Preliminary Research on Air Pocket Entrapments Caused by Shear-Flow Instabilities in Rapid-Filling Pipes

Understanding the behavior of air-water interactions in closed conduits is very important for urban water systems that are subject to rapid filling conditions, such as stormwater systems during intense rain events. Among different mechanisms for air pocket appearance in closed conduits, shear flow instability is one that have significant capability to capture large volumes of air. Upon capture, air can impact surging and, upon uncontrolled release, lead to issues such as manhole cover displacement and/or geysering. This work present results from ongoing experimental and numerical research on air pocket entrapment based on shear flow instabilities. A fully-filled horizontal water pipe is partially opened pipe at the downstream end and create a cavity flow. After some advance within the pipe, a second valve is maneuver at the upstream end, enabling pressurized flows from the upstream end. The pipe-filling bore that is created pushes air in high velocity over the air cavity. In some cases, air pocket entrapment follows and lead to interesting peaks of pressure that seem to be a characteristic of this type of these entrapments.