To investigate the evolution characteristics of the air pocket during the geyser process, a numerical simulation of the release of an entrapped air pocket in a drainage pipe system under double-sided inflow conditions was conducted. The geyser formation mechanisms, air discharge characteristics, and air-water energy evolutions were analyzed. The results indicate that the entry and subsequent release of an entrapped air pocket into the vertical shaft trigger an air pocket-driven geyser, followed by the occurrence of a rapid-filling geyser. Depending on whether these two processes operate independently or interactively, the geyser process can be classified as either a separated type or a hybrid type. A higher dimensionless pipeline pressure difference P^* or a smaller dimensionless initial air pocket volume V_a^* is more likely to trigger a hybrid geyser process. The air pocket discharge ratio during the air pocket-driven geyser is approximately 2%-47%; it first increases and then decreases with increasing P^*, and it decreases with increasing V_a^*. The air pocket discharge ratio during a rapid-filling geyser is approximately 0-5%, and it is minimally affected by P^* and V_a^*. During the geyser process, the peak kinetic energy of the air occurs in the air pocket-driven geyser stage, while the peak kinetic energy of the water in the vertical shaft occurs in the rapid-filling geyser stage. The geyser intensity decreases with increasing P^* and increases with increasing V_a^*. An air pocket-driven geyser occurs when the dimensionless maximum kinetic energy of the air per unit mass exceeds 1.5; a rapid-filling geyser occurs when the dimensionless maximum kinetic energy of the water per unit mass exceeds 0.5.

To alleviate sediment deposition in urban drainage pipelines, a hydraulic self-cleaning structure for pipelines was designed, incorporating a gate and flume.Numerical simulation methods were conducted to analyze the hydraulic characteristics of the dredging process under different slopes and initial inflow levels. The results show that at the initial stage of dredging, the flume shear stress and vertical mean velocity at the inlet of the pipeline can reach 16 and 1.55 times those at the end of the process, respectively. As the flushing wave moves to the end of the pipeline, the maximum flume shear stress and the maximum vertical mean velocity at the inlet of the pipeline can reach 5 and 2 times those at the end of the pipeline, indicating a stronger dredging effect in the upstream section. During dredging, the maximum shear stress of the flow in the flume and the maximum vertical mean velocity can reach 104 and 1.45 times those on the platform, respectively, indicating that the dredging efficiency in the flume is significantly superior to that on the platform.Specifically, the increased slope of the pipeline and higher initial inflow levels result in greater flushing wave shear stress and vertical mean velocity, with maximum recorded values of 156 Pa and 3.6 m/s, respectively, reflecting a better pipeline cleaning effect. During dredging, the flushing wave velocity and shear stress generated are significantly higher than the theoretical uplift flow velocity and critical shear stress of the sediment, which proves that the dredging effect of the hydraulic self-cleaning structure is good.