Improving swimming performance through detailed flow measurements

预测和测量作用在游泳者身体上的流体力是非常具有挑战性的，因为与动态自由表面相互作用、钝体流分离、大的非定常运动和柔软的可变形几何形状相关的复杂流动机制。在过去的9年里，性能运动工程实验室通过一系列的博士生为英国游泳队提供支持，然而，测量和理解游泳运动员周围形成的详细流动结构以及这些结构如何与人体相互作用，仍然存在一个明显的挑战。作用在身体上的推进力和阻力都受这些非定常流动特征的控制，因此提高我们对流动物理和生物力学的理解对于提高游泳成绩至关重要。关于如何为不同的运动员优化划水技术以最大限度地提高成绩，人们知之甚少。例如，在水下波动游泳中，推进力是由波浪状的身体运动产生的，这种运动已经被证明可以在游泳者身后产生一系列漩涡结构，从而增加产生的推力。除此之外，非定常流分离和自由表面相互作用使得阻力难以预测。这些复杂的流场很难评估，因此游泳者的效率和表现通常只能根据最大游泳速度来评估。最近数值模拟的发展使得模拟这种流动物理成为可能，但是目前还没有实验数据来验证这些非定常流场在游泳中的作用。该项目旨在与英国游泳协会、英国体育协会和Speedo合作，通过使用详细的流量测量来了解与游泳阻力和推进力相关的物理流动机制。游泳者周围的局部流动特征将以各种不同的方式进行评估，并提高保真度。最初，将使用气泡片确定关键的兴趣区域，以便将流量可视化与冲程运动学和关键性能指标（如最大速度）进行比较。在Boldrewood拖曳槽内，将使用新的水下粒子图像测速（PIV）系统对可变形人体模型进行详细的流量测量。水下数字图像相关（DIC）将用于评估人体的全场变形和泳衣对被动阻力的影响。为了量化实际游泳者周围的非定常流场，将开发气泡图像测速系统，以便在游泳池环境中进行测量。通过与英国游泳和Speedo的合作，这项研究有可能对泳装技术和英国在奥运会上的表现产生真正的影响。

Predicting and measuring the fluid forces acting on a swimmer's body is incredibly challenging due to the complex flow mechanisms associated with dynamic free surface interactions, bluff body flow separation, large unsteady motions and soft deformable geometries.The Performance Sports Engineering Laboratory has supported the British Swimming team for the last 9 years through a series of PhD students, however there is still a distinct challenge associated with measuring and understanding the detailed flow structures that develop around a swimmer and how these interact with the human body. Both the propulsive forces and the drag acting on the body are governed by these unsteady flow features therefore improving our understanding of the flow physics and biomechanics is essential to improving swimming performance. Little is known about how to optimise stroke technique for different athletes to maximise performance. For instance in underwater undulating swimming the propulsive force is generated by a wave like body motion which has been shown to create a series of vortex structures behind the swimmer, increasing the thrust generated. In addition to this the unsteady flow separation and free surface interactions makes the resistive forces difficult to predict. These complex flow fields are very challenging to assess and therefore a swimmer's efficiency and performance is typically only assessed based on maximum swimming speed. Recent developments in numerical modelling have made it possible to simulate some of this flow physics however there is currently no experimental data available to validate these unsteady flow fields in swimming.This project aims to work with British Swimming the English Institute of Sport and Speedo to understand the physical flow mechanisms associated with swimming resistance and propulsion through the use of detailed flow measurements. The local flow features that develop around a swimmer will be assessed in a variety of different ways with increasing levels of fidelity. Initially key areas of interest will be identified using a bubble sheet to allow flow visualisation to be compared to stroke kinematics and key performance indicators such as maximum velocity. Detailed flow measurements around a deformable mannequin will be conducted within the Boldrewood towing tank using the new underwater Particle Image Velocimetry (PIV) system. Underwater Digital Image Correlation (DIC) will be used to assess the full field deformation of the body and the impact of swim suits on the passive resistance. To quantify the unsteady flow field around an actual swimmer a bubble image velocimetry system will be developed to allow measurements to be taken in a swimming pool environment. Through the involvement with British Swimming and Speedo this research has the potential to have real impact on both swim suit technology and British performance at the Olympic games.