Research On Simulation And Control Of Aerodynamic Noise Characteristics In Automobile Side Window Area

In recent years,with the development of science and technology and the improvement of the China's economic level,in addition to basic properties such as practicability and safety,ride comfort has also become an important factor for consumers to choose a car.Due to the maturity of powertrain noise reduction technology and the emergence of quieter electric vehicles,aerodynamic noise contributes more importantly than ever to the ride comfort.The flow field around side window is highly turbulent and close to the passengers,which is known to be a significant source of interior noise.Therefore,it is of great significance to study the generation,propagation and influencing factors of the aerodynamic noise around the side window and propose practical and feasible noise reduction schemes.Based on the simulation method of coupled CFD with vibro-acoustic solver,this paper studies the flow field and aerodynamic noise characteristics of the side window area of the car.The main research contents are as follows:First,a simple cabin model was established to study the mechanism of aerodynamic noise,and the accuracy of the simulation is verified by comparing the simulation results with the experimental results.External turbulent flow induces strong wall pressure fluctuations on the side window,which excites side window glass vibrations and generates noise.The pressure field indicates that the wall pressure fluctuation can be split in two contributions acting on the side window: a turbulent contribution caused by the aerodynamic pressure fluctuations acting directly on the side window and an acoustic contribution due to the noise generated by the turbulent structures themselves and propagating to the side window.Pellicular mode decomposition and wavenumber decomposition are used to separate the acoustic field and turbulence field from the mixed pressure field on the side window.The differences between the two contributions in terms of wavenumber,energy,propagation direction,transmission efficiency through the glass,and relative contributions to internal noise are studied.Then,the characteristics of aerodynamic noise in the side window area of a real vehicle are studied.The flow field results show that the flow in the side window area can be divided into the following parts: A-pillar vortex,side mirror wake(including mirror hub wake and mirror pedestal wake),sail wake and the reattached flow.The results of the pellicular mode decomposition show that turbulent pressure fluctuation have a distribution characteristic based on regions and frequencies,and the amplitude of turbulent pressure fluctuations decreases with increasing frequency.The acoustic pressure fluctuation has a diffusive distribution characteristic,and it can be inferred that the acoustic source is located at the side mirror based on the distribution shape.The total sound pressure level of interior noise and the contribution of acoustic pressure excitation and turbulent pressure excitation to interior noise are simulated.Then,the influence of different side mirror mounting regions and yaw angles on aerodynamic noise in the side window area was studied.Due to the different mounting regions of the side mirrors,the glass mounted case show strong interaction of the mirror pedestal wake with the side glass while this is absent in the door mounted case.The case without mirror didn't show interaction of the mirror wake with the side glass.The results show that the interior noise level of the glass mounted case is the highest in the three cases,and the case without mirror is the lowest.The yaw angle affects the separation of the flow.For the left front window of the car,as the yaw angle increases from-20° to 20°,the interaction of the A-pillar vortex with the side glass increases,and the interaction of the mirror wake with the side glass decreases.The intensity of turbulent pressure excitation and acoustic pressure excitation on the side window and the interior noise level increase with the increase of yaw angle.Finally,based on the previous research,it is effective to reduce the aerodynamic noise by reducing the generation of sound sources,increasing the distance between the sound source and the receiver,and increasing the sound transmission loss of the side window glass.Based on these theories,several noise reduction schemes are proposed,including improving the shape of the mirror assembly(pedestal,hub and sail),smoothing the transition between the A-pillar and the front windshield,and using laminated glass for the side window.The results show that all schemes are effective in reducing interior noise level,and then the noise reduction mechanism of each scheme is analyzed.