【作者】 王海松；

【导师】 王福军；

【作者基本信息】 中国农业大学 ， 农业电气化与自动化， 2005， 博士

【摘要】 轴流泵是一种量大面广的水泵产品,在大型调水工程、灌溉工程及城镇给排水工程中应用广泛,也常被用作船舶和两栖车辆的推进器,因此,对其效率等性能指标进行深入研究显得尤为重要。本文针对目前轴流泵设计和分析过程中存在的主要问题,建立了完整的计算机辅助设计(CAD)系统,并通过计算流体动力学(CFD)手段,建立了分析和预测轴流泵内部流场及外特性的基本方法。应用实践表明,所提出的轴流泵CAD-CFD系统可快速、高效地完成主要过流部件的2D水力设计、3D实体造型,并可根据CFD分析结果快速判断CAD的设计质量,从而开发出高性能的水泵产品。本文的主要研究内容和取得的主要成果包括: 采用在CAD中的具有突出优势的面向对象技术,提出了将水力设计中内部数据和方法、外部图形表示及人机交互完整封装的新策略,给出了具体的CAD系统结构图及实施方案。在此基础上,研究了基于特征的自动和半自动建模方法,重点研究了参数化驱动、特征描述法和自定义特征法的特点并综合运用,给出了叶片和其他部件的建模实例以及核心代码,填补了轴流泵三维建模的空白,也为其他流体机械的建模提供了参考。 采用多种计算模式对轴流泵流场进行不同方案的数值计算。研究表明:(1)单通道方案具有简单快速的特点,而全流道计算虽然计算量大,但是预测结果更接近实验值;(2)计算区域的进口采用均匀速度进口、位置选为泵的进口是合适的;(3)计算区域的出口条件采用充分发展流,位置相对泵的出口延伸约叶轮直径的10%时,可取得最佳的计算结果;(4)局部加密对轴流泵的计算精度有比较重要的影响,在网格总节点数基本保持不变的前提下,对叶片附近进行细密的网格划分,可明显提高计算精度。文中选择了一低扬程轴流泵作为实例,预测了泵的内部流场特性及其外性能,并将外特性和实验值进行了对比,在采用全流道方案、近叶片区局部加密的前提下,采用约20万混合节点的网格模型时,扬程预测值相对实验值的误差的绝对值在4.5%以内,功率误差约为3.1%,总效率误差约为4.1%。研究还发现,叶片正面和背面的速度、压力分布有着明显的规律,背面的低压区和汽蚀区域相吻合;由于径向间隙的存在,叶片正面靠近轮缘处形成了狭长的带状低压区,叶片轮缘面的速度分布清楚的显示了间隙处的回流。 文中还对轴流泵设计有重要影响的流型进行了全面的分析和研究,指出现有等环量流型存在的不足,提出了改进流型设计:轴面速度在进口边前直线下降、出口边后呈抛物线分布、环量的分布规律由设计人员给定。与常规流型对比,改进流型设计更真实的反应了泵内的实际流动情况,改善了叶片的扭曲,提高了效率。 本文所取得的研究成果对于改善轴流泵设计手段、提高设计水平、改进泵的水力性能有重要的指导意义,具有广泛的工程应用前景。更多还原

【Abstract】 Axial-flow pumps are widely used in the water transfer project, irrigation, town water supply or drainag . They also work for ships and amphicars as thrusters, so it is very important to research their performance, especially the efficiency. To improve the design and analysis of axial-flow pumps, the Computer Aided Design (CAD) system and the basic methods of flow field simulation and performance prediction base on the Computational Fluid Dynamics (CFD) are developed in the paper. The applications show that the 2D hydraulic design and 3D modeling can be carried out satisfactorily, and that the design is evaluated soon according to the CFD results by making use of the CAD-CFD system. Therefore, the pumps with excellent performance could be expected. The main conclusions are as follows:The encapsulation of interior data and methods, exterior drawings, and intelligent user interface is brought forward by adopting object-oriented method. The object-oriented method has special advantages in CAD software. This approach makes the kernel framework and detailed solution of design software together. Furthermore, semiautomatic and automatic methods for feature-based modeling are studied. The performance and applicability of three methods including parameter driving, feature describing, and user-defined feature are grouped for the modeling of all parts including blades. The key program is offered. The proposed techniques could be used for other hydraulic machinary modeling.The flow field of an axial-flow pump is simulated under different grid patterns and different boundary conditions. The results are compared. (1) The performance is calculated quickly and simply through the single pasage, but it is not as accurate as the full pasage acoording to the experiment data; (2) The model inflow boundary can be assumed to be uniform velocity inlet that placed in the pump intake; (3) The outlet location is extended at least the tenth impeller diameter from the pump exit because the outflow boundary condition is obeyed in fully-developed flows; (4) The preciser flow field is obtained if the important parts grid are meshed better on condition that the mesh nodes are equivalent.The model of a low head pump selected for the field calculation and performance prediction is established. Its mesh nodes are about 200,000 for the full pasage and the parts near blades or vanes are meshed well. To compare with the experiment data, the prediction precision for pump-head is within 4.5%, the power’s is 3.1%, and the efficiency’s is 4.1%. The contours of flow parameters are investigated, the velocity and pressure of blade surfaces vary regularly. The low pressure area of blade suction surfaces accords with the cavitation region. The downstream backflows are obvious and a low presure band along the blade working surface outer edge is shaped because of the radial interspace between the impeller and pump body.At last the variable-distribution of design parameters is studied. A new distribution is proposed for the sake of the disadvantage of the constant circulation at present. The axial velocity in fornt of the blade intake along the radius reduces linearly, and the velocity trendline behind the blade export is close to parabolic curve, but the circulation should be decided by designers. The distribution performs factually, so the blade is distorted gentle and the efficiency should be improved.The study is of significance to axial flow pumps design and woud be helpful to improve the dydraulic performance.更多还原