Geysering Caused by the Sudden Release of Pressurized Air Pockets

Abstract

Uncontrolled air pockets released from water filled shafts can lead to geysering in stormwater systems. Such occurrences are deleterious from public health and environmental standpoints and can cause property and structural damage. Causes, frequency, magnitude, and location of geysering events are still poorly understood, and pose practical difficulties to designers as to how to create drop shafts that are less likely to present this issue. This work presents results from experimental and numerical investigations on air-related geysers that aimed to gain insight on the mechanisms of air release and the displacement of water in vertical shafts. A 302mm schedule 40 clear PVC apparatus was constructed with the essential features of a stormwater tunnel, and was fitted with vertical shafts with diameters ranging from 0.10m to 0.20m. During these experiments, predetermined air pocket volumes were released in the horizontal pipe, and eventually reached shafts causing water displacement and often geysers. Kinematics of the air pocket release were measured along with pressures at selected points in the apparatus. These results were used in the calibration of a CFD model based on OpenFOAM, which compared well with the experimental measurements. The model was subsequently used in a larger geometry that allowed the evaluation of air pocket release kinematics for a wider range of conditions. Findings of this work provide further details on the nature and strength of geysering events, and suggestions for future studies in this topic are also provided.