Download or read book On Simulating Tip leakage Vortex Flow to Study the Nature of Cavitation Inception written by Wesley Huntington Brewer and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Cavitation is detrimental to the performance of ships and submarines, causing noise, erosion, and vibration. This study seeks to understand cavitation inception and delay on a typical ducted propulsor by utilizing the SimCenter's unstructured simulation and design system: U2NCLE. Specifically, three fundamental questions are addressed: 1. What are the macroscale flow physics causing cavitation inception? 2. How does cavitation inception scale with Reynolds number? 3. How can tip-leakage vortex cavitation inception be suppressed? To study the physics of cavitation inception, a ducted propulsor simulation is developed and extensively validated with experimental results. The numerical method is shown to agree very well with experimental measurements made in the vortex core. It was discovered that the interaction of the leakage and trailing edge vortices cause the pressure to drop to a local minimum, providing ideal conditions for inception to occur. However, experimental observation shows that inception does not occur at the minimum pressure location, but rather at the point where the two vortices completely coalesce. At the point of coalescence, the simulation reveals that the streamwise core velocity decelerates, causing the air nuclei to stretch and burst. A Reynolds number scaling analysis is performed for the minimum pressure and maximum velocity in the vortex core. First, the numerical method is validated on a flate plate at various Reynolds numbers to assess the ability of typical turbulence models to predict Reynolds numbers ranging from one million to one billion. This scaling analysis methodology is then applied to the propulsor simulation, revealing that the minimum pressure in the vortex core is much less dependent on Reynolds number than was previously hypothesized. Lastly, to investigate means of delaying cavitation inception, the propulsor is parameterized and studied using design optimization theory. Concepts of vortex alleviation evident in nature are used to suggest suitable parameterizations. Also, dimension reduction is used to reduced the number of design variables. Finally, the concepts are implemented, evaluated, and shown to completely decouple the two vortices causing cavitation inception. Moreover, the minimum pressure in the vortex core is significantly increased.
Download or read book On Simulating Tip leakage Vortex Flow to Study the Nature of Cavitation Inception written by and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Cavitation is detrimental to the performance of ships and submarines, causing noise, erosion, and vibration. This study seeks to understand cavitation inception and delay on a typical ducted propulsor by utilizing the SimCenter's unstructured simulation and design system: U2NCLE. Specifically, three fundamental questions are addressed: 1. What are the macroscale flow physics causing cavitation inception? 2. How does cavitation inception scale with Reynolds number? 3. How can tip-leakage vortex cavitation inception be suppressed? To study the physics of cavitation inception, a ducted propulsor simulation is developed and extensively validated with experimental results. The numerical method is shown to agree very well with experimental measurements made in the vortex core. It was discovered that the interaction of the leakage and trailing edge vortices cause the pressure to drop to a local minimum, providing ideal conditions for inception to occur. However, experimental observation shows that inception does not occur at the minimum pressure location, but rather at the point where the two vortices completely coalesce. At the point of coalescence, the simulation reveals that the streamwise core velocity decelerates, causing the air nuclei to stretch and burst. A Reynolds number scaling analysis is performed for the minimum pressure and maximum velocity in the vortex core. First, the numerical method is validated on a flate plate at various Reynolds numbers to assess the ability of typical turbulence models to predict Reynolds numbers ranging from one million to one billion. This scaling analysis methodology is then applied to the propulsor simulation, revealing that the minimum pressure in the vortex core is much less dependent on Reynolds number than was previously hypothesized. Lastly, to investigate means of delaying cavitation inception, the propulsor is parameterized and studied using design optimization theory. Concepts of vortex alleviation evident in nature are.
Download or read book IUTAM Symposium on Reynolds Number Scaling in Turbulent Flow written by Alexander J. Smits and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 336 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume presents selected papers from the IUTAM Symposium on Reynolds Number Scaling in Turbulent Flow, convened in Princeton, NJ, USA, September I1-13, 2002. The behavior ofturbulence at high Reynolds number is interesting from a fundamental point of view, in that most theories of turbulence make very specific predictions in the limit of infinite Reynolds number. From a more practical point of view, there exist many applications that involve turbulent flow where the Reynolds numbers are extremely large. For example, large vehicles such as submarines and commercial transports operate at Reynolds 9 numbers based on length ofthe order oft0 , and industrial pipe flows cover a 7 very wide range of Reynolds numbers up to 10 • Many very important applications of high Reynolds number flow pertain to atmospheric and other geophysical flows where extremely high Reynolds numbers are the rule rather than the exception, and the understanding of climate changes and the prediction of destructive weather effects hinges to some extent on our appreciation ofhigh-Reynolds number turbulence behavior. The important effects of Reynolds number on turbulence has received a great deal of recent attention. The objective of the Symposium was to bring together many of the world's experts in this area to appraise the new experimental results, discuss new scaling laws and turbulence models, and to enhance our mutual understanding of turbulence.
Download or read book Dissertation Abstracts International written by and published by . This book was released on 2006 with total page 884 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Numerical Study of Cavitation Inception in Complex Flow Fields written by and published by . This book was released on 2007 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt: Prediction of cavitation inception on Navy propulsors is a very challenging task that has preoccupied propulsor designers for many years. This is in fact true for predictions using scaled experimental tests as well as for predictions based on analytical/numerical modeling. Over the past few years very significant progress has been accomplished by the community in terms of both experimental measurements and numerical techniques development and their application to the problem. Novel sophisticated velocity flow field measurement techniques and their efficient practical application to propulsor studies both at Navy research centers and at other Navy funded laboratories has enabled impressive measurements of the complex flow field in details never observed before. These observations quantified mainly the space variations of the flow field using some time and space averaging. Some effort, but so far less impressive, has also illustrated the time unsteady nature of the challenging phenomena. However, additional efforts are necessary but require tremendous capabilities in data storage and analysis to provide us with time fluctuations of pressures. In parallel impressive progress in computational techniques and in computer power has enabled more and more complex and large simulations. These have included Reynolds Averaged Navier Stokes (RANS) simulation, Large Eddy Simulations (LES) and Direct Numerical Simulations (DNS) applied to larger and larger problems.
Download or read book Cavitation and Wake Structure of Unsteady Tip Vortex Flows written by Douglas P. Hart and published by . This book was released on 1993 with total page 450 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Tip Vortex Cavitation Characteristics and Delay of Inception on a Three Dimensional Hydrofoil written by William G. Souders and published by . This book was released on 1981 with total page 59 pages. Available in PDF, EPUB and Kindle. Book excerpt: A research program was conducted to investigate both the fundamental aspects of, and techniques for delaying, tip vortex cavitation on a three-dimensional hydrofoil. The specific concepts considered for delaying tip vortex cavitation included: a bulbous tip, an artificially roughened tip, and a mass injected tip. The experiments were conducted in the David W. Taylor Naval Ship Research and Development Center 24-inch cavitation tunnel, where the effects of the various concepts on both foil tip vortex cavitation inception and performance were established. These measurements were made at a Reynolds number R subscript c, based on root chord length, of approximately 5,000,000. Some of the more fundamental aspects of the tip vortex rollup process have been documented through the use of flow visualization techniques. The results for the tip vortex cavitation delay concepts indicate substantial increases in the tip vortex cavitation inception speed relative to the unaltered tip; i.e., a 94 percent increase for the roughened tip, 38 percent for the bulbous tip, and 54 percent and 33 percent for the active and passive mass injected respectively. These results were obtained over a wide range of foil angle of attack and with little or no measurable loss in foil performance; i.e., no measurable lift decrease or drag increase. (Author).
Download or read book Tip Vortices in Unsteady Flows written by and published by . This book was released on 1992 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes in brief the activities of our research in, first, cavitation inception, and them, second, tip vortex problems in steady and unsteady flows. There are two components of this work. The first is an experimental study of cavitation inception and cavitation nuclei determination in a variety of laboratory and natural settings. Cavitation and cavitation inception are important aspects of the complex flow associated with propulsion in the ocean environment. Two specific features of this flow were addressed in a long series of reports and publications listed at the end of this report. These features are (1) cavitation inception processes in a large scale turbulent shear flow and (2) cavitation inception and the structure of trailing tip vortices in first steady and then unsteady flows. Finite aspect ratio hydrofoils were used in both studies; the latter unsteadiness was achieved by oscillating the foil in pitch of a point 35% of the chord from the leading edge.
Download or read book Tip Vortex Formation and Cavitation written by Brant Howard Maines and published by . This book was released on 1995 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Hydrodynamics of Pumps written by Christopher E. Brennen and published by Cambridge University Press. This book was released on 2011-03-28 with total page 287 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hydrodynamics of Pumps is a reference for pump experts and a textbook for advanced students. It examines the fluid dynamics of liquid turbomachines, particularly pumps, focusing on special problems and design issues associated with the flow of liquid through a rotating machine. There are two characteristics of a liquid that lead to problems and cause a significantly different set of concerns than those in gas turbines. These are the potential for cavitation and the high density of liquids, which enhances the possibility of damaging, unsteady flows and forces. The book begins with an introduction to the subject, including cavitation, unsteady flows and turbomachinery, basic pump design and performance principles. Chapter topics include flow features, cavitation parameters and inception, bubble dynamics, cavitation effects on pump performance, and unsteady flows and vibration in pumps - discussed in the three final chapters. The book is richly illustrated and includes many practical examples.
Download or read book The Role of nuclei in Tip Vortex Cavitation Inception written by Vijay Hanumappa Arakeri and published by . This book was released on 1986 with total page 25 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Methods for Prediction of Tip Vortex Cavitation Inception written by Monir F. George and published by . This book was released on 1993 with total page 278 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Fundamentals of Cavitation written by Jean-Pierre Franc and published by Springer Science & Business Media. This book was released on 2006-01-22 with total page 321 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book treats cavitation, which is a unique phenomenon in the field of hyd- dynamics, although it can occur in any hydraulic machinery such as pumps, propellers, artificial hearts, and so forth. Cavitation is generated not only in water, but also in any kind of fluid, such as liquid hydrogen. The generation of cavitation can cause severe damage in hydraulic machinery. Therefore, the prevention of cavitation is an important concern for designers of hydraulic machinery. On the contrary, there is great potential to utilize cavitation in various important applications, such as environmental protection. There have been several books published on cavitation, including one by the same authors. This book differs from those previous ones, in that it is both more physical and more theoretical. Any theoretical explanation of the cavitation phenomenon is rather difficult, but the authors have succeeded in explaining it very well, and a reader can follow the equations easily. It is an advantage in reading this book to have some understanding of the physics of cavitation. Therefore, this book is not an introductory text, but a book for more advanced study. However, this does not mean that this book is too difficult for a beginner, because it explains the cavitation phenomenon using many figures. Therefore, even a beginner on cavitation can read and can understand what cavitation is. If the student studies through this book (with patience), he or she can become an expert on the physics of cavitation.
Download or read book Cavitation Inception in Rectangular Two Dimensional Slots written by W. G. Blair and published by . This book was released on 1987 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt: The two dimensional fluid mechanics of flow over a rectangular slot along a flat wall were studied in air. A thick (greater than slot width) turbulent boundary layer was established at the slot entrance location. The flow field within and at the slot entrance was studied as the slot geometry was varied for depth-to-width ratios (aspects ratios) ranging from 0.5 to 3.0. Flow visualization inside the slot describes the internal flow field of the slot and reveals the highly unsteady nature of the vortex-like structure(s) that develop. Flow visualization of the slot region entrance shows that mass. Flow visualization as well as direct pressure measurements inside the slot document vortex location as a function of aspect ratio. The minimum pressure in the slot, found at the primary vortex center, is also documented as a function of aspect ratio. The measured pressure coefficients inside the slot are an order of magnitude lower than those of which cavitation has been observed in previous water tunnel experiments. These measurements therefore lead to question the interpretation of the previous water tunnel slot cavitation experiments. Specifically, it is likely that the previously reported cavitation was partially gaseous rather than purely vaporous cavitation, as had been assumed.
Download or read book Simulations of Tip Vortex Cavitation Flows with Nonlinear K Model written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental and Theoretical Study on Cavitation Inception and Bubbly Flow Dynamics written by Luca D'Agostino and published by . This book was released on 1987 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Cavitation Inception in Separated Flows written by Joseph Katz and published by . This book was released on 1981 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt: The phenomenon of cavitation was studied on four axisymmetric bodies whose boundary layers underwent a laminar separation and a subsequent turbulent reattachment. The conditions for cavitation inception and desinence were determined and several holograms were recorded just prior to and at the onset of cavitation. The population of microbubbles and the nature of the subsequent development of visible cavitation was determined from the reconstructed image. Cavitation inception occurred in the turbulent shear layer downstream of the transition region. When the separation zone was large the inception region was located within the most developed section of the mixing layer but upstream of the reattachment zone. When the separation region was small inception occurred close to the reattachment zone but still detached from the body surface. A comparison between the surface minimum pressure and the cavitation inception indices also indicated that inception could not occur near the surface of the bodies having a large separation region. The appearance of visible cavities was preceded by the appearance of a cluster of microbubbles only in the cavitation inception region. The nuclei population in the other sections of the flow field remained fairly uniform. This observation supports the assumption that cavitation is initiated from microscopic free stream nuclei.
