Bubble curtains in a lock-exchange flow: the importance of transient dynamics in the curtain-driven regime

TL;DR

This study uses multiphase large eddy simulations and a semi-analytical model to analyze the transient dynamics of bubble curtains in lock-exchange flows, highlighting the importance of timing for saltwater intrusion mitigation.

Contribution

It introduces a detailed simulation and semi-analytical model to understand the temporal evolution of bubble curtain effectiveness in lock-exchange flows.

Findings

Transient dynamics are crucial for bubble curtain effectiveness.

Simulations accurately reproduce experimental regimes.

Time since gate opening significantly impacts saltwater mitigation.

Abstract

Bubble curtains are line bubble plumes that are used to mitigate saltwater intrusion in shipping locks. When the lock gate that separates the saline seawater from the fresh river water is opened, a lock-exchange flow is initiated. Placing a bubble curtain at the gate location disrupts this flow and reduces saltwater infiltration. For practical applications, it is useful to quantify the effectiveness of the bubble curtain as a function of the governing parameters of the problem. To achieve this goal, we performed multiphase large eddy simulations that accurately reproduce previous experimental results including the two regimes of operation: the break-through and the curtain-driven regimes. This paper focusses on the curtain-driven regime and aims to unravel the temporal evolution of the effectiveness of bubble curtains. The detailed spatial and temporal information obtained from the simulations and the flexibility to vary the governing parameters allowed us to overcome several previous experimental limitations. In addition, the simulations were used to obtain parameters to build a semi-analytical model. Both the simulations and the semi-analytical model clearly describe and help to understand the time evolution of the density field and the effectiveness of the bubble curtain. These results show that the time elapsed since the opening of the gate and the transient dynamics are crucial for determining the effectiveness of bubble curtains.