Research On External Flow Field Induced Aerodynamic Noise Of A Hybrid Electric Vehicle

With continuous developments of automobile engineering, people now have higher requirements for the comfort of automobile performances. Taking a hybrid electrical vehicle as research object, numerical simulation method combined with road experiments were conducted to research characteristics of the external flow field induced aerodynamic noise, and the influence of which on inner sound fields was also studied. Research methods and innovations are as followed.Carbody model and inner sound cavity were established with CATIA software with reverse engineering function. GAMBIT software and HYPERMESH software were used to make geometry cleanup, meshing and flow field boundary condition settings. Flow fields results were solved in a CFD software FLUENT, and contours of dynamic pressure and contours of turbulent kinetic energy were obtained. Comparing several common used turbulence models when solving the transient flow fields,a new model, Detached Eddy Simulation(DES) was applied to it. Result of distributions of fluctuating pressure on carbody is the base of sound fields simulation.The most innovative point of the research is to apply the theory of Pseudo Excitation Method(PEM) to the solution of sound fields. Firstly the structural modal of carbody and the acoustical modal of cavity had been calculated, and the fluctuating pressure was viewed as random loads and could be decomposed into virtual power spectral densities. With VIRTUAL.LAB software with random acoustics module, mapping flow fields date to the structural grids, acoustical responses of ears of driver and rear passenger were obtained by using finite element method combined with vibro-acoustic coupling theory. To verify the correctness of simulation methods, aerodynamic noise road experiments were conducted referring to GB/T18697-2002 "acoustic car interior noise measurement method". Sound pressure level spectrums gained from experiments are generally in line with those from simulation, and possible reasons of difference had been discussed. At last the noise reduction effect of porous sound-absorbing material was investigated. Finally conclusions obtained are as followed(1)DES method is very suitable for solving separation flow phenomenon, and turbulent situations at the rearview mirror and vehicle tail are captured well.(2)Fluctuating pressure spectrum has a wide frequency band, main energy of which concentrates on low frequencies, and is the root cause of aerodynamic noise.(3)Aerodynamic noise spectrums peak at a characteristic frequency, then begin to decline, and the characteristic frequency becomes bigger with the increase of vehicle speed.(4)Sound pressure level of driver’s left ear is much bigger than that of driver’s right ear due that left ear is near the window, greatly influenced by turbulence around rearview mirror; Sound pressure level of rear passenger’s ear is much bigger than that of driver’s ear due that rear passenger is near the vehicle tail, greatly influenced by tail turbulence, besides the radiating surface area is large.(5) Due that the porous sound-absorbing material belongs to resistance material, the noise reduction effect of which at high frequency is obviously better than that at low frequency. On average, it can reduce the inner aerodynamic noise by 5 dB.