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1
Li, Hong, Zhenhua Shen, Nicholas Engen Pedersen, and Christian Brix Jacobsen. "Experimental and unsteady numerical research of a high-specific-speed pump for part-load cavitation instability." Advances in Mechanical Engineering 11, no. 3 (March 2019): 168781401982893. http://dx.doi.org/10.1177/1687814019828932.
Повний текст джерелаАнотація:
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.
2
Kikuta, Kengo, Noriyuki Shimiya, Tomoyuki Hashimoto, Mitsuru Shimagaki, Hideaki Nanri, and Yoshiki Yoshida. "Influence of Thermodynamic Effect on Blade Load in a Cavitating Inducer." International Journal of Rotating Machinery 2010 (2010): 1–7. http://dx.doi.org/10.1155/2010/302360.
Повний текст джерелаАнотація:
Distribution of the blade load is one of the design parameters for a cavitating inducer. For experimental investigation of the thermodynamic effect on the blade load, we conducted experiments in both cold water and liquid nitrogen. The thermodynamic effect on cavitation notably appears in this cryogenic fluid although it can be disregarded in cold water. In these experiments, the pressure rise along the blade tip was measured. In water, the pressure increased almost linearly from the leading edge to the trailing edge at higher cavitation number. After that, with a decrease of cavitation number, pressure rise occurred only near the trailing edge. On the other hand, in liquid nitrogen, the pressure distribution was similar to that in water at a higher cavitation number, even if the cavitation number as a cavitation parameter decreased. Because the cavitation growth is suppressed by the thermodynamic effect, the distribution of the blade load does not change even at lower cavitation number. By contrast, the pressure distribution in liquid nitrogen has the same tendency as that in water if the cavity length at the blade tip is taken as a cavitation indication. From these results, it was found that the shift of the blade load to the trailing edge depended on the increase of cavity length, and that the distribution of blade load was indicated only by the cavity length independent of the thermodynamic effect.
3
Chudyk, I. I., and Ya M. Femiak. "THE DEVELOPMENT OF THEORETICAL BACKGROUND OF CONTROLLING THE CAVITATION-IMPULSE EFFECT ON A BOTTOM-HOLE ON THE BASIS OF THE THEORY OF SPECTRA." Prospecting and Development of Oil and Gas Fields, no. 2(71) (June 25, 2019): 30–37. http://dx.doi.org/10.31471/1993-9973-2019-2(71)-30-37.
Повний текст джерелаАнотація:
The authors consider the technology of intensification of the rock failure during the drilling of the wells using the substantiation of physico-mechanical, cavitation and technological processes. Further development of the mechanism of rock failure due to the created cavitation processes, the manifestation of which is possible at the well bottom when drilling with modern types of drill bits, is an important scientific and technical problem. The solution of this problem will significantly increase the efficiency and reliability of drilling the wells. The development of the mechanism is of great practical importance for oil-and-gas industry. The authors have further developed the mechanisms of rock failure during drilling, which allow to take into account as constant actions both the mechanical effect of the drill bit cutting structure on the rock and the cavitation effect of the cooling flushing fluid on the bottom-hole surface. For the first time it has been proved that cavitation-impulse treatment of a bottom during drilling allows to evaluate the erosion effect of cavitation at various distances from the cavitator, taking into account dissipative losses, and to increase the proportion of energy directed to the rock. For the first time, the possibility of choosing the most optimal mode of cavitation-impulse load at the bottom of a well has been substantiated. To evaluate the effectiveness of the cavitation-pulsation washing technology, analytical dependencies have been proposed. Those dependencies allow to predict the frequency distribution of energy from the collapse of cavitation bubbles created by the cavitator at the bottom of the well. It allows to control actively the process of cavitation-impulse impact on rocks in course of their failure during drilling. The authors provide characteristics that show the cavitation-pulsation process fully. Thus, these characteristics allow to evaluate the effectiveness of the process in the rocks failure at the bottom-hole more accurately. When conducting cavitation-impulse treatment of the bottomhole, in order to create artificial cracking, the load mode, namely the distribution of the load energy over frequency ranges, is of importance. To expand the area of the cavitation-impulse treatment of the rock mass, it is necessary to form such loads that the main part of the energy is concentrated in the low frequency range. With the increase of the distance from the perturbance source (cavitator) low frequencies attenuate less in comparison with high frequencies. In order to choose the most optimal mode of cavitation-impulse load on the bottom hole, the distribution of energy over various frequency ranges in the process of the spread of cavitation-impulse effect on a rock massif has been studied. The suggested analytical dependencies allow to predict the frequency distribution of energy which is released when the cavitation bubbles collapse at the bottom-hole. It gives a possibility to control the process of cavitation-impulse effect on rocks in the process of their failure during drilling.
4
Wang, Xin, and Ting-Qiang Xie. "Cavitation erosion behavior of hydraulic concrete under high-speed flow." Anti-Corrosion Methods and Materials 69, no. 1 (December 16, 2021): 81–93. http://dx.doi.org/10.1108/acmm-03-2021-2459.
Повний текст джерелаАнотація:
Purpose Cavitation erosion has always been a common technical problem in a hydraulic discharging structure. This paper aims to investigate the cavitation erosion behavior of hydraulic concrete under high-speed flow. Design/methodology/approach A high-speed and high-pressure venturi cavitation erosion generator was used to simulate the strong cavitation. The characteristics of hydrodynamic loads of cavitation bubble collapse zone, the failure characteristics and the erosion development process of concrete were investigated. The main influencing factors of cavitation erosion were discussed. Findings The collapse of the cavitation bubble group produced a high frequency, continuous and unsteady pulse load on the wall of concrete, which was more likely to cause fatigue failure of concrete materials. The cavitation action position and the main frequency of impact load were greatly affected by the downstream pressure. A power exponential relationship between cavitation load, cavitation erosion and flow speed was observed. With the increase of concrete strength, the degree of damage of cavitation erosion was approximately linearly reduced. Originality/value After cavitation erosion, a skeleton structure was formed by the accumulation of granular particles, and the relatively independent bulk structure of the surface differed from the flake structure formed after abrasion.
5
Li, Wenguang, and Yuliang Zhang. "Numerical simulation of cavitating flow in a centrifugal pump as turbine." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 232, no. 2 (December 26, 2016): 135–54. http://dx.doi.org/10.1177/0954408916686126.
Повний текст джерелаАнотація:
In this study, the cavitating flow and cavitation performance are studied by employing the computational fluid dynamics method in the turbine mode of a centrifugal pump at part-load, best efficiency, and over-load points. The flow models are validated in the pump mode under noncavitation condition. The relationships between the performance variables and net positive suction head available are obtained, and the corresponding net positive suction heads required are extracted. The flow patterns, location, and shape of the cavity are illustrated; the pressure coefficient profiles on the blade surfaces are clarified and compared with those in the pump mode under both noncavitation and critical cavitation conditions. The cavitation performance and flow pattern as well as cavity shape in the turbine mode are distinguishably different from the pump mode. It is found out that the cavitation behavior in the turbine mode exhibits three notable features: a lower and less flow rate-dependent net positive suction head required, a flow rate-dependent suppressed rotational flow in the draft tube, as well as a rotational and extendable cavitating rope originated from the impeller cone. The results and methods can be important and useful for the design and selection of a centrifugal pump as turbine.
6
Yang, Jing, Qingjuan Hu, Zhengwei Wang, Jinghuan Ding, and Xianyu Jiang. "Effects of inlet cavitation on swirling flow in draft-tube cone." Engineering Computations 35, no. 4 (June 11, 2018): 1694–705. http://dx.doi.org/10.1108/ec-08-2017-0313.
Повний текст джерелаАнотація:
Purpose For Francis turbine, the vortex flow in the draft tube plays an important role in the safe and efficient operating of hydraulic turbine. The swirling flow produced at the blade trailing edge at off-design conditions has been proved to be the fundamental reason of the vortex flow. Exploring the swirling flow variations in the non-cavitation flow and cavitation flow field is an effective way to explain the mechanism of the complex unsteady flow in the draft tube. Design/methodology/approach The swirling flow in different cavitation evolution stages of varying flow rates was studied. The swirl number, which denotes the strength of the swirling flow, was chosen to systematically analyze the swirling flow changes with the cavitation evolutions. The Zwart–Gerber–Blemari cavitation model and SST turbulence model were used to simulate the two-phase cavitating flow. The finite volume method was used to discrete the equations in the unsteady flow field simulation. The Frozen Rotor Stator scheme was used to transfer the data between the rotor-stator interfaces. The inlet total pressure was set to inlet boundary condition and static pressure was set to outlet boundary condition. Findings The results prove that the mutual influences exist between the swirling flow and cavitation. The swirling flow was not only affected by the load but also significantly changed with the cavitation development, because the circumferential velocity decrease and axial velocity increase presented with the cavitation evolution. At the high load conditions, the system stability may improve with the decreasing swirling flow strength. Research limitations/implications Further experimental and simulation studies still need to verify and estimate the reasonability of the swirling flow seen as the cavitation inception signal. Originality/value One interesting finding is that the swirl number began to change as the inception cavitation appeared. This is meaningful for the cavitation controlling in the Francis turbine.
7
Tan, Lei, Baoshan Zhu, Yuchuan Wang, Shuliang CAO, and Shaobo Gui. "Numerical study on characteristics of unsteady flow in a centrifugal pump volute at partial load condition." Engineering Computations 32, no. 6 (August 3, 2015): 1549–66. http://dx.doi.org/10.1108/ec-05-2014-0109.
Повний текст джерелаАнотація:
Purpose – The purpose of this paper is to elucidate the detailed flow field and cavitation effect in the centrifugal pump volute at partial load condition. Design/methodology/approach – Unsteady flows in a centrifugal pump volute at non-cavitation and cavitation conditions are investigated by using a computation fluid dynamics framework combining the re-normalization group k-e turbulence model and the mass transport cavitation model. Findings – The flow field in pump volute is very complicated at part load condition with large pressure gradient and intensive vortex movement. Under cavitation conditions, the dominant frequency for most of the monitoring points in volute transit from the blade passing frequency to a lower frequency. Generally, the maximum amplitudes of pressure fluctuations in volute at serious cavitation condition is twice than that at non-cavitation condition because of the violent disturbances caused by cavitation shedding and explosion. Originality/value – The detailed flow field and cavitation effect in the centrifugal pump volute at partial load condition are revealed and analysed.
8
Li, Wen-Guang, and Yu-Liang Zhang. "Computational cavitating viscous liquid flows in a pump as turbine and Reynolds number effects." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 233, no. 3 (May 6, 2018): 536–50. http://dx.doi.org/10.1177/0954408918770057.
Повний текст джерелаАнотація:
Cavitating flows of viscous oils in an experimental centrifugal pump with low specific speed are modeled and simulated by using the time-averaged Navier–Stokes equations and standard [Formula: see text] turbulence model as well as full cavitation model based on the computational fluid dynamics method, when the pump operates in the reverse direction as turbine to generate power. The cavitation characteristics are identified at part-load, best efficiency and over-load points and five viscosities. Effects of viscosity on net positive suction head required are clarified. Net positive suction head required correction factor and conversion factor curves are obtained and correlated to impeller Reynolds number. The flow and cavitation models are validated with the existing experimental results and empirical correlations. Pressure and helix angle profiles at the draft tube entrance, cavity shape, swirling flow pattern in the draft tube, and the pressure coefficient distribution over the blade surfaces are presented. The presented results can be useful for design, selection, performance prediction, and impeller redesign of a pump as turbine.
9
Hong, Sung Mo, Min Ku Lee, G. H. Kim, Chang Kyu Rhee, K. H. Kim, and Wheung Whoe Kim. "Analysis on Fatigue Fracture of the Flame-Quenched 8.8Al-Bronze by Ultrasonic Vibratory Cavitation Erosion." Solid State Phenomena 118 (December 2006): 463–68. http://dx.doi.org/10.4028/www.scientific.net/ssp.118.463.
Повний текст джерелаАнотація:
In this study the fatigue properties due to cavitation damage of flame-quenched 8.8Al-bronze (8.8Al-4.5Ni-4.5Fe-Cu) as well as current nuclear pump materials (8.8Al-bronze, SUS316 and SR50A) have been investigated by using an ultrasonic vibratory cavitation test. For this the impact loads of cavitation bubbles generated by ultrasonic vibratory device quantitatively evaluated and simultaneously the cavitation erosion experiments have been carried out. The fatigue analysis on the cavitation damage of the materials has been made from the determined impact load distribution (e.g. impact load, bubble count) and erosion parameters (e.g. incubation period, MDPR). According to Miner’s law, the exponents b of the F-N relation (Fb N = Constant) at the incubation stage (N: the number of fracture cycle) were 5.62, 4.16, 6.25 and 8.1 for the 8.8Al-bronze, flame-quenched sample, SUS316 and SR50A alloys, respectively. At steady-state, the exponents b of the F-N curve (N: the number of cycles required for a 1μm increment of MDP) were determined as 6.32, 5, 7.14 and 7.76 for the 8.8Al-bronze, flame-quenched sample, SUS316 and SR50A alloys, respectively.
10
Jang, G. H., and D. I. Chang. "Analysis of a Hydrodynamic Herringbone Grooved Journal Bearing Considering Cavitation." Journal of Tribology 122, no. 1 (June 22, 1999): 103–9. http://dx.doi.org/10.1115/1.555333.
Повний текст джерелаАнотація:
The Reynolds equation, incorporating Elrod’s cavitaton algorithm, is discretized on a rectangular grid in computational space through coordinate mapping in order to accurately analyze a herringbone grooved journal bearing of a spindle motor in a computer hard disk drive. The pressure distribution and cavitation area are determined by using the finite volume method. Predicted results are compared to experimental data of previous researchers. It was found that positive pressure is developed within the converging section of the bearing and that a cavity occurs in the diverging section. Cavitation has been neglected in the previous analyses of the herringbone grooved bearing. Load capacity and bearing torque are increased due to the increase of eccentricity and L/D and the decrease of the groove width ratio. The maximum load capacity was found to occur at a groove angle of 30 degrees while bearing torque remains constant due to the variation of the groove angle. The cavitation region is significantly decreased with the inclusion of herringbone grooves. However, the region increases with the increase of the eccentricity, L/D, groove angle and the rotational speed and the decrease of the groove width ratio. [S0742-4787(00)01401-6]
11
Yang, Yongfei, Wei Li, Weidong Shi, Ling Zhou, and Wenquan Zhang. "Experimental Study on the Unsteady Characteristics and the Impact Performance of a High-Pressure Submerged Cavitation Jet." Shock and Vibration 2020 (June 16, 2020): 1–15. http://dx.doi.org/10.1155/2020/1701843.
Повний текст джерелаАнотація:
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.
12
Decaix, Jean, Andres Müller, Arthur Favrel, François Avellan, and Cécile Münch-Alligné. "Investigation of the Time Resolution Set Up Used to Compute the Full Load Vortex Rope in a Francis Turbine." Applied Sciences 11, no. 3 (January 27, 2021): 1168. http://dx.doi.org/10.3390/app11031168.
Повний текст джерелаАнотація:
The flow in a Francis turbine at full load is characterised by the development of an axial vortex rope in the draft tube. The vortex rope often promotes cavitation if the turbine is operated at a sufficiently low Thoma number. Furthermore, the vortex rope can evolve from a stable to an unstable behaviour. For CFD, such a flow is a challenge since it requires solving an unsteady cavitating flow including rotor/stator interfaces. Usually, the numerical investigations focus on the cavitation model or the turbulence model. In the present works, attention is paid to the strategy used for the time integration. The vortex rope considered is an unstable cavitating one that develops downstream the runner. The vortex rope shows a periodic behaviour characterized by the development of the vortex rope followed by a strong collapse leading to the shedding of bubbles from the runner area. Three unsteady RANS simulations are performed using the ANSYS CFX 17.2 software. The turbulence and cavitation models are, respectively, the SST and Zwart models. Regarding the time integration, a second order backward scheme is used excepted for the transport equation for the liquid volume fraction, for which a first order backward scheme is used. The simulations differ by the time step and the number of internal loops per time step. One simulation is carried out with a time step equal to one degree of revolution per time step and five internal loops. A second simulation used the same time step but 15 internal loops. The third simulations used three internal loops and an adaptive time step computed based on a maximum CFL lower than 2. The results show an influence of the time integration strategy on the cavitation volume time history both in the runner and in the draft tube with a risk of divergence of the solution if a standard set up is used.
13
Liu, Kailei, Shaopeng Kang, Hongbin Qiang, and Chengtao Yu. "Cavitation Prevention Potential of Hydromechanical Pressure Compensation Independent Metering System with External Active Load." Processes 9, no. 2 (January 29, 2021): 255. http://dx.doi.org/10.3390/pr9020255.
Повний текст джерелаАнотація:
This article studies the cavitation performance and preventing method of the hydromechanical pressure compensation independent metering system (HPCIMS). Compared with the conventional load sensing system (CLSS), the meter-in and meter-out orifices of HPCIMS can be regulated independently. A quasi-static behavior analysis of cavitation performance was applied to the HPCIMS and CLSS. The meter-in pressure equation of HPCIMS showed that keeping the ratio of the meter-in and meter-out orifices greater than the minimum value can avoid the cavitation phenomenon. Systems parameters were then kept as constant, and the key parameters related to cavitation performance of the two systems were compared by varying external force. Comparison results show that the cavitation phenomenon in the meter-in chamber of CLSS with the external active load is inevitable, but in HPCIMS, it can prevent the cavitation phenomenon by changing the ratio of the meter-in and meter-out orifices, so the HPCIMS has the cavitation prevention potential.
14
Xu, Wanjun, Shanhui Zhao, Yaoyao Xu, and Kang Li. "Reynolds Model versus JFO Theory in Steadily Loaded Journal Bearings." Lubricants 9, no. 11 (November 19, 2021): 111. http://dx.doi.org/10.3390/lubricants9110111.
Повний текст джерелаАнотація:
Cavitation has a potential effect on the performance of full circle journal bearings. This paper studied the effects of cavitation on steadily loaded journal bearings, with the purpose of analyzing the necessity of adopting a mass-conserving model for ordinary journal bearings. The Christopherson’s method and Elrod cavitation algorithm were implemented to represent the non-mass-conserving Reynolds model and the mass-conserving Jakobsson-Floberg-Olsson (JFO) theory, respectively. The difference in the oil film reformation boundaries predicted by the two methods was focused on. The typical performance parameters including oil film pressure, load-carrying capacity, attitude angle, friction force, and leakage were comprehensively compared. The results show that the load-carrying capacity is improved by the decrease in cavitation pressure, and the effect is significant in lightly loaded cavitated bearings. In non-cavitated cases and the cavitated cases with intermediate and heavy loads, the difference between the Reynolds model and the JFO theory can be effectively ignored, but the accuracy of the leakage predicted using the Reynolds model should be carefully evaluated.
15
Yu, An, Qinghong Tang, Xincheng Wang, Daqing Zhou, and Jintao Liu. "Investigation of the Pressure Fluctuation Alleviation in a Hydraulic Turbine by Runner Modification." Water 11, no. 7 (June 28, 2019): 1332. http://dx.doi.org/10.3390/w11071332.
Повний текст джерелаАнотація:
Cavitation and system instability are the most common problems occurring in hydraulic power systems, especially operated under part-load conditions. Previous research show that when the hydraulic turbine operates apart from designed conditions, such as part-load conditions, a helical vortex rope occurs from the runner exit, and usually generates severe pressure oscillations. Cavitation usually appears and turns the rope to become a two-phase cavitation rope. The occurrence of cavitation rope is believed to be the main reason of the severe pressure oscillations. Based on a new multiphase flow simulation method re-developed in ANSYS CFX, this paper did the runner modification by using grooves and made the investigation of pressure fluctuation alleviation in a hydraulic turbine at different cavitation numbers. The behavior of cavitation rope and the pressure fluctuations induced by cavitation under typical part load conditions with modified runner were analyzed in present research. The results show that besides the pressure fluctuation induced by the rope rotating, cavitation induced a new pressure fluctuation with a lower frequency. For the embedded analysis the results show that the modified runner can decrease the vortex rope eccentricity and increase the vortex core pressure and finally alleviate the two types of pressure fluctuations. Also, the turbine efficiency has a little rise when equipped with the modified runner.
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Yang, Jing, Lingjiu Zhou, and Zhengwei Wang. "The numerical simulation of draft tube cavitation in Francis turbine at off-design conditions." Engineering Computations 33, no. 1 (March 7, 2016): 139–55. http://dx.doi.org/10.1108/ec-12-2014-0257.
Повний текст джерелаАнотація:
Purpose – The vortex ropes in draft tube of Francis turbine always cause fluctuation and vibration, which consequently threaten the safety and stability of hydro turbines. The purpose of this paper is to use a cavitation flow computational method to simulate spiral vortex ropes under part load conditions and columnar vortex ropes under high-load conditions in draft tube. The unsteady cavitating flow characteristics in draft tube and its interaction with runner cavitation were analyzed. Design/methodology/approach – The calculation method was verified by cavitation simulation around a 3D hydrofoil. The results show that the Large Eddy Simulation (LES) turbulence model with the Zwart-Gerber-Blemari cavitation model have comparative advantage in cavitation simulations whether from capture of cavity shape or prediction of pressure changes. So it was chosen to simulate the two-phase cavitation flow in Francis turbine. The boundary conditions for inlet and outlet were set to inlet total pressure and outlet static pressure. The finite volume method with the central difference was adopted to discretize the equations. Findings – The calculated Thoma number agreed well with the experimental data. The vortex rope diameter and length increased with the cavitation development for both of the two types of vortex ropes conditions. The maximum peak-to-peak values of pressure pulsations located in the draft tube elbow part under all of the Thoma numbers conditions. Under spiral vortex rope conditions, the pressure pulsation in the same section of draft tube cone show obviously phase shift. The vortex rope affects the development of runner cavitation, which induces the symmetric and axisymmetric cavitation region in the suction side of blades for spiral and columnar vortex rope condition, respectively. Research limitations/implications – The mesh independence had been checked only in non-cavitation flow; in addition, the mesh density did not well satisfy the requirements of LES due to the limitations of computing power. The higher mesh density on a simplified model with one blade flow path and the entire draft tube may be helpful for obtaining more precise results. Originality/value – The spiral and columnar vortex ropes in a Francis turbine were compared and analyzed. The annular hydraulic jump appeared in the columnar vortex rope conditions has little effects on the pressure pulsations. The uneven flow field caused by spiral vortex led to the asymmetric cavitation development.
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Ding, Aoshuang, Xiaodong Ren, Xuesong Li, and Chunwei Gu. "A new gaseous cavitation model in a tilting-pad journal bearing." Science Progress 104, no. 3 (July 2021): 003685042110294. http://dx.doi.org/10.1177/00368504211029431.
Повний текст джерелаАнотація:
With the higher rotational speeds and loads in bearings, the gaseous cavitation becomes more and cannot be ignorable in the bearing designs. However, there is no enough research in non-equilibrium gaseous cavitation model. This paper builds a new gaseous cavitation model based on the Bunsen solubility and bubble dynamics. The equilibrium pressure is calculated by the Bunsen solubility based on the local pressure and its pressure difference with the local pressure decides the cavitation mass transfer rate in this new model for gaseous cavitation. A titling-pad journal bearing at 3000 rpm and under 299 kN load is chosen as the research object with this new model and an original equilibrium model applied. As for the minimum film thickness and bearing force balance, this new model performs in better accordance with the experiment than the equilibrium model. According to the multiphase distributions in the bearing film, the gaseous cavitation rate in this new model can simulate the non-equilibrium processes of dissolution and cavitation under the high rotational speed, which is close to the physical gaseous cavitation process. This new model is developed and applied successfully in tilting-pad journal bearings for simulating the non-equilibrium gaseous cavitation.
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Hattori, Shuji, Hiroyuki Mori, and Tsunenori Okada. "Quantitative Evaluation of Cavitation Erosion." Journal of Fluids Engineering 120, no. 1 (March 1, 1998): 179–85. http://dx.doi.org/10.1115/1.2819644.
Повний текст джерелаАнотація:
In order to evaluate the quantitative cavitation-erosion resistance of materials, a pressure-detector-installed specimen was developed, which can measure both the impact load produced by cavitation bubble collapse and the volume loss simultaneously. Test specimens (pressure-detection rod) used were nine kinds of metals and were exposed to vibratory cavitation. A linear relation was obtained for all materials between the accumulated impact energy ∑Fi2 calculated from the distribution of impact loads and the volume loss, independent of test conditions. Impact energy accumulated during the incubation period and the energy for a unit material removal in steady-state period were obtained from the relation. These values are very Important concerning quantitative erosion resistance evaluation. That is, when the distribution of impact loads is acquired for different cavitation conditions, the volume loss can be estimated. This idea was applied to the venturi cavitation erosion. The experimental results for venturi test corresponds well with the prediction using these impact energy values. It was concluded that the quantitative impact energy values of materials can be determined independent of the apparatus and the test condition by using the newly developed pressure-detector-installed specimen.
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Dörfler, Peter K. "Cavitation Compliance in 1D Part-load Vortex Models." International Journal of Fluid Machinery and Systems 10, no. 3 (September 30, 2017): 197–208. http://dx.doi.org/10.5293/ijfms.2017.10.3.197.
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Dörfler, P. K. "Cavitation Influence in 1D Part-load Vortex Models." IOP Conference Series: Earth and Environmental Science 49 (November 2016): 052003. http://dx.doi.org/10.1088/1755-1315/49/5/052003.
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Hujer, Jan, Menghuot Phan, Tomáš Kořínek, Petra Dančová, and Miloš Müller. "Photolithographically Home-Made PVDF Sensor for Cavitation Impact Load Measurement." MATEC Web of Conferences 328 (2020): 01004. http://dx.doi.org/10.1051/matecconf/202032801004.
Повний текст джерелаАнотація:
Piezoelectric PVDF sensors offer a unique option for the measurement of cavitation aggressiveness represented by the magnitude of impacts due to cavitation bubble collapses near walls. The aggressiveness measurement requires specific sensors shape and area, whereas commercial PVDF sensors are fabricated in limited geometry and size ranges. The photolithography method offers a possibility of production of home-made PVDF sensors of arbitrary shape and size. This paper deals with the calibration of a photolithographically home-made PVDF sensor for the cavitation impact load measurement. The calibration of sensors was carried out by the ball drop method. Sensors of different sizes were fabricated by the photolithography method from multi-purpose both side metallized PVDF sheet. The standard technology used for the fabrication of printed circuit boards was utilized. Commercial PVDF sensors of the same size were calibrated and the calibration results were compared with the home-made sensors. The effect of size and the effect of one added protective layer of Kapton tape on a sensor sensitivity were investigated.
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Kumar, A., and J. F. Booker. "A Finite Element Cavitation Algorithm." Journal of Tribology 113, no. 2 (April 1, 1991): 276–84. http://dx.doi.org/10.1115/1.2920617.
Повний текст джерелаАнотація:
A mass-conserving model is presented for the transient evolution of cavitation in lubrication analysis. Algorithms are given for its finite element implementation in both direct problems (specified motion) and indirect problems (specified load). Numerical examples demonstrate capabilities and applications of the model and algorithm (s).
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Chmiel, Jarosław, Robert Jasionowski, and Dariusz Zasada. "Cavitation Erosion and Corrosion of Pearlitic Gray Cast Iron in Non-Standardized Cavitation Conditions." Solid State Phenomena 225 (December 2014): 19–24. http://dx.doi.org/10.4028/www.scientific.net/ssp.225.19.
Повний текст джерелаАнотація:
A results of test of erosion and corrosion resistance of pearlitic gray cast iron (grade EN GJ 400) are showed. The NaCl solutions and of ethylene glycol solutions were used as the test environment. Examination were performed at varying cavitation load, in the range 2,8 ÷ 20 W/cm2.
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Xu, Pei, Chao Wang, Liyu Ye, Chunyu Guo, Weipeng Xiong, and Shen Wu. "Cavitation and Induced Excitation Force of Ice-Class Propeller Blocked by Ice." Journal of Marine Science and Engineering 9, no. 6 (June 19, 2021): 674. http://dx.doi.org/10.3390/jmse9060674.
Повний текст джерелаАнотація:
The presence of broken ice in the flow field around a propeller causes severe blade erosion, shafting, and hull vibration. This study investigates the performance of the propeller of a ship sailing in the polar regions under the propeller–ice non-contact condition. To this end, we construct a test platform for the propeller-induced excitation force due to ice blockage in a large circulating water channel. The hydrodynamic load of the propeller, and the cavitation and propeller-induced fluctuating pressure, were measured and observed by varying the cavitation number and ice–propeller axial distance under atmospheric pressure and decompression conditions. The results show that the fluctuation range of the blade load increases with a decrease in cavitation number and ice–propeller axial distance. The decrease in the cavitation number leads to broadband characteristics in the frequency-domain curves of the propeller thrust coefficient and blade-bearing force. Under the combined effects of ice blockage and proximity, propeller suction, the circumfluence zone around the ice, and the Pirouette effect, propeller–hull vortex cavitation is generated between the ice and propeller. The decrease in cavitation number leads to a sharp increase in the amplitude of the high-order frequency of the propeller-induced fluctuating pressure.
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Hujer, Jan, Petra Dančová, Tomáš Kořínek, and Miloš Müller. "Photolithographically Home-Made PVDF Sensor for Cavitation Impact Load Measurement." Processes 9, no. 10 (September 30, 2021): 1761. http://dx.doi.org/10.3390/pr9101761.
Повний текст джерелаАнотація:
Piezoelectric PVDF sensors offer a unique option for the measurement of cavitation aggressiveness represented by the magnitude of impacts due to cavitation bubble collapses near walls. The aggressiveness measurement requires specific sensor shape and area, whereas commercial PVDF sensors are fabricated in limited geometry and size ranges. The photolithography method offers a possibility of production of home-made PVDF sensors of arbitrary shape and size. The methodology of a unique application of the standard photolithography method, which is commonly used for the production of printed circuit boards, is described in this paper. It enables mass production of high quality sensors contrary to laboratory techniques. This paper deals with the fabrication and the calibration of a photolithographically home-made PVDF sensor for the cavitation impact load measurement. The calibration of sensors was carried out by the ball drop method. Sensors of different sizes were fabricated by the photolithography method from a multi-purpose, both side metallized PVDF sheet. Commercial PVDF sensors of the same size were calibrated, and the calibration results were compared with the home-made sensors. The effect of size and the effect of one added protective layer of Kapton tape on a sensor sensitivity were investigated. The theoretical and numerical analysis was conducted to explain some issues during the ball impact.
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Xu, Pei, Chao Wang, and Liyu Ye. "Experimental Study on the Influence of Water and Cavitation on Propeller Load during Ice-Propeller Milling." Applied Sciences 11, no. 24 (December 7, 2021): 11578. http://dx.doi.org/10.3390/app112411578.
Повний текст джерелаАнотація:
When the ice-class propeller sails in an icy sea, it is affected by external factors such as water, ice, and cavitation, and the process of mutual interference is extremely complicated. In order to study the influence of water and cavitation on propeller load during the ice-propeller milling process, a test platform for ice–water propeller milling action was constructed. The load and cavitation of the propeller and single blade were measured during ice-propeller milling in air and water (atmospheric pressure and decompression conditions). Simultaneously, the changes in the load and bearing force of the propeller and blade were studied at different working conditions. The results show that, in the process of ice–water propeller milling, the direction of the propeller thrust generated by the water is opposite to that of the axial force generated by ice; the combined action of the two causes propeller thrust loss, whereas the combined action of water and ice increases propeller torque. The presence of water increases the thrust, torque, and bearing force of the fluctuating amplitude of the blade. The occurrence of cavitation reduces the thrust and torque of the propeller and blade and increases thrust fluctuating amplitudes while decreasing the tangential force fluctuating amplitude of the blade.
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Jasionowski, Robert, Wojciech Polkowski, and Dariusz Zasada. "Cavitation Wear of CuZn10 Alloy in As-Cast State and after Plastic Working and Annealing." Solid State Phenomena 252 (July 2016): 51–60. http://dx.doi.org/10.4028/www.scientific.net/ssp.252.51.
Повний текст джерелаАнотація:
Copper alloys due to their very good corrosion properties are often used to a fabrication of components that are subjected to both a cavitational destruction and a corrosive action of an environment, e.g.. ships’ propellers, sliding elements, pump parts etc. The course of cavitational destruction depends mainly on a material’s structure (a grain size, a type of inclusions, morphology and phase distribution, etc.) but also on the load distribution, and a possible activity of chemical, electrochemical and thermal processes near cavitation bubbles. Properties of a material that is subjected to the cavitational damage are strongly affected by its structure formed upon manufacturing or applied processing. In the present paper, results of the cavitational resistance analysis of CuZn10 alloy in the as cast state (the grain size of 200 μm) and after thermomechanical processing (the grain size of 10 or 200 μm) evaluated on vibrational laboratory stand in accordance with ASTM G-32 standard, are shown.
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Hirayama, Tomoko, Takeo Sakurai, and Hiroshi Yabe. "A Theoretical Analysis Considering Cavitation Occurrence in Oil-Lubricated Spiral-Grooved Journal Bearings With Experimental Verification." Journal of Tribology 126, no. 3 (June 28, 2004): 490–98. http://dx.doi.org/10.1115/1.1691436.
Повний текст джерелаАнотація:
Performances of an oil-lubricated spiral-grooved journal bearing are investigated in this paper with special attention paid to cavitation occurrence. The “equivalent flow model,” which is a theoretical scheme for taking the cavitation occurrence into hydrodynamic lubrication theory, is applied to the analyses by a finite difference treatment of the Reynolds equation that deals with the geometry of a finite number of grooves. The calculated results are compared with experimental results under eccentric states, and verified in terms of cavitation map and pressure distribution. The cavitated area ratio, load capacity and bearing stiffness are also theoretically calculated. The difference between the theoretical results with and without consideration of the cavitation occurrence is considerable, and thus the influence of cavitation occurrence should not be ignored in theoretical studies on bearing characteristics.
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Zhang, Shuwei, Renhui Zhang, Sidai Zhang, and Junhu Yang. "Effect of Impeller Inlet Geometry on Cavitation Performance of Centrifugal Pumps Based on Radial Basis Function." International Journal of Rotating Machinery 2016 (2016): 1–9. http://dx.doi.org/10.1155/2016/6048263.
Повний текст джерелаАнотація:
Aiming at the cavitation problem, the blade leading edge shape has been changed to analyze its impact on the cavitation performance for centrifugal pumps. And the response model has been established based on the Radial Basis Function. The calculation case results show that the leading edge extending forward along the shroud can improve the inlet flow condition and cavitation performance. But the cavitation performance has been reduced immensely when the leading edge extends backward along the shroud. Along with the leading edge which extends forward along the hub, the cavitation performance increases at first and then decreases. A better cavitation performance for centrifugal pumps has lower load of blade inlet and higher pressure of blade suction side. The pressure pulsation is affected by the vortex out of the impeller and the falling-off and collapsing of the cavitation bubbles. The lower the pressure pulsation for blade passing frequency and the second harmonics of the samples is, the better the cavitation performance is. A relatively accurate response model based on the Radial Basis Function has been established to predict the effect of the shape of blade leading edge on the cavitation performance of centrifugal pumps.
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Meng, Fan Ming, and Ling Zhang. "Effect of Cavitation on Tribological Performances for Textured Surfaces." Advanced Materials Research 472-475 (February 2012): 391–94. http://dx.doi.org/10.4028/www.scientific.net/amr.472-475.391.
Повний текст джерелаАнотація:
The influence of cavitation in a lubricant between textured surfaces on tribological performances of the surfaces was investigated based on an extended Reynolds equation and other associated equations. The tribological performances of the surfaces holding dimples with divergent-convergent shape were analyzed with the cavitation effect consideration at different dimple numbers. In doing so, the elastic deformation of the surface is evaluated using continuous convolution fast Fourier transform (CC-FFT). Some mechanisms are revealed about the cavitation effect on the friction coefficient, friction force, load-carrying capacity and cavitated area of the textured surfaces.
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Mistry, K., S. Biswas, and K. Athre. "A New Theoretical Model for Analysis of the Fluid Film in the Cavitation Zone of a Journal Bearing." Journal of Tribology 119, no. 4 (October 1, 1997): 741–46. http://dx.doi.org/10.1115/1.2833879.
Повний текст джерелаАнотація:
Recent studies of the cavitation zone in the journal bearing indicate that a sublayer of lubricant adheres to the journal surface. Based on this observation, it is proposed in the present work that centrifugal force and surface tension should be considered as the primary cause for the lubricant film to be in equilibrium in the cavitation zone. Using this concept a cavitation model is proposed. The effect of the supply pressure on fluid film reformation is also studied. The proposed model is applied to study the cavitation zone of: (1) a journal bearing with lubricant entry along the line of centers and (2) a journal bearing with inlet groove located along the load line. It is found that the thickness of the lubricant layer adhering to the journal surface is an exponential function of the speed while the eccentricity ratio rather than speed has a predominant effect on the width of the streamers. The supply pressure has a remarkable effect on the film reformation when the lubricant supply is along the line of centers, with the possibility of film reformation at the supply groove, which does not happen when the lubricant inlet is located along the load line.
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Sun, Tiezhi, Qingmo Xie, Li Zou, Hao Wang, and Chang Xu. "Numerical Investigation of Unsteady Cavitation Dynamics over a NACA66 Hydrofoil near a Free Surface." Journal of Marine Science and Engineering 8, no. 5 (May 11, 2020): 341. http://dx.doi.org/10.3390/jmse8050341.
Повний текст джерелаАнотація:
Cavitation is a typical and unavoidable phenomenon for small waterline ships and high-speed vehicles. It creates a highly complex multiphase flow near the free surface and is primarily represented by the free surface-cavitation interaction. In this paper, the large-eddy method and Schnerr-Sauer cavitation model are combined to address the effects of a free surface on the cavitation dynamics of a NACA66 hydrofoil. The numerical method is validated by comparing the cavitation morphology and pressure with available experimental data. The results show that the presence of a free surface affects the cavitation evolution and hydrodynamic load characteristics. Compared with the non-free surface case for the same cavitation number, the free surface suppresses the cavitation intensity and increases the frequency of cavitation shedding. Furthermore, an improved dynamic mode decomposition method is applied to investigate the unsteady cavitation flow features. The results show a correlation between the characteristic mode and the flow state. Meanwhile, the presence of a free surface is found to reduce the energy content in each order mode and results in smaller scale of the coherent structure in higher-order modes. Moreover, with increasing distance from the hydrofoil to the free surface, the cavitation intensity increases, as well as the average lift and drag coefficients. In particular, significant free-surface unsteady fluctuations are observed in the wake region.
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Zhao, Hairui, Yao Shi, and Guang Pan. "Numerical simulation of cavitation characteristics in high speed water entry of head-jetting underwater vehicle." Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University 39, no. 4 (August 2021): 810–17. http://dx.doi.org/10.1051/jnwpu/20213940810.
Повний текст джерелаАнотація:
Autonomous underwater vehicle will be subjected to a huge impact load during high speed water entry, which will damage the structure and the internal instruments of the vehicle. Therefore, it is of great significance to study the buffer mechanism of the vehicle during the process of water-entry. In this paper, a kind of head-jetting device with disk cavitation is used. The complex cavitation forms, under the three-phase coupling of gas, liquid and solid, in the water entry process of the vehicle on which the device is installed. In this paper, the numerical simulation of high-speed water entry of the vehicle equipped with head jet device is carried out. Through the analysis of water entry cavitation under typical working conditions, the following conclusions are obtained. After the installation of head jet device, the water entry cavity of the vehicle changes gradually from cone to spindle shape. The air jet, compared with that without jet, can promote the formation of water inlet supercavitation, decrease the interaction area between the vehicle and water, and reduce the impact load during water entry. At the same water entry depth, the diameter of cavitation increases with the amount of air jet. The water entry velocity has a great influence on the difference of cavitation shape. The water entry depth closure phenomenon, when the water entry velocity is less than 100 m/s, can be observed in the depth of 3.5 times of the projectile length. The water entry angle has a significant effect on the cavitation shape. The cavity shows obvious asymmetry when the vehicle slants into the water, and the diameter and length of the bubbles decrease with the increase of the water entry angle. The research content of this paper provides technical support for the engineering practice of high-speed water entry and load reduction, and the conclusions are of great significance in related fields.
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Khmelev, V. N., R. V. Barsukov, and A. R. Barsukov. "Research of the influence of acoustic load on a piezoelectric emitter to control the cavitation erosion of materials." Journal of Physics: Conference Series 2094, no. 4 (November 1, 2021): 042031. http://dx.doi.org/10.1088/1742-6596/2094/4/042031.
Повний текст джерелаАнотація:
Abstract The paper analyzes the possibilities of research the cavitation erosion of materials that are subjected to cavitation effect. The study is carried out by a system for controlling the magnitude of the acoustic load on the piezoelectric emitter of the ultrasonic vibrating system. The analysis of the processes of interaction between the ultrasonic emitter and the processed environment was carried out on the basis of a research of the model, which was created on the basis of a system of electromechanical analogies. The analysis made it possible to reveal the dependence of the electrical impedance of the ultrasonic vibrating system on the magnitude of the acoustic load. The revealed dependencies made it possible to propose and develop a control system. It is able to provide a study of the properties that are located near the emitting surface of the ultrasonic emitter of materials influenced to cavitation ultrasonic, including under abnormal conditions (high temperatures and pressures).
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Yu, Rufei, Pei Li, and Wei Chen. "Study of grease lubricated journal bearing with partial surface texture." Industrial Lubrication and Tribology 68, no. 2 (March 14, 2016): 149–57. http://dx.doi.org/10.1108/ilt-03-2015-0028.
Повний текст джерелаАнотація:
Purpose – This paper aims to study the impact of surface texture on grease-lubricated journal bearing, load-carrying capacity, friction and friction coefficient. Design/methodology/approach – The paper opted for a basic application research using the commercial CFD software FLUENT 14.0. Findings – The load-carrying capacity can be enhanced if the surface texture is introduced from a suitable position. The textural shape has a more significant effect on the friction and load-carrying capacity than the friction coefficient. The rheological parameters of grease affect the load-carrying capacity in the same way, i.e. the load increases with the increase in the rheological parameters. With the decrease in the value of cavitation pressure, the cavitation area reduces but the dynamic pressure area gets enlarged. Research limitations/implications – Because of the chosen research method, the research results may lack the analysis of experiments. Practical implications – The research results can be applied to the domain in the high-speed spindle and lubricated multibody system. Originality/value – The investigation on the performances of grease-lubricated journal bearing with surface texture would be significant.
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Alligné, S., J. Decaix, A. Müller, C. Nicolet, F. Avellan, and C. Münch. "RANS computations for identification of 1-D cavitation model parameters: application to full load cavitation vortex rope." IOP Conference Series: Earth and Environmental Science 49 (November 2016): 082014. http://dx.doi.org/10.1088/1755-1315/49/8/082014.
Повний текст джерела
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Alligné, S., J. Decaix, A. Müller, C. Nicolet, F. Avellan, and C. Münch. "RANS computations for identification of 1-D cavitation model parameters: application to full load cavitation vortex rope." Journal of Physics: Conference Series 813 (April 4, 2017): 012032. http://dx.doi.org/10.1088/1742-6596/813/1/012032.
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Prata, A. T., and R. T. S. Ferreira. "The Accuracy of Short Bearing Theory in Presence of Cavitation." Journal of Tribology 112, no. 4 (October 1, 1990): 650–54. http://dx.doi.org/10.1115/1.2920311.
Повний текст джерелаАнотація:
The accuracy of the short bearing approximation in presence of cavitation is tested for bearing aspect ratios (length/diameter) ranging from 0.1 to 1, and for eccentricity to clearance ratios from 0 to 1. Results for short bearings are obtained via the method of matched asymptotic expansion of [3]. These results are compared to those for finite bearings, which are calculated by numerical integration of the Reynolds equation utilizing boundary fitted coordinates that accommodate to the cavitation boundary. Except for very high eccentricities, the short bearing theory was shown to be accurate in predicting the load, within ten percent, for bearing aspect ratios up to 0.5. For large aspect ratios the short bearing theory overpredicts the load.
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Fivel, Marc, Jean-Pierre Franc, and Samir Chandra Roy. "Towards numerical prediction of cavitation erosion." Interface Focus 5, no. 5 (October 6, 2015): 20150013. http://dx.doi.org/10.1098/rsfs.2015.0013.
Повний текст джерелаАнотація:
This paper is intended to provide a potential basis for a numerical prediction of cavitation erosion damage. The proposed method can be divided into two steps. The first step consists in determining the loading conditions due to cavitation bubble collapses. It is shown that individual pits observed on highly polished metallic samples exposed to cavitation for a relatively small time can be considered as the signature of bubble collapse. By combining pitting tests with an inverse finite-element modelling (FEM) of the material response to a representative impact load, loading conditions can be derived for each individual bubble collapse in terms of stress amplitude (in gigapascals) and radial extent (in micrometres). This step requires characterizing as accurately as possible the properties of the material exposed to cavitation. This characterization should include the effect of strain rate, which is known to be high in cavitation erosion (typically of the order of several thousands s −1 ). Nanoindentation techniques as well as compressive tests at high strain rate using, for example, a split Hopkinson pressure bar test system may be used. The second step consists in developing an FEM approach to simulate the material response to the repetitive impact loads determined in step 1. This includes a detailed analysis of the hardening process (isotropic versus kinematic) in order to properly account for fatigue as well as the development of a suitable model of material damage and failure to account for mass loss. Although the whole method is not yet fully operational, promising results are presented that show that such a numerical method might be, in the long term, an alternative to correlative techniques used so far for cavitation erosion prediction.
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Zhang, Hong Ming, and Li Xiang Zhang. "Numerical Investigation of Cavitating Turbulent Flow in a Francis Turbine Runner Fitted with Splitter Blades." Advanced Materials Research 662 (February 2013): 637–42. http://dx.doi.org/10.4028/www.scientific.net/amr.662.637.
Повний текст джерелаАнотація:
The paper presents numerical investigation of cavitating turbulent flow in a high head Francis turbine runner fitted with splitter blades at part load operation. Analysis was performed by OpenFOAM code. A mixture assumption and a finite rate mass transfer model were introduced. The finite volume method is used to solve the governing equations of the mixture model and the pressure-velocity coupling is handled via a Pressure Implicit with Splitting of Operators (PISO) procedure. Simulation results show that the volume fraction of water vapor and the pressure uneven distribution on the main blade and splitter blade. It will lead to cavitation and fatigue damage.
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Epps, Brenden, Oscar Víquez, and Chryssostomos Chryssostomidis. "A Method for Propeller Blade Optimization and Cavitation Inception Mitigation." Journal of Ship Production and Design 31, no. 02 (May 1, 2015): 88–98. http://dx.doi.org/10.5957/jspd.2015.31.2.88.
Повний текст джерелаАнотація:
Propeller blade design for fast ships is often driven by cavitation constraints. A tradeoff exists, in which larger chord lengths and section thicknesses typically improve cavitation performance but result in lower efficiency. Typically, chord lengths are optimized for the design condition (ship endurance speed) with some specified margin to prevent cavitation off-design (at maximum ship speed). Cavitation performance at the maximum speed is considered postfacto, and blade shape often needs to be modified for cavitation considerations in high-speed operation. This article presents an improved method for blade shape optimization. The present method simultaneously considers the cavitation performance at the endurance speed design point and a maximum speed off-design point, and blade chord lengths and thicknesses are set to prevent cavitation at both operational conditions. During the present design optimization routine, the on-design load distribution is optimized, and the off design performance is determined such that the chord lengths can be set to a minimum that still prevents cavitation at both the on- and off-design conditions. A case study is presented, considering the notional design of a propeller for the U.S. Navy DDG51 destroyer-class ship. Propellers designed using standard chord/thickness optimization procedures are compared with those designed using the present procedures. Cavitation performance is compared for the two design methods.
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Wang, Wei, Yongyong He, Yang Li, Bin Wei, Yutong Hu, and Jianbin Luo. "Investigation on inner flow field characteristics of groove textures in fully lubricated thrust bearings." Industrial Lubrication and Tribology 70, no. 4 (May 8, 2018): 754–63. http://dx.doi.org/10.1108/ilt-08-2017-0224.
Повний текст джерелаАнотація:
PurposeThe purpose of this study is to investigate the inner flow field characteristics of groove textures in thrust bearings. Cavitation and vortex are studied simultaneously to enrich the theories of surface texture.Design/methodology/approachNavier–Stokes equations are solved using computational fluid dynamics. The MIXTURE model is adopted to study the gas–liquid mixture flow under the cavitation condition.FindingsRe number, the depth ratio as well as the area ratio of the groove texture and the bottom shape are all influencing factors of the inner flow field characteristics. When cavitation region and vortex region occupy the bottom of the groove texture, these do not overlap because of the pressure gradient. The positive pressure gradient in the non-cavitation region introduces nonlinearity into the velocity profiles, which affects the load-carrying capacity and friction.Originality/valueCavitation and vortex are studied simultaneously only in this study. The characteristics of the textured thrust bearing can be analyzed and explained with the combined effect of cavitation and vortex.
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Ma, Jing, Bai Jing Qiu, Run Yan, and Bei Fen Zhu. "Study on the Working State of Jet-Mixing Apparatus." Applied Mechanics and Materials 563 (May 2014): 219–23. http://dx.doi.org/10.4028/www.scientific.net/amm.563.219.
Повний текст джерелаАнотація:
In order to study the working state of the export of jet-mixing apparatus under different loads,by comparing the bench test and its application in spray system, the working state of jet-mixing apparatus is studied.The results show that, in the bench test, the export of jet-mixing apparatus is unloaded and the state of jet-mixing apparatus is absorbing pesticide; the jet nozzle whose diameter is 2mm and suction chamber whose diameter is 3mm of the jet-mixing apparatus produce a large number of bubbles, the suction chamber emerges cavitation. The export of jet-mixing apparatus is connected with the F110 spray system, the working state of jet-mixing apparatus with a 2mm diameter jet nozzle is sucking pesticide; the working state of 3mm and 4mm jet nozzle diameter is reflux. The export of jet-mixing apparatus is connected with the outlet of F110 spray system suction chamber.They do not emerge cavitation. The load on the export of jet-mixing apparatus affect the working state of jet-mixing apparatus, also has certain influence on cavitation in the suction chamber.
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Vijayaraghavan, D., and D. E. Brewe. "Frequency Effects on the Stability of a Journal Bearing for Periodic Loading." Journal of Tribology 114, no. 1 (January 1, 1992): 107–15. http://dx.doi.org/10.1115/1.2920848.
Повний текст джерелаАнотація:
In this paper, stability of a journal bearing is numerically predicted when an unidirectional periodic external load is applied. The analysis is performed using a cavitation algorithm, which mimics the JFO theory by accounting for the mass balance through the complete bearing. Hence, the history of the film is taken into consideration. The loading pattern is taken to be sinusoidal and the frequency of the load cycle is varied. The results are compared with the predictions using Reynolds boundary conditions for both film rupture and reformation. With such comparisons, the need for accurately predicting the cavitation regions for complex loading patterns is clearly demonstrated. For a particular frequency of loading, the effects of mass, amplitude of load vibration and frequency of journal speed are also investigated. The journal trajectories, transient variations in fluid film forces, net surface velocity and minimum film thickness and pressure profiles are also presented.
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Solovyev, Igor, and Andrey Yermolayev. "Unsteady force measurements on propeller model in cavitation tunnels." Transactions of the Krylov State Research Centre 4, no. 398 (November 15, 2021): 61–67. http://dx.doi.org/10.24937/2542-2324-2021-4-398-61-67.
Повний текст джерелаАнотація:
Object and purpose of research. This paper discusses longitudinal unsteady force dynamometer for cavitation tunnel tests. The purpose of the study is to improve metrological performance of the dynamometer and extend the scope of its application. Materials and methods. The study is based on metrological parameters of dynamometers and model test data available with KSRC Large Cavitation Tunnel (LCT). Main results. Development, manufacturing, certification and commissioning of longitudinal unsteady force dynamometer based on piezoceramic load cell with improved metrological performance making it applicable for model testing of not only propellers but also other types of marine propulsors. Conclusion. Dynamometer with piezoceramic load cell offers more accurate measurement of unsteady forces, wider band of measurement frequencies, as well as wider spectrum of possible applications and lower susceptibility to interference.
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Muchammad, Mohammad Tauviqirrahman, J. Jamari, and D. J. Schipper. "Load Support Improvement on Superhydrophobic Surface in Lubricated-MEMS Using Numerical Investigation." Advanced Materials Research 1123 (August 2015): 3–6. http://dx.doi.org/10.4028/www.scientific.net/amr.1123.3.
Повний текст джерелаАнотація:
The development of micro-electro-mechanical systems (MEMS) faces a great challenge in commercial application with respect to lubrication issue recently. Short life time of lubricated MEMS is primarily caused by the failure of the lubrication. In this study, the use of superhydrophobic material applied on one or both of the opposing surfaces in lubricated MEMS was introduced to reduce this type of failure. The optimum parameter of the superhydrophobic effect that provides the greatest load support in MEMS was obtained using numerical analysis. A modified Reynolds equation combined with cavitation model was derived. The slip length model was used to address the superhydrophobic effect for the hydrodynamic analysis. It was shown that in the absence of the wedge effect, load support can be obtained using the superhydrophobic surface. In addition, the numerical analysis showed that the performance of MEMS using such surface depends on cavitation.
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Soyama, Hitoshi, Andrzej Lichtarowicz, Takahiro Momma, and Edward J. Williams. "A New Calibration Method for Dynamically Loaded Transducers and Its Application to Cavitation Impact Measurement." Journal of Fluids Engineering 120, no. 4 (December 1, 1998): 712–18. http://dx.doi.org/10.1115/1.2820728.
Повний текст джерелаАнотація:
The erosion produced by cavitation is a serious problem in hydraulic machinery. During investigations of the dynamic loading generated by collapsing cavitation on a surface, a dynamic pressure transducer was developed. The piezoelectric polymer PVDF (Polyvinylidene fluoride) was used as the pressure sensitive material. A novel method of dynamic calibration has also been developed. The transducer is loaded through pencil lead by a beam supported at its other end on a knife edge and loaded at the center by weights. As the static load is increased, the pencil lead breaks and the load is released suddenly. The unloading time is faster than for any other conventional calibration method and is of the same order as cavitation loading. Descriptions of the developments of both the calibration method and the transducer are given. The principal advantages of the new method are the short pulse duration and the simplicity of the test procedure. The paper is an extension of the previously reported work by Momma and Lichtarowicz (1994), giving further information on the operating characteristics of the transducer in comparison with the traditional ball-dropping method.
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Lee, Y. T., A. S. Yang, Y. H. Juan, C. S. Liu, and Y. H. Chang. "A New Micro-Hydrodynamic Herringbone Bearing Using Slant Groove Depth Arrangements for Performance Enhancement." Journal of Mechanics 33, no. 5 (August 18, 2017): 725–37. http://dx.doi.org/10.1017/jmech.2017.72.
Повний текст джерелаАнотація:
AbstractThis study presents a new groove profile using the slant groove depth arrangements to enhance the performance of micro-HGJBs. The computational analysis was based on the steady-state three-dimensional conservation equations of mass and momentum in conjunction with the cavitation model to examine the complex lubricated flow field. The simulated results of load capacity and circumferential pressure distribution of lubricant film are in good agreement with the measurement data and the predictions cited in the literature. Numerical experiments were extended to determine the pressure distribution, load capacity, radial stiffness and friction torque by varying the slant ratio of groove depth, eccentricity ratio, rotational speed and attitude angle. The cavitation extent of lubricant film was also studied for different slant groove patterns.
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Miwa, Reo, Norifumi Miyanaga, and Jun Tomioka. "Appearance of Hysteresis Phenomena on Hydrodynamic Lubrication in a Seal-Type Thrust Bearing with Dimples." Materials 14, no. 18 (September 10, 2021): 5222. http://dx.doi.org/10.3390/ma14185222.
Повний текст джерелаАнотація:
This paper described unique hysteresis phenomena that appear in the hydrodynamic lubrication properties of dimpled thrust bearings. A seal-type thrust bearing specimen was textured with dimples. The load-carrying capacity and frictional torque were measured with a constant film thickness and compared to those of a dimple-free specimen. For examining the size of cavitation bubbles that occurred in various conditions, the lubricating area was observed during experiments. The used dimpled specimen produced the load-carrying capacity, and it exhibited an interesting hysteresis phenomenon, the difference in the values in the increasing and decreasing processes of rotational speed. The visualization test results revealed that the size of cavitation bubbles occurring within the dimples strongly affected this phenomenon. In addition, the dimpled specimen was able to reduce the frictional torque compared to the dimple-free specimen. However, the frictional torque did not show the hysteresis loop similar to that shown in the load-carrying capacity.
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Ding, Aoshuang, Xiaodong Ren, Xuesong Li, and Chunwei Gu. "Numerical investigation for characteristics and oil–air distributions of oil film in a tilting-pad journal bearing." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 234, no. 2 (June 24, 2019): 193–204. http://dx.doi.org/10.1177/1350650119858241.
Повний текст джерелаАнотація:
This paper analyzes the effects of air in the oil film of a tilting-pad journal bearing on oil–air distributions and characteristics. With a gaseous cavitation model and shear stress transport model with low-Re correction included, the air backflow from the outlet boundary is analyzed in numerical simulations of a titling-pad journal bearing at 3000 r/min rotation speed and under 180 kN load. The simulated bearing load, pressure, and mechanical loss are in good accordance with the experimental data, indicating that the simulation results of the air backflow from the outlet boundary can catch the hydrodynamic characteristics accurately. Based on the turbulence viscosity ratio analysis, the turbulence effect cannot be ignored at the high rotational speed. With the comparison between the unloaded area and the loaded area, the boundary layer and turbulent flow develops with the film thickness increasing. Based on the analyses of simulated air volume fraction and pressure distribution, the gaseous cavitation occurs around the center part of the unloaded area, following the gaseous cavitation mechanisms. The backflow air flows into the low-pressure unloaded area from the outlet boundary and has a clear interval with the air from the gaseous cavitation. The air volume fraction increases with these two air sources and affects the mixture viscosity significantly, eventually influencing the shear stress on the rotor-side wall and bearing mechanical loss.