# Aerodynamic Analysis and Noise-Reducing Design of an Outside Rear View Mirror
## 3 Simulation Results
### Result Comparisons and Discussions  
Table 2 summarizes the airflow velocities at the gutter, the mirror surface, and the outer edge of the three mirror models. At high driving speeds, the average velocity increased for the reference and outer duct models. However, the inner duct model dramatically reduced the airflow velocity at all of the points. The velocity especially decreased at the outer edge of the inner duct model, which was quite large compared to the other cases. The additional inner dent on the mirror housing distributed the high-speed airflow that passed through the outer edge and enhance velocity profiles around the mirror housing. Accordingly, the velocity difference between the edge and gutter of the inner-duct OSRVM was quite small compared to the other mirror models. At the mirror surface of the inner duct model, the airflow velocity was less than 25 kph for all of the vehicle speeds. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Type**} & \multirow{2}{*}{**Vehicle Speed**} & \multicolumn{3}{c}{**Measure Points**} & \multirow{2}{*}{**Average (kph)**} & \multirow{2}{*}{**Difference**} \\ \cline{3-3} \cline{5-7}  & & & **Gutter (kph)** & & **Mirror (kph)** & & **Edge (kph)** \\ \hline \multirow{3}{*}{**Reference Model**} & **60** & 54 & 31 & 102 & 62.3 & 48 \\  & **80** & 54 & 43 & 135 & 77.3 & 81 \\  & **110** & 73 & 59 & 184 & 105.3 & 111 \\ \hline \multirow{3}{*}{**Outer Duct**} & **60** & 68 & 32 & 117 & 72.3 & 49 \\  & **80** & 58 & 45 & 156 & 86.3 & 98 \\ \cline{1-1}  & **110** & 86 & 47 & 214 & 115.7 & 128 \\ \hline \multirow{3}{*}{**Inner Duct**} & **60** & 27 & 13 & 29 & 23.0 & 2 \\ \cline{1-1}  & **80** & 33 & 17 & 39 & 29.7 & 6 \\ \cline{1-1}  & **110** & 44 & 23 & 53 & 40.0 & 9 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation results of velocities according to vehicle driving speed at the gutter, the mirror surface, and the edge of the three OSRVM models. Figure 6: Flow velocity contour with vector field (**a**–**c**) and maximum sound pressure level (**d**–**f**) of the third OSRVM model with two inner ducts at 23 \({}^{\circ}\)C and 50% humidity condition for three vehicle speeds: (**a,d**) 60 kph, (**b,e**) 80 kph, and (**c,f**) 110 kph. Figure 7 shows the average flow velocity of the three points (gutter, mirror, and edge) for the vehicle speeds (60 kph, 80 kph, and 110 kph). The increasing rate (slope) of the average velocity by the vehicle speed was similar for the reference and the outer duct models. However, the inner duct model shows the low rate of velocity change with the slope of 0.35. The addition of two inside ducts on the design of the mirror housing improved the homogenous airflow around the OSRVM. Aerodynamic noise is mainly due to pressure fluctuations by the changes of the flow velocity and the air density, which are related to vorticity. Table 3 represents the magnitude and variation of vorticity at the gutter and the edge of the three OSRVM models. High vorticity at the gutter between the A-pillar and the mirror of the reference and outer duct models resulted in dense airflow and high-pressure fluctuation. Moreover, a high vorticity difference between the gutter and the outside edge affected the flow separation and sound radiation at the trailing edge of the mirror. Unlike the cases of the reference and outer duct models, both the vorticity magnitude and the vorticity difference between the gutter and edge of the inner duct