless of temperature.
Qiao Lyu - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of the global Cavitation dynamic behavior in a venturi tube with special emphasis on the cavity length variation
International Journal of Multiphase Flow, 2017Co-Authors: Xinping Long, Junqiang Zhang, Jiong Wang, Qiao LyuAbstract:Abstract Experiments were conducted to investigate the global Cavitation behavior in a venturi tube. Images of various Cavitation stages were captured and analyzed to study the development characteristics of the cavity length and the factors influencing the cavity growth. The results show that once Cavitation occurs, the flow rate remains almost constant regardless of the outlet pressures variations, and the pressure ratio and Cavitation Number are linearly related. Cavitation occurs each time regardless of the inlet or outlet pressure at the same critical pressure ratio of 0.89, which corresponds to a critical Cavitation Number of 0.99. The cavity length is only the function of the pressure ratio or the Cavitation Number independent of the inlet pressures. The development tendency of the Cavitation structure and the cavity length can be divided into two sections by a transition pressure ratio of 0.47 (corresponding to a transition Cavitation Number of 0.51). When the pressure ratio is greater than the transition value, the upper and lower parts of the cavity cloud do not touch each other yet and the cavity length increases relatively slowly as the pressure ratio decreases. Below the transition value, the upper and the lower parts of the cavity cloud meet along the centerline and the Cavitation becomes more sensitive to the decreasing outlet pressure resulting in the cavity length increasing faster. However, the cavity lengths in the both parts are linearly related to the pressure ratios or Cavitation Numbers.
Zhang Jia-zhong - One of the best experts on this subject based on the ideXlab platform.
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STUDY OF THE INFLUENCE OF PHASE-CHANGE COEFFICIENTS IN THE Cavitation MODEL
Engineering mechanics, 2012Co-Authors: Wang Bai-qiu, Wang Cong, Huang Hai-long, He Chun-tao, Zhang Jia-zhongAbstract:The influence of phase-change coefficients in a Cavitation model was studied using a numerical method. By comparing the numerical results and experimental data, the relationships of evaporation coefficients & Cavitation Number and condensation coefficients & Cavitation Number are obtained. The results of a 2D axisymmetric hemispherical cylinder under different Cavitation Numbers show that: different Cavitation Numbers are corresponding to different phase-change coefficients, and variations of the coefficients of evaporation and condensation have a great influence respectively on the main cavity, secondary cavity, rear cavity, and other types of cavity in cavity shape, collapse position, collapse strength, and so on.
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Prediction of unsteady supercavities' length behind wedges
Journal of Qiqihar University, 2011Co-Authors: Zhang Jia-zhongAbstract:Based on the theory of potential flow and using the integral equation method,the problem of unsteady natural supercavity flow behind the thin wedges is investegated.Some numerical results are obtained using finite difference time discretization method.The history of unsteady supercavities' length are predicted when wedge' a angle and Cavitation Number for various changes.The more the changed frquency of wedge angle or Cavitation Number,the less of the changed cavity length,and the longer of the relatively time lag.
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Numerical simulation on ventilation rates of ventilated supercavity
Journal of Harbin University of Commerce, 2009Co-Authors: Zhang Jia-zhongAbstract:Some problems about ventilation rates of the ventilated supercavity are investigated using the theoretical analysis,numerical simulation and mechanical test.Numerical simulation of the ventilation rates of ventilated supercavity in small Cavitation Number are studied using the commercial software Fluent6.3.The influence of the natural Cavitation Number and Froude Number on ventilated coefficient as the ventilated Cavitation Number is invariable analyzed using results of the numerical simulation,and are proved using the experiment data.It can be concluded that the ventilated flux and ventilated rate increase as the natural Cavitation Number and Froude Number are increased.The simple relation of ventilated rate and the natural Cavitation Number and Froude Number are gained.