• Caltech senior Yuyang Fan (left) and research scientist Daegyoum Kim in front of the wind tunnel they built over the summer. The machine is powered by 100 computer fans (background).
08/16/2011 07:00:00

A Fan of Caltech

Over the coming weeks, we’ll be highlighting several undergraduates and their summer research at Caltech. Some are Techers; others hail from schools across the country. Most are participating in the Summer Undergraduate Research Fellowships (SURF) program, a unique opportunity for undergraduates to spend 10 weeks over the summer doing original research with Caltech faculty. At the end of the project, students write a paper and present their work at SURF Seminar Day, which will take place on October 15 this year.

When summer started, Caltech senior Yuyang Fan was handed a picture taken with a cell phone. The image showed a large box with an array of small fans covering one side. It was a wind tunnel—a simple one, but a wind tunnel nevertheless. Fan's mission? To build one himself as part of his SURF project.

And the catch? Other than the picture, he was given nothing. "That's all the information I got," he says.

It turns out that building a wind tunnel wasn't even the SURF project he had signed up for. Fan had proposed working with Mory Gharib, professor of aeronautics, and graduate student Julia Cosse on developing flexible wind-turbine blades; the blades were inspired by a shrub called the Spanish Broom, whose seeds are curled up in a pod that unfurls when wet. But when he showed up for work this summer, Gharib and Cosse asked if he would be willing to swap projects with someone else, since each project would be a better fit for the other student's backgrounds.

The wind tunnel would be for Daegyoum Kim, a research scientist working with Gharib, who needed the tunnel to test new ways of harnessing wind power. Kim wanted to see if he could extract wind energy using flapping flags instead of conventional spinning propellers. For his experiments, he would need a device that could simulate the gusts and shifting speeds of real-world wind. He also wanted to do some tests on vertical-axis wind turbines, which resemble eggbeaters jutting from the ground. Big, fancy facilities like the Lucas Adaptive Wall Wind Tunnel in the basement of Guggenheim can only blast air in a single, uniform flow—useful for analyzing the aerodynamics of objects ranging from cars to planes to soccer balls. But what Kim needed was a tunnel that produced shear flow—or flow in which wind speed changes with position or time. And he preferred a machine that didn't cost too much.

"There's no cheap tunnel that can do shear flow," Fan says. And so, with just some technical requirements, and guidance from Kim and Gharib, he would have to make one from scratch.

It was unexpected, but Fan was eager to do research on wind energy, so he accepted the challenge. "I thought it would be cool to build my own device," he says. After all, as someone who came to Pasadena from Nanjing, China, by way of Iowa, Fan seems to be quite good at adapting to change.

After high school, Fan left his home and family in Nanjing, a metropolis of eight million people, for Iowa's Grinnell College located in Grinnell, a town with a population of just 9,000. When he arrived at Grinnell, he hadn't yet fully mastered English, and Grinnell is a liberal arts college with a curriculum heavy on reading and writing. The first snow in October was exciting, but six months of it wore him down. "Food was an issue, too," he says. "They have a lot of corn."

At Grinnell, Fan majored in physics. In the summer of 2009, he came to Caltech as a SURF student to work on nuclear magnetic resonance studies of organic molecules with Jack Roberts, professor of chemistry. Fan liked Caltech so much that he applied to the Institute's 3/2 program, which allows students from a select group of liberal arts colleges to transfer to Caltech after their third year, spending two more years of study in a field not offered by their college and earning two bachelor's degrees in the process. Fan, who is interested in renewable energy, is studying mechanical engineering at Caltech. He's also a part of the Solar Decathlon team—a group of students from Caltech and the Southern California Institute of Architecture who are competing with other schools to build the most energy-efficient, attractive, and affordable house they can.

Having completed his first year at Caltech, Fan has spent much of his summer on the second floor of Guggenheim, building the wind tunnel. During the first two to three weeks of the project, he designed the machine, working out all the wiring and the control systems. By the end of July, the tunnel—which is six feet long, four feet wide, and four feet tall (excluding the stand)—was nearly complete. Fan's tunnel is more powerful than the one in the picture he was shown (it was built at Oklahoma State University to test small, flying vehicles). He used 100 relatively powerful, coaster-sized computer fans, the kinds usually reserved for souped-up gaming computers. These fans blow air at around nine meters per second (about 20 miles per hour), twice as fast as in the Oklahoma design.

The opportunity for hands-on work has been rewarding, Fan says. But as with any good research experience, the work has also sometimes been tedious (Fan had to turn hundreds of screws by hand to attach the fans, for example). Even though the tunnel is mostly assembled, there's still a lot of work to be done to calibrate and test the machine. Soon, though, it will be ready for the first experiments, and Fan will continue his research during the school year.

Fan has one more year left at Caltech, and then he plans to go to grad school. But for now he says he's loving Pasadena. "Here, the weather is so nice," he says. The large Asian community and the bounty of Asian cuisine also help. Even though Pasadena is an ocean away from Nanjing, he says he doesn't miss home too much. "There's not enough time to be homesick."

Written by Marcus Woo