Research On Noise Sound Quality For Automobile Aerodynamic Noise Based On LES-FE-SEA And ALE Method

As vehicle speed continues to increase,aerodynamic noise in the passenger compartment has become a crucial issue that affect riding comfortableness.Research shows that excessive aerodynamic noise in the vehicle will not only reduce riding comfortableness,but also increase the fatigue of passengers.Therefore,the level of aerodynamic noise in the car is getting more and more attention by automobile manufacturers.With the development trend of automotive quality research,on the basis of fulfilling the current noise standards and laws,and reducing the sound pressure level,higher acoustic design requirements are proposed for the quality characteristics of aerodynamic noise perceived by passengers.At present,the research on the sound quality of automobiles in China and abroad mainly focuses on the vehicle structural vibration noise.However,no attention has been paid to the sound quality problems of aerodynamic noise in vehicles.Therefore,it is necessary to develop a comprehensive evaluation system and control method based on the in-depth understanding of the specific aerodynamic noise characteristics.Hence,in view of the sound quality problems of dipole noise and wind buffeting noise generated when the vehicle is running at high speed,the numerical simulation are established respectively based on the FE-SEA and ALE methods.Based on the simulation results and the objective parameters such as loudness,roughness and sharpness,the quality characteristics of the two main aerodynamic noise in the vehicle are discussed.Based on the above analysis,a sound quality-based aerodynamic noise equalization control method is studied which provides a new research idea and has important engineering value.The main research contents are as follows:1.Aerodynamics foundation of vehicle aerodynamic dipole noise.The complicated flow field around the car body will generate intense fluctuating pressure when the car is driving at high speed,and the fluctuating pressure is an important foundation and basis for the dipole noise and its quality calculation and analysis.According to the MIRA international standard model and three-dimensional numerical calculation model of outflow field,from the point of ensuring the accuracy of numerical calculation,Re alizable k-? model was established for steady state calculation of flow field.In the process of calculation,the LES equation was used to simulate the fluctuating pressure of the vehicle body surface accurately.The accuracyof the flow field outside the vehicle body and the fluctuating pressure of the vehicle body surface was verified by PIV test and pressure data acquisition.2.LES-FE-SEA model aiming at the radiated noise of dipole in vehicle which can accurately predict the wide-band characteristics is proposed.The theoretical basis and implementation conditions of the FW-H and FE-SEA hybrid methods are introduced in detail.The fluctuating pressure obtained in the CFD calculation is taken as the noise source term.The acoustic Helmholtz equation is solved to realize the numerical simulation of the dipole noise in the passenger department in the wide frequency range.The road test shows that the method has higher computational accuracy in the intermediate frequency range,and compared with traditional finite element method,boundary element method and statistical energy analysis method,this method has comprehensive advantages in both the calculation accuracy and computational efficiency.3.Based on the four psycho-acoustic objective parameters including loudness,roughness,sharpness and fluctuation,the sound pressure level spectral curve is taken as the initial signal of acoustic post-processing.The calculation process of each objective parameter is obtained by Matlab.The objective parameters of the aerodynamic noise were analyzed and compared with the test results.Summarizing the relationship of the sound pressure level and other four parameters with the vehicle speed,which provides an important reference for the assessment of the aerodynamic noise quality of the dipole at the vehicle development stage.4.The calculation method of sound quality of side-window buffeting noise is established for the cavity.The derivation of the relaxation-weak compressible model and the fundamental theory of wind buffeting noise are introduced.The grid style,boundary conditions and the setup of solver,as well as the acoustic post-processing are mainly discussed.The results of simulation and wind tunnel experiments are compared and analyzed.The accuracy of this dynamic calculation method is verified.The relationship between four objective parameters of sound quality and the variation of sliding baffle opening degree are revealed.The corresponding mechanism of these changes is analyzed in detail,which provides a new research idea and method for the design of cavity wind buffeting noise.5.The calculation and analysis of automobile side-window wind buffeting noise sound quality under window dynamic open condition.Considering the vehicle has complex shape characteristics,the model is simplified,the moving mesh technology based on ALE method is introduced into the simulation of wind buffeting noise,andafter the corresponding acoustic post-processing,the objective parameters of sound quality are obtained.The generation mechanism of the wind buffeting noise of the left front window and the rear left window is analyzed.The calculation accuracy of the wind buffeting noise is verified by the road test and the fixed opening method.This paper elaborates the objective laws of the wind buffeting noise sound quality of the left front and left rear windows under the different vehicle speed and the opening degree of the side windows,and its internal mechanism is also analyzed.Finally,in view of the traditional sound pressure level and the four parameters of the objective parameters of sound quality,the reasonable suggestion is proposed for ventilating the passenger compartment.6.Aiming at the multi-attribute features of automotive aerodynamic noise,a noise reduction method that can balance the noise quality objective parameters in the passenger compartment is adopted.Aiming at the dipole noise in the vehicle,the multi-layer sound-absorbing material is arranged in the interior by combining the multi-objective optimization method and the genetic algorithm,which can control the objective parameters of the sound quality evenly.Aiming at the wind buffeting noise in the vehicle,through the noise reduction measure of placing the bionic rain gear near the side window,the main structural parameters of the front and rear rain gear are respectively designed as the variables,and the multi-objective optimization is performed with the genetic algorithm.In summary,the calculation method of automotive aerodynamic noise based on LES-FE-SEA and ALE provides an effective numerical prediction way for aerodynamic noise sound quality in the vehicle.This paper systematically studies the noise quality characteristics of dipole noise and wind buffeting noise,the equalization control for objective parameters of such two noise is presented,these work provide idea and reference to predicting and evaluating of the aerodynamic noise level at the automotive development stage.