Yuning Zhang

This book provides a comprehensive analysis of multiphase flow with bubbles, covering bubble dynamics, sound wave propagation in vapor/gas/liquid multiphase flow, and vapor/liquid/solid multiphase flow with sand particles. It begins by introducing the cavitation nucleation mechanism and examining bubble oscillation equations in liquids, including first-order and second-order models. Further discussions explore the mass transfer effects at the bubble wall, energy dissipation mechanisms, and bubble behavior under dual-frequency acoustic fields. Regarding sound wave propagation in vapor/gas/liquid multiphase flow, the book presents a wave speed prediction model, details the solution process and propagation characteristics, and examines how vapor fraction, bubble radius, and void fraction influence critical frequency and wave speed stability. The section on vapor/liquid/solid multiphase flow delves into the bubble collapse process, analyzing jet phenomena—including single jet, multi-jet, and needle jet formations—along with shock wave phenomena occurring during cavitation bubble nucleation, splitting, and collapse. Additionally, it explores the synergistic erosion effects of cavitation bubbles and sand particles on hydraulic machinery. Designed for academic researchers and graduate students in fluid dynamics, this book consolidates core theories, physical mechanisms, and the latest advancements in multiphase flow research.

This brief overviews the application and significance of high-speed photography in experimental fluid mechanics, specifically focusing on the detailed observation and analysis of bubble dynamics, drop dynamics, and wake dynamics. It explores the development and various application scenarios of high-speed imaging technology, using it to investigate microscopic phenomena within these areas. The book covers key topics such as bubble collapse and deformation, particle acceleration mechanisms, and cavitating flow patterns in bubble dynamics; droplet impact, coalescence, and fragmentation in drop dynamics; and the wake phenomena of bluff bodies during translation, rotation, and interactions with flat surfaces in wake dynamics. Through experimental observations and mechanism research, the book provides insights into the underlying processes and behaviors in fluid systems, making it a valuable resource for researchers and students in fluid mechanics and energy related fields.

This brief provides a comprehensive review of the rapidly expanding field of cavitation and bubble dynamics, covering the discussion of bubble dynamics equations, bubble oscillation dynamics, theoretical prediction models of jets, and high-speed photography technology. Among them, the core formulas, important research methods, and typical results related to bubble oscillation and collapse dynamics are systematically and comprehensively introduced. Specifically, in terms of the bubble dynamics equations, several classical dynamic equations utilized to describe the radial motion of the spherical bubble, cylindrical bubble, and the bubble in a droplet are derived and compared. In terms of the bubble oscillation dynamics, based on the perturbation method, multi-scale method, and Laplace transform method, the nonlinear oscillation characteristics of the bubble in free oscillation and driven oscillation are analyzed. In terms of the jet prediction theory, the Kelvin impulse model and various boundary treatment methods are given in detail, and the jet direction, intensity, and spatial sensitivity caused by the bubble collapse near various boundaries are discussed. In terms of the bubble collapse visualization based on the high-speed photography, taking the laser-induced bubble as an example, the system composition, operation process and experimental layout of the high-speed photography experimental platform are introduced, and a large number of typical bubble collapse deformation, jet evolution and shock wave propagation characteristics obtained from experiments are demonstrated. This book is intended for academic researchers and graduate students in fluid dynamics, aiming to consolidate the basic theory, physical mechanism, and latest progress in the field of bubble dynamics.

This brief explores the pivotal realm of droplet cavitation, a subject of great significance for enhancing fuel atomization and improving various industrial processes. The authors employ high-speed photography experiments, analyze bubble dynamics equations, and utilize numerical simulations to explore the dynamic behavior of cavitation bubbles and droplets. The book analyzes the entire lifecycle of cavitation bubbles, their interactions with different liquid droplets, and the key parameters governing their oscillation and collapse and sheds light on the collapse mechanisms and shock wave propagation influenced by liquid droplets. Additionally, it investigates the dynamics of droplet spattering by categorizing spatter patterns under diverse conditions, discusses the critical stability of droplet surfaces, and reveals the mechanisms by which cavitation bubble collapses induce droplet breakage. Taking vapor bubbles and diesel droplets as examples, the dynamic characteristics of specific droplets containing bubbles are also analyzed. This book offers an in-depth understanding of these phenomena with practical implications for a wide range of industrial applications and is a useful tool for researchers and engineers working in the fields of fluid dynamics, combustion engineering, and atomization processes.

This brief provides a comprehensive introduction on the flow-induced instabilities (e.g., the pressure fluctuations and the vibrations) of the reversible pump turbines (RPTs) in the pumped hydro energy storage power stations (PHSEPSs) in China based on long-term field tests. The pressure fluctuations and the vibrations of several RPTs in China under different operational conditions are analysed in detail to reveal their generation mechanisms and propagation characteristics. The book presents advanced signal analysis and processing methods which are used for obtaining the time-frequency information and for finding the internal correlations between several types of signals. Advanced artificial intelligence algorithms are adopted for understanding the effective fault diagnosis and the identification of different flow patterns. The book overviews the fundamentals of the RPTs and the signal analysis methods, while it demonstrates that the analysis results of the pressure fluctuation and vibration data may be employed for the calibration of numerical simulations and the comparisons of model tests. It is primarily targeted to researchers and engineers working on the fields of condition monitoring and fault diagnosis of hydraulic machineries.