Letteratura scientifica selezionata sul tema "Cavitation clouds"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Consulta la lista di attuali articoli, libri, tesi, atti di convegni e altre fonti scientifiche attinenti al tema "Cavitation clouds".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Articoli di riviste sul tema "Cavitation clouds":
1
Ahn, Byoung-Kwon, So-Won Jeong, Cheol-Soo Park e Gun-Do Kim. "An Experimental Investigation of Coherent Structures and Induced Noise Characteristics of the Partial Cavitating Flow on a Two-Dimensional Hydrofoil". Fluids 5, n. 4 (3 novembre 2020): 198. http://dx.doi.org/10.3390/fluids5040198.
Abstract (sommario):
In many practical submerged objects, various types of cavitation such as bubble, sheet, and cloud cavitation occur according to flow conditions. In spite of numerous theoretical, numerical, and experimental studies, there are still many problems to be solved such as induced noise and damage potential due to cavitation. In this paper, an experimental investigation on coherent structures and induced noise characteristics of partial cavitation on a two-dimensional hydrofoil is presented. Experiments that focused on the dynamics of cavitation clouds were conducted in a cavitation tunnel. Using high-speed visualization, the series process consisting of inception, growth, and desinence of the partial cavity was investigated. The noise generated during the process was also measured, and the correlation with the cavity pattern was examined. The results show that the periodic behavior of cavitation clouds is directly reflected in the noise characteristics. In addition, the visualization of coherent structures within the sheet and cloud cavity provides a qualitative understanding of hairpin vortices and their packets, which play a dominant role in turbulent cavitating flows.
2
Li, Lidong, Yan Xu, Mingming Ge, Zunce Wang, Sen Li e Jinglong Zhang. "Numerical Investigation of Cavitating Jet Flow Field with Different Turbulence Models". Mathematics 11, n. 18 (19 settembre 2023): 3977. http://dx.doi.org/10.3390/math11183977.
Abstract (sommario):
In numerous industries such as drilling, peening, cleaning, etc., a cavitating jet is adopted. However, it is challenging to simulate the cavitating flow field numerically with accuracy. The flow field of the organ pipe cavitation nozzle is simulated in this research using the RNG k−ε, DES, and LES turbulence models. The LES model can more accurately predict the periodic shedding of a cavitating cloud, which is basically consistent with the jet morphology captured with a high−speed camera. The flow pattern, cavitating cloud evolution and shedding period of a cavitating jet are analyzed. The findings demonstrate that the LES model produces a cavitating effect inside the nozzle that is superior to those produced by the RNG k−ε and DES models. The vortex rings in the diffusion section are simulated using the LES model, which accelerates cavitation. The cavitating clouds of the organ pipe nozzle show periodic evolutions, with stages of generation, development, shedding and collapse. The periodic shedding of the cavitating clouds exhibits a similar pattern in the vorticities simulated using the LES model, and the vorticities display the small-scale structures where the cavitating bubbles collapse. This study can provide a reference for the simulation of a cavitating jet and the analysis of the cavitating mechanism.
3
Wang, Hao, Jian Feng, Keyang Liu, Xi Shen, Bin Xu, Desheng Zhang e Weibin Zhang. "Experimental Study on Unsteady Cavitating Flow and Its Instability in Liquid Rocket Engine Inducer". Journal of Marine Science and Engineering 10, n. 6 (12 giugno 2022): 806. http://dx.doi.org/10.3390/jmse10060806.
Abstract (sommario):
To study instability in the unsteady cavitating flow in a liquid rocket engine inducer, visualization experiments of non-cavitating and cavitating flows inside a model inducer were carried out at different flow conditions. Visual experiments were carried out to capture the evolution of non-cavitating and cavitating flows in a three-bladed inducer by using a high-speed camera. The external characteristic performance, cavitation performance, and pressure pulsation were analyzed based on the observation of non-cavitation and cavitation development and their instabilities. Under non-cavitation conditions, the change of flow rate has a significant impact on the pressure pulsation characteristics in the inducer. The occurrence of cavitation aggravated the instability of the flow and caused the intensity of pressure pulsation at each measuring point to increase. This cavitation structure has strong instability, and the tail region is often accompanied by shedding cavitation clouds perpendicular to the blade surface.
4
REISMAN, G. E., Y. C. WANG e C. E. BRENNEN. "Observations of shock waves in cloud cavitation". Journal of Fluid Mechanics 355 (25 gennaio 1998): 255–83. http://dx.doi.org/10.1017/s0022112097007830.
Abstract (sommario):
This paper describes an investigation of the dynamics and acoustics of cloud cavitation, the structures which are often formed by the periodic breakup and collapse of a sheet or vortex cavity. This form of cavitation frequently causes severe noise and damage, though the precise mechanism responsible for the enhancement of these adverse effects is not fully understood. In this paper, we investigate the large impulsive surface pressures generated by this type of cavitation and correlate these with the images from high-speed motion pictures. This reveals that several types of propagating structures (shock waves) are formed in a collapsing cloud and dictate the dynamics and acoustics of collapse. One type of shock wave structure is associated with the coherent collapse of a well-defined and separate cloud when it is convected into a region of higher pressure. This type of global structure causes the largest impulsive pressures and radiated noise. But two other types of structure, termed ‘crescent-shaped regions’ and ‘leading-edge structures’ occur during the less-coherent collapse of clouds. These local events are smaller and therefore produce less radiated noise but the interior pressure pulse magnitudes are almost as large as those produced by the global events.The ubiquity and severity of these propagating shock wave structures provides a new perspective on the mechanisms reponsible for noise and damage in cavitating flows involving clouds of bubbles. It would appear that shock wave dynamics rather than the collapse dynamics of single bubbles determine the damage and noise in many cavitating flows.
5
Yuan, Miao, Yong Kang, Hanqing Shi, Dezheng Li e Hongchao Li. "Experimental Investigation on the Characteristic of Hydrodynamic-Acoustic Cavitation (HAC)". Journal of Marine Science and Engineering 10, n. 3 (22 febbraio 2022): 309. http://dx.doi.org/10.3390/jmse10030309.
Abstract (sommario):
This study aimed to investigate the Cavitation dynamics of Hydrodynamic-acoustic cavitation by employing experimental methods. The spatial distribution of cavitation clouds, the temporal and spatial distribution achieved by cavitation clouds, and the main flow structure in the flow field were extracted and analyzed by complying with the cavitating flow image captured with the high-speed camera. As indicated from the results, the widened cavitation region and the strength of cavitation under the synergy of ultrasound were reported. When the inlet pressure is 2 MPa, the average value of the volume-averaging cavitation intensity variable is 0.029, 0.058, and 0.092, respectively, and the corresponding growth rate is 95% and 58.5%. By adopting the Proper Orthogonal Decomposition method (POD), the ultrasound was revealed to primarily enhance the cavitation intensity by downregulating the cavitation threshold other than altering the large-scale vortex structure in the flow field. The high-frequency pressure pulsation of ultrasound strengthened the instability exhibited by the shear layer and induced small-scale vortex structures at the shear layer, which was suggested to be the more violently shed and collapse.
6
Simon, Alex, Connor Edsall e Eli Vlaisavljevich. "Effects of pulse repetition frequency on bubble cloud characteristics and ablation for single-cycle histotripsy". Journal of the Acoustical Society of America 152, n. 4 (ottobre 2022): A247. http://dx.doi.org/10.1121/10.0016161.
Abstract (sommario):
Histotripsy is a cavitation-based focused ultrasound ablation method in development for multiple clinical applications. This work investigates the effects of pulse repetition frequency (PRF) on histotripsy bubble cloud characteristics and ablative capabilities for single cycle histotripsy. Bubble clouds produced by a 500 kHz histotripsy system at PRF’s from 0.1 to 1000 Hz were visualized using high speed imaging in 1% agarose phantoms. Cloud images were analyzed to determine bubble cloud density (bubbles/mm2) and pulse-to-pulse bubble correlation. Ablation was assessed through lesion analysis in red blood cell (RBC) phantoms. Results showed cavitation clouds generated at low PRF were characterized by consistently dense bubble clouds (49.6 ± 7.7 bubbles/mm2, 1 Hz) that closely matched regions above the histotripsy intrinsic threshold. Bubble clouds formed at high PRF had significantly lower cloud density (20.0 ± 8.3 bubbles/mm2, 1000 Hz). In addition, bubbles in higher PRF clouds had significantly increased pulse-to-pulse correlation, characteristic of what has been reported as the cavitation memory effect. Results from RBC ablation showed that higher PRF generated lesions had lower adherence to the focal region and less repeatability compared to low PRF ablations. This study demonstrates essential differences in bubble cloud characteristics that will help guide future histotripsy pulsing strategies.
7
del Campo, David, R. Castilla, GA Raush, PJ Gamez-Montero e E. Codina. "Pressure effects on the performance of external gear pumps under cavitation". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 228, n. 16 (24 febbraio 2014): 2925–37. http://dx.doi.org/10.1177/0954406214522990.
Abstract (sommario):
The numerical analysis of an external gear pump with cavitation effects has been validated with experimental data obtained by applying Time-Resolved Particle Image Velocimetry. The effect of inlet and outlet pressure on volumetric efficiency has been studied numerically. First, the Particle Image Velocimetry method was used to analyze the two-dimensional velocity field in the middle plane of the suction chamber of the gear pump. The main improvement, with respect to previous similar analysis is the use of alginate micro particles as tracers. It is seen that the two-dimensional model is able to characterize the flow field of the real pump in the region of the inlet chamber in which cavitation is expected. In a previous study, it was seen that a cavitation cloud acted as a virtual contact point at low pressure, being responsible for an increase on the volumetric efficiency. The first set of simulations represents the pump working with high outlet pressure. Now, the cavitation cloud is not present and cavitation no longer helps to improve the efficiency of the pump. The second set of simulations represents the pump with an inlet loss factor, which implies a mean inlet pressure below atmospheric conditions. This allows cavitation clouds to propagate upstream. Despite the larger cavitation clouds, volumetric efficiency only drops at high operating velocities, when some clouds become trapped between gears and casing and are transported to the pressure side.
8
Cui, Yanyu, Manjun Zhao, Qingmiao Ding e Bin Cheng. "Study on Dynamic Evolution and Erosion Characteristics of Cavitation Clouds in Submerged Cavitating Water Jets". Journal of Marine Science and Engineering 12, n. 4 (10 aprile 2024): 641. http://dx.doi.org/10.3390/jmse12040641.
Abstract (sommario):
The dynamic evolution behavior of submerged water jet cavitation clouds was studied by combining experiments and simulation. The formation, development, shedding, and collapsing process of a void cloud was analyzed by high-speed camera technology, and the influence of jet pressure was studied. Cavitation water jet erosion experiments were carried out on AL6061 specimens with standard cylindrical nozzles, and the correlation between cavitation cloud evolution and material erosion was studied by surface analysis. The results showed that the evolution of a cavitation cloud has obvious periodicity, that one period is about 0.8 ms, and its action region can be divided according to the attenuation rate of the jet velocity of the nozzle axis. The attenuation rate of the jet velocity at the nozzle axis in the central jet action zone is less than or equal to 82.5%, in the mixed action zone greater than 82.5% and less than 96%, and in the cavitation action zone greater than or equal to 96%. The erosion damage characteristics in different regions of the mixed action zone are significantly different.
9
Yang, Yongfei, Wei Li, Weidong Shi, Ling Zhou e Wenquan Zhang. "Experimental Study on the Unsteady Characteristics and the Impact Performance of a High-Pressure Submerged Cavitation Jet". Shock and Vibration 2020 (16 giugno 2020): 1–15. http://dx.doi.org/10.1155/2020/1701843.
Abstract (sommario):
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.
10
Huang, Si, Yuxiong Hu, Yifeng Wei e Yushi Mo. "Analysis of Cavitation Flow Performance in Centrifugal Pump Using OpenFOAM". Journal of Physics: Conference Series 2610, n. 1 (1 ottobre 2023): 012023. http://dx.doi.org/10.1088/1742-6596/2610/1/012023.
Abstract (sommario):
Abstract In order to explore the cavitation mechanism and cavitation cloud development process of centrifugal pump, OpenFOAM7.0 open-source software was used to simulate the unsteady cavitation gas-liquid two-phase flow of IS125 centrifugal pump under different flow conditions. Based on the flow field simulation results, the relationship between the flow rate of the centrifugal pump and the NPSHr was predicted and compared with the experimental data. The comparison showed that it is feasible to use OpenFOAM software to simulate the cavitation flow of centrifugal pump under design condition. Under the design condition, when NPSHa was different, the distribution of cavitation clouds in each blade channel was asymmetric. With the decrease of NPSHa, cavitation clouds continue to develop downstream in the impeller channel and appear on the blade pressure surface. Regardless of whether cavitation occurred in the centrifugal pump, the pressure coefficient showed periodic pulsation, and the pulsation number of the impeller in a rotation cycle was equal to the number of blades of the impeller. The research results can provide an effective open-source software calculation method for centrifugal pump performance prediction.
Tesi sul tema "Cavitation clouds":
1
Malan, Leon. "Direct numerical simulation of free-surface and interfacial flow using the VOF method : cavitating bubble clouds and phase change". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066555/document.
Abstract (sommario):
La présente étude se fonde sur la méthode du volume de fluide (en anglais VOF pour Volume-of-Fluid), proposée à l'origine par Hirt et Nicols. L'objectif de la première partie de ce travail est l'étude hydrodynamique de la cavitation isotherme dans les grands nuages de bulles. Cette étude s'inscrit plus généralement dans un large effort de recherche en micro--écaillage mené par le CEA. Une méthode capable de traiter la présence de cavités de vapeur de volume variable ou encore de pores a été formulée et implémentée dans un code existant, PARIS. L'écoulement est idéalisé en supposant un liquide parfait, des effets thermiques négligeables et une pression de vapeur nulle. Une étude innovante est présentée, traitant de l'interaction du nuage de bulles dans un liquide en expansion par simulation numérique directe. Les résultats des simulations révèlent l'existence d'un concours de cavités dans un certain régime caractérisé par le nombre de Weber.Dans la deuxième partie de l'étude, le système d'équations à résoudre est modifié et généralisé afin de décrire l'écoulement incompressible d'un fluide diphasique tout en incluant la possibilité d'un changement de phase à l'interface. Une nouvelle méthode VOF est proposée, dans laquelle une nouvelle technique d'advection de la fonction VOF permet de traiter à la fois la conservation de la masse et de l'énergie sous une forme conservative. Les expériences numériques démontrent la précision, la robustesse et la généralité de la méthode proposée, et témoignent d'un développement fondamental important pour l'application des méthodes VOF à la modélisation des changements de phaseDirect numerical simulation of two-phase ow is used extensively for engineering research and fundamental fluid physics studies [54, 81]. This study is based on the Volume-Of-Fluid (VOF) method, originally created by Hirt and Nicols [30]. This method has gained increased popularity, especially when geometric advection techniques are used coupled with a planar reconstruction of the interface [14, 89]. The focus of the first part of this work is to investigate the hydrodynamics of isothermal cavitation in large bubble clouds, which originated from a larger study of micro-spalling [61], conducted by the French CEA. A method to deal with volume-changing vapour cavities, or pores, was formulated and implemented in an existing code, PARIS . The ow is idealized by assuming an inviscid liquid, negligible thermal effects and vanishing vapour pressure. A novel investigation of bubble cloud interaction in an expanding liquid using direct or detailed numerical simulation is presented. The simulation results reveal a pore competition, which is characterised by the Weber number in the ow. In the second part of the study the governing equations are extended to describe incompressible ow with phase change [79]. The description of the work commences with the derivation of the governing equations. Following this, a novel, geometric based, VOF solution method is proposed. In this method a novel way of advecting the VOF function is invented, which treats both mass and energy conservation in conservative form. New techniques include the advection of the interface in a discontinuous velocity field. The proposed algorithms are consistent and elegant, requiring minimal modifications to the existing code. Numerical experiments demonstrate accuracy, robustness and generality. This is viewed as a significant fundamental development in the use of VOF methods to model phase change
2
Sivadon, Audrey. "Contributions à l’imagerie passive de la cavitation ultrasonore : formation de voies adaptatives en 3D et extension spatiale de nuages de bulles". Electronic Thesis or Diss., Lyon 1, 2022. http://www.theses.fr/2022LYO10172.
Abstract (sommario):
L’imagerie passive s’appuie sur des algorithmes de formation de voie qui nécessitent des sondes de grande ouverture pour offrir de bonnes résolutions axiales ; or, en imagerie passive 3D, les sondes matricielles actuellement commercialisées ne vérifient pas cette contrainte. De plus, ces sondes présentent un grand nombre d’éléments, ce qui rend leur utilisation particulièrement lourde. Ce travail de thèse porte sur l’étude et l’amélioration de l’imagerie passive de la cavitation en s’intéressant à deux aspects en particulier : (i) la mise en œuvre pratique et efficace de l’imagerie passive en 3D, (ii) la problématique de l’imagerie de sources étendues telles que des nuages de cavitation. Nous avons combiné l’application des méthodes sparse (pour réduire le nombre d’éléments actifs de la sonde utilisée) et la transposition du 2D au 3D des algorithmes adaptatifs dans le domaine fréquentiel. Ce formalisme utilise l’estimation robuste de la matrice de densité inter-spectrale (CSM) et nous a permis d’implémenter simplement et efficacement différents algorithmes : Delay-And-Sum (DAS), Robust-Capon-Beamformer et Pisarenko. L’efficacité de ces algorithmes en 3D a été testée en termes de largeur à mi-hauteur, de contraste et d’erreur de position, sur une source ponctuelle en simulations et sur une expérience de réflecteur ponctuel. Enfin, pour répondre à la réalité des nuages de cavitation, nous nous sommes intéressés au comportement de ces méthodes de reconstruction dans le cas de sources étendues. Nos simulations en 2D montrent l’évolution des images reconstruites en fonction de caractéristiques du nuage de cavitation. Ce travail apporte une solution concrète de mise en œuvre simple de l’imagerie passive 3D ainsi que des éléments de réponse quant aux attentes sur la localisation et la caractérisation d’un nuage de cavitationPassive imaging relies on beamforming algorithms that require large aperture probes to provide good axial resolutions; however, in 3D passive imaging, the matrix probes currently marketed do not meet this constraint. Moreover, these probes have a large number of elements, which makes their use particularly unwieldy. This thesis work focuses on the study and improvement of passive cavitation imaging by addressing two aspects in particular: (i) the practical and efficient implementation of 3D passive imaging, (ii) the problem of imaging large sources such as cavitation clouds. We have combined the application of sparse methods (to reduce the number of active elements of the probe used) and the transposition from 2D to 3D of adaptive algorithms in the frequency domain. This formalism uses the robust estimation of the inter-spectral density matrix (CSM) and allowed us to implement simply and efficiently different algorithms: Delay-And-Sum (DAS), Robust-Capon-Beamformer and Pisarenko. The efficiency of these algorithms in 3D has been tested in terms of width to half height, contrast and position error, on a point source in simulations and on a point reflector in experiments. Finally, in order to address the reality of cavitation clouds, we have investigated the behavior of these reconstruction methods in the case of extended sources. Our 2D simulations show the evolution of the reconstructed images as a function of the cavitation cloud characteristics. This work provides a concrete solution for a simple implementation of 3D passive imaging as well as answers to the expectations on the localization and characterization of a cavitation cloud
3
Reisman, Garrett Erin Brennen Christopher E. "Dynamics, acoustics and control of cloud cavitation on hydrofoils /". Diss., Pasadena, Calif. : California Institute of Technology, 1997. http://resolver.caltech.edu/CaltechETD:etd-03302004-140539.
4
Wright, Michael Marshall. "Cavitation of a Water Jet in Water". BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3175.
Abstract (sommario):
Cavitation is a phenomenon that occurs in liquids when the pressure drops below the vapor pressure of the liquid. Previous research has verified that cavitation bubble collapse is a dynamic and destructive process. An understanding of the behavior of cavitation is necessary to implement this destructive mechanism from an axisymmetric jet for underwater material removal. This work investigates the influence of jet pressure and nozzle diameter on the behavior of a cloud of cavitation bubbles generated by a submerged high-pressure water jet. First, this investigation is put into context with a condensed historical background of cavitation research. Second, a description of the cavitation-generating apparatus is given. Next, the experimental methods used to explore the behavior of the cavitation clouds are explained. Finally, the results of the investigation, including propagation distance, cloud width and area, pulsation frequency, and cloud front velocity are presented. Among the results is a discussion of the significant experimental factors affecting the behavior of the cavitation clouds. It is shown that the Reynolds number, specifically the diameter of the nozzle, has a significant effect on the measurements. In some cases the jet pressure, and subsequent jet velocity, had a less significant effect than was expected. Overall, this research describes the cavitation cloud formed when a submerged high-speed water jet discharges.
5
Geng, Linlin. "Numerical investigation and modelling of the unsteady behavior and erosion power of cloud cavitation". Doctoral thesis, Universitat Politècnica de Catalunya, 2021. http://hdl.handle.net/10803/671490.
Abstract (sommario):
Cloud cavitation is a unwanted phenomenon taking place in many hydraulic machines which damages the surfaces of the solid walls due to the erosive aggressiveness induced by the collapse process. Therefore, it is necessary to accurately predict the occurrence of cloud cavitation and quantify its erosion intensity to improve the design and to extend the life cycle of existing machines and systems. The application of numerical simulation (CFD) offers the opportunity to predict unsteady cavitation. For that, it is of paramount importance to investigate how to select the most appropriate models to obtain more accurate results in an efficient way and how to relate the collapsing vapor structures with their erosion power. In the current study, the influence of the different turbulence models was assessed and the performance of cavitation models was improved. The relationship between the unsteady behavior and its erosion character was also considered by implementing an erosion model.
For the assessment of the turbulence models, three Unsteady Reynolds Average Navier-Stokes (URANS) turbulence models were employed to simulate the cloud cavitation around a NACA65012 hydrofoil at eight different hydrodynamic conditions. The results indicate that the Shear Stress Transport (SST) model can better capture the unsteady cavity behavior than the k-e and the RNG models if the near wall grid resolution is fine enough.
For the improvement of the cavitation models, the influence of the empirical constants of the Zwart model on the cavity dynamics was firstly investigated. The results show that the cavity behavior is sensitive to their variation, and thereby an optimal range is proposed which can provide a better prediction of the vapor volume fraction and of the instantaneous pressure pulse generated by the main cloud cavity collapse. Secondly, the original Zwart and Singhal cavitation models were corrected by taking into account the second order term of the Rayleigh-Plesset equation. The performances of the original and corrected models were compared for two different cavitation patterns. The results for a steady attached cavity demonstrate that the corrected model predicts better the pressure distribution at the cavity closure region and the cavity length in comparison with the experiment observations. The results for unsteady cloud cavitation also confirm that the prediction of the shedding frequency can be improved with the corrected Zwart model.
For the investigation of the cavitation erosion power, an erosion model based on the energy balance approach was employed. It has been found that the spatial and temporal distribution of the erosion aggressiveness is sensitive to the selection of the cavitation model and to the collapse driving pressure. In particular, the use of average pressure levels combined with the Sauer cavitation model permit to achieve reliable results. Then, two erosion mechanisms have been observed, one occurs at the closure region of the main sheet cavity characterized by low-intensity collapses but with high frequency, and the other is inducted by the collapse of the shed cloudy cavity which presents a high erosion intensity but with low frequency. Finally, it has been found that the erosion power follows a power law with the main flow velocity with exponents ranging from 3 to 5 depending on the erosion estimate being used.La cavitació de núvol és un fenomen no desitjat que té lloc en moltes màquines hidràuliques que danya les superfícies de les parets sòlides a causa de l'agressivitat erosiva induïda pel procés de col·lapse. Per tant, és necessari predir amb precisió l'ocurrència de la cavitació de núvol i quantificar-ne la intensitat d¿erosió per millorar el disseny i ampliar el cicle de vida de les màquines i sistemes existents. L'aplicació de la simulació numèrica (CFD) ofereix l'oportunitat de predir la cavitació inestable. Per a això, és de suma importància investigar com seleccionar els models més adequats per obtenir els resultats més precisos d'una manera eficient i com relacionar el col·lapse de les estructures de vapor amb el seu poder erosiu. En l'estudi actual, s'ha avaluat la influència dels diferents models de turbulència i s'ha millorat el rendiment dels models de cavitació. La relació entre el comportament inestable i el seu caràcter erosiu també s'ha considerat implementant un model d'erosió. Per a l'avaluació dels models de turbulència, s'han emprat tres models de turbulència Unsteady Reynolds Average Navier-Stokes (URANS) per simular la cavitació de núvol al voltant d'un perfil hidràulic NACA65012 en vuit condicions hidrodinàmiques diferents. Els resultats indiquen que el model Shear Stress Transport (SST) pot captar millor el comportament de la cavitat inestable que els models k-e i RNG si la resolució de la malla propera a la paret és prou bona. Per millorar els models de cavitació, s'ha investigat primerament la influència de les constants empíriques del model de Zwart en la dinàmica de la cavitat. Els resultats mostren que el comportament de la cavitat és sensible a la seva variació i, per tant, es proposa un rang òptim que pot proporcionar una millor predicció de la fracció de volum de vapor i del pic de pressió instantània generat pel col·lapse de la cavitat principal del núvol. En segon lloc, s'han corregit els models originals de cavitació de Zwart i Singhal tenint en compte el terme de segon ordre de l'equació de Rayleigh-Plesset. L'efectivitat dels models originals i dels corregits s'ha comparat per a dos patrons de cavitació diferents. Els resultats per una cavitat fixa demostren que el model corregit prediu millor la distribució de la pressió a la regió de tancament de la cavitat i la longitud de la cavitat en comparació amb les observacions de l'experiment. Els resultats per la cavitació de núvol inestable també confirmen que la predicció de la freqüència de despreniment es pot millorar amb el model Zwart corregit. Per a la investigació del poder erosiu de la cavitació, s'ha emprat un model d'erosió basat en el balanç energètic. S'ha comprovat que la distribució espacial i temporal de l'agressivitat de l'erosió és sensible a la selecció del model de cavitació i a la pressió motriu del col·lapse. En particular, l'ús de nivells mitjans de pressió combinats amb el model de cavitació de Sauer permeten obtenir resultats fiables. S'han observat dos mecanismes d'erosió, un que es produeix a la regió de tancament de la cavitat principal de la làmina caracteritzada per col·lapses de baixa intensitat però amb alta freqüència, i l'altre induït pel col·lapse de la cavitat de núvol que presenta una alta intensitat d'erosió però amb baixa freqüència. Finalment, s'ha comprovat que la intensitat de l'erosió segueix una llei de potència amb la velocitat de flux principal amb exponents que oscil·len entre 3 i 5 segons el paràmetre d'estimació que s'utilitzi.
6
Malan, Leon. "Direct numerical simulation of free-surface and interfacial flow using the VOF method: cavitating bubble clouds and phase change". Doctoral thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/27898.
Abstract (sommario):
Direct Numerical Simulation of two-phase ow is used extensively for engineering research and fundamental fluid physics studies. This study is based on the Volume-Of-Fluid (VOF) method, originally created by Hirt and Nicols. This method has gained increased popularity, especially when geometric advection techniques are used coupled with a planar reconstruction of the interface. The focus of the first part of this work is to investigate the hydrodynamics of isothermal cavitation in large bubble clouds, which originated from a larger study of micro-spalling, conducted by the French CEA. A method to deal with volume-changing vapour cavities, or pores, was formulated and implemented in an existing code, PARIS. The ow is idealized by assuming an inviscid liquid, negligible thermal effects and vanishing vapour pressure. A novel investigation of bubble cloud interaction in an expanding liquid using Direct or Detailed Numerical Simulation is presented. The simulation results reveal a pore competition, which is characterised by the Weber number in the ow. In the second part of the study the governing equations are extended to describe incompressible ow with phase change. The description of the work commences with the derivation of the governing equations. Following this, a novel, geometric based, VOF solution method is proposed. In this method a novel way of advecting the VOF function is invented, which treats both mass and energy conservation in conservative form. New techniques include the advection of the interface in a discontinuous velocity field. The proposed algorithms are consistent and elegant, requiring minimal modifications to the existing code. Numerical experiments demonstrate accuracy, robustness and generality. This is viewed as a significant fundamental development in the use of VOF methods to model phase change.
7
Lyu, Xiuxiu [Verfasser], Xiangyu [Akademischer Betreuer] Hu, Xiangyu [Gutachter] Hu, Julija [Gutachter] Zavadlav e Chaouki [Gutachter] Habchi. "Numerical Modeling and Simulation of Cavitation Bubble Cloud with a Lagrangian–Eulerian Approach / Xiuxiu Lyu ; Gutachter: Xiangyu Hu, Julija Zavadlav, Chaouki Habchi ; Betreuer: Xiangyu Hu". München : Universitätsbibliothek der TU München, 2020. http://d-nb.info/1215837682/34.
8
Zhang, Guangjian. "Etude expérimentale de la structure et de la dynamique des écoulements cavitants". Thesis, Paris, HESAM, 2020. http://www.theses.fr/2020HESAE050.
Abstract (sommario):
La cavitation est un phénomène complexe impliquant un transfert de masse entre la phase liquide et vapeur à des températures presque constantes.Les processus physiques qui contrôlent les instabilités dans les écoulements cavitants ne sont pas encore compris, principalement en raison du manque de données expérimentales quantitatives sur les structures diphasiques et la dynamique à l'intérieur des zones de cavitation opaques. Dans cette thèse, la cavitation partielle développée dans de petits canaux convergents-divergents (Venturi) a été étudiée expérimentalement en détail pour élucider ces mécanismes. Ceci a été réalisé en combinant une technique d'imagerie par rayons X ultra-rapide, la visualisation conventionnelle à haute fréquence et la vélocimétrie par images de particules. Les principales contributions de la présente étude portent sur les quatre aspects suivants:(1) une description détaillée des structures d'écoulement diphasique au sein des poches de cavitation quasi stables,qui se caractérisent par un écoulement rentrant à faible vitesse existant en continu sous la cavité; (2) analyse de l'effet complexe de la cavitation sur les fluctuations de vitesses turbulentes; (3) identification et discussion de trois mécanismes distincts responsables de la transition vers un comportement instable périodique ; (4) analyse de l'effet d'échelle sur les comportements cavitants, dans le cas des profils Venturi étudiésCavitation is a complex phenomenon involving mass transfer between liquid and vapour phase at nearly constanttemperature. Advances in the understanding of the physical processes of cavitating flows are challenging, mainlydue to the lack of quantitative experimental data on the two-phase structures and dynamics inside the opaquecavitation areas. In this thesis, partial cavitation developed in small convergent-divergent (Venturi) channels wasstudied experimentally in detail for a better knowledge of the physical mechanisms governing the cavitationinstabilities. This was achieved by using an ultra-fast synchrotron X-ray imaging technique aided withconventional high speed photography and Particle Image Velocimetry. The main contributions of the presentstudy can be summarized as follows: (1) detailed description of the two-phase flow structures in quasi-stablesheet cavitation, which is characterized by a low-speed re-entrant flow existing continuously underneath thecavity; (2) analysis of the complex effect of cavitation on turbulent velocity fluctuations; (3) identification ofthree distinct mechanisms responsible for the transition of sheet-to-cloud cavitation, with a discussion of thedifferences between them; (4) analysis of the scale effect on cavitation in the studied Venturi flows
9
Wang, Yi-Chun. "Shock waves in bubbly cavitating flows. Part I. Shock waves in cloud cavitation. Part II. Bubbly cavitating flows through a converging-diverging nozzle". Thesis, 1996. https://thesis.library.caltech.edu/804/1/Wang_yc_1996.pdf.
Abstract (sommario):
Two problems are considered in this thesis: the nonlinear dynamics of a cloud of cavitation bubbles, and bubbly cavitating flows in a converging-diverging nozzle. The focus of the first problem is to explore the characteristics of the growth and collapse of a spherical cloud of bubbles. The prototypical problem solved considers a finite cloud of nuclei that is exposed to a decrease in the ambient pressure which causes the cloud to cavitate. A subsequent pressure recovery then causes the cloud to collapse. This is typical of the transient behaviour exhibited by a bubble cloud as it passes a body or the blade of a ship propeller. The simulations employ the fully nonlinear, non-barotropic, homogeneous two-phase flow equations coupled with the Rayleigh-Plesset equation for the dynamics of individual bubbles. A Lagrangian integral method is developed to solve this set of equations. The computational results confirm the idea put forward by Morch and his co-workers (Morch [1980], [1981], [1982]; Hanson et al. [1981]) who speculated that the collapse of the cloud involved the formation of a shock wave on the surface of the cloud and that inward propagation and geometric focusing of this shock would lead to very large localized pressure pulses. The effects of varying the bubble population density, the cavitation number, and the ratio of the cloud size to the bubble size are examined. The theoretical results are shown to provide a satisfactory explanation for dynamic structures and acoustic signature observed in recently conducted experiments of cloud cavitation at California Institute of Technology (Reisman and Brennen [1996]; Brennen et al. [1996]). It is concluded that the formation and focusing of bubbly shock waves are responsible for the severe noise and damage potential in cloud cavitation.
The second problem investigates the nonlinear behavior of a bubbly cavitating flow, both steady and unsteady, through a converging-diverging nozzle. Two different flow regimes are found from steady state solutions: quasi-steady and quasi-unsteady. The former is characterized by the large spatial fluctuations in the downstream of the flow. Bifurcation occurs as the flow transitions from one regime to the other. An analytical expression for the critical bubble size at bifurcation is obtained. Finally, unsteady solutions in a period of consecutive times are presented. These solutions are characterized by the downstream spatial fluctuations coupled with large pressure pulses changing in both magnitude and location with time. The characteristics of these pulses are similar to the shock pulses of Part I and are produced by the local violent collapse of the bubbles in the flow.
10
Reisman, Garrett Erin. "Dynamics, acoustics and control of cloud cavitation on hydrofoils". Thesis, 1997. https://thesis.library.caltech.edu/1201/1/Reismen_ge_1997.pdf.
Abstract (sommario):
Cloud-cavitation, often formed by the breakdown and collapse of a sheet or vortex cavity, is responsible for severe cavitation noise and erosion damage. This thesis describes an experimental investigation of the dynamics and acoustics of cloud cavitation on a three dimensional hydrofoil and examines the injection of air as a means of noise suppression.
Part one of this work examines the large amplitude impulsive pressures which were measured on the suction surface of an oscillating hydrofoil experiencing cloud cavitation and these pressure pulses are correlated with the observation of shock waves propagating through the bubbly mixture. Recess mounted transducers were used to measure unsteady pressures at four locations along the chord of the suction surface of a hydrofoil. By examining the transducer output, two distinct types of pressure pulses were identified. Local pulses occurred at a single transducer location and were randomly distributed in position and time. Conversely, global pulses were registered by all the transducers almost simultaneously. The location of the global pulses relative to the foil oscillation was quite repeatable and these events produced substantial far-field noise. Correlation of the transducer output with high speed movies of the cavitation revealed that the global pulses were produced by a large scale collapse of the bubble cloud. Conversely, local pulses were generated by local disturbances in the bubbly mixture characterized by large changes in void fraction.
The large pressure pulse associated with the local and global cavitation structures, the geometric coherence of their boundaries and the nearly discrete change in void fraction across the boundaries of these structures indicate that these structures consist of bubbly shock waves. Qualitative and quantitative comparisons between the current experiments and the numerical, analytic and experimental bubbly shock wave analysis of other investigators support this conclusion.
Part two of this work examines the dramatic reduction in cloud cavitation noise due to both continuous and pulsed injection of air into the cavitating region of the foil. At sufficient air flow rates, the radiated noise could be reduced by a factor greater than 200 relative to the noise produced without air injection. Unsteady surface pressure measurements also showed a reduction in the acoustic impulse with air injection by a factor of up to two orders of magnitude. An explanation for this noise reduction can be found by examining the high speed motion pictures. The presence of the non-condensible gas in the cavitation cloud is shown to prevent any rapid or coherent collapse process. Although the formation of local structures is still observed, the presence of air in the bubbles diminishes both the magnitude and the frequency of occurrence of local pressure pulses. Finally, pulsed air injection results in a lower acoustic impulse than the impulse obtained by injecting the same mass of air continuously over the entire oscillation cycle.
Capitoli di libri sul tema "Cavitation clouds":
1
Hutli, E. A. F., e M. S. Nedeljkovic. "Formula for Upstream Pressure, Nozzle Geometry and Frequency Correlation in Shedding/Discharging Cavitation Clouds Determined by Visualization of Submerged Cavitating Jet". In New Trends in Fluid Mechanics Research, 194–97. Berlin, Heidelberg: Springer Berlin Heidelberg, 2007. http://dx.doi.org/10.1007/978-3-540-75995-9_58.
2
De Lange, D. F., e G. J. De Bruin. "Sheet Cavitation and Cloud Cavitation, Re-Entrant Jet and Three-Dimensionality". In In Fascination of Fluid Dynamics, 91–114. Dordrecht: Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-011-4986-0_7.
3
Chahine, Georges L., Chao-Tsung Hsiao e Reni Raju. "Scaling of Cavitation Bubble Cloud Dynamics on Propellers". In Advanced Experimental and Numerical Techniques for Cavitation Erosion Prediction, 345–72. Dordrecht: Springer Netherlands, 2014. http://dx.doi.org/10.1007/978-94-017-8539-6_15.
4
Yamamoto, Katsuhiro. "Investigation of Bubble Clouds in a Cavitating Jet". In Mathematical Fluid Dynamics, Present and Future, 349–73. Tokyo: Springer Japan, 2016. http://dx.doi.org/10.1007/978-4-431-56457-7_12.
5
de Lange, D. F., G. J. de Bruin e L. van Wijngaarden. "Observations of cloud cavitation on a stationary 2D profile". In Fluid Mechanics and Its Applications, 241–46. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-011-0938-3_22.
6
Pelz, Peter F., Thomas Keil e Gerhard Ludwig. "On the Kinematics of Sheet and Cloud Cavitation and Related Erosion". In Advanced Experimental and Numerical Techniques for Cavitation Erosion Prediction, 221–37. Dordrecht: Springer Netherlands, 2014. http://dx.doi.org/10.1007/978-94-017-8539-6_9.
7
Peng, Guoyi, Yasuyuki Oguma e Seiji Shimizu. "Visualization Observation of Cavitation Cloud Shedding in a Submerged Water Jet". In Fluid-Structure-Sound Interactions and Control, 229–34. Berlin, Heidelberg: Springer Berlin Heidelberg, 2015. http://dx.doi.org/10.1007/978-3-662-48868-3_37.
8
Petrov, N., e A. Schmidt. "Evolution of a Cloud of Cavitation Bubbles in a Disturbed Compressible Liquid: A Numerical Study". In 30th International Symposium on Shock Waves 2, 1251–55. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-44866-4_80.
9
Chiekh, Maher Ben, Jean-Christophe Béra, Adrien Poizat, Claude Inserra e Bruno Gilles. "Dynamics of a Cavitation Cloud Generated by Pulsed Focused Ultrasound: Study of the Re-initialization of the Cloud at a New Pulse". In Green Energy and Technology, 571–87. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-16-8278-0_37.
10
Wang, Changchang, Guoyu Wang e Biao Huang. "Coherent Structures Analysis Across Cavity Interface in Cloud Cavitating Flows Using Different Vortex Identification Methods". In Springer Proceedings in Physics, 393–403. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-19-8955-1_27.
Atti di convegni sul tema "Cavitation clouds":
1
Sou, Akira, Shinichi Nitta e Tsuyoshi Nakajima. "Bubble Tracking Simulation of Cavitating Flow in an Atomization Nozzle". In ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/fedsm2002-31018.
Abstract (sommario):
Numerical simulation of transient cavitating flow in a axisymmetric nozzle was conducted in order to investigate the detailed motion of cavitation bubble clouds which may be dominant to atomization of a liquid jet. Two-way coupled bubble tracking technique was assigned in the present study to predict the unsteady cloud cavitation phenomena. Large Eddy Simulation (LES) was used to predict turbulent flow. Calculated pressure distribution and injection pressure were compared with measured ones. Then, calculated motion of cavitation bubble clouds was carefully investigated to understand the cavitation phenomena in a nozzle. As a result, the following conclusions were obtained: (1) Calculated result of pressure distribution along the wall, the relation between injection pressure vs. flow rate, and bubble distribution agreed with existing experimental result. (2) Cavitation bubble clouds were periodically shed from the tail of vena contracta, which usually formed by the coalescence of a few small bubble clouds. (3) Collapse of cavitation bubbles due to the re-entrant jet was observed in the numerical simulation.
2
Sato, Keiichi, Naoya Takahashi e Yasuhiro Sugimoto. "Effects of Diffuser Length on Cloud Cavitation in an Axisymmetrical Convergent-Divergent Nozzle". In ASME/JSME/KSME 2015 Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/ajkfluids2015-05507.
Abstract (sommario):
Unsteady behavior of periodic cloud cavitation is typically observed in the field of fluid machinery under a high speed liquid flow such as a cavitating hydrofoil as well as cavitating water jet. The instability of cloud cavitation remains to be completely solved though it has been confirmed that there are two instabilities which is an intrinsic instability of cavitation and a system instability. Sato, et al. have found through previous investigations that the pressure wave at the collapse of shedding clouds can make a trigger to cause a reentrant motion. In the present study, the authors focus on a cavitating water jet to investigate the cavitation aspects in an axisymmetrical convergent-divergent nozzle and examine an unsteady behavior of cloud cavitation through high speed video observation and image analysis based on the frame difference method. Especially, the authors study the effect of nozzle divergent part (diffuser) as well as the upstream pressure effect on cloud cavitation in the nozzle. As a result the authors have found that there are two kinds in the shedding pattern and the reentrant motion pattern for cloud cavitation depending on the nozzle diffuser length.
3
Hosangadi, A., e V. Ahuja. "A New Unsteady Model for Dense Cloud Cavitation". In ASME 2005 Fluids Engineering Division Summer Meeting. ASMEDC, 2005. http://dx.doi.org/10.1115/fedsm2005-77485.
Abstract (sommario):
A new unsteady, cavitation model for dense cloud cavitation is presented wherein the phase change process (bubble growth/collapse) is coupled to the acoustic propagation in a multi-phase fluid. This cavitation model predicts the number density and radius of bubbles in vapor clouds by tracking both the aggregate surface area and volume fraction of the cloud. Hence, formulations for the dynamics of individual bubbles (e.g. Rayleigh-Plesset equation) may be integrated within the macroscopic context of a dense vapor cloud i.e. a cloud that occupies a significant fraction of available volume and contains numerous bubbles. This formulation has been implemented within the CRUNCH CFD, which has a compressible “real” fluid formulation, a multi-element, unstructured grid framework, and has been validated extensively for liquid rocket turbopump inducers. Rigorous validation of the formulation is presented for various cases including unsteady simulations of a cavitating NACA0015 airfoil where the frequency of pressure fluctuations and time-averaged mean cavity lengths were compared with experimental data. The model also provides the spatial and temporal history of the bubble size distribution in the vapor clouds that are shed, an important physical parameter that is difficult to measure experimentally and is a significant advancement in the modeling of dense cloud cavitation.
4
Ceccio, Steven L., e Darin L. George. "An Electrical Impedance Method for Measurements of Attached Cavitation". In ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-0790.
Abstract (sommario):
Abstract An electrical impedance probe is described which will be used to study the properties of attached cavitation. The method uses a series of electrodes mounted flush to the surface of a cavitating hydrofoil, and detects the presence of liquid or vapor through changes in the impedance of the local fluid medium. Characteristics of steady and unsteady attached cavitation, including cloud shedding and re-entrant jets, are reviewed. The impedance technique is shown to have the potential to measure advection velocities of bubble clouds, velocities of re-entrant jets, and frequencies associated with unsteady cavitation.
5
Wosnik, Martin, Qiao Qin, Damien T. Kawakami e Roger E. A. Arndt. "Large Eddy Simulation (LES) and Time-Resolved Particle Image Velocimetry (TR-PIV) in the Wake of a Cavitating Hydrofoil". In ASME 2005 Fluids Engineering Division Summer Meeting. ASMEDC, 2005. http://dx.doi.org/10.1115/fedsm2005-77467.
Abstract (sommario):
A Large Eddy Simulation (LES) approach for cavitating flow, based on a virtual single-phase, fully compressible cavitation model which includes the effects of incondensable gas, has been shown to be capable of capturing the complex dynamical features of highly unsteady cavitating flows of two-dimensional hydrofoils. Here the LES results are compared to Time-Resolved Particle Image Velocimetry (TR-PIV) in the wake of a cavitating NACA 0015 hydrofoil, with particular attention to the predicted vortex shedding mechanisms. Despite some difficulty with obtaining vector fields from vortical clouds of vaporous-gaseous bubbles with cross-correlation techniques, the initial results seem promising in that they confirm the existence of a primary vortex pair (type A-B). In addition to TR-PIV, the cavitation cloud shedding was also documented with phase-locked, time-resolved photography and high speed volume-illuminated video, both with simultaneous imaging of side and plan views of the foil. All three experimental techniques confirm the need for fully three-dimensional simulations to properly describe the unsteady, three-dimensional cavitation cloud shedding mechanism.
6
Kawakami, Damien T., Qiao Qin e Roger Arndt. "Water Quality and the Periodicity of Sheet/Cloud Cavitation". In ASME 2005 Fluids Engineering Division Summer Meeting. ASMEDC, 2005. http://dx.doi.org/10.1115/fedsm2005-77114.
Abstract (sommario):
Cloud cavitation is the rapid formation and shedding of vaporous clouds from a cavitating hydrofoil. This type of cavitation occurs under certain conditions that are characterized by the cavitation number [σ] and the angle of attack [α]. Associated with cloud cavitation are large, abrupt changes in surface pressure caused by the shedding of the attached cavity. Our experimental data display trends that are contained in the linearized flat plate theories of Acosta and Tulin. Near values of σ/2α equal to 4, a singularity exists in the flat plate theory. Experimental results and numerical simulations indicate that in this region a transition between competing mechanisms of cavity shedding occurs. A new finding is that water quality appears to have a significant effect on cavitation behavior. It is well known that nuclei content plays an important role in cavitation inception. However, a recent investigation made possible by high-speed video reveals that the cloud shedding is periodic and that, for each cycle, the cavitating surface becomes fully wetted. Thus, inception physics come into play for a fraction of each cycle. Experimental data shows that the fraction of time in each period that the hydrofoil is fully wetted varies with gas content. In addition, the spectral characteristics of lift and surface pressure measurements show a strong dependence on gas content. Numerical simulations made to incorporate gas content effects show surprisingly close agreement with experimental data. This is also factor that may be of importance in comparing the results from different experimental facilities since comparisons are often made without considering gas content as a factor.
7
D.Maxwell, Adam, e Zhen Xu. "Inception of Cavitation Microbubble Clouds in Tissue-Mimicking Media during Histotripsy". In 8th International Symposium on Cavitation. Singapore: Research Publishing Services, 2012. http://dx.doi.org/10.3850/978-981-07-2826-7_269.
8
Lu, Yuan, Joseph Katz e Andrea Prosperetti. "Generation and Transport of Bubble Clouds in High-Intensity Focused Ultrasonic Fields". In 8th International Symposium on Cavitation. Singapore: Research Publishing Services, 2012. http://dx.doi.org/10.3850/978-981-07-2826-7_052.
9
Maxwell, Adam D., Charles A. Cain, J. Brian Fowlkes e Zhen Xu. "Inception of cavitation clouds by scattered shockwaves". In 2010 IEEE Ultrasonics Symposium (IUS). IEEE, 2010. http://dx.doi.org/10.1109/ultsym.2010.5935897.
10
Ahuja, Vineet, e Ashvin Hosangadi. "Simulations of Cavitation in Orifice and Venturis". In ASME 2007 Pressure Vessels and Piping Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/pvp2007-26639.
Abstract (sommario):
Computational simulations can play an integral role in supporting testing and developmental activities by identifying and characterizing flow instabilities. However, the diversity of flow regimes and instability mechanisms place very stringent requirements on any computational framework that could be used for such analyses. For example, the identification of dominant frequencies associated with flow instabilities in such systems requires high order numerics, advanced turbulence modeling capabilities, sophisticated grid topologies to resolve local physics in complex geometries, embedded models for unsteady cavitation, capture thermal effects in cryogenic fluids, and dynamic motion of feed system components such as valves. In this paper, we discuss simulations of cavitating instabilities in feed system components and control elements used in the E-1 test facility at NASA Stennis Space Center (SSC). The two different feed system components considered here are: (a) orifice and (b) flow control venturi that is attached to a 90 degree turning duct. These two components represent the two disparate regimes of cavitating flows: the orifice is representative of traveling cavitation class of flows commonly observed in tip vortices of propeller blades, whereas the venturi represents a sheet cavitation type problem with periodic shedding of vaporous clouds from this well developed cavity. The simulations are performed with a well validated cryogenic cavitation model that takes into account evaporative cooling and other associated thermal effects.