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Journal ArticleDOI

A review of cavitation in hydraulic machinery

01 Jun 2016-Journal of Hydrodynamics (No longer published by Elsevier)-Vol. 28, Iss: 3, pp 335-358
TL;DR: In this paper, the authors summarized the recent progress for the cavitation study in the hydraulic machinery including turbo-pumps, hydro turbines, etc., and identified the 1-D analysis method, which is identified to be very useful for engineering applications regarding the cavitating flows in inducers, turbine draft tubes, etc.
Abstract: This paper mainly summarizes the recent progresses for the cavitation study in the hydraulic machinery including turbo-pumps, hydro turbines, etc.. Especially, the newly developed numerical methods for simulating cavitating turbulent flows and the achievements with regard to the complicated flow features revealed by using advanced optical techniques as well as cavitation simulation are introduced so as to make a better understanding of the cavitating flow mechanism for hydraulic machinery. Since cavitation instabilities are also vital issue and rather harmful for the operation safety of hydro machines, we present the 1-D analysis method, which is identified to be very useful for engineering applications regarding the cavitating flows in inducers, turbine draft tubes, etc. Though both cavitation and hydraulic machinery are extensively discussed in literatures, one should be aware that a few problems still remains and are open for solution, such as the comprehensive understanding of cavitating turbulent flows especially inside hydro turbines, the unneglectable discrepancies between the numerical and experimental data, etc.. To further promote the study of cavitation in hydraulic machinery, some advanced topics such as a Density-Based solver suitable for highly compressible cavitating turbulent flows, a virtual cavitation tunnel, etc. are addressed for the future works.
Citations
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Journal ArticleDOI
TL;DR: In this paper, a 3D Lagrangian Coherent Structures (LCS) was used to analyze the dynamics of cavitation-vortex interactions in the Delft twisted hydrofoil.

145 citations

Journal ArticleDOI
TL;DR: A review of the recent developments of smoothed particle hydrodynamics (SPH) method and its typical applications in fluid-structure interactions in ocean engineering can be found in this article.
Abstract: In ocean engineering, the applications are usually related to a free surface which brings so many interesting physical phenomena (e.g. water waves, impacts, splashing jets, etc.). To model these complex free surface flows is a tough and challenging task for most computational fluid dynamics (CFD) solvers which work in the Eulerian framework. As a Lagrangian and meshless method, smoothed particle hydrodynamics (SPH) offers a convenient tracking for different complex boundaries and a straightforward satisfaction for different boundary conditions. Therefore SPH is robust in modeling complex hydrodynamic problems characterized by free surface boundaries, multiphase interfaces or material discontinuities. Along with the rapid development of the SPH theory, related numerical techniques and high-performance computing technologies, SPH has not only attracted much attention in the academic community, but also gradually gained wide applications in industrial circles. This paper is dedicated to a review of the recent developments of SPH method and its typical applications in fluid-structure interactions in ocean engineering. Different numerical techniques for improving numerical accuracy, satisfying different boundary conditions, improving computational efficiency, suppressing pressure fluctuations and preventing the tensile instability, etc., are introduced. In the numerical results, various typical fluid-structure interaction problems or multiphase problems in ocean engineering are described, modeled and validated. The prospective developments of SPH in ocean engineering are also discussed.

145 citations

Journal ArticleDOI
TL;DR: In this article, a state-of-the-art review on the two most challenging pump-as-turbine (PAT) performance prediction and flow stability aspects are presented.
Abstract: Energy is unarguably the key factor for today's economic and social development within nations Electricity as one of many energy forms is a critical input to developing countries in the struggle to the national self-satisfaction in all domains Rural electricity supply involved institutions have recently recommended the pump as turbine (PAT)-based micro hydropower plant (MHP) schemes for remote off-grid electrification, mostly from their economic advantages However, from different published research findings, PAT-based MHP is not only simple and economically feasible, but has presented bottlenecks in the move to its full understanding Moreover, compared to other clean energy technologies, PAT technology has not found much literature in academic published researches, thus contributing to its limited understanding within the community Therefore, the PAT literature availability is one way to level up its understanding, which can be helpful to academic and professional communities In the present study, a state-of-the-art review on the two most challenging PAT aspects, namely PAT performance prediction and PAT flow stability aspects are presented In the presented literature, the selected energy sources history leading to the actual MHP global adoption was first briefly explained, followed by an intensive literature on PAT operations, where details about PAT selection and performance prediction were provided Finally, the PAT flow stability aspects where pump-turbine S-shape and Saddle-type characteristics constitute the main focus, were discussed It is worth an attention to mention that the words “pump-turbine”, “Pump as turbine”, and “reversible pump turbine”; are equally used throughout the whole literature It is within the authors wish that this paper can scale up the reader's PAT technology understanding, thus serving awareness in the same

117 citations

Journal ArticleDOI
TL;DR: In this article, the turbulent attached cavitating flow around a Clark-Y hydrofoil is investigated by the large eddy simulation (LES) method coupled with a homogeneous cavitation model.
Abstract: In this paper, the turbulent attached cavitating flow around a Clark-Y hydrofoil is investigated by the large eddy simulation (LES) method coupled with a homogeneous cavitation model. The predicted lift coefficient and the cavity volume show a distinctly quasi-periodic process with cavitation shedding and the results agree fairly well with the available experimental data. The present simulation accurately captures the main features of the unsteady cavitation transient behavior including the attached cavity growth, the sheet/cloud cavitation transition and the cloud cavitation collapse. The vortex shedding structure from a hydrofoil cavitating wake is identified by the criterion, which implies that the large scale structures might slide and roll down along the suction side of the hydrofoil while being further developed at the downstream. Further analysis demonstrates that the turbulence level of the flow is clearly related to the cavitation and the turbulence velocity fluctuation is much influenced by the cavity shedding.

97 citations

Journal ArticleDOI
11 Jan 2018
TL;DR: In this paper, the authors analyzed the cavitating flow at a normal flow rate using torsion flow analysis and showed that cavitation is a challenging flow abnormality that leads to undesirable effects on the hydraulic behavior of centrifugal pumps.
Abstract: Cavitation is a challenging flow abnormality that leads to undesirable effects on the hydraulic behaviour of centrifugal pumps. This study analyses the cavitating flow at a normal flow rate using t...

88 citations


Cites background from "A review of cavitation in hydraulic..."

  • ...Among the different pump types, cavitation in centrifugal pumps is relatively simple; leading edge cavitation is considered to be the major cavitation type observed in centrifugal pumps, as well as the main reason for severe erosion and abrupt head drop.(6,7) The mechanism in centrifugal pumps is significantly different from that of axial flow pumps or inducers, in which the tip leakage vortex is more significant on pump performance....

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References
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Journal ArticleDOI
TL;DR: In this paper, the authors present the full cavitation model, which accounts for all the first-order effects of cavitation and is called as the full-cavitation model and the phase change rate expressions are derived from a reduced form of Rayleigh-Plesset equation for bubble dynamics.
Abstract: Cavitating flows entail phase change and hence very large and steep density variations in the low pressure regions. These are also very sensitive to: (a) the formation and transport of vapor bubbles, (b) the turbulent fluctuations of pressure and velocity, and (c) the magnitude of noncondensible gases, which are dissolved or ingested in the operating liquid. The presented cavitation model accounts for all these first-order effects, and thus is named as the full cavitation model. The phase-change rate expressions are derived from a reduced form of Rayleigh-Plesset equation for bubble dynamics. These rates depend upon local flow conditions (pressure, velocities, turbulence) as well as fluid properties (saturation pressure, densities, and surface tension). The rate expressions employ two empirical constants, which have been calibrated with experimental data covering a very wide range of flow conditions, and do not require adjustments for different problems. The model has been implemented in an advanced, commercial, general-purpose CFD code, CFD-ACE+

1,329 citations

Book
14 Jul 2004
TL;DR: Kato et al. as mentioned in this paper studied the dynamics of cavitation in real liquid flows and proposed a steady potential flow theory to model the cavity flow dynamics of a liquid/vapor mixture with phase change.
Abstract: -Foreword Hiroharu Kato. -Preface. Symbols. -1: Introduction - The main features of cavitating flows. 1.1. The physical phenomenon. 1.2. Cavitation in real liquid flows. 1.3. Specific features of cavitating flow. 1.4. Non-dimensional parameters. 1.5. Some historical aspects. -2: Nuclei and cavitation. 2.1. Introduction. 2.2. Equilibrium of a nucleus. 2.3. Heat and mass diffusion. 2.4. Nucleus population. References. -3: The dynamics of spherical bubbles. 3.1. Basic equations. 3.2. The collapse of a vapor bubble. 3.3. The explosion of a nucleus. 3.4. The effect of viscosity. 3.5. Non-linear oscillations of a bubble. 3.6. Scaling considerations. 3.7. Stability of a spherical interface. References. -4: Bubbles in a non-symmetrical environment. 4.1. Introduction. 4.2. Motion of a spherical bubble in a liquid at rest. 4.3. Non-spherical bubble evolution. 4.4. The path of a spherical bubble. References. Appendix to Section 4.3.3. -5: Further insights into bubble physics. 5.1. The effect of compressibility. 5.2. Bubble noise. 5.3. Some thermal aspects. 5.4. A typical numerical solution. References. Appendix to Section 5.1.3. -6: Supercavitation. 6.1. Physical aspects of supercavities. 6.2. Supercavity flow modeling using steady potential flow theory. 6.3. Typical results. 6.4. Axisymmetric cavities. 6.5. Specific problems. References. Appendix: singular behavior at detachment. -7: Partial cavities. 7.1. Partial cavities on two-dimensional foils. 7.2. Partial cavities in internal flows. 7.3. The cloud cavitation instability. 7.4. Wakes of partial cavities. 7.5. Thermal effects in partial cavitation. References. Appendix: sonic velocity in a liquid/vapor mixture with phase change. -8: Bubbles and cavities on two-dimensional foils. 8.1. Attached cavitation. 8.2. Traveling bubble cavitation. 8.3. Interaction between bubbles and cavities. 8.4. Roughness and cavitation inception. References. -9: Ventilated supercavities. 9.1. Two-dimensional ventilated supercavities. 9.2. Axisymmetric ventilated supercavities. 9.3. Analysis of pulsating ventilated supercavities. References. -10: Vortex cavitation. 10.1. Theoretical results. 10.2. The non-cavitating tip vortex. 10.3. Cavitation in a tip vortex. References. -11: Shear cavitation. 11.1. Jet cavitation. 11.2. Wake cavitation. References. -12: Cavitation erosion. 12.1. Empirical methods. 12.2. Some global results. 12.3. Basic hydrodynamic mechanisms of energy concentration. 12.4. Aggressiveness of a cavitating flow. 12.5. Insight into the material response. References. Index.

641 citations

Journal ArticleDOI
TL;DR: In this paper, a bubble two-phase flow (BTF) model is proposed to explain the interaction between viscous effects including vortices and cavitation bubbles, which treats the inside and outside of a cavity as one continuum by regarding the cavity as a compressible viscous fluid whose density changes greatly.
Abstract: A new cavity model that can explain the interaction between viscous effects including vortices and cavitation bubbles is presented in this study. This model, which is named a bubble two-phase flow (BTF) model, treats the inside and outside of a cavity as one continuum by regarding the cavity as a compressible viscous fluid whose density changes greatly. Navier–Stokes equations including cavitation bubble clusters are solved in finite-difference form by a time-marching scheme, where the growth and collapse of a bubble cluster is given by a modified Rayleigh's equation. Computation was made on a two-dimensional flow field around a hydrofoil NACA0015 at angles of attack of 8° and 20°. The Reynolds number was 3 × 105. The experiments were also performed at the same Reynolds number for comparison. The computed results by the BTF cavity model can express the feature of cloud-type cavitation shed from the trailing edge of the attached cavities when the angle of attack is 8°. It shows the mechanism of cavitation cloud generation and large-scale vortices. The boundary layer separates at the cavity leading edge. Then it rolls up and produces the cavitation cloud. In other words, the instability of the shear layer may produce the cavitation cloud. When the angle of attack is 20°, the flow was fully separated from the leading edge of the hydrofoil and vortex cavitation occurs in the separated region. The BTF cavity model can also express the generation of such vortex cavitation and the effect of cavitation nuclei in the uniform flow.

586 citations