CFD Analysis And Low-noise Optimization Design On Vehicle Engine Cooling Fan

Based on extensive reading about literature home and abroad, connecting with the item"the analysis and control of vehicle noise"which is a branch of"863"project, this paper optimized a low-noise cooling fan for a certain domestic vehicle.The study on engine cooling fan was using experimental method in the past, this way had many shortcomings, long design cycle, high cost and product quality was not good also.In this paper, the method of CFD simulation analysis is used to study low-noise cooling fan.This paper explained the principium of engine cooling fan's two kinds of noises--rotating noise and turbulence noise;Introduced the two kinds noises'mathematical calculation formulas;Summarized the study actuality of engine cooling fan noise performance;Imparted the factors which influence cooling fan noise performance; Given the reduction noise criteria of engine cooling fan—to ensure the engine cooling performance.This paper simulates one homemade car's cooling fan minutely.First,using Pro/E to fabricate its three-dimensional model;Later,import it into GAMBIT which is a preprocessor software of FLUENT and according to cooling fan experimental device to build CFD simulation model.The simulation model contains four segments,rotating fluid section,pipeline section,inlet section and outlet section;Because the simulation model is complex, mesh every segments with different size.The cell of rotating fluid section is the smallest, the cell of pipeline section is larger and the cell of inlet section and outlet section is the largest. The final model is structured/unstructured hybrid grid, and all of those segments are meshed 296228 cells.Boundary conditions are defined in FLUENT. Fluid's temperature transformation range is not vast in conduit,and it affects medium's attribute very little,so flowing medium is used standard air.The flow analysis uses standard k -εmodel, and noise analysis uses LES model,the rotating speed is 2100r/min. The inspecting surface of mass flow rate is installed in pipeline section outlet,andthe inspecting point of noise is installed at the rotating axes and the distance to pipeline section inlet is 1m which according to GB/T 2888-91《Methods of noise measurement for fans,blowers compressors and Roots blowers》.The result indicates that the error of mass flow rate is only 0.2% and noise is 1.23%,both of them are smaller than 5%,so it shows that the result is reliable. Combining with the research problem,this paper choose seven factors from all of the factors which affect cooling fan noise performance to study .The seven factors are the number of blades(i ),the ratio between wheel and hub(υ),the fixing angle of blades(βA),the rotating speed of fan (n ),the unequal angel layout of blades,the blade type and pitch.The results indicate:①Mass flow rate is decreasing as the increasing of the number of blades,meanwhile noise is increscent;②The affection rule of the ratio between wheel and hub is the same with①;③Mass flow rate is increscent as increasing of the fixing angle of blades,but the noise is different.When the angle is samller than 20,they have opposite changing trend,as the angle is larger than 20°,the changing trend is uniform;④Both mass flow rate and noise have the same trend with the rotating speed;⑤Appropriate unequal angle layout of fan blades can improve the performance of cooling fan.As four blades fan,the blades by 70°-110°-70°-110°layout is a good one;⑥when pitch angle less than 15°,the mass flow rate of wing-shaped blades fan increased with the increase of angle;When pitch angle greater than 15°,the mass flow rate showed a downward trend;Noise transform with the pitch angle's change is undulate,and 10°is a watershed;Less than 10°,noise decreases with the increasing of pitch angle,larger than 10°,noise increases with the increasing of pitch angle.According to the rules that various factors affect the performance of fan,the original fan is optimized.The optimal fan has the same rate of wheel and hub,with four-wing-shaped pitch blades,and the pitch angle is 10°, the fixing angle of blades is 20°,and the blades layout by 70°-110°-70°-110°.Simulation analysis shows that the optimal fan has a better performance than the original fan.The mass flow rate increases by 13.5%,and noise reduces by 2.48dB(A).