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Faculty Highlights: Charles Williamson
Professor of Mechanical and Aerospace Engineering
College of Engineering
If there were one word to describe Professor Charles Williamson, it would be "Skipper," as his graduate students and friends call him. The nickname is appropriate in every sense: from his captaining of a cutting-edge research team studying fluid dynamics to his four consecutive gold medals for open-class sailboat racing in New York's Empire State Games.
Williamson's informal, friendly and charismatic manner belies his intense, busy life as a researcher and teacher. Publications by Williamson and his research team have been cited an impressive 1,800 times by other scientists. And Williamson has won nine teaching awards since arriving at the Sibley School of Mechanical and Aerospace Engineering 15 years ago.
It is no coincidence that this scientist and sailor is interested in the science of fluid dynamics: two fluids -- as described by scientists -- the wind and the sea, have played a major role in his life.
He was born to an English mother and Australian father who was a fighter pilot in the Royal Air Force during World War II and remained in uniform his whole career. As a result, Williamson spent the first 12 years of his life following his father and mother around Asia and Europe. "We lived on a 100-foot sailing yacht and then on a 322-ton ship until I was four years old," said Williamson. "Now I sail these little tiddly ones," he said, referring to the 14-foot, single-handed dinghies, called Lasers, that he races in the Empire State Games, U.S. National Championships and Masters' World Championships.
Originally, Williamson wanted to be a yacht designer, so he went to Southampton University, Britain's premier school for naval architecture. But while there, he was naturally drawn into the related field of fluid dynamics.
Explained Williamson, "I had a glimpse of what the life of a yacht designer would be like, because my brother-in-law, who won a gold medal with Great Britain's sailing team in the 1968 Olympics, introduced me to many people in the yachting industry while I worked in his sail-making company for a year. It looks great from the outside, but you never know if your next design is going to be fast."
Williamson earned his Ph.D. at Trinity College, the University of Cambridge, where his thesis focused on vortices formed in the wake of structures under ocean waves. Vortices can produce large forces on structures and induce them to vibrate, which is a serious problem in the offshore industry.
Today, Williamson's research has expanded to cover three primary areas: the transition from laminar to turbulent flow in wakes, fluid-structure interactions, and fundamental vortex dynamics and instabilities related to wing-tip vortices.
Williamson is particularly excited by his group's research into wing-tip vortex pairs -- an example is the white condensation trails in the sky behind a jet aircraft. "There was an absolutely fantastic one just over Cayuga Lake the other week. The weather was just perfect," he noted.
Said Williamson: "It's fascinating. You can start off with a counter-rotating vortex pair, and these two vortices can reconnect to form a set of vortex rings -- like smoke rings. But, under some conditions, these elliptic rings can subsequently deform, ultimately interconnecting again to form the original vortex pair that you started with."
While studying vortex-induced vibration, Williamson's group discovered the strange phenomenon that vibrating structures in a flow, which can resonate with the frequency of the vortex formation, can exhibit an infinitely wide regime of flow speeds for large-amplitude resonance. This is radically different from the classical understanding of resonance, which occurs over a small interval of flow speeds. However, this phenomenon only occurs if the mass of the vibrating body falls below a special critical value. A related discovery is that freely rising and falling bodies, such as spheres and cylinders, will suddenly start to vibrate only when their relative density falls below a similar special critical value.
Williamson's enthusiasm for his research is contagious even in the classroom, where his teaching has won him awards that include a national prize from the Keck Foundation in 1995 and being named a Stephen H. Weiss Presidential Fellow at Cornell in 1999.
"As a minor part of one class, I flew cylinders for my students," said Williamson. "We started off with pens and then graduated to meter-long cardboard tubes from Christmas wrapping paper. I threw it forward, but I also had a string wrapped around it which I pulled to provide a backward spin. The resulting phenomenon is often called the Magnus effect -- in essence, a lift force -- so the thing flies with some unexpected dynamics.
"One cylinder had so much lift force that it doubled back on itself and was doing little epicycles," he said, using an empty paper cup to demonstrate.
"I often give the impression to my students that the demonstrations are spontaneous, but of course they are all prepared in advance. I know exactly what I'm going to do. I even bring in things that don't work, because of the interest and discussion it generates," he said.
One day while Williamson was practicing his spinning demonstration in an Upson hallway, he ran into Bill Nye, Class of '77, who asked if he could use the demonstration on his now-ended children's TV program, "Bill Nye the Science Guy." Now the two are friends and have jointly presented classes during Nye's recent visits to Ithaca as a Frank H.T. Rhodes Class of '56 University Professor.
In his leisure time, Williamson enjoys the domestic life with his French-Canadian-born wife, Chantal Champagne, and their three children, Nicolas, 14, Emilie, 13, and Philippe, 10. And Skipper always finds time for going down to the lake in boats.