Computational Fluid Dynamics of a bubble curtain for the prevention of salt intrusion at sea locks

Thomas O'Mahoney, Mike van Meerkerk, Aris Twerda

Thursday 2 july 2015

17:15 - 17:30h at Amazon (level 1)

Themes: (T) Water engineering, (ST) Computational methods

Parallel session: 13B. Engineering - River

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. 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. The numerical model of the bubble curtain in the absence of slat is compared with experiments (Bulson 1962). Flow velocity profiles are in good agreement at lab scale and field scale. The model is reduced to a computational size which is practical for investigations into the salt exchange flows for locks at field scale. References Abraham, G., and v. d. Burgh, P., 1962, Reduction of salt water intrusion through locks by pneumatic barriers, Delft Hydraulics Laboratory, 28 Bulson, P. S. (1961). Currents produced by an air curtain in deep water. Dock and Harbour Authority Vol. 42, 15-22.