# Aerodynamic Analysis and Noise-Reducing Design of an Outside Rear View Mirror
## 1 Introduction  
Since noise, vibration and harshness (NVH) are now significant in passenger vehicles, automotive industries are interested in levels of NVH as a component of the development of comfortable vehicles. In particular, aerodynamic sound is the predominant component of interior vehicle noise at speeds above 100 kph [1]. Various design technologies have been developed in order to reduce the aerodynamic noises induced by high-speed driving. The design modification of the mechanical components interacting with airflow is needed for the reduction of aerodynamic noise. The outside rear view (or side view) mirror (OSRVM) is installed on the exterior of vehicles to help the driver see the areas behind and to the sides of the vehicle. During driving, the bluff body of the mirror interacts with high-speed airflow, causing flow separation, recirculation, and an irregular vortex. The protruding mirror generates strong pressure fluctuation on the door panels and windows, and the unsteady air pressure then propagates into the vehicle interior as noise [2]. In general, the side view mirror is also known to increase the total amount of drag by 2-7% [3]. Reports from recent decades indicate that the OSVRM generates intrinsic acoustic noise. [PERSON] et al. has reported that a whistle-like mirror noise radiates from the mirror housing. They showed that when the transition to a turbulent boundary layer over the housing of the mirror was not complete, pressure fluctuations near the trailing edges of the mirror housing rapidly changed flow patterns, resulting in the whistle noise [3]. Other researchers also demonstrated that whistle noise is attributed to the considerable change in the A-pillar vortex and increase in turbulent intensity [4; 5]. [PERSON] et al. has studied the velocity vector fields of the wake and pressure distribution over the mirror skin in order to investigate the wake structure and the vortex body frame interaction near theOSRVM. They measured the surface of the mirror by use of hot-wire anemometry and the pressure scanning system [6; 7]. [PERSON] et al. has investigated the flow field and the acoustic sources of the OSRVM by evaluating different advection schemes, turbulence models, and three levels of grid resolution. The paper showed that a match between the measured and computed results is found using several static pressure sensors located at the OSRVM [8]. Moreover, various experimental and simulation studies have been investigated to identify aeroacoustics sources and noise generation of the side mirror [9; 10; 11; 12; 13]. A design modification of the protruding mirror is needed in order to reduce the aerodynamic noise. Some typical strategies have been observed to reduce the traditional problems of the side mirror, such as noise and mirror surface vibration. The earlier studies have suggested aerodynamic optimization techniques in order to reduce the strength of the intrinsic shedding vortex and suppress the generation of aerodynamic noise by changing the geometric shape of the mirror, such as its bracket height, the housing height and size, the bezel shape, the elimination of sharp edges on all of the corners, and the tube-type extension of the mirror housing [2; 3; 10]. However, there are limitations to reducing the geometry of the side mirror for aerodynamic noise, because it also satisfies the size constraint to secure its visual angle. Very little study has been undertaken to reduce the aerodynamic sound of the side view mirror with additional dents while keeping its size, although some studies in the aerospace industry have reduced the noise by adding additional devices such as riblets or vortex generators [14; 15]. Accordingly, the object of this study is to enhance the aerodynamic flow and sound radiation by adding inner dents on the external shape design of the OSRVM. The commercial program FLUENT was used to analyze the drag coefficient variation according to the shape of the OSRVM.