Thursday 08 Dec 2016: Topics in the modelling and simulation of two-phase flows
Dr Lennon O'Naraigh - University College Dublin
In this talk I will describe several aspects of my research in two-phase stratified flows. The overall aim of this research is to develop a comprehensive theoretical picture of the dynamics of two-phase flows. Modelling such flows is challenging because of their complexity, and many outstanding questions remain concerning the generation of three-dimensional finite-amplitude waves, ligaments and droplets.
The foundation and starting-point for the research is a parallel computational fluid dynamics (CFD) solver called TPLS, developed by me and several collaborators. TPLS runs efficiently on 1000s of compute cores. I will describe this open-source solver and explain how it can be accessed by other research groups. I will also present some results concerning interfacial instability in liquid-liquid and gas-liquid flows that have been obtained with TPLS. In particular, I will outline the mechanisms responsible for the generation of three-dimensional waves and interfacial structures in parallel flow configurations that would appear to favour only two-dimensional waves.
Certainly, for a comprehensive picture of the fundamental dynamics at work, CFD is necessary but not sufficient. I am therefore always on the lookout for theoretical tools to explain the data emanating from the large-scale simulations. One useful avenue of investigation has been linear transient growth and global mode theories. I will introduce a simple mathematical model with exact analytical solutions that can be used to understand these theories at quite a deep level.
Finally, time permitting, I will discuss a more exotic two-phase flow scenario, namely phase-separating fluids in the presence of chaotic advection. A solver based on TPLS has been developed here to understand the role of dimensionality in shear-driven phase separation. I will present results from this study.