# Effect of High-Speed Train-Induced Wind on Trackside UAV Thrust Near Railway Bridge
## 3 Analysis of the Effect of High-Speed Train-induced Wind on UAV Thrust along a Track  
### Characteristics of Train-induced Wind by a High-Speed Train along the Track  
The wind induced by two types of high-speed trains (Figure 3), when passing through the Wolsan bridge, was measured along the track. The KTX (Alstom, Saint-Ouen, France; Hyundai Rotem Co., Uiwang-si, Korea) is the first high-speed rail vehicle in South Korea. A total of 20 cars, including two power cars and 18 passenger cars, are operated as one formation with a length of 388 m. The maximum design speed is 320 km/h, and the maximum operating speed is 300 km/h. The KTX is a representative high-speed rail vehicle, and KORAIL operates a total of 46 formations. The SRT (Hyundai Rotem Co., Uiwang-si, Korea) is a high-speed rail vehicle model, independently developed in South Korea. A total of 10 cars, including two power cars and 8 passenger cars, are operated as one formation, and its length is 201 m. The maximum design speed is 330 km/h, and the maximum operating speed is 300 km/h. SR Co.(Seoul, Korea) operates a total of 32 formations. Although the rail vehicle specifications of the KTX and SRT are similar, the number of passenger cars of the KTX is higher than that of the SRT; hence, the overall  
Figure 3: Two types of high-speed trains used in the experiment (**a**) KTX; (**b**) SRT. length is about 1.93 times longer. Figure 4 shows the train-induced wind velocity results measured at 0.8 m from the train surface during the passages of the KTX and SRT. When passing over the Wolsan bridge, the velocity of the trains was approximately 293 km/h. When the leading power cars of the SRT and KTX trains passed, the wind velocity sharply increased to 9.97 and 10.89 m/s, respectively, in approximately 0.2 s, and then rapidly decreased. The wind velocities of the two trains exhibited an approximately 9% difference. This is attributed to the influence of the nose shape [11,12]. The wind velocity slowly increased when the passenger cars passed, owing to the growth of the boundary-layer flow on the train's surface, and the maximum wind velocity was observed when the trailing power cars passed. During the passage of the trains, the wind velocity severely fluctuated over time, exhibiting turbulent characteristics [13, 14, 15]. After the passage of the tailing end of the trains, the wind velocity gradually decreased. The maximum wind velocities of the SRT and KTX trains during the passage of the trailing power cars were 20.29 and 22.19 m/s, respectively. The KTX required a longer passage time than the SRT because it comprised more passenger cars and a larger total length. Furthermore, the boundary-layer flow increased further for the KTX owing to its longer passage time, and this appears to have resulted in the maximum wind velocity of the KTX being approximately 9.3% higher than that of the SRT. Figure 5 shows the train-induced wind velocity in Figure 4 expressed in the U, V, and W directions. The wind velocity in the V direction exhibited a similar tendency to that of the wind velocity in Figure 4 and was the most dominant wind velocity. There were sharp fluctuations in wind direction when the leading and trailing power cars of the trains passed. The train-induced wind was not stable and exhibited turbulent characteristics for a considerable time, even after the passage of the trains [16]. In the case of the wind velocity in the U direction, there were sharp fluctuations in wind direction during the passage of the leading and trailing power cars of the trains in the same manner as in the \(V\)-axis wind velocity. However, the velocity was not high compared to the \(V\)-axis wind velocity. The wind direction toward the outside of the track was dominant. For the wind velocity in the W direction, there were sharp fluctuations when the leading power cars passed. The wind velocity showed a tendency to remain within 10 m/s, even during the passage of the trains.