涡轮出口旋流对扩大管压力回复性能的影响

为了研究涡轮出口旋流动能对入口锥角较大的直线型扩大管压力回复性能的影响,采用数值仿真的方法对其流体力学机理及规律进行探讨.选用可动翼灯泡贯流式水轮机作为研究对象,经水轮机进水管入口、固定导叶、导水机构叶栅、涡轮至尾水管（扩大管）出口实施了三维整体流动数值计算,计算了多运行工况下尾水管压力回复系数Cp,水力损失和比水能损率δD,得到了直线型扩大管内最优旋回动能与最大压力回复性能之间的流体力学关系,进而对于尾水管的水力性能进行了预测.提出了新定义的尾水管出口动能歪曲度Iek,进行了不同旋回入流条件下尾水管内部流动动能的比较.结果表明：Iek和Cp存在一定规律的内在关系,当尾水管动能歪曲度Iek具有最小值时,尾水管压力回复系数Cp最大、比水能损率δD最小.新提出的Iek可作为可动翼贯流式水轮机直线型尾水管内含旋回流动流体品质的评价指标.

Effect of runner outlet swirling flow on diffuser pressure recovery

In order to study the effect of swirling kinetic energy at runner outlet on the pressure recovery performance of a straight diffuser with a larger cone angle,the hydrodynamic mechanism and rules behind the effect were investigated with computational fluid dynamics.A bulb turbine with adjustable guide vanes and runner vanes was employed as the model.The 3D flow through the whole channel of the turbine,from the inlet to the case including bulb and stay vanes,guide vanes,runner vanes to the outlet of draft tube（diffuser） was computed.Through calculating the pressure recovery coefficient Cp and the specific hydraulic deficiency δD of the draft tube in a wide operating range,a hydrodynamic relationship between the optimum swirling kinetic energy and the maximum pressure recovery in the straight diffuser was established,subsequently,the hydraulic performance of the draft tube was predicted.A new parameter,named kinetic energy distortion rate Iek at the outlet of diffuser was defined,and the pattern of kinetic energy in diffuser was compared under various inflow swirls.The result revealed that there is a clear correlation between Iek and Cp,that is,when the distortion rate Iek is minimum,the recovery coefficient Cp is the peak and the deficiency δD is minimum.Thus,the new parameter Iek can be used as an index for evaluating the quality of swirling flow through a straight draft tube in the bulb turbine with adjustable guide vanes and runner vanes.