## 1 Introduction  
In recent years, a significant amount of research has been carried out on mechanical noise (such as engine noise, transmission noise, etc.), and effective noise control methods have been proposed; wind buffeting noise is becoming more and more prominent with the continuous increase in the practical speed of vehicles. Wind buffeting noise is caused by the coupling of flow instability of the shear layer and the air in the vehicle cabin while driving a vehicle with a sunroof or window open, and is a type of aerodynamic noise. Wind buffeting noise has the features of high strength and low frequency. It not only affects the vehicle ride comfort but also affects driving safety. Therefore, to improve the quality of automobile products, it is very important for automotive manufacturers to predict and analyze the wind buffeting noise at the designing stage.  
The characteristics of sunroof buffeting noise and its control methods have been extensively studied [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]. However, there are few research findings on the characteristics and the control methods of buffeting noise caused by opening the side window. [PERSON] et al. conducted road tests on the buffeting noise of a sedan caused by different side window openings [11]. The results showed that there exist discrepancies in the characteristics of wind buffeting noise. When a single rear window opens, or two rear windows open at the same time, buffeting noise exhibits a feature of multi-harmonic oscillation, while in other cases only a single peak appears in the _SPL_'s spectrum. [PERSON] et al. summarized the simulation and control measures of vehicle window buffeting noise [12; 13], such as installing a guide plate at the leading edge of the window, changing the opening size of windows, setting vents, etc., which promoted wind noise control technology in vehicle engineering. Utilizing CFD numerical simulation, [PERSON] et al. proposed five control measures to reduce the wind buffeting noise of an SUV [14], the results showed that certain noise reduction can be achieved through five passive control methods. [PERSON] et al. numerically studied the front wind buffeting noise characteristics caused by two mirror geometries: a glass-mounted mirror and a door-mounted mirror [15]. They found that the door mirror was noisier by approximately 6 dB. Door mirrors have a major impact on the wind noise observed at the driver's ear. [PERSON] and [PERSON] minimized buffeting by optimizing the mirror angle [16]. Any combination of open windows can suppress the buffeting of the side windows, and the validity of this method has been verified by numerical investigations on a car [17] and on an SUV [18]. [PERSON] et al. installed a cylindrical deflector on the B-pillar to suppress the rear window buffeting noise [19]. By optimization using the response surface method, the reduction of peak _SPL_ of buffeting noise was more than 12 dB in comparison with the original state without a deflector. These measures to suppress wind buffeting noise have achieved obvious results. However, the styling changes of some aerodynamic components are severely limited to the automotive design and the aerodynamic performance of the vehicle. Only minor shape changes are generally acceptable, and the choice of the car manufacturer is a suitable modification.  
The rain visor of the front side window can effectively prevent rain or strong wind blowing directly into the vehicle cabin, thus improving the ventilation efficiency and preventing the window from fogging in the rain. In addition to these functions, the visor can also reduce the wind buffeting noise caused by opening the front window. However, the related literature has not been seen. In this paper, the effect of reducing wind buffeting noise is discussed through CFD numerical simulation, and then the numerical simulation optimization is carried out to find the best shape of the visor, which can offer a reference for theoretical research and engineering application of vehicle wind buffeting noise.