Abstract
In order to mitigate the effects of salt water intrusion at sea locks, bubble screens are installed which act as a barrier between the dense sea water and the fresh water inland. In order to optimize the design of the bubble screen, in this study a state-of-the-art numerical model is developed based on the Euler-Lagrange CFD method which is expanded with a simple salt balance and concentration-density coupling. The model has been validated by means of experimental results on a laboratory-scale bubble screen. The liquid circulation and entrainment have been investigated for two types of bubble injection methods. It is found that the bubble screen is successful as a separator of salt and fresh water in an initial period of τsep=30 seconds but acts more as a mixer at later times due to the swaying of the screen. The rate of the mixing increases with the air flow rate. Two mechanisms of salt intrusion are distinguished; a delayed density current along the bottom and entrained liquid being circulated through the domain back to the screen. An optimum in air flow rate is found at a Froude air number Frair=0.91. Bubble screen behaviour is also checked at the lock-scale using lock-scale geometry and simulations. The amount of salt transmitted agrees well with the large-scale field tests up until the reported Frair numbers but Frair > > 1 need to be tested to check for the optimum as found in the lab-scale tests.
Original language | English |
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Article number | 103321 |
Journal | International Journal of Multiphase Flow |
Volume | 129 |
DOIs | |
Publication status | Published - Aug 2020 |
Funding
The authors would like to thank Deltares for making their experimental results available for use and assisting in the processing of the data. The authors also acknowledge SURF SARA (www.surf-sara.nl) and NWO for support in using the Cartesius supercomputer.
Keywords
- Bubble screen
- Computational fluid dynamics
- Euler-Lagrange
- Experimental validation
- Salt intrusion mitigation