Research On Unsteady Pressure Field And Aerodynamic Noise Of A Sedan Rear View Mirror Region

With the development of automobile industry, more and more cars are running on theroad and cars play an important role in people’s life. Comfort has been more significantwhen the traditional performance of a car like dynamic property, safety and stability stillcatch customer’s attention. The noise inside the car becomes an increasingly severe problemwhich including aerodynamic noise.It’s a trend that the study model has turned from simplified model to real model andthe research methods combine the simulations and experiments instead of the singleexperimental tests. These transformations help to understand the generating mechanism ofaerodynamic noise and provide foundation for noise reduction.In this paper, numerical simulation was applied to two parts of work: the first is theresearch of the simplified mirror model composed of a half-cylinder and a quarter of asphere. The reliability of the subdomain simulations was tested by the simplified model forcalculation of wind noise around the rear view mirrors. The influence of the size of the meshon the accuracy of simulations was studied by dividing the subdomain mesh of thesimplified model. Also calculating aero-acoustics (CAA) and acoustic analogy (AA) werecompared in the subdomain, providing a research basis for following simulations of complexmodels. The second part is the simulations of the50%scale vehicle model including theflow field around the car and aerodynamic noise in the region of rear view mirrors, A-pillar,side windows and the front door. In the steady calculation, k-ω SST and k-Realizableturbulence models were used to simulate different flow conditions near the body. Flowcondition in the near wall area can be determined by the first height of boundary layer,expressed as y+. The turbulence models can be ensured for different value of y+by flowstructure around the body and pressure coefficient (Cp). In the unsteady calculation, thesteady calculation result was assigned to the subdomain which is an enclosed region including the rear view mirrors, A-pillar, side windows and the front door. Large eddysimulation (LES) was used to gain the information of the flow field and sound field in thesubdomain.In wind tunnel test, the50%scale model was used to observe the flow conditionthrough the oil film method. The steady pressure at the measuring points was recorded toanalyze the correlation between pressure fluctuation and noise, which is, the largepressure-fluctuate points are near the re-attached line where the noise level is high. The noisespectra were obtained as a benchmark to validate the simulation results. The sound pressurelevel (SPL) decreases with the frequency goes up and in the low frequency range thesimulation data is lower than the tests and in the high frequency range the simulation data ishigher.