NUMERICAL MODELLING OF AIR-WATER FLOW FORCED BY DOWNSTREAM PRESSURE RISE IN CULVERTS

摘要

In this paper, modelling transition from free-surface to pressurised flow in a sewer system is presented. During this transient, formation of air pockets moving around the pipe may occur. When trapped air reaches a manhole, air release induces sharp pressure fluctuations. Observations from a physical model underline the evolution of mixed flow parameters (air and water pressure, velocity and length of the pocket, ... ) during the air movement and release. Experiments were carried out for several discharges and initial conditions, using pressure gauges and video cameras. Following the experiments, numerical simulations of the flow were run. The model used here is based on continuity and momentum equations. Flow is divided in water columns which correspond to evolving control volumes. Comparisons with the measured data show that the model accurately describes the parameters during air movement, but air release modelling needs improvements including modifications in assumptions.