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Seasons in the Sun
Posted Mon April 21, 2014 @08:27AM
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Application By Ahthavan Sureshkumar,
Chief Engineer (2011Ė2013),
Blue Sky Solar Racing,
University of Toronto, Canada

During the 2013 Bridgestone World Solar Challenge in Australia, 38 solar-powered vehicles from 22 countries participated in a grueling 3,000-kilometer timed race. The technical and logistical challenges for this student competition are almost insurmountable; they require a truly dedicated team of individuals to make it a reality.

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Blue Sky Solar Racing relied on the enthusiasm of team members as well as support from the University of Toronto and a significant number of industry partners to place eighth in the challenger class.

In designing the solar car, engineering students used ANSYS Mechanical for static structural analysis of the vehicle's double wishbone suspension system, roll cage and rims. They applied ANSYS CFD to design an aerodynamic car body. ANSYS Workbench, CAD interfaces and ANSYS HPC solutions further streamlined the analysis workflow.

Solar cars participating in the challenge have unique packaging constraints, due to high-priority aerodynamic considerations, such as a streamlined body and wheel fairings, and a minimized wetted area, around which a new suspension must be designed. Blue Sky Solar Racing wanted to design a light, strong, robust suspension system to withstand the worst-case loads that the car would encounter. In general, reliability and driver safety are the highest priorities. For the 2013 race, the roll cage was particularly challenging because it had to fit the streamlined canopy of the (upper) aerobody (outer shell of the car), be strong enough to protect the driver from roll-overs, and shield him or her from any lateral movement of the top aerobody, which by design detaches during impact.

The team used the static structural module of ANSYS Mechanical within the ANSYS Workbench environment to analyze mechanical parts. The design of the suspension geometry gave students a significant moment arm to contend with. ANSYS capabilities allowed them to model the entire suspension system, providing a more-realistic model for expected stresses and deflection. By looking at the system as a whole, rather than just analyzing individual parts, team members easily identified components that would be significantly affected by changes in the moment arm and, thus, optimized the suspension accordingly. By determining resulting reaction forces and moments at various joints and bolt locations, Blue Sky Solar Racing properly sized rod ends and bolts to ensure that the system would perform reliably and robustly during the race.

The World Solar Challenge continues to push for development of a more practical solar car. This encouraged the team to consider a variety of form factors, each expected to have certain advantages/disadvantages in the race. The team assessed each aerobody based on drag, obtaining adequate downward force, positioning the center of pressure, and diminishing sensitivity to pitch ó all for anticipated race conditions. The center of pressure and pitching moment are crucial for the carís dynamic stability. The team had to identify areas of pressure separation and turbulence transition to help reduce the aerodynamic drag.

Pressure contour plot
Pressure contour plot for headwind case, given symmetry wall.

Team members took advantage of the full range of ANSYS CFD tools to design an excellent aerobody. ANSYS ICEM CFD provided very fine control over the mesh definition, particularly to create a high quality inflation layer next to the aerobody surface. The team has used ANSYS CFX CFD technology for a number of years, and the software allowed the participants to use an effective turbulence transition model and define appropriate turbulent inlet boundary conditions. ANSYS CFD-Post delivered a variety of ways to visualize the flow and its impact on the car body. The team also created customized performance indicators in CFX-Post expression language to help quantify performance metrics with ease.

Pressure contour plot
Pressure contour plot for headwind case, given symmetry wall. Bottom view.

Early on, the use of ANSYS software identified a significant downforce experienced by the car at high speeds. Although this resulted in an aerodynamic penalty, this downforce resulted in exceptionally safe and reliable operation of the car during the 100 kph winds experienced during the race. Many other teams had great difficulty driving in the strong winds of the Australian Outback.

turbulence kinetic energy plot
Top, bottom, side views of the turbulence kinetic energy contour plots indicating presence of laminar and turbulent flow regions.

At the 2013 Bridgestone World Solar Challenge, the Blue Sky Solar Racing car performed better than any of the teamís previous entries to the solar challenge; it achieved the highest placing to date. Team participants attribute this accomplishment to the robustness of the suspension system, the low drag of the aerobody and the reduced rolling resistance of the new tires.

Designing, building and racing a solar car is probably the most challenging and rewarding university experience that students can have. The problems encountered are unique and require team members to look beyond what they have learned, supplementing established methods with new insight gained from modern computational techniques.

This article originally appeared as a web exclusive in ANSYS Advantage magazine.

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Related Links
  • ANSYS Advantage
  • Blue Sky Solar Racing
  • Bridgestone World Solar Challenge
  • University of Toronto
  • More on Application
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