###### Abstract  
The aerodynamic loads of a sedan experience significant fluctuations when passing by a sand dune at the roadside under crosswinds, which can easily cause yawing and overturning. Computational fluid dynamics (CFD) methods, based on different turbulence modeling approaches, yield different aerodynamic results for sedans. This study aims to investigate the effects of three prevailing turbulence modeling approaches (renormalization group (RNG) \(k\)-\(e\), large eddy simulation (LES), and improved delayed detached eddy simulation (IDDES)) on the aerodynamic characteristics of a sedan passing by a sand dune under crosswinds. The CFD dynamic mesh models are constructed using the \"mosaic\" mesh technique to account for the dune-air-sedan interaction. The reliability of the CFD prediction method is verified by comparing it with field test results. The predictive capabilities of the three turbulence modeling approaches are compared in terms of aerodynamic loads and flow field characteristics. The simulation of sand particle movement is conducted through the discrete phase model, aiming to assess the impact of wind-sand flow on the aerodynamic properties of sedans. Corresponding results show that the aerodynamic loads predicted by the LES model closely match (within 4.4-7.5%) the corresponding data obtained from field tests. While the IDDES and LES models demonstrate similar abilities in characterizing the wind field details, and their results exhibit maximum differences of 8.3-15.7%. Meanwhile, the maximum difference between the results obtained by the RNG \(k\)-\(e\) and LES models ranges from 14.8% to 18.4%, attributed to its inability to capture subtle changes in the vortex structure within the flow field. This work will provide a numerical modeling reference for studies on the wind-sand flow and the aerodynamic characteristics of sedans running through the desert, and it has implications for the safe driving of sedans under extreme conditions. turbulence modeling approaches; sand dune; crosswind; sedan; aerodynamic characteristics 2024 202  
dune, the aerodynamic lateral force, yaw moment, and other loads of the sedan will change dramatically under crosswinds, which may threaten the stability and safety of the sedan. Therefore, selecting an appropriate research methodology is essential for evaluating the sedan's aerodynamic behavior under wind-sand flow. To analyze and optimize the aerodynamic performance of cars in windy environments, researchers have developed a number of research methods, which focus on field tests, wind tunnel tests, and computational fluid dynamics methods (CFD) [5; 6; 7; 8]. [PERSON] et al. investigated the aerodynamic parameters of vehicles under crosswind effects by a combination method of road field tests and wind tunnel tests [9]. [PERSON] et al. tested the drag reduction performance of a vehicle deflector in wind tunnels [10]. To assess the safety of road vehicles driving in windy environments, [PERSON] et al. tested the wind loads on a vehicle model by wind tunnel tests [11]. However, providing sufficient information for visualizing the flow field, using road and wind tunnel tests is difficult and expensive. The wind tunnel test mainly utilizes the ground moving system to simulate the driving of sedans, and there are differences between wind tunnel tests and real-world scenarios [12; 13]. For example, in wind tunnel tests, the blockage rate is required to be controlled at about 10% to reduce interferences of the flow in the boundary layer on test results. Therefore, a full-scale sedan model requires a wind tunnel with sufficient space, and the construction cost of such a wind tunnel is very expensive. The wind tunnel test using a scaled-down sedan model needs to take into account the difference in Reynolds number due to scaling. In addition, a wind tunnel with large space is required to meet the driving conditions of the sedan.