The effect of hand posture on swimming efficiency

• Published in: Experiments in fluids 2021-12, Vol.62 (12), Article 245
• Main Authors: van den Berg, Joris, Bazuin, Rens, Jux, Constantin, Sciacchitano, Andrea, Westerweel, Jerry, van de Water, Willem
• Format: Article
• Language: English
• Subjects: Drag; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Fingers; Fingers & toes; Flexing; Fluid- and Aerodynamics; Forearm; Hand (anatomy); Heat and Mass Transfer; Image reconstruction; Particle image velocimetry; Pressure distribution; Research Article; Swimming; Velocity distribution; Velocity measurement; Wind tunnels
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-021-03333-1

Our quest is for the thumb and finger positions that maximize drag in front crawl swimming and thus maximize propulsion efficiency. We focus on drag in a stationary flow. Swimming is in water, but using Reynolds similarity the drag experiments are done in a wind tunnel. We measure the forces on real-life models of a forearm with hands, flexing the thumb and fingers in various positions. We study the influence on drag of cupping the hand and flexing the thumb. We find that cupping the hand is detrimental for drag. Swimming is most efficient with a flat hand. Flexing the thumb has a small effect on the drag, such that the drag is largest for the opened (abducted) thumb. Flow structures around the hand are visualized using robotic volumetric particle image velocimetry. From the time-averaged velocity fields we reconstruct the pressure distribution on the hand. These pressures are compared to the result of a direct measurement. The reached accuracy of ≈  10% does not yet suffice to reproduce the small drag differences between the hand postures. Graphical Abstract