Preliminary numerical investigation in open currents-water swimming: Pressure field in the swimmer wake

The drafting in swimming is a sports practice usually used during the open water race of triathlon. Indeed, it is well known that swimming drafting behind or close to the lead swimmer induces a reduction in drag, once the draft swimmer is located in the low pressure field of the lead swimmer's wake. For this purpose, in order to determine the best position for the draft swimmer, a preliminary perfect knowledge of the lead swimmer's wake is necessary in presence or not of currents. The present preliminary study focuses this point before developing further analyses on reducing drag and enhancing performance in drafting by considering both lead and draft swimmers. In this work, the computational fluid dynamics (CFD) method was used in order to evaluate the hydrodynamic drag during the swimmer's displacement in presence of currents. The standard k-ω turbulence model was chosen to predict the resistance forces with currents-negative (α = 0°: aligned position of the swimmer's body relative to the main flow direction) and cross-currents (angle of incidence of the swimmer's body relative to the main flow direction, respectively 10 and 20°). The analysis of the CFD results have shown that the best position for a draft swimmer was found to be directly behind the lead swimmer (close to the toes) and very close to the side of the lead swimmer when drafter's head is between shoulders and hip level of the leader.