August 2nd 2004
High-Performance Swimsuits Covering Shoulder to Knee or Ankle Reduce Drag, Provide Competitive Edge, UB Researchers Show
Analysis techniques can be used to reduce drag in other aquatic sports
BUFFALO, N.Y. -- Be sure to pay attention to the suits that male swimmers wear when they compete in this year's Olympic Games.
Swimmers wearing a suit covering their torso from shoulder to knee or ankle should have a performance edge over competitors wearing suits that provide less body coverage, a study conducted at the University at Buffalo's Center for Research and Education in Special Environments has shown.
Using special facilities that can test the effect of the suit alone, not the swimmer's technique or style, UB researchers found that shoulder-to-knee and shoulder-to-ankle coverage decreased overall drag by 10-15 percent compared to waist-to-ankle, waist-to-knee suits or the minimal coverage brief traditionally used by swimmers.
Results of the study appeared in the June issue of Medicine and Science in Sports and Exercise.
"This study confirmed the reported reduction in total drag of modern total-body-coverage suits. In short, better informed swimsuit design could result in better performance," said Joseph C. Mollendorf, Ph.D., first author on the study and co-associate director of the Center for Research and Education in Special Environments. Molledorf is a professor of mechanical and aerospace engineering in the UB School of Engineering and Applied Sciences and professor of physiology and biophysics in the UB School of Medicine and Biomedical Sciences.
Mollendorf noted that "more importantly, and for the first time, the methods we developed allowed drag to be decomposed into its component parts quantitatively. This allowed the evaluation of friction, pressure and wave drag as a function of velocity. Understanding the components of drag will allow scientists to use drag-reducing methods that selectively affect the type of drag predominant at the velocities of interest for swimming and other aquatic sports. Scientists then can test their theories to insure that they produced the desired reductions in the components of drag and thus total drag."
The purpose of the current study was to develop a method to determine quantitatively the relative contribution of friction, pressure and wave drag to total drag as a function of velocity.
Five suits from a single manufacturer (Speedo) constructed of the same fabric (Fastskin), each providing different amounts of body coverage (shoulder-to-ankle, shoulder-to-knee, waist-to-ankle, waist-to-knee and briefs) were tested.
The drag of each suit was measured during passive towing at increasing speeds to simulate the velocity of competitive swimmers in the UB center's annular (doughnut-shaped) pool, and during starts and turns in the university's Olympic-sized pool. Seven males on UB's varsity swim team wore each suit once and the suits were tested in random order.
Results showed that overall drag decreased by 10-15 percent when the swimmers wore the shoulder-to-ankle or shoulder-to-knee suits, with no statistical difference between the two kinds of coverage, compared to the remaining suits.
Contrary to common belief in the competitive swimming field, the drag-reducing suits tested actually increased friction drag. Mollendorf hypothesized that the increase in friction drag may have resulted in a phenomenon in flow dynamics called "tripping the boundary layer," an artificial way of causing the flow of water over the body to remain attached to the body, which in this study reduced pressure drag by an average of 37 percent and wave drag by 60-80 percent, resulting in less overall drag.
"Before the results of this study were known, efforts to reduce swimsuit drag involved mainly attempts at reducing (skin) friction drag," said Mollendorf. "We now know that this may not be the most effective strategy.
"Although methods of measuring total drag are available, the resulting data do not allow a detailed understanding of what causes drag, and thus how to alter it to improve swimming performance," said Mollendorf. "Since total drag is comprised of three major components -- friction, pressure and wave -- and each is speed dependent, understanding the contribution of each of them independently provides a better understanding of drag and potential methods to reduce it."
UB has applied for a patent on drag-reducing technology for swimwear.
Additional researchers on the study were Albert C. Termin II, UB head swimming coach; Eric Oppenheim, former graduate student in the UB Department of Mechanical and Aerospace Engineering, and David Pendergast, Ed.D., professor in the UB Department of Physiology and Biophysics and co-associate director of the Center for Research and Education in Special Environments.
The research was supported by the United States Navy, NAVSEA, Navy Experimental Diving Unit. No funding or support was provided by the swimsuit manufacturer.
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