INTRODUCTION: It has long been accepted that understanding fluid flow patterns in swimming should lead to performance enhancements. Unfortunately, the ability to quantify the effects of these flow patterns experimentally when swimming is limited and is typically only able to provide approximations of total body effects at best. Computational Fluid Dynamics (CFD) can be used to model and solve complex problems of fluid flow and is ideally suited to analysing drag and propulsion across the body when swimming.METHODS: A case-study approach was undertaken to examine the propulsion and drag forces across the body experienced during full body freestyle swimming using CFD. The swimmer used held the 50m and 100m freestyle World Record at the time of the testing and a full 3D surface scan of the swimmer was used for the CFD simulations. Manual 3D digitising was used to provide the 3D kinematics to animate the model. A realisable Kepsilon turbulence CFD model was used in the analysis.RESULTS: The overall changes in forces throughout the stroke were characterised by six clear cycles, containing four small peaks and two large peaks. These peaks represent the six beat kick pattern that was adopted, with the two large peaks correlating with the peak propulsion of the left and right arm strokes; which occurred simultaneously with two of the kick cycles. These peaks, and in particular the peaks associated with the arm stroke propulsion, were reflected in increases in the swimmer`s instantaneous velocity. An examination of the breakdown in the distribution of forces revealed that the arms and legs create a significant amount of the total propulsion, with the trunk contributing to the majority of the drag force. The hands provided a total propulsive momentum of 23.8Ns while the combined contribution of the wrist, forearm and elbow was 27.6Ns. This highlights that the forearm position during the underwater arm stroke is as critical as that of the hands. Likewise the thighs, knees and shanks also contributed a greater percentage of the propulsion than the feet. DISCUSSION: The current study provided insight into how propulsion and drag forces are generated throughout a full freestyle swimming stroke through the use of CFD analysis. The resultant outcome of the analysis is both an increased level of foundational knowledge related to the production of propulsion and drag forces, as well as the provision of practical points that may be used to improve freestyle performance.
© Copyright 2010 Biomechanics and Medicine in Swimming XI. Published by Norwegian School of Sport Sciences. All rights reserved.