Hongbo Shi

The dynamics of cavitation bubbles critically affect the stability of gas layers and induce intense impact forces on adjacent surfaces. This study numerically investigates the complex interaction mechanisms among a cavitation bubble, a free surface, and three representative biomimetic gas–entrapping microstructured surfaces. A compressible volume of fluid multiphase model with equations of state is developed and validated against experimental observations of bubble morphology, gas layer evolution, and free surface deformation. The effects of bubble–surface (γf = 0.25–1.0) and bubble–wall (γw = 0.8–1.5) stand–off distances are systematically examined, focusing on liquid jet characteristics, shock wave propagation, wall shear stress, and the resulting force and impulse on the microstructured surface. The results reveal that the hierarchical microstructure provides superior gas layer retention, sustaining a higher gas volume fraction (αg = 0.87) and attenuating impact loading (p/p* = 45) compared to micropillar and re-entrant microstructures. The evolution of wall shear stress shows alternating outward and inward patterns driven by bubble-induced radial flows, with peak values of 282 kPa (outward) and 89 kPa (inward) for the hierarchical microstructure. Furthermore, variations in γf and γw significantly influence the jet dynamics, modify the spatial distribution of wall pressure and shear stress, and determine the resulting force and impulse on the microstructured surface. These findings offer theoretical insight into mitigating cavitation-induced erosion and enhancing gas layer stability in marine hydrodynamics and fluid machinery.

This work is devoted to numerical studies of transient evolution characteristics and drag reduction mechanisms of ventilated cavitating flow over an underwater axisymmetric vehicle under periodic flow disturbances. The unsteady Reynolds-averaged Navier–Stokes approach is adopted along with the volume-of-fluid method and the shear-stress transport k−ω turbulence model. The results show that the numerical method can accurately predict the cavity shedding dynamics and internal pressure fluctuations at the cavity development stage. Under various inflow conditions, the pressure fluctuations are consistent with the transient cavity behaviors in the spectral–temporal domain. The increased amplitude and frequency of fluctuating inflow intensify the randomness of cavity shedding, leading to higher drag on the underwater vehicle. Additionally, the new Ω identification method reveals the topological features of multiscale vortex structures in the cavity shedding process. The strength and scale of the vortices vary significantly with the vehicle's angle of attack, which is primarily governed by vortex stretching and baroclinic torque terms. Although the drag reduction rate decreases with increasing angle of attack, the novel double-ventilated ring configuration effectively suppresses cavity shedding and substantially enhances drag reduction efficiency. These findings offer valuable insights into the design and control of ventilated cavitating flows around underwater vehicles.

Plasma activated water(PAW) is water that is treated with cold plasma discharge. The dissolved reactive oxygen and nitrogen species in PAW are desirable for wastewater treatment, environment remediation, food processing and storage, enhanced plant growth in agriculture and many other applications. In this work, we develop microbubble-enhanced PAW production through a self-suction mechanism. Microbubbles form under the strong turbulence effect at the throat of a cavitation tube, transferring active species into a stream of water. As demonstrated by degradation rate of sulfathiazole, a model antibiotic compound in water, the main parameters identified from our experiments to be essential for the activation efficiency are the design of the cavitation tube, the flow rate of the water stream, and the distance from the discharge to the flow. Our three-dimensional numerical simulations reveal the impact of the tube dimensions on the multiphase flow characteristics. The simplicity of self-suction mechanism allowed us to set up a solar-driven, stand-alone cold plasma system to generate PAW outdoor. The as-prepared PAW can boost the growth rate of bean and peanut sprouts in hydroponics about 80% and 66%, respectively. The portable PAW production may open the door to even broader applications of field activated water for applications in sustainable agriculture and in environment remediation.

In order to study the characteristics of a bidirectional shaft tubular pump with S-type symmetric airfoil blades, a prototype model was designed, manufactured, and tested. The energy characteristics, cavitation characteristics, and runaway characteristics of the pump were obtained under forward and reverse operating conditions for five different blade angles. Based on the basic equations of the pump and the inlet and outlet velocity triangles, combined with model tests and numerical simulations, the hydraulic performance of the pump was extensively analyzed and evaluated. In addition, semi-empirical equations for reverse efficiency and runaway characteristics were proposed. The dynamic pressure-drop coefficients were introduced to compare the cavitation performance under different flow rates in forward and reverse operations. The results reveal that the efficiency of the pump in reverse operation is greater than that of forward operation only under a very small flow rate. While the cavitation performance of the bidirectional pump in the two operating modes is almost the same, the runaway speed and backflow rate in forward operation are considerably greater than those of reverse operation. The results provide an important reference for the safe and stable operation of bidirectional shaft tubular pumps.

Centrifugal pumps are the critical components in deep-sea mining. In order to investigate the particle motion in the curved channel of the impeller, three different types of curvature conform to blade profile to simplify the impeller design of pumps. A numerical study is conducted to investigate the flow field in a varying-curvature channel for solid-liquid two-phase flow. The flow of particles within the varying curvature channel is studied by combining the discrete element method (DEM) with computational fluid dynamics (CFD) and a comparison with Particle Image Velocimetry (PIV) test results. The results show that a polyhedral mesh with a small mesh number yields very accurate results, which makes it very suitable for CFD-DEM. Based on this method, the movement of a single particle is compared and analyzed, and the particle-motion law is obtained. The effects of the curvature ratio Cr and area ratio Ar on the motion law for a single particle are studied, and the simulation results are analyzed statistically. The results show that the effect of Cr on both the particle slip velocity and the turbulent kinetic energy only changes its strength, while the distribution law does not change significantly. Compared with the curvature ratio Cr, the area ratio Ar has a greater impact on the particles, and its distribution law becomes clearly different. As the area ratio Ar increases, the arc radius and length of the corresponding particle trajectory decrease.