A Hydraulic Performance Comparison of Centrifugal Pump Operating in Pump and Turbine Modes

The modifications of impeller may show diverse impact on centrifugal pump operating in pump and turbine modes.To clarify this problem,the hydraulic performance of a low specific speed centrifugal pump operating in both modes was firstly obtained by CFD method and verified by experiment.Then,based on the single-factor design method,a series of calculations have been conducted to identify the effects of impeller geometry parameters on the hydraulic performance in different modes.The variations of head,shaft power and hydraulic efficiency curves with different impeller parameters were explored.It is found that compared with turbine,the pump shows a more obvious variation of head.The outlet angle has positive impact both on the head consumed by pump or generated by turbine.The change of turbine shaft power is apparently smaller than that of pump for different impeller geometry parameters.Only the outlet width somewhat changes the turbine shaft power.The hydraulic efficiency in both modes shows different variation under different impeller geometric parameters,while the hydraulic efficiency of both modes is reduced with the outlet angle increasing.Meanwhile,the response amount of hydraulic efficiency caused by certain change of impeller parameters was estimated by sensitivity analysis method.It is found that only the appropriate blade number and outlet width can improve the hydraulic performance both in pump and turbine modes.Eventually,the hydraulic loss,skin friction loss and theoretical analysis were performed to explore the reason of hydraulic performance variation due to different impeller parameters.The change of slip factor,impeller inlet area,impeller outlet area or hydraulic loss results in the change of hydraulic performance in both modes.The results can be useful for hydraulic performance improvement for both pump and turbine modes through impeller geometry modification.

Numerical simulation of hydraulic force on the impeller of reversible pump turbines in generating mode

The hydraulic force on the reversible pump turbine might cause serious problems（e.g., the abnormal stops due to large vibrations of the machine）, affecting the safe operations of the pumped energy storage power plants. In the present paper, the hydraulic force on the impeller of a model reversible pump turbine is quantitatively investigated through numerical simulations. It is found that both the amplitude of the force and its dominant components strongly depend on the operating conditions（e.g., the turbine mode, the runaway mode and the turbine brake mode） and the guide vane openings. For example, the axial force parallel with the shaft is prominent in the turbine mode while the force perpendicular to the shaft is the dominant near the runaway and the turbine brake modes. The physical origins of the hydraulic force are further revealed by the analysis of the fluid states inside the impeller.

Self-adjustment of a nonlinear lasing mode to a pumped area in a two-dimensional microcavity [Invited]

We numerically performed wave dynamical simulations based on the Maxwell–Bloch(MB) model for a quadrupole-deformed microcavity laser with spatially selective pumping. We demonstrate the appearance of an asymmetric lasing mode whose spatial pattern violates both the x-and y-axes mirror symmetries of the cavity.Dynamical simulations revealed that a lasing mode consisting of a clockwise or counterclockwise rotating-wave component is a stable stationary solution of the MB model. From the results of a passive-cavity mode analysis, we interpret these asymmetric rotating-wave lasing modes by the locking of four nearly degenerate passive-cavity modes. For comparison, we carried out simulations for a uniform pumping case and found a different locking rule for the nearly degenerate modes. Our results demonstrate a nonlinear dynamical mechanism for theformation of a lasing mode that adjusts its pattern to a pumped area.

A double-stage start-up structure to limit the inrush current used in current mode charge pump

A double-stage start-up structure to limit the inrush current used in current-mode charge pump with wide input range,fixed output and multimode operation is presented in this paper.As a widely utilized power source implement,a Li-battery is always used as the power supply for chips.Due to the internal resistance,a potential drop will be generated at the input terminal of the chip with an input current.A false shut down with a low supply voltage will happen if the input current is too large,leading to the degradation of the Li-battery＇s service life.To solve this problem,the inrush current is limited by introducing a new start-up state.All of the circuits have been implemented with the NUVOTON 0.6 μm CMOS process.The measurement results show that the inrush current can be limited below 1 A within all input supply ranges,and the power efficiency is higher than the conventional structure.