Bubble Screen Effectiveness Prediction Using Numerical Simulation

Bubble screens are applied at shipping locks between salt and fresh water bodies, in order to reduce the amount of salt intrusion as a result of the locking process. The importance of limiting this salt intrusion is found in the required quality of the fresh water, which is given by ecological reasons or due to its use for agriculture and/or drinking water.

Recent shipping traffic developments contribute negatively to salt intrusion unless proper mitigating measures are taken. Increasing shipping intensity demands more frequent lockages, with every lockage adding to the amount of salt intrusion through the lock. Furthermore, the enormous size of modern locks means they contain a large amount of salt water that potentially flows towards the inland water bodies. These developments have called for a renewed assessment of the potential of bubble screens to mitigate salt intrusion.

Compared to the application of a freshwater flushing discharge through the lock, the primary alternative, bubble screens are obviously more expensive as the required flow rate and pressure demand a significant compressor size. An important question therefore is to optimize the design or use of the bubble screen such that the required salt intrusion reduction is met at a minimum use of energy. An additional question is how the bubble screen technology scales up towards the larger depths of modern locks.

Various research methods have been applied to address the application of bubble screens in shipping locks: in situ measurements, scale model measurements and numerical methods; as presented by Van der Ven et al. (2018).

Aresearch method with great potential is the application of computational fluid dynamics (CFD). Forexample Meerkerk et al. (2015). More recent studies are presented in Van der Ven (2018). The potential of these methods show a promising increase of numerical stability which helps in the application of these methods in advisory or research projects. The numerical approaches range from coarse and pragmatic methods to full simulations that are more suitable for the simulation of a specific aspect of the bubble screen physics, as the simulation of the full shipping lock geometry would lead to unfeasible computation times.

This paper will give an overview of recent developments of numerical methods and their applicability and accuracy when assessing the performance of bubble screens as a means to mitigate salt intrusion through locks. The goal of this research is to develop sufficiently accurate methods that are applicable in design projects.