Research On Calculating Method Of Interior Aerodynamic Noise For High-speed Automobile

With the effective control of other noise sources and the increasing driving speed, the aerodynamic noise derived from the high-speed vehicle has been becoming one of the main sources of interior noise of vehicle. Owing to its serious influence on the comfort of car. we should take immediate measures to research and control it.In this dissertation, at first, by using the FEM software of ANSYS. we take the numerical simulation for external airflow around vehicle with some selected turbulent model. Then, we make a qualitative analyses of the characteristics of the external airflow through the speed distribution and static pressure distribution of surface, and by a direct numerical calculation of N-S equation with the boundary of car shape, we' ve got the numerical solution of fluctuating pressure on the surface of car, which is the main source of interior aerodynamic noise. What' s more, it turns out to be consistent with the experimental results.On the basis of that, we set up a mathematical model of the internal sound field through Helmholtz Equation and Green Function. By Corcos model and Smolyakov-Tkachenko model, through energy flow analyses on a thin transversely vibrating plate, we understand a theoretical solution of the surface vibrating speed of the sheet metal model. Then we make a BEM (Boundary Element Method) Program, calculating the solid sound portion in the interior aerodynamic noise theoretically, and compared with the corresponding experimental results, the results show that there is a good consistence in the low frequency stage and a high error in the middle & high frequency stage.In the meantime, according to the Statistic Energy Analysis (SEA), we establish the solid transmission model and leakage sound model for the car model, and determine the SEA parameters of each subsystem of car model through the theoretical calculation and experimental measure. Then we program a SEA program to calculate the internal noise field theoretically, and the results show that there is a good consistence in the middle &high frequency stage and a high error in the low frequency stage, compared with the experimental results.In addition, we make a series of wind tunnel test for reduced scale model of car, and by this, we research the airflow state of high-speed car, airfield condition of A-pillar, the surface fluctuating pressure of the side plate, the influence of surface fluctuating pressure of side window on the internal noise field and the influence of the leakage of different position on the interior aerodynamic noise.Then, as a kind of innovation, we combine BEM with SEA at the same time to evaluate the interior aerodynamic noise of high-speed car theoretically for the very first time, that is to say, using the BEM to analyze solid sound portion of the low frequency stage in the interior aerodynamic noise, and using the SEA to analyze the solid sound portion of middle & high frequency stage and air sound portion in the interior aerodynamic noise. Through the adding of the air sound energy and solid sound energy, we can get the theoretical results of interior aerodynamic noise, which include the solid sound transmission and leakage noise simultaneously. The comparison with the results of the wind tunnel tests of reduced scale model car, show that the results with the combination of BEM and SEA have better precision than the results, which only use the BEM or SEA respectively. Furthermore, that is more complied with the actual situation of car (especially for the car with a bad seal).