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Investigation of the Dynamics and Structures of Fuel Sprays in Gas Turbine Injectors

Ajisafe, Adesile H.; (2020) Investigation of the Dynamics and Structures of Fuel Sprays in Gas Turbine Injectors. Doctoral thesis (Ph.D), UCL (University College London).

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This work focuses on the experimental investigation of dynamical and structural characteristics of dense sprays from pressure-swirl atomisers used in an industrial gas turbine engine. A range of combustor operating pressures and fuel injection pressures which are representative of the actual engine conditions was investigated. Varieties of advanced optical diagnostics techniques and modal decomposition techniques are applied in this work to elucidate more insights into the dynamics and structures of the liquid spray. The effects of operating conditions, viscosity, and nozzle geometry on the spray structure were investigated. For all injectors tested the spray cone angle tends to decrease, and the Sauter Mean Diameter (SMD) tends to increase with an increase in ambient pressure. Increase in viscosity was found to decrease the spray cone angle for all tested nozzles, with the largest orifice nozzle yielding the narrowest spray cone angle. The nozzle with the smallest flow number was found to yield a narrower spray cone angle in comparison to a nozzle with similar geometric characteristics but with a higher flow number. The results also show that lower flower number doesn’t necessarily translate into smaller SMD values. This work also deals with the application of modal decomposition techniques for the identification of spatial patterns and frequencies of coherent structures in sprays emanating from pressure swirl atomisers. These coherent structures affect the fuel mass flux distribution in the combustion chamber, and thus, it is essential to study the dynamical behaviour of these structures. Using stable instantaneous spray snapshots obtained from the laser imaging technique the results show that for non-linear dynamics and complex flow such as spray, Proper Orthogonal Decomposition (POD) tends to identify structures composed of multi-frequencies, a sign of convoluted dynamics. Dynamic Mode Decomposition (DMD) is recommended instead since it can associate a specific coherent structure with a single distinct frequency. However, for stochastic and complex phenomena, such as that encountered in dense sprays, selecting dynamically relevant structures with DMD is difficult and comes with compromises. This work proposes a new technique named CP-DMD. The proposed CP-DMD technique is based on merging the benefits of both POD (obtaining most energetic structures) and DMD (associating structures with a single distinct frequency). CP-DMD proved to be an accurate and efficient approach to extracting Spatio-temporal coherent structure and their associated frequencies from a complex and turbulent flow field

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Investigation of the Dynamics and Structures of Fuel Sprays in Gas Turbine Injectors
Event: UCL (University College London)
Language: English
Additional information: Copyright © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Mechanical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/10109280
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