可控进口叶片角的圆柱形叶片设计

Research on a New Type of Cylindrical Blades with Controllable Entrance Angles

圆柱形叶片是低比转速离心泵叶轮常用的叶片形式。在过去圆柱形叶片设计实践中,只根据选定冲角准确计算叶片进口边与后盖板相交处的叶片安放角,进口边与前盖板相交处的叶片冲角与安放角则是自然形成的。这种设计过程造成了在上述点处及其附近范围内叶片表面方向与来流方向不匹配,叶片进口边上叶片角随机分布的结果形成了叶片入口不可低估的冲击损失。本文提出的设计新方法则在保持圆柱形叶片二维几何特征的条件下,同时准确确定叶片进口边与前、后盖板相交两点处的流动冲角及叶片角,沿叶片进口边各处叶片角分布改善的结果,将避免过大的叶片入口冲击损失,提升叶轮水力效率。为实现上述目标,叶片表面的平面投影不同于传统设计仅含一条曲线,而是由一等变角螺旋线与一Hermite插值曲线光滑、连续地拼接而成。对这两种曲线各自的优点及适应性进行对比,结果表明,本文新方法形成的圆柱形叶片能在较大运行范围内改进泵的能量指标。

Cylindrical blades are extensively used in low specific centrifugal impellers.In the traditional design process,in order to draw blade projection in plan view,an incidence at the intersection of blade leading edge and inner streamline on the meridional section is selected for calculating the blade angle accurately.Because the incidences and the blade angles at the intersection of blade leading edge and outer streamline,and along the entire blade leading edge,are shaped automatically,the blade angles at these points are not suitable for oncoming flow direction,generating noticeable shock losses along the blade leading edge.In the new design program,after selecting two incidences at the intersections of blade leading edge and the outer and inner streamlines on the blade meridional section,blade angles at both intersections are accurately calculated.This minimized the shocking losses generated by blade leading edge.In conventional design,the projection of blade pressure surface into plan view consists of only one planar curve.However,in the new design way,to obtain an optimum blade angle distribution along the blade leading edge,projection of blade surface into plan view has included two curves joined smoothly and continuously.The first curve is a special spiral curve located at the blade inlet and the second curve is based on Hermite interpolating function located at the blade outlet.Mathematic analysis indicates that geometrical features of these two curves satisfy particular requirements at the blade entrance and exit,respectively.Comparison tests have revealed that untwisted blades configured by the new design can improve pump efficiency in a wide operating range.