| Based on extensive using research results and experiences home and abroad, connecting with the item"the development of heavy commerical vehicle cab"which is a branch of"863"project, this paper optimizes a low-noise cooling fan for a certain heavy commerical vehicle.The study on engine fan is almost using experimental methods in the past, this way has many shortcomings: long designing cycle, high costs and poor product qualitys as well. The method of CFD simulation analysis can overcome the shortcomings, which is used to study low-noise cooling fan in this paper.This paper explaines noise hazards and classification of engine cooling fan noise, analyzes and studies the factors which influents cooling fan noise performance,summarized the study actuality of engine cooling fan noise performance; next the basic idea, governing equations and the solve of governing equations of CFD(Computational Fluid Dynamics) simulation for aerodynamic performance and CAA(Computational Aero-Acoustics) simulation for aerodynamic noise on the cooling fan are discussed; Given the reduction noise criteria of engine cooling fan-ensure the engine cooling performance.This paper simulates one homemade car's cooling fan minutely.First, use CATIA 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 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 sizes.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 about 97,000 cells. Then aerodynamic performance simulation is carried out on the vehicle cooling fan using CFD software FLUENT. The cooling fan region is defined as rotate region in rotating coordinate system. Windsail is defined as static region. Multiple Reference Frame model is apply to couple between the rotate region and static region. The CFD technology based on the Navier-Stokes equations and RNG k?εturbulence model are selected in calculation, SIMPLE algorithm and segregated implicit solver are applied to simulation. The second-order upwind schemes are used to turbulent kinetic energy equations, turbulent dissipation rate equations and momentum equations. Pressure-inlet boundary condition in the inlet and pressure-outlet boundary condition in the outlet. Numerical simulation is carried out on vehicle cooling fan's internal flow. Static pressure, dynamic pressure, and velocity distribution on the blade surface and in airflow between the fan blades are acquired; when aerodynamic performance is emulated, noise analysis uses LES model. According to GB/T 2888-91《Methods of noise measurement for fans, blowers compressors and Roots blowers》, the inspecting point of noise is installed at the rotating axes and the distance to the center of fan is lm.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, and the inspecting point of noise is installed at the rotating axes and the distance to pipeline section inlet is 1m 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 and noise are both smaller than 5%, so it showes that the result is reliable.According to the research problem, this paper chooses six factors from all of the factors which affectes cooling fan noise performance to study. The six factors are the rotating speed of fan,the number of blades,the ratio between wheel and hub,the fixing angle of blades,the blade shape and the unequal angel layout of blades, on whose conditions the mass flow rate and noise are simulated and analysed with FLUENT. The results indicated:①Both mass flow rate and noise has the same trend with the rotating speed;②Mass flow rate is increasing with the increase of the number of blades. When the blade number is less than 9, it increases rapidly and then slowly as it is more than 9. The noise increases by 0.7dB(A) with every blade number increasing 1. When the blade number is more than 10, it increases slowly;③Mass flow rate decreases with the increasing of the ratio between wheel and hub.When the ratio is 0.45, the noise is lowest.Then it increases with the increasing of the ratio;④Mass flow rate is increasing with the increase of the fixing angle of blades. It changes rapidly when the angle is less than 34°and changes slowly when it is more than 34°. With the angle increasing, the noise first decreaces then increases, and there is a trough at the angle of 31°. The overall performance is best when the angle is 34°;⑤Based on the original fan, the blade shape is changed, and a group of fans is self-designed.Among them, the overall performance of NO. S1,S2,S5 and S6 fans is improved to different extents. The mass flow of NO. S6 fan is highest, the noise is lowest and the overall performance is best.Use CATIA to fabricate its optimization three-dimensional model, simulate and research the fan model. The overall performance is improved a lot, which is that the mass flow is increased from 5.221kg/s to 5.703kg/s by 9.23% and the noise is decreased by 4.48dB(A).
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