Gas turbine combustor design represents an ambitious task in numerical and experimental analysis. A significant number of competing criteria must be optimised within specified constraints in order to satisfy legislative and performance requirements. Currently, preliminary combustor flow and heat transfer design procedures, which by necessity involve semi-empirical models, are often restricted in their range of application. The objective of this work is the development of a versatile design tool able to model all conceivable gas turbine combustor types. A network approach provides the foundation for a complete flow and heat transfer analysis to meet this goal. The network method divides the combustor into a number of independent interconnected sub-flows. A pressure-correction methodology solves the continuity equation and a pressure-drop/flow-rate relationship. A constrained equilibrium calculation, incorporating mixing and recirculation models, simulates the combustion process. The new procedures are validated against numerical and experimental data within three annular combustors and one reverse flow combustor. A full conjugate heat transfer model is developed to allow the calculation of liner wall temperature characteristics. The effects of conduction, convection and radiation are included in the model. Film cooling and liner heat pick-up effects are included in the convection calculation. Radiation represents the most difficult mode of heat transfer to simulate in the combustion environment. A discrete transfer radiation model is developed and validated for use within the network solver. The effects of soot concentration on radiation is evaluated with the introduction of radial properties profiles. The accuracy of the heat transfer models are evaluated with comparisons to experimental thermal paint temperature data on a reverse flow and annular combustors. The resulting network analysis code represents a powerful design tool for the combustion engineer incoporating a novel and unique strategy.

The aim of this study is to advance the present capability for modelling soot production and thermal radiation from turbulent jet diffusion flames. Turbulent methane / air jet diffusion flames at atmospheric and elevated pressure are studied experimentally to provide data for subsequent model development and validation. Methane is only lightly sooting at atmospheric pressure whereas at elevated pressure the soot yield increases greatly. This allows the creation of an optically thick, highly radiating flame within a laboratory scale rig. Essential flame properties needed for model validation are measured at 1 and 3 atm. These are mean mixture fraction, mean temperature, mean soot volume fraction, and mean and instantaneous spectrally resolved radiation intensity. These two flames are modelled using the parabolic CFD code GENMIX. The combustion/turbulence interaction is modelled using the conserved scalar/laminar flamelet approach. The chemistry of methane combustion is modelled using a detailed chemistry laminar flame code. The combustion model accommodates the non-adiabatic nature of the flames through the use of multiple flamelets for each scalar. The flamelets are differentiated by the amount of radiative heat loss that is included. Flamelet selection is carried out through the solution of a balance equation for enthalpy, which includes a source term for the radiative heat loss. A new soot model has been developed and calibrated by application to a laminar flame calculation. Within the turbulent flame calculations the soot production is fully coupled to the radiative loss. This is achieved through the use of multiple flamelets for the soot source terms and the inclusion of the radiative loss from the soot (as well as the gases) in the enthalpy source. Spectral radiative emission from the flames has been modelled using the RADCAL code. Mean flame properties from the GENMIX calculations are used as an input to RADCAL.

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In current design methods for gas turbines there are important features of the flow which are not yet within the scope of the available prediction methods for both the calculation of surface pressures and heat transfer rates. Such features include the prediction of three-dimensional viscous flowfields, the accurate location and strengths of the secondary flow regimes in a turbine passage, and allowance for time-dependent variations. It is the understanding of the time-varying phenomena which is the subject of this study. Such phenomena occur due to the periodic interaction between stages in a turbine, either that of a nozzle guide vane on a rotor downstream or vice-versa. In most contemporary designs of turbines the effects are due primarily to the wakes from the trailing-edge of the upstream airfoil, and to any associated shock structures resulting from transonic exit flow Mach numbers. The present investigation is concerned with furthering knowedge of these wake and shock interactions, using a method of simulation established in the Isentropic Light Piston Tunnel and Oxford. Measurements of heat transfer rates and pressures are presented, supported by flow visualisation methods such as surface oil-dots and schlieren photography, for two examples of high-pressure turbine rotor blades. The majority of analysis deals with the first of these (a highty-loaded transonic profile) whilst the second blade (designed for use in a large civil engine) is included for investigation of the effects of flow unsteadiness on the film cooling process The transition process is examined in detail by use of wide bandwith heat transfer measurements, and a new method derived for modelling this process. It has been possible to observe the effect of the enhanced turbulence in the simulated nozzle guide vane wake and effects due a shock-boundary layer interaction. The reaction of the blade boundary layers to these disturbances is identified, and trajectories of disturbed events tracked along the blade surfaces. The measurements which have been taken allow for some aspects of wake and shock interactions to be included in the design process for turbine blading. A better understanding has been obtained of how these types of transient flow regimes affect the boundary layers on the blade surfaces.

This thesis reports the results of a detailed programme of research on airblast atomization carried out using a specially designed atomizer in which the liquid is first spread into a thin sheet and then exposed on both sides to high velocity air. The primary aim of the investigation was to examine the influence of air and liquid properties on atomization quality. The work was divided into four main phases:- (1) The first phase was confined to the effects of liquid properties, namely viscosity, surface tension and density on mean drop size. Special liquids were produced to study the separate effect of each property on atomization quality. They presented a range of values of viscosity from 1.0 to 124 centipoise, while surface tension and density were varied between 26 and 73.5 dynes/cm and 0.8 and 1.8 gm/cm3 respectively. Atomizing air velocities covered the range of practical interest to the designers of continuous combustion systems and varied between 60 and 125 m/sec.(2) To obtain experimental data on the influence of air properties, notably air density, on mean drop size, the air temperature was varied between 23 and 151°C at atmospheric pressure in one series of experiments, while a separate study on the effect of air pressure on atomization quality was undertaken, where tests were conducted at constant levels of air velocity and temperature, using a range of liquid flows from 5 to 30 gm/sec, at various levels of air pressure between 1 and 8.5 atm. (3) In order to provide a comprehensive picture of airb1ast atomizer performance over a wide range of conditions the separate effects of varying air velocity, liquid flow rate, and hence atomizing air/liquid mass ratio on SMD were examined. This study enabled a better understanding of the effects of changes in operation on the atomizer's performance. (4) In all three phases above, velotities of both inner and outer atomizing air streams were kept equal. This last phase was aimed at studying the effect of varying the velocity between the inner and outer air streams. Best atomization quality was achieved when 65% of the total atomizing air was flowing through the outer stream. A detailed description of the light-scattering technique for drop size measurement is included. A discussion on the importance of the results obtained and their direct relevance to the design of airblast atomizers is given. A dimensional analysis and inspection of all the data obtained on the effects of air and liquid properties on atomization quality showed that over the following range of conditions: Liquid viscosity 1.0 to 44 centipoise Liquid surface tension 26 to 73.5 dynes/cm Liquid density 0.78 to 1.5 gm/cm³ Air velocity 70 to 125 m/sec Air temperature 20 to 151 °c Air pressure 1.0 to 8.5 kgf/cm².

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No description available.