This paper systematically reviews the research progress on the flow characteristics of bubble plumes from three aspects: theoretical models, behavioral characteristics, and flow field properties. In terms of theoretical models, it reviews the development process from early single-phase plume models to modern integral models that incorporate bubble swarm dynamics, stratified environments, and line-source effects, elucidating key mechanisms such as buoyancy-driven flow, fluid entrainment, and bubble slip. Regarding behavioral characteristics, this paper summarizes experimental and numerical simulation findings on the diffusion laws, oscillation characteristics, and wall-attachment effects of bubble plumes. For flow field properties, it reviews advances in utilizing experimental measurement techniques (e.g., PIV and PTV) and numerical simulations to reveal flow field information, including three-dimensional velocity fields, turbulent structures, and bubble distributions. It is pointed out that future research directions for bubble plumes should include integrating artificial intelligence algorithms, incorporating complex physical processes such as bubble deformation, coalescence, and breakup, deepening the theoretical models for line-source bubble plumes, improving the characterization of three-dimensional flow fields, and enhancing the prediction accuracy of pollutant interception.

To improve the hydraulic flow pattern and energy dissipation rate of the step energy dissipator in the double-layer pumping station for urban sewage lifting and reduce the impact on the step surface, based on the numerical simulation method, the renormalization group (RNG) k-ε turbulence model and the volume of fluid (VOF) model were used to analyze the hydraulic characteristics of the step energy dissipator. There are adverse flow patterns of the mainstream being biased to the right and “water wings” in the water flow of the step energy dissipator. To address this issue, a combined rectification optimization scheme of “diversion ramp + diversion pier + tail ramp of steps” was proposed, and its optimization effect was analyzed. The results show that the diversion ramp can effectively increase the flow on the left side of the step and improve the adverse flow pattern of the deflected flow. The diversion piers and the tail piers of the steps can reduce and homogenize the axial velocity of the water flow at the exit section of the steps and suppress the formation of “water wings”. Under the design flow conditions of the pumping station, the uniformity of the total flow distribution of the first step of the combined step energy dissipator has increased by 0.42; the maximum pressure on the left side of the horizontal plane has decreased by 17%; the maximum pressure on the right side has decreased by 21%, and the energy dissipation rate of the combined step energy dissipator has increased by 4.12%.

In order to investigate the hydraulic characteristics of urban drainage pumping stations with curved inlet box culvert and explore the rectification measures to improve the adverse flow state inside the pumping station, the hydraulic flow state and rectification measures of urban drainage pumping stations were studied using the numerical simulation method, and the physical model was used to verify the rectification effect. It is found that the main stream of the forebay in the urban drainage pumping station with curved inlet box culvert is skewed and separated. The main stream of the forebay is concentrated in the middle and upper layers, and there is a large range of facade circulation in the middle and lower layers, and backflow in the bottom layer. The flow in the inlet pool is turbulent and vortices appear, resulting in the water not being able to enter the pump smoothly. The combined rectification measure of square column and combined beam was designed and optimized, and it is found that the combined rectification measure can improve the hydraulic flow pattern of the forebay and the inlet pool. The deviation and separation flow in the forebay are eliminated, the bottom backflow disappears, and the vortex in the inlet pool is effectively suppressed. The uniformity values of the inlet flow velocity distribution of the three water pumps were increased by 12.0%, 8.7%, and 8.3%. The weighted average angles of the inflow velocity were increased by 7.08°, 9.07°, and 11.40°.

To study the flow characteristics of the vortex-type grit chamber and improve the sand removal efficiency, the flow characteristics and sand removal efficiency of the vortex-type grit chamber initially set up in a sewage pumping station were analyzed by RSM model and DPM model based on the numerical simulation method. In view of the shortcomings of the vortex-type grit chamber, the optimization scheme of adding deflector plate were proposed, and the flow characteristics and sand removal efficiency of deflectors in different schemes with different lengths were compared. The results show that the water flow in the vortex-type grit chamber presents a spiral shape due to the horizontal circulation and elevation circulation caused by wall barrier and impeller blade rotation. When the water flow enters the pool along the inlet channel, it has an impact on the rotating water flow in the pool body, and the inlet flow with high velocity shifts to the center of the pool under the action of pressure difference, which easily rolls away the sand particles near the center of the pool, affecting the sand removal effect of the vortex-type grit chamber. Adding a baffle at the end of the inlet channel can effectively reduce the impact of the inlet flow on the rotating water flow in the sand settling basin and make the water flow that hits the baffle turn down to the bottom of the pool, thus improving the sand removal efficiency. Comparing the three baffle schemes, the sand removal effect is better when the length of the baffle is 2000 mm. The sand removal efficiency of 0.10, 0.15, 0.20 mm sand particles increased by 7%, 11% and 2%, respectively.