Picture a fish swimming in water. As its fins move, they’re constantly creating new flows and swirls in the fluid and producing vortices in the fish’s wake.
Such turbulent flows are highly complex and ever-changing. And for researchers who study fluid flow, it’s challenging to uncover the fundamental fluid mechanics that govern the flow. In fact, it’s even difficult for a supercomputer to do it in a way that’s practical for an engineering application.
“This area has a big challenge in that the computational resources needed to resolve one of these really complicated flows is insurmountable,” says Jennifer Franck. “So instead you have to create models and make informed guesses about what the flow will do.”
Franck, who joined the Department of Engineering Physics as an assistant professor in fall 2018, works in the area of computational fluid dynamics. In her research, she focuses on developing new computational tools to investigate the physics of unsteady fluid flows.
“By gaining a better understanding of the flow physics, my goal is to harness these fundamental principles to help improve the performance of existing engineering systems and also to push new technologies forward,” Franck says. “I tend to take new computational methods and apply them to real engineering challenges.”
Franck is especially interested in applying her computational tools to renewable energy applications such as wind energy. For example, by modeling the interaction between the wind and turbine blades, she aims to enable better blades. These larger blades could produce more energy while also being less susceptible to vibration and mechanical failure as they’re buffeted by the wind.
This research involves exploring how placing actuators on the surface of a turbine blade could modify airflow to produce desired results. The actuators might pulse and, in turn, generate flows that would reduce the wind load on a section of the turbine blade. The concept also has aeronautics applications. For example, actuators on an airplane wing could alter the flow around the wing to more efficiently produce lift or reduce drag. By collaborating with engineers who are experimenting with new kinds of actuators, Franck hopes her models will help advance this emerging technology.
Franck is trained as an aerospace engineer, and she also has a passion for coding and computation. “So this research blends my two interests very nicely,” she says. “I get to do a lot of coding, and I also get to help people build things and design new engineering systems, which is very satisfying.”
After earning her master’s degree in aeronautics and PhD in mechanical engineering from the California Institute of Technology, she completed a postdoctoral fellowship at Brown University. She was on the faculty at Brown for seven years before joining UW-Madison.
During her time at Brown, Franck was part of a team that developed a prototype tidal energy harvesting system. The system uses underwater devices shaped like flat plates, which are connected to a generator. As the water flows through the system, it moves the devices and generates electricity.
Using Franck’s models, the team found that oscillation is the best way for the devices to move, and that stacking them close to each other in arrays would generate more energy.
“But stacking them is complicated, because each device leaves behind wakes of swirling fluid, so you have to optimize the placement to take advantage of these ‘vortex wakes,’” she says. “By modeling the unsteady fluid mechanics, I’m trying to come up with optimal stacking configurations.”
Franck also draws inspiration from phenomena like geese flocking and fish swimming in schools. “I’m getting some ideas from the patterns these animals are arranged in, and looking at it from an energy-harvesting angle,” she says.
In addition to her research, Franck is passionate about teaching and working with students. She is excited to be teaching aerodynamics in fall 2018. “I think it’s really cool,” she says. “It’s a course that I love to teach.”
Author: Adam Malecek