DEVELOPMENT OF A CFD MODEL OF AN AIR CURTAIN FOR SALTWATER INTRUSION PREVENTION

摘要

Bubble curtains are a method of reducing salt intrusion at sea locks. In the absence of a bubble curtain a gravity current flow forms as the lock doors are opened owing to the density difference at the interface between salt and fresh water regions. A bubble curtain is a screen of bubbles injected from the canal floor, across the lock opening, forming a hydrodynamic barrier which slows down the exchange of salt water. However, if too much air is injected the screen acts as an effective mixer which increases the amount of salt intrusion. The engineering challenge is to inject enough air into the curtain to slow down salt exchange but not too much that it starts acting as a mixer. A numerical model to predict the required air flow would be a useful tool in bubble curtain design. Bubble curtains are currently installed at the Stevin lock in the Netherlands, among others, and could be installed at a number of other locations in the future where salt intrusion is or becomes a problem. Computational Fluid Dynamics (CFD) is used here with the 3D finite-volume code Star-CCM+ to model a bubble curtain and the results are compared with theoretical results (Abraham & v.d. Burgh, 1962) and experimental results at field scale. A 3D Euler-Euler multiphase fluid model is used for the liquid and air phases with salt water modeled as a scalar within the liquid phase and with its own transport equation. The aim is to validate a numerical tool which can predict the required air injection in the bubble curtain to achieve a desired and given salt reduction factor, a measure of the extent to which the transfer of salt has been reduced from the situation without measures to reduce salt intrusion.