Download Supermileage Car Body Design

Supermileage Car Body Design
Ivan Monroy Ortiz, Charles Wong, Victor Bobadilla Garcia, Ching Hei Sum
Supervisor: Dr. Filippo Salustri
Abstract
As team captains and team members of the
Ryerson Supermileage team, a project to
improve on the aerodynamics of the previous
Ryerson Supermileage vehicle was undertaken.
By integrating theories from fluid mechanics,
aerodynamics of road vehicles, and studies of
existing benchmark low drag coefficient
vehicles in the present day, a series of vehicle
body designs were developed under the
packaging restrictions set out by the 2010
Ryerson
Supermileage vehicle chassis.
Iterative testing and fine-tuning of different
vehicle body geometries were conducted using
SolidWorks’ built-in CosmosFloWorks module
for Computational Fluid Dynamics simulation.
The final design features a low drag coefficient
of 0.08915, which represents a 50.5%
improvement in the drag coefficient from the
2007 Ryerson Supermileage vehicle body.
plane exhibits a drag coefficient of 0.04, whereas a
streamlined half-body at a ground plane will inherit
a much higher drag coefficient of 0.15 [1]. A design
solution that approximates a streamlined body in air
removed from a ground-plane became apparent as
the ultimate goal of the project towards the
finalization of the design concepts. To aid in
addressing the problems of the 2007 Ryerson
Supermileage vehicle body, the new 2010 vehicle
body was adapted to a tubular chassis to allow more
freedom in the design of the underbody. It will also
feature a small projected frontal surface area
permissible by an ultra-low driver seating position
and a vehicle tail that is well tapered to prevent the
drag-inducing effect of vortices traditionally
developed in the rear of most road vehicles, as well
as the high drag force contribution from uneven
pressure distribution along the body surfaces. In
total, five designs were devised before the final
design was chosen. The vehicle height and track
width for all designs were kept to be as consistent as
possible (with slight variability due to the geometry
of the bodies) to allow the design process to be
undertaken with a higher emphasis on optimization
of the different body geometries.
Design #1: Streamlined Half Body
Figure 1 2007 Ryerson Supermileage Vehicle
Introduction
Although fabricated from rigid and lightweight
carbon fiber, the body of the Ryerson
Supermileage vehicle from 2007 inherited
many deficiencies, which greatly negated any
benefits gained from the use of this expensive
material. Namely, the vehicle body was not
well-designed with its 1) large wheel humps, 2)
large frontal surface area, 3) rough surface
finish, 4) flat underbody 5) and unnecessarily
high body thickness. A streamlined body
placed in the air far-removed from a ground-
The first design was based heavily on the shape of a
streamlined half-body placed at the ground-plane.
According to literature from [2], the streamlined
half-body offset from the ground-plane with the
addition of wheels will experience a drag coefficient
of 0.15. CFD simulations within CosmosFloWorks
revealed a drag coefficient of 0.16681. However,
due to the height of the rear wheels, the total vehicle
length was increased to 4.22m vs. the original
vehicle length of 2.57m for the 2007 Ryerson
Supermileage vehicle body to allow the body to
properly taper at its tail, which is characteristic of a
dramatic increase in body weight due to the
requirements for the larger surface area. To
accurately recreate the semi-circular frontal surface
area while completely enclosing the tires within the
body, the projected frontal surface area of the body
was an unreasonably large 0.6248m2, which was
much larger than the 0.55m2 frontal surface area of
the 2007 vehicle body.
Design #2 and #3: Lofted Vehicle Body and
Lofted Vehicle Body with Tapered Tail
For design #2, a lofted vehicle body with
smoothly-transitioning body curves was
devised.
A drag coefficient of 0.12627
resulted from this design despite a larger
surface area than design #1, which is likely due
to its much lower body length at 3.14m (and
hence, lower friction drag), as well as a vehicle
underbody that tapers up gently from the
ground-plane near the body tail. This allows
the pressure gradient between the lower and
upper body to be closer in magnitude to each
other. In order to reduce the overall length, the
taper at the rear of the vehicle was not tapered
to a point. In design #3, the addition of a long
1.5m tail to design #2 was implemented to help
minimize the flow separation and occurrence of
vortices at the tail to a minimum. Results
indicated a drag coefficient of 0.11047, which
represents a marked improvement over the
similarly shaped design #2 in its basic form
without the addition of a tapered tail. The
improvement in the drag coefficient value was
consistent with analysis from literature [3].
wheel fairings integrated into the basic body shape,
design #5 inherited a slightly larger frontal surface
area of 0.44m2 than design #4, but the flow
characteristics were much more favorable due to a
simpler surface geometry for the air flow to traverse.
Similar to design #4, the upper body was derived
from a NACA 64-012 aerofoil due to its superior
aerodynamic performance. However, the aerofoil
was made larger to fully envelop the front wheels
within the basic body shape to reduce the likelihood
of vortices forming at the rear of the wheel fairings.
The bottom of the vehicle was constructed to follow
the curved contours of the tubular chassis as much
as possible to better equalize the pressure
distribution on the upper and lower surfaces of the
vehicle body. Simulations from CosmosFloWorks
demonstrated that the airflow characteristics were
excellent, with a low amount of flow separation at
the tail of the body and the rear of the front wheel
fairings.
Delta-wing shaped vortex generators
modeled accurately based on those from a
Mitsubishi Lancer Evolution VIII were implemented
fore of the flow separation point at the rear of the
front wheel fairings to delay the point at which the
flow separates on the vehicle underbody.
Design #4: Minimal Frontal Surface Area
A minimal frontal surface area was sought in
this design concept. By covering the front
wheels in low-profile wheel fairings, deriving
the upper body shape from a NACA 64-012
aerofoil, and creating a smooth vehicle
underbody, this concept featured the lowest
projected frontal surface area of all the designs
tested at 0.42m2. The drag coefficient was a
good 0.13386, and an impressive 0.12507 when
the rear wheel fairing’s diffuser angle was set to
3 degrees, which was discussed in literature as
an optimal value in reducing the drag
coefficient [4].
Unfortunately, the semidetached front wheel fairings were responsible
for creating large vortices at near the rear of the
fairings, which paved the way for further
improvements in the next design.
Figure 2 Airflow Trajectories on Final Design
The vortex generators were angled (both left/ right)
at 15 degrees from the direction of oncoming air for
optimum effect in delaying the flow separation point
to
a
location
further
downstream
[5].
Design #5: Final Design
Of all the design concepts studied, design #5
featured a drag coefficient of 0.09206 in its
basic form, and a drag coefficient of 0.08915 in
its improved form with the use of vortex
generators near the flow separation point of the
front wheel fairings. Owing to the unitized
Figure 3 Vortex Generators near Flow Separation Point of Fairing
Table
Table 1 Results from Different Designs
Design
Drag
Coefficient,
Cd
Old Design
0.18024
Design 1
0.16681
Design 2
0.12627
Design 3
0.11047
Design 4 with large diffuser
angle
0.13386
Design 4 with small diffuser
angle(3 degrees)
0.12507
Design 5
0.09206
Design 5 with Vortex
Generator
0.08915
IM7 6k yield moderate values of all the AS and IM
fibers that were studied, it was strong without being
too brittle. IM7 6k fibers can also help to reinforce
the frame making the overall vehicle more rigid and
to minimize the chassis deflection, giving the carbon
fiber a dual purpose, due to its superior strength.
The 2010 vehicle body has a total surface area of
6.17m2, whereas the old body from 2007 had a total
surface area of 5.94m2. An increase in surface area
of the new design was a reasonable compromise that
resulted from seating the driver in a much lower
driving position. Although a slightly higher surface
area resulted from the new design, the fabrication of
the body will be contracted out to a 3rd party such
that a lower body thickness can be constructed to
lower the total weight of the vehicle body to be less
than that of the 2007 vehicle body.
Succession Planning for Future Competitions
Material Considerations
Carbon fiber and glass fibers were both studied
for their use in the Supermileage body design.
The advantages of carbon fiber were its low
density, high tensile modulus and strength. Its
disadvantages were that the fiber was
anisotropic, low strain to failure, and lower
compressive strength compared to its tensile
strength.
The advantages of glass fibers are that they are
easily drawn into high-strength fibers from a
molten state, and are readily available.
Although fiberglass is a lightweight and
affordable material, it did not measure up to the
superior strengths and moduli of carbon fibers.
S Glass fibers had the highest tensile strength of
4.585 GPa. This fiber also had a modulus of
82.737kPa. IM7 6k Carbon fiber was chosen
over S glass fiber. This fiber has a tensile
strength of 5.310 GPa and a tensile modulus of
276 GPa.
To help motivate future members of the Ryerson
Supermileage team to advance further in the annual
Supermileage competition, and to develop a low
drag coefficient body for subsequent use on the
Ryerson Supermileage vehicle, a female mold will
be used to construct the body. With this method of
body fabrication, it is possible to mold multiple
copies of the same body design, with the possibility
of modifications of body surface geometries
integrated into each copy of the body. From an
aesthetics point of view, the body also features a
sleek and elegant design that is sure to also help
motivate future members on the Ryerson
Supermileage team to add further fuel-efficiency
improvements to the vehicle, allowing Ryerson to
develop a solid-footing in the Supermileage
competition standings once again in the near future.
Conclusions and Recommendations
Starting with a basic streamlined body placed near
the ground-plane, and transitioning to a lofted body
design, and finally to an ultra-low drag coefficient
vehicle body design derived from a NACA 64-012
aerofoil, the design of a lower drag and lighter
weight was realized. It was determined that the
ideal streamlined shapes with low drag coefficients
in free air do not perform well when used in their
basic configurations for road vehicles. In the end,
design #5, which had the lowest drag coefficient,
closely resembled a streamlined shape offset from
the ground-plane supported by three slim profiles
for the wheel fairings. It is predicted that a
vehicle body that is even more offset from the
ground-plane will exhibit even lower drag
coefficients at the expense of a higher vehicle
height, and likely, a higher center of gravity.
The final design featured many 3D surfaces that
were difficult to model in SolidWorks, but its
basic body geometry was very smooth. Deltawing shaped vortex generators were used near
the flow separation points of the wheel fairings
to decrease the drag coefficient on the final
vehicle body from 0.09206 (without vortex
generators) to 0.08915 (with vortex generators).
This represents a 50.5% reduction in the drag
coefficient of the 2007 vehicle body, which
inherited a drag coefficient of 0.18024. This is
a highly impressive result and will be an
excellent body for use by the Ryerson
Supermileage team for years to come.
To further lower the vehicle body’s drag
coefficient for future years, it is possible to
shorten the chassis’ track width such that the
driver is more well encapsulated within the
vehicle body, allowing a similar reduction in
the body’s projected frontal surface area.
Another method of reducing the frontal surface
area (and hence, drag coefficient), is by
designing a new vehicle without the use of a
separate vehicle chassis. Instead, the body will
also function as a structural component for
placement of chassis components within. In
such a design, the vehicle height can be reduced
by the height of the current chassis platform
(plus any allowances made for tolerances
between the body and the chassis).
Acknowledgements
The team would like to acknowledge Dr.
Filippo Salustri for his support throughout the
project, the Faculty of Mechanical and
Industrial Engineering for the opportunity to
provide a platform for designing and competing
a full-sized Supermileage vehicle, and the
Faculty of Architecture in helping create rapid
prototyping scaled models of the final body
design. Additionally, the team would like to
extend their acknowledgement to Franco
Acacia for his continued dedication in helping
the team realize the vision in creating a highly
streamlined vehicle body for the 2010 Ryerson
Supermileage project.
References
[1] Hucho, W. H. (1987). Aerodynamic of Road
Vehicles. Cambridge: University Press. p.202
[2] Hucho, W. H. (1998). Aerodynamics of Road
Vehicles (Fourth Edition ed.). United States of
America: Society of Automotive Engineers,
Inc.p20
[3] Hucho, W. H. (1998). Aerodynamics of Road
Vehicles (Fourth Edition ed.). United States of
America: Society of Automotive Engineers,
Inc.p165.
[4] Hucho, W. H. (1987). Aerodynamic of Road
Vehicles. Cambridge: University Press. p.143
[5] Hamamoto, N. (2004). Reduction, Research on
Aerodynamic Drag. Tokyo: Mitsubishi Motors.
p.13.