Numerical Modeling of Atomization in Spray Systems

Licentiate thesis, 2019

Dispersed multiphase flows refer to dynamic systems comprising two or more phases where at least one phase is in the form of fine particles evolving in and interacting with a surrounding fluid. Spray systems fall into that category. Several technical applications highlight the significance of sprays, one of which is the injection of liquid fuel in propulsion systems, where the spray formation, vaporization and subsequent mixing prior to combusion determine fuel efficiency and the emission of pollutants that are hazardous to human health and nature. Optimization of such systems requires the understanding of spray physics. While theoretical analysis and experiments remain essential methods with regard to the optimization of such systems, the advance in computer performance over the past few decades has made numerical simulation an additional powerful tool to improve spray systems. However, the existence of physical and predictive models is crucial. This thesis is concerned with the physical phenomena that are present in spray systems and the transfer to suitable computational models. In terms of spray physics, the focus is on atomization which refers to the disintegration of liquid structures. Another central aspect of spray modeling is the representation of the particulate phase. The numerical models studied as part of this work are the one-dimensional turbulence model for the breakup of a liquid jet combined with standard Lagrangian methods as well as a family of Eulerian population balance models, the so-called quadrature-based moment methods. Numerical investigations were carried out on a gasoline spray as well as less complex configurations and give many suggestions for future research.