A Study On The Numerical Simulation Of High-Speed Vehicle’s External Aerodynamic Acoustic Field

With the development of high-speed rail and highway,the speed of the vehicle continuously improve. Thanks to the development of vehicle engineering technology, the vehicle’s gross noises (such as the power system noise, power train noise, intake and exhuast noise, etc.) have been effectively controlled and reduced. However, the vehicle aerodynamic noise is six square of the speed, so the aerodynamic noise has been gradually become an important part of the gross vehicle noise. In this paper, based on the Lighthill’s acoustic analogy theory, the bondary element method (BEM) combined with the computational fluid dynamics (CFD) was utilized to analysys the distribution characteristics of high-speed vehicle’s external aerodynamic noise field. The main research work and conclusion were divided into following areas:1) Study of the moving monopole and dipole acoustic source’s directivity factorBased on the acoustic equation in the ideal fluid medium, the generalized Green’s function combined with the Doppler Effect of moving acoustic source were utilized in this paper to study the characters of monopole (point source) and dipole acoustic source under uniform moving state. The directivity factor of the moving monopole, dipole and aerodynamic dipole acoustic source have been study, and compared with the corresponding type of acoustic source under stationary state.2) Study of the numerical analysis programs on vehicle’s external steady flow-fieldConsidering the improvement of calculation accuracy, the Realizable k-s two-equation turbulence model combined with the enhanced wall function method was applied to simulating the high-speed vehicle’s external flow field. And the aerodynamic characteristics of external flow field of the car and the high-speed train were carefully discussed in this paper.3) Prediction of vehicle’s acoustic source based on broadband sound source modelBased on the broadband acoustic model theory, two broadband acoustic models (the Proudman formula broadband acoustic model and the Curie internal equation broadband acoustic model) were utilized to simulating the distribution of aerodynamic acoustic source on the high-speed vehicle surface in the opening-environment respectively. And the comparative analysis of the simulation results of these two kinds of broadband acoustic source models was completed in this paper. Then the distribution of aerodynamic acoustic sources on the vehicle and the tunnel surface were simulated by utilizing the broadband acoustic source model based on Curie integral equation with higher accuracy. In order to reduce the strength of aerodynamic noise source on vehicle surface and tunnel wall, an improved design for the highway tunnel’s cross-section in the original standard was also discussed here. Then the effectiveness of the tunnel cross-section geometry improved design was verified.4) Numerical analysis of the aerodynamic dipole source distribution on vehicle’s surfaceThe vehicle’s aerodynamic noise comes mainly from the aerodynamic dipole source on vehicle surface, and its intensity and distribution determine the characteristics of the vehicle’s external acoustic field. In this paper, the large-eddy simulation was firstly executed to get the pressure fluctuations near vehicle surface, then the boundary element method (BEM) combined with the computational fluid dynamics (CFD) was utilized to simulate the distribution of aerodynamic dipole acoustic source near vehicle surface.5) Simulation of the high-speed-vehicles external aerodynamic noise fieldIn this paper, the aerodynamic dipole sources on vehicle body surface were converted to the acoustic source boundary conditions, then the boundary element method (BEM) was applied to simulating the high-speed vehicle’s external aerodynamic noise field by converting the volume integral of the relevant basic acoustics equations into the boundary integral of the infinite external space (i.e., solving the acoustic Helmholz equation on the vehicle’s surface boundary). The distribution characteristics of vehicles’ external aerodynamic noise field under different speed conditions were studied, and the directivity of aerodynamic dipole source on vehicle’s surface was also discussed here.