Transient performance of fluid machinery during transient operating periods,such as startup and stopping,has been drawn more attentions recently due to the growing engineering needs.In this paper,the transient behavior of a prototype centrifugal pump with an open impeller during rapid startup period is studied experimentally.The variations of the rotational speed,flow rate,head,and shaft power during rapid startup period are recorded in experiments at different discharge valve openings.In addition,the non-dimensional flow rate and head are also used to analyze the transient behavior.The research result shows that the rise characteristic of the rotational speed is not basically changed by working points,while mainly depends on the startup characteristics of the driving motor.Compared with the rapid rise of the rotational speed,the flow rate rises slowly in the initial stage of startup.Moreover,the flow rate lags behind the rotational speed to rise to final stable value,and the delay becomes more severe with the increase of the discharge valve opening.The shaft power impact phenomenon generally exists in the process of startup.The non-dimensional analysis shows that the non-dimensional head is very high at the very beginning of startup,and quickly falls to the minimum,then gradually rises to final stable value,while the non-dimensional flow rate always shows the rise tendency during whole startup period.In conclusion,it is found from the non-dimensional results that the quasi-steady analysis is unable to accurately assess the transient flow during startup period.
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-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.
