In a simulation run at the Ohio Supercomputer Center, an isolated view of a wheel on the Buckeye Bullet illustrates airflow within the wheel well with the vehicle traveling at 300 mph.. |
Building a battery-powered land speed vehicle capable of
achieving a speed of 400+ miles per hour requires innovative components,
corporate partnerships, hours of diligent preparation, and a powerful
supercomputer.
A team of engineering students at The Ohio State
University’s (OSU) Center for Automotive Research (CAR) recently began running
aerodynamics simulations at the Ohio Supercomputer Center (OSC), one of the
first steps in the long and careful process of designing, building, and racing
the fourth iteration of their record-breaking, alternative-fuel streamliner fluctuations.
“The third-generation electric land speed record vehicle to
be designed and built by OSU students, the Buckeye Bullet 3, will be an entirely
new car designed and built from the ground up,” notes Giorgio Rizzoni, PhD,
professor of mechanical and aerospace engineering and director of CAR. “Driven
by two custom-made electric motors designed and developed by Venturi, and
powered by prismatic A123 batteries, the goal of the new vehicle will be to
surpass all previous electric vehicle records.”
In 2004, the team achieved distinction on the speedway at
Bonneville Salt Flats in Wendover, Utah, by setting the U.S. electric land speed record at
just over 314 mph with the original Buckeye Bullet, a nickel-metal hydride
battery-powered vehicle.
Several years later, the team returned with the Buckeye
Bullet 2, a completely new vehicle powered by hydrogen fuel cells, and set the
international land speed record for that class at nearly 303 mph. The team then
replaced the power source, once again, using the same frame and body with a new
generation of lithium-ion batteries and set an international electric vehicle
record in partnership with Venturi Automobiles and A123 Systems at just over
307 mph.
“OSC has been a partner of the Buckeye Bullet team throughout
the project’s history,” says Ashok Krishnamurthy, OSC interim co-executive
director. “We’ve been extremely pleased to provide computational resources and
technical assistance to the student engineers as they learn valuable
computational science skills that they can easily transfer to careers in the
automotive industry and elsewhere.”
This spring, the Buckeye Bullet team, again in partnership
with Venturi and A123 Systems, began the development process for a completely
re-engineered vehicle designed to break the 400-mph mark. In consideration of
that blistering speed, one of the first critical aspects the team had to
consider was the aerodynamic design of the vehicle.
“This goal places the team in direct competition with many
of the fastest internal combustion cars in the world,” says Cary Bork, chief
engineer for the team and an OSU graduate student in mechanical engineering.
“What sets the new design apart from the previous Buckeye Bullet vehicles is
that at these higher speeds it is possible to produce shock waves under the
vehicle. Such shock waves under the vehicle negatively affect the vehicle drag
and can produce lift. Lift is undesirable in this application. Minimizing or
eliminating these shock waves is critical to ensuring the safety and stability
of the vehicle.”
For both versions of the Buckeye Bullet 2, student engineers
ran aerodynamics simulations on OSC computer systems to compliment studies of
physical models tested in wind tunnels. However, the current team quickly found
that wind tunnels with a “rolling-road” component required to test land-bound
vehicles at the target speeds don’t exist. Rizzoni and Bork, therefore,
leveraged the flagship IBM 1350 Opteron Cluster at OSC to run extensive
simulations, initially focusing on validating performance of Buckeye Bullet 2
and eventually giving shape to the lean, new streamliner.
“We’re using computational fluid dynamics (CFD) to design
and optimize the vehicle shape,” says Cary Bork, a graduate student and chief
engineer for the project. “The simulations are needed to accurately predict the
aerodynamic forces on the vehicle at these speeds and can only be run on large
computing clusters. Various mesh sizes have been used from 1 million to 50
million cells. Most of the simulations use 25 million cells.”
In addition to an overall optimization of the body and fin
shape, the new aerodynamic design features several additional areas of
improvement over its predecessors. The vehicle will incorporate a layout where
the driver is placed forward of the front tires to improve volume utilization,
reduce overall vehicle length, decrease the vehicle drag by five percent and
improve the vehicle balance. Also, the team is studying the addition of wind
deflectors beneath the vehicle and in front of the tires to decrease the amount
of air that enters the wheel well, thereby reducing drag as much as 14.9%.
Finally, the team is studying simulations of new air-brake equipment to determine
the system’s effect on vehicle stability.
Most of the CFD design is being completed using OpenFOAM, a
free, open-source software package, and meshing is done using OpenFOAM’s
automated utility snappyHexMesh. Vehicle geometry for the vehicle is being generated
using Catia solid modeling and surfacing software, while post-processing is
performed using Paraview. Some additional CFD testing also will be completed
using Fluent software for comparative purposes. The team has brought on the Dublin, Ohio,
firm TotalSim LLC, a frequent collaborative partner of OSC, as a technical
partner and CFD consultant.
The Buckeye Bullet team plans to complete the design process
by the end of the summer and spend the upcoming academic year constructing and
testing the vehicle. Then, in Fall 2012, the students intend to return to the
Bonneville Speedway to unveil yet another record-setting Buckeye Bullet.