考虑射流掺气的改进冲刷模型

摘要

基于受高速射流冲击的水垫塘中掺气对岩块稳定性影响的系统试验研究，本文给出了一种基于物理特性冲刷模型的适应性研究成果。在综合冲刷模型中实现了对射流掺气模型的改进，使其得以再现有关冲刷形成的物理–机械过程，其中涉及三相，即水、岩体和空气。改进方法考虑了因挟带气泡引起的掺气射流动量减少以及射流扩散剪切层的能量消耗。岩块从岩体脱离取决于掺气的时均压强系数及修正的最大动力冲击系数的组合，对于深水垫塘中的高速射流，该系数为定值0.2。上述改进模型的模拟结果与卡里巴大坝冲坑原型观测结果吻合良好。%Based on systematic experiments on the influence of air entrainment on rock block stability in plunge pools impacted by high-velocity jets, this study presents adaptations of a physically based scour model. The modifications regarding jet aeration are implemented in the Comprehensive Scour Model (CSM), allowing it to reproduce the physical-mechanical processes involved in scour formation concerning the three phases; namely, water, rock, and air. The enhanced method considers the reduction of momentum of an aerated jet as well as the decrease of energy dissipation in the jet diffusive shear layer, both result-ing from the entrainment of air bubbles. Block ejection from the rock mass depends on a combination of the aerated time-averaged pressure coefficient and the modified maximum dynamic impulsion coef-ficient, which was found to be a constant value of 0.2 for high-velocity jets in deep pools. The modified model is applied to the case of the observed scour hole at the Kariba Dam, with good agreement.