边界层理论在低比转速离心泵叶片设计中的应用

【作者】 马雷；

【导师】 杨军虎；

【作者基本信息】 兰州理工大学 ， 流体机械及工程， 2005， 硕士

【摘要】 低比转速离心泵在工农业领域被广泛的应用。由于低比转速离心泵效率较低,H-Q性能曲线不稳定,长期以来,研究泵内液体的流动规律,以期提高低比转速离心泵效率、增加H-Q性能曲线的稳定性,一直是流体机械研究者关注的课题。 低比转速离心泵之所以效率低下主要原因有:（1）圆盘摩擦损失较大;（2）由于相对流动扩散度大,叶轮内易发生边界层分离。为得到能够使叶轮流道内液体（即边界层）不发生分离的叶片型线方程,本文提出了一种将湍流边界层理论应用于圆柱形叶片型线的设计方法。该方法以N-S方程为基础,给出了雷诺方程,在边界层内对其进行量级比较,得到边界层动量微分方程;对其积分,得到边界层动量积分方程;通过变换的动量积分方程,求得了损失厚度近似解的表达式。分析了叶片边界层内的速度分布规律,运用尾流律推导出各种边界层厚度的表达式,作为求解边界层厚度的辅助关系式;运用了结合湍流边界层厚度系数κ_v和动量损失厚度δ₂由无离心流动计算逐渐逼近离心流动来求解动量损失厚度的计算方法,它是进一步判定边界层分离的基础。依据对主流区速度场的分析,给出了含有速度系数的离心泵叶片型线参数方程:并分析了速度系数边界层分离和理论扬程的关系。最后,分析了上述理论在叶片设计中应用的计算过程。 通过对上述方法的研究,取得以下结论:在进行叶片设计时,既要考虑叶轮参数的情况,又考虑叶片表面中间的流动状态;叶片型线的设计,其整体水平是特别重要的,尤其是结合叶片的沿程变化规律来探索出入口参数的方法更显得有意义。更多还原

【Abstract】 Low specific speed centrifugal pump is used in agriculture and industry in large range . In long time, as the efficiency of low specific speed centrifugal pump is low and Q-H characteristic curve is unstable, the research of the fluid flow law in the pump is an important project of fluid machinery researchers in order to improve the efficiency and the stabilization of Q-H characteristic curve.A method is given that the theory of turbulent boundary layer is used to design cylindrical vane in order to gain the equations of vane’ s modular curve that can not cause boundary layer separateness in the papero Reyonds equations is given on the basis of N-S equation, the relevant quantities are analyzed and momentum integral equation is given. By transitional momentum integral equation the approximate expression of momentum thickness is presented, velocity distributing in turbulent boundary layer is analysed. Wake laws are applied to deduce corressioning expressions of turbulent boundary layer thickness, the expressions are regarded as the auxiliary relational expressions to solve momentum thickness. Amethod is applied that by boundary layer thickness coefficient ks and momentumthickness d2 the fluid calculation without centrifugal force approaches the fluidcalculation with centrifugal force in order to solve momentum thickness . these will be the basis of further analyzing boundary layer separateness. according to the analysis velocity field of main fluid zone, the parameter equations of vane’ s modular curve of low specific speed centrifugal pump are given. The relation of velocity coefficient and boundary layer separateness and theory head is analysed. Finally, the calculation process is given in vane design as the applications on boundary layer theory. Through above study, the following conclusions can be made: In designing process of cylindrical vane’ s modular curve , not only the parameter but also flow properties on vane surface should be considered. Total consideration is very important to design cylindrical vane’ s modular curve, especially the method to study the output and input parameter according to flow properties on vane surface is very valuable.更多还原