  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.
