轴流泵叶轮导水锥型式设计及其流道水力特性模拟

Design of axial-flow impeller guide cone and simulation on hydraulic performance of its passage

为探究轴流泵叶轮导水锥的设计方法，揭示导水锥流场的内部流动特性。基于三维不可压缩流体的雷诺平均N-S方程和k-ε湍流模型，结合典型的收缩曲线，设计了维多辛斯基式、五次方曲线式、双三次方曲线式等5种导水锥。利用Fluent 软件对各型导水锥进行三维流场计算，分析了导水锥流道的流动特性，归纳了导水锥流场的3个流动部分以及流场轴面的速度分布规律。总结了轴向速度分布均匀度、加权平均偏流角随导水锥收缩型面的变化规律。分析各型导水锥水力损失发现：不同型式导水锥水力损失不同，直锥式导水锥损失略小，其他型式的导水锥水力损失相近。对流场均匀性相比较得出：在导水锥流场急剧收缩的断面上，轴向速度分布均匀度降低，速度加权平均偏流角和径向速度梯度增大。导水锥出口段收缩越平缓，整流能力越出色。综合考虑轴向速度均匀度和速度偏流角等指标，维多辛斯基式导水锥的整流能力最优，出口流场均匀性较好。当导水锥长度为叶轮外径的0.25～0.8倍时，导水锥长度增加，水力损失减小，导水锥出口流场品质提升。结合工程实际应用，给出导水锥长度最优取值范围为叶轮外径的0.5～0.6倍。

Axial flow pumps have advantages of large capacity and low head and the impeller is an important component of axial-flow pump. Guide cone is usually installed on the top of impeller and its appropriate design can enhance flow quality of pump inlet, lower turbulivity, make velocity steady, and so on. To meet with engineering demands, find feasible design and investigate the internal flow characteristics of guide cone, we designed different types of guide cones installed on the impeller. Based on three dimensional incompressible Navier-Stokes equation andk-ε turbulent model, SIMPLEC algorithm was applied to solve a discretization governing equation, five different types of guide cones were designed with contraction curves such as Witozinsky, Bicubic, Fifth degree polynomial curves. The CFD method was used to simulate 3D flow field of guide cone. In order to verify the feasibility of simulation models, the guide cones were installed on the impeller and the simulated head and efficiency values were obtained using simulation method same as the flow field simulation of guide cone. Meanwhile, a laboratory test was performed on a DN200 test bench to measure the pumping head, discharge, and other parameters for calculation of head and efficiency. Results showed that the simulated and measured head and efficiency had relative error less than 4%, indicating the feasibility of the simulation method for flow field simulation of guide cones. Simulation on flow velocity of guide cones suggested three flow processes： 1） flow velocity is even in inlet passage and slightly increased; 2） the flow velocity starts to increase and change its direction in contraction passage of guide cone flow field; and 3） the flow field contraction becomes slow in the outlet passage of guide cone. Hydraulic loss of different guide cones varied. The head loss of circular cone was lower than the others. In the sharp contraction cross section of guide cone passage, the uniformity of axial velocity distribution was low, but the velocity weighted average drift angle and radial velocity gradient was high. The rectification capability was better when the contraction at outlet section of guide cone flow field was slow and gentle. Taking into account of uniformity of axial velocity, velocity weighted average drift angle, and the others, the guide cone based on Witozinsky curve had the best rectification capacity and better flow field uniformity. When the length of guide cone was 0.25-0.8 times as impeller diameter, increasing cone length could decrease the hydraulic loss and velocity weighted average drift angle, and improve flow field quality of cone. The results above in combination with practical application, we suggested that the optimal length of the guide cone was 0.5-0.6 times as impeller diameter. This study is helpful to design hydraulic models of high-efficient axial-flow pumps.