Study On Aerodynamic Noise Of Road Vehicle With High Speed

As engine, drive trains, intake, exhaust, tire and other automobile noise is reduced and as driving speeds increase, aerodynamic noise on ground vehicle under high speed cruise condition is becoming relatively more important. This study focused on analysis of pressure fluctuation on the body surface, prediction of exterior far-field noise and interior noise and the road tests.It is the airflow-generated fluctuating pressures on the outside surface of the body that causes aerodynamic noise, thus the study on external flow field and pressure fluctuation is the foundation of vehicle aerodynamic noise research works. In the dissertation, external unsteady flow was simulated for Santana using the CFD software FLUENT. The analysis on the results shows that the fluctuating pressures on front hood, front side, vent windows, side windows, rear window and roof are relatively higher, especially on vent windows and front side windows are strongest. The airflow at the A-pillar are separated into two different flow patterns, one is the rotating flow in the separated flow region, another non-rotating flow in the reattached region. The fluctuating pressures generated in separated flow regions are stronger than one in reattached region. The fluctuating pressure level on the body surface is higher at the low frequency, and decreases with increasing frequency.With numerical solution of surface fluctuating pressures calculated, the aero- dynamic noise radiation to exterior far-field and interior was researched. Based on the solution characteristics of exterior far-field noise and interior noise, direct BEM (Boundary Element Method) and indirect BEM and structure FEM (Finite Element Method) coupled were selected, respectively. Using the vibro-acoustic software SYSNOISE, exterior far-field noise was solved 82dB and interior noise 90dB at the front seats and 91dB at the rear seat.On account of mainly no low-noise wind tunnel in China, a useful exploration for the road tests was made. Based on the road tests the interior wind noise SPL (Sound Pressure Level) and side windows vibration acceleration was obtained. Comparing the simulation results and experimental measurements of the interior noise, it can be found that there is certain error between them, and the error mainly concentrates in 400Hz below. Two main reasons cause this: one is the contributions of other noise sources to interior sound field, which make the measurements over-predicted; other is that leak noise is ignored and pressure boundary condition is only loaded on roof and windows, which leads to the results under-predicted.