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Статті в журналах з теми "Cavitation load"
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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]
Дисертації з теми "Cavitation load"
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Roy, Samir Chandra. "Analyse et modélisation du comportement de divers matériaux en érosion de cavitation." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI081/document.
Повний текст джерелаАнотація:
A ce jour il n'est toujours pas possible de prédire avec exactitude le phénomène d'érosion par cavitation. La raison principale est qu'il est difficile de caractériser l'agressivité de l'écoulement. Cette thèse propose d'utiliser une méthode inverse pour estimer l'agressivité de l'écoulement à partir de l'observation des cratères (pits) imprimées sur la surface dans les premiers instants de l'érosion de cavitation. Trois matériaux ont été testés dans la veine d'écoulement PREVERO disponible au LEGI de Grenoble dans les mêmes conditions expérimentales. La géométrie des pits laissés sur la surface est précisément mesurée à l'aide d'une méthode systématique permettant de s'affranchir de l'effet de rugosité. Supposant que chaque pit a été généré par une bulle unique dont le champ de pression est assimilé à une forme Gaussienne, des calculs par éléments finis permettent d'estimer le chargement qui a créé l'empreinte résiduelle. On montre que la distribution des chargements suit une loi universelle indépendante du matériau testé; le matériau le plus tendre (alliage d'aluminium) mesurant les plus faibles impacts tandis que le matériau le plus résistant (Acier inoxydable) donne accès aux plus grandes pressions d'impact. On en conclu que le matériau peut être utilisé comme capteur de pression mesurant le niveau d'agressivité de l'écoulement. La méthode inverse repose sur une caractérisation mécanique des matériaux prenant en compte la sensibilité de la contrainte à la vitesse de déformation. On montre que les essais de nanoindentation sont mieux adaptés que les essais de compression pour déterminer les paramètres de la loi de comportement, notamment pour l'alliage d'aluminium pour lequel la microstructure est très hétérogène. Des essais de compression à haute vitesse par barres de Hopkinson complètent la loi de comportement en donnant la sensibilité à la vitesse de déformation. Des simulations prenant en compte la dynamique du chargement montrent que des impacts de fort amplitude mais appliqués sur un temps court ne laissent pas d'empreinte résiduelle si la fréquence est plus élevée que la fréquence naturelle du matériau assimilé à un oscillateur amorti. Un mécanisme d'accumulation dynamique de la déformation plastique pouvant conduire à la rupture par fatigue est proposé. Finalement, la courbe de perte de masse est simulée en appliquant aléatoirement sur un maillage 3D, la population d'impacts estimée par la méthode inverseNumerical prediction of cavitation erosion requires the knowledge of flow aggressiveness, both of which have been challenging issues till-date. This thesis proposes to use an inverse method to estimate the aggressiveness of the flow from the observation of the pits printed on the surface in the first moments of the cavitation erosion. Three materials were tested in the same experimental conditions in the cavitation tunnel PREVERO available LEGI Grenoble. The geometry of the pits left on the surface is precisely measured using a systematic method to overcome the roughness effect. Assuming that each pit was generated by a single bubble collapse whose pressure field is treated as a Gaussian shape, finite element calculations are run for estimating the load that created each residual imprint. It is shown that the load distribution falls on a master curve independent of the tested material; the softer material (aluminum alloy) measuring the lowest impacts while the most resistant material (duplex stainless steel) provides access to the largest impact pressures. It is concluded that the material can be used as a pressure sensor measuring the level of aggressiveness of the flow. The inverse method is based on a material characterization taking into account strain rate effects. It is shown that nanoindentation tests are more suitable than compression tests to determine the parameters of the behavior law, particularly for the aluminum alloy for which the microstructure is very heterogeneous. High-speed compression tests with split Hopkinson pressure bars complement the constitutive law giving the sensitivity to the strain rate. Simulations considering the dynamic loading show that impacts of strong amplitude but applied in a short time do not leave any residual pit if the frequency is higher than the natural frequency of the material treated as a damped oscillator. A dynamic mechanism of plastic strain accumulation that could eventually lead to fatigue failure is proposed. Finally, the mass loss curve of cavitation erosion is simulated by applying randomly on a 3D mesh, the impact force population estimated by the inverse method
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Ješe, Uroš. "Numerical study of pump-turbine instabilities : pumping mode off-design conditions." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI090/document.
Повний текст джерелаАнотація:
Actuellement, la flexibilité et le stockage de l'énergie sont parmi les principaux défis de l'industrie de l'énergie. Les stations de transfert d'énergie par pompage (STEP), en utilisant des turbines-pompes réversibles, comptent parmi les solutions les plus rentables pour répondre à ces besoins. Pour assurer un réglage rapide du réseau électrique, les turbines-pompes sont sujettes à de rapides changements entre modes pompage et turbinage. Elles sont souvent exposées à un fonctionnement prolongé dans des conditions hors nominal. Pour assurer la stabilité du réseau, la zone d'exploitation continue de turbines-pompes réversibles doit être libre de toute instabilité hydraulique. Deux sources principales d'instabilités en mode pompage peuvent limiter la plage de fonctionnement continu. Il s'agit de la présence de cavitation et de décollement tournant, tous deux survenant à charge partielle. La cavitation peut conduire à des vibrations, des pertes de performance et parfois même à l'érosion de la turbine-pompe. En outre, en raison de décollements tournants (apparition et décomposition périodique de zones de recirculation dans les régions du distributeur), la machine peut être exposée à un changement incontrôlable entre les points de fonctionnement, avec une modification de charge et une baisse significative des performances. Les deux phénomènes sont très complexes, tri-dimensionnels et délicats à étudier. Surtout le phénomène de décollement tournant dans les turbines-pompes est peu abordé dans la littérature. Le premier objectif de l'étude du doctorat présenté a été d'utiliser un code numérique, testé au laboratoire, et de développer une méthodologie de calcul pour permettre la prévision des phénomènes à charge partielle. L'étude a été faite sur une géométrie à échelle réduite d'une turbine-pompe de haute chute. Des calculs numériques ont été effectués en utilisant le code FINE/Turbo avec le modèle de cavitation barotrope qui a été développé au laboratoire. L'analyse des écoulements cavitants a été faite pour des débits et de niveaux de cavitation différents. Les principales analyses portent sur des valeurs naissantes de cavitation, des courbes de chute et sur le prédiction des formes de cavitation pour différents débits et valeurs de NPSH. Une attention particulière a été portée sur l'interaction entre les formes de cavitation à l'entrée de la roue et la baisse de performance (zone de feston), causée par le décollement tournant qui apparaît dans la région du distributeur. Les résultats numériques ont montré un bon accord avec les données expérimentales disponibles. La deuxième partie de la thèse a concerné la prédiction et l'analyse de décollements tournants. Des simulations ont été utilisées pour prédire les régions d'exploitation stables et instables de la machine. La méthodologie mentionnée pourrait fournir des résultats globaux précis pour différents points de fonctionnement avec un faible coût de calcul. Afin d'obtenir des informations détaillées sur les écoulements instables, des simulations instationnaires plus précises ont été réalisées. L'analyse locale des écoulements a permis la description des mécanismes gouvernant le phénomène de décollement tournant. Les analyses permettent l'étude du nombre, de l'intensité et des fréquences de rotation des cellules tournants. En outre, les calculs instationnaires donnent une très bonne prédiction de la performance de la turbine-pompe. L'approche proposée est fiable, robuste et précise. La méthodologie de calcul proposée peut être utilisée sur plusieurs géométries de turbine-pompe (ou pompe centrifuge), pour une large gamme de débits et de géométries de directrices. Les simulations proposées peuvent être utilisées à l'échelle industrielle pour étudier les effets de géométrie, d'angles d'ouverture de directrices ou de l'influence du jeu entre la roue et le distributeur afin de réduire ou même éliminer les effets négatifs des décollements tournantsFlexibility and energy storage seem to be the main challenges of the energy industry at the present time. Pumped Storage Power Plants (PSP), using reversible pump-turbines, are among the most cost-efficient solutions to answer these needs. To provide a rapid adjustment to the electrical grid, pump-turbines are subjects of quick switching between pumping and generating modes and to extended operation under off-design conditions. To maintain the stability of the grid, the continuous operating area of reversible pump-turbines must be free of hydraulic instabilities. Two main sources of pumping mode instabilities are the presence of the cavitation and the rotating stall, both occurring at the part load. Presence of cavitation can lead into vibrations, loss of performance and sometimes erosion. Moreover, due to rotating stall that can be observed as periodic occurrence and decay of recirculation zones in the distributor regions, the machine can be exposed to uncontrollable shift between the operating points with the significant discharge modification and the drop of the efficiency. Both phenomena are very complex, three-dimensional and demanding for the investigation. Especially rotating stall in the pump-turbines is poorly addressed in the literature. First objective of the presented PhD study has been to develop the cost-efficient numerical methodology in order to enable the accurate prediction and analysis of the off-design part load phenomena. The investigations have been made on the reduce-scaled high head pump-turbine design (nq = 27rpm) provided by Alstom Hydro. Steady and unsteady numerical calculations have been performed using code FINE/Turbo with barotropic cavitation model implemented and developed before in the laboratory. Some of the numerical results have been compared to the experimental data. Cavitating flow analysis has been made for various flow rates and wide range of cavitation levels. Flow investigation has been focused on the cavitation influence on the flow behavior and on the performance of the machine. Main analyses include incipient cavitation values, head drop curves and cavitation forms prediction for wide ranges of flow rates and NPSH values. Special attention has been put on the interaction between cavitation forms and the performance drop (hump zone) caused by the rotating stall. Cavitation results showed good agreement with the provided experimental data. Second part of the thesis has been focused on the prediction and analysis of the rotating stall flow patterns. Computationally fast steady simulations has been presented and used to predict stable and unstable operating regions. The analyses have been done on 4 different guide vanes openings and 2 guide vanes geometries. In order to get detailed information about the unsteady flow patterns related to the rotating stall, more exact unsteady simulations have been performed. Local flow study has been done to describe in details the governing mechanisms of the rotating stall. The analyses enable the investigations of the rotating stall frequencies, number of stalled cells and the intensity of the rotating stall. Moreover, the unsteady calculations give very good prediction of the pump-turbine performance for both, stable and unstable operating regions. Numerical results give very good qualitative and quantitative agreement with the available experimental data. The approach appears to be very reliable, robust and precise. Even though the numerical results (rotating stall frequencies, number of cells...) on the actual geometry should be confirmed experimentally, author believes that the methodology could be used on any other pump-turbine (or centrifugal pump) geometry. Moreover, the simulations can be used industrially to study the effects of the guide vanes geometries, guide vanes opening angles and influence of the gap between the impeller and the distributor in order to reduce or even eliminate the negative effects of the rotating stall
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Дрозденко, Олександр Іванович. "Конструювання електроакустичних перетворювачів з урахуванням кавітаційних, електричних та теплових навантажень". Doctoral thesis, Київ, 2012. https://ela.kpi.ua/handle/123456789/3982.
Повний текст джерела
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Gherca, Andrei. "Modélisation de la lubrification des surfaces texturées - Application à la butée en régime hydrodynamique." Phd thesis, Université de Poitiers, 2013. http://tel.archives-ouvertes.fr/tel-00943143.
Повний текст джерелаАнотація:
La compréhension et la modélisation d'un contact lubrifié en présence de texturation nécessitent une description physique très fine pour comprendre les analyses contradictoires et pour expliquer les résultats très différents en terme de performance présentés dans la littérature internationale. De nombreuses études théoriques et expérimentales ont montré que la texturation des surfaces pourrait améliorer les caractéristiques tribologiques des contacts. La capacité de charge, le coefficient de frottement et la résistance à l'usure sont les principales caractéristiques susceptibles d'être améliorées. La texturation de surface fait appel à de nombreux paramètres géométriques, qui peuvent agir de façon très différente selon le contact. Enfin, les phénomènes supposés expliquer l'apport de la texturation ne font pas l'unanimité dans la communauté scientifique. Ainsi, les différentes contradictions font que ce domaine de recherche est en pleine évolution. Dans ce contexte scientifique, l'objectif principal de cette thèse est de conduire, à travers une étude théorique et numérique approfondie, vers une meilleure compréhension des effets induits par la texturation dans un contact lubrifié. Les paramètres géométriques, essentiels par rapport aux phénomènes physiques générés, font l'objet d'une analyse étendue. Les éléments théoriques obtenus à travers cette étude permettront une optimisation opérationnelle de tous types de dispositifs fonctionnant dans un milieu lubrifié. Parmi ces nombreuses applications, la butée en régime hydrodynamique a été choisie afin d'illustrer la pertinence des résultats de nos recherches.
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Roberts, Thomas Patton. "A model of cavitating journal bearing performance under dynamic loads." Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/18887.
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"Analysis of Cavitation-Induced Pressure Loads on Compliant Polymer Coatings." Master's thesis, 2015. http://hdl.handle.net/2286/R.I.29702.
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abstract: Cavitation erosion is a significant cause of wear in marine components, such as impellers, propellers or rudders. While the erosion process has been widely studied on metals, the effect of cavitation on polymers is not well-understood. The stress response in metals differs greatly from that of polymers, e.g. rate and temperature effects are far more important, thus damage and wear mechanisms of polymers under cavitating flows are significantly different. In this work, heat-driven failure caused by viscous dissipation and void nucleation resulting from tensile stresses arising from stress wave reflections are investigated as two possible material failure mechanisms.
As a first step in developing a fundamental understanding of the cavitation erosion process on polymer surfaces, simulations are performed of the collapse of individual bubbles against a compliant surface e.g. metallic substrates with polyurea coatings. The surface response of collapse-driven impact loads is represented by a idealized, time-dependent, Gaussian pressure distribution on the surface. A two-dimensional distribution of load radii and durations is considered corresponding to characteristic of cavitating flows accelerated erosion experiments. Finite element simulations are performed to fit a response curve that relates the loading parameters to the energy dissipated in the coating and integrated with collapse statistics to generate an expected heat input into the coating.
The impulsive pressure, which is generated due to bubble collapse, impacts the material and generates intense shock waves. The stress waves within the material reflects by interaction with the substrate. A transient region of high tensile stress is produced by the interaction of these waves. Simulations suggests that maximum hydrostatic tension which cause failure of polyurea layer is observed in thick coating. Also, the dissipated viscous energy and corresponding temperature rise in a polyurea is calculated, and it is concluded that temperature has influence on deformation.Dissertation/Thesis
Masters Thesis Mechanical Engineering 2015
Книги з теми "Cavitation load"
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Brewe, David E. Elasticity effects on cavitation in a squeeze film damper undergoing noncentered circular whirl. [Cleveland, Ohio: NASA Lewis Research Center, 1988.
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Symposium on Naval Hydrodynamics (21st 1996 Trondheim, Norway). Twenty-First Symposium on Naval Hydrodynamics: Wave-induced ship motions and loads, frontier experimental techniques, wake dynamics, viscous ship hydrodynamics, water entry, wave hydrodynamics/stratified flow, bluff body hydrodynamics, hydrodynamics in ship design, shallow water hydrodynamics, cavitation and bubbly flows, propulsor hydrodynamics/hydroacoustics, fluid dynamics in the naval context, CFD validation. Washington, D.C: National Academy Press, 1997.
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Stoffel, B., and K. Weiss. "Different Types and Locations of Part-Load Recirculations in Centrifugal Pumps Found from LDV Measurements." In Hydraulic Machinery and Cavitation, 1034–43. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-010-9385-9_105.
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Toussaint, Michel, and François Hureau. "Analysis of Flow Measurements in the Impeller and Vaned Diffuser of a Centrifugal Pump Operating at Part Load." In Hydraulic Machinery and Cavitation, 419–27. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-010-9385-9_42.
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Raabe, J. "Prediction of Natural Frequencies in a Hydro Power Plant Supplying an Electric Network by Itself Having a Known Load Type." In Hydraulic Machinery and Cavitation, 779–88. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-010-9385-9_79.
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Wack, Jonas, and Stefan Riedelbauch. "Cavitation Simulations of a Tip Leakage Vortex for a NACA0009 Hydrofoil and a Francis Turbine at Stable Full Load Operating Point." In High Performance Computing in Science and Engineering ' 18, 351–65. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-13325-2_22.
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Wrona, Frank, Panagiotis A. Adamidis, Uwe Iben, Rolf Rabenseifner, and Claus-Dieter Munz. "Dynamic Load Balancing for the Parallel Simulation of Cavitating Flows." In Recent Advances in Parallel Virtual Machine and Message Passing Interface, 545–49. Berlin, Heidelberg: Springer Berlin Heidelberg, 2003. http://dx.doi.org/10.1007/978-3-540-39924-7_72.
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Bazarov, Dilshod, Bakhtiyor Obidov, Bekhzod Norkulov, Oybek Vokhidov, and Ikboloy Raimova. "Hydrodynamic Loads on the Water Chamber with Cavitating Dampers." In Lecture Notes in Civil Engineering, 17–24. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-85236-8_2.
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"Measurements of Cavitation Compliance in the Draft Tube Cone of a Reduced Scale Francis Turbine Operating at Part Load." In Proceedings of the 10th International Symposium on Cavitation (CAV2018), 696–701. ASME Press, 2018. http://dx.doi.org/10.1115/1.861851_ch133.
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Banerjee, Avijit, and Timothy F. Watson. "Principles of management of the badly broken down tooth." In Pickard's Guide to Minimally Invasive Operative Dentistry. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780198712091.003.0009.
Повний текст джерелаАнотація:
This textbook has covered the common causes of broken down teeth: dental caries, tooth wear, and trauma. In addition, long-term failure of parts, or all, of the existing tooth–restoration complex can be significant and may require further operative intervention for its successful management (see Chapter 9). Many intra-coronal defects can be repaired with direct adhesive restorations, as discussed in Chapters 5 and 9. However, the situation can be complicated by the loss of significant portions of existing restoration or tooth structure (e.g. cusps, buccal/lingual walls), which influence the restorative procedures used in an attempt to maintain the tooth longevity, as well as pulp viability, for as long as possible. For direct restorations to succeed clinically, they require healthy dental tissues to aid support, retention, and ideally provide an element of protection from excessive occlusal loads. With diminishing amounts of tooth structure to work with, greater thought and care are required to manage and prepare the remaining viable hard tissues to support and retain the larger restoration. The core restoration describes the often large direct plastic restoration used to build up the clinically broken down crown. It is retained and supported by remaining tooth structure wherever possible (sometimes including the pulp chamber and posts in root canals of endodontically treated teeth). These large restorations often benefit from further overlying protection to secure their clinical longevity, by means of indirect onlays, and partial or full coverage crowns. Before carrying out a detailed clinical examination of the individual tooth and the related oral cavity, it is always important to justify your clinical decisions, for both operative and non-operative preventive interventions. The five key reasons for minimally invasive (MI) operative intervention are:… • to repair hard tissue damage/cavitation caused by the active, progressing caries/tooth-wear process (where non-operative prevention has failed repeatedly) • to remove plaque stagnation areas within cavities/defects which will increase the risk of caries activity due to the lack of effective plaque removal by the patient • to help to manage acute pulpitic pain caused by active caries by removing the bacterial biomass and sealing the defect, thereby protecting the pulp • to restore the tooth to maintain structure and function in the dental arch • aesthetics.
Тези доповідей конференцій з теми "Cavitation load"
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Shen, Zhenhua, Nicholas Pedersen, Hong Li, Christian Brix Jacobsen, and Xiaofen Ma. "Part-Load Cavitation Instability Investigation of a High Specific Speed Pump." In ASME 2017 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/fedsm2017-69159.
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Cavitation instability in pump part-load condition is an ongoing subject of research due to erosion and noise. For some high specific speed (nq) pumps, NPSH3%-peak at part-load represents one of the cavitation instabilities. This paper describes the recent investigations and results on performance and cavitation instabilities of a high nq pump. An nq 99 impeller that shows a NPSH3%-peak at 70% of nominal flow rate is investigated by using numerical calculations and experiments. Both experimental and numerical results show that the head curves also have instability phenomenon near 70–80% of nominal flow rate. By analyzing simulation results, part-load recirculation near the shroud is found both under non-cavitating and cavitating conditions. With the pressure decreasing, the recirculation zone become larger and cavitation bubbles influence the flow pattern near the trailing edge at the suction side.
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Yuan, Jianping, Yanxia Fu, and Shouqi Yuan. "A Study of Cavitation Flow in a Centrifugal Pump at Part Load Conditions Based on Numerical Analysis." In ASME 2012 Fluids Engineering Division Summer Meeting collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/fedsm2012-72153.
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In order to predict cavitation performance of the centrifugal pump, including cavitating structures and vapour volume at the blade suction side, as well as its relationship with the backflow in the impeller eye, a 3D numerical simulation of detailed steady and unsteady cavitating flow was applied to reproduce its inner flow fields at part load conditions (0.5Qd and 0.4Qd). The comparisons of cavitation characteristics of the current centrifugal pump at an on-design point (1.0Qd) and a high flow rate (1.2Qd) were achieved as well. In addition, Frequency analysis of pressure fluctuations at the blade passages and the inlet pipe were also obtained during cavitation for a flow coefficient of 50%. The results further show that successive blade cavitation patterns and the creeping cavitation number dropping appear for a wide range of flow rates when the inlet total pressure decreases from cavitation inception to the breakdown of the centrifugal pump, as is quite different from that when cavitation occurs at 1.0Qd or 1.2Qd. Unbalanced attached cavities on the blade suction side were also observed at 0.5Qd. Meanwhile, the unsteady behaviour of cavities attached to the blade suction side and cavitation number dropping depend on the flow rate and cavitation number. Another significant characteristic of the phenomenon is that all the domain frequencies in blade passages and inlet pipe at part load conditions are 0.048Hz∼48.285Hz, which is typically lower than the shaft rotational frequency of the model centrifugal pump.
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Pacot, Olivier, Chisachi Kato, Yang Guo, and Yoshinobu Yamade. "Prediction of the Pressure Pulsation in a Draft Tube for a Part Load Condition Using the LES Approach." In ASME/JSME/KSME 2015 Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/ajkfluids2015-09281.
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The present paper focuses on the vortex rope that arises when operating a model Francis turbine at a part load condition: 65% of the Best Efficiency Point (BEP). The investigation is performed numerically using the Large Eddy Simulation (LES) approach with the Dynamic Smagorinsky Model (DSM). Such approach and turbulence model are implemented in the overset finite element open source code, FrontFlow/blue (FFB). Furthermore, a cavitation model is implemented allowing computations for non-cavitating and cavitating conditions. Thanks to the use of the K supercomputer, located at Kobe in Japan, and to the use of large computational mesh (123 million elements), it is shown that the frequency of the precession of the vortex rope as well as the head can be accurately computed. However, the predicted amplitude of the fluctuation did not fully agree with the experiment. Differences in a particular region near the back side of the elbow are about 35%. A comparison between the variation of the size of the vortex rope and the swirl number has been investigated and showed a clear relation. The location of the vortex rope and the minimum of the pressure were also investigated and showed that they do not fully share the same location. Furthermore, in a preliminary study to the computation of the cavitating vortex rope, computations of the flow around a Clark-11.7% hydrofoil under cavitation condition and for angles of attack of 2° and 8° are carried out. The results showed the common issue for this computation, i.e. the sharp change of the lift and drag coefficients could not be accurately predicted. Currently underway are the computation of the cavitating vortex rope. The effect of the cavitation on the vortex rope will be studied and reported at a later stage.
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Harwood, Casey, Antoine Ducoin, and Yin Lu Young. "Influence of Gap Flow on the Cavitating Response of a Rectangular Hydrofoil." In SNAME 13th Propeller and Shafting Symposium. SNAME, 2012. http://dx.doi.org/10.5957/pss-2012-006.
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A commercial URANS solver is used to analyze the cavitating flow field around a rectangular, cantilevered hydrofoil with a small gap between the free end and the wall of a cavitation tunnel. A transport-equation based cavitation model is used along with an artificial compressibility correction for the turbulent eddy viscosity. The objective is to improve the understanding of the unsteady interactions between the 3-D gap flow, sheet-cloud cavitation, gap cavitation, tip vortices, and their dependence on the cavitation index. It is found that the numerically-predicted wetted pressure distributions, cavitation patterns, and load coefficients agree well with experimental measurements and observations. The results suggest that the presence of cavitation significantly modifies the boundary layer flow near the tip and the tunnel wall, disrupts the formation of the tip-leakage vortex, and enhances other secondary flows. Although the numerical model was able to simulate the general dynamics of sheet and gap cavitation, a more refined mesh and higher fidelity turbulence models (e.g. DES or LES) are needed to resolve the fine vortex structures in the tip, tip vortex cavitation, and the highly transient features of 3-D cloud cavitation.
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Shen, Xi, and Desheng Zhang. "Experiments of Tip Leakage Vortex Cavitation Cloud and Suction-Side-Perpendicular Cavitating Vortices in an Axial Flow Pump." In ASME 2018 5th Joint US-European Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/fedsm2018-83134.
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The tip leakage vortex (TLV) cavitation mechanism of axial flow pump was investigated with the results of high speed photography and pressure pulsation measurement. The tip leakage vortex cavitation morphology and the transient characteristics of the TLV-induced suction-side-perpendicular cavitating vortices (SSPCV) were analyzed under different flow rates and different cavitation numbers which were combined with the time domain spectrum of pressure fluctuation to elucidate the relationship between the tip cavitation and pressure pulsation. The results showed that cavitation inception occurs earlier with more unstable tip leakage vortex cavitation shape under part-load flow rate condition, and the cavitation is more intense with the decrease of the cavitation number. The inception of SSPCV is attributed to the tail of the shedding cavitation cloud originally attached on the suction side (SS) surface of blade, moving toward the adjacent blade perpendicular to the suction surface, resulting in a flow blockage. With further decrease of pressure, the SSPCVs grow in size and strength, accompanied with a rapid degradation in performance of the pump. The cavitation images and the corresponding circumferential pressure distribution with the same phase showed that the lowest pressure coincides with the suction surface (SS) corner, The pressure was found to decrease along with the occurrence of the cavitation structure.
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Harihara, Parasuram P., and Alexander G. Parlos. "Sensorless Detection of Cavitation in Centrifugal Pumps." In ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-14655.
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Analysis of electrical signatures has been in use for some time for estimating the condition of induction motors, by extracting spectral indicators from motor current waveforms. In most applications, motors are used to drive dynamic loads, such as pumps, fans, and blowers, by means of power transmission devices, such as belts, couplers, gear-boxes. Failure of either the electric motors or the driven loads is associated with operational disruption. The large costs associated with the resulting idle equipment and personnel can often be avoided if the degradation is detected in its early stages prior to reaching failure conditions. Hence the need arises for cost-effective detection schemes not only for assessing the condition of the motor but also of the driven load. This prompts one to consider approaches that use no add-on sensors, in order to avoid any reduction in overall system reliability and increased costs. This paper presents an experimentally demonstrated sensorless approach to detecting varying levels of cavitation in centrifugal pumps. The proposed approach is sensorless in the sense that no mechanical sensors are required on either the pump or the motor driving the pump. Rather, onset of pump cavitation is detected using only the line voltages and phase currents of the electric motor driving the pump. Moreover, most industrial motor switchgear are equipped with potential transformers and current transformers which can be used to measure the motor voltages and currents. The developed fault detection scheme is insensitive to electric power supply and mechanical load variations. Furthermore, it does not require a priori knowledge of a motor or pump model or any detailed motor or pump design parameters; a model of the system is adaptively estimated on-line. The developed detection algorithm has been tested on data collected from a centrifugal pump connected to a 3 φ, 3 hp induction motor. Several cavitation levels are staged with increased severity. In addition to these staged pump faults, extensive experiments are also conducted to test the false alarm performance of the algorithm. Results from these experiments allow us to offer the conclusion that for the cases under consideration, the proposed model-based detection scheme reveals cavitation detection times that are comparable to those obtained from vibration analysis with a detection threshold that is significantly lower than used in industrial practice.
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Skelley, Stephen. "Inducer Hydrodynamic Forces in a Cavitating Environment." In ASME 2004 Heat Transfer/Fluids Engineering Summer Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/ht-fed2004-56115.
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Marshall Space Flight Center has developed and demonstrated a measurement device for sensing and resolving the hydrodynamic loads on fluid machinery. The device — a derivative of the six-component wind tunnel balance — senses the forces and moments on the rotating device through a weakened shaft section instrumented with a series of strain gauges. This “rotating balance” was designed to directly measure the steady and unsteady hydrodynamic loads on an inducer, thereby defining the amplitude and frequency content associated with operating in various cavitation modes. The rotating balance was calibrated statically using a dead-weight load system in order to generate the 6 × 12 calibration matrix later used to convert measured voltages to engineering units. Structural modeling suggested that the rotating assembly first bending mode would be significantly reduced with the balance’s inclusion. This reduction in structural stiffness was later confirmed experimentally with a hammer-impact test. This effect, coupled with the relatively large damping associated with the rotating balance waterproofing material, limited the device’s bandwidth to approximately 50 Hertz. Other pre-test validations included sensing the test article rotating assembly built-in imbalance for two configurations and directly measuring the assembly mass and buoyancy while submerged under water. Both tests matched predictions and confirmed the device’s sensitivity while stationary and rotating. The rotating balance was then demonstrated in a water test of a full-scale Space Shuttle Main Engine high-pressure liquid oxygen pump inducer. Experimental data was collected a scaled operating conditions at three flow coefficients across a range of cavitation numbers for the single inducer geometry and radial clearance. Two distinct cavitation modes were observed: symmetric tip vortex cavitation and alternate-blade cavitation. Although previous experimental tests on the same inducer demonstrated two additional cavitation modes at lower inlet pressures, these conditions proved unreachable with the rotating balance installed due to the intense dynamic environment. The sensed radial load was less influenced by flow coefficient than by cavitation number or cavitation mode although the flow coefficient range was relatively narrow. Transition from symmetric tip vortex to alternate-blade cavitation corresponded to changes in both radial load magnitude and radial load orientation relative to the inducer. Sensed moments indicated that the effective load center moved downstream during this change in cavitation mode. An occurrence of “higher-order cavitation” was also detected in both the stationary pressures and the rotating balance data although the frequency of the phenomena was well above the reliable bandwidth of the rotating balance. In summary the experimental tests proved both the concept and device’s capability despite the limitations and confirmed that hydrodynamically-induced forces and moments develop in response to the unbalanced pressure field, which is, in turn, a product of the cavitation environment.
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Kerr, Thomas, and Adolfo Delgado. "Novel Approach for Optical Characterization of Thrust Collar Lubricated Area: Experimental and Numerical Results." In ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-15467.
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Abstract Thrust collars (TCs) are bearing elements used in geared machinery that transmit axial loads from one shaft to another. TCs are primarily used in integrally geared compressors (IGCs), but are also found in gearboxes and marine propulsion applications. TCs are hydrodynamic elements featuring a converging-diverging wedge to generate a pressure field that reacts axial loads. Accurate modeling requires knowledge of the film characteristics such as cavitation, turbulence, and air ingestion, all of which reduce load capacity. Current models in the literature do not include mass-conserving cavitation algorithms or turbulent flow. The following paper introduces a new test rig that optically characterizes the thin film region of a thrust collar. The test rig geometries, speeds, and loads match those typically seen in IGC applications. The test rig utilizes a transparent acrylic window in conjunction with a high-speed camera to obtain high-speed images of the oil film. Images are filtered and averaged to obtain areas of interest in the oil film. Cavitation and turbulence areas are captured for pinion speeds of 2.5, 5, and 7.5 krpm, and axial loads of 0.5, 1, and 1.5 kN. Cavitation occurs in the diverging (upper) region of the TC and appears at pinion speeds over 5,000 rpm, but does not change in shape after that speed. The cavitation is independent of applied load. Turbulence at the inlet region (bottom) occurs at all speeds, but increases to almost 35% of the total area at the highest speed. This paper also presents a finite element (FE) model that includes predictions for the static characteristics of the TC, specifically the cavitation area. The cavitation modeling uses an iterative Elord’s method, which conserves mass. The model predicts a similar cavitation area for all speeds and loads. A computation fluid dynamics (CFD) study predicts a similar cavitation area, and pressure field to the FE model. The CFD model predicts turbulence in the lower region that increases for increasing spin speed, which matches the experimental results. The CFD model tends to underpredict the turbulence area when compared to the experiments. As IGCs move into novel application areas to satisfy new needs, the increase in efficiency and capacity comes at a cost of more load and higher speed requirements on the TCs. This work will help original equipment manufacturers model TCs more accurately to ensure safe and efficient operation.
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Ding, Aoshuang, Xuesong Li, and Yuhong Li. "Improvement and Analysis for a Gaseous Cavitation Model Applied in a Tilting-Pad Journal Bearing." In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-90626.
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Abstract Considering the gaseous cavitation rate is influenced by local pressure, a transient gaseous cavitation model is developed from an equilibrium gaseous cavitation model in consideration of transient gaseous cavitation theories and the Bunsen solubility. With the shear stress transport (SST) model with low-Re correction and air backflow from the bearing outlets, the transient gaseous cavitation model is applied to the three-dimensional simulations of an entire tilting-pad journal bearing at 3000 rpm speed and under 180 kN load. The simulated bearing pressure and load are in good agreement with the experimental data, indicating that the transient gaseous cavitation model performs well in the bearing simulations. Based on the comparisons of the simulated air and dissolved air distributions between the transient and equilibrium gaseous cavitation models, the simulated cavitation process of the transient gaseous cavitation is proved to be not in equilibrium and mass transfer occur between the backflow air and oil. The purpose of building the transient gaseous cavitation model is thus met. Analyses of the air distributions indicate that high cavitation rates and low dissolution rates makes air volume a major part of the total air volume and close to the physical gaseous cavitation process.
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Ding, Aoshuang, and Xuesong Li. "Numerical Investigation for Characteristics and Oil-Air Distributions of a Tilting-Pad Journal Bearing Under Different Loads." In ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-15151.
Повний текст джерелаАнотація:
Abstract This paper analyses the flow characteristics and oil-air distributions of oil flows in a tilting-pad journal bearing under different bearing loads. This titling-pad journal bearing is working at 3000 rpm rotation speed and its minimum film thicknesses have been measured under different loads from 180 kN to 299 kN. Based on the previous researches of this bearing under 180 kN, the gaseous cavitation and low-turbulence flow exists in this bearing flow. A suitable gaseous cavitation model and the SST model with low-Re correction are used in the film flow simulations. With the rotor and pads assumed to be rigid, the dynamic mesh and motion equations are applied to simulate the motions of the rotor and the rotations of the pads. Based on the simulation results under different bearing loads, the simulated minimum film thicknesses agrees well with the measured data. It indicates that the simulation results can catch the film geometries and flows correctly. With the load increasing, the rotor moves closer to the loaded pads and the minimum film thickness decreases. Taking the effect of boundary layers into consideration, the turbulence has a negative relationship with the film thickness and decreases in the loaded area under higher bearing load. It can be verified by the simulated lower turbulent viscosity ratio distributions in the loaded pads. In the unloaded area, both the film thickness and turbulence viscosity ratio are positively related to the bearing loads. Thus, the higher bearing load may lead the flow to be more different in the loaded and unloaded area, and the turbulence in the loaded pads may transfer to laminar in the end. As for the oil-air distributions, in the unloaded pads, with the bearing load increasing, the simulated air volume fraction increases in the unloaded pads with lower pressure. It should be caused by the higher film thickness of the unloaded pads under higher loads. In sum, the flow turbulence and cavitation process changes with the bearing load. With a higher load, the cavitation becomes more in the unloaded pads and the flow changes sharper from the high-turbulence unloaded area to the low-turbulence loaded area. As the simulation results is in good accordance with the experimental data, the SST model with low-Re correction and the gaseous cavitation model are verified to be suitable for bearing film simulations under different loads.