双向贯流式水轮机工况转换过程流动特性研究

潮汐发电机组在运行过程中工况转换频繁，在转换过程中容易引起事故的发生。为了探究潮汐发电机组在过渡过程中的瞬态特性和流动机理，本文基于格子Boltzmann方法（LBM），对贯流式水轮机由正向水轮机工况向泄水工况转换及泄水工况向反水泵工况转换这两个过渡过程进行了数值模拟，计算中采用自定义函数控制导叶和桨叶的运动，模拟得到了两种过程中水轮机工作参数的变化规律以及内部的瞬态流动特性。结果表明：当贯流式水轮机从水轮机工况向泄水工况转换时，单位流量随时间逐渐增加，其泄水单位流量约为初始值的2.88倍，与试验测量值吻合良好，证明了本文采用的计算方法是准确可靠的。在转换过程中，由于流态的变化，转轮叶片吸力面出现明显的低压区，容易引起叶片的空化空蚀。同时，转轮受到的径向力会出现明显的周期性波动，容易引起轴系的振动；而在尾水管内部会产生多个湍流涡，由于内部压力的降低会形成螺旋的空腔涡带。

Investigation of flow characteristics in a bidirectional tubular turbine during switch working modes

A tidal hydroelectric unit switches working modes frequently creating a transition condition that is easy to become the cause of operational faults. To explore the transient flow characteristics of a bidirectional tubular turbine, numerical simulations of the flows were conducted using a lattice Boltzmann method (LBM) focusing on the transients created by two types of switching: turbine mode switched to discharge mode, and discharge mode switched to pump mode. The simulations used self-defined functions to control the movement of guide vanes and blades, as well as variations in the working parameters of the turbine. Further, the internal flow characteristics were also obtained for the two transient conditions. During the flow transition from turbine to discharge mode, the flow rate was found to increases gradually with time and the calculated unit flow rate was found to be 2.88 times the initial flow on completion of the transition agreeing well with the measured values. It shows the accuracy and reliablility of the applied methodology in this research. During flow transition, apparent low pressure occurred in certain areas on the suction surface of runner blades due to flow pattern changes, which may cause cavitation erosion of the blades. The radial force on the runner was fluctuating periodically, being a potential excitation to vibrations in the shafting. Several turbulent vortices in the draft tube were observed and a spiral cavity vortex was formed due to the decrease in internal pressure.