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

对于人类游泳者在循环水通道中的实验，PIV（粒子图像测速）技术可以将非定常流场可视化，并可以检测手周围的涡流行为。此外，运动分析在运动生物力学领域得到了广泛的应用。运动分析可以定量地分析游泳运动员的非定常运动，也可以对游泳运动员的复杂运动进行评价。将两种方法相结合，了解了游动推力的产生机理。对两个受试者进行了测量；一名是奥运女游泳运动员（实验对象1），另一名是没有竞技生涯的男子（实验对象2）。从流场的可视化结果来看，受试者1在相位由内掠转向外掠后产生强烈的涡或涡对。此外，在水槽流动的方向上，棚内涡对跟随射流。相比之下，受试者2没有脱落任何漩涡对。结果表明：游泳时的手部运动与涡旋的产生密切相关，也与推力密切相关。在风洞实验中，为了研究前缘型线对非定常流动力的影响，安装了几种模型（圆形、三角形和方形）。在平稳条件下，俯仰模型的最大升力系数大于最大升力系数。由于前缘型线的不同，前缘涡的不同会影响非定常流动力。此外，为了研究前爬泳的推进机制，我们利用热线风速仪和PIV测量了模拟人手的盘状翼型周围的流场。对俯仰和升沉翼型周围的流动结构也进行了测量。在高降频下，前缘涡和尖涡在翼型尾迹中形成，并在翼型周向速度达到最大值时脱落。结果表明，非定常流动力与大涡的产生密切相关。在俯仰运动过程中，由于翼型边缘的涡脱落行为而引起的流动结构受到频率降低的强烈影响。在高降频下，在翼型踏面边缘附近形成明显的涡，在翼型尾迹处形成大规模涡。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