PhD Oral Exam - Georgios Bakalis, Mechanical Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

A detonation is a self-sustained, supersonic, combustion-driven compression wave which causes significant pressure and temperature changes. This phenomenon is relevant to the safety of engineering applications and industrial processes, as well as to the development of aerospace propulsion systems. A detonation wave typically displays a complex, nonlinear and unstable structure. This work aims to better quantify and predict characteristic length scales of the detonation structure, to clarify the influence of cellular regularity on detonation dynamics and to explore ways to modulate it. To that effect, the first half of this work is focused on developing a series of Artificial Neural Networks (ANN) using different chemical kinetic and thermodynamic input parameters to predict two main characteristic length scales, the detonation cell size and the critical tube diameter. The feedforward neural networks are trained and validated using available experimental data from the Caltech detonation database, covering a wide variety of gaseous combustible mixtures at different initial conditions. The second half of this work uses one- and two-dimensional numerical simulations to study the effect of O3 as an additive in the reactive mixture to study how it can change the instability and cellular structure of detonations. The use of microplates to modulate cellular regularity is also explored, with the modulated detonation used in the critical tube diameter problem in order to conclusively demonstrate the role of cellular instabilities on detonation dynamics and critical phenomena.