阶梯-深潭系统的水力特性

Study on hydraulic characteristics of step-pool system

阶梯-深潭系统是山区河流中常见的河床形态，具有稳定河床和消能减灾的作用，其水力特性较为复杂。在温峡水库下游温峡河修建典型的阶梯-深潭系统开展野外实验以研究阶梯-深潭系统的水力特性。利用先进的高频声学多普勒流速仪测量阶梯-深潭系统阶梯上游、阶梯上、深潭中和沿深泓线的水力特性。实验在10 L/s、50 L/s、100 L/s、150 L/s、290 L/s 和 420 L/s 6种流量工况下进行。实验结果表明：阶梯-深潭系统流场尤其是深潭流场具有很强的三维性，阶梯上与深潭中水力特性相差很大。阶梯上沿流向的时均流速远大于横向和垂向的时均流速，三向紊动强度处在一个量级且较小。深潭中的时均流速比阶梯上小，但紊动强度远大于阶梯，紊动强度随流量变大增大。实验工况下，阶梯上的相对紊动强度在0.1左右，深潭中则最大超过8.0。随着水流从阶梯上跌入深潭，机械能大量转化为紊动能消耗。实验流量范围内，雷诺应力随流量小幅增大，深潭中的雷诺应力约为阶梯上的50倍。阶梯-深潭系统消能率在实验工况下为64%-91%。

Step-pool system is a typical bed micro-morphology in high gradient （〉3%） mountain rivers, which creates extremely high turbulence intensity and thus dissipates most of the flow energy. An artificial step-pool system was constructed in the Wenxia River downstream of the Wenxia Reservoir and experiments were conducted to study the characteristics of turbulence in step-pool system. The velocity and turbulence intensity were measured with the three dimensional acoustic doppler velocimeter （Vectrino） made by the Nortek Cooperation. The sampling frequency of the instrument was 200 Hz. The fluctuating velocity was measured at 3 cross sections at upstream of the step, on the step, in the pool and along the thalweg. The flow discharge was controlled stable during the measurement at 10 L/s, 50 L/s, 100 L/s, 150 L/s, 290 L/s and 420 L/s. The results showed that the flow around the step-pool was very three dimensional. At the cross-sections upstream of and on the step, turbulence intensity was small and the mean velocity was high. In the pool, however, the mean velocity was greatly reduced and turbulence intensity became extremely high. The relative turbulence intensity, defined as the ratio of the turbulence intensity over the mean velocity, was around 0.1 at upstream of the step, and increased to 8.0 in the pool. Most of the flow energy transformed from mechanical energy to the tubulence energy as water flowed from upstream of the step to the pool. The Reynolds stress was calculated with the fluctuating velocity components and the results showed that the Reynolds stress in the pool was about 50 times higher than that on the step. Following increasing flow discharge from 10 L/s to 420 L/s the energy dissipation ratio reduced from 91% to 64%.