Computational aero-acoustic 3 analysis of a passenger car 123 with a rear spoiler 指導教授：張烔堡教授 學生：黃中衞 目錄 Introduction 緒論 M ethodology R esults and D iscussion 研究方法、結果與討論 Summary 總結 Introduction
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In the process of car design, the aerodynamics and aero-acoustics must be seriously considered. A car design can only be acceptable if its form drag and aerodynamic noise are both reduced at the same time.
Acoustic holography was adopted to identify thenoise sources of a vehicle underbody . Wind noise from a vehicle underbody due to the complex flow structure accountsfor a large portion of the overall noise level generated.
As Ogawa and Kamioka  pointed out, the flows outside of a vehiclethat generate noise can be either two-dimensional or three-dimensional.
For validation, a two-dimensional cylinder in the airflow was analyzed to obtain the key parameters. Through Fluent [10, 11], this work used RNG k- ε turbulence model to compute the flow properties around the car and its spoiler.
In general, the design criteria of rear spoiler are only limited to considering the aerodynamics aspect due to the rear spoilerand endplate but the aspect of noise-vibration-harshness has never been considered.
Car drivers usually install a rearspoiler that successfully reduces the lift and improves traction leading to better maneuver. However, the aero-acoustics performancecorresponding to the rear spoiler has deteriorated severely.For this reason, this work has introduced the designersof rear spoiler a new direction, tool, and idea for rear spoiler design process.
Finally, the design of rear spoiler corresponding to the most suitable combination of aerodynamics and aero-acoustics performanceis introduced.
Computational fluid dynamics (CFD) simulations of the transient flow field around a 2D cylinder and six vehicle modelswith different spoiler designs were presented and compared to relevant experimental data reported in the literature.
Based on the cases considered in this work, the installation of a spoiler reduces the lift coefficient that leads to better conditionsfor high speed driving and improves the vertical stability of driving.
The lift coefficient of case 4, which is approximately-0.001, is the lowest among all the cases studied. This indicates that the spoiler design of of disordered flow. case 4 has the best verticalstability.
The spoiler configuration in case 4 represents the best design as far asthe aerodynamics and aero-acoustics are concerned.