## 2 Methods for Drag Reduction in Drafting Formations in Race Walking
### Numerical Simulation Method Based on Computational Fluid Dynamics  
#### 2.2.1 Race Walker Geometry  
This study employs static models of race walkers in typical drafting formations. A 3D scanner is used to acquire a model of the core race walker in a standard race walking pose. The 3D-scanned human body model exhibits high precision and captures intricate details such as clothing folds, ears, and noses. Nevertheless, these gaps pose challenges for subsequent mesh generation. During the pre-processing stage, Spaecclaim v19 offers the Shrinkwrap feature, which generates a patch-based enclosure, wraps the model, closes gaps, and smooths sharp areas, thereby improving the mesh quality. It is crucial for researchers to meticulously determine the ideal size of the gaps around the ears and nose. The study investigates the impact of gap sizes (3 mm, 5 mm, and 10 mm) on drag and observes that the drag error remained below 0.5%. Consequently, a gap size of 10 mm is selected in this paper to improve the grid quality and decrease the number of grids. Figure 2 presents the model of the core race walker and an example of drafting formations in CFD simulation. The model of the core race walker has a height of 1.76 m, an orthographic windward area of 0.46 m\({}^{2}\), a mass of 61.2 kg, and a volume of 0.656 m\({}^{3}\). In wind tunnel experiments and CFD simulations, static human models are typically preferred over dynamic models. This preference arises from the complexity introduced by dynamic models and the associated challenges, such as accommodating the changing postures of athletes. Presently, there is a deficiency in well-established technologies for effectively addressing these challenges. Static models can partially meet our needs for studying the drafting effect of the human body model. Static human models partially  
Figure 1: Positions of seven different double drafting formations and a race walking scene. Red point indicates core race walker, blue points indicate auxiliary race walkers. **(a)** Positions of double drafting formation, **(b)** double drafting formation 4 experiment site [22]. fulfill our needs for studying the drafting effect of the human body model by allowing us to gather essential data on aerodynamic drag and drafting effects. This approach proves particularly suitable for comparing aerodynamic variations among athletes under different speeds and wind conditions. For instance, the majority of recent studies investigating the drafting effect of humans in motion employ static models, encompassing a range of sports including cycling, running, swimming, and cross-country skiing [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17]. While static models cannot replicate all the intricacies and dynamics of real motion, they can still yield valuable insights and guidance through a thorough analysis of comprehensive experimental data and computational models. These research findings offer valuable assistance in sports equipment design, training optimization, and the formulation of competitive strategies. In actual competitions, each athlete's body shape and movement posture are different, and the situation is also very complicated. This poses challenges for wind tunnel experiments and CFD calculations to account for differences between multiple athletes. Current studies generally employ some simplifying methods and assumptions. For example, in wind tunnel experiments, multi-person experiments are usually performed. Although the body shape of each athlete is different, the movement posture remains the same. This makes it easier to compare differences in aerodynamic properties between athletes of different body shapes. These experiments are usually analyzed using averaged parameters and metrics to draw general conclusions about aerodynamic drag and other aerodynamic properties. Similarly, CFD simulations typically employ a single-scanned human body model.