## 2 Methods for Drag Reduction in Drafting Formations in Race Walking
### CFD Numerical Simulation Results and Verification
#### 2.3.2 Race Walking in Drafting Formations
Figure 6: Comparison of Cd and drag reduction rate of the core race walker in 15 drafting formations between wind tunnel experiment and CFD simulation; (**a**) Cd of race walking in double drafting formation, (**b**) Cd of race walking in triple and quadruple drafting formation, (**c**) drag reduction rate of race walking in double drafting formation, (**d**) drag reduction rate of race walking in triple and quadruple drafting formation. Regarding triple drafting formations, the most notable reduction in drag is observed in triple drafting formation 4, where an additional race walker is added behind the core race walker of the optimal double drafting formation. This drafting formation resulted in a drag reduction rate of 72% in the CFD simulation and a 66% reduction in the wind tunnel experiment. The second highest reduction is achieved by triple drafting formation 5, where an additional race walker is added in front of the front race walker of the optimal double drafting formation. This drafting formation results in a drag reduction rate of 62% in the CFD simulation and a 64% reduction in the wind tunnel experiment. The other triple formations have minimal or negative effects on drag reduction. Thus, in triple drafting formation, it is advisable for the core race walker to position themselves between two race walkers in front and behind him. Among the quadruple drafting formations, the aerodynamic drag experienced by the core race walker is reduced, although to different extents. The quadruple drafting formation 3, which adds one race walker to the front left and right of the optimal double drafting formation, forming a V shape in front of the core race walker, demonstrates the most significant reduction in drag. This formation achieves the highest drag reduction rate, with a reduction of up to 85% in the CFD simulation and 81% in the wind tunnel experiment. If the two side race walkers in front move back to a side-by-side position (quadruple drafting formation 1), the drag reduction rate decreases to 71% in the CFD simulation and 65% in the wind tunnel experiment. If they move further back to an inverted V position (quadruple drafting formation 2), the drag reduction rate further deteriorates to 44% in the CFD simulation and the wind tunnel experiment. Thus, in quadruple drafting formations, it is ideal for the three auxiliary race walkers in front of the core race walker to form a V shape. Figure 7 displays the fitting results of the drag reduction rate obtained from the wind tunnel experiment and CFD simulation, demonstrating a strong agreement between the two methods with a fitting error below 10%. This further illustrates the consistency of the drag reduction rate between the two methods and validates the accuracy of the CFD numerical simulation results. The primary cause of the drag error in the drafting formation lies in the use of different race walker models in the wind tunnel experiment, whereas the CFD simulation employs the core race walker model. Consequently, significant disparities exist in their model  
Figure 7: Wind tunnel experiment and CFD simulation fitting result of drag reduction rate of core race walker while race walking in 15 drafting formations (error line, 10%). postures. Interestingly, notwithstanding the substantial shape disparities between the models, the error in the drag reduction rate remains below 10%. This confirms that within a drafting formation, the primary influence on the drag reduction effect stems from the relative positions of athletes, with the variation in model posture having a lesser impact. To validate this conclusion, the following experiments were carried out:  
(1) The front race walker model in the optimal double drafting formation was mirrored, and the results showed that the drag reduction rate of the core race walker was reduced from 65% to 62%, with an error of 4.6%;  
(2) The drag reduction performance of optimal double and triple drafting formations, as observed in both [PERSON]'s [17] study and this article, was compared.