Locks are key-structures for the accessibility of ports and navigable waterways. Different systems exist for filling and emptying of the lock chamber. For locks with a high head between the upstream and downstream reservoir mostly long culverts, short culverts bypassing the lock gates or culverts with openings in the bottom of the lock chamber are considered. In Flanders, the head for most inland navigation locks is limited to 2 à 3 m. For such low-head locks, filling and emptying through openings in the lock gate, usually mitre gates are considered, is quite common. The filling of the lock chamber has to be done with special precautions, taking into account the forces experienced by the moored vessels during the levelling process. In case of filling through openings in the lock gate, one of the potential methods to minimize the hydrodynamic forces on the ships, is to insert breaking logs (‘energy dissipation bars’) at the downstream side of the gate openings, aiming at an enhanced spreading and energy dissipation of the filling jets.
In order to investigate the influence of breaking logs on the induced flow patterns in the lock chamber and their role in the energy dissipation of a turbulent filling jet, Flanders Hydraulics Research is executing a research project in which both physical model research (phase 1) and numerical modeling using Computational Fluid Dynamics (CFD; phase 2) are applied.
In the first phase, a dedicated (generic) physical model was built, consisting of one circular opening in a lock gate sealed by a vertical lift valve. Stationary tests are carried out both for configurations with and without breaking logs and for two different heads between the upstream and the downstream reservoir. The configurations with breaking logs differ with respect to the spacing between, the number and the section of the breaking logs (square section or I-profile) . For all these configurations the flow velocity in the lock chamber was measured and the flow pattern in the lock chamber was visualised using dye injection. Also, the influence of the breaking logs and the associated blockage of the opening by the breaking logs onto the discharge coefficient of the opening was assessed.
In the second phase of the project, first CFD modelling of the configurations studied in the physical model was carried out, using the OpenFOAM CFD package. Stationary simulations were carried out of scale model tests with and without breaking logs. The computed discharge coefficient, the flow pattern and the flow velocity in the lock chamber were compared with data from the physical model experiments and with literature data. Next, CFD modeling of the flow pattern and the flow velocities in a lock chamber during lock filling was carried out. Therefore a CFD model was set up of a schematic lock chamber with mitre gates and in total six openings in the lock gate. Non-stationary simulations were performed using the volume of fluid method, considering different configurations for the openings in the lock gate.
The outcome of this research project contributes to the design of filling and emptying systems for new (or renovated) inland navigation locks and to a better understanding of the influence of the breaking log configuration on the flow patterns in the lock chamber.