ORCID Identifier(s)

0000-0001-6659-0128

Graduation Semester and Year

2020

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Aerospace Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Donald R. Wilson

Second Advisor

Ramakanth Munipalli

Abstract

The propagation of detonation waves is governed by their stability characteristics. Interest in highly unstable detonation grew when early experiments revealed limits of operation to be directly proportional to the stability of detonation. This research focuses on reinitiation pathways of highly irregular self-sustaining detonation. This is an important aspect of stability which is not yet fully understood, while many possible mechanisms have been proposed in the literature. First, a one-dimensional instability model simulation was performed using a global one-step chemistry mechanism to understand the different unstable modes by increasing the activation energy of a mixture of hydrogen and oxygen. The reinitiation mode of a regular detonation was studied using a highly diluted hydrogen-oxygen mixture at 6.67 kPa. A comparative study was made with three models of reacting gas dynamics: (a) inviscid flow with a global one-step chemistry, (b) inviscid flow with multistep chemistry, and (c) viscous flow with a global one-step chemistry. Reinitiation mechanism with shock-induced combustion played a major role in the survival of a regular detonation. The drawbacks of using global one-step chemistry for a highly diluted reactant mixture were noted. The ability of a two-dimensional, inviscid CFD code with a simple ad-hoc one-step chemistry model to capture successful reinitiation of a marginal and ordinary highly irregular self-sustaining detonation was tested. Two types of reinitiation modes were categorized as triple point reinitiation and Mach reflection reinitiation. Flow features such as curved slip line and hotspot interaction were found to be the major mechanisms for a Mach reflection-based reinitiation. Inviscid numerical simulation was observed to be acceptable for regular detonations since the primary combustion mechanism is shock heating. Due to the presence of reactant jets and pockets, effects of including transport terms on the flame velocity at the unburnt reactant interface were investigated with a two-dimensional viscous oxymethane detonation simulation using a spatially fourth-order accurate WENO scheme. With the reduction in artificial diffusion using fine grid resolution, the number of minor triple points was found to reduce. Most of the numerical study in similar works regarding the reinitiation of methane-oxygen detonation has been obtained from a single step chemistry model. An inviscid multistep chemistry model was used to simulate the highly irregular detonation using a reduced chemistry mechanism which was derived from the GRI-1.2 detailed mechanism. Two types of transverse wave structures categories based on their strength and evolution which was not captured using a single-step chemistry model were observed. The evolution of the strong transverse wave structure was addressed by studying the feedback mechanism of the Mach reflection reinitiation. Finally, the presence of transverse detonation in the highly irregular detonation has been identified and studied in detail.

Keywords

Detonation, CFD, Combustion, Reinitiation

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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