To improve the performance of particle image velocimetry in measuring instantaneous velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.

Theory of cross-correlation analysis of PIV images : Image analysis as measuring technique in flows

The growth of a vapor bubble in a superheated liquid is controlled by three factors: the inertia of the liquid, the surface tension, and the vapor pressure. As the bubble grows, evaporation takes place at the bubble boundary, and the temperature and vapor pressure in the bubble are thereby decreased. The heat inflow requirement of evaporation, however, depends on the rate of bubble growth, so that the dynamic problem is linked with a heat diffusion problem. Since the heat diffusion problem has been solved, a quantitative formulation of the dynamic problem can be given. A solution for the radius of the vapor bubble as a function of time is obtained which is valid for sufficiently large radius. This asymptotic solution covers the range of physical interest since the radius at which it becomes valid is near the lower limit of experimental observation. It shows the strong effect of heat diffusion on the rate of bubble growth. Comparison of the predicted radius‐time behavior is made with experimental observations in superheated water, and very good agreement is found.

The growth of vapor bubbles in superheated liquids. report no. 26-6

Failure diagnosis using deep belief learning based health state classification

A review on data-driven fault severity assessment in rolling bearings

A summary of fault modelling and predictive health monitoring of rolling element bearings

Condition monitoring is the process of monitoring a condition parameter in machinery, so that a significant change is indicative of a developing failure. The use of conditional monitoring allows maintenance to be scheduled, or other actions taken to avoid the consequences of failure before it actually occurs.

Vibration-Based Condition Monitoring

In high-head pump-turbines, observations in the engineering field show that the most detrimental hydraulic instabilities are pressure fluctuations in the vaneless space. For example, these pressure fluctuations can cause vibrations and fatigue failures in hydraulic components. It has been recognized that pressure fluctuations in vaneless space are induced primarily by the interactions between runner blades and guide vanes, i.e., rotor–stator interactions (RSI). The present paper presents and discusses studies in this field, which are carried out by various investigators. Studies include mechanism research on RSI, experimental and numerical investigations on RSI characteristics, discussions on the relationship between vibrations and pressure fluctuations, studies on the geometric and operating parameters of the unit that influence the pressure fluctuations in vaneless space, and precautions and countermeasures to reduce these pressure fluctuations.

Pressure fluctuations in the vaneless space of High-head pump-turbines—A review

S-shaped characteristics on the performance curves of pump-turbines in turbine mode promote instability problems in associated transient processes, e.g., difficulties in synchronizing with power grid in turbine start-ups, unstable performance in turbine load rejections, etc. The present paper presents and discusses relative studies on the S-shaped characteristics, which have been carried out by various investigators. Studies include system instability analysis, experimental and numerical investigations on the flow mechanism of pump-turbines, studies on the influencing geometric and operating parameters of the unit, and precautions and countermeasures to improve the S-shaped characteristics and instability problems in associated transient processes.

S-shaped characteristics on the performance curves of pump-turbines in turbine mode – A review

If large pressure fluctuation is observed in the draft tube of a Francis turbine at part-load operation, we have generally called it draft-tube-surge. As occurrence of this phenomenon seriously affects the limit of turbine operating range, extensive studies on the surge have been made since proposal of surge-frequency criterion given by Rheingans. According to the literature survey of related topics in recent IAHR symposiums on hydraulic machinery and systems, in which state-of-the-art contributions were mainly presented, a certain review of them may be desirable for an outlook on the future studies in this research field. Thus, in this review paper, the authors' previous attempts for the last three decades to challenge the following topics: a rational method for component test of a draft tube, nature of spiral vortex rope and its behavior in a draft tube and cavitation characteristics of pressure fluctuations, are introduced together with other related contributions, expecting that more useful and significant studies will be accomplished in the future.

Shuhong Liu

Papers

Vibration-Based Condition Monitoring

Pressure fluctuations in the vaneless space of High-head pump-turbines—A review

S-shaped characteristics on the performance curves of pump-turbines in turbine mode – A review

An Outlook on the Draft-Tube-Surge Study

Numerical investigation of the hump characteristic of a pump-turbine based on an improved cavitation model