Modeling the influence of drafting formations in running on the experienced drag force using fixed and free-to-move bluff bodies

Based on a series of numerical simulations, we show that simple 2D simulations using bluff bodies (cylinders) in different drafting formations can be used to investigate the relative change in drag experienced by runners. We first show that cylinders that are placed in different formations experience similar relative drag reductions as those previously observed based on 3D simulations of runners. We show that if the cylinders are allowed to move freely in a direction perpendicular to the direction of running, then if the overall drag reduction in the group is not significant initially, then the cylinders reconfigure themselves such that the total drag that the group experiences as a whole is reduced. This reconfiguration sometimes results in drag reduction for the main runner (as opposed to pacers who run to support the main runner) as well. If significant drag reduction is already observed in the original configuration, then the cylinders do not tend to reconfigure themselves and stay in their original locations. Our results show that using cylinders free to move laterally is a computationally efficient method to search for efficient running formations.