自由液面对贯流式水轮机性能影响的数值研究

贯流式水轮机已成为开发低水头和超低水头水力资源及潮汐能的良好机型，但振动、出力不足等问题频繁出现。同时贯流式机组水头与转轮直径之比（H/D1）较小，受比尺效应的影响，依靠模型机所得到的水轮机性能与实际存在差异。鉴于此，文章在考虑与不考虑库区自由液面及水流重力两种情况下对贯流式水轮机真机进行数值研究，对比分析自由液面及水流重力对水轮机性能的影响，并揭示贯流式水轮机内部真实流动状态以及出力不足的原因。研究结果表明：在自由液面及水流重力影响下，贯流式水轮机进口段水流呈现明显的不均匀性，转轮内压力分布由顶部到底部逐渐增大，叶片在旋转过程中要经历周期性的压力波动；不同位置的叶片对转轴产生的扭矩不同，水轮机的出力及效率有较大幅度的下降。研究结果将对贯流式水轮机的设计及运行具有一定的指导意义。

Numerical investigation of free surface effect on performance of bulb turbine

The bulb turbine has become a good model for developing low head or ultra-low head water resources and tidal energy, but the problems of vibration and insufficient output frequently occur. Certain differences exist between the performance of its prototype and that predicted by the model test, due to the scaling effects and the small ratio of water head to its runner diameter (H/D1). This paper presents numerical simulations of a prototype bulb turbine working under two conditions of considering and neglecting the effects of free surface and water gravity, focusing on analysis of the effects in terms of its running performance and the cause of its insufficient output through examining the details of its internal flows. The results show that under the effects of free surface and water gravity, the turbine features a poor uniformity of the flow around its inlet and a gradual pressure increasing from top to bottom, and consequently a blade undergoes periodic pressure fluctuations during its rotation. And the blades at different positions contribute different torques to the shaft and the power output and efficiency of the bulb turbine are decreased considerably.