His aim: to advance understanding of turbulence from a mathematical standpoint. After all, even if these currents were first identified over a century ago, there is – astonishingly – not yet a solid mathematical theory on the phenomenon as a whole.
In most cases, the first thing Nguyen van yen receives from Professor Rupert Klein for his work within the Department of Mathematics and Computer Science is a gigantic data set, which might include measurements taken in a turbulent current or figures extracted from a numerical simulation of this type of current. One of his tasks is to identify hidden structures that lend an overall sense to these data. To this end, the young researcher has come up with his own method, which was one important factor in his being granted the research fellowship. He divides the numbers into two groups. The first comprises data that reflect large, coherent eddy structures – also termed simply “coherent structures” – within the turbulent air current. The second is made up of data that depict the less structured, or “uncorrelated,” movement of air that also exists in these currents, aside from large eddies.
The idea of splitting up the data in this way is not new in itself, and the literature on the subject includes various suggestions for how to divide the data into coherent structures and uncorrelated air movement. But what is new about Nguyen van yen’s approach is that it draws on advanced mathematical tools in information theory in order to evaluate these suggestions and pinpoint the most efficient ways to solve a particular task.
For example, Nguyen van yen aims to find out, with as much precision as possible, what effect all of the uncorrelated “noise” has on the large eddies, and how the large eddies behave in response. This information could be important to meteorologists and construction engineers alike, for instance in connection with calculating the lift of aircraft wings, where larger and smaller eddy structures form. Thus far, however, researchers have had to rely on semi-empirical approaches to calculate how these eddies affect flight mechanics. A stable mathematical model is still lacking.
It is safe to say that research fellow Nguyen van yen also experienced some turbulence in his winding path to this research field. Born in Paris, Nguyen van yen initially focused on physics, spending four years at the prestigious École normale supérieure (ENS), in Paris, on a scholarship provided by the French government. The young Frenchman, whose last name comes from his Vietnamese grandfather, completed not only a program in physics, but also an exam for math teachers, during his time in the French capital. After that, he decided to embark on a doctoral program.
His dissertation, for which he also received a scholarship, was on a topic drawn from meteorology. “It was back then that I discovered my interest in numerical calculation of turbulence and started my theoretical research.” For Nguyen van yen, who learned German as a second foreign language in school and gained advanced proficiency in German during a two-month intensive course, the project at Freie Universität represents a perfect combination of all of the fields he has studied so far, as he says. And no wonder: After all, he calls himself “a physicist who works a lot with mathematics, studying topics including meteorological phenomena.”