Research On The Aerodynamic Noise Characteristics And Noise Reduction Of Axial Cooling Fan For Special Vehicle Engine

As a device that provides traction power to the vehicle,the engine of needs to be able to dissipate the heat generated by special vehicles in a timely manner,otherwise the safety of the entire vehicle operation will be affected.As a cooling device for the engine,the axial cooling fan generates an ear-splitting noise when dissipating heat,which causes serious harm to the driver’s physiological and psychological health.Therefore,the noise characteristics of the axial cooling fan and noise reduction measures for special vehicle engines are of great engineering value.In this paper,the noise characteristics and noise reduction measures of the axial cooling fan of special vehicle engines are studied and analysed using a combination of experimental and numerical simulation methods.First,with the reference of national standard design test,the axial cooling fan was tested for aerodynamic performance and noise,and the noise spectrum characteristics of the cooling fan were analysed based on the test data;the percentage of rotational noise of the cooling fan was calculated,and the influence of the static pressure of the fan on the noise was analysed.Finally the sound radiation of the casing vibration was estimated.The research results show that the noise contribution of the fan is mainly rotational noise,accounting for about 90%,followed by broadband noise,accounting for about 10%,of which the rotational noise in the first three orders of blade passing frequency noise is more prominent.With the increase of static pressure,the sound power level of the cooling fan is roughly linearly reduced.Through the static pressure control noise,the need to control the static pressure within a reasonable range.Casing vibration noise sound radiation can be ignored.Secondly,the numerical calculation model of the fan’s aerodynamic performance and noise was established.According to the model,the aerodynamic performance and noise of the fan were calculated,and the predicted results were compared with the test results.The internal flow field characteristics of the axial fan were analysed and the specific noise source parts were identified.The far-field noise characteristics of the axial fan and the correlation between the flow field and the sound field was analysed.The results of the study show that the predicted results of the aerodynamic performance and noise of the fan are in good agreement with the test results.The maximum pressure of the dynamic impeller is mainly distributed at the leading edge of the blade and at the trailing edge of the blade near the top of the blade.The low pressure area appears at the leading edge of the blade on the suction side.The high pressure area on the surface of the inlet impeller appears at the leading edge of the blade,and the pressure gradient distribution is relatively narrow.The high pressure area on the surface of the outlet blade is mainly distributed at the trailing edge,and the pressure gradient distribution is poor.The sound source intensity of the dynamic impeller and the outlet impeller is greater than that of the inlet impeller.The outer circle of the hub of the inlet impeller,the tip of the rear end of the blade,the tip of the front end of the dynamic impeller,the top of the blade of the dynamic impeller and the part of the outlet blade near the leading edge are the locations where the sound source is prominent.The areas where the sound source intensity is more obvious and the vortex structure is also more prominent.Finally,noise reduction measures(changing the blade mounting angle at the blade root and wavy leading edge structure blade)are proposed for this turbine with regard to the deterioration of the flow field and the bionic design.Based on the validated prediction model,the two noise reduction measures are simulated and their noise reduction mechanisms are analysed.The results show that changing the blade mounting angle at the blade root reduces the noise of the wind turbine by up to 9.6 d B(A),because changing the blade mounting angle at the blade root improves the vortex flow at the impeller grille,reducing the rotational noise of the wind turbine.The wavy leading edge structure changes the pressure gradient distribution at the leading edge of the blade,destroys the distribution of the vortex nucleus and reduces the intensity of the leakage flow at the top of the blade,thus reducing the broadband noise of the fan.The aerodynamic performance,noise characteristics and noise reduction measures of the cooling fan of a special vehicle engine obtained provide engineering references for the research and control of the fan noise.