oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Analysis of Cavitation Instabilities in a Four-Blade Inducer  [PDF]
O. Coutier-Delgosha,A. Dazin,G. Caignaert,G. Bois
International Journal of Rotating Machinery , 2012, DOI: 10.1155/2012/213907
Abstract: The cavitating behavior of a four-blade inducer tested in the LML laboratory large test facility is considered in the present paper. Experimental investigations based on unsteady pressure measurements and records from a six-component balance mounted on the inducer shaft are performed. Spectral analysis of the signals enables to detect several characteristic frequencies related to unbalanced two-phase flow patterns. The objective of the present paper is the understanding of the physical phenomena associated to these frequencies. Therefore, wavelet decomposition, flow visualizations, and direct analysis of the high-frequency force, moment, and pressure signals are applied. Results at nominal flow rate only are considered. Not only classical unbalanced cavitation patterns, but also unexpected flow organizations are discussed. 1. Introduction Rocket engine turbopump inducers are designed to operate in cavitating conditions, because of the low pressure of LH2 and LOX in the tanks. However, development of cavitation must be controlled to avoid any reduction of the inducer performance. Attention is also focused on instabilities associated with cavitation, since they are responsible for unbalanced flow pattern that compromise the rotor equilibrium. Self-oscillation of the sheet cavities on the blades may also generate problematic pressure fluctuations at the inducer outlet. The understanding of these different unsteady flow behaviors has not been completed, yet, although significant progress has been achieved in the last decades. Experimental investigations of the behavior of various inducers, characterized by a blade number varying usually between 2 and 5, have been conducted for example in Pisa University (Italy) in collaboration with Avio, in Arts et Metiers ParisTech and CREMHyG (France) in collaboration with SNECMA Moteurs, and in Osaka University (Japan) by Tsujimoto and colleagues in cooperation with the JAXA program. In these different studies, several recurrent unstable behaviors have been identified: (i) rotating cavitation is characterized by a nonsymmetrical two-phase flow pattern, which rotates faster or slower than the inducer, leading to so-called super-synchronous or subsynchronous regimes, respectively. Rotation speed in the inducer rotating frame is generally low, leading in the absolute frame to frequencies close to the inducer rotation one. Such phenomenon, which leads to significant radial forces, has been detected in nearly all tested inducers [1–3] (Tsujimoto et al. 1997). (ii) A surge mode oscillation characterized by a global pulsation
Quantum Cavitation  [PDF]
Paola Zizzi,Eliano Pessa,Fabio Cardone
Physics , 2010,
Abstract: We consider the theoretical setting of a superfluid like 3He in a rotating container, which is set between the two layers of a type-II superconductor. We describe the superfluid vortices as a 2-dimensional Ising-like model on a triangular lattice in presence of local magnetic fields. The interaction term of the superfluid vortices with the Abrikosov vortices of the superconductor appears then as a symmetry breaking term in the free energy. Such a term gives a higher probability of quantum tunnelling across the potential barrier for bubbles nucleation, thus favouring quantum cavitation.
扣锅煅藕节  [PDF]
彭云寿
中国中药杂志 , 1985,
Abstract: <正>据我院多年实践证明,扣锅煅藕节简单易行,成炭率高达98%,有效成分损失小,具体作法是:将净干藕节置一大铁锅中,装藕节量为锅容积的3/5为宜,上扣直径比底锅直径小1~2寸的铁锅一个,盖锅底部压一重物,两锅结合处用事先准备好的粘合剂(2/3黄土、1/3石灰、头发食盐少许加适量水混合而成)糊严,待粘合剂七、八成干时用武火煅制。判断煅藕节成功与否可用下列几种办法:1.往盖锅脐中滴水即沸,立即停火;2.在两锅合缝处留一筷子粗细的小
扣锅煅姜  [PDF]
徐永柏,王玉林
中国中药杂志 , 1983,
Abstract: <正>姜炭为常用中药,有温中止血之功效。据我们在五台县药材公司实践,扣锅煅姜简单易行,成炭率高,有效成分损失小。具体做法是:将干姜置一大铁锅中,上倒扣比底锅直径小1~2寸的铁锅,盖锅上压一重物,两锅合缝处用事先准备好的粘合剂(2/3黄土、1/3石灰、头发食盐各少许混合而成)糊严,待粘合剂7成干时用武火开始煅制,判断煅姜成功与否可用下列几种方法:1.往盖锅脐中滴水即沸,立即停火。2.在两锅合缝
Higher Order Rotating Cavitation in an Inducer  [PDF]
Akira Fujii,Seiji Azuma,Yoshiki Yoshida,Yoshinobu Tsujimoto,Hironori Horiguchi,Satoshi Watanabe
International Journal of Rotating Machinery , 2004, DOI: 10.1155/s1023621x04000260
Abstract: In the present study, a higher order rotating cavitation predicted by the stability analysis was identified through the measurements of inlet pressure fluctuations and blade stress fluctuations. The propagation speed ratio of the higher order rotating cavitation is approximately 5, and the amplitude of the blade stress fluctuation caused by this rotating cavitation is the same level as that by the conventional rotating cavitation. In addition, a higher order cavitation surge was observed at the transition point from the conventional to the higher order rotating cavitation.
Cavitation During Superplastic Forming  [PDF]
John Campbell
Materials , 2011, DOI: 10.3390/ma4071271
Abstract: Cavitation is the opening of pores during superplastic forming, typically at grain boundary triple points or on second phase grain boundary particles during slip of grain boundaries. Theories for the initiation of cavitation are reviewed. It seems that cavitation is unlikely to occur by processes intrinsic to metals such as dislocation mechanisms or point defect condensation. It is proposed that cavitation can only occur at non-bonded interfaces such as those introduced extrinsically ( i.e., from the outside) during the original casting of the metal. These defects, known as oxide bifilms, are naturally introduced during pouring of the liquid metal, and are frozen into the solid, often pushed by dendritic growth into grain boundaries where they are difficult to detect because of their extreme thinness, often measured in nanometres. Their unbonded central interface acts as a crack and can initiate cavitation. Second phase precipitates probably do not nucleate and grow on grain boundaries but grow on bifilms in the boundaries, explaining the apparent association between boundaries, second phase particles and failure initiation. Improved melting and casting techniques can provide metal with reduced or zero bifilm population for which cavitation would not be possible, promising significant improvements in superplastic?behaviour.
Taming Acoustic Cavitation  [PDF]
David Fernandez Rivas,Bram Verhaagen,Oscar R. Enriquez,Michel Versluis,Andrea Prosperetti,Han Gardeniers,Detlef Lohse
Physics , 2012,
Abstract: In this fluid dynamics video we show acoustic cavitation occurring from pits etched on a silicon surface. By immersing the surface in a liquid, gas pockets are entrapped in the pits which upon ultrasonic insonation, are observed to shed cavitation bubbles. Modulating the driving pressure it is possible to induce different behaviours based on the force balance that determines the interaction among bubbles and the silicon surface. This system can be used for several applications like sonochemical water treatment, cleaning of surfaces with deposited materials such as biofilms.
Cavitation in holographic sQGP  [PDF]
Aleksandra Klimek,Louis Leblond,Aninda Sinha
Physics , 2011, DOI: 10.1016/j.physletb.2011.05.045
Abstract: We study the possibility of cavitation in the nonconformal N=2^* SU(N) theory which is a mass deformation of N=4 SU(N) Yang-Mills theory. The second order transport coefficients are known from the numerical work using AdS/CFT by Buchel and collaborators. Using these and the approach of Rajagopal and Tripuraneni, we investigate the flow equations in a 1+1 dimensional boost invariant set up. We find that the string theory model does not exhibit cavitation before phase transition is reached. We give a semi-analytic explanation of this finding.
STUDY UPON THE CAVITATION PHENOMENON OF THE ROTORS  [PDF]
Beazit ALI,Gheorghe SAMOILESCU
Revista Fiabilitate si Durabilitate , 2011,
Abstract: The main problem of the hydrodynamics of cavitation implosion of a single bubble, consists inpressure and velocity fields determination, including the collapse velocity of the bubble wall. By analysis thetheoretic and experimental phenomenon it establish the implicit function which describes this phenomenon. Byapplication the theorem for this implicit function it finds the criterion equation of phenomenon.Depending on operating condition various cavitation patterns can be observed on a body surface astravelling bubbles, attached sheet cavitation, shear cavitation or vortex cavitation. Leading edge attachedpartialcavitation is commonly encountered on rotor blades or on hydrofoil. It corresponds to the case for whichavapor cavity is attached in the vecinity of the leading edge and extends over a fraction of the foil surface. Itgenerally takes places at incidence angles for which a leading edge pressure peak occurs and reduced belowtheliquid vapor pressure. At the early phases of development, leading edge partial cavitation is steady.
Multibubble cavitation inception  [PDF]
Masato Ida
Physics , 2009, DOI: 10.1063/1.3265547
Abstract: The inception of cavitation in multibubble cases is studied numerically and theoretically to show that it is different from that in single-bubble cases in several aspects. Using a multibubble model based on the Rayleigh-Plesset equation with an acoustic interaction term, we confirmed that the recently reported suppression of cavitation inception due to the interaction of non-identical bubbles can take place not only in liquid mercury but also in water, and we found that a relatively large bubble can significantly decrease the cavitation threshold pressure of a nearby small bubble. By examining in detail the transition region where the dynamics of the suppressed bubble changes drastically as the inter-bubble distance changes, we determined that the explosive expansion of a bubble under negative pressure can be interrupted and turn into collapse even though the far-field liquid pressure well exceeds the bubble's threshold pressure. Numerical results suggest that the interruption of expansion occurs when the bubble radius is exceeded by the instantaneous unstable equilibrium radius of the bubble determined using the total pressure acting on the bubble. When we extended the discussion to systems of larger numbers of bubbles, we found that a larger number of bubbles have a stronger suppression effect. The present findings would be useful in understanding the complex behavior of cavitation bubbles in practical applications where in general many cavitation nuclei exist and may interact with each other.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.