Ansell Joins AE Faculty to Study Unsteady Flow

Already a familiar face in Aerospace Engineering at Illinois as a graduate student and postdoctoral research associate, Phillip J. Ansell has joined AE as an assistant professor.

Having completed his graduate work under the direction of AE Emeritus Prof. Michael B. Bragg, Ansell is an experimental aerodynamicist working in unsteady flow.

“All flows are inherently unsteady, though to simplify certain problems in aerodynamics we will often ignore the unsteady contributions.  However, there are times when these unsteady components become increasingly important,” he said. “We can actually measure and use these unsteady components of the flow to tell us the state of the aerodynamics around an aircraft.”

Ansell has been conducting experiments on airfoils, which are the cross-sectional shapes that make up wings, using a large wind tunnel in the Aerodynamics Research Laboratory on the east end of the Urbana campus.  One of his areas of active research is related to airfoil stall.  As the angle of attack is increased, the lift produced by the airfoil also increases.  However, pushing the limits of an aircraft’s lift can result in stall. At a critical angle of attack, flow separation at the airfoil surface becomes so dominant that further increases in the angle of attack produce less lift and vastly more drag, the force opposing the vehicle’s motion through the air.

This phenomena can be predicted and avoided by studying the air flow, Ansell maintains. “Stalls are typically undesirable. They cause an aircraft to lose lift and impair controllability,” he said. “There’s a drastic increase in unsteady content right before an aircraft goes into a stall. By identifying that unsteadiness we can predict an impending stall and use various methods to manipulate the flow in order to prevent stall from occurring.”

As a faculty member, Ansell wants to expand his research to study effects of unsteady flow of vortices for formation flying and other complex flows, particularly rotorcraft.

He said energy efficiency in aircraft can be gained by mimicking collective groups of birds flying in nature, in which the lead expends the most energy and subsequent flyers conserve energy. When a bird flies, it sheds wingtip vortices, the circular patterns of rotating air left behind a wing as it generates lift. Birds that fly in formation with these vortices can use them to achieve lower drag than flying alone. Some of the unsteady aspects of formation flight, though, have made it difficult to achieve in a practical sense.

“We want to find that sweet spot to conserve energy,” he said.

Unsteady flow with rotorcraft, such as in Army and Air Force helicopters, becomes even more complicated. “You’re taking a wing and swinging it,” Ansell said. “This produces a flowfield that is constantly changing, and can lead to some complicated aerodynamic problems that we don’t know how to deal with very effectively.” One of these problems is dynamic stall, which occurs on airfoils during a rapid change in angle of attack. “Dynamic stall can lead to excessive vibration, large increases in unsteadiness, and an overall impairment of vehicle performance. By better understanding it we can find ways to avoid these issues.”

He hopes to collaborate with AE Associate Profs. Daniel Bodony and Michael Selig on future work. In addition to research, Ansell will start teaching courses in flight mechanics and wing theory in Spring 2015.

He came to Illinois in 2009 after earning a bachelor’s degree in aerospace engineering from Pennsylvania State University. He was a stellar graduate student, having won the American Institute of Aeronautics and Astronautics William T. Piper General Aviation Systems Graduate Award, and, from the AE Department, the Roger A. Strehlow Memorial Award, the Aerospace Alumni Advisory Board Fellowship, and the Aerospace Engineering Graduate Teaching Fellowship, the department’s highest teaching honor for doctoral students. The College of Engineering chose Ansell for the Mavis Future Faculty Fellowship, and after teaching an applied aerodynamics course in 2012 he was included among the List of Teachers Ranked as Excellent by their Students.

In explaining his choice of Illinois to begin his faculty career, Ansell said, "At the end of the day, the reason I wanted to start here was the same reason why I came to graduate school here. Illinois is one of the world leaders in engineering education and research. The aerospace engineering department at Illinois provides a place where faculty members can make a large impact, through both active scientific research and inspiring future leaders in the field. It has also been amazing to see how supportive and cohesive the faculty body is. Everyone genuinely wants to see you succeed as a new faculty member, and will do whatever they can to help you get there. Illinois is a great place to be,” he said.

Ansell credits AE Profs. Greg Elliott and J. Craig Dutton for mentoring him.