As the core for energy conversion in pumped storage plants, the pump turbine is also a key component in the process of building a clean power grid, owing to its fast and accurate load regulation. This paper introduces the current status of research and development of pump turbines from the perspectives of significance, design and optimization, operational performance, advanced research methods, etc. Internal and external characteristics such as transient flow evolution, structural vibration, flow-induced noise, etc., not only reflect operational performance (hydraulic, cavitation, sediment abrasion, and stability performance, etc.) but also directly affect the safe and efficient operation of the system. It is worth mentioning that the space-time evolution of internal and external characteristics is an emerging research direction, the results of which can be used to predict the operational conditions of pump turbines. Moreover, the development and application of intelligent condition monitoring and fault diagnosis aim to prevent failures and accidents in pumped storage plants.

The load regulation capability of hydropower station ensures power system efficiency and stability while supporting the development of renewable energy-integrated smart grids. Seeking a better way to study internal fluid characteristic and performance of turbine is a long-standing subject, numerical simulation demonstrates significant advantages due to its cost-effectiveness and fully visualization capabilities, with turbulence models playing a pivotal role in ensuring simulation precision. A dynamically defined MPANS (Modified Partially Averaged Navier Stokes) turbulence model is developed in this work by integrating considerations of real-time turbulence scale and mesh size. Comparative analyses between experimental data and numerical results reveal that the MPANS model exhibits a higher degree of agreement with experimental data. Compared with RNG (Renormalization Group) k-ε model, MPANS significantly reduces the maximum deviations in torque, efficiency, and water head. Under steady conditions, the vortex volumes captured in the runner and draft tube are increased by 18% and 126% with MPANS, respectively, relative to those predicted by the RNG k-ε model. Under load-increasing condition, the vortex volumes in the runner and draft tube show increases of approximately 6% and 87% with MPANS, respectively. Parameter like eddy viscosity is considered based on flow characteristic, MPANS demonstrates enhanced capability in resolving intricate details of vortex structure and offers a more comprehensive depiction of dynamic vortex evolution, under both steady and transient condition of Francis turbine.

The oil-free compressor is a key component in fabricating polyethylene terephthalate (PET) bottles for beverages and water. At present, the main compressor type used for blowing PET bottles is the reciprocating compressor. However, compared to screw compressors, reciprocating compressors have shortcomings of high energy consumption and too many consumable parts. Many manufacturers of PET bottles in Asia are seeking to replace reciprocating compressors with screw compressors, as we know. Screw compressors can be classified as single-screw compressors (SSC) and twin-screw compressors. Since the load in a twin-screw compressor is far larger than that in an SSC, SSCs are more suitable for being developed for high-pressure applications such as PET bottle blowing. This paper presents a performance study on an oil-free single-screw compressor as the first stage of the PET compressor unit. A 5.4 m³·min⁻¹ prototype and its test rig were developed. The thermophysical process of the moist air is theoretically analyzed. The pressure loss on the flow path and the influence of the important parameters are experimentally investigated. It is found that water vapor cannot be separated during the adiabatic compression process. The results also show that the pressure loss from the discharging duct to the check valve accounts for the largest percentage of the total pressure loss. The experimental results further show that the discharge capacity and shaft power increase almost linearly with the motor speed. The efficiency declines with increasing injected water temperature. The discharge capacity and shaft power all increase with the injected water flowrate, and an optimum flowrate is found to ensure a highest isentropic efficiency. With the increase in discharge pressure, the discharge capacity decreases, and the shaft power increases. The isentropic efficiency is found to have its maximum value at a certain discharge pressure.