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1
Wang, Xin Hua, Zhi Jie Li, Shu Wen Sun und Gang Zheng. „Research on the Influence Factors of Cavitating Jet in Jet Pipe Amplifier Nozzle“. Applied Mechanics and Materials 229-231 (November 2012): 617–20. http://dx.doi.org/10.4028/www.scientific.net/amm.229-231.617.
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The cavitation flow characteristics in jet pipe amplifier with different nozzles were simulated using commercial computational fluid dynamics (CFD) software. The influence of operating parameters and structural parameters of jet nozzles on cavitation jets are the key objective. These parameters mainly include inlet pressure, outlet pressure, temperature of water, nozzle convergence angle, the length of the nozzle cylindrical section, nozzle diameter and nozzle export chamfer angle. The results provide methods to limit the emergence and development of the nozzle jet internal cavitations.
2
YANG, Yongfei, Wei LI, Weidong SHI, Chuan WANG und Wenquan ZHANG. „Experimental Study on Submerged High-Pressure Jet and Parameter Optimization for Cavitation Peening“. Mechanics 26, Nr. 4 (15.09.2020): 346–53. http://dx.doi.org/10.5755/j01.mech.26.4.27560.
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To increase the performance of high pressure submerged cavitation jet that has been used for cavitation peening, the effect of stand-off distance and the nozzle geometry on the impact capacity is investigated and optimized. High speed photography of the cavitation bubble clouds taken to reveal the unsteady characteristics of the cavitating jet. The impact ability of the jet with different nozzles and standoff distance is tested using Al 1060 at first, and the optimized jet is used then for cavitation peening on 304 stainless steel. The surface profile as well as the grain structures before and after peening using different nozzles are observed from SEM images. It is found that, the divergent angle of the nozzle has a great effect on the impact capability of the submerged high-pressure jet, which is important for improving the peening efficiency. In the nozzles with divergent angle 40°, 60° and 80°, the 60° nozzle shows the best performance. After peening, grain cells under the metal surface are changed and a twin layer is formed. The current research reveals the transient characteristics of the submerged cavitation jet and main factors that affect its impact rate, which provides guide for the nozzle design and application for the high-pressure cavitation jet peening.
3
Yang, Yongfei, Wei Li, Weidong Shi, Ling Zhou und Wenquan Zhang. „Experimental Study on the Unsteady Characteristics and the Impact Performance of a High-Pressure Submerged Cavitation Jet“. Shock and Vibration 2020 (16.06.2020): 1–15. http://dx.doi.org/10.1155/2020/1701843.
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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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Zhang, Feng Hua, Hai Feng Liu, Jun Chao Xu und Chuan Lin Tang. „Experimental Investigation on Cavitation Noise of Water Jet and its Chaotic Behaviour“. Applied Mechanics and Materials 121-126 (Oktober 2011): 3919–24. http://dx.doi.org/10.4028/www.scientific.net/amm.121-126.3919.
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The cavitation noise signals were collected separately for the cavitation nozzle and general nozzle at the target position and the nozzle exit in the condition of different standoff distance. The features of signal’s frequency spectrum and power spectrum were analyzed for different nozzles. Based on chaotic theory, phase space reconstruction was processed and the maximum Lyapunov exponent was calculated separately for each cavitation signal’s time series. Under the condition of this experiment, the difference between the general nozzle and cavitation nozzle was mostly marked at the target position while the standoff distance is 35 mm, which mainly displayed at the high frequency segment. The maximum Lyapunov exponent calculated appeared at standoff distance 35 mm. At the nozzle exit, the noise signal of cavitation nozzle is different from the general nozzle. The difference also displayed at the high frequency segment, and no changing with the standoff distance
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GIANNADAKIS, E., M. GAVAISES und C. ARCOUMANIS. „Modelling of cavitation in diesel injector nozzles“. Journal of Fluid Mechanics 616 (10.12.2008): 153–93. http://dx.doi.org/10.1017/s0022112008003777.
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A computational fluid dynamics cavitation model based on the Eulerian–Lagrangian approach and suitable for hole-type diesel injector nozzles is presented and discussed. The model accounts for a number of primary physical processes pertinent to cavitation bubbles, which are integrated into the stochastic framework of the model. Its predictive capability has been assessed through comparison of the calculated onset and development of cavitation inside diesel nozzle holes against experimental data obtained in real-size and enlarged models of single- and multi-hole nozzles. For the real-size nozzle geometry, high-speed cavitation images obtained under realistic injection pressures are compared against model predictions, whereas for the large-scale nozzle, validation data include images from a charge-coupled device (CCD) camera, computed tomography (CT) measurements of the liquid volume fraction and laser Doppler velocimetry (LDV) measurements of the liquid mean and root mean square (r.m.s.) velocities at different cavitation numbers (CN) and two needle lifts, corresponding to different cavitation regimes inside the injection hole. Overall, and on the basis of this validation exercise, it can be argued that cavitation modelling has reached a stage of maturity, where it can usefully identify many of the cavitation structures present in internal nozzle flows and their dependence on nozzle design and flow conditions.
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Ishak, M. H. H., Farzad Ismail, Sharzali Che Mat, M. Z. Abdullah, M. S. Abdul Aziz und M. Y. Idroas. „Numerical Analysis of Nozzle Flow and Spray Characteristics from Different Nozzles Using Diesel and Biofuel Blends“. Energies 12, Nr. 2 (17.01.2019): 281. http://dx.doi.org/10.3390/en12020281.
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In this paper, the discrete phase model (DPM) was introduced to study the fuel injector cavitations process and the macro spray characteristic of three different types of nozzle spray shape with diesel and hybrid biofuel blend for several injection pressures and backpressures. The three types of nozzle spray shapes used were circle, elliptical A type, and elliptical B type. The cavitations’ flows inside the injector nozzles were simulated with Computer Fluid Dynamics (CFD) simulations using the cavitations mixture approach. The effect of nozzle spray shape towards the spray characteristic of hybrid biofuel blends is analyzed and compared with the standard diesel. Furthermore, a verification and validation from both the experimental results and numerical results are also presented. The nozzle flow simulation results indicated that the fuel type did not affect the cavitation area vastly, but were more dependent on the nozzle spray shape. In addition, the spray width of the elliptical nozzle shape was higher as compared to the circular spray. Moreover, as the backpressure increased, the spray width downstream increased as well. The spray tip penetration for the elliptical nozzle shape was shorter than the circular nozzle shape due to circular nozzles having smaller nozzle widths and lesser spray cone angles. Thus, this resulted in smaller aerodynamic drag.
7
Soyama, Hitoshi. „Cavitating Jet: A Review“. Applied Sciences 10, Nr. 20 (17.10.2020): 7280. http://dx.doi.org/10.3390/app10207280.
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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.
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Yang, Han, Yu Yong Lei, Huan Tao, Li Zhang und Xuan Chen. „Simulation Study on Oscillating Cavitation Nozzle for Cleaning Based on FLUENT“. Advanced Materials Research 997 (August 2014): 684–87. http://dx.doi.org/10.4028/www.scientific.net/amr.997.684.
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Abstract: Based on the basic theory of fluid dynamics and Fluent software, numeric simulation of self-excited oscillating cavitation jet nozzle for cleaning was carried out. The flow field characteristics within tubular organ cavitation nozzle is studied. By numerical simulation, the exit velocity, velocity vector distribution, pressure inside the nozzle as well as static pressure distribution were obtained. The simulation results show that there is a maximum speed at cylindric section inside the cavitation nozzle. When water jet getting into the cylindric section of the cavitation nozzle, there is a significant zone with high negative pressure.Also there is a obvious zone with negative pressure at the outlet end. When the pressure is below the saturation vapor pressure of the liquid, cavitation bubbles occured. Therefore the cavitating water jet was generated. The simulation results also show that there is a higher negative pressure inside the nozzle region when the nozzle inlet diameter Ds = 6 mm, the diameter of the cavity D = 3 mm, the diameter of the cylindric section d = 1.8mm, the resonator length L = 6.2 mm, spread angleα= 60 °, the length of the cylindric segment s = 6 mm, Thererfore it is beneficial effect for the cavitation generating.
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Wo, Heng Zhou, Ya Fang Zhang, Xian Guo Hu und Yu Fu Xu. „Effect of Hardness of Needle-Sealing Surface of Pintle Nozzle on Cavitation Erosion“. Applied Mechanics and Materials 130-134 (Oktober 2011): 946–49. http://dx.doi.org/10.4028/www.scientific.net/amm.130-134.946.
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Nozzle is one of key parts in the diesel engine. The cavitation erosion of needle-sealing surface in the pintle nozzle has important influence on the fuel atomization, combustion and power performance of diesel engine. In order to investigate the effect of hardness of needle-sealing surface on cavitation erosion, two kinds of nozzles were selected and operated in S195 diesel engine for 10 hours. One nozzle is heat-treated one which has lower surface hardness; the other with higher surface hardness is real commercial nozzle. The surface appearances of original and operated nozzle-sealing surface were observed by SEM. It was found that the cavitation erosion on the seal surface of nozzle with lower hardness was severer than that of nozzle with higher hardness. However, their wear ways and formations are similar.
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ANDRIOTIS, A., M. GAVAISES und C. ARCOUMANIS. „Vortex flow and cavitation in diesel injector nozzles“. Journal of Fluid Mechanics 610 (08.08.2008): 195–215. http://dx.doi.org/10.1017/s0022112008002668.
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Flow visualization as well as three-dimensional cavitating flow simulations have been employed for characterizing the formation of cavitation inside transparent replicas of fuel injector valves used in low-speed two-stroke diesel engines. The designs tested have incorporated five-hole nozzles with cylindrical as well as tapered holes operating at different fixed needle lift positions. High-speed images have revealed the formation of an unsteady vapour structure upstream of the injection holes inside the nozzle volume, which is referred to as ‘string-cavitation’. Computation of the flow distribution and combination with three-dimensional reconstruction of the location of the strings inside the nozzle volume has revealed that strings are found at the core of recirculation zones; they originate either from pre-existing cavitation sites forming at sharp corners inside the nozzle where the pressure falls below the vapour pressure of the flowing liquid, or even from suction of outside air downstream of the hole exit. Processing of the acquired images has allowed estimation of the mean location and probability of appearance of the cavitating strings in the three-dimensional space as a function of needle lift, cavitation and Reynolds number. The frequency of appearance of the strings has been correlated with the Strouhal number of the vortices developing inside the sac volume; the latter has been found to be a function of needle lift and hole shape. The presence of strings has significantly affected the flow conditions at the nozzle exit, influencing the injected spray. The cavitation structures formed inside the injection holes are significantly altered by the presence of cavitation strings and are jointly responsible for up to 10% variation in the instantaneous fuel injection quantity. Extrapolation using model predictions for real-size injectors operating at realistic injection pressures indicates that cavitation strings are expected to appear within the time scales of typical injection events, implying significant hole-to-hole and cycle-to-cycle variations during the corresponding spray development.
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Wang, Yi-Chun. „Stability Analysis of One-Dimensional Steady Cavitating Nozzle Flows With Bubble Size Distribution“. Journal of Fluids Engineering 122, Nr. 2 (20.12.1999): 425–30. http://dx.doi.org/10.1115/1.483273.
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A continuum bubbly mixture model coupled to the Rayleigh-Plesset equation for the bubble dynamics is employed to study one-dimensional steady bubbly cavitating flows through a converging-diverging nozzle. A distribution of nuclei sizes is specified upstream of the nozzle, and the upstream cavitation number and nozzle contraction are chosen so that cavitation occurs in the flow. The computational results show very strong interactions between cavitating bubbles and the flow. The bubble size distribution may have significant effects on the flow; it is shown that it reduces the level of fluctuations and therefore reduces the “cavitation loss” compared to a monodisperse distribution. Another interesting interaction effect is that flashing instability occurs as the flow reaches a critical state downstream of the nozzle. A stability analysis is proposed to predict the critical flow variables. Excellent agreement is obtained between the analytical and numerical results for flows of both equal bubble size and multiple bubble sizes. [S0098-2202(00)00702-1]
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Wang, Xing, Fei Hu Zhang, Yong Zhang und Ming Zhou. „An Experimental Study of the Nanoparticle Colloid Hydrodynamic Cavitation Jet Polishing Performance under Different Nozzle Designs“. Advanced Materials Research 325 (August 2011): 633–37. http://dx.doi.org/10.4028/www.scientific.net/amr.325.633.
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Nanoparticle colloid hydrodynamic cavitation jet polishing (HCJP) is a super-smooth machining technology. This technology utilizes the interface reaction to remove material from the workpiece and uses cavitation effect to improve the processing efficiency. In this paper, the prototype equipment of HCJP is researched. Based on the prototype equipment, the processing experiments of pulsed jet nozzle, swirling jet nozzle and common cone-shaped nozzle have been done and the results of the experiments are compared with each other. The experiment results indicate that the roughness of the surfaces polished by three nozzles has remarkably decreased. The material removal rate of pulsed jet nozzle is the highest among the three types of nozzles. The material removal rate of the swirling jet nozzle is not improved obviously compared with the common cone-shaped nozzle. The processing experiment of monocrystalline silicon by the pulsed jet nozzle has been done and the roughness of processed surface is Ra 0.475 nm.
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Poussou, Stephane, und Michael W. Plesniak. „Near-Field Flow Measurements of a Cavitating Jet Emanating From a Crown-Shaped Nozzle“. Journal of Fluids Engineering 129, Nr. 5 (30.10.2006): 605–12. http://dx.doi.org/10.1115/1.2717615.
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The effect of a crown-shaped nozzle on cavitation is studied experimentally in the near-field of a 25 mm diameter (D) water jet at ReD=2×105 using particle image velocimetry (PIV) and high speed shadowgraphy recorded with a 5000 fps digital camera. The objectives are to passively control the jet flow structure and to examine its consequences on the physical appearance of cavitating bubbles. The experiments are performed in a closed-loop facility that enables complete optical access to the near-nozzle region. The cavitating and noncavitating mean velocity fields are obtained up to three nozzle diameters downstream and compared to those of a companion round nozzle. PIV measurements are taken in two distinct azimuthal planes passing through the tip and bottom points of the crown nozzle edge. The data include shear layer momentum thickness and vorticity thickness, spanwise vorticity distribution and streamwise normal Reynolds stress. Significant deviation from an axisymmetric shear layer is observed in the noncavitating flow consistently up to one diameter downstream, after which identical asymptotic conditions are achieved in both round and crown-shaped nozzles. Maximum magnitudes of spanwise vorticity and streamwise normal Reynolds stress are the highest downstream of the nozzle tip edges under noncavitating conditions. Significant modifications in trends and magnitudes are observed for the shear layer momentum thickness under cavitating conditions up to one diameter downstream. Qualitative flow visualization reveals that bubble growth occurs at different conditions depending on azimuthal location. Bubbles, in the form of elongated filaments, are the dominant structures produced downstream of the valley edges of the nozzle with an inclination of 45 deg with respect to the direction of the flow, and are observed to persist with significant strength up to two diameters downstream. These filaments are stretched between periodic larger-scale, spanwise bubbly clusters distorted in the shape of the nozzle outlet. The tip edges produce cavitating bubbles under conditions similar to that of a classical round nozzle. In summary, it was demonstrated that passive control of turbulent structures in the jet does impact the cavitation process.
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López, J. Javier, Oscar A. de la Garza, Joaquin De la Morena und S. Martínez-Martínez. „Effects of cavitation in common-rail diesel nozzles on the mixing process“. International Journal of Engine Research 18, Nr. 10 (20.03.2017): 1017–34. http://dx.doi.org/10.1177/1468087417697759.
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A study to experimentally analyze the effect of cavitation on the mixing process in diesel nozzles was carried out. The mixing process was studied through the spray cone angle. It was characterized in two different scenarios: with the liquid length (nearly realistic conditions, that is, evaporative but non-reactive spray) and the heat release fraction (fully realistic conditions, that is, evaporative and reactive spray). In both studied scenarios, the increase in spray cone angle caused by the cavitation phenomenon, which leads to a better mixing process, has been confirmed. Nevertheless, when the variations of the effective injection velocity and the spray cone angle obtained by comparing a cylindrical nozzle (i.e. a nozzle that promotes the cavitation phenomenon) with a conical nozzle (i.e. a nozzle that inhibits this phenomenon) were analyzed together, it was found that, for the cases studied here, the mixing process worsens with the cylindrical nozzle.
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Fang, Zhenlong, Xiang Gao, Xia Tao, Deng Li, Mengda Zhang, Ting Xiong und Pan Jiang. „Impact Performance of Helmholtz Self-Excited Oscillation Waterjets Used for Underground Mining“. Applied Sciences 9, Nr. 16 (08.08.2019): 3235. http://dx.doi.org/10.3390/app9163235.
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Pulsed waterjets are widely used in exploitation of fossil fuels for their high efficiency. With the aim to further clarify the impact performance of Helmholtz self-excited oscillation waterjets (HSEOW), numerical and experimental studies were conducted. The morphological characteristics of the erosion surfaces between conical and HSEOW nozzles were compared and the cavitation evolution was obtained. Results show that the cavitation damage caused by the HSEOW nozzle on the specimen was mainly caused by the jet cavitation cloud under submerged conditions. The cavitation effect produced by the HSEOW nozzle had a much greater destructive effect than that of a conical nozzle. The mass loss caused by HSEOW nozzles increased first with the increase of standoff distance, then decreased rapidly after reaching the maximum value. Moreover, the density of holes and the damage intensity weakened with the increase of radial distance. A dimensionless cavity length of 2 and a dimensionless cavity diameter of 8 was the optimal structure that led to maximum mass loss. These results provide a further understanding of cavitation mechanism which leads to the impact performance of pulsed water jets and optimal working parameters in the field of energy exploitation.
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Zhang, H., B. Han, X. G. Yu und D. Y. Ju. „Numerical and Experimental Studies of Cavitation Behavior in Water-Jet Cavitation Peening Processing“. Shock and Vibration 20, Nr. 5 (2013): 895–905. http://dx.doi.org/10.1155/2013/910613.
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Water-jet cavitation peening (WCP) is a new technology for the surface modification of metallic materials. The cavitation behavior in this process involves complex and changeable physics phenomena, such as high speed, high pressure, multiple phases, phase transition, turbulence, and unstable features. Thus, the cavitation behavior and impact-pressure distribution in WCP have always been key problems in this field. Numerous factors affect the occurrence of cavitation. These factors include flow-boundary conditions, absolute pressure, flow velocity, flow viscosity, surface tension, and so on. Among these factors, pressure and vapor fraction are the most significant. Numerical simulations are performed to determine the flow-field characteristics of both inside and outside the cavitating nozzle of a submerged water jet. The factors that influence the cavitation intensity of pressure are simulated. Fujifilm pressure-sensitive paper is used to measure the distribution of impact pressure along the jet direction during the WCP process. The results show that submerged cavitation jets can induce cavitation both inside and outside a conical nozzle and a convergent-divergent nozzle when the inlet pressure is 32 MPa. Moreover, the shock wave pressure induced by the collapse of the bubble group reaches up to 300 MPa.
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Szymczak, M., S. Tavoularis, A. Fahim und M. M. Vijay. „Flow Visualization of Cavitating, High-Speed, Submerged Water Jets“. Journal of Engineering for Industry 113, Nr. 4 (01.11.1991): 485–89. http://dx.doi.org/10.1115/1.2899728.
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Instrumentation and procedures have been developed for the visualization of high-speed, submerged water jets of the type used in cleaning, cutting, and drilling applications. As examples of these techniques, cavitation characteristics of jets produced by two plain conical nozzles as well as by a similar nozzle equipped with a transverse pin are presented. The results can be used to identify the regions of cavity inception, transport, and collapse. A semi-empirical expression relating the extent of the cavitation region to the cavitation index and the nozzle diameter is also presented.
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Koukouvinis, Phoevos, Homa Naseri und Manolis Gavaises. „Performance of turbulence and cavitation models in prediction of incipient and developed cavitation“. International Journal of Engine Research 18, Nr. 4 (28.07.2016): 333–50. http://dx.doi.org/10.1177/1468087416658604.
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The aim of this article is to assess the impact of turbulence and cavitation models on the prediction of diesel injector nozzle flow. Two nozzles are examined, an enlarged one, operating at incipient cavitation, and an industrial injector tip, operating at developed cavitation. The turbulence model employed includes the re-normalization group k–ε, realizable k–ε and k–ω shear stress transport Reynolds-averaged Navier–Stokes models; linear pressure–strain Reynolds stress model and the wall adapting local eddy viscosity large eddy simulation model. The results indicate that all Reynolds-averaged Navier–Stokes and the Reynolds stress turbulence models have failed to predict cavitation inception due to their limitation to resolve adequately the low pressure existing inside vortex cores, which is responsible for cavitation development in this particular flow configuration. Moreover, Reynolds-averaged Navier–Stokes models failed to predict unsteady cavitation phenomena in the industrial injector. However, the wall adapting local eddy viscosity large eddy simulation model was able to predict incipient and developed cavitation, while also capturing the shear layer instability, vortex shedding and cavitating vortex formation. Furthermore, the performance of two cavitation methodologies is discussed within the large eddy simulation framework. In particular, a barotropic model and a mixture model based on the asymptotic Rayleigh–Plesset equation of bubble dynamics have been tested. The results indicate that although the solved equations and phase change formulation are different in these models, the predicted cavitation and flow field were very similar at incipient cavitation conditions. At developed cavitation conditions, standard cavitation models may predict unrealistically high liquid tension, so modifications may be essential. It is also concluded that accurate turbulence representation is crucial for cavitation in nozzle flows.
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Salvador, Francisco J., Joaquin de la Morena, Marcos Carreres und David Jaramillo. „Numerical analysis of flow characteristics in diesel injector nozzles with convergent-divergent orifices“. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 231, Nr. 14 (01.02.2017): 1935–44. http://dx.doi.org/10.1177/0954407017692220.
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The geometry of diesel injector nozzles is known to significantly affect the characteristic spray behavior and emissions formation. In this paper, a novel nozzle concept, consisting of orifices with a convergent–divergent shape, is investigated through Computational Fluid Dynamics techniques. Three of these nozzles, characterized by different degrees of conicity, are compared to a nozzle with cylindrical orifices, which acts as a baseline. A homogeneous equilibrium model, validated against experimental data in previous works by the authors, is used to calculate the eventual cavitation formation inside these orifices. Additionally, the characteristics of the flow at the orifice outlet are analyzed for the four aforementioned nozzles in terms of their steady-state mass flow, effective outlet velocity and area coefficient. The results show that convergent-divergent nozzles exhibit a high cavitation intensity, located in the transition between the convergent and the divergent sections. This high cavitation intensity tends to compensate for the expected velocity decrease induced by the divergent shape, producing effective velocity values similar to those achieved by the cylindrical nozzle in many of the simulated conditions. The characteristics of the flow, together with the higher spray opening angles expected due to the divergent section of the nozzle, may improve atomization and fuel-air mixing processes.
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Wang, Yan Hua, Shi Chun Yang und Yun Qing Li. „Numerical Simulation of Transient Flow Inside Nozzle on Gasoline Direct Injection Engine“. Advanced Materials Research 466-467 (Februar 2012): 1237–41. http://dx.doi.org/10.4028/www.scientific.net/amr.466-467.1237.
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To achieve transient flow characteristics at exit of nozzle orifice on gasoline direct injection engine, two phase Euler-Euler schemes was used to simulate the internal flow of the swirl nozzle. Different flow characteristics were calculated in the simulation. Different kinds of nozzle configuration were studied. Cavitaion and swirl flow occured in the nozzles. Injection hole configuration matters more than area variation of swirl tangential slot to discharge coefficient of the studied nozzle. Discharge coefficient changes a little along the injection hole length. The area of the swirl tangrntial slot plays an important throttling action in nozzle internal flow. Smaller area of swirl tangential slot generates larger degree cavitation but smaller mean injection velocity. Turbulence kinetic energy changes with the time of cavitation and swirl field occurring and the nozzle configuration. Before the appearance of cavitation, smaller inclination angle of orifice can generate more turbulence kinetic energy. After that moment, turbulence kinetic energy varies with different configuration. Along injection hole length, turbulence kinetic energy obviously varies. These flow characteristics affect primary atomization and will be as input for next spray simulation. They are also applied to design reference for injection nozzle.
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Benajes, J., J. V. Pastor, R. Payri und A. H. Plazas. „Analysis of the Influence of Diesel Nozzle Geometry in the Injection Rate Characteristic“. Journal of Fluids Engineering 126, Nr. 1 (01.01.2004): 63–71. http://dx.doi.org/10.1115/1.1637636.
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An experimental research study was carried out to analyze the influence of different orifice geometries (conical and cylindrical) on the injection rate behavior of a Common-Rail fuel injection system. For that purpose, injection tests in two different injection test rigs were conducted. This behavior of the injection rate in the different nozzles was characterized by using the non-dimensional parameters of cavitation number (K), discharge coefficient (Cd) and Reynolds number (Re). First, some relevant physical properties of the injected fuel were accurately characterized (density, kinematic viscosity and sound speed in the fluid) in a specific test rig as a function of the operating conditions (pressure and temperature). The behavior of both nozzles was analyzed at maximum injector needle lift under steady flow conditions in a cavitation test rig. Injection pressure and pressure at the nozzle discharge were controlled in order to modify the flow conditions. In addition, the nozzles were characterized in real unsteady flow conditions in an injection-rate test rig. From the raw results, the values of the relevant parameters were computed, and the occurrence of cavitation was clearly identified. The results evidenced interesting differences in the permeability of both nozzle geometries and a clear resistance of the conical nozzle to cavitation.
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Yang, Yongfei, Wei Li, Weidong Shi, Wenquan Zhang und Mahmoud A. El-Emam. „Numerical Investigation of a High-Pressure Submerged Jet Using a Cavitation Model Considering Effects of Shear Stress“. Processes 7, Nr. 8 (15.08.2019): 541. http://dx.doi.org/10.3390/pr7080541.
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In the current research, a high-pressure submerged cavitation jet is investigated numerically. A cavitation model is created considering the effect of shear stress on cavitation formation. As such, this model is developed to predict the cavitation jet, and then the numerical results are validated by high-speed photography experiment. The turbulence viscosity of the renormalization group (RNG) k-ε turbulence model is used to provide a flow field for the cavitation model. Furthermore, this model is modified using a filter-based density correction model (FBDCM). The characteristics of the convergent-divergent cavitation nozzle are investigated in detail using the current CFD simulation method. It is found that shear stress plays an important role in the cavitation formation in the high-pressure submerged jet. In the result predicted by the Zwart-Gerber-Belamri (ZGB) cavitation model, where critical static pressure is used for the threshold of cavitation inception, the cavitation bubble only appears at the nozzle outlet and the length of the cavity is much shorter than the actual length captured by the high-speed photography experiment. When the shear stress term is added to the critical pressure, the length of the predicted cavity is close to the experimental result and three phenomena of the jet are captured, namely, growth, shedding, and collapsing, which agrees well with the experimental high-speed image. According to the orthogonal analysis based on the simulation result, when the jet power is unchanged, the main geometry parameter of the divergent-convergent nozzle that affects the jet performance is the divergent angle. For the nozzle with three different divergent angles of 40°, 60°, and 80°, the one with the medium angle generates the most intensive cavitation cloud, while the small one shows the weakest cavitation performance. The obtained simulation result is confirmed by cavitation erosion tests of the Al1060 plate using these three nozzles.
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Hutli, Ezddin, Salem Abouali, Ben Hucine, Mohamed Mansour, Milos Nedeljkovic und Vojislav Ilic. „Influences of hydrodynamic conditions, nozzle geometry on appearance of high submerged cavitating jets“. Thermal Science 17, Nr. 4 (2013): 1139–49. http://dx.doi.org/10.2298/tsci120925045h.
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Based on visualization results of highly-submerged cavitating water jet obtained with digital camera, the influences of related parameters such as: injection pressure, nozzle diameter and geometry, nozzle mounting (for convergent / divergent flow), cavitation number and exit jet velocity, were investigated. In addition, the influence of visualization system position was also studied. All the parameters have been found to be of strong influence on the jet appearance and performance. Both hydro-dynamical and geometrical parameters are playing the main role in behavior and intensity of cavitation phenomenon produced by cavitating jet generator. Based on our considerable previous experience in working with cavitating jet generator, the working conditions were chosen in order to obtain measurable phenomenon.
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He, Zhi Xia, Qing Mu Mu, Qian Wang und Jian Ping Yuan. „Effect of Diesel Nozzle Geometry on Internal Cavitating Flow“. Advanced Materials Research 97-101 (März 2010): 2925–28. http://dx.doi.org/10.4028/www.scientific.net/amr.97-101.2925.
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The presence of cavitation and turbulence in a diesel injector nozzle has significant effect on the subsequent spray characteristics. However, the mechanism of the cavitating flow and its effect on the subsequent spray is unclear. The initiation, development and collapse of the cavity are strongly influenced not only by the injection pressure and back pressure but also by the nozzle geometry. The numerical simulation of cavitating flow in nozzle holes of a vertical multi-hole injector with mixture multi-phase cavitating flow model was carried out. The effects of sac geometry, hole entrance curvature radius and hole inclination angle on the cavitating flow in nozzle holes were investigated. It is finally concluded that the performance of IMPROVED nozzle is better than that of STD nozzle and VCO nozzle and small inlet turning angle of the orifice can enhance the atomization of the spray.
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Ferrari, A. „Fluid dynamics of acoustic and hydrodynamic cavitation in hydraulic power systems“. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 473, Nr. 2199 (März 2017): 20160345. http://dx.doi.org/10.1098/rspa.2016.0345.
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Cavitation is the transition from a liquid to a vapour phase, due to a drop in pressure to the level of the vapour tension of the fluid. Two kinds of cavitation have been reviewed here: acoustic cavitation and hydrodynamic cavitation. As acoustic cavitation in engineering systems is related to the propagation of waves through a region subjected to liquid vaporization, the available expressions of the sound speed are discussed. One of the main effects of hydrodynamic cavitation in the nozzles and orifices of hydraulic power systems is a reduction in flow permeability. Different discharge coefficient formulae are analysed in this paper: the Reynolds number and the cavitation number result to be the key fluid dynamical parameters for liquid and cavitating flows, respectively. The latest advances in the characterization of different cavitation regimes in a nozzle, as the cavitation number reduces, are presented. The physical cause of choked flows is explained, and an analogy between cavitation and supersonic aerodynamic flows is proposed. The main approaches to cavitation modelling in hydraulic power systems are also reviewed: these are divided into homogeneous-mixture and two-phase models. The homogeneous-mixture models are further subdivided into barotropic and baroclinic models. The advantages and disadvantages of an implementation of the complete Rayleigh–Plesset equation are examined.
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Wen, Hua, Yulong Jiang und Jinglong Ma. „Effect of Fuel Mass Flow at the End of Injection on Cavitation and Gas Ingestion in the Nozzle“. Applied Sciences 11, Nr. 1 (29.12.2020): 258. http://dx.doi.org/10.3390/app11010258.
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The fuel flow in the diesel engine nozzle has a vital impact on the fuel atomization and spray, and the fuel mass flux affects the internal flow of the nozzle. The visual experimental platform for a transparent nozzle was built to obtain the image of fuel flow in a nozzle with a small sac combining the back-light imaging technology and a high-speed framing camera. A two-phase three-component numerical model, based on the OpenFOAM solver, was calculated to quantitatively analyze gas ingestion and cavitation in the nozzle. The results indicate that at the end of injection (EOI), fuel cavitation and external air backflow (gas ingestion) occur successively in the nozzle, and both phenomena first appear in the orifice and then transition to the sac. Cavitation collapse is the major factor of gas ingestion, and the total amount of gas ingestion and cavitation mainly depends on the sac. The outflow of fuel largely depends on the total amount of cavitation and the inertial outflow of fuel at the EOI. The type of cavitation in the nozzle mainly presents annular and bulk cavitation, the former primarily exists in the sac, while the latter is established within the orifice. Therefore, larger mass flows will contribute to stronger cavitation and gas ingestion.
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Wang, Lifu, Dongyan Shi, Zhixun Yang, Guangliang Li, Chunlong Ma, Dongze He und Liang Yan. „Numerical simulation and experimental research of cavitation nozzle based on equation curve“. Water Supply 21, Nr. 5 (04.03.2021): 2261–72. http://dx.doi.org/10.2166/ws.2021.058.
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Abstract To further investigate and improve the cleaning ability of the cavitation nozzle, this paper proposes a new model that is based on the Helmholtz nozzle and with the quadratic equation curve as the outer contour of the cavitation chamber. First, the numerical simulation of the flow field in the nozzle chamber was conducted using FLUENT software to analyze and compare the impact of the curve parameters and Reynolds number on the cleaning effect. Next, the flow field was captured by a high-speed camera in order to study the cavitation cycle and evolution process. Then, experiments were performed to compare the cleaning effect of the new nozzle with that of the Helmholtz nozzle. The study results demonstrate that effective cavitation does not occur when the diameter of the cavitation chamber is too large. For the new nozzle, with the increase of the Reynolds number, the degree of cavitation in the chamber first increases and then decreases; the cleaning effect is much better than that of a traditional Helmholtz nozzle under the same conditions; the nozzle has the best cleaning effect for the stand-off distance of 300 mm.
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Qiang, Yan. „Effects of properties of silt particles on cavitating flow characteristics in a nozzle“. Modern Physics Letters B 32, Nr. 21 (26.07.2018): 1850242. http://dx.doi.org/10.1142/s0217984918502421.
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To research the effects of properties of silt particles on cavitating flow, silt-laden cavitation flow in one 3D nozzle is simulated. Silt mean diameters are 0.005 mm, 0.007 mm, 0.009 mm, 0.010 mm, 0.012 mm, 0.013 mm, 0.015 mm, 0.020 mm, 0.026 mm, 0.030 mm, 0.035 mm, 0.040 mm, 0.046 mm, 0.050 mm and 0.056 mm. Silt concentrations vary from 1.0% to 10%. To measure the effects of silt particles, vapor contents under pure water cavitation flow and silt-laden cavitation flow conditions are calculated and compared. Results show that silt particles first promote the development of cavitation then inhibit the evolution of cavitation with the increase of silt concentration. Silt particles promotion scope decreases gradually and inhibition span increases constantly with the increase of silt mean diameter. Cavitation nuclei, vortices, slip velocity, virtual mass force and Saffman lift force have a closed relation with the promotion of silt particles. Vortices, viscosity and silt abrasion deeply influence the inhibition of cavitation.
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URA, Naoya, Yasuhiro SUGIMOTO und Keiichi SATO. „Behavior of unsteady cloud cavitation in a cavitating nozzle“. Proceedings of Conference of Hokuriku-Shinetsu Branch 2018.55 (2018): E016. http://dx.doi.org/10.1299/jsmehs.2018.55.e016.
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Zhao, Xin Ze, Hou Lin Yan, Zhen Xing Yang und Wen Ling Xian Yu. „The Study on Cavitation Phenomena of Zoom Nozzle Based on Orthogonal Experimental and Spraying Mechanics“. Applied Mechanics and Materials 468 (November 2013): 119–23. http://dx.doi.org/10.4028/www.scientific.net/amm.468.119.
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Abstract: The simulation model of zoom nozzle was established in this article.The numerical simulation of flow field in the zoom nozzle was completed with the Fluent software and based on orthogonal experimental method the structure size optimization of the nozzle was completed too.The results showed that the cavitation phenomenon is easy to form near the transition area of the cylindrical section and expansion section of the nozzle.Using orthogonal experimental method,we can achieve structure size optimization of the nozzle from reducing cavitation rate and increase the distance that emergence point of maximum cavitation rate with the cylindrical section of nozzle.
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Shao, Zhuang, Zhi Xia He, Zhi Wei Zhou und Xi Cheng Tao. „Experimental Study of Hydraulic Flip Phenomenon inside Diesel Nozzles Using Diesel and Biodiesel“. Advanced Materials Research 945-949 (Juni 2014): 940–43. http://dx.doi.org/10.4028/www.scientific.net/amr.945-949.940.
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As cavitation inside diesel nozzles can improve the spray characteristics, it has long been a hot issue. And together with the increasing attention of biodiesel, it is essential to identify the difference of cavitating flow characteristics between diesel and biodiesel. What’s more, the hydraulic flip phenomenon and cavitating flow with decreasing injection pressure hasn’t been studied. Based on this, cavitating flow inside transparent nozzles of diesel and biodiesel fuels with increasing and decreasing injection pressure was investigated in this paper. Experimental results showed that are quite different from the disappearance of it and it is harder to disappear. Biodiesel and longer nozzle orifices were hard for the hydraulic flip phenomenon to occur, and the disappearance of hydraulic flip phenomenon has great influence on the spray cone angle and the discharge coefficient.
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GOTO, SHISEI, HIROMICHI TSUJI, ISAO ONODERA, KEIGO WATANABE und KATSUMASA ONO. „Pilot-scale development of cavitation-jet deinking“. September 2014 13, Nr. 9 (01.10.2014): 19–25. http://dx.doi.org/10.32964/tj13.9.19.
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A new deinking method for paper recycling using a fluid-jet cavitation technique has been developed. An in-house, laboratory-scale device revealed that cavitation-jet treatment without deinking chemicals decreases ink and dirt content in deinked pulp. As the next step, a pilot-scale deinking device, 10 times larger than the laboratory device, was designed. The specifications of the pilot device were determined by experiments using the laboratory device. The pilot device was installed in a deinked pulp mill, and the effects of multijet nozzles within a reacting vessel, depending on consistencies of the deinked pulp, were investigated. The operation stability of the device was examined as well. The shape and size of an effective cavitation zone for ink detachment were changed by nozzle diameter and upstream pressure of the jet. The results from batch cavitation treatment of deinked pulp revealed that the device could treat the pulp with consistency up to 3.8% by weight and decrease attached ink, dirt specks, and macrostickies without addition of deinking chemicals. Hydrophobic colloidal materials, including microstickies after cavitation treatment, became more difficult to attach to hydrophobic surfaces. Continuous cavitation treatment gave similar results to those from batch treatment. Two types of multiple nozzle arrangements, parallel and cross-nozzle modes, decreased dirt specks to the same level as a mill disperser. On the other hand, the reductions of macrostickies by those modes were higher than with the disperser. Because treatment consistency increased more than 3%, treatment efficiency and device performance were significantly improved. This could be a big step toward practical use of cavitation treatment.
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Yuan, Weixing, und Gu¨nter H. Schnerr. „Numerical Simulation of Two-Phase Flow in Injection Nozzles: Interaction of Cavitation and External Jet Formation“. Journal of Fluids Engineering 125, Nr. 6 (01.11.2003): 963–69. http://dx.doi.org/10.1115/1.1625687.
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The present investigation demonstrates the strong interaction of cavitating nozzle flow with the outside jet formation. Due to the strong sensitivity of cavitation on the imposed boundary conditions, simulations with restriction on the internal problem are qualitatively and quantitatively incorrect, so that phenomena like hydraulic flip and supercavitation cannot be revealed. Our results indicate the potential of cavitation for enhancement of atomization and spray quality.
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Niedźwiedzka, Agnieszka. „Numerical modeling of cavitation phenomenon in a two-dimensional converging-diverging nozzle using a homogeneous approach“. Mechanik 91, Nr. 7 (09.07.2018): 520–22. http://dx.doi.org/10.17814/mechanik.2018.7.71.
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The article presents results of numerical simulations of cavitation phenomenon in a converging-diverging nozzle using the homogeneous approach. Three cavitation models are considered: the Schnerr and Sauer model, the Singhal et al. model and the Zwart et al. model. The simulations are performed for transient. The geometry is two-dimensional and planar. In the numerical calculations Fluent software was used. The aim of the work is to estimate the possibility of applying of two-dimensional planar numerical simulations of cavitating flows for small-sized converging-diverging nozzles. The motivation to conduct numerical simulations for two-dimensional and planar geometry are difficulties in obtaining results, which reflect experimental measurements, both for two- and three-dimensional geometry. The achieved results show a big similarity between the results of performed numerical simulations and the material from the experimental measurements for all the analyzed models.
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Zhang, Feng Hua, Nian Li und Chuan Lin Tang. „Design of Choking Cavitator and its Feasibility Study in Wastewater Treatment“. Applied Mechanics and Materials 535 (Februar 2014): 298–308. http://dx.doi.org/10.4028/www.scientific.net/amm.535.298.
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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.
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DELALE, C. F., G. H. SCHNERR und J. SAUER. „Quasi-one-dimensional steady-state cavitating nozzle flows“. Journal of Fluid Mechanics 427 (25.01.2001): 167–204. http://dx.doi.org/10.1017/s0022112000002330.
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Quasi-one-dimensional cavitating nozzle flows are considered by employing a homogeneous bubbly liquid flow model. The nonlinear dynamics of cavitating bubbles is described by a modified Rayleigh–Plesset equation that takes into account bubble/bubble interactions by a local homogeneous mean-field theory and the various damping mechanisms by a damping coefficient, lumping them together in the form of viscous dissipation. The resulting system of quasi-one-dimensional cavitating nozzle flow equations is then uncoupled leading to a nonlinear third-order ordinary differential equation for the flow speed. This equation is then cast into a nonlinear dynamical system of scaled variables which describe deviations of the flow field from its corresponding incompressible single-phase value. The solution of the initial-value problem of this dynamical system can be carried out very accurately, leading to an exact description of the hydrodynamic field for the model considered.A bubbly liquid composed of water vapour–air bubbles in water at 20 °C for two different area variations is considered, and the initial cavitation number is chosen in such a way that cavitation can occur in the nozzle. Results obtained, when bubble/bubble interactions are neglected, show solutions with flow instabilities, similar to the flashing flow solutions found recently by Wang and Brennen. Stable steady-state cavitating nozzle flow solutions, either with continuous growth of bubbles or with growth followed by collapse of bubbles, were obtained when bubble/bubble interactions were considered together with various damping mechanisms.
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Yii Shi Chin, Ronny, Shahrin Hisham Amirnordin und Amir Khalid. „Effects of Nozzle Shape on the Flow Characteristics of Premix Injector Using Computational Fluid Dynamics (CFD)“. Applied Mechanics and Materials 773-774 (Juli 2015): 450–54. http://dx.doi.org/10.4028/www.scientific.net/amm.773-774.450.
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The burner system is a patented, unique, higher-efficiency and fuel-injector system that works with a specially designed oil burner to create ultra-efficient combustion that reduces oil use, greenhouse gases and other harmful emissions. This research shows the injector nozzle geometries play a significant role in spray characteristics, atomization and formation of fuel-air mixture in order to improve combustion performance, and decrease some pollutant products from burner system. The aim of this research is to determine the effects of nozzle hole shape on spray characteristics of the premix injector by using CFD. Multiphase of volume of fluid (VOF) cavitating flow inside nozzles are determined by means of steady simulations and Eulerian-Eulerian two-fluid approach is used for performing mixing of Jatropha oil and air. Nozzle flow simulations resulted that cavitation area is strongly dependent on the nozzle hole shape. Conical hole with k-factor of 2 provides higher flow velocity and turbulent kinetic energy compared with conical hole with k-factor of 1.3 and cylindrical hole. The results show that the premix injector nozzle hole shape gives impact to the spray characteristics and indirectly affects the emission of the system.
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Koukouvinis, Phoevos, Nicholas Mitroglou, Manolis Gavaises, Massimo Lorenzi und Maurizio Santini. „Quantitative predictions of cavitation presence and erosion-prone locations in a high-pressure cavitation test rig“. Journal of Fluid Mechanics 819 (18.04.2017): 21–57. http://dx.doi.org/10.1017/jfm.2017.156.
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Experiments and numerical simulations of cavitating flow inside a single-orifice nozzle are presented. The orifice is part of a closed flow circuit, with diesel fuel as the working fluid, designed to replicate the main flow pattern observed in high-pressure diesel injector nozzles. The focus of the present investigation is on cavitation structures appearing inside the orifice, their interaction with turbulence and the induced material erosion. Experimental investigations include high-speed shadowgraphy visualization, X-ray micro-computed tomography (micro-CT) of time-averaged volumetric cavitation distribution inside the orifice as well as pressure and flow rate measurements. The highly transient flow features that are taking place, such as cavity shedding, collapse and vortex cavitation (also known as ‘string cavitation’), have become evident from high-speed images. Additionally, micro-CT enabled the reconstruction of the orifice surface, which provided locations of cavitation erosion sites developed after sufficient operation time. The measurements are used to validate the presented numerical model, which is based on the numerical solution of the Navier–Stokes equation, taking into account compressibility of both the liquid and liquid–vapour mixture. Phase change is accounted for with a newly developed mass transfer rate model, capable of accurately predicting the collapse of vaporous structures. Turbulence is modelled using detached eddy simulation and unsteady features such as cavitating vortices and cavity shedding are observed and discussed. The numerical results show agreement within validation uncertainty with the obtained measurements.
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Soyama, Hitoshi. „High-Speed Observation of a Cavitating Jet in Air“. Journal of Fluids Engineering 127, Nr. 6 (14.07.2005): 1095–101. http://dx.doi.org/10.1115/1.2060737.
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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.
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QIN, Z., K. BREMHORST, H. ALEHOSSEIN und T. MEYER. „Simulation of cavitation bubbles in a convergent–divergent nozzle water jet“. Journal of Fluid Mechanics 573 (Februar 2007): 1–25. http://dx.doi.org/10.1017/s002211200600351x.
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A model for simulating the process of growth, collapse and rebound of a cavitation bubble travelling along the flow through a convergent–divergent nozzle producing a cavitating water jet is established. The model is based on the Rayleigh–Plesset bubble dynamics equation using as inputs ambient pressure and velocity profiles calculated with the aid of computational fluid dynamics (CFD) flow modelling. A variable time-step technique is applied to solve the highly nonlinear second-order differential equation. This technique successfully solves the Rayleigh–Plesset equation for wide ranges of pressure variation and bubble original size and saves considerable computing time. Inputs for this model are the pressure and velocity data from CFD calculation. To simulate accurately the process of bubble growth, collapse and rebound, a heat transfer model, which includes the effects of conduction plus radiation, is developed to describe the thermodynamics of the incondensable gas inside the bubble. This heat transfer model matches previously published experimental data well. Assuming that single bubble behaviour also applies to bubble clouds, the calculated distance from the nozzle exit travelled by the bubble to the point where the bubble size becomes invisible is taken to be equal to the bubble cloud length observed. The predictions are compared with experiments carried out in a cavitation cell and show good agreement for different nozzles operating at different pressure conditions.
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Kumar, Aishvarya, Ali Ghobadian und Jamshid M. Nouri. „Assessment of Cavitation Models for Compressible Flows Inside a Nozzle“. Fluids 5, Nr. 3 (13.08.2020): 134. http://dx.doi.org/10.3390/fluids5030134.
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This study assessed two cavitation models for compressible cavitating flows within a single hole nozzle. The models evaluated were SS (Schnerr and Sauer) and ZGB (Zwart-Gerber-Belamri) using realizable k-epsilon turbulent model, which was found to be the most appropriate model to use for this flow. The liquid compressibility was modeled using the Tait equation, and the vapor compressibility was modeled using the ideal gas law. Compressible flow simulation results showed that the SS model failed to capture the flow physics with a weak agreement with experimental data, while the ZGB model predicted the flow much better. Modeling vapor compressibility improved the distribution of the cavitating vapor across the nozzle with an increase in vapor volume compared to that of the incompressible assumption, particularly in the core region which resulted in a much better quantitative and qualitative agreement with the experimental data. The results also showed the prediction of a normal shockwave downstream of the cavitation region where the local flow transforms from supersonic to subsonic because of an increase in the local pressure.
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Liu, Chengting, Gang Liu und Zuoxiu Yan. „Study on Cleaning Effect of Different Water Flows on the Pulsed Cavitating Jet Nozzle“. Shock and Vibration 2019 (11.06.2019): 1–15. http://dx.doi.org/10.1155/2019/1496594.
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The method of cleaning by self-excited pulsed cavitating jet was proposed according to cleaning characteristics and requirements of large storage equipment. This method has many advantages compared with other cleaning methods. In order to achieve the optimum cleaning effects, experimental research on working status of the nozzle at different flow rates was conducted and analysis was carried out from the following four aspects: cavitation morphology, pressure pulse frequency, velocity fluctuation amplitude, and erosion effect. The research results showed that flushing effects in the nozzle without cavitation were far below those with cavitation; when the flow rate increased to over 2.7 m3/h, cavitation began to appear in the chamber. When Q = 7.2 m3/h, the velocity fluctuation amplitude was about 17.25 m and pressure fluctuation occurred for 86 times (maximum) within 1 s. During the experiment on erosion effects, the flow rate had little influence on outside diameter of the erosion circle. The erosion rate increased with the increase of the flow rate, reached the peak value at Q = 7.2 m3/h, but slightly decreased subsequently.
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Li, Quan Chang, Kai He und Ru Xu Du. „Fatigue Analysis of Pure Waterjet Nozzle-A CFD and FEA Approach“. Advanced Materials Research 328-330 (September 2011): 1359–64. http://dx.doi.org/10.4028/www.scientific.net/amr.328-330.1359.
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The utilization of pure waterjet for Incremental Sheet Metal Forming (ISMF) is growing. However, the fatigue of pure waterjet nozzle is not fully clear. In the current study, based on the computational fluid dynamics (CFD) and finite element analysis (FEA), the fatigue failure of pure waterjet nozzle was simulated and analyzed. The influence of uneven equivalent stress distribution and generation of cavitation on nozzle fatigue failure was discussed. The results obtained from two simulations (velocity, pressure) show a good agreement with the theoretical predictions, which indicates that the approach based on CFD and FEA is absolutely feasible. Due to the uneven equivalent stress distribution, there is the first failure point inside the nozzle, which reduces the whole life of the nozzle. The unreasonable nozzle structure is one of main causes of cavitation generation; cavitation damage is reduced by optimizing the structure to improve the overall life of the nozzle.
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Dong, Pengbo, Keiya Nishida und Youichi Ogata. „Characterization of multi-hole nozzle sprays and internal flow for different nozzle hole lengths in direct-injection diesel engines“. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 231, Nr. 4 (05.08.2016): 500–515. http://dx.doi.org/10.1177/0954407016653890.
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Multi-hole nozzles have a wide range of application in the fuel supply system of modern diesel engines, although single-hole nozzles dominate basic internal flow and spray research. The parameters of the nozzle geometry are crucial factors that can alter the internal flow dynamics of the nozzle and the consequent spray behaviours. The novelty of this study lies in implementing the application of practical prototype mini-sac multi-hole diesel nozzles to experimental and numerical studies. The internal flow and spray characteristics generated by practical multi-hole (10-hole) nozzles with different sac wall thicknesses (0.4 mm, 0.6 mm and 0.8 mm) were investigated in conjunction with a series of experimental and computational methods using a constant injection quantity (2 mm3/hole). Globally, the analysis mainly concentrated on different nozzle flow dynamics, different injection processes and different spray morphologies. Specifically, the high-speed video observation method was applied to visualize the injection processes and the spray evolution of different nozzles inside a high-pressure vessel. Furthermore, numerical simulations were conducted to reveal the three-dimensional nature of the internal flow inside different configurations; this was instructive in helping us to understand better the mechanism behind the spray behaviours. The results indicate that intense cavitating, turbulent and spiral rotating flow patterns occur inside practical multi-hole nozzles, and the consequent sprays emerging from the nozzles are perturbed, asymmetrical and unstable in both the near field and the far field. Moreover, a decrease in the nozzle hole length can increase the effects of cavitation, turbulence, the void fraction and the axial and radial injection velocity components on the nozzle hole exit; this is accompanied by an intriguing longer injection duration, wider near-field and far-field spray widths, a lower injection rate, and overlapping or even shorter spray propagation. However, these changes are not linear, and different parameters have different sensitivities to the variation in the nozzle hole length.
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Guo, Genmiao, Zhixia He, Xicheng Tao, Shenxin Sun, Zhen Zhou und Xiongbo Duan. „Optical experiments of string cavitation in diesel injector tapered nozzles“. Thermal Science 24, Nr. 1 Part A (2020): 193–201. http://dx.doi.org/10.2298/tsci180405005g.
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Flow inside the diesel nozzle is crucial to spray, combustion, and emissions. This work aimed to improve the understanding of effects of internal fuel-flow on diesel spray, especially the special string cavitating flow. Optical experiments were employed for characterizing the formation of string cavitation inside the transparent scaled-up tapered diesel orifices. Simultaneously, the corresponding evolution of spray cone angles were obtained. Results show that there were two origins of the string cavitation, which were originated from inlet and outlet of the orifice, respectively. Moreover, there were two typical development processes of the string cavitation between hole and hole, which were defined as type-A and type-B string cavitation. Furthermore, effects of string cavitation were analyzed: it could trigger the geometry-induced cavitation and make a sharp increase of spray cone angle. Finally, the relationships between the occurrence regularity of string cavitation, the needle lift and the injection pressure were revealed by comparison of different needle lifts and different injection pressures.
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Falcucci, Giacomo, Stefano Ubertini, Gino Bella und Sauro Succi. „Lattice Boltzmann Simulation of Cavitating Flows“. Communications in Computational Physics 13, Nr. 3 (März 2013): 685–95. http://dx.doi.org/10.4208/cicp.291011.270112s.
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AbstractThe onset of cavitating conditions inside the nozzle of liquid injectors is known to play a major role on spray characteristics, especially on jet penetration and break-up. In this work, we present a Direct Numerical Simulation (DNS) based on the Lattice Boltzmann Method (LBM) to study the fluid dynamic field inside the nozzle of a cavitating injector. The formation of the cavitating region is determined via a multi-phase approach based on the Shan-Chen equation of state. The results obtained by the LBM simulation show satisfactory agreement with both numerical and experimental data. In addition, numerical evidence of bubble break-up, following upon flow-induced cavitation, is also reported.
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Yii Shi Chin, Ronny, Shahrin Hisham Amirnordin, Norani Mansor und Amir Khalid. „Numerical Analysis of Nozzle Hole Shape to the Spray Characteristics from Premix Injector in Burner System : A Review“. Applied Mechanics and Materials 773-774 (Juli 2015): 610–14. http://dx.doi.org/10.4028/www.scientific.net/amm.773-774.610.
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Fuel injection system is widely used in the field of burner system nowadays. Spray nozzles having various operating conditions depends on the design of nozzle and it is precision components designed to perform very specific spray characteristics under specific conditions. This review paper focuses on spray characteristics, effects of geometry of injector, influence of fuel and hole shaped nozzle with cylindrical and conical holes on spray characteristics. The parameters were discussed based on an overview of the research in the field of simulations with nozzle shaped injectors. A massive majority researcher reported that conical nozzle hole is better due to it contributed suppression of cavitation in nozzle hole, slowed down primary breakup process and thus produced larger spray droplets, high spray penetration.
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Li, Xinhai, Yong Cheng, Xiaoyan Ma und Xue Yang. „A correction method of hole-to-hole variation mass flow of diesel injector equipped on a common-rail DI diesel engine“. European Physical Journal Applied Physics 83, Nr. 3 (September 2018): 30902. http://dx.doi.org/10.1051/epjap/2018180155.
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In the present paper, the inner flow characteristic and cavitation phenomena for different injector shapes (characterized by angle α and length–diameter ratio) are analyzed experimentally and numerically. Mathematical models including multi-phases model, volume of fluid model and the k-epsilon turbulence model are validated by experiment. The numerical results show that with the increase of injection angle α, the inception time of cavitation is earlier, the extension velocity of cavitation to nozzle exit is higher and the nozzle fuel mass is less for each cycle. With the increase of length–diameter ratios, the time consumed from the inception to stable state of cavitation is longer and the single nozzle fuel mass increases. Furthermore, a correction method is proposed based on inconsistent length–diameter ratios. It could amend the difference of single nozzle fuel mass and guarantee the uniform fuel mass in axis symmetry direction of engine cylinder.
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Yang, Zhendong, Yalong Cao, Qiaoling Zhang, Feng Wu, Suqi Shi, Simao Zhao und Hui Zhan. „Influence of Rectifier Nozzles on the Flow Distribution Characteristics of Parallel Pipes“. Water 12, Nr. 9 (13.09.2020): 2558. http://dx.doi.org/10.3390/w12092558.
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The inhomogeneous distribution of parallel pipe flow leads to difficulty in the efficient and reliable operation of fluid power equipment. In view of this, a new type of rectifier nozzle has been proposed in parallel pipelines. Numerical simulation and experimental studies were used to reveal the influence of the rectification nozzle on the flow distribution characteristics. The hydraulic characteristics of the parallel pipelines with and without rectifier nozzles were compared and analyzed. The effects of the temperature and inlet flow on the flow uniformity were studied. The results showed that the initial temperature had little effect on the flow distribution of parallel pipelines, and the flow rates of the branches were not much different. The inlet flow had great influence on the distribution characteristics of the parallel pipelines, but the rectifier nozzles changed the local resistance structure and pressure distribution at the shunt, thereby improving the non-uniformity of the flow distribution of the parallel pipelines, and the maximum difference between the two pipes was optimized from 28.89 t/h (20.3%) to 2.2 t/h (1.5%). The rectifying nozzle could distort the flow field of each branch during the split, making the distribution of flow rate and flow state more uniform and stable. At high inlet fluid temperatures, cavitation could occur under the pressure drop of the nozzle, and partial cavitation had little effect on the flow distribution.
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Ni, Xiaonan, und Hua Wen. „Formation of Residual Bubbles in Diesel Engine Nozzle and Their Influence on Initial Jet“. Modelling and Simulation in Engineering 2021 (12.08.2021): 1–12. http://dx.doi.org/10.1155/2021/6679699.
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The method of combining experiment and numerical simulation was used to study the cavitation and gas backflow phenomena during nozzle off-flow stage and the influence of residual bubbles on the initial jet in the near field. An equal-size optical nozzle based on acrylic material is designed, and the injection process of the fuel nozzle is photographed using high-speed photography technology. Establish a cavitation mathematical model to analyze the details of internal flow and initial jet. The results show that after the needle valve starts to close, cavitation occurs in the orifice and the sac in sequence, and the amount of cavitation in the sac is large. The collapse of cloud of cavitation bubbles will cause the outside air to flow back into the nozzle. The volume of the backflow air is slightly larger than the total volume of cloud of cavitation bubbles. The study found that the initial position of the residual bubbles has a significant effect on the initial atomization shape. When the residual bubble was in the front of the orifice, the initial tip was formed at the front of jet, and then, it stretched into a thin ligament due to vortex ring motion around the jet.