The Study Of Optimization Design For Centri-Fugal Fan Impeller By Controlling Velocity Distribution And Internal Flow Analysis

Centrifugal fan is a kind of universal machinery which is used widely in our life and industry, energy consumption is huge, especially for large centrifugal fan. A method of optimization design for centrifugal fan impeller by controlling velocity distribution has developed in this paper, the fan can be easily redesigned by use of this method and the efficiency improves in the same operation condition, then a prediction of overall performance and the analysis of the flow field have been done based on numerical simulation.The design method is aimed at controlling internal flow of impeller, which is the growth of boundary layer, flow separation, secondary flow and stratification effects, in order to reduce the flow loss. The flow control parameters, such as reduction ratio in the inlet velocity and the overall reduction ratio of velocity, are set up based on the analysis of flow characteristic, these parameters effect internal flow and directly relate to velocity distribution. In order to study these parameters whether or not realize optimization design of impeller, firstly, the integral equation of turbulent boundary layer, which is considered the influence of rotation and curvature, is used to analyze the affection of velocity distribution on the growth and separation of boundary layer, then the relationship between the velocity distribution and secondary flow, stratification effects are discussed, the results show that the velocity distribution can represent the control of internal flow. A mathematical model for optimizing the velocity distribution is developed, this model is divided in two cases, if the flow separation will not happen, the velocity distribution is optimum when the boundary layer of outlet has minimum thickness; if the flow separation occurs inevitably, the best velocity distribution will get when the flow separation happen at latest, the pressure and load requirements must be satisfied during optimization. Finally, the blade shape will be determined by the relationship between velocity distribution and blade angle.The optimum impeller was constructed and tested to verify the reliability of the method. Test result shows that the efficiency has been increased about4.45%in design point, and equally increased about5.01%in whole working condition. The results of numerical simulation show that flow separation in the flow passage near volute tongue, and secondary flow in outlet of impeller have been weakened, stratification effects in large flowrate is restrained obviously.