## 1 Introduction  
China's high-speed railway operation mileage ranks first in the world, reaching 40,000 km, and the high-speed railways annually transport 2.5 billion passengers [1, 2]. The rapid development of the high-speed railway means that more requirements are needed for the safe and stable operation of the trains. The online monitoring device used to determine the high-speed train operation status (hereinafter referred to as the device) is a device that is installed on the top of the power car and is exposed to the air to optically monitor the operation status of the high-speed train by using infrared technology [3, 4, 5]. The monitoring device is the key equipment that provides power to the locomotive in high-speed railways. Its reliability is related to the safety and efficiency of the entire railway transportation system. It has six characteristics: a complex space environment, a large impact on climate conditions, no standby, uncertain load, a huge space mechanical system,and a multidisciplinary complex. The monitoring device completes the extraction of the geometric parameters of the catenary along the route; the analysis of the current collection parameters; and the accurate positioning of the fault points and bird's nest early warning by using a video detection camera, a pillar number plate camera, and a scene camera on the operating electric multiple units (EMUs), and then it finally dynamically detects the operation status of the high-speed railway catenary. For running trains, the aerodynamic load cannot be ignored. In addition, because the outer layer of the device is a shell, whether its rigidity, strength, and stability meet the design requirements also needs to be carefully verified. All these require the aerodynamic characteristics of the device to be analyzed under rated conditions. When the EMU runs at a low speed, the proportion of air resistance in the overall EMU resistance is very small. With the increase in the train speed, the proportion of aerodynamic resistance in the total resistance will exponentially increase. When the speed reaches 200 and 300 km/h, the proportion will increase by 70 and 85%, respectively [4, 5]. China is developing and constructing new technologies, such as side-suspension high-speed trains with speeds up to 400-600 km/h. The detection device installed on the top of the train will inevitably affect the aerodynamic performance of the whole vehicle. Given the impact of monitoring devices, the researchers conducting aerodynamic research on high-speed EMUs at home and abroad are mainly focused on model tests [6] (including wind tunnels, dynamic models, etc. ), numerical simulations [7, 8, 9, 10], and real-vehicle aerodynamic tests [11]. The model test is not limited by the tunnel, vehicle head shape, external meteorological conditions, etc. Still, the construction cost is high, and the test accuracy and model speed are limited by the model material and launching device, which makes meeting the test requirements for higher vehicle speeds difficult. The real vehicle test is the most direct and reliable test used to study the tunnel pressure wave and verify the theoretical model. The test is limited by the test environment, personal safety, resource investment, test cycle, and many other limitations. With the continuous development of numerical simulation technology, many simulation analyses on the aerodynamic performance of high-speed multiple units have been conducted. [PERSON] et al. [12, 13] simulated the air distribution in an equipment cabin under an open-line meeting of an EMU. [PERSON]. [14] simulated and analyzed a scaled model of a high-speed train that included the monitoring device, and they found that the separation of the air boundary layer of the monitoring device produced relatively atmospheric dynamic resistance, and the numerical calculation results agreed with the wind tunnel test data.