| Aerodynamic-noise became one of the most primary noise sources in high-speed vehicles, especially nowadays when the speed of vehicles is rising and effective noise control methods were proposed with respect to other types of noise. It also can greatly affect driving comfort and environmental sustainability. At the same time, from automotive manufacture point of view, it is important to have the aerodynamic noise predicted and analyzed in the designing stage so as to speed up the development cycle, cut the cost and maintain the market competitiveness.At present, the wind rush noise and wind buffeting noise are considered as the main complaints by customer and there is some problems is existing in computational aerodynamic noise. The current research is to explore a computational method to obtain more accurate aerodynamic noise sources, to analyze the characteristic and mechanism of wind rush noise and wind buffeting noise, to develop new control methods of wind buffeting noise, to provide a reliable theoretical basis and effective research method to decrease the interior noise and improve ride comfort. Therefore, the two-dimension circular cylinder and generic three-dimension mirror models are used to investigate the influence of different SGS models to the exterior aerodynamic noise; in order to get more realistic near-wall flow flied, a wall function and quasi-κ-ε-v2/LES hybrid approach are introduced, and the former is used to compute the exterior aerodynamic noise of blunt body and wind buffeting noise, the latter is used to compute the wind rush noise; A new type sunroof deflector is proposed to control the wind buffeting noise, and the control mechanism is illustrated by simulation, then the effectiveness of the deflector is validated by wind tunnel test; the active control method is employed to control the wind buffeting noise; in the end, the research was applied to the noise control of an actual car model-Zhongqi car. The main research contents are as follows:1. The exterior aerodynamic noise of blunt body is broadband noise in low Mach number, which is induced by surface fluctuation pressure. And the surface fluctuation pressure is also broadband, in which low frequency components are attributed to large scale vortices, whereas high frequency components to small scale vortices. In LES, the small scale vortices are modeled that they can not be resolved directly. Therefore, different pressure fluctuation will be resulted in when different SGS models are chosen. Therefore, the two-dimension circular cylinder and generic three-dimension mirror models are used to investigate the influence of different SGS models, and according to the particularity of the near-wall flow field, the wall function is introduced. Through comparing the computational results with experimental results, the Smagorinksy-Lilly model with wall function is considered as a relatively reasonable approach. Then the far-field sound field is calculated by Lighthill-curle acoustic analogy.2. When the LES is used to compute the exterior aerodynamic noise of automobile, because there is complex separated and reattached flow on the surface of car body, the simple wall function can not meet the requirement of the realistic situation. Therefore, a new hybrid approach which mixes the merit of RANS and LES is proposed. And the selection of the RANS is the key of the hybrid approach. In current research, the three equations model κ-ε-v2is selected as the RANS parts of the hybrid approach, and aiming to the problem of κ-ε-v2, some simplified measurements are adopted to simplify the three equations model. Then the quasi-κ-ε-v2/LES is obtained which is more suitable for computing the automotive exterior flow field. Through comparing the results obtained by quasi-κ-ε-v2/LES with other hybrid model, LES and experimental results, we can get the conclusion that the quasi-κ-ε-v2/LES can get more accurate unsteady exterior flow field, meanwhile, greatly reduce computation resources. The aerodynamic noise can then be calculated by applying Lighthill-Curle integral equation on pressure pulses on surfaces.3. Wind buffeting noise of sunroof, generated by large scale vortices and usually in low frequency, was simulated by applying LES and wall function technique. Compressible fluid must be assumed in the computation of sunroof wind buffeting noise. However, if fully compressible fluid is assumed in the low-march motion case, numerical divergence will be likely to occur. In this dissertation, therefore, a model of weak compressible fluid was applied, add the compressible term into incompressible equation as a source term, to incorporate fluid compressibility while avoid numerical divergence. The accuracy of the method was verified by experiment result.4. In controlling the wind buffeting noise, conventional deflector can only deal with noise in a certain frequency range. This problem was tackled by the introduction of a new type of deflector in this dissertation. Wind buffeting noise can be effectively controlled with independence on driving speed, validated by simulation and wind tunnel measurement, by the implementation of this new type of deflector. Moreover, preliminary progress was achieved in active control of wind buffeting noise based on the understanding of its noise generation.5. The related studies is used to analysis the wind buffeting noise characteristics of an upscale cars when side-windows or sunroof is opened. The analysis result shows: The wind-buffeting noise closely related with the size of side-windows and sunroof, the volume of crew department, vehicle speed. According to the simulation results, some measures are used to suppress the wind buffeting noise, such as in order to suppress the rear window wind buffeting, after B pillar a groove is opened and the rear window is divided; in order to suppress the sunroof wind buffeting, the deflector is added and the sunroof opened position is optimized. Furthermore, in order to obtain a more ideal installation angle and height, the deflector relevant parameters is optimized. In the research of the sunroof open position, an empirical formula is summed up to predict the wind buffeting frequency.In conclusion, this paper systematically conducts an intensive study on wind rush noise and wind buffeting noise, and contributes valuable reference for thinking and approaches to the research on this subject. |
PDF Full Text Request