Study Of CAD-CFD System Of Axial-Flow Pumps

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.