Spray formation in non-Newtonian uids

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While both several experimental and numerical studies for Newtonian sprays have been conducted, the exploration of the non-Newtonian ows has received comparatively little attention. Achieving fundamental understanding of the physical phenomena governing spray formation of this type of ow remains a challenge. The present project aims to set the basis for the numerical examination of non-Newtonian atomisation and spray systems. To achieve this, a Direct Numerical Simulations (DNS) approach is followed where all the temporal and spatial scales are completely resolved. We begin with the simulation of the filament thinning of an Oldroyd-B viscoelastic two-dimensional/axisymmetric framework, using the volume-of-fluid technique to track the interface and the log-conformation transformation for the solution of the viscoelastic constitutive equation. This permits the rapid exploration of parameter space, capturing the effect of the elastic, viscous and inertia forces (i.e. Deborah and Ohnesorge numbers), which characterise the internal relaxation and macroscopic time scales that viscoelasticity presents. This serves as a departure point for the development for the very first time of two-dimensional numerical simulations of an Oldroyd-B impulsive, as well as released with constant velocity jets into a stagnant gas phase for exploring the effect of viscoelasticity on the ejected droplet size. These simulations constitute the basis for further work involving three-dimensional simulations of atomisation processes of viscoelastic jets. The numerical simulations of the spray formation of a non-Newtonian fluid still offers substantial challenges, but it is reflective of industrial applications (e.g. spray-drying) and can lead to the optimisation of spray processes, containing fluids of a very complex behaviour.