## 1 Introduction
They specifically concentrated on drag reduction using CFD simulation without incorporating analyses of the flow field or the mechanism behind drag reduction. [PERSON] (2021) [17] employed CFD simulation to investigate the effects of various drafting formations (one double, two triple, and one quadruple) during a marathon race. They discovered that the most significant drag reduction of 75.6% and a performance improvement of 154 s were achieved when a runner positioned themselves between two runners, one in front and one behind. Furthermore, a basic analysis of the drag reduction mechanism suggested that the reduction in drag is a result of no sharp deceleration of air and the resulting formation of areas of high stagnation pressure on the core runner's surface. However, the study lacked an explanation of the pressure reduction mechanism and did not quantify the pressure changes. Additionally, no conclusions have been reached regarding the impact of other athletes on pressure and the mechanism by which it influences the drag reduction effect when exploring additional formations. Moreover, there is currently limited research on drafting formations in race walking, and the existing research on drafting formations in track and field events primarily focuses on the simple formations mentioned above, neglecting more complex formations. Furthermore, the majority of drag calculations for athletes in drafting formations are based on CFD simulations and lack verification through wind tunnel experiments. Due to the complex structure of the human body, the geometry and motion of the athletes need to be simplified during CFD numerical simulations compared to wind tunnel experiments. Consequently, there is often a significant disparity in drag obtained by these two methods. [PERSON] (2018) [18] was the first to perform numerical simulations of tandem interactions,considering various cyclist postures. The result showed that the greatest reduction in drag was observed for trailing riders when two riders maintained an upright position at the closest distance, resulting in a drag reduction of 27% compared to riding alone. This drag reduction trend was consistent with the results of the wind tunnel experiment by [PERSON] (1996) and [PERSON] (1993) [19; 20], where the drag reduction benefit decreased linearly as the traction distance increased for all riders' postures. However, the drag variation was large, especially when the spacing was 1 m, and the difference in drag between the CFD simulation and wind tunnel experiment reached 21%. The drag results from different wind tunnel experiments on complex human structures sometimes differ as well. [PERSON] (2015) [21] performed a full-scale wind tunnel experiment under controlled conditions and observed a significant 40% reduction in drag at a distance of 0.7 m, showing a large difference of about two times the results of [PERSON]'s [19] wind tunnel experiment. Whether this difference is attributable to differences in posture or experimental artifacts (e.g., high blockage rates) remains unclear. Therefore, it is crucial to verify the results of the wind tunnel experiment through CFD numerical simulations. The accuracy of the findings can be ensured by validating the agreement between the aerodynamic drag obtained from both methods. Furthermore, if any discrepancies exist between the drag of the two methods, further investigations should be conducted to explore alternative explanations for the inconsistencies. This study aims to achieve the following objectives: firstly, to investigate the drag reduction in drafting formations involving two, three, and four race walkers using both wind tunnel experiments and CFD simulations. The comparison of the drag coefficients obtained from both methods will be analyzed to identify the contributing factors leading to the differences between them. Additionally, the drag reduction rates of the two methods will be assessed to verify their consistency.