蜗壳轴向出流式低比转数水轮机设计与数值模拟

Design and Numerical Simulation of Volute Axial Outflow Hydraulic Turbine with Low Specific Speed

基于流体机械设计理论和数值模拟分析方法,设计了一种新型低比转数水轮机,其不仅适用于小水电机组的更新完善,也可作为冷却塔风机的直接驱动装置。该水轮机采用蜗壳轴向出水方式,使其径向尺寸约为相似常规水轮机的1/2,除降低造价成本外,更有利于冷却塔内通风;为适应冷却塔内部结构,采用反击式环形叶片作功,在很大程度上降低了水轮机径向尺寸;对应水轮机转轮出水形式,环形尾水管进水模式将尾水接入对称布置的4个布水管,均匀出水结构在很大程度上改善了尾水管内流场,同时可使水轮机直接安装在中心基座上。数值模拟结果表明:蜗壳出口速度满足等速度矩定律,采用轴向出水方式的反击式水轮机的流场分布符合要求;水轮机预测效率约90%,各部分水力损失均较小。

Considering the trend of small hydropower towards low head,and reusing the water surplus head of cooling tower,a new type of turbine with small size,high efficiency and super low specific speed was proposed to be as direct drive for fan in large cooling tower or applied in small hydropower plants for generating electricity,which was designed and validated based on design theory of fluid mechanics and validation method of numerical simulations. Combining binary theory and spiral potential flow to design the flow streamline in volute,the new type volute adopted axial outlet to ensure the turbine radial dimension was about half compared with similar conventional turbines,this kind of structure was a great benefit to decrease manufacturing cost,which was more conducive to ventilation in cooling tower. The work of impact annular blades reduced the turbine specific speed to a large extent which adapted to the internal structure of the cooling tower,the tangent of runner blade was perpendicular to the runner axis.Corresponding to the runner outlet,draft tube was designed with annual inlet,the water flow through the four water distribution pipes in the draft tube which was propitious to improve flow field performance in draft tube,meanwhile,the turbine was able to mount on the central base directly with this structure.Theoretical calculation on hydraulic loss in each domain was given and it was compared with corresponding data that acquired from numerical calculations; the results showed that the hydraulic loss in each domain was relatively small, and differences between them were less than 5%. Numerical calculations were carried out with model which was built in Solidedge and meshed in ICEM,SST k-ω was used in all simulations to capture fluid details,while monitoring points were located on guide vane andrunner blade for obtaining pressure values. Numerical results showed that velocity at the volute outlet was consistent with constant velocity moment law and the flow field characteristics illustrated this model with good performance,and the predicting efficiency was around 90%.