Due to the high safety, low cost, and environmental friendliness, water jet cleaning has become an ideal dredging method for rivers and reservoirs dredging. To accurately investigate the impact of impingement height on the flow characteristics near the impingement wall, this study, in conjunction with comparisons to experimental measurements, selected the RNG (Renormalization Group) k-ε turbulence model and LES (Large Eddy Simulation) method to analyze the time-averaged and transient flow fields of submerged impinging jets with impingement angles θ = 90°, Re (Reynolds number) = 35 100, and various impingement heights H/d = 1, 2, 3, 4, 6, 8. The research reveals that: (1) The axial and radial velocities near the wall depend on the impingement height; the wall blockage effect is confined to within 0.75d, and the jet completes the transition from axial to radial flow at about x/d = 1.8. (2) In the range of 1d from the jet axis, the impingement height significantly affects the distribution of turbulent kinetic energy k/Uj2. (3) The impingement height influences the diffusion of turbulence in the near-wall area; the higher the impingement height, the more fully the shear layer diffuses radially, finally, the jet shear layer completes its inward penetration while the impingement height reaches H/d = 6.

This study investigates the influence of roughness on the transient flow behavior in the chamber based on the performance requirements of the pump rotor–stator chamber, aiming to elucidate the mechanism of roughness in real operating conditions. Three-dimensional models under two types of flow (centrifugal and centripetal) are developed, and transient numerical analyses are performed through numerical simulation and experimental validation. The results show that roughness significantly accelerates turbulence development in centrifugal through-flow, particularly in the middle- and high-radius regions, increasing the turbulent kinetic energy by approximately 18% compared to smooth surfaces. Transient flow analyses indicate that roughness leads to an overall pressure drop of around 10% within the cavity while facilitating the formation of high-pressure zones near the rotor. In centrifugal flow, high-pressure regions develop rapidly in the high-radius area, resulting in a stepped pressure distribution with a peak pressure increase of 12% at the outermost radius. In centripetal flow, the pressure distribution remains more uniform, yet significant pressure rise trends emerge over time, with pressure increasing by 8% due to the presence of roughness. This study presents a systematic analysis of the effects of roughness on transient flow characteristics in rotor–stator cavities across two flow modes for the first time, providing valuable insights for optimizing pump design and performance under real-world conditions.

This study numerically investigates the flow characteristics of submerged impinging jets at a standoff distance of H/d = 3. The computational analysis is performed utilizing large eddy simulation (LES) alongside the one-equation Wray-Agarwal and the two-equation SST k-ω and RNG k-ε turbulence models. The current work emphasizes the hydrodynamic structures developing in the unconfined jet region and the variations in flow behavior at the stagnation zone across a range of impact angles (θ ≤ 90°) at Re (Reynolds number) = 23,400. Compared with PIV data, the Wray-Agarwal model accurately predicts the free-jet flow, whereas the RNG k-ε model excels in the wall-jet region. As the impingement angle increases, the pressure distribution calculated by the LES method gradually approaches the experimental results. When the impinging angle θ = 90°, LES has high prediction accuracy in both regions. In general, under the grid scheme used in this study, RNG k-ε can make a more accurate prediction of the average characteristics of the submerged impinging jet flow field.