Pumped storage units often deviate from the optimal operating conditions in the process of regulating new energy fluctuations. To effectively improve the performance of the units, the variable speed of the units is one of the more feasible means at present. This paper focuses on the part-load condition of turbine operation, with an emphasis on the internal flow characteristics and pressure pulsation characteristics of the pump turbine during the linear reduction of the rated speed. It is found that the streamlines in the runner become turbulent in the process of speed reduction, forming a vortex at the inlet of the runner, and the vortex scale gradually increases with the speed reduction. The vortex rope in the draft tube undergoes three types of changes during the speed reduction: helical eccentric vortex rope, vanishing vortex rope, and columnar vortex rope. Before the speed change, the low-frequency components with high amplitude exist in each flow-passing part, but gradually disappear with the speed reduction. Except for the runner, the frequency affected by rotor–stator interference of each flow-passing part increases with the decrease of speed, and the growth is most obvious in the vaneless region. The findings of this research can serve as a valuable reference for the variable speed operation of pumped storage units.

In oil–gas mixed transportation using spiral-vane-type multiphase pumps, high sand content often causes wear on flow-passing components. To reveal the motion patterns of particles, a three-stage spiral-vane-type multiphase pump was selected as the research subject. A visualization test bench was constructed, and the pump’s performance curve was obtained by experimental measurements. High-speed photography was used to capture the flow process of a single particle within the pump, and CFD-DEM was used to study the motion characteristics of four particle sizes (0.5 mm, 1 mm, 1.5 mm, and 2 mm). The results showed that 0.5 mm and 1 mm particles had smaller trajectory angles in the guide vanes, while 1.5 mm and 2 mm particles had larger angles, with wall collisions observed. Velocity changes were similar: When they just enter the impeller, the circumferential velocity increases sharply and then stabilizes around 15 m/s. After entering the guide vane passage, the circumferential velocity exhibits an initial abrupt decrease followed by a gradual reduction. The axial velocity increases gradually along the impeller passage, reaches the highest value at the impeller outlet, and begins to decrease gradually after entering the guide vane. The particles had higher volume fractions in the guide vane and collided more with impeller walls. Collisions with guide vane walls increased with particle size.

The helical-bladed multiphase pump demonstrates significant advantages in transporting complex media. However, the presence of solid particles complicates the fluid–structure interaction mechanism, posing challenges to studying solid–liquid two-phase flow within the pump. This research focuses on a self-developed three-stage helical-bladed multiphase pump, employing numerical simulation with experimental validation, to systematically investigate the effect of particle mass concentration (Cm = 1‰, 5‰, and 1%) on particle motion characteristics. The results indicate particle velocity distribution follows similar trends under different Cm conditions. In the impeller flow passage, the circumferential velocity of particles increases significantly while axial velocity changes marginally. Upon entering the guide vanes, circumferential velocity decreases, whereas axial velocity increases. The absolute velocity rises axially along each impeller stage but declines axially in each guide vane stage. As Cm increases, particle backflow intensifies, leading to aggravated flow blockage in the reflux zone at the first-stage impeller inlet. Under high-concentration conditions, particles aggregate into clusters within the flow passage, elevating collision probability. Particle distribution shifts from low-speed to medium-speed regions: dispersed at low Cm but concentrated toward medium-speed zones at medium-to-high Cm. Particle collision frequency rises with Cm, with increased proportions of collisions against the shroud and hub but decreased proportions against blades. The total particle–wall contact force escalates with higher Cm, with impeller-wall forces exceeding guide-vane-wall forces. In the guide vane region, contact forces distribute as blades > shroud > hub. These findings elucidate the kinetic characteristics of solid particles, providing a basis for the optimal design of multiphase pumps.