## 3 Drag Reduction Mechanism in Race Walking Drafting Formations
From Figures 11b and 12b, it can be observed that only a small portion of the incoming airflow directly passes through the gap, impacting the core race walker, while the majority of the airflow is diverted towards the sides due to the obstruction created by the front race walker. The diverted airflow gradually converges towards the center as a result of the pressure difference between the diverted airflow and the inner airflow, impacting the core race walker. The extent of convergence of the diverted airflow primarily depends on the velocity of the air on both sides, wherein higher velocity leads to lower pressure and slower convergence. Consequently, the core race walker experiences reduced impact from the airflow, resulting in lower pressure on the front surface of the core walker. Furthermore, Figure 13b illustrates that the reduction in the number and velocity of incoming airflow directly leads to a decrease in the air velocity behind the core race walker. This reduction mitigates the formation of turbulence and vortex at the rear, thereby increasing the pressure in the rear regions. Analyzing the flow field in the optimal double drafting formation reveals that achieving superior drag reduction necessitates minimizing the quantity and speed of incoming airflow affecting the core race walker. Firstly, minimizing airflow that directly affects the core race walker through gaps between front race walkers is crucial. Secondly, delaying the convergence of airflow on both sides is necessary to alleviate its impact. Figure 10: Speed contour of race walking in optimal drafting formations: (**a**) race walking alone, (**b**) race walking in optimal double formation, (**c**) race walking in optimal triple formation, and (**d**) race walking in optimal quadruple formation. Figure 11: Streamline of race walking in optimal drafting formations: (**a**) race walking alone, (**b**) race walking in optimal double formation, (**c**) race walking in optimal triple formation, and (**d**) race walking in optimal quadruple formation. Figure 12: Velocity vector diagram of 0.2 m in front of the core race walker: (**a**) race walking alone, (**b**) race walking in optimal double formation, (**c**) race walking in optimal triple formation, and (**d**) race walking in optimal quadruple formation. Figure 13: Speed contour of 0.1 m behind the core race walker of race walking in optimal drafting formations: (**a**) race walking alone, (**b**) race walking in optimal double formation, (**c**) race walking in optimal triple formation, and (**d**) race walking in optimal quadruple formation. The optimal triple drafting formation improves upon the optimal double drafting formation by introducing an additional race walker behind the core race walker. This augmentation further enhances the drag reduction effect, achieving a rate of 72%. Additionally, Figure 8c displays an additional decrease in frontal pressure and an elevation in rear pressure on the core race walker in comparison to Figure 8b, leading to a reduction in the disparity between front and rear pressures. Figure 9a-c depicts that the frontal chest pressure coefficient of the core race walker measures \(-0.01\), while the rear chest pressure coefficient stands at \(-0.03\). As a result, a pressure differential of 0.02 emerges, which is 0.6 units lower than race walking alone and 0.1 lower than race walking in double drafting formation. Additionally, Figure 10c presents a continued reduction in the velocity ahead of the core race walker. Moreover, Figures 11c and 12c visually depict instances of backflow caused by the airflow colliding with the trailing race walker, leading to a delay in the inward convergence of the airflow. These factors contribute to a continued reduction in the impact of airflow on the core race walker. Meanwhile, the sustained decrease in the quantity and speed of airflow affecting the core walker leads to a decrease in the rear air velocity, as demonstrated in Figure 13c.