On the search to reduce a swimmer’s resistance: Surface-piercing bluff bodies over the critical Re-Fr range

Abstract

Swimming as an Olympic sport is getting ever more competitive. Since the ban of the full-body length suits in 2009, research in swimming has had the aim of re-establishing new world records. This research investigates the likely dominance of the flow regime around the swimmer’s head on their overall drag resistance. Both pool testing of swimmers and numerical simulations were initially undertaken to provide an insight into the measurement challenges at stake when evaluating a swimmer's resistance. Due to the inherent variability of a swimmer's performance, limited access to elite swimmers and excessive computational requirements the work concentrates on the use of rigid models for testing in a towing tank. A methodology aimed at breaking down the complexity of the flow physics around a swimmer's body is developed through the study of three models arrangements: a sphere, a head and a mannequin. A surface-piercing sphere is drag-tested over the critical Re-Fr range (1x10⁵ ≤ Re ≤ 7x10⁵, and 0.4 ≤ Fr ≤ 1.5). Using a combination of above-water still photographs/videos and drag/vertical force measurements, a flow taxonomy is established. The existence of a drag crisis over the laminar to turbulent boundary layer transition is highlighted as a key feature that influences a swimmer’s resistance. It is coupled with a sharp change of free surface deformation, from a large breaking wave to a thin sheet of fluid that passes cleanly over the sphere. A similar flow taxonomy is observed in the case of a head and visual observations of a flow regime change over the head are noticed when part of the mannequin. Various caps/goggles and head positions/shapes are tested on either the head only or with the mannequin’s body. These studies indicate that equipment can have a large influence on a swimmer’s resistance. Although a pre-selection process in a towing tank environment proved to be useful for manufacturers, an elite athlete still needs to be drag-tested to determine the best equipment for their head shape and body morphology. An initial protocol to select the best equipment (goggles, cap and suit) for each individual athlete is therefore suggested.

More information

Identifiers

ORCID for Marion Carole James: orcid.org/0000-0002-6964-4598

ORCID for Stephen Turnock: orcid.org/0000-0001-6288-0400

ORCID for Dominic Hudson: orcid.org/0000-0002-2012-6255

ORCID for Dominic Taunton: orcid.org/0000-0002-6865-089X

Catalogue record

Export record