Summary

The fundamental understanding of droplet dynamics is the critical prerequisite to the prediction of natural processes and the optimization of technical systems. Many of these processes happen under extreme ambient conditions - e.g. high pressure or extreme temperatures - and can already be found in technical applications, despite the absence of fundamental knowledge. This is exactly what the new Collaborative Research Center focuses on. The goal is to gain a profound physical understanding of the essential processes. This understanding is the basis for new ways of analytical and numerical descriptions. Thereby, an improved prediction of large systems in nature or in technical applications shall be possible.

The obtained insights shall be showcased by applying them on ﬁve selected systems, so-called ‘leading examples’:

The behavior of supercooled and potentially electriﬁed droplets in clouds is of major importance to the prediction of precipitation.
The impact of Supercooled Large Droplets (SLD) on planes results in the generation of ice layers which can ﬁercely affect the ﬂight quality or even provoke crashing of the plane.
The behavior of strongly electriﬁed drops on isolator surfaces, which can be found on high voltage power lines, affects the discharge behavior and thus the performance of the isolator.
Looking at the behavior of droplets in rocket combustion chambers, various processes under extreme ambient conditions are of importance. These comprise the under- and/or trans-critical injection of fuel as well as the so-called ‘Flash Boiling’ which is caused by overheating of the fuel.
The behavior of fuel sprays in future combustion systems with rising pressure is essentially characterized by the appearing supercritical conditions.

A consecutive critical assessment of the obtained results is assured by comparing the predictions to the actual behavior of the systems. The quintessential scientiﬁc subject of the Collaborative Research Center is the multi-scale modeling and description of processes. Multi-scale denotes the fact that the relevant length scales of the considered processes vary from 10^-10 m looking at the growth of ice crystals up to several kilometres (10⁴ m) looking at entire clouds. Accordingly, the characteristic time scales vary greatly.

The Collaborative Research Center SFB-TRR 75 has the following goals:

Profound physical understanding of droplet dynamics under non-equilibrium conditions and/or conditions that arise from extreme ambient conditions, e.g. conditions near the critical point.
Mathematical and numerical modeling of the relevant processes, description and analysis.
Experimental investigation in order to validate analysis and numerical methods and to derive models.
Concentration on overall processes, dominating subsystems or determining phases, obtainment of assured experimental and mathematical fundamentals, inclusion of state-of-the-art methods of data transfer and visualization of the obtained results.
Application of the ﬁndings on the above mentioned systems which serve as ‘lead examples’

These challenges can only be met by the multidisciplinary combination of the expertise of mathematics, physics, chemistry, computer sciences, and the engineering sciences. Accordingly, the members of the SFB-TRR 75 are from the mentioned ﬁelds.