Comittee
Reviewers
Stéphane Zaleski
Christophe Dumouchel
Nicolas Rimbert
Examiners
Leonie Canet
Rui Ni
Jean-Philippe Matas
François Gallaire
Fragmentation mechanisms in coaxial two-fluid atomization
The destabilization and subsequent fragmentation of a liquid phase by a turbulent gas phase is at the core of many applications that aim at producing high-quality sprays. Certain underlying physical mechanisms of spray formation remain unresolved, hindering process efficiency and control. I will present a multiscale characterization of these mechanisms in a two-fluid atomizer, where a round liquid jet is fragmented by a turbulent annular gas jet. The interfacial instabilities, and resulting large-scale dynamics, are experimentally characterized using two high-speed imaging methods, back-lit optical imaging and synchrotron X-ray radiography. A spatial characterization of the flapping dynamics of the liquid jet indicates that the flapping dimensionality is related to the change between shear break-up to bag break-up. At higher gas velocities, the scaling laws of the transport of the interfacial instabilities highlight the change to fiber-type atomization. Similarly, studying statistics and temporal dynamics of the length of the liquid jet in a broad parameter space poses a framework to quantitively describe changes in fragmentation mechanisms. In addition, I will show how introducing angular momentum (swirl) in the gas jet dramatically changes the topology and dynamics of the atomized liquid jet, resulting in drastic changes in the spray.