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1
Romanov, Alexey, Sergey Evdokimov e Vladimir Seliverstov. "Cavitation research results of hydroturbine impeller blades and their analysis". MATEC Web of Conferences 196 (2018): 02006. http://dx.doi.org/10.1051/matecconf/201819602006.
Testo completoAbstract (sommario):
Abstract. Cavitation erosion affects the hydropower plants operation mode, destroys the surface of water-conducting way, affects the efficiency coefficient as well as the turbine output. The most common damage is observed on water-conducting ways having poor streamline shape, various ledges, irregularities along the water flow. Disruptive cavitations are formed initially on the rotation axes of vortexes, and the caverns of disruptive cavitation develop with the period subordinating the Strouhal Law. One of the methods of cavitational erosion field studies is the method of obtaining high-speed cavitational erosion of metal plates, which has low resistance to cavitation mechanical effects. It provides an opportunity to determine erosion degree and intensity at different modes of hydropower plants operation. The paper demonstrates the results of studying the cavitational erosion process of hydroturbine impeller blades of Zhiguli Hydroelectric Station (HS). Cavitation tests are conducted for three operating modes. Technological peculiarities are also described. The paper presents results of turbine blades of Unit 5 for three operation modes. The destruction areas of impeller blades peripheral edges are visualized. The study provides the results of field and laboratory cavitation tests of hydroturbine elements that serve as recommendations for repairing and restoration of damaged hydroelectric units of Zhiguli HS.
2
Viitanen, Ville M., Tuomas Sipilä, Antonio Sánchez-Caja e Timo Siikonen. "Compressible Two-Phase Viscous Flow Investigations of Cavitation Dynamics for the ITTC Standard Cavitator". Applied Sciences 10, n. 19 (7 ottobre 2020): 6985. http://dx.doi.org/10.3390/app10196985.
Testo completoAbstract (sommario):
In this paper, the ITTC Standard Cavitator is numerically investigated in a cavitation tunnel. Simulations at different cavitation numbers are compared against experiments conducted in the cavitation tunnel of SVA Potsdam. The focus is placed on the numerical prediction of sheet-cavitation dynamics and the analysis of transient phenomena. A compressible two-phase flow model is used for the flow solution, and two turbulence closures are employed: a two-equation unsteady RANS model, and a hybrid RANS/LES model. A homogeneous mixture model is used for the two phases. Detailed analysis of the cavitation shedding mechanism confirms that the dynamics of the sheet cavitation are dictated by the re-entrant jet. The break-off cycle is relatively periodic in both investigated cases with approximately constant shedding frequency. The CFD predicted sheet-cavitation shedding frequencies can be observed also in the acoustic measurements. The Strouhal numbers lie within the usual ranges reported in the literature for sheet-cavitation shedding. We furthermore demonstrate that the vortical flow structures can in certain cases develop striking cavitating toroidal vortices, as well as pressure wave fronts associated with a cavity cloud collapse event. To our knowledge, our numerical analyses are the first reported for the ITTC standard cavitator.
3
Hu, Xiao, e Ye Gao. "Investigation of the Disk Cavitator Cavitating Flow Characteristics under Relatively High Cavitation Number". Applied Mechanics and Materials 29-32 (agosto 2010): 2555–62. http://dx.doi.org/10.4028/www.scientific.net/amm.29-32.2555.
Testo completoAbstract (sommario):
Simulations on two-phase cavitating flows containing water and vapor, on axisymmetric body with disk cavitator have been implemented through the cavitation model in Fluent 6.2, the flow field around cavitator under different incoming conditions is studied respectively, and analyses to parameters pertinent to cavity including dimension, streamlines, vapor volume fractions and pressure distributions along the body surface are given when the incoming cavitation number ranges from 0.3 to 0.8, the results show that the vapor volume fraction and threshold phase-change pressure within the cavity under the same cavitation number gradually ascends as the Reynolds number increases ; the effects of incoming pressure on threshold phase-change pressure inside the cavity is insignificant.
4
Soyama, Hitoshi. "Cavitating Jet: A Review". Applied Sciences 10, n. 20 (17 ottobre 2020): 7280. http://dx.doi.org/10.3390/app10207280.
Testo completoAbstract (sommario):
When a high-speed water jet is injected into water through a nozzle, cavitation is generated in the nozzle and/or shear layer around the jet. A jet with cavitation is called a “cavitating jet”. When the cavitating jet is injected into a surface, cavitation is collapsed, producing impacts. Although cavitation impacts are harmful to hydraulic machinery, impacts produced by cavitating jets are utilized for cleaning, drilling and cavitation peening, which is a mechanical surface treatment to improve the fatigue strength of metallic materials in the same way as shot peening. When a cavitating jet is optimized, the peening intensity of the cavitating jet is larger than that of water jet peening, in which water column impacts are used. In order to optimize the cavitating jet, an understanding of the instabilities of the cavitating jet is required. In the present review, the unsteady behavior of vortex cavitation is visualized, and key parameters such as injection pressure, cavitation number and sound velocity in cavitating flow field are discussed, then the estimation methods of the aggressive intensity of the jet are summarized.
5
Wang, Hao, Jian Feng, Keyang Liu, Xi Shen, Bin Xu, Desheng Zhang e Weibin Zhang. "Experimental Study on Unsteady Cavitating Flow and Its Instability in Liquid Rocket Engine Inducer". Journal of Marine Science and Engineering 10, n. 6 (12 giugno 2022): 806. http://dx.doi.org/10.3390/jmse10060806.
Testo completoAbstract (sommario):
To study instability in the unsteady cavitating flow in a liquid rocket engine inducer, visualization experiments of non-cavitating and cavitating flows inside a model inducer were carried out at different flow conditions. Visual experiments were carried out to capture the evolution of non-cavitating and cavitating flows in a three-bladed inducer by using a high-speed camera. The external characteristic performance, cavitation performance, and pressure pulsation were analyzed based on the observation of non-cavitation and cavitation development and their instabilities. Under non-cavitation conditions, the change of flow rate has a significant impact on the pressure pulsation characteristics in the inducer. The occurrence of cavitation aggravated the instability of the flow and caused the intensity of pressure pulsation at each measuring point to increase. This cavitation structure has strong instability, and the tail region is often accompanied by shedding cavitation clouds perpendicular to the blade surface.
6
Liu, Qian Kun, e Ye Gao. "Numerical Simulation of Natural Cavitating Flow over Axisymmetric Bodies". Applied Mechanics and Materials 226-228 (novembre 2012): 825–30. http://dx.doi.org/10.4028/www.scientific.net/amm.226-228.825.
Testo completoAbstract (sommario):
The hydrodynamic characteristics of bodies are greatly affected by cavitation. Coupling with natural cavitaion model, a multiphase CFD method is developed and is employed to simulate supercavitating and partial cavitating flows over axisymmetric bodies using FLUENT 6.2. The results of supercavitation of a disk cavitator agree well with the boundary element method (BEM), the analytical relations and available experimental results. The present computations and the BEM results are compared with experiments for partial cavitating flows over three typical axisymmetric bodies and the results are discussed. Limitations are on the pressure prediction in the cavity closure region for the BEM, although fairly good quantitative agreement is obtained for three axisymmetric bodies at most of cavitation region. The present computational model on cavitating flows are validated, offering references and bases for hydrodynamic researches.
7
Lee, Insu, Sunho Park, Woochan Seok e Shin Hyung Rhee. "A Study on the Cavitation Model for the Cavitating Flow Analysis around the Marine Propeller". Mathematical Problems in Engineering 2021 (17 giugno 2021): 1–8. http://dx.doi.org/10.1155/2021/2423784.
Testo completoAbstract (sommario):
In this study, a cavitation model for propeller analysis was selected using computational fluid dynamics (CFD), and the model was applied to the cavitating flow around the Potsdam Propeller Test Case (PPTC) propeller. The cavitating flow around the NACA 66 hydrofoil was analyzed to select a cavitation model suitable for propeller analysis among various cavitation models. The present and the experimental results were compared to select a cavitation model that would be applied to propeller cavitation analysis. Although the CFD results using the selected cavitation model showed limitations in estimating some of the foam cavitation and bubble cavitation identified in the experimental results, it was identified that foam cavitation and sheet cavitation around the tip were well simulated.
8
Xu, Gaowei, Huimin Fang, Yumin Song e Wensheng Du. "Optimal Design and Analysis of Cavitating Law for Well-Cellar Cavitating Mechanism Based on MBD-DEM Bidirectional Coupling Model". Agriculture 13, n. 1 (5 gennaio 2023): 142. http://dx.doi.org/10.3390/agriculture13010142.
Testo completoAbstract (sommario):
A variable velocity parallel four-bar cavitating mechanism for well-cellar can form the well-cellar cavitation which suits for well-cellar transplanting under a continuous operation. In order to improve the cavitating quality, this paper analyzed the structural composition and working principle of the cavitating mechanism and established the bidirectional coupling model of multi-body dynamics and the discrete element between the cavitating mechanism and soil through Recurdyn and EDEM software. Based on the model, a three-factor, five-level quadratic orthogonal rotational combination design test was conducted with the parameters of the cavitating mechanism as the experimental factors and the parameters of the cavitation as the response index to obtain the optimal parameter combination, and a virtual simulation test was conducted for the optimal parameter combination in order to study the cavitating law of the cavitating mechanism and soil. The test results showed that the depth of the cavitation was 188.6 mm, the vertical angle of the cavitation was 90.4°, the maximum diameter of the cavitation was 76.1 mm, the minimum diameter of the cavitation was 68.5 mm, and the variance in the diameters for the cavitation was 5.42 mm2. The cavitating mechanism with optimal parameters based on the Recurdyn–EDEM bidirectional coupling mode could further improve the cavitating quality.
9
Cui, Baoling, e Jie Chen. "Visual experiment and numerical simulation of cavitation instability in a high-speed inducer". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 234, n. 4 (6 agosto 2019): 470–80. http://dx.doi.org/10.1177/0957650919867173.
Testo completoAbstract (sommario):
Cavitation instabilities in a high-speed inducer at a design flow rate were investigated for different cavitation numbers in numerical simulations and visual experiments. On the basis of a shear stress transport k–ω turbulence model and Zwart–Gerber–Belamri cavitation model, the transient cavitating flow in a high-speed centrifugal pump with an inducer is numerically simulated using ANSYS-CFX 15.0 software. Visual experiments were carried out to capture the evolution of cavitating flow in the inducer by using a high-speed camera. The performance and cavitation characteristic curves from numerical simulation agree with those from experiment. With a decreasing cavitation number, the cavitation development in the high-speed inducer goes through incipient cavitation, developing cavitation, critical cavitation, and deteriorated cavitation and presents vortex cavitation, sheet cavitation, cloud cavitation, backflow cavitation, and a cavitation surge. The region having a high vapor volume fraction basically coincides with the region of low local pressure at the same cavitation number. The position of largish blade loading on the inducer changes with the development of cavitation. A cavitation surge as one type of cavitation instability appears in the inducer at lower cavitation numbers. The drop or rise of the head coefficient is affected by an increasing or decreasing cavitation area in the cycle of a cavitation surge.
10
ZHANG, YAO, XIANWU LUO, SHUHONG LIU e HONGYUAN XU. "A TRANSPORT EQUATION MODEL FOR SIMULATING CAVITATION FLOWS IN MINIATURE MACHINES". Modern Physics Letters B 24, n. 13 (30 maggio 2010): 1467–70. http://dx.doi.org/10.1142/s0217984910023888.
Testo completoAbstract (sommario):
A new transport equation model is proposed for simulating cavitating flows in miniature machines. In the developed model, the surface tension, viscous force, and thermal effect of cavitation are considered to reflect their influence on the cavitation bubble growth. The cavitating flow in a miniature pump is calculated by applying the proposed cavitation model. The comparison between numerical results and experimental data indicates that the new cavitation model is applicable for simulating the cavitating flow in miniature machines.
11
Lin, Yuxing, Ebrahim Kadivar e Ould el Moctar. "Experimental Study of the Cavitation Effects on Hydrodynamic Behavior of a Circular Cylinder at Different Cavitation Regimes". Fluids 8, n. 6 (23 maggio 2023): 162. http://dx.doi.org/10.3390/fluids8060162.
Testo completoAbstract (sommario):
In this work, we experimentally investigated the cavitation effects on the hydrodynamic behavior of a circular cylinder at different cavitating flows. We analyzed the cavitation dynamics behind the circular cylinder using a high-speed camera and also measured the associated hydrodynamic forces on the circular cylinder using a load cell. We studied the cavitation dynamics around the cylinder at various types of the cavitating regimes such as cloud cavitation, partial cavitation and cavitation inception. In addition, we analyzed the cavitation dynamics at three different Reynolds numbers: 1 × 105, 1.25 × 105 and 1.5 × 105. The results showed that the hydrodynamics force on the circular cylinder can be increased with the formation of the cavitation behind the cylinder compared with the cylinder at cavitation inception regime. The three-dimensional flow caused complex cavitation behavior behind the cylinder and a strong interaction between vortex structures and cavity shedding mechanism. In addition, the results revealed that the effects of the Reynolds number on the cavitation dynamics and amplitude of the shedding frequency is significant. However the effects of the cavitation number on the enhancement of the amplitude of the shedding frequency in the cavitating flow with a constant velocity is slightly higher than the effects of Reynolds number on the enhancement of the amplitude of the shedding frequency at a constant cavitation number.
12
Cai, Cindy X., John Choong, Sina Farsiu, Stephanie J. Chiu, Emily Y. Chew e Glenn J. Jaffe. "Retinal cavitations in macular telangiectasia type 2 (MacTel): longitudinal structure–function correlations". British Journal of Ophthalmology 105, n. 1 (9 marzo 2020): 109–12. http://dx.doi.org/10.1136/bjophthalmol-2019-315416.
Testo completoAbstract (sommario):
Background/aimsTo quantify retinal cavitation size over time in macular telangiectasia type 2 (MacTel) and to correlate changes with visual acuity and area of ellipsoid zone loss.MethodsOptical coherence tomography (OCT) macula volume scans from sham eyes included in a prospective, phase II clinical trial of human ciliary neutrophic factor for MacTel at baseline, 1 year and 2 years of follow-up were analysed. Cavitations were segmented by two independent readers. Total cavitation volume was compared with area of ellipsoid zone loss and best-corrected visual acuity (BCVA).ResultsFifty-one eyes from 51 unique patients (mean age 62 years, range 45–79 years) were included. Intraclass correlation between readers for cavitation volume was excellent (>0.99). Average cavitation volume was 0.0109 mm3, 0.0113 mm3 and 0.0124 mm3 at baseline, 1 year and 2 years, respectively. The average rate of cavitation volume change was +0.0039 mm3/year. 10 eyes (20%) had a significant change in cavitation volume during the study (3 decreased, 7 increased). Eyes with increased cavitation volume had worse BCVA compared with eyes with no change/decreased cavitation volume (71.5 vs 76.1 ETDRS letters, respectively). Cavitation volume was negatively correlated to BCVA (r=−0.37) but not to area of ellipsoid zone loss. Cavitation volume was negatively predictive of BCVA in both univariate and multivariate mixed-effects modelling with ellipsoid zone loss.ConclusionsRetinal cavitations and their rate of change in MacTel can be reliably quantified using OCT. Cavitations are negatively correlated with visual acuity and may be a useful OCT-based biomarker for disease progression and visual function in MacTel.
13
Dolgopolov, S. I. "Determining the coefficients of a hydrodynamic model of cavitating pumps of liquid-propellant rocket engines from their theoretical transfer matrices". Technical mechanics 2024, n. 1 (11 aprile 2024): 16–25. http://dx.doi.org/10.15407/itm2024.01.016.
Testo completoAbstract (sommario):
The characterization of cavitating pumps of liquid-propellant rocket engines (LPRE) is an important problem because of the need to provide the pogo stability of liquid-propellant launch vehicles and the stability of liquid-propellant propulsion systems for cavitation oscillations. The development of a reliable mathematical model of LPRE cavitating pumps allows this problem to be resolved. The goal of this work is to determine the cavitation number and operating parameter dependences of the coefficients of a lumped-parameter hydrodynamic model of LPRE cavitating pumps from their theoretical transfer matrices obtained by a distributed-parameter model. The following coefficients are found as a function of operating parameters: the cavitation elasticity, the cavitation resistance, the cavity-caused disturbance transfer delay time, and the cavitation resistance distribution coefficient. The last two coefficients are new in the hydrodynamic model of cavitating pumps, and they were introduced when verifying the model using experimental and theoretical pump transfer matrices. Analyzing the cavitation resistance distribution coefficient as a function of operating parameters shows that it markedly decreases with increasing cavitation number. This testifies to that the location of the lumped cavity compliance is shifted from the mid position towards the pump inlet. Therefore, the assumption that the lumped cavity compliance is located in the middle of the attached cavity regardless of the cavitation number is not justified. The fact that the distribution coefficient as a function of cavitation number intersects the abscissa axis near a cavitation number of 0.25 may indicate the boundary of existence of attached cavities and thus the applicability boundary of the theoretical model. The disturbance transfer delay time as a function of cavitation number sharply increases at cavitation numbers of about 0.05. At cavitation numbers of about 0.25, it is close to a constant.
14
Lu, L., J. Zou, X. Fu, X. D. Ruan, X. W. Du, S. Ryu e M. Ochiai. "Cavitating flow in non-circular opening spool valves with U-grooves". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 223, n. 10 (12 giugno 2009): 2297–307. http://dx.doi.org/10.1243/09544062jmes1504.
Testo completoAbstract (sommario):
Cavitating flow in non-circular opening spool valves with U-grooves has been investigated in this article. Multifarious cavitating properties, including acoustic cavitation, morphologic cavitation, and discharge performance with cavitation, are investigated, the correlations of which are discussed. The critical opening condition in each valve is obtained based on the analysis of a throttling model. It is found that the cavitating properties show remarkable differences in the two situations when the opening is larger and smaller than the critical opening. Additionally, cavitation impacts on the discharge performance are investigated with the assistance of acoustic and visual detection.
15
Gao, Bo, Pengming Guo, Ning Zhang, Zhong Li e Minguan Yang. "Experimental Investigation on Cavitating Flow Induced Vibration Characteristics of a Low Specific Speed Centrifugal Pump". Shock and Vibration 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/6568930.
Testo completoAbstract (sommario):
Cavitating flow developing in the blade channels is detrimental to the stable operation of centrifugal pumps, so it is essential to detect cavitation and avoid the unexpected results. The present paper concentrates on cavitation induced vibration characteristics, and special attention is laid on vibration energy in low frequency band, 10–500 Hz. The correlation between cavitating evolution and the corresponding vibration energy in 10–500 Hz frequency band is discussed through visualization analysis. Results show that the varying trend of vibration energy in low frequency band is unique compared with the high frequency band. With cavitation number decreasing, vibration energy reaches a local maximum at a cavitation number much larger than the 3% head drop point; after that it decreases. The varying trend is closely associated with the corresponding cavitation status. With cavitation number decreasing, cavitation could be divided into four stages. The decreasing of vibration energy, in particular cavitation number range, is caused by the partial compressible cavitation structure. From cavitation induced vibration characteristics, vibration energy rises much earlier than the usual 3% head drop criterion, and it indicates that cavitation could be detected in advance and effectively by means of cavitation induced vibration characteristics.
16
Zhao, Wei Guo, Xiao Xia He, Xiu Yong Wang e Yi Bin Li. "Numerical Simulation of Cavitation Flow in a Centrifugal Pump". Applied Mechanics and Materials 444-445 (ottobre 2013): 509–16. http://dx.doi.org/10.4028/www.scientific.net/amm.444-445.509.
Testo completoAbstract (sommario):
Based on two phase homogeneous mixture model, numerical simulation of the cavitating flow was performed on a centrifugal pump. Cavity shapes and performance of the pump in variable cavitation numbers were obtained. Numerical results show that the numerical method can be used to predict the cavitation performance of centrifugal pump; the incipient cavitation number is predicted, and the cavity shape is similar with the experiment; cavitation usually appears in the suction surface of the blade and locates in the inlet side, and becomes longer to the outlet direction with lower cavitation number; when the cavitation number is relatively higher, cavitating region locates in the inlet area of the blade and is relatively stable, while develops and separates when cavitation number becomes lower; when the cavitation number equals to the incipient cavitation number, performance of the centrifugal pump has no change almost, only when cavitation number reduces to some extent, the head decreases abruptly and also the efficiency, which means the pump operates in a bad condition and this condition should be avoided in the practical operation.
17
Huang, D. G., e Y. Q. Zhuang. "Temperature and cavitation". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 222, n. 2 (1 febbraio 2008): 207–11. http://dx.doi.org/10.1243/09544062jmes815.
Testo completoAbstract (sommario):
Pressure, density, and temperature are the fundamental thermodynamic parameters. In a liquid flow field, once the local pressure drops to the saturated pressure, the liquid vapourizes and local cavitation occurs. The cavitation region of the flow is characterized by a mixture of liquid and vapour. Vapourization is an endothermic process. However, in the literature of the past several decades, this vapourization induced thermal effect was sometimes ignored in cavitating flows, and the temperature was always assumed as a constant in the whole flow field. In order to gain a deep insight into the mechanism of cavitation, temperature effects of cavitation are hereby investigated in this paper. An appreciable temperature drop has been found when cavitation occurs, which suggests that thermal effects in cavitating flows from the view of thermodynamics may be of great value to understand the mechanism of cavitation.
18
KHOO, B. C., e J. G. ZHENG. "THE NUMERICAL SIMULATION OF UNSTEADY CAVITATION EVOLUTION INDUCED BY PRESSURE WAVE". International Journal of Modern Physics: Conference Series 34 (gennaio 2014): 1460374. http://dx.doi.org/10.1142/s2010194514603743.
Testo completoAbstract (sommario):
The present study is focused on the numerical simulation of pressure wave propagation through the cavitating compressible liquid flow, its interaction with cavitation bubble and the resulting unsteady cavitation evolution. The compressibility effects of liquid water are taken into account and the cavitating flow is governed by one-fluid cavitation model which is based on the compressible Euler equations with the assumption that the cavitation is the homogeneous mixture of liquid and vapour which are locally under both kinetic and thermodynamic equilibrium. Several aspects of the method employed to solve the governing equations are outlined. The unsteady features of cavitating flow due to the external perturbation, such as the cavitation deformation and collapse and consequent pressure increase are resolved numerically and discussed in detail. It is observed that the cavitation bubble collapse is accompanied by the huge pressure surge of order of 100 bar, which is thought to be responsible for the material erosion, noise, vibration and loss of efficiency of operating underwater devices.
19
Soyama, Hitoshi, e Mitsuhiro Mikami. "Improvement of Fatigue Strength of Stainless Steel by Using a Cavitating Jet with an Associated Water Jet in Water". Key Engineering Materials 353-358 (settembre 2007): 162–65. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.162.
Testo completoAbstract (sommario):
Peening method using cavitation impacts have been developed. In this peening method, cavitation bubbles were generated by a cavitating jet. In order to increase peening intensity, a low speed water jet was injected around a cavitating jet, as the water jet swept away residual bubbles, which weaken the cavitation impact. In the present paper, improvement of fatigue strength of stainless steel by using a cavitating jet with an associated water jet was investigated compared with the results of conventional cavitating jet. It was concluded that the cavitating jet with an associated water jet can peen the stainless steel more effectively compared with the conventional cavitating jet.
20
Zhang, Hu, Jun Wang, Desheng Zhang, Weidong Shi e Jianbo Zang. "Numerical Analysis of the Effect of Cavitation on the Tip Leakage Vortex in an Axial-Flow Pump". Journal of Marine Science and Engineering 9, n. 7 (16 luglio 2021): 775. http://dx.doi.org/10.3390/jmse9070775.
Testo completoAbstract (sommario):
To understand the effect of cavitation on the tip leakage vortex (TLV), turbulent cavitating flows were numerically investigated using the shear-stress transport (SST) k–ω turbulence model and the Zwart–Gerber–Belamri cavitation model. In this work, two computations were performed—one without cavitation and the other with cavitation—by changing the inlet pressure of the pump. The results showed that cavitation had little effect on the pressure difference between the blade surfaces for a certain cavitation number. Instead, it changed the clearance flow and TLV vortex structure. Cavitation caused the TLV core trajectory to be farther from the suction surface and closer to the endwall upstream of the blade. Cavitation also changed the vortex strength distribution, making the vortex more dispersed. The vortex flow velocity and turbulent kinetic energy were lower, and the pressure pulsation was more intense in the cavitating case. The vorticity transport equation was used to further analyze the influence of cavitation on the evolution of vortices. Cavitation could change the vortex stretching term and delay the vortex bending term. In addition, the vortex dilation term was drastically changed at the vapor–liquid interface.
21
Hong, Feng, Jianping Yuan, Banglun Zhou e Zhong Li. "Modeling of unsteady structure of sheet/cloud cavitation around a two-dimensional stationary hydrofoil". Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 231, n. 3 (7 ottobre 2015): 455–69. http://dx.doi.org/10.1177/0954408915607390.
Testo completoAbstract (sommario):
Compared to non-cavitating flow, cavitating flow is much complex owing to the numerical difficulties caused by cavity generation and collapse. In the present work, cavitating flow around a two-dimensional Clark-Y hydrofoil is studied numerically with particular emphasis on understanding the cavitation structures and the shedding dynamics. A cavitation model, coupled with the mixture multi-phase approach, and the modified shear stress transport k-ω turbulence model has been developed and implemented in this study to calculate the pressure, velocity, and vapor volume fraction of the hydrofoil. The cavitation model has been implemented in ANSYS FLUENT platform. The hydrofoil has a fixed angle of attack of α = 8° with a Reynolds number of Re = 7.5 × 105. Simulations have been carried out for various cavitation numbers ranging from non-cavitating flows to the cloud cavitation regime. In particular, we compared the lift and drag coefficients, the cavitation dynamics, and the time-averaged velocity with available experimental data. The comparisons between the numerical and experimental results show that the present numerical method is capable to predict the formation, breakup, shedding, and collapse of the sheet/cloud cavity. The periodical formation, shedding, and collapse of sheet/cloud cavity lead to substantial increase in turbulent velocity fluctuations in the cavitation regimes around the hydrofoil and in the wake flow.
22
Li, Tao, Bin Liu, Jinzhi Zhou, Wenxuan Xi, Xiulan Huai e Hang Zhang. "A Comparative Study of Cavitation Characteristics of Nano-Fluid and Deionized Water in Micro-Channels". Micromachines 11, n. 3 (16 marzo 2020): 310. http://dx.doi.org/10.3390/mi11030310.
Testo completoAbstract (sommario):
Hydrodynamic cavitation has been widely applied in micro-fluidic systems. Cavitating flow characteristics are closely related to the fluid properties. In this paper, the cavitation characteristics of Cu nano-fluid in micro-channels were numerically investigated and compared with those of the deionized (DI) water. The mathematical model was verified by comparing the numerical results with the experiment observation. The curved orifice (R = 0.3 mm) was found to have the highest efficiencies of cavitation for both fluids. With the increase of inlet pressure, cavitating jet lengths of the two fluids significantly increased. While, the cavitating jet length of the nano-fluid was shorter than that of the DI water at the same inlet pressure. The cavitation inception number of the DI water and nano-fluid were approximately 0.061 and 0.039, respectively. The results indicate that the nano-particles played negative effects on the cavitation inception. In addition, with the decrease of outlet pressure, the cavitation strength gradually increased and the mass flow rate remained nearly unchanged at the same time.
23
Wei, Aibo, Shunhao Wang, Xu Gao, Limin Qiu, Lianyan Yu e Xiaobin Zhang. "Investigation of unsteady cryogenic cavitating flow and induced noise around a three-dimensional hydrofoil". Physics of Fluids 34, n. 4 (aprile 2022): 042120. http://dx.doi.org/10.1063/5.0088092.
Testo completoAbstract (sommario):
In this paper, the Large Eddy Simulation (LES) combined with the Schnerr–Sauer cavitation model and the permeable Ffowcs Williams–Hawkings (FW-Hpds) acoustic analogy approach are introduced to study the unsteady cavitation behaviors and the radiated noise characteristics of the transient liquid nitrogen (LN2) cavitating flow around a NACA66 (National Advisory Committee for Aeronautics) hydrofoil. Satisfactory agreement is obtained between the numerical predictions and experimental measurements. The cavitation noise is predicted based on the sound radiation theory for spherical bubbles and compared with the sound pressure levels of non-cavitating flow from the FW-Hpds equation. It is found that the cavity volume acceleration is directly responsible for driving the generation of cavitation noise, and the sound pressure caused by the development of LN2 cavitation is shown to vary with the periodic pulsing cavity volume evolution, indicating a strong link between cavity evolutions and radiated noises. The transient cavitation structures of the sheet and cloud cavitation are well captured, and the evolution features of the cavities and vortex structures are analyzed in detail. The collapse of the detached small cloud cavity downstream is the main mechanism for generating intense acoustic impulses for both sheet and cloud cavitation. While the strong interaction between the re-entrant jet and the main flow results in violent pressure fluctuations, and thus produces instantaneous extreme dipole noise, which accounts for another distinctive mechanism to induce intense acoustic impulses for cloud cavitation, the presented study provides a deep understanding of the nature of cavitation-dominated noise for cryogenic cavitating flow.
24
Dolgopolov, S. I. "Verification of a hydrodynamic model of a liquid-propellant rocket engine’s cavitating pumps using experimental and theoretical pump transfer matrices". Technical mechanics 2020, n. 3 (15 ottobre 2020): 18–29. http://dx.doi.org/10.15407/itm2020.03.018.
Testo completoAbstract (sommario):
Cavities at the pump inlet may lead to inadmissible cavitation self-oscillations in the feed system of liquid-propellant rocket engines (LPREs) and to POGO instability if the oscillation frequency of the liquid is close to that of the rocket structure. Because of this, it is important to prevent both cavitation and POGO oscillations as early as at the engine and rocket design stage. This calls for a reliable mathematical model of the dynamics of LPRE cavitating pumps. In this paper, a hydrodynamic model of LPRE cavitating pumps is verified using theoretical and experimental transfer matrices of cavitating pumps. The experimental transfer matrix was borrowed from Brennen, Meissner, Lo, and Hoffman’s work because it features the least spread of values among the matrices reported in the literature. The theoretical matrix was borrowed from Pilpenko and Kvasha’s work where is was constructed for a cavitating pump as a distributed-parameter system. Four versions of the hydrodynamic model of LPRE cavitating pumps are verified, and six possible model coefficients are considered. Only one coefficient, namely, the liquid inertance at the cavity location, takes a physically meaningless negative value, which makes its use impossible. The verification results show that a four-coefficient model of cavitating pipe dynamics adequately describes cavitation effects in LPRE pumps over the frequency range up to 200 Hz. The four coefficients are the cavitation elasticity, the cavitation resistance, the cavity-caused disturbance transfer delay time, and the cavity time constant or the cavitation resistance distribution coefficient.
25
Li, Hong, Zhenhua Shen, Nicholas Engen Pedersen e Christian Brix Jacobsen. "Experimental and unsteady numerical research of a high-specific-speed pump for part-load cavitation instability". Advances in Mechanical Engineering 11, n. 3 (marzo 2019): 168781401982893. http://dx.doi.org/10.1177/1687814019828932.
Testo completoAbstract (sommario):
Net positive suction head peak is a well-known cavitation instability phenomenon in high-specific-speed pumps. Both non-cavitating performance and cavitating performance of a high-specific-speed pump were investigated by experiments and numerical simulations. According to the cavitating performance results, net positive suction head peak is found at 80% of nominal flow. The head curves of non-cavitating performance also have saddle-type instabilities near 70%–80% of nominal flow. Water vapor volume fraction distributions show that cavitation region at net positive suction head peak flow only covers 3% of the blade length when head drops 6%. It proves that net positive suction head peak is not caused by huge amounts of cavitation bubbles, which indicates that net positive suction head peak does not represent excessive cavitation. The velocity vector and pressure distribution plots reveal that net positive suction head peak is related to recirculation near the trailing edge. With inlet pressure decreasing, the flow pattern is sensitive to the cavitation bubbles, and recirculation region from the pressure side to the suction side becomes larger and larger.
26
Amromin, E. L. "STATE-OF-THE ART IN COMPUTATIONAL ANALYSIS OF CAVITATION INCEPTION AND ITS SCALE EFFECTS". International Journal of Maritime Engineering 164, A4 (3 aprile 2023): 385–96. http://dx.doi.org/10.5750/ijme.v164ia4.814.
Testo completoAbstract (sommario):
Mathematical analysis of cavitation inception is an important topic for naval engineering, but several circumstances make it difficult. First, cavitating flows are substantially multi-zone flows, where the appearing cavities are incomparably smaller than a cavitating body is. Second, inception is substantially influenced by characteristics of the inflow and of the body surfaces. Third, validation of employed mathematical methods by comparison with experimental data is a non-trivial task because of the complexity of experiments themselves and scale effects. This paper is emphasized on multi-zone quasi-steady approaches for prediction of cavitation inception and desinence numbers. The obtained computational results are compared with the known experimental data for sheet cavitation, vortex cavitation and cavitation behind surface irregularities. Procedures of scaling of cavitation inception number and the eventual combinations of various CFD solvers are also discussed.
27
Jasionowski, R., W. Polkowski e D. Zasada. "Destruction Mechanism of ZnAl4 as Cast Alloy Subjected to Cavitational Erosion Using Different Laboratory Stands". Archives of Foundry Engineering 16, n. 1 (1 marzo 2016): 19–24. http://dx.doi.org/10.1515/afe-2015-0096.
Testo completoAbstract (sommario):
Abstract The main reason of a cavitational destruction is the mechanical action of cavitation pulses onto the material’s surface. The course of cavitation destruction process is very complex and depends on the physicochemical and structural features of a material. A resistance to cavitation destruction of the material increases with the increase of its mechanical strength, fatigue resistance as well as hardness. Nevertheless, the effect of structural features on the material’s cavitational resistance has been not fully clarified. In the present paper, the cavitation destruction of ZnAl4 as cast alloy was investigated on three laboratory stands: vibration, jet-impact and flow stands. The destruction mechanism of ZnAl4 as cast alloy subjected to cavitational erosion using various laboratory stands is shown in the present paper.
28
Rhee, Shin Hyung, Takafumi Kawamura e Huiying Li. "Propeller Cavitation Study Using an Unstructured Grid Based Navier-Stoker Solver". Journal of Fluids Engineering 127, n. 5 (2 maggio 2005): 986–94. http://dx.doi.org/10.1115/1.1989370.
Testo completoAbstract (sommario):
The cavitating flow around a marine propeller is studied using an unstructured grid based Reynolds-averaged Navier-Stokes computational fluid dynamics method. A cavitation model based on a single-fluid multi-phase flow method is implemented in the Navier-Stokes solver. The proposed computational approach for cavitation is validated against a benchmark database for a cavitating hydrofoil as well as measured data for a cavitating marine propeller. The leading edge and mid-chord cavitation on the hydrofoil is reproduced well and shows good comparison with the well-known experimental data. The predicted noncavitating open water performance of the marine propeller geometry agrees well with the measured one. Finally, the cavitating propeller performance as well as cavitation inception and cavity shape are in good agreement with experimental measurements and observation. The overall results suggest that the present approach is practicable for actual cavitating propeller design procedures without lengthy preprocessing and significant preliminary knowledge of the flow field.
29
Soyama, Hitoshi. "High-Speed Observation of a Cavitating Jet in Air". Journal of Fluids Engineering 127, n. 6 (14 luglio 2005): 1095–101. http://dx.doi.org/10.1115/1.2060737.
Testo completoAbstract (sommario):
The use of cavitation impact is a practical method for improving the fatigue strength of metals in the same way as shot peening. In the case of peening using cavitation impact, cavitation is produced by a high-speed submerged water jet with cavitation, i.e., a cavitating jet. A cavitating jet in air was successfully generated by injecting a high-speed water jet into a low-speed water jet injected into air using a concentric nozzle. In order to investigate the various appearances of cavitating jets in air, an observation was carried out using high-speed photography and high-speed video recording. In this study, periodical shading of the cavitation cloud was observed and the frequency of the shading was found to be a function of the injection pressure of the low-speed water jet. Unsteadiness of the low-speed water jet, which is related to the periodical shading of the cloud, was also observed.
30
Soyama, H., J. D. Park e M. Saka. "Use of Cavitating Jet for Introducing Compressive Residual Stress". Journal of Manufacturing Science and Engineering 122, n. 1 (1 settembre 1999): 83–89. http://dx.doi.org/10.1115/1.538911.
Testo completoAbstract (sommario):
In an attempt to strengthen the surface of materials, the potential of using a cavitating jet to form compressive residual stress has been investigated. Introducing compressive residual stress to a material surface provides improvement of the fatigue strength and resistance to stress corrosion cracking. In general, cavitation causes damage to hydraulic machinery. However, cavitation impact can be used to form compressive residual stress in the same way as shot peening. In the initial stage, when cavitation erosion progresses, only plastic deformation, without mass loss, takes place on the material surface. Thus, it is possible to form compressive residual stress without any damage by considering the intensity and exposure time of the cavitation attack. Cavitation is also induced by ultrasonic, high-speed water tunnel and high-speed submerged water jet, i.e., a cavitating jet. The great advantage of a cavitating jet is that the jet causes the cavitation wherever the cavitation impact is required. To obtain the optimum condition for the formation of compressive residual stress by using a cavitating jet, the residual stresses on stainless steel (JIS SUS304 and SUS316) and also copper (JIS C1100) have been examined by changing the exposure time of the cavitating jet. The in-plane normal stresses were measured in three different directions on the surface plane using the X-ray diffraction method, allowing for the principal stresses to be calculated. Both of the principal stresses are found changing from tension to compression within a 10 s exposure to the cavitating jet. The compressive residual stress as a result of the cavitating jet was found to be saturated after a certain time, but it starts decreasing, and finally, it approaches zero asymptotically. It could be verified in the present study that it was possible to form compressive residual stress by using a cavitating jet, and the optimum processing time could also be realized. The great difference between the water jet in water and air has also been shown in this regard. [S1087-1357(00)00501-3]
31
Jasionowski, Robert, Dariusz Zasada e Wojciech Polkowski. "The Evaluation of the Cavitational Damage in MgAl2Si Alloy Using Various Laboratory Stands". Solid State Phenomena 252 (luglio 2016): 61–70. http://dx.doi.org/10.4028/www.scientific.net/ssp.252.61.
Testo completoAbstract (sommario):
Evaluation of cavitation erosion resistance of is carried out by using various testing stands, that differ by the way of cavitation excitation and its intensity. These various testing conditions have led to a standardization of some part of laboratory stands, that in turn allows a direct comparison of results obtained in different laboratories. The aim of this study was to determine the course of cavitational destruction of MgAl2Si alloy samples tested on three different laboratory stands. The research was conducted on a vibration stand according to ASTM G32, where cavitation is forced by the vibrating element; in the cavitation tunnel reflecting actual flow conditions, and on a jet impact stand- simulating the impact microjet in the final phase of the cavitational bubbles implosion. Each laboratory stand has given a different course of cavitational destruction.
32
Wang, Zhe, Ruizhi Zhang, Jiajian Zhou e Xianwu Luo. "Cavitating flow investigation in low specific speed axial flow waterjet pumps". Journal of Physics: Conference Series 2217, n. 1 (1 aprile 2022): 012008. http://dx.doi.org/10.1088/1742-6596/2217/1/012008.
Testo completoAbstract (sommario):
Abstract In this paper, the cavitating flow in low specific speed axial flow waterjet pumps are treated at different cavitation conditions. In order to analyze the cavitating turbulent flow comprehensively, three axial flow waterjet pumps with the specific speed less than 650 min-1·m3s-1·m are chosen to compare the internal flow phenomenon. The investigations are conducted by numerical simulation, where RANS method is applied with k-ω SST turbulence model and homogeneous cavitation model. The results show that there are several types of cavitation such as tip leakage vortex cavitation, sheet cavitation attached on blade suction surface, and shedding cavity in the pumps. The vortex structure in the low specific speed waterjet pump contains tip leakage vortex, shedding vortex downstream of the sheet cavitation and perpendicular cavitation vortex. It is noted that the cavity firstly occurs at the leading edge near blade tip, and the sheet cavity covering the blade suction surface extends from leading edge to the middle part, while the tip leakage vortex cavitation develops with the decreasing cavitation number. Further analysis using relative vortex transport equation depicts that the vortex stretching term is the main contributor for the vorticity production in the pump, and the vortex dilation and baroclinic torque occur at the interface between cavity and water.
33
Laborde, R., P. Chantrel e M. Mory. "Tip Clearance and Tip Vortex Cavitation in an Axial Flow Pump". Journal of Fluids Engineering 119, n. 3 (1 settembre 1997): 680–85. http://dx.doi.org/10.1115/1.2819298.
Testo completoAbstract (sommario):
A combined study of tip clearance and tip vortex cavitations in a pump-type rotating machine is presented. Cavitation patterns are observed and cavitation inception is determined for various gap heights, clearance and blade geometries, and rotor operating conditions. An optimum clearance geometry is seen to eliminate clearance cavitation when the clearance edge is rounded on the blade pressure side. The gap height has a strong effect on clearance cavitation inception, but the trends vary considerably when other parameters are also modified. The gap height and clearance geometry have less influence on tip vortex cavitation but forward and backward blade skew is observed to reduce and increase tip vortex cavitation, respectively, as compared to a blade with no skew.
34
Zhang, De-Sheng, Hai-Yu Wang, Lin-Lin Geng e Wei-Dong Shi. "Detached eddy simulation of unsteady cavitation and pressure fluctuation around 3-D NACA66 hydrofoil". Thermal Science 19, n. 4 (2015): 1231–34. http://dx.doi.org/10.2298/tsci1504231z.
Testo completoAbstract (sommario):
The unsteady cavitating flow and pressure fluctuation around the 3-D NACA66 hydrofoil were simulated and validated based on detached eddy simulation turbulence model and a homogeneous cavitation model. Numerical results show that detached eddy simulation can predict the evolution of cavity inception, sheet cavitation growth, cloud cavitation shedding, and breakup, as well as the pressure fluctuation on the surface of hydrofoil. The sheet cavitation growth, detachment, cloud cavitation shedding are responsible for the features of the pressure fluctuation.
35
Major Md. Nur-E-Mostafa, Eare Md Morshed Alam e Mohammad Monir Uddin. "Numerical Analysis of Cavitating Flow on Hydrofoil". MIST INTERNATIONAL JOURNAL OF SCIENCE AND TECHNOLOGY 10 (29 dicembre 2022): 11–19. http://dx.doi.org/10.47981/j.mijst.10(03)2022.351(11-19).
Testo completoAbstract (sommario):
Numerical study is presented in this work for turbulent cavitating flow pattern simulation on a hydrofoil, using state equation of cavitation model along with combined turbulence model for mixed fluid based on commercial software FLUENT 6.0. This solver is based on finite volume method. Cavitating study yield irregular behavior with the variation of cavitation values ( . This study is focused on pressure variation, vapor volume fraction, lift and drag forces on the foil section for various cavitation values at angle of attack. Cavitation initiation begins at the foremost surface and covers towards the end chord with reducing cavitation value. Moreover, the change of vapor region pattern is predicted towards the front of the foil. Finally, transitional flow range is observed for values 0.8 to 1.2 with large standard deviation.
36
Macodiyo, D. O., H. Soyama e Masumi Saka. "Effect of Cavitation Number on the Improvement of Fatigue Strength of Carburized Steel Using Cavitation Shotless Peening". Key Engineering Materials 261-263 (aprile 2004): 1245–50. http://dx.doi.org/10.4028/www.scientific.net/kem.261-263.1245.
Testo completoAbstract (sommario):
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.
37
Podnar, Andrej, Marko Hočevar, Lovrenc Novak e Matevž Dular. "Analysis of Bulb Turbine Hydrofoil Cavitation". Applied Sciences 11, n. 6 (16 marzo 2021): 2639. http://dx.doi.org/10.3390/app11062639.
Testo completoAbstract (sommario):
The influence of a bulb runner blade hydrofoil shape on flow characteristics around the blade was studied. Experimental work was performed on a bulb turbine measuring station and a single hydrofoil in a cavitating tunnel. In the cavitation tunnel, flow visualization was performed on the hydrofoil’s suction side. Cavitation structures were observed for several cavitation numbers. Cavitation was less intense on the modified hydrofoil than on the original hydrofoil, delaying the cavitation onset by several tenths in cavitation number. The results of the visualization in the cavitation tunnel show that modifying the existing hydrofoil design parameters played a key role in reducing the cavitation inception and development, as well as the size of the cavitation structures. A regression model was produced for cavitation cloud length. The results of the regression model show that cavitation length is dependent on Reynolds’s number and the cavitation number. The coefficients of determination for both the existing and modified hydrofoils were reasonably high, with R2 values above 0.95. The results of the cavitation length regression model also confirm that the modified hydrofoil exhibits improved the cavitation properties.
38
Xing, Tao, Zhenyin Li e Steven H. Frankel. "Numerical Simulation of Vortex Cavitation in a Three-Dimensional Submerged Transitional Jet". Journal of Fluids Engineering 127, n. 4 (7 aprile 2005): 714–25. http://dx.doi.org/10.1115/1.1976742.
Testo completoAbstract (sommario):
Vortex cavitation in a submerged transitional jet is studied with unsteady three-dimensional direct numerical simulations. A locally homogeneous cavitation model that accounts for non-linear bubble dynamics and bubble/bubble interactions within spherical bubble clusters is employed. The velocity, vorticity, and pressure fields are compared for both cavitating and noncavitating jets. It is found that cavitation occurs in the cores of the primary vortical structures, distorting and breaking up the vortex ring into several sections. The velocity and transverse vorticity in the cavitating regions are intensified due to vapor formation, while the streamwise vorticity is weakened. An analysis of the vorticity transport equation reveals the influence of cavitation on the relative importance of the vortex stretching, baroclinic torque, and dilatation terms. Statistical analysis shows that cavitation suppresses jet growth and decreases velocity fluctuations within the vaporous regions of the jet.
39
Klenow, B., e A. Brown. "Prevention of Pressure Oscillations in Modeling a Cavitating Acoustic Fluid". Shock and Vibration 17, n. 2 (2010): 137–59. http://dx.doi.org/10.1155/2010/904390.
Testo completoAbstract (sommario):
Cavitation effects play an important role in the UNDEX loading of a structure. For far-field UNDEX, the structural loading is affected by the formation of local and bulk cavitation regions, and the pressure pulses resulting from the closure of the cavitation regions. A common approach to numerically modeling cavitation in far-field underwater explosions is Cavitating Acoustic Finite Elements (CAFE) and more recently Cavitating Acoustic Spectral Elements (CASE). Treatment of cavitation in this manner causes spurious pressure oscillations which must be treated by a numerical damping scheme. The focus of this paper is to investigate the severity of these oscillations on the structural response and a possible improvement to CAFE, based on the original Boris and Book Flux-Corrected Transport algorithm on structured meshes [6], to limit oscillations without the energy loss associated with the current damping schemes.
40
Son, Min, Michael Börner, Wolfgang Armbruster e Justin S. Hardi. "Orifice Flow Dynamics in a Rocket Injector as an Excitation Source of Injector-Driven Combustion Instabilities". Aerospace 10, n. 5 (15 maggio 2023): 452. http://dx.doi.org/10.3390/aerospace10050452.
Testo completoAbstract (sommario):
To investigate a hypothesis of the orifice flow-induced instability in rocket engine thrust chambers, a single liquid oxygen (LOX) injector with an optically accessible orifice module was used for experiments, with water as a simulant for LOX. The unsteady pressure downstream of the orifice was measured using high-speed piezoelectric sensors under cavitating and non-cavitating intra-injector flow conditions. The cavitating orifice flows were directly visualized via backlight imaging with a high-speed camera through the optically accessible orifice module. Cavitation initiated at the cavitation number of 2.05, and the downstream bubble cloud formation started below 1.91. The unsteady pressure spectrum arising from cavitation comprises multiple peaks over a broad frequency range, which can cause low- and high-frequency instabilities. The dominant frequencies from cavitation decrease with increasing pressure drop, while the frequencies during non-cavitating flow increase. The non-cavitating orifice flow excites the second longitudinal acoustic mode of the injector tube. The acoustic mode excited by the non-cavitating flow becomes stronger when the pressure peak in the range of whistling phenomenon is close to the first longitudinal acoustic mode. In conclusion, the excitation mechanisms of the orifice-induced instability for the cavitating and non-cavitating flows were well identified, despite the limitations of water as a simulant for LOX.
41
Szantyr, J., P. Flaszyński, K. Tesch, W. Suchecki e S. Alabrudziński. "An Experimental and Numerical Study of Tip Vortex Cavitation". Polish Maritime Research 18, n. 4 (1 gennaio 2011): 14–22. http://dx.doi.org/10.2478/v10012-011-0021-z.
Testo completoAbstract (sommario):
An Experimental and Numerical Study of Tip Vortex Cavitation The article presents the results of the research project concerning tip vortex cavitation. This form of cavitation is very important in operation of many types of rotary hydraulic machines, including pumps, turbines and marine propellers. Tip vortex cavitation generates noise, vibration and erosion. It should be eliminated or significantly limited during the design of these types of machines. The objective of the project was to develop an accurate and reliable method for numerical prediction of tip vortex cavitation, which could serve this purpose. The project consisted of the laboratory experiments and numerical calculations. In the laboratory experiments tip vortex cavitation was generated behind a hydrofoil in the cavitation tunnel and the velocity field around the cavitating kernel was measured using the Particle Image Velocimetry method. Measurements were conducted in three cross-sections of the cavitating tip vortex for a number of angles of attack of the hydrofoil and for several values of the cavitation index. In the course of numerical calculations two commercial CFD codes were used: Fluent and CFX. Several available approaches to numerical modeling of tip vortex cavitation were applied and tested, attempting to reproduce the experimental conditions. The results of calculations were compared with the collected experimental data. The most promising computational approach was identified.
42
Orekhov, Genrikh. "Cavitation in swirling flows of hydraulic spillways". E3S Web of Conferences 91 (2019): 07022. http://dx.doi.org/10.1051/e3sconf/20199107022.
Testo completoAbstract (sommario):
During operation of high-head hydraulic spillway systems, cavitation phenomena often occur, leading to destruction of structural elements of their flow conductor portions. The article is devoted to the study of erosion due to cavitation in the circulation flows of eddy hydraulic spillways, including those equipped with counter-vortex flow energy dissipators. Cavitation destructive effects depend on many factors: intensity consisting in the rate of decrease in the volume or mass of a cavitating body per unit of time, the stage of cavitation, geometric configuration of the streamlined body, the content of air in water, the flow rate, the type of material. The objective of the study consisted in determination of cavitation impacts in circulating (swirling) water flows. The studies were conducted by a method of physical modeling using high-head research installations. Distribution of amplitudes of pulses of shock cavitation impact is obtained according to the frequency of their occurrence depending on the flow velocity, the swirl angle, the height of the cavitating drop wall and the stage of cavitation. The impact energy depending on the stage of cavitation and the flow rate is given for different operating modes of the counter-vortex flow energy dissipators of a hydraulic spillway. In the conclusions, it is noted that cavitation impacts in the circulation flows occur mainly inside the flow, which is a fundamental difference from similar processes in axial flows.
43
Yang, Yongfei, Gaowei Wang, Weidong Shi, Wei Li, Leilei Ji e Hongliang Wang. "Turbulence Characteristics in the Mixing Layer of a Submerged Cavitating Jet at High Reynolds Numbers". Sustainability 14, n. 19 (22 settembre 2022): 11963. http://dx.doi.org/10.3390/su141911963.
Testo completoAbstract (sommario):
In this paper, unsteady and time-averaged turbulence characteristics in a submerged cavitating jet with a high Reynolds number are studied using large eddy simulation. The simulation is validated by comparing the vapor distribution using CFD and a high-speed photography experiment. The results indicate that the currently used numerical method can predict the evolution of the cavitation cloud in the jet accurately. The instantaneous and time-averaged flow fields of the submerged jet with three different cavitation numbers are studied. Comparing the frequency spectral of jets with different cavitation numbers, it is found that, for a fixed location, the frequency increases with the decrease in the cavitation number. Comparing the vorticity distribution at different streamwise locations, the instability process of the ring-shapes vortexes is revealed. Comparing the shape of the cavitation cloud and the vortexes in the jet finds that their spatial distribution and the temporal evolution are similar, indicating that the dynamic characteristics of the vortex and the cavitation affect each other. For the currently investigated cavitating jets, the Reynolds number increases with the decrease in the cavitation number. However, the spreading rate is lower for the jet with higher Reynolds numbers here. This is means that the momentum exchange between the jet and submerging water is reduced by the cavitation phenomenon.
44
Hatzissawidis, G., L. Kerres, G. J. Ludwig e P. F. Pelz. "Spatiotemporal analysis of sheet and cloud cavitation and its damage potential". IOP Conference Series: Earth and Environmental Science 1079, n. 1 (1 settembre 2022): 012046. http://dx.doi.org/10.1088/1755-1315/1079/1/012046.
Testo completoAbstract (sommario):
Abstract The cavitation regime has a substantial influence on the damage potential, thus it has to be considered in any specific investigation. For this purpose, we set up a test rig at the Technische Universität Darmstadt using a Circular Leading Edge hydrofoil (CLE) to analyse the damage potential of sheet and cloud cavitation. Exceeding a critical Reynolds number Re c, the cavitation regime transitions from harmless sheet cavitation to aggressive cloud cavitation. High-speed recordings of the cavitation regime are correlated with high frequency pressure data from a wall-mounted piezoelectric pressure transducer. Spatial and temporal content of the cavitating flow are captured applying proper orthogonal decomposition (POD) to the high-speed recordings. In order to determine the damage potential of the cavitation regime we apply a copper foil on the hydrofoil surface, on which plastic, crater-shaped deformations due to bubble collapses occur. Images of the surface are recorded before and after each run via two-dimensional Pit-Count microscopy. We correlate spatial modes from the cavitating flow field with the eroded surface rate from pitting tests leading to the result that cloud cavitation associated with increasing cloud size is more aggressive. A power law is identified where pitting rate increases with fourteenth power of the Reynolds number.
45
Zhang, Feng Hua, Nian Li e Chuan Lin Tang. "Design of Choking Cavitator and its Feasibility Study in Wastewater Treatment". Applied Mechanics and Materials 535 (febbraio 2014): 298–308. http://dx.doi.org/10.4028/www.scientific.net/amm.535.298.
Testo completoAbstract (sommario):
A new cavitator-choking cavitator is designed on the basis of analyzing the choking cavitation phenomena that occurs in gas-liquid mixed flow of straight pipe ,in jet pump under operating limits and in steady adiabatic flashing flow of stepped circular tube as well as in a cylindrical pipe with a sharp edged-corner for the steady and unsteady flows. The feasibility preliminary research of choking cavitator is carried out with analysis the signals of cavitation noise and treating simulated wastewater (phenol solution). The results offers a new approach in cavitator development field at home and abroad because of the effect that treating simulated wastewater with choking cavitator is preferable,and the cavitation per energy produced by choking cavitator is higher than that by self-oscillated chamber nozzle.
46
Liu, Cheng, Qingdong Yan e Houston G. Wood. "Numerical investigation of passive cavitation control using a slot on a three-dimensional hydrofoil". International Journal of Numerical Methods for Heat & Fluid Flow 30, n. 7 (7 novembre 2019): 3585–605. http://dx.doi.org/10.1108/hff-05-2019-0395.
Testo completoAbstract (sommario):
Purpose The purpose of this paper is to study the mechanism and suppression of instabilities induced by cavitating flow around a three-dimensional hydrofoil with a particular focus on cavitation control with a slot. Design/methodology/approach The transient cavitating flow around a Clark-Y hydrofoil was investigated using a transport-equation-based cavitation model and the stress-blended eddy simulation model was used to capture the flow turbulence. A homogeneous Rayleigh–Plesset cavitation model was used to model the transient cavitation process and the results were validated with test data. A slot was applied to the hydrofoil to suppress cavitation instabilities, and various slot widths and exit locations were applied to the blade and the cavitation behavior, as well as drag/lift forces, were simulated and compared to investigate the effects of slot geometries on cavitation suppression. Findings The large eddy simulation based turbulence model was able to capture the interactions between the cavitation and turbulence. Moreover, the simulation revealed that the re-entrant jet was responsible for the periodic shedding of cavities. The results indicated that a slot was able to mitigate or even suppress cavitation-induced instabilities. A jet flow was generated at the slot exit and disturbed the re-entrant jet. If the slot geometry was properly designed, the jet could block the re-entrant jet and suppress the unsteady cavitation behavior. Originality/value This study provides unique insights into the complicated transient cavitation flows around a three-dimensional hydrofoil and introduces an effective passive cavitation control technique useful to researchers and engineers in the areas of fluid dynamics and turbomachinery.
47
Wu, Kaipeng, Asad Ali, Changhong Feng, Qiaorui Si, Qian Chen e Chunhao Shen. "Numerical Study on the Cavitation Characteristics of Micro Automotive Electronic Pumps under Thermodynamic Effect". Micromachines 13, n. 7 (1 luglio 2022): 1063. http://dx.doi.org/10.3390/mi13071063.
Testo completoAbstract (sommario):
In order to study the influence of thermodynamic effects on the cavitation performance of hydromechanics, the Singhal cavitation model was modified considering the influence of the thermo-dynamic effects, and the modified cavitation model was written into CFX using the CEL language. Numerical simulation of the cavitation full flow field at different temperatures (25 °C, 50 °C and 70 °C) was carried out with the automotive electronic water pump as the research object. The results show that the variation trend of the external characteristic simulation and experimental values is the same at all flow rates, and the calculation accuracy meets the subsequent cavitation demand. With the increase in temperature, the low-pressure area inside the automotive electronic pump’s impeller decreases. NPSHr decreases and the cavitation resistance is enhanced. During the process of no cavitation to cavitation, the maximum pressure pulsation amplitude in the impeller channel gradually increases. The generation and collapse of cavitations cause the change of pressure pulsation in the internal flow field, causing pump vibration.
48
Li, Dawe, Jiangbo Wen, Ning Ge, Guihua Han, Yipeng Zhu e Chengjun Wang. "Study of the Mechanism of Cavitation in Inner-Hole Rotating Cavitators". Journal of Physics: Conference Series 2660, n. 1 (1 dicembre 2023): 012038. http://dx.doi.org/10.1088/1742-6596/2660/1/012038.
Testo completoAbstract (sommario):
Abstract To investigate the mechanism of cavitation, a mathematical model of the cavitation region and an expression for the gas volume fraction in the inner hole of a rotating cavitator are developed. Then, based on the realizable k-ε turbulence model and the Schner & Sauer cavitation model, the flow field is simulated numerically. With the help of pressure and streamlined distribution contours, velocity contours, and gas phase contours, the three stages of the cavitation process are simulated by the cavitation evolution model. Finally, the rate of heat generation is used as the experimental characterization of cavitation, and the cavitation mechanism is confirmed by experiments involving rotation speed and pressure. The results indicate that the cavitation effect can be measured by the generation of cavitation heat and that the influence of the rotation speed on the cavitation effect is more significant than that of the inlet pressure.
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Meng, W. J., C. Lei, W. T. Su e B. Li. "Study on microchannel cavitation phenomena based on experiment and simulation". Journal of Physics: Conference Series 2707, n. 1 (1 febbraio 2024): 012126. http://dx.doi.org/10.1088/1742-6596/2707/1/012126.
Testo completoAbstract (sommario):
Abstract Cavitation phenomenon is a common fluid mechanics phenomenon. Its special flow limiting structure generates abundant microchannel cavitation in the microchannel, and the existence of these cavitation flow field with complex flow field structure characteristics is formed in the microchannel. In order to better understand the cavitation phenomenon in the microchannel, this paper takes the microchannel as the research object, adopts the method of comparison between experimental research and numerical simulation, changes the cavitation number by adjusting parameters, and analyses the cavitation phenomenon of the microchannel under different working conditions. From the experimental point of view, a micro-channel with rectangular current limiting structure was designed. In order to observe and analyse the microchannel hydraulic cavitation phenomenon, the hydraulic cavitation micro-channel experiment platform was designed and built, which could analyse the cavitation flow pattern of the microchannel. The computational fluid dynamics simulation software Fluent was used to simulate and study the microchannel cavitation phenomenon characteristics by changing the boundary conditions. It is found that the cavitation phenomenon becomes more obvious as the number of cavitations decreases. Finally, the simulation results are compared with the experimental results, and the simulated cavitation flow pattern is in good agreement with the experimental results.
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Kumano, H., H. Soyama e Masumi Saka. "Gettering of Cu in Silicon Wafer by Using Cavitation Impacts". Key Engineering Materials 261-263 (aprile 2004): 1409–14. http://dx.doi.org/10.4028/www.scientific.net/kem.261-263.1409.
Testo completoAbstract (sommario):
A novel gettering method using cavitation impacts is presented. Gettering is very important technique for IC manufacturing. Silicon wafers used as a substrate for semiconductors are often exposed to contamination during the device processes. If crystal defects are intentionally introduced into back-side of silicon wafer, metal impurities such as Cu and Fe in the wafer are trapped in the defects and gather into the region during heat cycles. As a result, the zone near the surface of the wafer that is used as active device region is kept off unwanted impurities. This technique is called gettering. In this paper, to introduce backside damage, which is one of the gettering techniques, cavitation impacts are utilized. Cavitation bubbles produce high-pressure impacts upon collapsing. The suitable damage can be introduced by controlling the intensity of cavitation impacts. The high speed submerged water jet with cavitation, i.e., a cavitating jet, was used to cause cavitation impacts. The cavitating jet can introduce backside damage without the use of particles, as in shot blasting that is popular technique. In order to confirm the gettering effectiveness of the damage introduced by a cavitating jet, an experimental study was carried out. The silicon wafer treated by the cavitating jet was intentionally contaminated with solution of Cu(NO3)2. The wafer was then thermally treated. The surface was observed after etching that makes defects on the surface observable. On the surface of the wafer having no gettering effectiveness, defects which were induced by contamination are observed. If the wafer has gettering effectiveness, defects are not observed on the surface. Gettering effectiveness of the damage introduced by the cavitating jet was shown.