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Modelling and Simulation in Engineering
Volume 2018, Article ID 3194935, 12 pages
Research Article

Transient Air-Water Flow and Air Demand following an Opening Outlet Gate

1Hydraulic Engineering, Royal Institute of Technology (KTH), 10044 Stockholm, Sweden
2R&D Älvkarleby Laboratory, Vattenfall AB, 81426 Älvkarleby, Sweden
3Tyrens AB, 11886 Stockholm, Sweden
4Water Conservancy & Hydropower Engineering, Hohai University, Nanjing, China

Correspondence should be addressed to James Yang; moc.llafnettav@gnay.semaj

Received 30 September 2017; Revised 30 December 2017; Accepted 14 January 2018; Published 1 March 2018

Academic Editor: Dimitrios E. Manolakos

Copyright © 2018 James Yang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


In Sweden, the dam-safety guidelines call for an overhaul of many existing bottom outlets. During the opening of an outlet gate, understanding the transient air-water flow is essential for its safe operation, especially under submerged tailwater conditions. Three-dimensional CFD simulations are undertaken to examine air-water flow behaviors at both free and submerged outflows. The gate, hoisted by wire ropes and powered by AC, opens at a constant speed. A mesh is adapted to follow the gate movement. At the free outflow, the CFD simulations and model tests agree well in terms of outlet discharge capacity. Larger air vents lead to more air supply; the increment becomes, however, limited if the vent area is larger than 10 m2. At the submerged outflow, a hydraulic jump builds up in the conduit when the gate reaches approximately 45% of its full opening. The discharge is affected by the tailwater and slightly by the flow with the hydraulic jump. The flow features strong turbulent mixing of air and water, with build-up and break-up of air pockets and collisions of defragmented water bodies. The air demand rate is several times as much as required by steady-state hydraulic jump with free surface.