泄洪消力池水流流态对有效削弱下泄水流能量，保障枢纽结构安全及其下游河道河岸稳定与通航建筑物引航道口门区通航水流条件具有重要影响。以向家坝枢纽高低跌坎式出流消力池为例，采用雷诺平均纳维-斯托克斯（Reynolds-averaged Navier-Stokes）方程，Realizable k-ε湍流模型和VOF自由表面追踪模型，建立用于复杂固壁边界条件下具有大自由液面变形的强非线性水气二相流三维数值计算模型，对坝面泄洪射流及其在消力池内的流动特性进行模拟研究。首先，基于向家坝枢纽单池泄洪水流运动物理模型试验，通过对比坝面泄洪射流产生的消力池下泄水流流态及表孔与中孔坝面时均压强的模拟结果与实测数据，验证本数值计算模型的模拟精度。在此基础上，模拟分析表孔、中孔单独泄洪及表、中孔联合泄流情景下消力池射流形态、水流结构及消力池与尾坎水面波动特性。结果表明，对高低跌坎式出流底流消能消力池，在相同泄洪流量条件下，不同的表、中孔坝面泄洪调度方式显著影响消力池淹没射流的三维水流运动结构；表、中孔联合泄流可实现多层多股射流的强烈掺混、有效耗散下泄水流能量、降低消力池及尾坎水面波动；所建立的三维湍流运动数值计算模型能够较好地再现高速射流及消力池水流运动。

The flow pattern and its characteristics in the flood discharge stilling basin with step-down floors play dominant roles in effectively dissipating the discharged flooding water energy, guaranteeing the safety of the hydraulic structure and its downstream river bank stability as well as navigable flow conditions. A three-dimensional numerical model for water-air two-phase flows with strong nonlinearity, involving large free surface deformation and complicated solid-wall boundary conditions was established, and was applied to analyze flow characteristics in Xiangjiaba flood discharge stilling Basin with step-down floors. RANS(Reynolds-averaged Navier-Stokes) equations, Realizable k-ε turbulence model and VOF free surface tracking method were used in the developed numerical model. The model was firstly validated through comparisons of the simulated results and measured data for the flow patterns as well as the time-averaged pressure at the dam surface induced by the flood discharge jet. It is then applied to simulate the 3-D flow structure and fluctuation characteristics in the stilling basin with step-down floors induced by flood discharge from dam under the same discharge amount but different flood discharge scenarios. The results show that, for the flood discharge stilling basin with high and low step-down floors, under the same flood discharge condition, different scenarios of dam discharge gate open mode significantly affects the three-dimensional structure and characteristics of discharged flow in the dissipative pool induced by flood jets. The combined discharge from dam surface and middle holes results in the strong turbulent mixing of submerged multi-layer and multi-jet flows, effectively dissipating the energy of the discharged water and reducing the water surface fluctuations. The established numerical model can better reproduce the high-speed flooding jets and its turbulent motion in the dissipative pool associated with flood water discharge.