Title: Dispersion of waves and instabilities on fluid interfaces
Speaker: Dr. Fabian Denner
Affiliation: Institute of Process Engineering, Otto-von-Guericke-University Magdeburg, Germany
Date: Friday March 6th 2020
Abstract: Interfacial flows, where two (or more) immiscible fluids are separated by a fluid interface, are ubiquitous in nature as well as in engineering and technological applications, ranging from rain drops to inkjet printing. An example is a water film flowing down an inclined wall, which is a seemingly simple example of an interfacial flow, is subject to complex hydrodynamics, which include gravitational acceleration, surface tension, shear instabilities and recirculations. At length scales ranging from nanometres to millimetres, where surface tension is a dominant hydrodynamic mechanism, interfacial flows have become the focus in a variety of established and emerging industrial and technological applications, for instance in additive manufacturing, medical imaging, ultrasonic cleaning, food sciences and microfluidic cooling devices. Yet our current understanding of the governing physical mechanisms is still incomplete. In this seminar, I will present three examples of our work on interfacial flows in which we have been able to unveil some previously unknown physical characteristics and phenomena using numerical simulation tools together with carefully conducted experiments: (i) the frequency dispersion of capillary waves, (ii) fast moving solitary waves on falling liquid films, and (iii) the
breakup of a liquid jet driven by the Rayleigh-Plateau instability. All these flows have in
common that surface tension and viscosity play a dominant role, yet the governing dispersion mechanisms driving the interfacial waves and instabilities as well as the behaviour these flows exhibit are rather different. We will explore the governing dispersion mechanisms (stabilising and destabilising surface tension, and inertia) as well as the self-similarity of the resulting interface behaviour. In addition, I will show that capillary waves can help us to predict the stability of foams when we consider their transition to the overdamped state, and that the studied waves on falling liquid films and liquid jets can reverse, or at least slow down, their dominant instability mechanism when the applied flow rate is sufficiently large.
Bio: Fabian Denner graduated with a PhD in Mechanical Engineering from Imperial College London in 2013, with his PhD thesis on the numerical modelling of interfacial flows in complex geometries, for which he was awarded the Margaret Fishenden Centenary Memorial Prize 2015 for the best PhD thesis in the previous 5-year period at the Department of Mechanical Engineering of Imperial College London. This was followed by a position as a postdoctoral research associate, also at Imperial College London, during which his work focused on waves and instabilities in thin-film flows. In 2015, Fabian secured a prestigious research fellowship from the Engineering and Physical Sciences Research Council (EPSRC) in the UK, with which he continued his research on interfacial flows with surface tension and the corresponding numerical methods for another 3 years at Imperial College London. Since July 2018, Fabian has been Junior Professor in Multiphase Flow Modelling at the Institute of Process Engineering of Otto-von-Guericke-University Magdeburg, Germany. His current research focuses on the numerical modelling of compressible interfacial flows, such as cavitation processes, and of microfluidic phenomena, such as atomisation and wetting processes.