## 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  
Given that the primary objective of this article is to investigate the drag reduction mechanism of drafting formations, demonstrating the consistency of drag reduction results in these formations takes precedence over verifying the accuracy of individual drag calculations. Therefore, this paper proposes a new parameter, drag reduction rate \(\theta\), to evaluate the drag reduction effect of the drafting formation. The drag reduction rate is defined as the rate of the difference in drag between the core race walker in drafting formations and race walking alone. \[\theta=\frac{F_{d0}-F_{d}}{F_{d0}}\times 100\%, \tag{4}\]  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Author** & **Activities** & **Method** & **Speed (m/s)** & **Cd** & **Corrected Cd** & **Correction Reason** & **Error** \\ \hline This study & Race & \multirow{2}{*}{CFD} & \multirow{2}{*}{6} & \multirow{2}{*}{0.70} & \multirow{2}{*}{0.70} & \multirow{2}{*}{Basis} \\  & walking & & & & & & Moving ground + \\  & & & & & (2.8\%) & \\ [PERSON] et al. [22] & Race & Wind & \multirow{2}{*}{6} & \multirow{2}{*}{0.77} & \multirow{2}{*}{0.69–0.75} & System error + & \multirow{2}{*}{\(-1.4\)–\(7.1\%\)} \\ (2022) & walking & & tunnel & & & (\(-3.9\%\)–\(4.2\%\)) & \\  & & & & & & Model discrepancy – \\ [PERSON] et al. [17] & & & & & (8.2\%\)–\(10\%\)) & \\ (2021) & Running & CFD & 5.83 & 0.68 & 0.68 & & \(-2.8\%\) \\ [PERSON] et al. [16] & & & & & (2020) & & \\ [PERSON] and [PERSON] [31] & & & & & (2020) & & \\ [PERSON] and [PERSON] [31] & & & & & (2020) & & \\  & & & & & (2020) & & \\  & & & & & & (2020) & \\  & & & & & & (2 where \(F_{d0}\) is the aerodynamic drag when race walking alone, \(F_{d}\) is the current aerodynamic drag. Figure 5 depicts the positions for five triple drafting formations and three quadruple drafting formations. Figure 6 depicts Cd and the drag reduction rate of the core race walker for 15 drafting formations obtained from both the wind tunnel experiments and CFD simulations. The maximum absolute error in drag reduction rate for all drafting formations is 6%, with a corresponding maximum relative error of 9.2%, which falls below 10%. Importantly, the optimal drafting formations of different numbers of race walkers are consistent in the CFD simulations and wind tunnel experiments. Specifically, double formation 3, triple formation 4, and quadruple formation 3 exhibit the highest drag reduction rates among their respective numbers of race walkers. The drag reduction rates of these formations in  
Figure 5: Race walking positions of triple and quadruple drafting formations. Red points indicate core race walker, blue points indicate auxiliary race walkers. (**a**) Triple formation, (**b**) quadruple formation. the wind tunnel experiment are 67%, 66%, and 81%, respectively. In the CFD numerical simulation, the corresponding drag reduction rates are 65%, 72%, and 85%. According to Figure 6, both the wind tunnel experiment and CFD simulation demonstrate that double drafting formations 1, 2, and 3 can significantly reduce the aerodynamic drag experienced by the core race walker who is following behind another one. Among the three formations, double drafting formation 3, where the two walkers are closest to each other, exhibits the highest effectiveness, achieving a drag reduction rate of 65% in the CFD simulation and 67% in the wind tunnel experiment. Conversely, the other double drafting formations have minimal effect on drag reduction. Therefore, it is recommended that the core race walker maintain a position as close as possible directly behind the front race walker to achieve the greatest reduction in drag when utilizing double drafting formation in race walking.