| Axial-flow fans are widely used in ventilation and fire protection and smoke extraction because of their mass flow, low noise level and stable operation. However the existing fans are of low efficiency and narrow range of operating conditions, hence it is hard to meet the modern industrial request of high efficiency and low energy consumption. The key issue of developing energy-saving products is to implement wide high efficiency performance range in the existing fan with combining CFD technology and optimization theory. In this paper, a low pressure axial flow fan used in industry is chosen as the research object, based on the CFD numerical simulation results,multi-objective optimization design method is used to redesign the axial fan on multi-points, and to validate the feasibility and optimization results of the multi-objective and multi-points optimization system. At the same time, it aims to increasing the total pressure of the fan in multiple working conditions, expanding the range of high efficiency and improving the flow instability.(1) Based on the numerical simulation method, the aerodynamic performance of three-dimensional whole passage model of low pressure axial fan is predicted in whole flow range. And the selected numerical strategies, boundary conditions, the grid size are verified, it shows that optimization design is feasible on the basis of numerical method.(2) A multi-objective and multi-points optimization design process based on CFD simulation is build. Then, through problem of two-dimensional optimization design of CLARKY airfoil, this paper discussed how to build optimization mathematical model in detail, including the optimization variables, optimization constraints and optimization goals. Different experimental design method and approximation model are compared to analyze influences on the optimization results and are also to provide technical guidance for multi-objective design of axial flow fan on multiple working condition.(3) As for the multi-objective and multi-points optimization problem of threedimensional axial flow fan, a single rotor axial flow fan is chosen as the research object,the distribution law of chord length, camber radius length and stagger angle along the radius direction were parameterized through Fourier function, Gaussian function and power function separately. Coefficients of three functions were selected as the design variables. Minimum efficiency, minimum total pressure and maximum power among four working flow rates were chosen as the optimum constraints. The objective functions were weighted average total pressure and weighted average efficiency of four points.Where the weighted vectors were calculated based on the fuzzy set theory. Whole optimization strategy, which including 3-D modeling, 3-D mesh generation, 3-D flow field simulation, experimental design method, approximation method and multi-objective genetic algorithm, was used to optimize the model fan. Finally the research results show that the optimum fan has great improvement on pressure and efficiency during whole mass flow range. And the weighted average total pressure increased by 13.5%, the weighted average efficiency increased by 20.22%.(4) The internal flow and the dynamic characteristics of the fan before and after optimization are studied, the results show that the optimum fan can improve the internal flow field and the stability of flow in low flow rate. Such as reducing the intensity and influence area of the blade tip vortex, improving the pressure distribution in different blade sections along the blade radius direction and reducing the flow separation area and the pressure loss near the hub of the blade.In all,it can obtain great optimum results with multi-objective and multi-points optimization to optimize the axial flow fan, and also provide reference and bases for other type of fan and turbo-machinery. |
PDF Full Text Request