Improving swimming performance through detailed flow measurements

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.