Kenneth S. Brentner, Ph.D.
Professor of Aerospace Engineering
233 Hammond Building
Penn State University
University Park, PA 16802
Phone: 814-865-6433 / Fax: 814-865-7092
E-mail: ksbrentner@psu.edu
Someday, Ken Brentner wants to develop a system for real-time noise prediction so that the remote pilot of a UAV (uninhabited aerial vehicle) doing surveillance in an urban area, for example, can fly it as quietly as possible. Likewise, such a noise prediction system might be built into the control of a helicopter to help its onboard pilot avoid disturbing nearby residents, soldiers, or sensors.
Brentner is a Penn State professor of aerospace engineering specializing in aeroacoustics, in particular the acoustics of helicopters, so in a sense most of his research furthers the goal of real-time noise prediction. However, he has no immediate project aimed at that end and is so busy as editor of the Journal of the American Helicopter Society, associate director of the Army Vertical Lift Research Center of Excellence, principal investigator of projects for Boeing, Sandia Labs, the Army and the Navy, and adviser to five graduate students, that he doesn’t have much time left over to think about it.
In fact, to Brentner, a defining characteristic of being a professor is being busy. “I like everything I do,” he said. “There is just too much of it.”
A lot of engineering professors work in industry or government before landing in the academy, but Brentner is unusual in that he had established a successful career over 20 years at NASA Langley Research Center in Hampton, Virginia, before being recruited to Penn State University Park and joining the faculty as an associate professor in 2000. He was promoted to full professor in 2007.
In spite of the workload, Brentner appreciates having greater control and flexibility about his research than he did when he was working in government. “If I have a good idea here, I have the freedom to pursue it,” he said. “And there’s more variety.” Besides helicopters, Brentner currently has projects focused on wind turbines and landing gear, subjects he probably wouldn’t have had the opportunity to look at had he stayed with NASA.
Another plus to academia is the students themselves because their ideas are often fresh and unexpected. A former master’s student of Brentner’s wrote his thesis on wind turbine noise, specifically on calculating the turbulence of the boundary layer. Wind turbine noise is a bigger problem in Europe than in the United States because people live closer to the turbines. Today, the turbines typically are operated more slowly than is efficient in an effort to make them quieter. Ultimately, understanding what causes the noise will be a step toward making turbines better neighbors and better generators of power.
Another of Brentner’s students, this one a doctoral candidate, has developed an innovative means of considering acoustic scattering in the time domain. To determine the source strength, the student used singular value decomposition, which enabled him to reduce the size of the problem and to make it tractable as well as numerically more stable.
“I didn’t think it would work,” Brentner admits, noting that students in aeroacoustics frequently are able to make an original contribution because the field is arcane and fast changing so that often “no one got there first.”
What’s propelling change in the field of aeroacoustics is the advent and wide availability of powerful computers capable of dealing with the seemingly infinite number of variables involved: the power source for the aircraft, what it is made of and its shape, how it and its moving parts interact with the atmosphere around it and with the geography and objects nearby. Making things even more complicated is the fact that an aircraft moves– and not necessarily in a straight line – so that the variables themselves change from moment to moment. Before the human brain was buttressed by the electronic brain, pretty much all that a scholar could effectively look at was how much noise an engine made in controlled conditions, or how much noise air made as it flowed across a structure in a wind tunnel. Today, however, approximate predictions are possible about aircraft noise in the real world – how much there will be, where it will go, how long it will last.
As humans get better at harnessing computer power, faster and more accurate approximations become possible – leading eventually to the real-time noise prediction Brentner envisions.
Brentner earned his bachelor’s degree from Purdue University, his master’s at George Washington University and his Ph.D. at Cambridge University in England. His twin daughters started kindergarten while the family was in England, and Brentner’s wife worked three hours in the morning as a bed-maker at Kings College so she would have something to do. Brentner recalls that his English colleagues were surprised if not horrified that his wife would take a menial job. “The English have different attitudes than we do,” he said.
The English also have different ideas about how to title a doctoral dissertation, Brentner learned. His initial proposal title, according to his adviser, was long enough to be an abstract. And so the title was shortened to the much more poetic: “The Sound of Moving Bodies.”
Growing up on a small farm near Rowley, Iowa, Brentner wanted to be an astronaut, but he knew his eyesight wasn’t up to NASA standards. Then one day in high school, he heard his algebra teacher griping the way teachers will: “I should have been an engineer.” With very little idea about what engineers did, Brentner did some research in the school library.
“When I found out what an engineer was, I was convinced that was what I wanted to do,” he recalls. He took every math class offered by his high school – student population of 250 – even sacrificing driver training for geometry. When as a high school junior he visited Purdue University, the faculty and staff went out of their way to be friendly, and he was sold. As a co-op student, his undergraduate responsibilities also included working at NASA. His initial interest had been rockets, but they needed him for aeronautics, and he embraced the challenge. “It didn’t really matter to me whether it was rockets or not,” he said. “I could have been a lawyer for that matter. All problems are puzzles to me, and I enjoy solving them. But I love aerospace problems – they are fascinating and challenging.”