Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 32 for “"thermoacoustics"”.
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Optimisation of chaotic thermoacoustics
In an acoustic cavity with a heat source, such as a flame in a gas turbine, the thermal energy of the heat source can be converted into acoustic energy, which may generate loud oscillations. If uncontrolled, these acoustic oscillations, also known as thermoacoustic instabilities, can cause …
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Inverse problems in thermoacoustics
Thermoacoustics is a branch of fluid mechanics, and is as such governed by the conservation laws of mass, momentum, energy and species. While computational fluid dynamics (CFD) has entered the design process of many applications in fluid mechanics, its success in thermoacoustics is limited by the …
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Adjoint-accelerated Bayesian inference in thermoacoustics
… a second use for Bayesian inference in thermoacoustics: obtaining flame transfer functions, and their uncertainties, from pressure observations. We do this with the flame *in situ*, without a need for optical access. If the flame's response is sensitive to its environment, which is …
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Physics-Based Statistical Learning in Thermoacoustics
… model, which is a significant challenge in thermoacoustics.
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Harnessing thermoacoustics for waste heat recovery
… and research applications to determine how thermoacoustics may serve a role in furthering the use of waste heat recovery units. A literary review of the most common waste heat recovery units was compiled to determine the advantages and disadvantages of the different technologies by comparing …
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Hydrogen Enrichment Effects on Thermoacoustics of Turbulent Partially Premixed Flames
Power generation and aircraft gas turbine combustors are frequently operated under fuel lean conditions to mitigate harmful emissions, rendering them susceptible to undesirable thermoacoustic instabilities. Additionally, meeting decarbonisation targets require incorporation of hydrogen into the …
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A Method for Measuring Spatially Varying Equivalence Ratios with Application to Thermoacoustics
Computed tomography for flame chemiluminescence emissions allows for 3D spatially resolved flame measurements to be acquired using a series of discrete viewing angle camera images. To determine fuel/air ratios, the ratio of excited radical species (OH*/CH*) emissions using chemiluminescence can be …
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Prototype Design for Thermoacoustic Flashover Detector
… flashover detector integrates the phenomenon of thermoacoustics into a fire fighting application. This report presents the prototype design for the thermoacoustic flashover detector to ultimately be implemented in a firefighter's gear. Upon increases in compartment fire heat flux and temperature …
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Methods for Analysis of Nonlinear Thermoacoustic Systems
… high-amplitude oscillations exist. Triggering in thermoacoustics is examined in a simple model of a horizontal Rijke tube. A triggering mechanism is presented whereby the system transitions from a stable fixed point to a stable limit cycle, via an unstable limit cycle. The practical stability of …
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A Thermoacoustic Characterization of a Rijke-type Tube Combustor
… chambers. To understand the phenomena related to thermoacoustics, a simple Rijke-type tube combustor was built and studied. Extensive experimental results, as well as theoretical analyses related to the Rijke tube are presented in this thesis. The results, attributable to both the analyses and the …
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Nonlinear thermoacoustic oscillations of a ducted laminar premixed flame
… is one of the central problems of nonlinear thermoacoustics. However, a limit cycle is not the only type of self-excited oscillation in a nonlinear system. Nonlinear systems can have quasi-periodic and chaotic oscillations. This thesis examines the different types of oscillation in a …
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Experimental Sensitivity Analysis and Control of Thermoacoustic Systems in the Linear Regime
… these dangerous oscillations do not arise. In thermoacoustics, adjoint-based sensitivity analysis has shown promise at predicting the parameters which have the most influence on the linear growth and decay rates as well as oscillation frequency observed during periods of linear growth and …
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Real-time data assimilation in nonlinear dynamical systems
… we develop a real-time digital twin of azimuthal thermoacoustics of a hydrogen-based laboratory combustor using data from raw sensors’ measurements (which may be subject to measurement bias). We generalize the bias-regularized ensemble Kalman filter (r-EnKF) to infer both biases in the model and …
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Shape optimization for thermoacoustic instability with an adjoint Helmholtz solver
Thermoacoustic instabilities, which occur due to the feedback between confined flames and acoustics, constitute a major threat to the safe operation of gas turbines and rocket engines. These oscillations can become large enough to cause noise, vibrations or, in the worst cases, extinction of the …
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Numerical modelling of thermoacoustic engines and coolers
Thermoacoustic systems offer a promising alternative for sustainable energy conversion, leveraging the interaction between temperature gradients and acoustic waves to facilitate both power generation and cooling applications. These devices operate without moving parts, enhancing reliability and …
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Thermoacoustic Analysis and Experimental Validation of Statistically-Based Flame Transfer Function Extracted from Computational Fluid Dynamics
Thermoacoustic instabilities arise and sustain due to the coupling of unsteady heat release from the flame and the acoustic field. One potential driving mechanism for these instabilities arise when velocity fluctuations (u') at the fuel injection location causes perturbations in the local …
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Data assimilation into physics-based thermoacoustic models using Bayesian neural network ensembles
Thermoacoustic instabilities, driven by the interaction between the heat release rate from the combustion process with the combustion chamber pressure waves, have long been a problem in jet and rocket engine design. Unacceptably large oscillations often appear during full-scale engine tests, …
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Dynamics of Lean Direct Injection Combustors
Improvements to heritage gas turbine engines will be needed in the coming years as the demand made on these systems increase. While industry continually presses for higher performance of both military and civilian aero engines, the government simultaneously raises the bar for emissions standards in …
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Sensitivity analysis and optimization in low order thermoacoustic models
Lean combustion technologies in gas turbines reduce the generation of NOx but increase the susceptibility to thermoacoustic oscillations. These oscillations can produce structural damage and need to be eliminated. The stability of a given configuration can be examined with a thermoacoustic model. …
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