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By Steve Haake, University of Sheffield, Sheffield,
and Leigh Bramall, Fluent Europe Ltd.
View the pdf of this article
Surface pressure and pathlines for the unoptimized chair geometry
Visualization done using EnSight from CEI
Due to its successful use by the America’s
Cup and Formula 1 series teams
around the world, CFD has become
widely recognized as an effective tool in yacht
and automotive racing design. One outgrowth
of this success has been the crossover of CFD
technology to other areas of the sporting world.
While swimming, cycling, and skiing have already
benefited from CFD analysis, the sport of wheelchair
racing in Great Britain has recently begun
to make use of fluid flow modeling to help its
athletes in their quest for Paralympic glory in
the 2004 Athens games and beyond. Toward
this goal, in August 2001 UK Athletics commissioned
a feasibility study from the Sports
Engineering Research Group (SERG), a leading
center for research in sports technology
based at the University of Sheffield, and the
Center for Sports & Exercise Science at Sheffield
Hallam University. Together, the two institutions
have applied a range of sports science
and technology resources, including CFD, to
the project.
Surface pressure on the athlete before (left) and after (right)
optimization
Recirculation zone behind the athlete after optimization of
the wheelchair; the athlete is in an un-optimized position
The CFD focus of the project has been to
provide visual and numerical data on the aerodynamic
performance of Dave Holding, a British
athlete competing in the 100-meter and 200-meter wheelchair sprints, and whose physical
shape was considered the least aerodynamic
among the five athletes in the overall study.
Assessing the performance of Holding and his
chair required mechanical studies to be initiated,
in which a series of resistant forces were
analyzed to measure their impact on his performance.
The wheel alignment of the chair
was tested to identify its effect on rolling resistance,
and the effect of the chair’s mass was
also thoroughly investigated. Eventually, a final
optimized design was achieved. The mechanical
modifications were further supplemented
by conceptual ideas for specialized sportswear,
such as an aerodynamically optimized helmet,
to ensure minimum resistance for Holding and
his chair in racing position.
To compare the aerodynamics of each chair
design, two geometries were created - one
representing Holding in the chair prior to any
design changes, and the other incorporating
the suggested modifications. Solid CAD
models of the wheelchair were built using
Pro/ENGINEER, while two human forms representing
Holding were constructed using
SAMMIE CAD Ergonomics Design software.
The geometries were imported into GAMBIT,
and meshes were generated for each model
of Holding in position in the chair. The geometries
were complex, requiring tetrahedral
meshes of several hundred thousand cells to
ensure the accuracy of the results. The meshes
were read directly into FLUENT, where inlet
boundary conditions were used to simulate
wheelchair speeds of approximately 7 m/s.
The initial results showed the existence of
a recirculation zone behind the wheelchair and
a large wake effect, caused by separation over
the shoulders of the athlete. Design modifications
to the clothing and wheelchair structure,
however, were found to minimize the impact
of these phenomena, making a 3% reduction
in drag possible - equivalent to a reduction
of 0.03 seconds over 100 meters. Other tests
showed that these drag reductions, combined
with modifications that resulted in a total mass
reduction of 2.2% and improvements to the
alignment of the rear wheels, could deliver a
further improvement of 0.16 seconds over 100
meters. For the 100-meter race at the Sydney
Paralympics in 2000, a time reduction of this
magnitude would have propelled the thirdplace
competitor into first place! These findings
reinforced the potential significance of the
research. The success of the project has prompted
further study across an expanded range of
sports with a view toward boosting the success
of UK athletes in forthcoming Olympic
and Paralympic games.
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