## 2 Methods
### Field Experiment Verification  
To verify the reliability of the CFD methods used in this study and their results, a series of field tests were carried out on the wind speed and pressure at a desert road. Three-cup anemometers and wind vanes were employed for the extended monitoring of wind speed and direction in the dune section. As shown in Figure 6, the sedan was running at 16.67 m/s without crosswinds, and a micro differential pressure sensor was used to monitor the pressure change in the surface of the passenger door. The passage of a sedan through a dune section induces disturbances in the surrounding flow field, resulting in fluctuations and an increase in wind speeds and pressures along the roadside, proportional to the sedan's speed. The presence of sand on the surface of the desert highway exacerbates the issue, as the dust stirred up by the sedan's wake during passage adversely affects individuals and facilities along the roadside. Therefore, a pressure measurement point and an ultrasonic anemometer, Gill Wind Master Pro (manufactured by GILL in the Lymington, UK), are installed at the 0.9 m height of the road shoulder at the end of the dune. The corresponding CFD models are built according to the field conditions, and the differences between the field test results and the corresponding CFD prediction results are compared. Figure 7 presents the time history curves of the pressure at a measurement point on the sedan surface obtained from the field test, the RNG \(k\)-\(\varepsilon\), LES, and IDDES models. The differences between the sedan surface pressures predicted by the RNG \(k\)-\(\varepsilon\), LES, and IDDES models (\(-\)36.16, \(-\)37.46, and \(-\)36.94 Pa) and the corresponding values in the field (\(-\)39.18 Pa) are 7.7%, 4.4%, and 5.7%, respectively, and the fluctuations range roughly between \(-\)20 and \(-\)60 Pa. Therefore, the surface pressures on the sedan as forecasted by the LES model align more closely with the field test data compared to those predicted by the RNG \(k\)-\(\varepsilon\) and IDDES models. Comparing the fluctuation amplitudes of pressures at the measurement point obtained by three turbulence modeling approaches with the corresponding results obtained from the field test during the time period of 0-2.5 s, it can be found that the fluctuation amplitude (33.15 Pa) of the pressure obtained based on the IDDES model is the closest to the corresponding result (58.5 Pa) of the field test. This discrepancy cannot be ignored, and further analysis reveals that the results obtained based on the field tests fluctuate substantially between the periods 0-1.0 s and 2.0-2.5 s, which may be attributed to the fact that the speed of the sedan did not stabilize during the starting and stopping periods. After comparing the pressure fluctuations during 1.0-2.0 s obtained based on the three turbulence modeling approaches with the corresponding results of the field tests, it can be found that the fluctuation amplitude (32.27 Pa) of the pressure obtained based on the LES model was the closest to the corresponding result (30.2 Pa) of the field test. Figure 8 shows the time interval curves of wind velocity and pressure recorded at the point on the road shoulder during the crossing of the sedan. The average results of the 10 reproducible experiments performed in the field tests were obtained and then compared with the corresponding results predicted by RNG \(k\)-\(\varepsilon\), LES, and IDDES models. As depicted in Figure 8, at the 0.9 m height on the road shoulder, the wind velocity at the point evolves between \(-\)1.0 m/s and 0.7 m/s, while the pressure evolves between \(-\)12 and 8 Pa. The time interval curves of the pressure and the wind velocity measured at the measured points of the road shoulder are basically consistent with the corresponding results predicted by  
Figure 6: Layout of the measurement points on the surface of the sedan and the shoulder of the road. the CFD models.