Study On Characteristics And Mechanism Of Buffeting Noise Base On LBM-LES

With the rapid development of China’s highways and the popularity of automobiles,highway travel is becoming more and more popular.During the high-speed driving,the aerodynamic noise caused by window opening seriously affects the comfort.While the long-term closure of windows,the increase of carbon dioxide concentration are prone to fatigue to induce traffic accidents.It is of great significance to analyze aerodynamic noise in depth.Based on a full-scale vehicle model,the direct computational LBM-LES method and road test are used to research and analyze the broadband aerodynamic noise including buffeting noise.This paper reveals the mechanism of buffeting noise,analyses the main influence factors of buffeting noise,summarizes the variation law of buffeting noise under different conditions,and offers reasonable suggestions of wind opening mode during high-speed driving of vehicle.The main conclusions are as follows:(1)The periodic shearing,migration,collision and dissipation of vortices in the shear layer causes wind buffeting noise.The frequency of vortex shearing in the shear layer at a given vehicle speed more closer to the natural frequency of the chamber,the wind buffeting noise and the velocity fluctuation in the shear layer are more intense.When the frequency of vortex shedding equals the natural frequency of the chamber,Helmholtz resonance occurs and the wind buffeting noise is the strongest.For model vehicle in this paper,Helmholtz resonance occurs when the inflow velocity is 25m/s under sunroof full open.The peak sound pressure is 135.67 dB and the buffeting frequency is 28.00 Hz.(2)Sunroof buffeting noise increases with the increase of opening degree.And there is no sunroof buffeting noise in inclined opening mode.There are three different regions in the flow distribution of the front side-window,and the wind buffeting noise increases first and then decreases with the increase of the opening.The wind buffeting noise of the rear side-window increases with the increase of opening degree because of the dissipation of the mirror wake.And the flow distribution of the rear side-window is more stable.When rear side-window is opened,the gas influx is more than that when front side-window opened,while the gas export and expansion are less.And the scale of vortex is obviously larger.So the wind buffeting noise is much stronger.(3)Wind buffeting phenomenon belongs to low frequency phenomenon.Its wavelength is much larger than the size of chamber.Different positions have the same peak value and buffeting frequency of wind buffeting noise.In the simulation results of the front-side window opening condition,the peak sound pressure increases from the window to the inside due to the interference of the irregular pressure fluctuation generated by the airflow.(4)The maximum value of wind buffeting noise occurs under the opening of maximum wind buffeting noise opening of both windows.“Ventilation Effect” exists in asymmetrical open patterns.It can be used as a measure to reduce buffeting noise.Under symmetrical opening patterns,the fluctuating pressure amplitude increases so that increases the wind buffeting noise.(5)During the high-speed driving,if the sunroof need to be opened separately for ventilation,it is suggested that the sunroof should be opened with less than 60% opening or inclined opening.If the side-window needs to be opened separately for ventilation,it is suggested that the front side-window opening should be less than 40% or more than 80%,and the rear side-window opening should be less than 60%.If there is no special ventilation need,the front side-window should be opened instead of the rear side-window.If there is a need for rapid ventilation and based on “Ventilation Effect”,it is suggested that the opening pattern of sunroof and side-window should be used instead of the single sunroof,and the opening degree of sunroof should not exceed 60%.The opening pattern of front-side window and rear-side window should be used instead of the single rear-side window.The asymmetric opening pattern of two front-side windows should be used instead of the single front-side window.The opening pattern of two rear-side windows should be avoid.If two rear-windows are opened at the same time,the opening degree of each window should not exceed 50%.(6)When the windows are opened,in addition to the special frequency of buffeting noise,there are also broadband aerodynamic noise.The simulation and test results show that the influence of window opening on aerodynamic noise in mid-frequency band is small.