Vortex structure and fluid force changed by altering whole-body kinematic parameters during underwater undulatory swimming.

ABSTRACT

Swimmers generate vortices around their bodies during underwater undulatory swimming (UUS). Alteration of UUS movement would induce changes in vortex structure and fluid force. This study investigated whether a skilled swimmer's movement generated an effective vortex and fluid force for increasing the UUS velocity. A three-dimensional digital model and kinematic data yielded during UUS with maximum effort were collected for one skilled and one unskilled swimmer. The skilled swimmer's UUS kinematics were input into the skilled swimmer's model (SK-SM) and unskilled swimmer's model (SK-USM), followed by the kinematics of the unskilled swimmer (USK-USM and USK-SM, respectively). The vortex area, circulation, and peak drag force were determined using computational fluid dynamics. A larger vortex with greater circulation at the ventral side of the trunk and a greater circulation vortex behind the swimmer were observed in SK-USM compared to USK-USM. USK-SM generated a smaller vortex on the ventral side of the trunk and behind the swimmer, with a weaker circulation behind the swimmer compared to SK-SM. The peak drag force was larger for SK-USM than for USK-USM. Our results indicate that an effective vortex for propulsion was generated when a skilled swimmer's UUS kinematics was input in the other swimmer's model.