## 4 Identification of Noise Sources around Rearview Mirror
### Relationship between Noise Sources and Flow Field
As shown in Figure 11, the same method as above was used to create streamlines in the rearview mirror shell surface prisms; we selected one of the streamlines to extract the relevant flow field physical quantities and then applied linear normalization to obtain the results shown in Figure 12. According to the trend of each physical quantity in the figure, it can be seen that:  
1. Like the previous law, the flow velocity \(\mathbf{u}\) peaks first near point 10, and the sinusoidal value of the angle between the flow velocity and the vorticity, sin\(\theta\), also peaks earlier. This is due to the more obvious prismatic features on the surface of the mirror shell of the rearview mirror, and the drastic change of the airflow before and after the prism. 2. The vorticity \(\mathbf{\omega}\) and the intensity of the sound source \(\mathbf{\omega}\times\mathbf{u}\) peak near point 13, and both of them change more drastically before and after point 13. Figure 11: Rearview mirror windward face shunt line drawing. Figure 10: Variation of each physical quantity at the mirror stalk of the rearview mirror with streamline. A comparison of the trends of the physical quantities shows that the vorticity and the noise source intensity peak near point 13, and there are obvious changes in the velocity, vorticity, and noise source intensity before and after the peak. Subsequently, vortices are generated due to the interaction of the downward flowing portion of the separated airflow passing through the point with the airflow from the mirror stalk. Therefore, a certain peak value of vorticity, velocity, noise source intensity, and the sine of the angle between the flow velocity and vorticity is generated near points 18 and 26. From Figure 12, it can be concluded that the angle between the flow velocity and the vorticity has some effect on the generation of the dipole noise source. As shown in Figure 13, as above, streamlines were created at the rearview mirror camera installation, and one of the streamlines was selected to extract the relevant physical quantities of the flow field above and then linearly normalized to obtain the results shown in Figure 14. According to the trend of each physical quantity in the figure, it can be seen that:  
1. The change of the angle between the flow velocity \(\mathbf{u}\) and the vorticity \(\mathbf{\omega}\) is more drastic in the early stage due to the influence of the prisms on the surface of the rearview mirror shell. The sinusoidal value of the angle between the flow velocity \(\mathbf{u}\) and the vorticity \(\mathbf{\omega}\) reaches its maximum value at point 16, and remains basically unchanged thereafter. 2. The flow velocity \(\mathbf{u}\) peaks near point 18, and the vorticity \(\mathbf{\omega}\) and source intensity \(\mathbf{\omega}\times\mathbf{u}\) peak near point 20. However, the changes of physical quantities before and after the peaks are more drastic. Figure 12: Variation of each physical quantity on the windward side of the rearview mirror with streamlines. Figure 8.0 Partial flow diagram of the rearview mirror camera mounting location. Comparison of the trends of the physical quantities shows that the vorticity, the intensity of the noise source, and the sine of the angle between the vorticity and the velocity peak near point 20. The angle between vorticity and velocity is always around 90 degrees. The drastic changes in vorticity, velocity, and noise source intensity are the main reasons for the dipole noise source. At the same time, the airflow is separated by the camber and then converges at the rear to produce vortices, so that the vorticity and the intensity of the noise source produce a certain peak near point 26. From the above analysis of the relationship between dipole noise sources and physical quantities in the flow field, it can be concluded that the dipole noise sources are mainly distributed in the airflow separation region.