A generalised eulerian lagrangian framework for the modelling of non-spherical droplet dynamics in sprays

Student thesis: Doctoral Thesis


Sprays are used in a variety of engineering applications, including fuel injec tion in heat engines, biomedical aerosols and so on. Spray behaviour is gov erned by complex fluid dynamics and multiphase interactions, making it an in tense field of study with numerous experimental and numerical investigations. In this research project, the Eulerian-Lagrangian numerical framework is used to investigate sprays and a new modelling tool is developed to address limita tions in this framework, characterising non-spherical droplets. The Eulerian Lagrangian approach tracks droplets’ position, velocity and forces using New ton’s second law. The droplets, namely the Lagrangian particles, are then coupled with the Eulerian fields of the surrounding gas by means of trans port equations (for mass, momentum, energy, etc.). However, the standard Eulerian-Lagrangian approach has limitations due to both the numerical meth ods and the physical characterisation of the Lagrangian particles. Available computational fluid dynamics tools use the Eulerian-Lagrangian formulation assuming that Lagrangian particles are spherical; in turn, the submodels used to describe the droplet dynamics are also based on this same assumption. However, experimental observations indicate that aerodynamic perturbations, as well as extreme ambient conditions, distort the droplet.

During this project, a range of sprays has been investigated: sprays for in ternal combustion engines operating in transcritical conditions, biomedical sprays and jets in crossflows. These investigations demonstrated the limita tions of the standard Eulerian-Lagrangian approach and supported the devel opment of a novel Eulerian-Lagrangian model (i.e. ELPSA), to improve the characterisation of the Lagrangian particles and to achieve a better description of microscale droplet dynamics. ELPSA aims to provide a physical charac terisation of the particles accounting for their distortion, shape and surface, based on droplet characteristics and the local properties of the gas field at the particle location. The concept for this novel approach is based on the Eulerian-Lagrangian Spray Atomisation (ELSA) model, which uses a fully Eulerian description to capture the liquid/gas interface. The model makes the hypothesis that spray particles can be described by three main shapes: spher ical droplets, ligaments and lens-shaped particles. Two novel submodels (for the drag and the vaporisation of the particles) have been developed based on the shape of the droplets and successfully implemented. The performance of these submodels is investigated, addressing the physical phenomena involved and identifying the aspects of the model that need future development (such as breakup). ELPSA has been primarily implemented for diesel and a gaso line sprays, with promising results. The model is shown to be capable of describing the characteristics of sprays in a range of different conditions.
Date of AwardFeb 2023
Original languageEnglish
SupervisorPenny Atkins (Supervisor)

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