Study on the influence of contraction ratio of flaring gate pier on flow pattern of high arch dam

Abstract

[Objective] The flaring gate pier contraction jet technology is commonly employed in narrow valley high arch dams to facilitate collision-free flood discharge and energy dissipation of the surface spillway and deep hole. Excessive contraction ratio of the flaring gate pier result in inadequate longitudinal tension of the jet flow, causing water inflow concentration and exacerbating downstream scouring. Conversely, if the contraction ratio is too small, backwater can develop in the flow channel, leading to a potential reduction in the discharge capacity of the surface spillway and degradation of the jet shape. Determining the critical value of the contraction ratio for backwater can serve as a foundation for designing the shape of the flaring gate pier.[Methods] The effects of contraction ratio, initial turning point, contraction section length, weir surface pitch angle, and head on weir crest on the flow state of a flaring gate pier are investigated through hydraulic model experiments and three-dimensional numerical simulations.[Results] The results indicate that, with all other parameters held constant and only the contraction ratio varied, a critical contraction ratio exists for the flaring gate pier. When the contraction ratio falls below this critical value, backwater flow occurs in the surface spillway. Through over 360 calculation cases, 48 sets of experimental data on the critical contraction ratio are collected.[Conclusion] The results provide a quantitative relationship between the critical contraction ratio and the head on weir crest, stereotyped design head, height difference between the crest and initial turning point, length of the contraction section, and angle of the weir surface. The formula's high accuracy has been verified, providing valuable reference for designing the flaring gate pier of a high arch dam.

Keywords

surface orifice / flaring gate piers / model test / numerical simulation / head on weir crest / contraction ratio