| The emergency plane gate takes an important task in the operation of discharge structures, since it has to be closed down in any emergent hydrodynamic conditions so as to prevent the accident expanding further. Therefore, the operation reliability of the emergency gate will directly affect the safety of the project. In the process of gate closure in hydrodynamic conditions, the characteristics of the hydrodynamic loads on the gate are often difficult to be estimated accurately, affected by many factors such as the gate profile, the water head, the flow velocity, the closing speed and the aeration. This will easily lead to the problems that the design capacity of the gate hoist is insufficient or that the gate can not be closed down satisfactorily. In addition, if the gate profile is poorly designed, the flow separation may occur on the gate bottom edge, and then the pressure fluctuations may bring negative influence such as gate vibrations. Since the number of high-water-head plane gates is increasing, the hydrodynamic characteristics of the gates are getting more complex and their operation reliability is becoming more important. Therefore, it is necessary to study the complex hydrodynamic characteristics of the high-water-head plane gate and to study the influence of gate profile and hydraulic parameters on hydrodynamic loads. It is a critical issue that needs to be solved in the design and application of current high-water-head plane gates.In this paper, the characteristics of the flow near the gate, as well as hydrodynamic loads on the gate, are studied in the process of gate closure based on the model tests of two typical emergency plane gates. With the numerical simulation method that has been verified by the results of model tests and prototype observations, the relations between hydrodynamic loads and some parameters, such as the profile, the water-head and the closing speed of the gate, are analyzed in various conditions. The influence of high-velocity flow on the hydrodynamic characteristics of the gate is analyzed, and the hydraulic characteristics of the anomalous gate slot are also studied. Some suggestions are proposed for the design of the gate profile and the hydraulic parameters. The main innovative results are summarized as follows:1. A numerical simulation method, which is suited for the study of unsteady air-water two-phase flow in the process of gate closure, is proposed firstly. The calculated results have been verified by experimental data and prototype observation data. It is demonstrated that the feasibility of the method and the precision of the results can meet the needs of project design. Therefore, a new way is provided for the calculation and research of hydrodynamic loads on high-water-head plane gate.2. The relations between hydrodynamic loads and various parameters, such as the angle and thickness of upstream gate bottom edge, the water head and the closing speed, are studied systematically for the first time. The change of the uplift force with various water heads on the gate is revealed. The results show that the minimum coefficient of the uplift force will increase linearly with the angle and decrease with the decline of the thickness of the upstream gate bottom edge. The appropriate parameters about the angle and thickness of the gate are recommended, which can provide scientific reference for the project design and the revision of current relevant specifications for high-water-head plane gates.3. The relations between downpull force and various parameters, such as the angle of downstream gate bottom edge, and the upstream/downstream water head, are studied firstly in details. It is shown that the maximum negative pressure on gate bottom edge will increase with the upstream water head and the intensity of downpull force recommended by the gate specifications (20kPa) can only be used for the gate under low water head. This provides a basis for the adjustment and revision of existing specifications about the intensity of downpull force in high-water-head plane gates. In view of downstream submerged water head on the gate, the quantitative relation between the coefficient of downpull force and that of the submerged water head is proposed. The results provide a scientific basis for the hydraulic design of high water-head plane gate with downstream gate bottom edge.4. The hydraulic characteristics of the anomalous and skew gate slots are studied detailed firstly. The influence on hydraulic and cavitation characteristics by the layout of anomalous slot is analyzed. The effect due to the increasing ratio of the width and depth of the skew slot is studied. Some suggestions are given about the design parameters of the anomalous gate slot. |
PDF Full Text Request