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Abstract: In order to achieve non-impinging flood discharge between surface spillway and deep outlet jet flow and energy dissipation and reduce downstream impact load, flaring gate piers are utilized to disperse jet flow in the surface spillway of many high dams located at narrow valleys. The concentrated load of the water inlet flow will aggravate the downstream erosion when the outlet of the surface spillway narrows too much or too little. In order to reduce the issue of downstream impact concentrated load, it is critical to find the appropriate contraction ratio of flaring gate piers for the design of surface spillway. The influence of the contraction ratio of the flaring gate piers on the impact pressure distribution of the bottom plate of the downstream plunge pool and the influence of the position of the initial contraction point of the flaring gate pier, the length of the contraction section and the angle of the weir surface on the critical contraction ratio are studied by combining the physical model experiment and the three-dimensional numerical simulation experiment. The results show that under the condition of 0.813Hd head on weir crest, 2.71Hd (30m) contraction section length and 35 ° weir surface pitch angle, when the surface spillway is in the supercritical shock wave flow, the maximum impact pressure of the bottom plate is the highest when the contraction ratio is 0.3, which is 1.54 times of the maximum impact pressure under the free falling flow state when the contraction ratio is 1. When the contraction ratio is 0.18, the maximum impact pressure of the bottom plate is the smallest, which is 0.77 times of that when the contraction ratio is 1. The maximum impact pressure of the bottom plate under the backwater flow state is all higher than the maximum impact pressure when the contraction ratio is 1. Among them, the maximum impact pressure is the highest when the contraction ratio is 0.129, which is 1.56 times that when the contraction ratio is 1. The contraction ratio corresponding to the minimum value of the maximum impact pressure of the bottom plate is slightly larger than the critical contraction ratio. Under the conditions of 0.813Hd head on weir crest, 35 ° weir surface pitch angle and 2.71Hd (30m) contraction section length, with the initial contraction point increasing from 0.275 to 1.538, the critical contraction ratio increases from 0.130 to 0.218. Under the condition of 0.813Hd head on weir crest and 35 ° weir surface angle, the critical contraction ratio decreases from 0.157 to 0.110 with the increase of contraction section length from 2Hd (22.5m) to 3.39Hd (37.5m). Under the condition of 0.813Hd head on weir crest and 2.71Hd (30m) contraction section length, the critical contraction ratio decreases from 0.206 to 0.113 with the increase of weir surface pitch angle from 20 ° to 40 °. According to the experimental results, the formulas for calculating the critical contraction ratio, the initial contraction point, the length of the contraction section and the weir surface pitch angle are given quantitatively, which provides support for the design of the flaring gate piers of surface spillway in high dam.
Year: 2024