The flow with solid-liquid two-phase media inside centrifugal pumps is very complicated and the relevant method for the hydraulic design is still immature so far. There exist two main problems in the operation of the two-phase flow pumps, i.e., low overall efficiency and severe abrasion. In this study, the three-dimensional, steady, incompressible, and turbulent solid-liquid two-phase flows in a low-specific-speed centrifugal pump are numerically simulated and analyzed by using a computational fluid dynamics (CFD) code based on the mixture model of the two-phase flow and the RNG k-ɛ two-equation turbulence model, in which the influences of rotation and curvature are fully taken into account. The coupling between impeller and volute is implemented by means of the frozen rotor method. The simulation results predicted indicate that the solid phase properties in two-phase flow, especially the concentration, the particle diameter and the density, have strong effects on the hydraulic performance of the pump. Both the pump head and the efficiency are reduced with increasing particle diameter or concentration. However, the effect of particle density on the performance is relatively minor. An obvious jet-wake flow structure is presented near the volute tongue and becomes more remarkable with increasing solid phase concentration. The suction side of the blade is subject to much more severe abrasion than the pressure side. The obtained results preliminarily reveal the characteristics of solid-liquid two-phase flow in the centrifugal pump, and are helpful for improvement and empirical correction in the hydraulic design of centrifugal pumps.

The transient behavior of centrifugal pumps during transient operating periods, such as startup and stopping, has drawn more and more attention recently because of urgent needs in engineering. Up to now, almost all the existing studies on this behavior are limited to using water as working fluid. The study on the transient behavior related to solid-liquid two-phase flow has not been seen yet. In order to explore the transient characteristics of a high specific-speed centrifugal pump during startup period delivering the pure water and solid-liquid two-phase flow, the transient flows inside the pump are numerically simulated using the dynamic mesh method. The variable rotational speed and flow rate with time obtained from experiment are best fitted as the function of time, and are written into computational fluid dynamics (CFD) code-FLUENT by using a user defined function. The predicted heads are compared with experimental results when pumping pure water. The results show that the difference in the transient performance during startup period is very obvious between water and solid-liquid two-phase flow during the later stage of startup process. Moreover, the time for the solid-liquid two-phase flow to achieve a stable condition is longer than that for water. The solid-liquid two-phase flow results in a higher impeller shaft power, a larger dynamic reaction force, a more violent fluctuation in pressure and a reduced stable pressure rise comparing with water. The research may be useful to understanding on the transient behavior of a centrifugal pump under a solid-liquid two-phase flow during startup period.

The parameters of blade trailing edge have an important influence on the performance of centrifugal pump and internal unstable flow. In this study, the influences of cutting angles of blade trailing edge on unstable pressure pulsation and unstable flow structure are investigated using a centrifugal pump under off-design conditions through large eddy simulation. Three typical blade trailing edges, namely, original trailing edge (OTE), 15° cutting angle of blade trailing edge (OBS15) and 30° cutting angle of blade trailing edge (OBS30), are analysed. Results show that the cutting angle of blade trailing edge has a certain effect on the performance of the centrifugal pump. Under part-load conditions, the OBS30 impeller evidently contributes to the reduction in pressure pulsation intensity. By contrast, the OBS15 impeller has opposite effect because of the increase in wake vortex intensity. The OBS30 impeller can effectively improve the unstable vortex structure caused by backflow at the centrifugal pump tongue using a new Ω method. Consequently, reduction in the unstable flow structure mainly contributes to the reduction in pressure pulsation used by the proper cutting angle of blade trailing edge.

The transient startup and shutdown of centrifugal pumps is inevitable and its transient performance has thus attracted increasing attention in recent years. This study aims to reveal the transient characteristics of centrifugal pumps during the start-stop process by using the dimensionless analysis method and quasi-steady-state method. The research objects are three typical centrifugal pumps with an impeller structure. The startup process includes quick and slow startup, and the shutdown process includes low-speed and high-speed idle rotation. Results show that the similarity law of centrifugal pumps can be applied to transient hydraulic performance prediction under full flow conditions during slow startup and under small flow conditions during quick startup and idle shutdown. Quick or slow startup does not affect the evolution of the dimensionless power coefficients. The research result may be useful for the design of the new fluidmachinery equipment by utilizing transient hydraulic performance.

In order to meet the needs in engineering, an existing low specific speed centrifugal pump may have to be run at a high rotating speed. Unfortunately, experiments on transient performance of such a kind of centrifugal pump in starting and stopping periods at a high speed have been unavoidable so far. In this paper, the transient hydraulic performance of a low specific speed centrifugal pump with an open impeller during starting and stopping periods is measured with an updated test rig. The correlations of rotating speed, flow rate, head, static pressures at the pump inlet and outlet, and shaft power with time are obtained at different discharge valve openings. The results show that the flow rate rises slowly at the beginning of starting period, and suddenly drops at the end of stopping process. There is an obvious impact phenomenon in local static pressure curves at the pump inlet and outlet during starting period. With the augment of discharge valve opening, the required time for flow rate to reach a steady value is gradually prolonged, and the impact phenomenon in local static pressures at the pump inlet is postponed and the impact difference is also decreased step by step. The impact phenomenon in shaft powers is also very prominent, especially at small discharge valve openings. At the beginning of stopping process, the flow rate declining delay phenomenon becomes weak with increasing discharge valve opening, and the time for flow to stop fully is also extended gradually.

Intensity inhomogeneity and noise are two major parts in image segmentation. Aiming at these problems, this work proposes a novel hybrid active contour method which combines local and global statistical information into an improved signed pressure force (SPF) function. First, by considering the global information extracted from a region of interest, a new global-based SPF function is created that effectively adjusts the signs of the pressure force inside and outside the evolving curve. Second, a new local-based SPF function utilizes the normalized local intensity differences as the coefficients of local internal and external regions, which can segment complicated areas easily. Third, by combing the global-based SPF and the local-based SPF functions, an improved hybrid SPF function is constructed based on active contour approach. Experiments on many kinds of real and synthetic images show that our method makes superior segmentation accuracy and is more robust to initial contour and noises.