基于DANS方程的粗糙床面明渠水力特性研究

Research on hydraulic characteristics of open-channel flow over rough bed based on DANS equations

基于双向平均NS方程(DANS方程)建立粗糙床面明渠水流数学模型,应用修正的S-A湍流模型对其紊流过程进行模拟,采用涡黏系数法计算明渠湍流在粗糙床面上存在障碍物时的形状应力,结果表明:形状应力在障碍物层以内不可忽略,而在障碍物上部,会迅速减小直至可忽略不计;速度值会随形状应力的增大而减小;障碍物顶部附近的雷诺应力也会因为形状应力的存在而有明显的减小。此外,针对障碍物孔隙率的研究表明:障碍物孔隙率的分布对速度、雷诺应力及形状应力等存在一定的影响,并且当孔隙率的分布越光滑时,其影响越小。

A numerical model of open-channel flow over a rough bed was established based on double-averaged NS （ DANS） equations. The turbulence was simulated by a modified Spalart-Allmaras （ S-A） turbulence model, and the form-induced stress was calculated with a sub-layer-scale eddy viscosity model. The results show that the form-induced stress within the roughness layer cannot be ignored, and it decreased rapidly with the distance above the top of the roughness layer. The form-induced stress accounted for the dispersion of the velocity profiles and caused a slight reduction of the mean velocity. It also significantly decreased the Reynolds stress at the top of the roughness layer. In addition, this study shows that the velocity profile, the Reynolds stress profile, and the form-induced stress profile are affected by the distribution of the porosity. A smoother profile of porosity has less impact on the flow and turbulence characteristics.