The Study Of Impeller Design Of Centrifugal Fan Based On The 3-D Numerical Simulation

Forward centrifugal fan, such as 9-19,9-26, is widely used in gas transportation and ventilation in industry. But it usually has lower efficiency and more noise than backward centrifugal fan. A new method of optimal design about forward centrifugal fan has developed in this paper, this method is consisted of two parts, one is the aerodynamic design based on a series of design rules, and another is the three dimensional numerical simulation and optimal analysis. The forward centrifugal fan can be changed in backward centrifugal fan use this method and the efficiency improves in the same operation conditions.The main idea is that according to the flow characteristics in impeller, a suitable velocity distribution in blade channel, to control the growth of boundary layer, flow separation in suction side, stratification effects and secondary flow, is determined by design rules, so as to reduce wake region and energy loss in impeller. This design method has obvious advantage over the traditional methods because these rules are from the real flow in impeller. Aerodynamic design mainly controls the relative velocity distribution, and uses a series of rules to choose the better structure. Then the numerical simulation is used for further analysis and optimization.A three-dimensional numerical simulation of the internal flow field in centrifugal fan has been developed with the three-dimensional Reynolds averaged Navier-Stokes equations and RNG k-epsilon turbulent model. The comparison of computational and measured values shows good agreement and the result of numerical simulation gives a good prediction of overall performance including total pressure rise and efficiency. The comparison of the performance and flow characteristics between the different design models and original models is shows that the efficiency of the optimum design model has been increased about 5%, and some flow characteristics, such as flow separation, secondary flow, and jet-wake have been weakened, compared to the original model. Velocity and pressure distribution at different flow rates have been analyzed, and some essential characteristics of the internal flow field, such as flow separation, circulatory secondary flow, and jet-wake structure, have been observed by this numerical simulation. Near the shroud side of the impeller outlet, there are obvious detached flow regions. Also, circulatory secondary flow is seen in the volute because of the impeller-volute interaction. A strong jet-wake flow is found in almost all exits of the blade channels. In some blade channels, especially at low flow rate condition, the flow separation is significant. Additionally, the flow through the gap between inlet and impeller has been observed which is considered to have a remarkable effect on the fan performance.