Analysis And Reduction Of Aero-dynamic Noise Of Automobile Sunroof

With the increase of vehicle running speed,wind noise will become the main noise source and the most disgusting noise for drivers and passengers.At the same time,noise is an important index to evaluate the comfort and quality of vehicles.Because there are two kinds of loads in aero-dynamic noise,sound wave and turbulent wave,they are separated according to their wave numbers;The distribution of external aero-dynamic noise ranges from tens to thousands of Hertz,and each analysis method has its own adaptive range.Therefore,the finite element method and statistical energy analysis method are used to predict the low-frequency and medium high-frequency noise of automobile sound cavity respectively.After analyzing the noise contribution by power flow method,the acoustic package of automobile sunroof is optimized.The specific research contents of this paper include:Firstly,the triangular coordinates of the points are obtained by the automobile optical scanner,and the points are fitted into a curve.The simplified data of 1:1 is used to model the aero-dynamic structure of the vehicle.Fluent is used to simulate the motion process of the vehicle with a speed of 72km/h.After simulating the simulation analysis method of aerodynamic noise,it is finally determined to use the SST k-ω method for steady-state loading,and then take the steady-state result as the initial condition of large eddy simulation,and carry out 1000 steps of simulation operation to obtain the external excitation load of the vehicle sunroof.According to the different wave numbers of acoustic wave and turbulent wave,the fluctuating pressure of flow field is decomposed into turbulence component and acoustic component by wave number decomposition method,the separation of different characteristic loads is realized,and the energy of acoustic component and turbulence component at different frequencies is obtained.Aiming at the noise below 200Hz,a finite element model suitable for predicting the sound pressure level of low-frequency automobile cavity is established.The turbulence component and acoustic component are loaded to obtain the sound pressure level of automobile cavity noise at low frequency.Aiming at the medium and high frequency noise of 200Hz～4000Hz,a statistical energy model suitable for medium and high frequency noise analysis is established.The model includes 27 subsystems and 4 cavity subsystems.The modal density,internal loss factor and coupling loss factor of the statistical energy model subsystem are calculated by theoretical calculation method.After loading the acoustic component and turbulence component,The sound pressure level of vehicle cavity noise in medium and high frequency band is obtained.After the connection of low frequency and medium high frequency noise,the response analysis of cavity noise in different frequency bands is realized.The energy transfer between different systems is simulated and analyzed by power flow method,and the contribution of acoustic turbulence component,acoustic component and other structural subsystems to cavity noise is obtained.Based on the statistical energy model,the sound absorption coefficient of felt is simulated and analyzed,and the influence of thickness on the sound absorption coefficient is explored;The sound absorption coefficient of the acoustic package in the front wall and floor of the car is simulated and analyzed.The theoretical and simulation comparison of sound insulation performance is made to verify the accuracy of statistical energy sound insulation model.For the acoustic package of the sunroof,taking the thickness as the variable,the genetic algorithm is used to optimize the quality of the acoustic package and the sound pressure level of the sound cavity.After finding the optimal solution,the objectives of lightweight of the acoustic package and noise reduction of the sound cavity of the sunroof are realized.