This study employs numerical simulation to investigate the transient flow and cavitation performance of centrifugal pumps with rough impellers, validating the numerical method with experimental data. Initially, the effect of blade roughness on the external characteristics of centrifugal pumps is examined. Subsequently, the study specifically addresses the impact of roughness on internal flow characteristics during cavitation, including vapor volume distribution, three-dimensional vortex structures, and vorticity distribution in the impeller channel. Furthermore, the influence of blade roughness on local energy loss is analyzed using entropy production theory. Finally, several monitoring points are arranged in the impeller channel to assess pressure pulsation effects. The results show that blade roughness generally reduces the head and efficiency of centrifugal pumps. During the non-cavitation and cavitation incipient stages, roughness marginally increases the head, with a maximum increase in only 0.1%. Impeller roughness causes vacuole collapse and vortex structure enlargement, disrupting the stable flow path within the channel. Blade roughness also escalates energy loss within impeller components, particularly under full cavitation conditions, where the impeller's entropy production accounts for up to 50%. Pressure pulsation results reveal that while blade roughness can slightly suppress cavitation, it also disturbs the flow field pressure. These insights provide guidance and data support for mitigating roughness and cavitation, the two primary instability factors in centrifugal pump operations.

Buried pipes are widely used for submarine water transportation, but the complex operating conditions in the seabed pose challenges for the modeling of buried pipes. In order to more accurately capture the dynamic behavior of the buried pipes in the seabed, in this study, considering the pipeline and soil as a systematic structure is proposed, improving the fluid–structure interaction four-equation model to make it applicable for the calculation of buried pipe system modes. After verifying the practicality of the model, considering the external seawater as uniform pressure, the coupling at the joints, and the Poisson coupling of submarine pipelines during transient processes are discussed, revealing that structural vibrations under both forms of coupling will cause greater hydraulic oscillations. The impact of soil elastic modulus on the system’s response is further discussed, revealing that increasing the modulus from 0 to 10¹⁵ Pa raises the wave speed from 498 m/s to 1483 m/s, causing a 40% increase in the amplitude of pressure oscillations. Finally, the vibration modes of the combined structure of pipe wall and soil are discussed, revealing that the vibration modes are mainly dominated by water hammer pressure, with the superposition of pipeline stress waves and soil stress waves. In this study, the dynamic behavior of submarine pipelines is elucidated, providing a robust foundation for regulating and mitigating fatigue failures in such systems.

Boundary conditions significantly influence the near-field dynamics of bubbles. This study employs numerical simulations to investigate the coupling characteristics of high-pressure bubbles near solid boundaries and moving spherical boundaries. It focuses on the effects of the sinking velocity of the sphere and the initial bubble–boundary distance on bubble evolution and loading characteristics. The results indicate that an increase in the sphere's sinking velocity or a decrease in the initial bubble–boundary distance leads to bubble tearing during the collapse process. This generates high-speed water jets directed either toward the bubble center or the boundary, significantly reducing the kinetic energy of the sphere. The shock waves and water jets caused by bubble tearing temporarily impede the sphere's motion, while the lagging flow induced by bubble expansion and contraction has a relatively minor impact. As the initial bubble–boundary distance increases, the bubble tearing phenomenon gradually weakens and may even disappear. This attenuation is attributed to the suppression of the Bjerknes effect by the boundary, which reduces the tendency of the bubble to migrate toward the boundary. Furthermore, the intensity of the tearing phenomenon significantly affects the pressure distribution near the bubble region around the sphere. Strong tearing induces a double-peaked pressure profile, while weak tearing results in a single-peaked profile primarily dominated by bubble collapse. This study reveals the critical influence of bubble–boundary interactions on sphere motion and pressure distribution, providing valuable insights for engineering design and applications in related fields.

As a crucial energy equipment, the highly efficient and stable comprehensive hydraulic performance of the mixed-flow pump has made it a focal point of research in the field of fluid engineering. However, cavitation is easily induced due to the complex multi-scenario operating environments, while the complexity of rotating turbulence can exacerbate the cavitation instability. Consequently, a vortex design method based on the potential flow function theory is developed to achieve mesoscale modulation of cavitation inside mixed-flow pumps. Based on current high-precision numerical simulations, primary conclusions are drawn as follows: vortex design strategy significantly enhances the anti-cavitation performance of the pump: compared with the original impeller, the critical net positive suction head for scheme 2 (S2) impeller under the forced vortex design and scheme 3 (S3) impeller under the compound vortex design decreased by 0.33 and 0.47 m, respectively. From the perspective of flow control mechanisms, the decreased blade curvature of S2 effectively reduces the low-pressure region on the suction side, suppressing the disturbance mechanism of vapor on the mainstream and the cavitation development. Furthermore, S3 optimizes the blade leading edge profile and reconstructs the local pressure gradient, not only significantly decelerating the cavitation growth, but also effectively attenuating the turbulent energy dissipation induced by cavitation.

Bubble–structure interaction studies rarely consider nearby moving boundaries. This study extends these works by numerically analyzing large (∼10 mm) bubbles near a moving sphere and a fixed elastic–plastic plate, and the resulting elastic–plastic structural response of the plate. The Rayleigh lifespan is defined as the time from bubble initiation to its first complete collapse, and the structural response encompasses the elastic–plastic energy transfer and deformation. The focus is on how boundary distribution and motion affect the Rayleigh lifespan, bubble morphology, and structural response. A multi-material Euler method with remapping was employed. Its reliability was verified through comparisons with previous experiments and analytical solutions, and grid-independence tests were performed. Results show that boundary configurations strongly affect bubble deformation and energy release. Increased boundary interference and reduced sphericity accelerate collapse, shortening the Rayleigh lifespan. For moving boundaries, a critical velocity range relative to the bubble center was identified. Exceeding this range causes the bubble to lose coherence and split into multiple smaller bubbles. The structural response is closely linked to bubble dynamics, including internal energy transfer and effective strain. Shortened collapse time enhances local flow momentum but limits the conversion of elastic energy into plastic deformation, weakening the plate's structural response. These findings clarify the influence of nearby boundaries on bubble dynamics and provide theoretical guidance for predicting underwater bubble-induced loads and designing protective structures.