Unsteady flow field around a human hand and propulsive force in swimming

Abstract

Much effort has been undertaken for the estimation of propulsive force of swimmers in the front crawl. Estimation is typically based on steady flow theory: so-called the quasi-steady analysis. Flow fields around a swimmer, however, are extremely unsteady because the change direction of hand produces unsteady vortex motions. To evaluate the force correctly, it is necessary to know the unsteady properties determined from the vortex dynamics because that unsteadiness is known to make the force greater. Unsteady flow measurements were made for this study using a sophisticated technique called particle image velocimetry (PIV) in several horizontal planes for subjects swimming in a flume. Using that method, a hundred time-sequential flow fields are obtainable simultaneously. Each flow field was calculated from two particle images using the cross-correlation method. The intensity of vortices and their locations were identified. A strong vortex was generated near the hand and then shed by directional change of the hand in the transition phase from in-sweep to out-sweep. When the vortex was shed, a new vortex rotating in the opposite direction around the hand was created. The pair of vortices induced the velocity component in the direction opposite to the swimming. Results of this study show that the momentum change attributable to the increase of this velocity component is the origin of thrust force by the hand.

Individual–Environment Interactions in Swimming: The Smallest Unit for Analysing the Emergence of Coordination Dynamics in Performance?

“…Such results were complemented with 2-D [60] and 3-D [61] PIV studies to analyse the stroke of a robotic arm in water. In both approaches, the motion resulted in the production of vortices [4], similar to those previously observed [59] when the hand adapted its orientation. An important advantage of PIV is that it does not disturb the swimmer's actions [55] in experiments.…”

“…A similar method is particle image velocimetry (PIV), a technique that uses a laser to track illuminated particles introduced into fluids (see [58]). This experimental approach has been used in competitive swimming to identify fluid motions associated with an upper limb stroke [59][60][61], a sculling sequence [62] and a dolphin kick [63]. A pioneer PIV work [59] focused on fluid perturbations occasioned by a front crawler's hand.…”

“…This experimental approach has been used in competitive swimming to identify fluid motions associated with an upper limb stroke [59][60][61], a sculling sequence [62] and a dolphin kick [63]. A pioneer PIV work [59] focused on fluid perturbations occasioned by a front crawler's hand. This twodimensional analysis revealed that adaptations in hand orientation were linked to the emergence of a starting vortex on the dorsal aspect of the hand (the water particles adopted a circular motion [4]).…”

“…A second vortex was observed around the hand, rotating in the opposite direction to the first vortex, creating changes in fluid momentum. This interaction led to jet flows between the two vortices and a modification in fluid hydrodynamics (lift force on the hand that contributes to thrust production [59]). Such results were complemented with 2-D [60] and 3-D [61] PIV studies to analyse the stroke of a robotic arm in water.…”

Investigation of the Unsteady Mechanism in the Generation of Propulsive Force While Swimming Using a Synchronized Flow Visualization and Motion Analysis System

“…Using PIV Matsuuchi et al (2004) first demonstrated the flow field occurring around a moving hand while swimming, which may be the main source of propulsion for the crawl stroke. Momentum generation was estimated from this flow field obtained through PIV (Matsuuchi et al (2009). According to Newton's second law of motion, the increment of momentum leads directly to the force generation.…”