Northwestern Solar Car Team
Status: In Progress
Role: Chief Mechanical Engineer
Project Type: Engineering Team
Project Timeframe: 9/22/2021 - Present
Categories: Manufacturing, CAD, automotive design
Skills/Software used: lathe, mill, waterjet, sheet metal, machine shop tools, SolidWorks
NU Solar is a car team that builds a solar-powered racecar from scratch every year and attends the FSGP grand prix in the summer, where universities all around the continent come and race their solar cars. Our team has 4 teams: mechanical, electrical, software, and business. As the mechanical chief engineer, I lead over 20 students spread out in chassis, aerobody, suspension, and ergonomics teams and I am responsible for the overall mechanical integrity of the car.
One project I am responsible for this design cycle aside from leading the team is the aerobody design and optimization. As the outermost component of the car, the aerobody has to be aerodynamic, structurally strong (enough), not too difficult to manufacture, and compatible with inner subsystems such as the chassis elements. Starting with the design from our last car, I analyzed the drag concentrations in CFD and identified two areas where the drag can be reduced, namely a canoe-shaped extension at the bottom, as well as the double-faring design. After reorganizing inner components, I designed a compatible aeroshell that eliminated the canoe structure as well and joined the fairings together for aerodynamic and increased storage capabilities. The coefficient of drag was reduced from about 0.15 to about 0.11, and the drag force reduced from about 60 N to about 50 N, as shown in the pictures below.
Another project I have worked on was the airflow optimization of the cells within the battery box. Since battery overheating is a major safety concern for the driver, proper air cooling is needed. First, pressure drop and temperature information was extracted from a simulation of the actual battery geometry at given air flow rates. A simplified model of the battery was constructed from this that takes the average temperature of the whole pack, which sacrifices individual cell accuracy but greatly reduced computational costs.
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Then, the whole layout of the battery pack was build in CAD with the simplified battery models. Since the location of the packs are fixed, only the battery box lid and sides are subject to geometry change. I generated 3 such designs: one with a 50 mm gap from the lid to the top of the packs, one with no gap, and one with a curved lid and side intended to direct air towards the center packs, which historically showed worse cooling than the others. The models were then ran with a mass flow rate inlet condition with room temperature air, which simulates a fan-driven cooling air stream. The outlet temperature as well as the individual pack temperatures were monitored.
The three configurations in the order mentioned above are shown below. The first design demonstrated the highest average pack temperature at 313 degrees Celsius. The second design greately reduced the maximum average pack temperature to 305 degrees Celsius, although the packs near the outlet are cooled less effectively than those in front (shown in red). The last design, which targeted the middle cells, indeed showed a more even cooling distribution compared to the first two designs, although the maximum average cell temperature was at 308 degrees Celsius, which is 3 degrees Celsius hotter than option 2. As a result, option 2 was selected as the best choice moving forward.
As a trainer in the Ford Motor Company Design Center, I also serve a part in the machine shop teaching newer members and students how to use machine tools safely and correctly. Some tools I've trained people on include the likes of the horizontal bandsaw, the lathe, the mill, etc.
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In Baja, I also helped train people who are unfamiliar with CAD the basics of design on computer.