Cranfield Institute of Technology - PhD, EngD, MSc, MSc by research theses, (CIT)

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Open Access
Acoustic emission pulse analysis: an integrated system for transducer calibration and signal processing
(1982-10) Oliveras, Juan M.; Bannister, R. H.
The present thesis covers the pioneering effort of establishing an infrastructure for conducting research into the analysis of Acoustic Emission signatures, with emphasis being placed upon the recovery of the true surface waveform for a given transient input. The topics covered in this work are: The p·rovi s ion of the necessary computer software for the handling and processing of the data. Here, a method is included for the correction of phase errors introduced by the sampling/multiplexing of ·the signals, which provides the basis for the implementation of data convolution.techniques in the frequency domain. J°he development of an experimental rig and source of excitation, later applied to the design of transducers. The development of a new transducer configuration, capable of producing a relatively flat frequency response (±7dB) over the frequency range 300 KHz - 2 MHz. The development of a procedure for the calibration of transducers, based upon a modified reciprocity method. The technique produces the calibration of transducers in relative terms, requiring a comple- . . mentary method to provide the reference level for the calibration. As a means of assessing the proposed techniques, the transducer calibration was applied to the de-convolution of pulses generated with a step forcing function, and the results compared with an equivalent theoretical model previously published.
Open Access
Aerodynamic surface pressure measurement in atmosphere and wind tunnel on a vertical axis wind turbine blade using pressure transducers
(1989-09) Oram, C. E.; Garside, A. J.; Hales, R. L.; Moss, J. B.
Blade aerodynamic loads during operation of a wind turbine are poorly understood. Better measurements of these forces are needed for the design of more cost effective turbines. Existing estimates have been inferred from strain gauges in the blade structure, but such measurements are confused by the complexity of the blade's structural response. This present work has pressure tapped the blade surface and recorded at high speed, giving a highly detailed picture of dynamic events and blade loads. A modular blade was constructed for the 6m diameter Rutherford Appleton Vertical Axis Wind Turbine and instrumented with 32 semiconductor pressure transducers. A flow probe using a further three transducers projected ahead of the blade during some of the tests. The instrumented module was also operated in the oscillating mounting of the University of Glasgow's 1.6m by 2.4m wind tunnel. 1760 revolutions of data were collected in atmosphere with blade speed ratios down to about 2.0 and with a variety of blade leanout angles. Some 118 runs of a variety of waveform types and Reynolds numbers from 0.3 to 1.1 million, were collected from the blade in tunnel. Analysis of transducer calibrations concluded that the novel temperature correction technique used allowed pressure readings to 40Pa or better with 95% confidence. Confidence in measured pressures has allowed use of leading edge stagnation point pressure and position as a measure of wind in the rotor flowfield and as a surrogate measure of blade angle of attack. Blade surface pressures and integrated forces show the progression of dynamic stall with increase in wind speed, the dominance of the upstream blade pass in usefulness at low and moderate windspeeds and the rough equality at high windspeeds. Comparisons of wind tunnel and on-rotor data show much lower force and moment coefficients in atmosphere. Rotor 'goodness1 ratios of average blade tangential force to maximum blade and rotor force coefficients peak at a blade speed ratio of about 2.8. Goodness ratios show a mixed pattern with blade leanout. Analysis of pressure coefficient traces through stall indicate a mixed stall type starting at mid chord, moving to leading edge and thence to trailing edge.
Open Access
Airblast atomization : the effect of linear scale on the mean drop size
(1978-12) El-Shanawany, M. S. M. R.; Lefebvre, A. H.
Stationary prefilming-cup airblast atomizers, in which the fuel is first spread into a thin cylindrical sheet and then exposed on both sides to high velocity air, have several important advantages over other common methods of fuel injection in their application to continuous combustion systems. This thesis reports the results of a detailed programme of research on airblast atomization directed primarily to the investigation of the effect of atomizer linear scale, or size, on the mean drop diameter of sprays and, to the provision of a comprehensive picture of the performance of thin-sheet airblast atomizers over a wide range of working conditions. Three geometrically similar atomizers giving cross-sectional areas in the ratio of 1 : 4 : 16 were used; covering the range of prefilming cup diameter, D, from 19.05mm. to 76.20 millimeters, and were capable of handling various liquids at flow rates from 0.003kg/s up to 0.225 kg/s, at fuel pressures below 33 x 10^ N/m^ (about 50 p.s.i.). . It was found that atomizer scale has an appreciable direct effect on atomization quality. The Sauter mean diameter of low liquid viscosity sprays increases with the 0.44 power of atomizer linear dimension (D), while for liquids of high viscosity this effect is slightly higher.
Open Access
Airline deregulation: an analysis under different regulatory and operating environments
(1989-07) Etemadi-Nejad Alamdari, F.; Cordey-Hayes, M.
Like other transportation modes the airline industry has a long history of government regulation. In recent years however the theoretical and empirical bases for air service regulatory schemes have been questioned by opponents of such policies. In Western Europe there have been pressures for relaxation of regulation of the air transport industry with respect to air fares, service frequency and market access. Because changes in such public policies are likely to have a major impact, there is a considerable interest in their possible implications. It is the objective of this study to explore the interactions between fare and service frequency in different competitive environments, and to examine the rivalrous behaviour of airlines and their possible equilibrium position under deregulation. The study also considers the effect of a competing mode (rail) on air carriers performance under various competitive conditions. The individual carrier's performance is quantified in terms of fare, service frequency, resulting generalised costs, market share and financial results. A competition model is developed by which the objectives set above are achieved. The study is divided into three parts. The first part provides a framework within which the competition model can be built. This part also generates the policy questions which must be addressed, should relaxation of regulation take place in Europe. The second part explains the structure of the competition model and its characteristics. The assumptions upon which the model is built and its limitations are also discussed. The model consists of three sub-models: the market share model, the costing model and the reaction model. In the third part, with the aid of the model the policy questions generated in the first part are addressed and the general implications for carriers operating under different competitive conditions are discussed. Finally the technical and the policy conclusions are discussed. It is generally concluded that: competition results in lower fares and a more efficient airline industry; the impacts of competition are not evenly distributed amongst markets, routes and carriers; and the competition on equal terms amongst carriers plays an important role in maintaining the effectiveness of deregulation.
Open Access
An alternative approach to inventory control and forecasting methods in the public and private sectors
(1989-10) Southworth, M. S.; Saw, R.
This research was spawned by the questions and answers from the 33rd report of the committee of Public Accounts session 1983-84. The Key to the ensuing arguments about the report hinged on 3 words "Best Commercial Practice". In order to deduce a baseline the present systems of public and private concerns were investigated to find out what is actually being done. The thesis research examined what is actually happening today and in certain instances where companies have been prepared to speculate (and be open) what they believe they will be doing in the future. A review of the American and Germany Army systems has been included to ensure that the question 'best practice' could be examined between other systems having identical constraints^ The research includes both new and old literature by both academics and practitioners of the science of inventory. The hypothesis is that inventory is regarded in the singular whereas for all large concerns it should be considered in the plural, how the plural should be defined, what and how these sub inventories are and how they should be identified. The hypothesis whilst proven has the caveat that it only relates to inventories which are subject to similar structures and constraints. The effect of implementing the hypothesis in a working environment, possible areas for future work and research, largely due to the embryonic technical breakthroughs in information technology are examined briefly. The recommendations and conclusions represent an alternative approach to inventory control and forecasting not previously covered by either theoretical or practical work.
Open Access
The application of electrolytic photoetching and photopolishing to AISI 304 stainless steel and the electrolytic photoetching of amorphous cobalt alloy
(1986-01) Talib, Talib Naji; Allen, David
The results presented cover broad aspects of a quantitative investigation into the elecrolytic etching and polishing of metals and alloys through photographically produced dielectric stencils (Photoresists). A study of the potential field generated between a cathode and relatively smaller anode sites as those defined by a dielectric stencil was carried out. Numerical, analytical and graphical methods yielded answers to the factors determining lateral dissolution (undercut) at the anode/stencil interface. A quasi steady state numerical model simulating the transient behavior of the partially masked electrodes undergoing dissolution was obtained. AISI 304 stainless steel was electrolytically photoetched in 10% w/w HC1 electrolyte. The optimised process parameters were utilised for quantifying the effects of galvanostatic etching of the anode as that defined by a relatively narrow adherent resist stencil. Stainless steel was also utilised in investigating electrolytic photopolishing. A polishing electrolyte (orthophosphoric acid —glycerol) was modified by the addition of a surfactant which yielded surface texture values of 70nm (Ra) and high levels of specular reflectance. These results were used in the production of features upon the metal surface through photographically produced precision stencils. The process was applied to the production of edge filters requiring high quality surface textures in precision recesses. Some of the new amorphous material exhibited high resistance to dissolution in commercially used spray etching formulations. One of these materials is a cobalt based alloy produced by chill block spinning. This material was also investigated and electro etched in 10% w/w HC1 solution. Although passivity was not overcome, by selecting suitable operating parameters the successful electro photoetching of precision magnetic recording head laminations was achieved. Similarly, a polycrystalline nickel based alloy also exhibiting passivity in commercially used etchants was successfully etched in the above electrolyte.
Open Access
The application of signal analysis techniques based on chaos theory to flow regime identification.
(1996-12) Rawes, W; Yeung, H.
The aim of the research presented in this thesis has been to develop an objective measurement technique to improve the detection of flow patterns in closed ducts. This activity is important for the safe and efficient running of many processes, particularly within the oil production, nuclear power, chemical and process industries. Signal analysis techniques based on nonlinear dynamic (chaos) theory have been applied to simulated and experimental transducer signals measuring properties of gas-liquid (air-water) flows in horizontal and vertical pipes. The techniques provide a method of measuring properties of the signals that are related to patterns within the signals. Signals from various non-invasive transducers (including differential pressure transducers, an electrical conductance transducer, a light attenuation transducer, an ultrasonic transducer and a gamma-ray densitometer) have been analysed. Signal analysis techniques include the use of singular value decomposition, the correlation integral and power spectra analysis. The results of signal analysis on the simulated signals illustrate their potential for flow regime identification. When applied to experimental signals it is shown that changes in some of the signal characteristics correlate well with changes in the flow regimes. Discernment between horizontal stratified-wavy, plug and slug and vertical slug and bubbly flow regimes has been achieved. The most successful analysis technique (using singular value composition) is more robust than previously used techniques and can be computed much more efficiently.
Open Access
The behaviour of polyurethane foam beams reinforced with thin walled steel sections for use in bus structures
(1980-08) Gaafar, Labib A.; Tidbury, G. H.
The thesis is directed to the theoretical determination of the behaviour of rigid skin polyurethane foam beams reinforced with thin walled steel sections. The aim is to enable the designer to predict the behaviour of bus body structure during accident situations in order to build safe buses. A literature search has revealed that very little work has been done in this particular field of research. Thus a preliminary test programme was made to investigate the beam behaviour in bending particularly at high deflection. The test results shown in Chapter 1 gave promising results for continuing the research. Chapter 2 is directed to elastic analysis of composite beams. One of the advanced methods to predict the elastic stiffness of sandwich beams is the interfacial shear method. This assumes an interfacial shear between the core and the faces of sandwich beams. So, by considering a similar assumption, i.e. an interfacial shear between the matrix and the reinforcement, an analysis was made to predict the stiffness of composite beams. Although this method highly overestimated the stiffness, it represents a good basis for the inelastic bending analysis which is more important for the present study. Chapter • 3 shows the inelastic bending analysis of composite beams. This analysis is based on TIMOSHENKO and JAMES curvature area method. The experimental verification of the theory is shown in Chapter 4. The theory shows good agreement with the experimental results. The shape of the reinforcement was optimised for uniaxial bending. This optimum composite section showed a weight saving when it was compared with equivalent energy absorbing rectangular steel tube. Impact tests were made using a pendulum designed specially to test cantilever beams at different speed and impact energies. The test results are presented in Chapter 5. These results showed that the composite beams behaviour is similar for both static and dynamic loading. To compare the composite beam with the constituent beams, the large deflection behaviour of thin walled channel section beams made of thin sheet steel has been investigated. The experiments consisted of cantilever bending tests with the beam loaded through the shear centre and through the centroid. When loaded through the shear centre the beam buckling took place in the compression flange at the root of the cantilever. When loaded through the centroid however, it was noted that the compression flange buckled at a fixed distance from the fixed end. The general theory of thin walled beams developed by Vlasov was applied to the problem and indicated that the maximum compression stress at the free edge of the flange would be a maximum at some distance from the fixed end. The value of the maximum compression stress obtained by the general linear theory was small and its position did not coincide with the experimental position. The Vlasov analysis has been modified to include the increase in the twisting moment due to the lateral deformation- of the beam along its length. Good agreement between the modified theory and experiment both for the position of the maximum compressive stress and for the twist of the cantilever at three points along its length. Because of the very low torsional stiffness of thin walled channel sections, the small deflection theory is only applicable for small bending loads applied through the centroid and the modified theory should be used for practical loading cases.
Open Access
Biosensor and bioelectrocatalysis studies of enzymes immobilized on graphite electrode materials
(1987-05) Schneider, B. H.; Higgins, I. J.; Turner, Anthony P. F.
The immobilization of glucose oxidase and lipoamide dehydrogenase on graphite electrodes was studied for their application in mediated bioelectrochemical systems. These are techniques where the electrons involved in an enzymatic redox reaction are either supplied by, or given to an electrode from the enzyme. In the biosensor mode, where a current is measured due to product oxidation, the immobilized enzyme may be used to monitor its substrate, for example a biosensor for glucose based on the enzyme glucose oxidase. In the bioelectrosynthesis mode, when a cathodic potential is applied to the electrode, electrons may be transferred to the enzyme via a mediator thereby driving a thermodynamically difficult reaction, such as the reduction of the coenzyme NAD+ . A glucose sensor based on glucose oxidase immobilized onto graphite foil electrodes which had been doped with the mediator dimethylferrocene was found to produce both a linear and rapid response to changes in glucose concentration in solution. The kinetics of this particular system were studied in depth in order to explain its behaviour. Results showed that the porous nature of the electrode material resulted in immobilization of the enzyme throughout a number of layers• Consequently, diffusion of glucose into the electrode became the rate limiting process at low glucose concentrations, which resulted in linear calibration curves. This was characterized by a substrate modulus, which was found to be sufficiently large to predict diffusional limitations. From this the effective rate of glucose diffusion within the electrode was estimated, and found to be up to 5 times smaller than that in free solution. The rapid response of the sensor, on the other hand, was due to the absence of any mass transfer limitations external to the electrode surface. When lipoamide dehydrogenase was employed in the same system it was found that complications arose due to coupling of NADH oxidation with the adsorbed mediator. By employing a less anodic potential of +150 mV vs. Ag/AgCl at NADH concentrations below 1 mM the detection of enzymatic oxidation of the coenzyme was achieved. Enzymatic reduction of NAD+ was achieved using lipoamide dehydrogenase immobilized onto graphite felt electrodes. This reaction was mediated by methyl viologen, with the enzyme-modified electrode used to reduce the mediator at a potential of -0.7 V ( vs. SCE ). In this fashion the reduced form of methyl viologen was recycled, thereby driving the reduction of NAD . By coupling this system to lactate dehydrogenase it was possible to effect the reduction of pyruvate.
Open Access
Characterisation of dwelling electricity demand with reference to DCHP
(2002-04) Geslot, Olivier; Newborough, Marcus
The research relates to the introduction of dwelling micro combined heat and power to the domestic sector as a mean of improving the efficiency with which primary energy is used, and the economic efficiency of supplying electricity via the national grid. Such small generators may constitute Stirling engine or solid polymer fuel cells. This research is orientated towards the electrical demand side issues. The context is to maximise the feasibility of such technologies when the typical domestic consumer's heat demand varies significantly with season and the associated electrical power varies substantially every minute of the day. The main issue was to ensure that the system could effectively and economically satisfy a considerable proportion of the electricity demand the typical demand profile is very peaky by virtue of the way inhabitants behave at home and the design of domestic appliances. To derive the characteristic of dwelling electricity demand, a total of 45 dwellings were sampled, monitored and classified, in order to analyse the parameters influencing the shape, magnitude and duration of the profile data collected. A survey was issued to . complete the research regarding appliances time of use. Then a model was designed with an interface allowing dynamism. The research concluded there are attractive reasons for micro combined heat and power to be implemented in dwelling. It could save up to 15% of primary fuel. On an annual basis, and with the 15 dwelling data provided by British Gas, the average saving for a constant lkWe DCHP is determined to be £44.78, and the saving is increased to £124.61 for a system that would allows a tumdown from lkWe DCHP during winter to 500We DCHP during summer. Furthermore utility companies should be gaining from this introduction because peak power demand reduction on the grid should reduce costs.
Open Access
Characterisation of mixture preparation in lean premixed prevaporised combustor modules by planar laser fluorescence imaging and computational fluid dynamics modelling
(2001-04) Davoudi, Henrik; Greenhalgh, Douglas A.
In order to minimise the environmental impact of combustion emissions, radically new combustor concepts are under development. Lean premixed prevaporised (LPP) combustion has the greatest potential to achieve low emissions, particularly with respect to oxides of nitrogen. The role of fuel preparation is crucial in the success of the LPP combustor concept. Planar laser-induced fluorescence (PLIF) has been used to determine fuel placement and concentration, while computational fluid dynamics (CFD) has provided insight into the internal aerodynamics of two premixers. In order to determine the local equivalence ratios in a realistic device a calibration method, for the PLIF signal, has been derived. The vapour phase fluorescence of naphthalene, in the presence of oxygen, was calibrated against known conditions of temperatures and air-fuel ratios. This calibration was undertaken for an atmospheric and isothermal (non-combusting) flow. With regard to the small engine LPP module, PLIF measurements of the vapour fuel provided images of quantitative local equivalence ratios, at the exit of the premixer. In addition, based on the results of the liquid-phase measurements the evaporated fuel fraction was estimated. The computed droplet trajectories, within the premixing duct, highlighted the importance of the initial fuel dispersion from the injector. Two approaches were identified for improving the vaporisation and increasing the homogeneity of the air-fuel mixture. The large engine LPP module was investigated for several geometries and operating conditions. The evolution of the fuel dispersion, for those geometries, was characterised by PLIF images of the vapour fuel. In addition, the flame position inside the optical premixing duct was captured by video imaging for each geometry. 2D and 3D CFD simulations were performed to provide an insight into the aerodynamics of the premixer. These results were the basis of a schematic fuel jet breakup study, for two different injector configurations. Finally, the operational characteristics of this novel LPP module, featuring a conical centre-body, are discussed.
Open Access
The characterisation of multicomponent (liquid) flows using scattered ultrasound.
(1992) Oddie, G. M.; Lenn, C. P.
The aim of this work is to determine the applicability of ultrasonic techniques to developing a non invasive flow meter capable of characterising multicomponent (liquid) flows. The possibility of detecting flow parameters such as velocity distributions, droplet/particle size distributions, spatial distribution and void fraction of the discontinuous phase has been investigated. An early consideration of the likely applications of this meter, revealed that an ultrasonic technique would be the most versatile and suitable. Consequently, a theoretical study of the interaction of an ultrasonic wave and a disperse system has been carried out, as well as a study of the possible regimes where these principles may be applied. The work begins from first principles, studying both experimentally and theoretically the interaction of an acoustic wave with a single particle. This is then extended to characterising a flowing multicomponent system on a larger scale. The nature of complex flows was then investigated from the point of view of a chaotic dynamical system. Both theoretical and experimental methods show this to be a valid approach to understanding the flow of mixtures.
Open Access
Combined gas/steam cycle power generation from a user’s viewpoint
(1990-05) Wright, M. R.; Singh, R.
Gas turbines have been used since the 1940's to provide electric power at times of peak demand, but this is due to low initial cost and short starting times. Historically low efficiency and a higher quality fuel requirement has kept the gas turbine on the high end of the load curve. The combined cycle uses a gas turbine as the prime engine, then uses an exhaust heat recovery boiler to raise steam for a steam turbine cycle. High efficiencies are achievable and the gas turbines can now b u m fuels from natural gas through to crude oil and coal via gasification. High efficiency, short construction time,, competitive installation costs and smaller plant power ratings, has led to increasing and extensive use of the combined cycle. During the next two decades large numbers of gas turbines will be purchased for all load curve requirements with combined cycles in the mid to base load range. Gas turbines and combined cycles are studied in a holistic way, from performance theory to issues of procurement and maintenance. Gas turbines are discussed more fully than steam turbines as they are a less mature technology and dictate the operation of the combined cycle. A mathematical, model of a hypothetical engine is used to find performance trends. This model includes the gas turbine, single pressure boiler and steam turbine. Off design of the gas turbine is studied using the Cranfield program Turbomatch. A mathematical model of the off design of the boiler is developed to give off design trends for the combined cycle. Other issues discussed are applications, fuels, rating, operation, maintenance and various configurations. Past development, current state-of-the-art and future prospects are also discussed.
Open Access
Computational design for micro fluidic devices using lattice boltzmann and heuristic optimisation algorithms
(Cranfield University, 2010-09) D'Ammaro, Antonio; Savill, Mark A.; Kipouros, Timoleon
The study on micro devices is gaining importance in various fields from biological to engineering. The dimensions of these devices range from millimetres (mm) to micrometres (μm) and they work within the laminar flow regime due to their low Reynolds number. Although diffusivity dictates the mixing in such conditions, this work is based on the simulation of two non reacting iso-thermal and incompressible fluids for both streams, so the mixing is governed only by turbulence. A numerical study using the Lattice Boltzmann method (LBM) is carried out in order to examine the mixing in one configuration. In the second part of the work an interface is developed between the LBM code and multi objective optimisation software in order to investigate new configurations which enhance the mixing. The objectives are to maximise the vorticity and minimise the pressure drop, which are conflicting between themselves. The tool that integrates the optimiser and the LBM code for simulating microreactor, can run on a multi level parallelisation, hence the time required for the whole simulation has been drastically reduced. A preliminary optimisation is performed on a microreactor with multi holed baffle plate. Despite small number of iterations, three totally different configurations have been found: greatest vorticity, smallest pressure drop and a compromise. The first two configurations satisfy the expectations, whereas the compromise solution presents an innovative configuration. In fact, it has a low pressure drop and a high vorticity, which is achievable by having high Reynolds number and big diameters of the holes. Hence, this tool proves to be robust and efficient in the multi objective optimisation of microreactor.
Open Access
Condition monitoring of slow speed rotating machinery using stress waves
(1998-06) Mba, David Uzo; Bannister, R. H.
Condition monitoring through the use of vibration analysis is an established and effective technique for detecting loss of mechanical integrity of a wide range and classification of rotating machinery. Equipment rotating at low rotational speeds present an increased difficulty to the maintenance engineer, since conventional vibration measuring equipment is not capable of measuring the fundamental frequency of operation, also, component distress at low operational speeds does not necessarily show an obvious change in vibration signature. This thesis presents a study of high frequency stress wave analysis as a means of detecting early stages of loss of mechanical integrity in slow speed machinery, the first of its kind. Investigations were centred on the Rotating Biological Contactor (RBC) which is used for sewage treatment in small communities and rotates between 0 .6 to 1 revolutions per minute. The mechanism of stress wave generation was the relative movements between mating components that were experiencing loss of mechanical integrity, for instance, the loss of tightening torque between clamped components. Development of the stress wave monitoring technique was accomplished by firstly, simulating a variety of mechanical faults on the test-rig, and secondly, by numerous ‘on-site’ tests on operational RBCs and their bearings. In application of this technique to operational RBCs and bearings, as well as cataloguing evidence of mechanical deficiencies associated with RBCs operated within the Severn Trent Water region, the author inspected 261 RBCs and covered over 35,000 miles, contributing to the uniqueness of this research programme. This research has provided Severn Trent Water limited with a PC-based monitoring system comprising an AE transducer, pre/post amplifiers, ADC board and software on which all diagnosis was undertaken. Furthermore, during the process of investigating reasons for the mechanical failures of the RBC, technical information was uncovered thereby assisting Severn Trent Water in perusing a more robust design of RBC. Moreover this work has assisted Severn Trent Water to maintain that envious reputation that over a number of years not one of the RBC sewage treatment works has failed its consent level as set by the Environmental Agency.
Open Access
The design and analysis of pipe diffusers for centrifugal compressors
(1997-12) Bennett, Ian; Elder, R. L.
Diffusers are necessary to convert the high velocity head of centrifugal compressor discharge flow into useful static pressure. One diffuser type that has shown a great deal of promise, particularly at high pressure ratios, are pipe diffusers. These have been successfully incorporated into centrifugal compressor stages in North America since the early 1970’s. With their commercial sensitivity, however, little design or detailed flow information has been published, and most of this literature is old, dating back twenty years to the design’s conception. This thesis is a compilation of pipe diffuser information, formed from the limited literature works and an intensive experimental parametric study. Two themes run through this thesis and are brought about by different reader needs. The first need is for design information. This must show the strengths and weakness of pipe diffusers and be of sufficient accuracy to potentially produce designs at the first attempt. The second need is to understand the flows within the diffuser itself, in order that through this knowledge further improvements can be made. Both of these requirements are addressed in this thesis. The studies are centred on, what was originally, a Rolls-Royce research centrifugal compressor impeller of 6:1 pressure ratio operating at 35,000 rpm with a tip speed of 533ms'1 consuming up to a nominal 1MW of power. Significant modifications to the original compressor assembly were made to allow modular changes of diffuser and permit detailed measurement access. Initially, a vaneless diffuser investigation was carried out with the primary aim of determining the flow entering the diffusers. This was followed by a diffuser throat sizing exercise as it is well recognised that the diffuser throat has a governing control over the complete stage performance. An exercise in changing the number of diffuser pipes was then undertaken, followed by a hybrid diffuser investigation incorporating an oval, rather than circular, cross-section. In all of these cases, detailed flow measurements were carried out using both conventional pneumatic instrumentation and a purposely developed unsteady pressure measurement data acquisition system. This system enabled detailed traverses of the diffuser throats to be undertaken. These unique measurements shed new light on the flow ‘seen’ by the pipe diffuser channel. Computational investigations using computational fluid dynamics (CFD) codes are carried out to compliment the experimental investigations.
Open Access
Design of a decision support system for combined cycle schemes
(1998-01) Gayraud, S.; Singh, R.
The growing desire for sponsors of power generation projects to share risk with the lenders has promoted the use of computational tools, simulating and evaluating from a techno-economic viewpoint long-term, high-risk projects. Such models need to include reliable engine diagnostics, life cycle costing and risk analysis technique. This work consisted in designing a Decision Support System (DSS) for the assessment of power generation projects using industrial gas turbines in combined cycle. The software, programmed in Visual Basic in Excel in a windows-frame, runs an external application named Pythia, which has been developed by the Department of Propulsion, Power; Energy and Automotive Engineering at Cranfield University. It can perform gas turbine performance simulations, including off-design conditions, with or without degradation effects providing thus reliable engine diagnostics. Steam cycle models including different heat recovery steam generator configurations have been developed to simulate steam turbine design and off-design performance. Plant performance simulation takes into account off-design conditions, part-load governing strategies and degradation effects. Besides a robust economic mode and a life cycle costing model including maintenance planning assessments offer a wide range of possible operating and economic scenarios. The degree of uncertainty relating to technical and economic factors is assessed using normal distributions, and the level of risk is then evaluated using a risk analysis, technique based upon the Monte Carlo method. The DSS provides all sorts of charts and techno-economic figures in order to support the decision making through an effective user-friendly window-oriented interface.
Open Access
Design of an interactive finite element computer package for the analysis of the ride of a generalised off-road vehicle
(1987-02) Kamar, Elsayed Abdrabboh; Cookson, R. A.; El-Zafrany, A.
A versatile computer package, to evaluate ground vehicle ride comfort has been designed. Wheeled, tracked, and semitracked vehicles have been modelled. The emphasis has been placed upon the tracked vehicle suspension systems with the neatly ”standard" torsion bar arrangement operating with either telescopic or rotary-vane dampers. Substantial investigation of the four-bar linkage, associated with the rotary-vane damper, has been carried out and is presented here.The package includes linear ,nonlinear ,[2-V) ,and I3-Vj vehicle models. A new technique employing the finite element method (FEM) fat suspension system modelling has been developed. Several methods of numerical integration are available in the package .A new evident scheme based on a hypetosculatory Hermitian weighted residual of the second order for the solution of the system of differential equations which simulate the vehicle has been derived. Whenever necessary the error developed during the integration process was limited. The graphic display facility of digital computers has been used extensively in the present code. As an example, the damped eigen-value problem has been solved graphically. The graphical solution is simple, direct, and tellable compared to the analytical solution. The terrain configuration might be of either harmonic or atbitrary shape function. Two tolerence critetia have been employed fat tide comfort evaluation ,namely, the absorbed power critetion and the international standard organization ISO 2631 critetion.The two critetia are fully integrated into the package and operate automatically. All individual subroutines have been tested successfully for the purpose intended. Complete sectors have been validated by running various case studies. The results obtained from the package agree reasonably well with the analytical or experimental results. The package allows updating in response to new vehicle and vehicle-terrain technology and can be run on both time-skating or batch processing computer machines. The main package structute is independent of computer type.
Open Access
Design optimisation of axial flow steam turbines
(2004-05) Eyre, C. J.; Tourlidakis, A.
This study at Cranfield University was initiated by my sponsoring company’s desire to improve its Steam Turbine design capability. In particular it was thought that emerging Computational Fluid Dynamics software might provide an alternative and improved approach to existing turbomachinery design techniques in use. My course of study has enabled me to understand the fundamentals of the numerical approaches and methods employed by the commercially available software codes. The brief was to review and if appropriate select and implement a CFD solution into Peter Brotherhood Ltd. The current range of steam turbines have power outputs ranging from 500 kW to 30 MW. These machines are primarily Rateau impulse turbines operating under a pressure compounding arrangement. More recent developments particularly on condensing machines incorporating twisted and tapered blades have led to partial reaction stages being used. Most of the machines produced today are impulse combined with partial reaction. After a review of software vendors AEA TASCflow software was purchased and was used throughout this study. This work concentrates on the technical design o f steam turbine nozzles and blading. It proposes alternative blade and nozzle geometry along with new methods of construction and manufacture. It is recognised however that in order to evaluate nozzle performance it is necessary to consider the downstream blade and thus the performance of the complete turbine stage. Throughout comparisons are made with existing fortran PITCH software described in chapter 1. A literature survey investigated many approaches and factors that can improve turbine efficiency and power output. A selection of these more applicable to the smaller power output designs of turbine produced by Peter Brotherhood Ltd have been investigated to evaluate their merits. These are outlined in chapters 2, 3 and 4. Results from these studies indicate that new complex geometry nozzles when matched to improved blading with improved flow incidence angles, correct axial spacing and casing shroud flaring can lead to stage power increases of over 15%. CFD has provided a much improved insight into the three dimensional aspects and flow phenomena. The introduction of CFD has provided a boost to the design capability and it is used regularly with confidence as a development tool within turbomachinery research.
Open Access
Design Project 1974/75 A 74 Aircraft Elevator Design.
(Cranfield University, 1975-05) Mani Abraham, P.; Howe, D.; Tetlow, R.; Ward, R. E.
Part 1 of this thesis contains the symmetric loading calculations and evolution of the design of elevator for the A 74 Reduced Take off and landing aircraft. Part 2 contains the analysis of final design of elevators. The aircraft is designed to the specifications of DES 7400 and satisfies the British Civil Airworthiness Requirement. A 74 project aircraft has longitudinal control from the tail plane and elevator combination. Tail plane is used for trimming and elevators for pitch controls. All control surfaces are hydraulic power operated. The tailplane uses an inverted supercritical section. The elevator is a four piece arrangement with duplicated hydraulic actuator system. It is of round nose type and the elevator hinge line is at 0.6 C. perpendicular to the aircraft centre line. As elevators are fully power operated mass balancing is not provided. Section 5 in part 1 gives the schemes considered in the design of elevator leading to the final choice of each major part. Section 6 gives the description of final design. Elevator is made of conventional built up construction using Aluminium alloy L 72 sheets and L 65 forgings. Part 2 gives the detailed stress analysis of the final design in accordance with normal aircraft design practise.