Which of us has never seen rain drops landing in a puddle? Whilst keen amateurs claim to be able to predict the duration of a shower of rain based on the nature of the impact, researchers at the German-Italian DROPIT graduate college at the University of Stuttgart are conducting research in to how rain drops interact with one another and their environment. The answers to these questions are important for many industrial applications.
In a laboratory at the Institute of Aerospace Thermodynamics (ITLR) at the University of Stuttgart, doctoral students Anne Geppert and Ronan Bernard are using a new, highly modern system. The technology, known as Micro-Particle-Image-Velocimetry (Micro-PIV), is a non-contact, laser-optic velocity measuring system based on the detection of the tiniest particles added to a fl ow, or rather their defl ection. To this end, the researchers implant a droplet with luminescent particles that fl uoresce when illuminated by a green laser. By photographing the positions of the particle at defi ned points using a high-resolution camera, the speed of the particles can be measured by calculating the distance they have covered due to the fl ow within a specifi ed period. “What’s special about this process”, says Anne Geppert, an associate member of DROPIT, “is that we can even measure fl ow fi elds in the micrometre range by combining a PIV system with a microscope.”
Understanding How Drops Interact
What happens when droplets interact with, are atomised or evaporate upon contact with specifi c media, materials and surface structures is still largely unknown. “Drops are more than just rain”, says Professor Bernhard Weigand, Director of the ITLR, when describing the research team’s fascination for the “life” of these objects, which is so short but yet so complex. “Our research objective”, Weigand explains, “is to get to the bottom of the infl uence of microscopic structures on visible effects.” What has already become clear is that even the most minute changes to the surface structure of the droplet or the surface which it strikes can lead to completely different results. That is all pure science. Yet, the DROPIT researchers are also thinking in terms of practical applications. Whether the spray cooling of food, evaporation processes or combustion processes are concerned – success is always dependent on the behaviour of tiny droplets.
Three target defi nitions were defi ned for the DROPIT area of study. In one series of experiments, the doctoral students are looking into vaporisation processes with a view to improving carburation in internal combustion engines. As Dr. Grazia Lamanna, senior academic adviser at the ITLR, explains in summing up the ambitious research objective: “it is possible to reduce fuel consumption by altering the frictional resistance.” Another point of attention involves so-called super hydrophobic surfaces, of the kind found in extremely water repellent textiles or windscreens. The third area of research is dedicated to interactions between different liquids. “For example, these methods are useful for the development of new medicines in which one liquid is surrounded by another”, Anne Geppert explains.
A Lively Exchange Across National and Academic Boundaries
The graduate college was found in Bergamo in the north of Italy in October 2016. DROPIT, which is an acronym for “Droplet Interactions Technologies”, is one of the collaborative projects launched as part of the strategic partnership between the Universities of Stuttgart and Bergamo. The University of Trento is also involved. Around 20 researchers are working in parallel in Germany and Italy. Annual seminars and special lectures for doctoral students will be held throughout the active period of the graduate college, which has initially been set at four years. Study exchange periods of six months in the respective partner countries are also planned. Contributions from many fi elds of knowledge will be required to cover the wide range of scientifi c questions raised by the various aspects of droplet interactions. That is why the DROPIT team includes researchers from a broad range of disciplines including Mathematics, Computer Science, Fluid Mechanics and Thermodynamics.
In Weigand’s opinion, “the very high number” of applications is as much a result of the excellent technical equipment available to the college as to the project’s thematic scope. Grazia Lamanna is certain that: “the intensive training given to the doctoral students in combination with their ability to carry out independent project work will open up great career opportunities for each of the graduates.” All participants also agree that the intensive collaboration with the University of Bergamo offers great benefi ts in terms of content. A micro-CT scanner of such excellent quality like the one built by Maurizio Santini at the University of Bergamo is, as Bernhard Weigand explains, so far unique in the world. The device enables 3D scanning to illuminate and photograph objects in the micrometre range.
Jens Eber
- Prof. Dr.-Ing. habil. Bernhard Weigand, Director of the Institute of Aerospace Thermodynamics (ITLR), phone +49 (0) 711 685-63590,
E-Mail, Website - Dr.-Ing. Grazia Lamanna, Academic Employee at the Institute of Aerospace Thermodynamics (ITLR), phone +49 (0) 711 685-62173,
E-Mail, Website - Dipl.-Ing. Anne Geppert, Academic Employee at the Institute of Aerospace Thermodynamics (ITLR), phone +49 (0) 711 685-62173,
E-Mail, Website - Ronan Bernard M.Sc., Academic Employee at the Institute of Aerospace Thermodynamics (ITLR), phone +49 (0) 711 685-62325,
E-Mail, Website