## 1 Introduction  
Transportation is the foundation of economic development, and it enhances connectivity between regions and improves travel efficiency for residents [1]. Bridges play a pivotal role in transportation infrastructure, particularly the long-span bridge, which is able to cross natural obstacles and significantly improve transportation efficiency [2]. Meanwhile, due to the complex terrain and numerous natural obstacles, it is very inconvenient to travel for those living in mountain valleys. Therefore, the construction of bridges in mountain valleys is urgently needed. The bridges in mountain valleys are often characterized by long spans and low stiffness, which make them highly susceptible to wind disasters [3]. The current bridge design specifications [4] primarily cater to flat terrains such as plains, while for mountain valley terrains, the continued adoption of specifications solely applicable to flat terrains may result in the structural design of bridges being insecure. Therefore, it is necessary to refine the analysis of the wind characteristics at the bridge site in a mountain valley to enhance bridge safety. To better control variables and obtain the pattern of turbulence development over terrain, the complex mountains and canyons are simplified to an ideal hill or ridge in many studies, and preliminary analysis and prediction of the wind characteristics near the simplified terrain are conducted [5; 6; 7]. [PERSON] et al. [8] employed a wind tunnel test to study the wind characteristics near a simplified three-dimensional hill with a maximum slope of 30\({}^{\circ}\), and the flow separation at the hilltop and the formation of a recirculation zone on the leeward side of the hill were observed. [PERSON] et al. [9; 10] and [PERSON] et al. [11; 12] adopted a numerical simulation approach to investigate the influence of slopes, wind directions, and sub-grid scale models on the wind characteristics over simplified hills. However, the influence of different oncoming wind speeds on the wind characteristics was not considered in their studies. [PERSON] et al. [1] used the large-eddy simulation (LES) approach to study the wind characteristics in simplified U-shaped and V-shaped canyons. The result indicated that the wind speed amplification effect was gradually diminished when the V-shaped canyon angle exceeded 160\({}^{\circ}\) or the width-to-height ratio of the U-shaped canyon was approximately 5:1. It is evident that the selection of model parameters such as the slope of simplified hills, the width-to-height ratio of U-shaped canyons, and the opening angle of V-shaped canyons has a significant influence on wind characteristics. Similarly, [PERSON] et al. [13] pointed out that there is a considerable difference between the simplified terrain and the actual mountain canyon terrain. Consequently, studying the wind characteristics only on the simplified terrain is insufficient. With the improvement of experimental equipment and computer hardware, the wind characteristics of actual mountainous and canyon terrains are being established by more and more scholars [14; 15; 16]. [PERSON] et al. [17] conducted a field measurement of the wind characteristics at a bridge site in an L-shaped mountain valley and found significant differences between parameters such as turbulence intensity, probability density function, and spatial coherence at the bridge site compared to the standard values in existing specifications. [PERSON] et al. [18] used meteorological balloon measurements and numerical simulation methods to study the airflow characteristics over complex terrain. The measured and simulated results were compared, and the results indicated that the accuracy of numerical simulation software in modeling mountainous and adjacent terrains is sufficiently accurate. [PERSON] et al. [19] employed the LES approach to study the spatial wind field in complex terrain.