A non-uniform inflow caused by an elbow structure is one of the main reasons for the low energy transformation efficiency of a centrifugal pump. Prototype experiments for the centrifugal pump are used to analyze the transformation rule of pump energy characteristics under the uniform inflow and non-uniform elbow inflow. The non-uniform elbow inflow increases the hydraulic losses in the centrifugal pump to reduce the pump head and operation efficiency. The pump efficiency decreases by 8% under the design flow condition. The large eddy simulation with a shear-modified eddy viscosity model is applied to simulating flow excitation characteristics and energy development features. The non-uniform inflow increases the impact loss at an impeller inlet and produces unsteady flow excitation in the impeller passage. The elbow inflow affects the pressure fluctuation frequency, and the main frequency is twice the blade-passing frequency (250 Hz). The high entropy production regions are mainly concentrated at the suction surface of the blade and the interface of impeller and volute, coinciding with the unsteady flow areas in the pump. The asymmetrical entropy yield distribution in the elbow inflow pump is intensified because of the increase in the flow loss caused by the non-uniform inflow.

Geometrical structures and operating performance of volutes used in centrifugal pumps are assessed in cross sections. By a volute, we mean the wetted part surrounding the impeller in a pump that converts the kinetic energy of water into potential energy. It is important to develop improved design principles and approaches for volutes to reduce hydraulic loss and increase the efficiency of pumps. However, when designing volutes, pump designers often neglect a key factor related to pump efficiency, namely, the energy loss due to the friction at the volute sidewall is directly proportional to the wetted perimeter of the cross section. In this paper, we show that the length of the wetted perimeter of the cross section is mathematically proportional to the friction loss in the volute. In addition, we present the design principles and calculation process to minimize the wetted perimeters of two kinds of cross section based on the velocity coefficient method using the same statistical data. The structures and shapes of the new cross sections are completely different from those of traditional volutes. Moreover, two different volutes with different cross sections are numerically investigated using a verified computational fluid dynamics technique. Both the head and the efficiency of the pump with the new volute are higher than those of a conventional pump under all working conditions. This paper provides a new design approach for the energy-saving volutes of centrifugal pumps.

In order to understand the complex nature of the system dynamic phenomena, such as the strong vibration and noise caused by blade passage in the pump turbine, a state-of-the-art three-dimensional (3D) compressible transient simulation would be desirable to study the problem in depth. This study investigated the phase resonance (PR) that occurred during a full-load operation in the turbine mode of a pump turbine on a prototype scale. As a first step, the wave reflection at the boundaries, and the influence of the timestep and sound speeds on the behavior of traveling pressure waves inside a spiral casing, were studied. It was found that nonreflective boundary conditions and an appropriately small timestep are critical to capturing the wave reflection and superposition process inside a spiral casing; a certain kind of direct PR risk was detected in its system design. The detected direct PR differed from the well-known PR with two features: firstly, it was almost independent of the sound speeds, and secondly, the pressure distribution over the spiral circumference varied among the amplitudes. The latter feature was caused by pressure waves at every stator channel induced by a rotor stator interaction (RSI). The 3D flow simulation with an acoustic model, which couples the RSI and PR phenomena, would predict better results for understanding the problem than the simplified one-dimensional (1D) method.