Tip leakage vortex has an important influence on the performance of semi-open centrifugal pumps. Simulations based on the three-dimensional Reynolds-Averaged Navier–Stokes were conducted to study the structural characteristics of tip leakage vortex and its effects on the internal flow field, and the Shear Stress Transport k-ω turbulence model was used to simulate the whole flow passage of centrifugal pumps with tip clearances of 0 mm and 1 mm. Then, the tip leakage vortex was analyzed using the relative vorticity transport equation. The numerical data and experimental results agreed well. The leakage vortex formed in the tip clearance led to 18.7% and 14.4% decrease in head and efficiency under design condition, respectively, and the bigger the flow rate, the fast the performance decreased. Tip leakage vortex formed at the leading edge of the blade moved along the suction surface. Whereas the tip leakage vortex formed near the middle of the blade extended to the pressure surface of the adjacent blade. This phenomenon deteriorated the flow field and induced passage vortex, thereby reducing the static pressure and blade load and changing the static pressure distribution law. The formation and development of leakage vortex could be attributed to the relative vortex stretching the term. The Coriolis force term could reflect the change of vorticity caused by leakage flow, and the viscous diffusion term served as the vorticity source.

The flow passage components in hydraulic machinery will be eroded rapidly when running in sand water. The wear resistance of materials commonly used in hydraulic machinery needs to be improved to prevent the failure of hydraulic machinery. New wear-resistant materials are urgently needed to improve the service life of hydraulic machinery. Eutectic high entropy alloy (EHEA) is a new kind of alloys with in situ lamellar structure. NiCoCrFeNb_0.45 EHEA has combined excellent strength and toughness. In this study, slurry erosion tests of NiCoCrFeNb_0.45 EHEA were carried out with different impact angles and impact velocities using a rotary jet erosion test apparatus. The NiCoCrFeNb_0.45 EHEA exhibited significant slurry erosion resistance compared with medium carbon steel 1045 and stainless steel 04Cr13Ni5Mo. The erosion rate of EHEA is much slower. Compared with medium carbon steel and stainless steel, the erosion of EHEA is completed via the accumulation and removal of platelets after plowing and work hardening, accompanied by partial micro-cutting.

Increasingly functional microscopic machines are poised to have massive technical influence in areas including targeted drug delivery, precise surgical interventions, and environmental remediation. Such functionalities would increase markedly if collections of these microscopic machines were able to coordinate their function to achieve cooperative emergent behaviors. Implementing such coordination, however, requires a scalable strategy for synchronization—a key stumbling block for achieving collective behaviors of multiple autonomous microscopic units. Here, we show that pulse-coupled complementary metal-oxide semiconductor oscillators offer a tangible solution for such scalable synchronization. Specifically, we designed low-power oscillating modules with attached mechanical elements that exchange electronic pulses to advance their neighbor’s phase until the entire system is synchronized with the fastest oscillator or “leader.” We showed that this strategy is amenable to different oscillator connection topologies. The cooperative behaviors were robust to disturbances that scrambled the synchronization. In addition, when connections between oscillators were severed, the resulting subgroups synchronized on their own. This advance opens the door to functionalities in microscopic robot swarms that were once considered out of reach, ranging from autonomously induced fluidic transport to drive chemical reactions to cooperative building of physical structures at the microscale.