14 Jul Wind Tunnel Testing Luminos
The first week of this summer saw Luminos and accompanying team members making a cross-country road trip to Aerodyn, a wind tunnel in North Carolina.
This is the second time in as many years, as well as in team history, that the team has made the trip. Overall, it was a great success, and well worth the 5700 mile drive.
With the World Solar Challenge approaching in a matter of months, our hope is to use the data gathered from the wind tunnel to improve the car, fully maximizing the potential of our aero-body design for race-time performance. This is different from last year’s trip, which was intended to characterize a car that had already raced.
The team brought the previous car, Xenith, to Aerodyn last year with a second goal of gaining experience in wind tunnel testing and learning how to use testing time most efficiently. After a successful four hours of wind tunnel test time, preceded and followed by set-up and take-down that ran with hardly a hitch, the team certainly achieved its goal in that regard. Wesley Ford and Nathan Golshan were the only two members on this trip that had been to Aerodyn with Xenith, but their prior experience was immensely helpful in guiding this year’s trip. Furthermore, with Luminos’s four-wheeled design, we were able to bolt our car directly to the actuators installed in the wind tunnel floor. This allowed testing to run much more efficiently than it had with Xenith, as we could adjust yaw, pitch, and ride height from the control room. (Xenith’s three-wheeled design did not fit the actuators, meaning the tunnel had to be spun down and the car manually adjusted between tests.) Testing Luminos was, in short, fluid—pun intended.
In terms of aerodynamics, Luminos proved to be just as successful, if not more so. Our best value obtained from the wind tunnel was even better than the 8.43 lbs of drag that CFD (Computational Fluid Dynamics) modeling had predicted. At our ideal average speed of 55 mph, Luminos should experience a mere 35 Newtons of drag force. For comparison, an average production vehicle experiences drag forces upwards of 230 Newtons (50 lbs). Luminos’s are roughly equivalent to that of a square foot of material held up against the wind.
One reason for this is that Luminos was designed to minimize wetted area, or the area in contact with external air flow. Wetted area experiences skin friction—the friction between a fluid and the surface moving through it. On a streamlined vehicle, it is skin friction over the entire wetted area that contributes significantly to drag. This was something that the team learned after designing Xenith, which had minimized frontal area, rather than wetted area. Luminos faced the added design challenge of significant rule changes for WSC 2013, mandating four wheels (instead of the usual three) and increased driver vision requirements. From an aerodynamic perspective, these were two challenging changes, both requiring more space on a vehicle. However, the team handled these adaptations well, incorporating both new requirements without compromising aerodynamic performance.
Overall, this trip to Aerodyn was a great success. We validated our existing aerodynamic modeling, while also gathering data that will allow us to optimize Luminos’s performance for the race. The team’s previous experience with wind tunnel testing allowed this session to run smoothly, and the experiences of this year’s team at Aerodyn will help the team continue with this endeavor. Lastly, the Aerodyn staff was nothing short of fantastic—we would like to thank them for all of their help, shared knowledge, and passion for what they do.