| With the rapid development of the automotive industry, China has a growing volume of vehicles. Vehicle exterior noise pollutes the environment seriously and vehicle interior noise reduces ride comfort remarkably. Therefore, in order to effectively control and reduce vehicle noise, China government constituted and enacted National Standard GB1495-2002"The limits and measurement of exterior accelerating noise of vehicles"in 2002. With the cooling turbo-charged, direct injection combustion system and high-pressure electronic control injection technology widely used, engine is increasingly intensified with engine load and thermal load more exposed. With the development of engine design and technics, the optimization of combustion and the installation of muffler, mechanical noise, combustion noise and intake/exhaust noise has been effectively controlled, the specific weight of cooling fan noise increased. Therefore, it has a higher requirements for the cooling fan: to meet the cooling system, the cooling fan speed need grow higher and bear a greater load; in the other hand to meet noise limits, the cooling fan must reduce noise radiation.This paper first learned about noise hazards and the basic theory of cooling fan and summarized the state of cooling fan's research.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.Then according to test method about aerodynamic performance and aerodynamic noise on the cooling fan in FAW Technology Center, aerodynamicperformance and aerodynamic noise are tested under different speed on five cooling fans of two groups. Test results are as follows:1,For the same cooling fan and keeping the speed of cooling fan constant, with the mass flow rate of cooling fan increased, the static pressure of cooling fan goes down, the static pressure efficiency of cooling fan goes up first and then goes down, the input power of cooling fan goes up just a little, the SPL (sound pressure level) of cooling fan goes down first and then goes up. When the SPL of cooling fan reaches a certain value, the changes of mass flow rate do not influence the SPL of cooling fan.2,For the same cooling fan and keeping the mass flow rate of cooling fan constant, when the speed of cooling fan increases, the maximal mass flow rate of cooling fan increase, the input power of cooling fan increases, the SPL of cooling fan increase. This indicates that the increase of cooling fan speed can improve the cooling capacity, in the same time the input power of cooling fan become greater and the SPL of cooling fan become higher.3,For the same cooling fan and keeping other parameters of cooling fan constant, when the cooling fan diameter increases, the static pressure of cooling fan increase, the maximal mass flow rate of cooling fan increases, the input power of cooling fan increase. Therefore the increase in the cooling fan diameter can improve the cooling capacity, in the same time, as the increase in the cooling fan speed, the input power of cooling fan become greater and the SPL of cooling fan become higher. However, increase the cooling fan diameter makes the SPL of cooling fan noise increase smaller than increase cooling fan speed to acquire the same cooling capacity.4,A loop fan can avoid eddy losses at the end of blades in the open fan and decrease friction and impact losses of continuous air at the end of blade in the open fan, the loop fan can improve the efficiency of cooling fan as well as reduce the SPL of cooling fan.Then aerodynamic performance and aerodynamic noise simulation are 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 staticregion. Multiple Reference Frame model is apply to couple between the rotate region and static region. The inlet and outlet of cooling fan are extended properly and the entire calculation area of cooling fan is divided into 4 region: cooling fan region, windsail region, inlet region and outlet region. Body-fitted grid is used in the blade surface and the mesh grids in the blade surface are refined, structured / unstructured hybrid grid are acquired. The CFD technology based on the Navier-Stokes equations and RNG turbulence model are selected in calculation, SIMPLE algorithm and segregated implicit solver are applied to simulation. The second-order upwind scheme are used to turbulent kinetic energy equations, turbulent dissipation rate equations and momentum equations. Two different boundary conditions that choose pressure-inlet boundary condition in the inlet and pressure-outlet boundary condition in the outlet and select mass-flow-inlet boundary condition in the inlet and outflow boundary condition in the outlet are adopted. No-slip adiabatic boundary conditions in wall and standard wall functions in the near wall region are adopted. Numerical simulation is carried out on vehicle cooling fan's internal flow. Static pressure, dynamic pressure, total pressure and velocity distribution on the blade surface and in airflow between the fan blades and static pressure of the cooling fan-mass flow rate curve are acquired.Aerodynamic noise prediction for the fan often uses semi-empirical formula of simplified model previous. With the progress of computer hardware and numerical techniques, the CAA method to predict Aerodynamic noise of the fan is developed recently. CAA numerical simulation based on the matching technology between LES (large eddy simulation) and FW-H equation is carry out on the acoustic field of cooling fan in this paper. Pressure-inlet boundary condition in the inlet and pressure-outlet boundary condition in the outlet are selected. The sound pressure level (SPL) spectrum and third-octave band sound pressure level and attenuation properties of aerodynamic noise in the pipeline are acquired. It is found that cooling fan noise is consist of Blade-Passing-Frequency noise induced by the periodic unsteady force and broadband eddy noise induced by random force field. The aerodynamic noise spectrum characteristics of cooling fan is a broadband continuous spectrum and there are several prominent component of the regulation. When thesound wave spread along the pipeline, discrete frequency noise attenuation faster than broadband eddy noise.CFD simulation of aerodynamic performance simulation and aerodynamic CAA simulation noise provide important theoretical basis and a new approach to seek the main parameters to influence the cooling fan performance and improve the cooling fan design and enhance the efficiency and reduce noise.At last, the means to enhance vehicle cooling fan efficiency and reduce noise are summarized. Under no changes in the diameter, the wheel/hub ratio, speed, the blade number and other parameters of cooling fan, the cooling fan is improved by optimization design, the plate section of cooling fan is changed from arc-type to wing-type and adjusted installation angle and chord length of blade. Through the flow CFD simulation and aerodynamic noise CAA simulation, it is found that mass flow rate of wing-type fan is greater than arc-type fan in the ideal conditions, but the noise is lower than arc-type fan.
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