2D Modelling and energy analysis of entrapped air-pocket propagation and spring-like geysering in the drainage pipeline system

Abstract

Transient (highly unsteady) air–water two-phase flows and spring-like geysers have been one of the critical concerns in drainage pipeline systems, which may cause or exacerbate drainage flooding problems and associated damage consequences. In this paper, the flow dynamics and energy evolution mechanism of the induced spring-like geysers are innovatively investigated through a two-phase full-2D numerical model developed in this study. After full validation by laboratory experimental tests conducted in this study, the proposed 2D model is systematically applied to simulate transient air–water flows in drainage pipelines. The results have shown acceptable accuracy of this full-2D model to capture the complex flow interactions between the air and water phases, and indicated that the velocity and pressure distribution patterns are highly relevant to the air–water interface deformation and energy exchange. The in-depth energy analysis demonstrates that the intermittent eruption of geysers could be attributed to the conservation and release of different energy forms during the transient air–water two-phase flow process. Besides, the numerical applications for the systems with different boundaries and initial conditions indicate that the different ventilation conditions and initially entrapped air volume may significantly affect the velocity distribution of the air phase, thereby playing an essential role to provide effective measures to mitigate unexpected geyser events and pressure oscillations in the system. The results and findings of this paper could provide insights to improve the theory and practice of transient air–water two-phase flows in drainage pipeline systems.