Improving swimming performance through detailed flow measurements

预测和测量作用在游泳者身上的流体力是非常具有挑战性的，因为与动态自由面相互作用、钝体流动分离、大型非定常运动和柔软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博士生为英国游泳队提供支持，然而，在测量和了解围绕游泳者发展的详细流动结构以及这些流动结构如何与人体相互作用方面，仍然存在一个明显的挑战。作用在人体上的推动力和阻力都是由这些非定常流动特征决定的，因此，提高我们对流动物理和生物力学的理解是提高游泳成绩的关键。对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，在水下起伏游泳中，推进力是由波浪状的身体运动产生的，这已经被证明在游泳者身后产生一系列的漩涡结构，增加产生的推力。此外，非定常流动的分离和自由面的相互作用使阻力难以预测。这些复杂的流场很难评估，因此，通常只根据最大游泳速度来评估游泳者的效率和表现。最近在数值模拟方面的发展已经使得模拟这种流动物理成为可能，然而目前还没有实验数据来验证游泳中的这些非定常流动。该项目旨在与英国游泳、英国运动和Speedo学院合作，通过使用详细的流动测量来了解与游泳阻力和推进相关的物理流动机制。随着保真度的提高，将以各种不同的方式评估游泳者周围形成的局部流动特征。最初，将使用气泡表确定感兴趣的关键区域，以便将流动可视化与行程运动学和关键性能指标(如最大速度)进行比较。使用新的水下粒子图像测速系统(PIV)，将在博尔德伍德拖车水箱内对可变形人体模型周围的流动进行详细测量。水下数字图像相关(DIC)将被用来评估身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，将开发一种气泡图像测速系统，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衣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.