| Rapid development of vehicle industry brings us some new problems though convenience and comfort. Recent years, vehicle's driving speed has increased greatly as advanced high way's construction. The vehicle's wind noise has become an important problem of both vehicle technology and city environment. Car-body is a three-dimension geometry entity with protrusive objects, so air flow surrounding car is unsteady and easy to be separated, which caused great difficulty to analyze wind noise. In this thesis, numerical simulation and theoretical method were combined to analyze vehicle wind noise. The main work of thesis included:Firstly, theory of vehicle fluid noise and its basic characters were illuminated and physical model with governing equations were described. Three methods for predicting sound noise (direct method, acoustic analogy, broadband noise source model) were introduced and compared. According to the introduction above, the selected methods in this thesis were reasonable.Secondly, considering the effect of mirror and tire to wind noise, two kinds of car model were built with software CATIA. Unstructured mesh type was adopted to generate meshes.Thirdly, Large Eddy Simulation and acoustic analogy method were used to compute wind noise in different spaces around car. By comparing the results of different models, the contribution of side mirror and tire to wind noise was summarized. By comparing the results in different speed, relationship between wind noise and velocity was founded. Noise measuring points were settled on certain parts, by FFT (Fast Fourier Transform), spectrum analysis was done to show the relationship between sound pressure and frequency.Fourthly, through k-ε model and broadband noise source model, acoustic power of car was computed and quantity differences in different driving speed were stated.Optimizing model and reducing noise is final purpose, all efforts above may supply an available way for wind noise analysis of original car. |
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