This research programme has studied the possibilities and difficulties of using 50 kg microsatellites to perform remote imaging of the Earth. The design constraints of these missions are quite different to those encountered in larger, conventional spacecraft. While the main attractions of microsatellites are low cost and fast response times, they present the following key limitations: Payload mass under 5 kg, Continuous payload power under 5 Watts, peak power up to 15 Watts, Narrow communications bandwidths (9.6 / 38.4 kbps), Attitude control to within 5°, No moving mechanics. The most significant factor is the limited attitude stability. Without sub-degree attitude control, conventional scanning imaging systems cannot preserve scene geometry, and are therefore poorly suited to current microsatellite capabilities. The foremost conclusion of this thesis is that electronic cameras, which capture entire scenes in a single operation, must be used to overcome the effects of the satellite's motion. The potential applications of electronic cameras, including microsatellite remote sensing, have erupted with the recent availability of high sensitivity field-array CCD (charge-coupled device) image sensors. The research programme has established suitable techniques and architectures necessary for CCD sensors, cameras and entire imaging systems to fulfil scientific/commercial remote sensing despite the difficult conditions on microsatellites. The author has refined these theories by designing, building and exploiting in-orbit five generations of electronic cameras. The major objective of meteorological scale imaging was conclusively demonstrated by the Earth imaging camera flown on the UoSAT-5 spacecraft in 1991. Improved cameras have since been carried by the KITSAT-1 (1992) and PoSAT-1 (1993) microsatellites. PoSAT-1 also flies a medium resolution camera (200 metres) which (despite complete success) has highlighted certain limitations of microsatellites for high resolution remote sensing. A reworked, and extensively modularised, design has been developed for the four camera systems deployed on the FASat-Alfa mission (1995). Based on the success of these missions, this thesis presents many recommendations for the design of microsatellite imaging systems. The novelty of this research programme has been the principle of designing practical camera systems to fit on an existing, highly restrictive, satellite platform, rather than conceiving a fictitious small satellite to support a high performance scanning imager. This pragmatic approach has resulted in the first incontestable demonstrations of the feasibility of remote sensing of the Earth from inexpensive microsatellites.

This thesis discusses several methods that can be used to analyse gas turbines, based on an optimal estimation algorithm called the Kalman Filter. These techniques overcome the difficulties of more 'traditional' analysis methods, which can give misleading results because they do not explicitly consider the possibility of measurement error. An enhancement to the Kalman Filter (the 'Concentrator') is presented, which overcomes the Kalman Filter's tendency to 'smear' the effects of genuine changes in a small number of component changes and/or sensor biasses over the whole set of changes and biasses being considered. To complement this, methods of optimising some of the statistical inputs to the Kalman Filter in order to improve the ability of the 'Concentrator' to carry out the required analysis are discussed. These are based on analytical methods developed to determine the sensitivity of the Kalman Filter to its inputs. Techniques are also presented for determining the gas-path measurements in a gas turbine that are needed to enable the required analysis of component changes and/or sensor biasses to be performed, including determination of both possible measurement redundancy and the ability of a set of measurements to successfully differentiate between all the component changes and sensor biasses being sought. A recursive algorithm for time series analysis (the Smoothing/Trending Algorithm) is also presented. This produces, for each point in a time series, best estimates of the underlying levels and trends (rates of change of level) of the process generating the observations. A method of combining the 'Concentrator' and the Smoothing/Trending Algorithm is also presented, which reduces the effects of sensor noise on the analysis of component changes and sensor biasses from time series data. Many types of prime movers and process plant could be effectively analysed using the methods described in this thesis.

This Thesis reports the design, build and test of two sets of blading for the Cranfield University low speed research compressor. The first of these was a datum low speed design based on the fourth stage of the DERA high speed research compressor C 147. The emphasis of this datum design was on the high-to-low speed transformation process and the evaluation of such a process through comparing detailed flow measurements from both compressors. Area traverse measurements in both the stationary and rotating frame of reference were taken at Cranfield along with overall performance, blade surface static pressure and flow visualisation measurements. These compare favourably with traverse and performance measurements taken on C147 before commencement of the PhD work. They show that despite the compromises made during the transformation process, due to both geometric and aerodynamic considerations, both the primary and secondary flow features can be successfully reproduced in the low speed environment. The aim of the second design was to improve on the performance of the datum blading through the use of advanced '3D' design concepts such as lean and sweep. The blading used nominally the same blade sections as the datum, and parametric studies were conducted into various lean/sweep configurations to try to optimise the blade performance. The final blade geometry also incorporated leading edge recambering towards the fixed endwalls of both the rotor and stator. The '3D' blading demonstrated a 1.5% increase in efficiency (over the datum blading) at design flow rising to around 3% at near stall along with an improvement in stall margin and pressure rise characteristic. The design work was completed using the TRANSCode flow solver for both the blade-to-blade solutions (used in the SI-S2 datum design calculation) and the fully 3D solutions (for the advanced design and post datum design appraisal). The 3D solutions gave a reasonable representation of the mid-span and main 3D flow features but failed to model the corner and tip clearance flow accurately. An interesting feature of the low speed flowfield was the circumferential variation in total pressure observed at exit from all rotors for both designs. This was not present at high speed and represents one of the main differences between the high and low speed flow. Unsteady modelling of mid- height sections from the first stage indicate that part of this variation is due to the potential interaction of the rotor with the downstream stator while the remainder is due to the wake structure from the upstream stator convecting through the rotor passage. Finally, the implications for a high speed design based on the success of the 3D low speed design are considered.

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.

No description available.

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.

No description available.

No description available.

No description available.