Research On Exterior Aerodynamic Noise By Non-smooth Styling Of Car Rearview Mirror

Automobile industry is developing quickly in our country recent years. Guarantee thequality of safety, lightweight and drivability, riding comfortability is put forward as animportant standard of evaluating automotive performance. When the car is running, theaerodynamic noise outside comes into vehicle through the air and body panels, and it willincrease interior noise level. Some studies show that accessories outside are the mainsource of the aerodynamic noise, especially the exterior rearview mirror which is bulgingfrom the car body has the most influence on the interior noise.Nowadays, domestic research on aerodynamic noise of the rearview mirror is mainlyfocused on the optimization of mirror shape and installation form to reduce theaerodynamic noise. Although the major research of this paper is also the aerodynamic noiseof the rearview mirror, it focuses on the influence of the rearview mirror with non-smoothsurface on aerodynamic noise.The simulation involves two stages, the steady state simulation and the unsteady statesimulation. Because the realizable k-c model can accurately simulate the flow filed of thevehicle, the realizable k-c model is adopted in the steady state stage. The unsteady statesimulation uses LES model, and the FW-H acoustics model is introduced so that we canobtain the noise information of the monitoring points. Through transient calculation we canobtain the fluctuation pressure, the Sound Pressure Level (SPL) on frequency spectrum istransformed from fluctuation pressure via Fast Fourier Transform (FFT).Considering the great influence of A-pillar, rearview mirror and side window on theaerodynamic noise, a wedge-shaped cab model was created. This paper also creates twosimplified rearview mirror model, and they have the same shape but one of them hasnon-smooth surface. By comparison the simulated results of the sound pressure level, we find that the noise level of rearview mirror model with non-smooth surface has beenimproved. And the mechanisms of the non-smooth model in reducing noise are analyzedthrough the flow field and the static pressure distribution.On that basis, a real car model and streamlined rearview mirror are created to verifythe simplified model simulation results. And the calculation results are consistent with theprevious analysis. Through introducing Broadband Noise Sources Model, we can analyzethe car Surface Acoustic Power Level, and optimize the distribution of the non-smoothsurface. And the optimized non-smooth model can distinctly reduce the aerodynamic noise.This paper also has a research on the rearview mirror with different kinds of thenon-smooth unit, and put forward the optimum distribution. At last, the influence of thenon-smooth unit size on aerodynamic noise is discussed in this paper.Through the research on the aerodynamic noise of the vehicle with non-smoothrearview mirror, we can find that the rearview mirror with non-smooth surface couldreduce noise and improve acoustic environment. Using the optimum distribution,appropriate pit pattern and size, the aerodynamic noise level can be further reduced.