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Cavitation vortex dynamics of unsteady sheet/cloud cavitating flows with shock wave using different vortex identification methods

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Journal of Hydrodynamics 2019年第3期31卷 475-494页

作者： Chang-chang Wang Ying Liu Jie Chen Fu-yi Zhang Biao Huang Guo-yu Wang School of Mechanical Engineering Beijing Institute of Technology Beijing 100081 China

Cavitation is a complex multiphase flow phenomenon with an abrupt transient phase change between the liquid and the vapor, including multiscale vortical motions. The transient cavitation dynamics is closely associated with the evolution of the cavitation vortex structures. The present paper investigates the cavitation vortex dynamics using different vortex identification methods, including the vorticity method, the Q criterion method, the Omega method (Ω), the method and the Rortex method. The Q criterion is an eigenvalue-based criterion, and in the Ω method, the parameter is normalized, is independent of the threshold value and in most conditions Ω= 0.52 . The Rortex method is based on an eigenvector-based criterion. Numerical simulations are conducted using the implemented compressible cavitation solver in the open source software OpenFOAM for the sheet/cloud cavitating flows around a NACA66 (mod) hydrofoil fixed at a = 6°,= 1.25 and Re = 7.96 × 10^5 . The flow is characterized by the alternate interactions of the re-entrant flow and the collapse induced shock wave. Results include the vapor structures and the vortex dynamics in the unsteady sheet/cloud cavitating flows, with emphasis on the vortex structures in thecavitation region, the cavity interface, the cavity closure, the cavity wakes, and the foil wakes with the shedding cavity. The comparisons of the various methods, including that the vorticity method, the Q criterion method, the Ω method, the λ2 method and the Rortex method, show the performances of different methods in identifying the cavitation vortex structures. Generally, during the attached cavity growth stage, the Q criteria can well predict the vortex structures in the cavitation region and at the foil trailing edge in the pure liquid region, while with the Ω method and the Rortex method, the vortex structures outside the attached cavity and on the foil pressure side can also be predicted. The λ2 method can well predict the vortex structures in t

关键词： Cavitation vortex dynamics vortex identification sheet/cloud cavitating flow re-entrant jet shock wave OpenFOAM

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A review of transient flow structure and unsteady mechanism of cavitating flow

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Journal of Hydrodynamics 2019年第3期31卷 429-444页

作者： Biao Huang Si-cong Qiu Xiang-bin Li Qin Wu Guo-yu Wang School of Mechanical Engineering Beijing Institute of Technology Beijing 100081 China Department of Nuclear Science and Engineering North China Electric Power University Beijing 102206 China

The flow structure and the unsteady mechanism of the unsteady cavitating flow are reviewed in this paper. The flow patterns and structures in different cavitation regime, for the attached cavitation and the vortical cavitation, are shown with both the visualization and the quantitative information. The attached cavitating flow around the Clark-Y hydrofoil and the vortical cavitating flow around the Tulin hydrofoil are considered. In particular, the phenomena such as the large-scale vortex structure and the re-entrant flow associated with the cloud cavitation, and the cavitating vortex street's forming and crumbling are described. The evolution of the cavitation structure in the transient sheet/cloud cavity forming, along with the cavity collapse induced by the re-entrant flow and the shock wave propagation are discussed. The perspective future research of higher fidelity simulations, and the accurate identifications of the cavitating vortex structure is commented.

关键词： cavitating flow flow structure unsteady mechanism

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Computational theory of cavitating flows for hydraulic turbomachinery with consideration of influence of water quality

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Science China(Technological Sciences) 2010年第12期53卷 3341-3348页

作者： WANG Lei1,2 & CHANG JinShi2 1 Huadian Electric Power Research Institute, Hangzhou 310030, China 2 College of Water Conservancy and Civil Engineering, China Agricultural University, Beijing 100083, China Huadian Electric Power Research Institute Hangzhou China College of Water Conservancy and Civil Engineering China Agricultural University Beijing China

Previously it was assumed that the pressure within the cavity or on the cavity surface remained constant and the vapor pressure of clean water at 20°C and 0 m altitude was utilized as the computational boundary for cavitating flows in hydraulic turbomachinery. Cavitation was confused with vaporization, and the effect of water quality on cavitation pressure characteristics was not taken into account. In recent years, lots of experiments of cavitation pressure characteristics of different water qualities including different sand concentrations of sand water and different altitudes of clean water have been performed by the authors, and the important influences of water quality on cavitation pressure characteristic have been validated. Thus the water quality should be involved in the cavitating flows computation. In the present paper, the effect of water quality on the cavitation pressure characteristic is analyzed and the computational method and theory of cavitating flows for hydraulic turbomachinery that considers the influence of water quality are proposed. The theory is suitable for both the potential flow method and the two-phase flow method for cavitating flows simulation. Finally, the validation results for cavitating flows in a hydraulic tur- bine indicate the significant influences of water quality on the cavitating flow performance.

关键词： cavitating flows cavitation pressure water quality hydraulic turbomachinery

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Characteristic analysis of unsteady viscous flow around a cavitating propeller

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Science China(Technological Sciences) 2010年第7期53卷 1983-1992页

作者： ZHU ZhiFeng1, 2, FANG ShiLang1 & WANG XiaoYan1 1 Key Laboratory of Underwater Acoustic Signal Processing of Ministry of Education, Southeast University, Nanjing 210096, China 2 School of Electrical Engineering and Information, Anhui University of Technology, Maanshan 243002, China Key Laboratory of Underwater Acoustic Signal Processing of Ministry of Education Southeast University Nanjing China School of Electrical Engineering and Information Anhui University of Technology Maanshan China

Based on viscous multiphase flow theory, this paper presents some recent validation results with a hybrid grid and sliding mesh solving Unsteady Navier-Stokes (N-S) and Bubble Dynamics equations as applied to prediction of pressure, velocity and vapor volume fraction in the wake in an uniform inflow. Comparable to experimental results, numerical predictions of sheet cavitation, tip vortex cavitation and hub vortex cavitation are in agreement with the corresponding experimental data, the same as numerical predictions of pressure in wake. Tip vortex cavitation is the most important to generate the pressure fluctuation within the near wake. The characteristics such as blade and shaft rate frequency of propeller pressure in wake coincide with its geometric model and parameters. With increasing distance from propeller disk, the pressure signals at blade frequency de-crease. The process of attenuation becomes fast with the decreased advance coefficient and cavitation number.

关键词： cavitating flow RANS propeller sliding mesh multiphase flow

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Shadowgraph Imaging of cavitating Jet

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Journal of Flow Control, Measurement & Visualization 2015年第3期3卷 106-110页

作者： Ryuta Watanabe Takayuki Kikuchi Takayuki Yamagata Nobuyuki Fujisawa Graduate School of Science and Technology Niigata University Niigata Japan Visualization Research Center Niigata University Niigata Japan

This paper deals with the statistical properties of unsteady structure of cavitating water-jet issuing into a stagnant fluid of water using the shadowgraph imaging combined with the proper orthogonal decomposition (POD) analysis. The experimental result indicates that the cavitating jet is composed of axisymmetric mode, while the periodic axial oscillation is found along the jet centerline. The reconstructed cavitation images show the presence of growing, shrinking and shedding motion in the cavitation cloud, which sustains a periodic behavior of the cavitating jet.

关键词： cavitating Jet POD Analysis Shadowgraph Periodic Structure

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关于通气空泡及其路径数值求解的挑战性问题（英文）

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Journal of Marine Science and Application 2019年第3期18卷 260-270页

作者： E. L. Amromin Mechmath LLC

Ventilated cavitation has been successfully employed as ship drag reduction technology and potentially can mitigate flowinduced vibration. The obtained successes were based on solutions of design problems considered in the framework of ideal fluid theory with their following validation by towing tank tests. However, various aspects of the interaction of ventilated cavities with the viscous flows around the ship hulls remain unclear, whereas there is usually no possibility to simultaneously keep the full-scale Froude number and cavitation number in the test facilities. So, the further progress of the application of ventilated cavitation substantially depends on the ability of computational tools to predict this interaction. This paper briefly describes the state-of-the-art computation of ventilated cavitation and points out the most challenging unsolved problems that appeared in the model tests (prediction of air demand by cavities, ventilation effect on ship drag, on hydrofoil lift, and on the propagation of shock waves in cavities).

关键词： Ventilated cavitation Computational fluid dynamics Lift, drag, and air demand of cavitating bodies Shockwaves in cavities

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