Research Of Noise Reduction Method And Structure Improvement Design Of Engine Cooling Fans

With the development of powerful engines,the heat removed by cooling system increases.Besides,the space remaining for cooling system decreases as the number of components arranged in the engine compartment increases.The most method to enhance heat dissipating capacity of the cooling system is to improve the rotation speed of cooling fans,which will lead an obvious rise in noise.Therefore,the key to improve overall performance of cooling fans is to solve the contradictory relationship between aerodynamic and acoustic performance well.Due to the dominant influence of blade shape on its performance,it is of great significance to study the design of cooling fans' blade structure.Based on fluid dynamics and aeroacoustic theories,this paper carried out an in-depth research on the blade structure,including its influence on aerodynamic and acoustic performance and its optimized design.The basic parameters of camber line and thickness curve of the planar blade shape were defined firstly.And a parametric model of a cooling fan provided by a cooperative company was built.Then the flow field and acoustic field model were established successively.The numerical simulation of aerodynamic and acoustic performance were implemented with CFD/CAA coupling method.The comparison results between simulation data of parametric model and test data of original model indicate the accuracy both of parametric modeling method and simulation method.An orthogonal test was arranged,with structural parameters of planar blade shape as test factors,flow and noise value as evaluation indexes.It aimed at analyzing the influence rules of these parameters on fan's performance.The results showed that chord length B0 and maximum relative deflection Fmax influence fan's acoustic performance obviously.Finally,with response surface optimization design method,an optimal planar blade shape was put forward.Its noise value at the monitoring point decreased by 5.1% on the basis of satisfaction of flow requirements.In order to realize a further reduction of the fan's noise,this paper proposed a new blade structure,that is,to install wedges on the suction surfaces of the cooling fan with optimum planar blade shape.Another orthogonal test was arranged with structural parameters of wedges as test factors.Its purpose was to investigate the influence of these parameters on fan's performance.The results showed that the number of wedges n and angle ? influence fan's acoustic performance most.The fan with optimum wedge structure parameters was selected to compare with the fan without wedges.The noise value at monitoring point reduced by 8.8% while the flow changed little,which providing a guidance for the development and design of cooling fans with low noise and high performance.