Experimental and numerical simulations of river-crossing pipelines for different water fill patterns

Abstract

In the process of water filling in long-distance water transfer projects, the transient flow of water and air, along with the fluctuation in pressure, indicates the complexity of the hydraulic transition process, particularly when there are curved pressurized pipes, and the movement of air inside the pipes is not easily determined. This study focuses on pipeline systems with significant changes in elevation, such as those crossing rivers or roads. It employs a combined approach of generalized model experiments and numerical simulations to investigate the formation and transformation of flow patterns in the pipeline system during the filling process. It also analyses the fluctuation of pressure on both sides of the curved pipe under different filling modes and reveals the coupling mechanism between the movement of large-scale air bubbles and turbulent vortex structures within the curved pipe. When the water filling velocity at the pipeline inlet is v = 0.8 m s–1, the size of the bubbles formed by the air is larger, the variety of flow patterns is greater, and the evolution of flow patterns is more complex. When impounded water occurs in the river crossing pipeline due to maintenance, the pipeline system forms slug flow at a filling flow velocity of v = 0.8 m s–1. This leads to an abrupt change in the overall pressure of the pipeline system, with the maximum pressure being 1.36 times that of the filling flow velocity of v = 0.4 m s–1. At a filling flow velocity of v = 0.8 m s–1, bends in the pipe readily foster the formation of large-scale bubbles. The interaction between the buoyancy and drag forces acting on these bubbles and the centrifugal forces provided by the bends results in continuous changes in the hydraulic conditions within the pipe. The research findings not only enrich the study of the hydraulic transition process in pipeline systems but also hold significant importance for expediting the construction pace of long-distance water transfer projects.