Discours de remerciement – Rome, 23.11.2018 (vidéo + text, anglais)

Allemagne / Pays Bas

Detlef Lohse

Prix Balzan 2018 pour la dynamique des fluides

Pour ses contributions exceptionnelles à des domaines variés de la dynamique des fluides, tels que la transition vers la turbulence dans la convection de Rayleigh-Bénard, l’étude des écoulements turbulents multi-phases, la sonoluminescence, les propriétés des bulles et des gouttes à des niveaux microscopiques, la micro et nanofluidique.

Mr. President,
Mr. Chairman and Members of the Balzan Foundation,
Ladies and Gentlemen:

It is my great honor to be selected as recipient of the Balzan Prize for Fluid Dynamics. When looking at the list of famous scientists, scholars and artists who have received the Prize in the past, I feel very humble.

I am particularly happy that, with this award, the Balzan General Prize Committee recognizes the field of fluid dynamics. In the last century, great minds like Ludwig Prandtl and G. I. Taylor have worked in the field and set the standards. Some people had considered this field as classical, in the sense that there are no longer any challenging problems, but in the last decades it has become overwhelmingly clear how topical the field is, with outstanding scientific questions and extremely relevant challenges for many applications.

Indeed, it is nearly impossible to overestimate the relevance of fluid dynamics for mankind. We ourselves are systems far from equilibrium. This implies that everything flows – panta rhei. But the same holds for the ocean, the atmosphere, industrial plants in the chemical or food industry, power stations for energy supply, transportation devices like airplanes, cars, ships, or pipelines, or, on the small scale, bacteria or microfluidic devices and processes for medical diagnostics and the pharmaceutical industry. All these systems are far from equilibrium, which implies flow, whether it be blood circulation in your body and through your heart, or the flow in the ocean or in the atmosphere that determines and affects climate. Fluid dynamics is also essential for energy production, as in combustion or in the hydrogen economy or for CO2 storage, or for additive manufacturing, which is also relevant in the health sector for printing artificial tissue or organs. These are all huge challenges for mankind, to which fluid dynamics majorly contributes and will also have to contribute in the future.

Today, fluid dynamics is multidisciplinary at its best, somewhere in between physics, geophysics, mechanical and chemical engineering, applied mathematics, and data and computer science, and ranging from the nanometer length scale to astrophysical length scales. What I particularly like about fluid dynamics is that experiments, theory, and numerical simulations go hand-in-hand, and often only by combining these methods is it possible to solve a problem.

From my point of view, we presently live in the golden age of fluid dynamics. The reasons are: (i) Moore’s law continues to be followed for computational power, so that simulations which we did not dare to dream of even ten years ago are now possible, and (ii) a similar revolution (for the same reason) in digital high-speed imaging – thanks to which we can now routinely resolve the millisecond time scale and even smaller scales, revealing new physics on these scales, which up to now was inaccessible, and producing a huge amount of data on the flow. Moreover, other advanced equipment like confocal microscopy, digital holographic microscopy and atomic force microscopy are coming to be used more and more in fluid dynamics. Considering all of these advances together, the gap between what can be measured and what can be simulated ab initio is narrowing more quickly than we had anticipated at the end of the last century.

Other gaps are also closing. Fluid dynamics is bridging out into various neighboring disciplines, such as chemistry, and in particular colloidal science, catalysis, electrolysis, medicine, biology, computational and data science, among many others. Here the techniques, approaches and traditions from fluid dynamics can offer a great deal of help to solve outstanding problems. Vice versa, these fields can offer wonderful questions to fluid dynamics. Academic fluid dynamics is also bridging out not only into traditional applications on large scales, such as in chemical engineering, in the food industry, or in geophysics, but also into various new high-tech applications, whether they be in inkjet printing, immersion and XUV lithography, chemical diagnostics, and lab-on-a-chip microfluidics.

Out of these many and relevant questions, how do I find the problems to work on? And what is the difference between fundamental and applied research? These are questions I am often asked. My short answer to the first question is: “Be curious!” And to the second one: “In principle, none.” And in particular, as regards what holds for both fundamental and applied problems, both in finding and in solving them: “Watch, listen, and be open.” The answer to both questions can be summarized as: “Work on problems you most enjoy. Strange things can happen on the way.” (Walter Munk, UCSD).
A problem I like to work on is both scientifically outstanding and at the same time relevant – or at least has an application perspective – and there are many such problems in fluid dynamics. I have tremendously enjoyed working on them, whether on fully developed turbulence and thermal convection (both with great relevance for climate research and the energy challenge), single bubble sonoluminescence (from which we learned about ultrasound diagnostics), inkjet printing (a truly high-tech endeavor), droplet impact, granular matter, or surface nanobubbles and nanodroplets (with great bearing on liquid-liquid extraction and chemical diagnostics). Solving a scientific question is like solving a puzzle: over many years, one works very hard and collects pieces, trying to put them together. Often they do not fit together; and others are missing. So you have to collect new ones, and recombine them differently. And then, all of a sudden, when you are lucky – and often at an unexpected moment – all the pieces fall together in your mind and you know that you have solved the problem. It is this moment for which you do science. I have been lucky enough to have had several such moments. But after each one, the story is not over, because you then have to start to convince your peers that you are right, which is a very creative process and an important discourse, too.

Indeed, science is a collective activity. The scientific insight we gained during my scientific journey over nearly three decades was gained together with my colleagues, postdocs, PhD students, and students, and I would like to thank them for all their work and contributions, and for the stimulation and intellectual pleasure we have enjoyed when doing physics. It has been a great pleasure and privilege to work with all of them, and again, here I have also been lucky to be able to collaborate with such great scientists and colleagues. I see the Balzan Prize as a distinction for my whole Physics of Fluids group in Twente. It is my particular pleasure that three of my close colleagues and friends can be present here today.

Last, but by far not least, I would like to express my deep gratitude to my scientific teachers, Professor Siegfried Grossmann (Marburg), Professor Leo Kadanoff (Chicago, deceased), and Professor Andrea Prosperetti (now Houston) for everything I learned from them, which goes far beyond physics. They truly have been a great example for me.

I am trying my best to be a good example for young scientists, too, and I hope that sometimes I will succeed, at least by working very hard, being collaborative, emphasizing scientific honesty, and identifying good and relevant problems. It is a very nice feature of the Balzan Prize that part of it is used to support young scientists, and it is my great pleasure to do so in this extremely relevant field of fluid dynamics.

I close with again thanking you as Members of the Balzan Foundation General Prize Committee for the great honor of awarding me the Balzan Prize for Fluid Dynamics.

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