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No description available.

Typical modem fighter aircraft use two-spool, low by-pass ratio, turbojet engines to provide the thrust needed to carry out the combat manoeuvres required by present-day air warfare tactics. The dynamic characteristics of such aircraft engines are complex and non-linear. The need for fast, accurate control of the engine throughout the flight envelope is of paramount importance and this research was concerned with the study of such problems and subsequent design of an optimal linear control which would improve the engine's dynamic response and provide the required correspondence between the output from the engine and the values commanded by a pilot. A detailed mathematical model was derived which, in accuracy and complexity of representation, was a large improvement upon existing analytical models, which assume linear operation over a very small region of the state space, and which was simpler than the large non-analytic representations, which are based on matching operational data. The non-linear model used in this work was based upon information obtained from DYNGEN, a computer program which is used to calculate the steady-state and transient responses of turbojet and turbofan engines. It is a model of fifth order which, it is shown, correctly models the qualitative behaviour of a representative jet engine. A number of operating points were selected to define the boundaries used for the flight envelope. For each point a performance investigation was carried out and a related linear model was established. By posing the problem of engine control as a linear quadratic problem, in which the constraint was the state equation of the linear model, control laws appropriate for each operating point were obtained. A single control was effective with the linear model at every point. The same control laws were then applied to the non-linear mathematical model adjusted for each operating point, and the resulting responses were carefully studied to determine if one single control law could be used with all operating points. Such a law was established. This led, naturally, to the determination of an optimal linear tracking control law, and a further investigation to determine whether there existed an optimal non-linear control law for the non-linear model. In the work presented in this dissertation these points are fully discussed and the reasons for choosing to find an optimal linear control law for the non-linear model by solving the related two-point, boundary value problem using the method of quasilinearisation are presented. A comparison of the effectiveness of the respective optimal control laws, based upon digital simulation, is made before suggestions and recommendations for further work are presented.

A novel, fast switching, reliable, and economical fluidic gaseous fuel injector system designed for natural gas engines has been developed in this research. The system consists mainly of no-moving-part fluidic devices and piezo-electric controlling interfaces. The geometric parameters of a fluidic device seriously affect its performance. Traditionally, these parameters can only be optimised through "trial and error" exercise. In this research, a computer simulation model for the jet steady state attachment and dynamic switching has been developed. The good agreements between predicted results and experimental ones show that the model can not only explain the jet attaching and switching mechanism, but also optimise the design of geometric parameters of a fluidic device. The steady state and dynamic characteristics of the system were tested on a laboratory experimental rig. The results show that the system can handle the large gas volume flow rate required by natural gas engines and is capable of operating via pulse width modulation. A few typical commercial solenoid type gas injectors were also tested and the results were compared with those from the fluidic system. It was found that the fluidic gaseous fuel injector system has faster switching responses and smaller injection cycle-to-cycle variations.

Competitive pressure and stringent emissions legislation have placed an urgent demand on research to improve our understanding of the gas turbine combustor flow field. Flow through the air admission ports of a combustor plays an essential role in determining the internal flow patterns on which many features of combustor performance depend. This thesis explains how a combination of experimental and computational research has helped improve our understanding, and ability to predict, the flow characteristics of jets entering a combustor. The experiments focused on a simplified generic geometry of a combustor port system. Two concentric tubes, with ports introduced into the inner tube's wall, allowed a set of radially impinging jets to be formed within the inner tube. By investigating the flow with LDA instrumentation and flow visualisation methods a quantitative and qualitative picture of the mean and turbulent flow fields has been constructed. Data were collected from the annulus, port and core regions. These data provide suitable validation information for computational models, allow improved understanding of the detailed flow physics and provide the global performance parameters used traditionally by combustor designers. Computational work focused on improving the port representation within CFD models. This work looked at the effect of increasing the grid refinement, and improving the geometrical representation of the port. The desire to model realistic port features led to the development of a stand-alone port modelling module. Comparing calculations of plain-circular ports to those for more realistic chuted port geometry, for example, showed that isothermal modelling methods were able to predict the expected changes to the global parameters measured. Moreover, these effects are seen to have significant consequences on the predicted combustor core flow field.

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No description available.

Thesis (Ph. D.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains xiv, 273 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 184-189).

Thesis (M.App.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 217-230). Also available in electronic format on the Internet.