Research on generation mechanism of unsteady fluid forces and application to propulsion in swimming

对于人体游泳者在循环水通道中进行的实验，PIV(粒子图像测速)技术可以直观地显示非定常流场，并可以检测手部周围的涡流行为。此外，运动分析在运动生物力学领域得到了广泛的应用。运动分析可以对游泳运动员的非定常运动进行定量的分析，也可以对运动员复杂的运动进行评价。将两种方法结合起来，研究了游泳推力的产生机理。对两名受试者进行了测量；一名是女性奥运会游泳运动员(受试者1)，另一名是没有竞技生涯的男性(受试者2)。从流场可视化的结果来看，研究对象1在相态由内扫向外扫后产生较强的旋涡或涡对。此外，脱落涡对沿水槽流动方向跟随着一股喷流。相比之下，受试者2没有脱落任何涡对。经证实：游泳…中的手部动作在风洞实验中，为了研究前缘剖面对非定常流体力的影响，安装了几种不同形状的模型(圆形、三角形和方形)。在定常条件下，俯仰模型存在失速滞后现象，且最大升力系数大于最大升力系数。非定常流体力受前缘涡的影响，前缘涡因前缘轮廓不同而不同。此外，为了研究爬行前推进的机理，我们用热线风速仪和PIV测量了盘状翼型模拟人类手部的流场。还测量了俯仰和升沉翼型周围的流动结构。在高折合频率下，前缘涡和尖涡在翼型尾迹处形成，并在翼型周向速度达到最大时脱落。证实了非定常流体力与大涡的产生密切相关。降低的频率对俯仰运动过程中翼型边缘脱落的涡流结构有很大影响。在较高的折算频率下，显著的涡流形成在靠近翼型踏面边缘的位置，并在翼型尾迹处产生大尺度的涡流。较少

For experiments in circulating water channel by a human swimmerThe PIV (Particle Image Velocimetry) technique can visualize the unsteady flow field and can detect the vortex behavior around a hand. Moreover, motion analysis has been widely used in the field of biomechanics of sport. A motion analysis can analyze the unsteady motion of swimmer quantitatively, and can also be expected to evaluate the swimmer's complicated motion. Two methods were combined to know the generating mechanism of swimming thrust. Measurements were made for two subjects; one is a female Olympic swimmer (subject 1) and the other is a male with no competitive career (subject 2). From the results of visualization of flow field, subject 1 generates strong vortices or vortex pair after the phase turned from in-sweep to out-sweep. In addition, the shed vortex pair follows a jet flow in the direction of the flume flow. In contrast, subject 2 did not shed any vortex pairs. It was confirmed that: the hand motion in swim … More ming was closely related to the vortex generation and also to the thrust.For wind tunnel experimentsIn order to investigate the effect of leading edge profile on unsteady fluid forces, several types of model (circular, triangular and square shapes) were installed. The delay of stall for the pitching models is observed and also the value of maximum lift coefficient is greater than the maximum lift coefficient under stationary condition. The unsteady fluid forces are affected by the differences of the leading edge vortex due to the different leading edge profile. Furthermore, to investigate the mechanism of propulsion in front crawl swimming, we measured the flow field around a discoid airfoil simulating a human hand by using hot-wire anemometry and PIV. The structure of flow around the pitching and heaving airfoil was also measured. At high reduced frequency, the leading edge vortex and tip vortex are formed in the wake of the airfoil and shed when the circumferential velocity of the airfoil reaches maximum. It was confirmed that the unsteady fluid forces are closely related to the generation of large vortices. The flow structures due to the behavior of vortices shedding from the airfoil edge during the pitching motion were strongly affected by the reduced frequency. At high reduced frequency, the significant vortices were formed close to the airfoil's treading edge, and large scale vortices were generated in the wake of the airfoil. Less