岸边并联泄洪洞下游河道冲坑预测

Prediction of river scour in downstream of bankside parallel spillway tunnel

挑流水舌对下游河道的冲刷关系到工程安全。根据动量方程推导了射流在下游水垫中的扩散规律,分析了下游水垫流速对射流扩散的影响,提出了动水垫下射流的临底流速计算方法。研究结果表明:动水流速增加了射流在水中的扩散距离,促进了射流扩散及射流流速衰减,降低了射流临底流速。将研究结果应用于白鹤滩岸边泄洪洞下游河道的冲坑深度预测。模型试验结果表明:在鼻坎水流参数相同的情况下,河道中水流为动水时的冲坑深度较静水时冲坑深度减小约10%,且位于河道下游侧的挑流水舌形成的冲坑深度小于上游侧挑流水舌形成的冲坑深度。与常规预测公式相比,该方法能准确预测不同位置挑流水舌的冲坑深度,研究结果可为泄洪设施下游河道消能防冲设计提供依据。

The river scouring caused by air jet is important to engineering safety. In this paper, the diffusion law of jet flow in downstream water cushion is deduced based on momentum equation, the influence of water cushion velocity on jet diffusion is analyzed, and the calculation method of bottom velocity under moving water cushion is proposed. It is shown that the moving water cushion increases the jet diffusion distance, promotes the jet diffusion and the jet velocity attenuation, and reduces the bottom velocity. The results of the research are applied to the prediction of the depth of the flushing pit downstream of the spillway tunnel of the Baihetan project. It is shown that the scour depth under the condition of moving water cushion is about 10% less than that under the condition of still water, and the depth of the scour pit formed by the flow on the downstream side of the channel is smaller than that formed by the flow on the upstream side of the river. The method proposed in this paper can well predict the depth of the scour pit at different locations, and the experimental results are in good agreement with the calculated results. The research results can provide a basis for the energy dissipation and anti-scour design of the downstream channel of flood discharge facilities.