The effect of finger spreading on drag of the hand in human swimming

TL;DR

This study investigates how spreading fingers affects hydrodynamic drag in swimming through numerical simulations, experiments, and an analytical model, revealing modest drag reductions and force moment improvements at optimal finger spreading.

Contribution

It introduces a combined numerical, experimental, and analytical approach to quantify the impact of finger spreading on swimming hand hydrodynamics, highlighting optimal spreading angles.

Findings

Drag coefficient increases by 2-5% with finger spreading.

Force moment improves by 5-8% at 10 degrees spreading.

Analytical model explains drag variation with finger spacing.

Abstract

The effect of finger spreading on hydrodynamic drag in swimming is studied both with a numerical simulation and with laboratory experiments. Both approaches are based on the exact same 3D model of the hand with attached forearm. The virtual version of the hand with forearm was implemented in a numerical code by means of an immersed boundary method and the physical version was studied in a wind tunnel experiment. An enhancement of the drag coefficient of 2 and 5% compared to the case with closed fingers was found for the numerical simulation and experiment, respectively. A 5 and 8% favourable effect on the (dimensionless) force moment at an optimal finger spreading of 10 degrees was found, which indicates that the difference is more outspoken in the force moment. Also an analytical model is proposed, using scaling arguments similar to the Betz actuator disk model, to explain the drag coefficient as a function of finger spacing.