bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of deterministic correlations on the steady flow field
Authors: Bardoux F , Leboeuf F
Published: October 2002

A time-dependent numerical simulation of a single-stage transonic turbine is used as a direct simulation of stator-rotor interactions. The different parts of the deterministic correlations are computed and compared. The present work aims to provide insight into the influence of these correlations on the steady flow field of the average-passage equation system. This is related to the deterministic models of the literature. Several steady computations are performed with the various correlations. These results are compared with the time-averaged flow field. The impact of boundary conditions is also studied to highlight the importance of the non-uniform circumferential distribution at the so-called ‘mixing plane’. This work establishes that a non-uniform circumferential distribution is a key to ensure the success of steady computation. Furthermore, it demonstrates that full deterministic correlations are necessary to reproduce the time-averaged flow field. Spatial correlations are thus insufficient to model the stator wakes that interact with the rotor. Steady computations using only spatial correlations give less accurate results than those obtained without any correlation. This is a serious flaw of most of the literature's models.
On the choice of variables and matching criteria for the steady simulation of transonic axial turbine stages
Authors: Michelassi V , Giangiacomo P , Martelli F
Published: October 2002

A transonic axial turbine stage is computed by solving the time-averaged Navier-Stokes equations in the turbulent flow regime. The stator and rotor rows are interfaced using a mixing plane. The sensitivity of the stator-rotor coupling to the boundary conditions and mixing strategies is investigated. The mass or area tangential averaging is found to have slight impact on the stator-rotor match. The relative and absolute formulation of the rotor inlet boundary condition is found to alter the match of the two rows. The computations indicate that both relative and absolute boundary conditions should be used to estimate and control part of the uncertainty in the stator-rotor match, which can be greatly reduced by an iterative procedure, based on the stator exit pressure. The area averaging allows a unique matching point to be estimated for both absolute and relative properties.
Development of an unsteady parallel approach for three-dimensional stator-rotor interaction
Authors: Belardini E , Adami P , Martelli F
Published: October 2002

An unstructured time-accurate simulation is proposed and discussed for the inviscid stator-rotor interaction of a three-dimensional turbine stage. The solver, based on an upwind total variation diminishing finite volume scheme, is briefly described. To allow a time-accurate simulation for the unsteady flow behaviour, two possible approaches are considered. The first proposal consists of a classical explicit multistep Runge-Kutta scheme. The second approach is based on a dual time-stepping strategy, which exploits the implicit time-marching Newton-Krylov method for the inner iteration. In this case the linear solver of the implicit method is the generalized minimal residual method with right preconditioning obtained by an ILU(0) incomplete factorization. The multiblock parallel version of the solver developed for stage investigations is applied to the turbine annular stage of the VKI Institute, developed and tested under the framework of the BRITE EURAM III Project TATEF. Particular concern is devoted to the development of the numerical strategy and validation of the new approach. Memory and central processing unit time costs are both addressed to verify the performances of the numerical schemes proposed.
Non-axisymmetric turbine end wall profiling
Authors: Gregory-Smith D. G. , Ingram G , Jayaraman P , Harvey N. W. , Rose M. G.
Published: October 2002

A design method for profiling the end wall to reduce secondary flow has been reported previously. A profile has been tested in the Durham Linear Cascade and the results confirmed the design method. This paper describes the design and testing of a second-generation end wall, where the profiling is more suited to a real turbine. The new end wall has been tested in the linear cascade and a comprehensive set of measurements have been taken. These include traverses of the flow field upstream and downstream of the blade row, surface static pressure distributions on the end wall and flow visualization. Comparisons have been made with the results with a planar end wall and the earlier profiled end wall. Observed reductions in exit angle deviations are even greater than for the first design, although the loss reduction is not as great. The results verify the design, confirming profiled end walls as a means of reducing secondary flow, kinetic energy and loss. Overall an improved understanding of the effects of end wall profiling has been obtained although further work is required in this area.
Wind energy technology—the state of the art
Authors: Milborrow D
Published: October 2002

Wind energy technology has developed extremely rapidly, and many commercial wind turbines now on the market have capacity ratings of 1MW or more. Energy productivity per unit of rotor area has steadily improved. Turbine prices have decreased per unit capacity, so the cost of wind-generated electricity has fallen steadily. This paper examines the underlying reasons behind the changes in design, explores the economics of wind and discusses integration issues. It looks, finally, to further developments, including offshore wind energy.
The characteristics of pressure ripple in variable displacement vane pumps: Comparison between theory and experiment
Authors: Jang J-S , Kim K-H , Cho M-R , Han D-C
Published: October 2002

This paper reports on the theoretical and experimental study on the discharge pressure ripples in a variable displacement vane pump. The pressure ripple in the delivery port is caused by flow ripple, which is induced by variation of pumping chamber volume. The other reason is the reverse flow from the outlet volume produced by the pressure difference between the pumping chamber and the outlet volume when the pumping chamber is connected to the outlet volume. In this study, a mathematical model is presented for analysing discharge pressure ripple, which includes vane detachment, cam ring movement and fluid inertia effects in a V-groove in the side plate. The model is applied to predict the level and the waveform of the discharge pressure ripples for various operating conditions. An experiment was performed to verify the theoretical analysis. The theoretical results provided in this study show a good agreement with the experimental results. This analytical model can predict the magnitude of discharge pressure ripple in variable displacement vane pumps and thus is useful for achieving optimal design of vane pumps.
Clean coal technologies
Authors: McMullan J T , Williams B C , Sloan E P
Published: October 2002

Power generation in Europe and elsewhere relies heavily on coal as the source of energy and this reliance will increase in the future as other fossil fuels become progressively more expensive. The existing stock of coal-fired power stations mainly use pulverized fuel boilers and present designs based on ultrasupercritical steam cycles are as efficient and as low in SOx and NOx emissions as is possible without incurring excessive additional costs. This paper examines the options for coal-based power generation technologies and compares their technical, environmental and economic performance. These options include atmospheric and pressurized fluidized bed combustion and a range of integrated gasification combined cycle systems. Integrated gasification combined cycles give good efficiency and very low emissions, but further optimization is required to make them economically attractive. Conceptual cycles based on pressurized pulverized combustion, dual fuel hybrid cycles, fuel cells and magnetohydrodynamics are also covered in outline.
Shock-boundary layer interaction and transition modelling in turbomachinery flows
Authors: Michelassi V
Published: October 2002

The transonic turbulent compressible flow in channels and turbine linear cascades is computed by using a Navier-Stokes solver. Turbulence effects are simulated by means of the k-ω turbulence model. A realiability constraint is introduced to improve the turbulence model performances and stability in the presence of stagnation points. In both the flow over the bump and the turbine blade, the shock induces a flow separation that affects the boundary layer development. In both cases the proposed model succeeds in predicting the flow separation. For the flow over the turbine blade a simple transition model based on integral parameters is introduced to mimic the effect of the boundary layer transition across the shock wave on the suction side. Relaminarization is also properly predicted on the pressure side, thereby allowing a good description of the boundary layer development and shock pattern.
Extended surface convective cooling studies of engine components using the transient liquid crystal technique
Authors: Neely A J , Ireland P T , Harper L R
Published: October 2002

A heat transfer tunnel used for local convective heat transfer coefficient measurements on liquid crystal instrumented models is described. The tunnel uses the new mesh heater device to produce a good approximation to a step change in the test section flow temperature. A simple analytical model of the cooling performance of cylindrical extended surfaces is derived from empirical relations obtained from the literature. Experiments conducted on a smooth cylinder and selected cylindrical finned geometries are discussed. In the configurations investigated, the relative sizes of the fin diameter to the fin array greatly exceed any geometries previously reported. The use of liquid crystal mapping techniques is shown to provide the full distribution of local heat transfer coefficients across the fin surface. This enables a greater understanding of the convective cooling process than could be obtained from the simple average measurements of h previously reported in the literature. Existing finned tube correlations are shown to be unable to predict the measured heat transfer levels. The investigation shows that correct selection of fin geometry can result in a significant increase in overall convective cooling performance.
Advances in solid oxide fuel cells and integrated power plants
Authors: Bevc F
Published: October 2002

In the last ten years, the solid oxide fuel cell (SOFC) development programme at Westinghouse has evolved from basic material science to the development of fully integrated electric power systems. Since 1986, 11 such systems have accumulated over 45 000 operating hours including 25 kWc atmospheric SOFC systems installed at customer sites in the United States and Japan. A 100 kWe atmospheric SOFC power system is being delivered to a European consortium in 1997.

By pressurizing SOFC systems and integrating the fuel cells with a combustion turbine, efficiencies of between 60 and 70 per cent (net LHV, or lower heating value) can be attained. SureCELL™ plant concept designs are being evaluated at 3, 5 and 10 MWe. The plants are characterized by the high efficiencies noted, low emissions, a compact modular design and excellent performance over a wide range of operating conditions. The cost of electricity studies indicates that the integrated plants have a 30–45 per cent economic advantage over similar sized combustion turbine systems. A 3 MWe SureCELL™ SOFC-combustion turbine integrated power system is planned to be operational by the end of this decade.
Thermodynamic processes in solid oxide and other fuel cells
Authors: Gardner F J
Published: October 2002

Following a review of thermodynamic processes in a generalized fossil-fuelled power system, the theoretical efficiencies of systems based on the isothermal oxidation of methane are discussed. The fuel cell is introduced as a device that converts the change of Gibbs free energy (Δ G) in isothermal oxidation directly to electricity. Ideal efficiencies of fuel cell systems are presented.

The Gibbs free energy change in isothermal oxidation of methane is 99 per cent of its lower heating value (LHV). However, direct electrochemical oxidation is not practical yet. Taking this and other factors into account the reversible electrical work from an internally reforming fuel cell could represent ∼79 per cent of the lower heating value at 600°C, falling to ∼67 per cent at 1000°C. With a bottoming heat engine the combined reversible work could be >80 per cent of LHV over this range. Adding such a device as a topping element to a conventional heat engine based system seems a logical next step in the evolution of the efficient fossil-fuelled power plant.
Towards intelligent systems for boiler design
Authors: Lu S
Published: October 2002

This paper describes the application, through examples and comparisons, of artificial intelligence including neural networks, fuzzy logic, genetic algorithms in three levels of computer aided boiler design: design by mathematical modelling, design by optimization and design by knowledge-based systems. It reviews the state-of-the-art situation and trends for future development in boiler design practice.
Study of thermodynamic performance of an integrated gasification combined cycle power plant
Authors: Nag P K , De S
Published: October 2002

Computational analysis is performed to investigate the effects of the pressure ratio of the gas cycle (Rp) and the temperature ratio across the combustion chamber (RT) on the thermodynamic performance of an integrated gasification combined cycle (IGCC) power plant with single pressure power generation for both the gas and steam cycles. The gases are assumed to be real ones that follow the Redlich-Kwong equation of state. The overall efficiency of the cycle (η) is found to be maximum at an optimum pressure ratio of the gas cycle for a given temperature ratio. The second law analysis indicates that maximum exergy is destroyed in the process of gasification and is not at all affected by the temperature ratio, while the effect of the pressure ratio on it is also not very significant. The exergy loss in the combustor is found to decrease with an increase in either of the ratios. For the heat recovery steam generator (HRSG), it increases with a higher temperature ratio and decreases with a higher pressure ratio. The total exergy loss of the cycle is found to decrease with either of these two ratios while the other is held constant.
Optimum incidence angle in centrifugal pumps and radial inflow turbines
Authors: Ardizzon G , Pavesi G
Published: October 2002

A theoretical method is presented for establishing the optimum incidence angle in outward- and inward-flow runners. Relative through-flow and eddy vortex are considered separately in order to examine their influence on the vane inlet conditions. The action of the counter-rotating vortex and of the blade camber is analysed and an algorithm is given for the evaluation of the optimum incidence angle. The validity of the procedure is finally verified by comparing the theoretical results with experimental observations and with numerical computations.
Performance prediction of mixed-flow pumps
Authors: Yoon E S , Oh H W , Chung M K , Ha J S
Published: October 2002

This paper presents the mean streamline analysis using the empirical loss models for performance prediction of mixed-flow pumps with high specific speeds. A new internal loss model to describe the effect of flow separation on the characteristic head-capacity curve with a dip in the low flow range is developed and a modified recirculation loss model for calculation of parasitic loss due to flow recirculation at the impeller exit is suggested in this study. The prediction performance of the proposed method here is tested against four sets of measured total heads and efficiencies of mixed-flow pumps, and it is also compared with that based on two-dimensional cascade theory. Predicted results by the present set of loss models agree very well with experimental data for a variety of mixed-flow pumps over the normal operating conditions.
A comparative throughflow analysis of axial flow turbines
Authors: Bohn D , Kim T S
Published: October 2002

A throughflow analysis is performed for a single-stage axial flow turbine to demonstrate the predicted differences between the two-dimensional streamline curvature analysis and the mean line analysis. It is found that the streamline curvature analysis results in far better agreement with the experiment, which shows the importance of considering the spanwise variation of loss and flow. It is also revealed that the present streamline curvature analysis leads to better correspondence with the experiment than other authors’ analyses.
A loss analysis based on experimental data for a 99.0 mm radial inflow nozzled turbine with different stator throat areas
Authors: Artt D W , Spence S W T
Published: October 2002

The results of experimental performance tests on a 99.0 mm radial inflow turbine with seven different nozzle throat areas were reported by the same authors in a previous publication (1). In order to perform a loss analysis, dividing the turbine losses between the stator and the rotor, a theoretical model of the stator loss was required. Several stator loss models were evaluated and the model described by Rohlik (9) was used as the basis for a loss analysis. Plots are given for the breakdown of losses at two operating speeds for each nozzle size. Both the stator and the rotor losses decreased markedly as the stator throat area increased towards a stator-rotor throat area ratio of 0.5. A significant step change in the magnitude of the rotor loss was evident at every stator size and appeared to correlate with the volumetric flowrate in the turbine exducer. Therefore a transition to a more efficient flow pattern in the exducer seemed to occur at higher flow-rates.
Performance improvement of a mixed-flow fan through the application of guide fences in the vaneless diffuser
Authors: Konishi T , Sakai T , Whitfield A
Published: October 2002

In the conical annular diffuser of mixed-flow machines a skewed boundary layer develops on the hub wall due to the swirling flow, and flow reversals, which cause poor performance of the diffuser, are liable to occur. An experimental study was carried out to suppress this unfavourable flow by applying low-height guide fences on the diffuser hub wall. Through the application of the guide fences the performance of the diffuser was improved and the optimum number of fences and the best location in the vaneless diffuser was found. Furthermore, the improved understanding of the internal flow structure can be applied to future diffuser design studies.
Numerical optimization of a stator vane setting in multistage axial-flow compressors
Authors: Sun J , Elder R L
Published: October 2002

This paper presents a numerical methodology for optimizing a stator stagger setting in a multistage axial-flow compressor environment. The method involves simultaneous resetting of several blade rows, which influences overall performance in a complex manner. The paper is presented in four parts: modelling the effect of stagger setting on individual stage performance, overall performance including surge point prediction, stagger setting optimization and numerical examples. The stage performance model is a one-dimensional meanline method where correlations are used to introduce real flow effects. The method uses (experimental or predicted) stage characteristics at design (nominal) setting to generate characteristics at other settings. A stage-by-stage model is used to ‘stack’ the stages together with a dynamic surge prediction model. A direct search method incorporating a sequential weight increasing factor technique (SWIFT) was then used to optimize stagger setting. The objective function in this optimization is penalized externally with an updated factor which helped to accelerate convergence. The methodology has been incorporated into a FORTRAN program and validated using data from a seven-stage aircraft compressor with hypothetical variable stagger vanes.

Results have demonstrated that variable stagger is a powerful method to rematch stages which can be used to improve desired overall performance. Parametric studies on the optimization algorithm have also been conducted where it showed numerical stability and fast convergence.
Simulation of the subsonic flow in a high-speed centrifugal compressor impeller by the pressure-based method
Authors: Wang Y , Komori S
Published: October 2002

A pressure-based finite volume procedure developed previously for incompressible flows is extended to predict the three-dimensional compressible flow within a centrifugal impeller. In this procedure, the general curvilinear coordinate system is used and the collocated grid arrangement is adopted. Mass-averaging is used to close the instantaneous Navier-Stokes equations. The covariant velocity components are used as the main variables for the momentum equations, making the pressure-velocity coupling easier. The procedure is successfully applied to predict various compressible flows from subsonic to supersonic. With the aid of the k-ɛ turbulence model, the flow details within a centrifugal impeller are obtained using the present procedure. Predicted distributions of the meridional velocity and the static pressure are reasonable. Calculated radial velocities and flow angles are favourably compared with the measurements at the exit of the impeller.
High-temperature fuel gas cleaning and removal of alkalis using molten slag
Authors: Gudenau H W , Hoberg H , Pande A R , Weinberg M , Becker J-E
Published: October 2002

Fuel gas cleaning is an important step in the development of coal-based combined cycle technologies. By integrating hot gas cleaning facilities in the combined cycle power plant, higher operating temperatures can be achieved. Research is being carried out at the Institute of Ferrous Metallurgy, Technical University of Aachen, to develop a process for gas cleaning at temperatures above 1300°C using a venturi scrubber with molten slags as sorbents. This process offers simultaneous removal of particulate matter and alkali vapours in the gas stream. The present paper deals with the particulate removal tests, with major emphasis on investigations carried out to study the reaction between molten slags of various compositions and alkali vapours. These investigations included thermochemical calculations as well as an experimental reaction study.
Design issues and performance of a chemically recuperated aeroderivative gas turbine
Authors: Carcasci C , Facchini B , Harvey S
Published: October 2002

A number of innovative gas turbine cycles have been proposed lately, including the humid air turbine (HAT) and the chemically recuperated gas turbine (CRGT). The potential of the CRGT cycle lies in the ability to generate power with a high efficiency and ultra-low NOx emissions. Much of the research work published on the CRGT cycle is restricted to an analysis of the thermodynamic potential of the cycle. However, little work has been devoted to discussion of some of the relevant design and operation issues of such cycles. In this paper, part-load performance characteristics are presented for a CRGT cycle based on an aeroderivative gas turbine engine adapted for chemical recuperation. The paper also includes discussion of some of the design issues for the methane-steam reformer component of the cycle. The results of this study show that large heat exchange surface areas and catalyst volumes are necessary to ensure sufficient methane conversion in the methane steam reformer section of the cycle. The paper also shows that a chemically recuperated aeroderivative gas turbine has similar part-load performance characteristics compared with the corresponding steam-injected gas turbine (STIG) cycle.
The prediction of horizontal axis wind turbine performance in yawed flow using an unsteady prescribed wake model
Authors: Coton F. N. , Wang T
Published: October 2002

This paper describes a fast, accurate, fully unsteady aerodynamic prediction scheme for the calculation of horizontal axis wind turbine performance in yawed flow. The method couples a prescribed wake vortex model with a semi-empirical unsteady aerofoil model to provide the unsteady aerodynamic response of the blades owing to the cyclic variation of incidence. Predictions from the model are shown to compare well with experiment, both in terms of gross performance prediction and detailed blade loads. Finally, the potential for future improvements to the predictive capability of the model is discussed.
The potential role of organic bottoming Rankine cycles in steam power stations
Authors: Angelino G , Invernizzi C , Molteni G
Published: October 2002

Firstly it is observed that in a large number of existing steam power plants the energy potential of the cooling medium is not fully utilized owing to turbine limitation in exhaust volume flow-handling capability. A method is proposed by which a fraction of the low-pressure steam is extracted and fed to an auxiliary organic Rankine cycle (ORC) module of small capacity which, besides being perfectly suited to exploiting even the coldest cooling agent, improves the working conditions of the main turbine by reducing its exhaust volume flow. Through the implementation of an appropriate computer program the performance of a typical power station supplemented with an ORC system is analysed for different cooling situations. Alternatively, as an obvious reference option, the performance of the same plant is evaluated under the assumption that the turbine is provided with an additional exhaust section. The characteristics of the ORC module are then considered. Working fluid selection within the new classes of ambient friendly refrigerants is discussed. Particular attention is devoted to turbine optimization, leading to high-efficiency low-stress two- and three-stage turbine configurations. With reference to the extended geothermal experience in the use of low-temperature ORC conversion systems a preliminary economic analysis is performed, giving encouraging indications about the potential viability of the proposed method.
Aerodynamic loss prediction of axial flow turbine blade rows with coolant injection
Authors: Bohn D , Kim T. S.
Published: October 2002

This work presents a calculation routine for the prediction of the aerodynamic loss of axial flow turbines with coolant injection, which can be easily incorporated into throughflow calculation programs. The concept of the mixing layer is introduced and the one-dimensional method is used to estimate the local mixing pressure loss. For a real annular nozzle guide vane, calculations are performed with the aid of the mixing model and viscous loss correlations in order to predict loss at the blade mid-height. Predictions for various single-row configurations show favourable agreement with experimental results. Losses are also calculated for the multi-row configuration with a consideration of flow recirculation among cooling holes. It is found that the coolant recirculation may cause a considerable increase in the pressure loss when the amount of net coolant supplied is relatively small. The effect of coolant temperature is also examined for both single-row and multi-row cases.
Hydraulic ram analysis: a new look at an old problem
Authors: Najm H. N. , Azoury P. H. , Piasecki M
Published: October 2002

The discretized method of characteristics was used to develop a new numerical model for the analysis of the wave processes in the hydraulic ram. The model encompasses all parts of the device including, for the first time, the air chamber and the delivery pipe. This in turn allows a comprehensive study of the unsteady flows in the unit as the air chamber extensively interacts with the supply side of the ram. The program accounts for all possible flow states of the ram, i.e. with impulse and discharge valves closed, with both valves open and with either of the valves closed or open. The state of the partially or fully open discharge valve requires extensive and careful treatment of all physical phenomena involved, namely the transient boundary conditions, relevant to the air chamber and its connection to the drive pipe. The treatment is for the special case of constant sonic velocity in each of the ram pipes. The numerical model was validated against experimental data obtained from various test set-ups. Comparing the velocity and pressure head variations from numerical and experimental tests at selected points along the ram supply pipe performed the most stringent test. Excellent agreement was shown to exist, validating the analytical approach.
Performance analysis of a hydraulic air compressor
Authors: Bidini G , Grimaldi C. N. , Postrioti L
Published: October 2002

The combined exploitation of different kinds of primary energy source in innovative power plants is a promising way to enhance the energy conversion efficiency. In recent years, a possible utilization of the hydraulic resource for power generation in non-conventional plants has been proposed. The basic concept is to couple a conventional gas turbine combustion chamber and expander with a hydraulic air compressor, a device whose main characteristic is the capability to compress air isothermally using a hydraulic energy source. A hydraulic air compressor-gas turbine power plant, with an extended regeneration at the turbine exhaust, can be characterized by an attractive overall efficiency.

The performance of a hydraulic air compressor-gas turbine power plant is strongly influenced by the characteristics of the hydraulic compressor itself. In the present paper, an improved (with respect to the previous literature) model of the hydraulic air compressor and an original loss analysis model are presented. The results of a performance and loss parametric analysis are presented and discussed; maps which relate to the natural site characteristics, the obtainable performance and main plant design parameters are also reported and discussed.
Structural design of a probe system for a high-temperature pressurized fluidized-bed combustor
Authors: Thompson G. J. , Clark N. N. , Smith J. E.
Published: October 2002

A lack of information about the operating characteristics of a jetting pressurized fluidized-bed combustor (PFBC) can be attributed to the environment (1227 K and 2.93 MPa) in the bed. To gain information about a PFBC's operation, a pressure and temperature probe has been designed to measure the small pressure fluctuations and bulk fluid temperature in the feed jet area. This research concentrates on the structural design and analysis of a multi-tier dual-static-pressure and temperature probe system. Each tier contains two branches placed one above the other in the axial direction; they are arranged to measure the differential pressure and temperature at a given radial and axial location in the feed jet. Each branch is a structural tube member, of 6.35 mm outside diameter, with a smaller tube, of 1.07 mm inside diameter, placed inside for the pressure measurement. A thermocouple is placed on the upper branch of each tier for the temperature measurement. Inconel 600 alloy is selected for the structural and pressure measurement tubing and thermocouple sheathing material because of cost, availability and manufacturing concerns. This paper presents the results of the structural design of the probe system to be fitted in the bed.
The role of research in the aerodynamic design of an advanced low-pressure turbine
Authors: Harvey N. W. , Cox J. C. , Schulte V , Howell R , Hodson H. P.
Published: October 2002

The new BR715 engine features an advanced low-pressure turbine aerodynamic design which includes ‘high-lift’ aerofoils. This paper shows how every part of the design methodology has been derived from extensive research instigated by both Rolls-Royce and BMW Rolls-Royce. Of particular importance has been the investigation of unsteady wake-boundary layer interaction on low-Reynolds-number blading and the generation of a database for the validation of the design methods.

Preliminary results from cold-flow rig testing have verified the design aims. In particular the aerodynamic efficiency is approximately 1 per cent above the prior technology base.
Throughflow model for design and analysis integrated in a three-dimensional Navier-Stokes solver
Authors: Sturmayr A , Hirsch Ch
Published: October 2002

A multiblock multigrid Navier-Stokes solver has been extended to include a throughflow model for the design and analysis of turbomachines. The presence of the blades in the inviscid axisymmetric flow is modelled in the classical way through a distributed blade force to produce the desired turning, a blockage factor that accounts for the reduced area due to blade thickness, and a distributed frictional force representing the entropy increase due to viscous stresses and heat conduction. The exact blade geometry is not required. All features of the three-dimensional code concerning the physical fluid model, boundary conditions, spatial and time discretization, convergence acceleration techniques and data visualization are available to the throughflow module. This includes the capability to treat the entire range of relevant Mach numbers, from strictly incompressible (through a preconditioning technique) to supersonic, as well as any number of blade rows in any configuration, including, for example, bypass engines. Selected elements comprising the throughflow model are discussed, with special emphasis on the blade force and its discretization. The properties of analysis and design mode with respect to shocks and the associated losses are investigated. The methodology is demonstrated on a transonic compressor rotor and a four-stage low-speed turbine.
The nature of wakes in multistage axial flow compressors
Authors: Read S , Elder R. L.
Published: October 2002

This paper describes the measurement and processing of unsteady turbulence data from a multistage low-speed compressor. In this study, a two-element hot-wire probe was traversed along a circumferential path downstream of the third rotor row of a large-scale low-speed four-stage facility. Simultaneous circumferential and axial velocity measurements were made. Three flow conditions were measured: peak efficiency with blade Re = 200000. peak efficiency with blade Re = 55 000 and close to stall with blade Re = 200 000. Ensemble averaging has been used to deduce the periodic components of the velocity. In addition, measurements have been made of turbulence intensity, turbulence length scale and turbulent shear stress (Reynolds stress).
Small gas turbine design: a total technology educational experience
Authors: Court A. W. , Pullen K. R. , Besant C. B.
Published: October 2002

This paper describes the progress made on a small gas turbine design project undertaken by 45 final year engineering students and 15 members of staff spread across four engineering departments at Imperial College, and held over a 3-year period. The students were provided with state-of-the-art software including ProEngineer®, ANSYS®, Star CD® and the Concepts® turbomachinery design tools and the result has demonstrated that realistic designs can be produced by undergraduates with the guidance of experienced gas turbine engineers. This paper also examines the progress made, the educational goals achieved and the design and analytical lessons learnt.
Noise hazards: the issues, the remedies and the trends in regulation
Authors: Snow D. J.
Published: October 2002

In this paper the history of noise control legislation, its implementation and the possible future trends in legislation are outlined from the perspective of the electricity generation industry. The risks resulting from long-term noise exposure at noise levels associated with power plant operation are examined in some detail, but other effects such as stress, performance and heart disease are also considered. It is concluded that the current Noise at Work Regulation 1989 mandatory limit for employee noise exposure of 90 dB(A) Leq (8 h) and the lower advisory limit of 85 dB(A) Leq (8 h) are unlikely to be reduced in the medium term. However, the lower advisory limit is commonly applied as a mandatory level within the power industry. The practical implications of this decision are usually that such control is exercised at a sound level of 85 dB(A), rather than a noise exposure level of 85 dB(A) Leq (8 h). Where such a policy is implemented the noise-induced hearing loss element within overall hearing loss will become extremely small. This trend and the threshold risk levels suggest that in the future the two regulatory limits might eventually be reduced, respectively, by 5 dB(A). There are technical and practical limitations to the benefits arising from hearing protector usage so that the legal requirement ‘to reduce the risk of hearing damage… to the lowest level reasonably practical’ requires greater emphasis upon the need to reduce noise emission at source. It is possible that the inclusion of noise within the integrated pollution, prevention and control regulations during 1999 will give some impetus to this aim. Finally, it is shown that there is no conclusive evidence to date that demonstrates ‘that disease is caused or aggravated by noise exposure at sound pressure levels insufficient to cause hearing impairment’.
An experimental investigation of steam ejectors for applications in jet-pump refrigerators powered by low-grade heat
Authors: Eames I. W. , Wu S , Worall M , Aphornratana S
Published: October 2002

The jet-pump refrigerator cycle offers a low-capital-cost solution for utilizing low-grade waste heat in the production of cooling for buildings and process refrigeration. The heart of the jet-pump refrigerator is an ejector, the performance of which strongly determines the thermal efficiency of the cycle. This paper describes and evaluates the results of an experimental investigation into the operation of ejectors primarily for use in jet-pump refrigerators. The construction of a steam-steam ejector test facility and experimental method are described. Experimental results are provided concerning the effects of primary nozzle exit position within the mixing-entrainment section, primary nozzle exit and diffuser throat areas. The causes and effects of flow instability under conditions of high secondary pressure ratio are also discussed and methods of increasing the critical condenser pressure are identified and rated in order of effect.
Interaction diagram for the study of energy conversion in dielectric solids
Authors: Kloos G
Published: October 2002

From a macroscopic point of view, the interaction of caloric, mechanical and electrical quantities in a dielectric solid can be described using thermodynamics. If second-order effects are included in the considerations, the Taylor series expansion of the Gibbs energy function and the corresponding three equations of state become relatively lengthy. A visual representation is proposed that brings out the underlying symmetry of the interactions and serves to obtain a better overview. The proposed diagram is considered helpful in planning experiments in materials science and in analysing experiments, in which spurious effects might intervene.
Reconstruction of multiple-input multiple-output non-linear differential equation models from the generalized frequency response function matrix
Authors: Billings S A , Swain A K
Published: October 2002

A new algorithm is introduced to identify differential equation models for linear and non-linear multiple-input multiple-output systems from frequency response data using a weighted complex orthogonal estimator. The estimation procedure is progressive beginning with the estimation of the linear terms and then sequentially adding higher-order non-linear terms to build up the model. Simulated examples are included to demonstrate the performance of the new algorithm.
Reduction of axial piston pump pressure ripple
Authors: Harrison K A , Edge K A
Published: October 2002

The reduction in source flow ripple in hydraulic systems is the most effective method of reducing pump-generated pressure ripple and system noise. This paper describes reductions in axial-piston pump delivery flow ripple achieved using a novel timing mechanism which is inherently speed, flow and pressure sensing.

Fixed-speed tests have shown that the mechanism can significantly reduce axial-piston pump delivery flow ripple over a wide range of delivery pressures and pump displacements. Furthermore, the reduction in pressure ripple achieved with the mechanism has been shown to contribute towards reductions in overall air-borne noise levels of up to 6 dB in a simple system.

A simulation model has been produced to predict the behaviour of the prototype mechanism. The model has been compared with the measured delivery flow ripple and achieves good agreement.
Adaptive sliding mode tracking control of hydraulic servosystems with unknown non-linear friction and modelling error
Authors: Cho S H , Edge K A
Published: October 2002

This paper deals with the use of adaptive discrete-time sliding mode tracking control in order to assure good tracking performance as well as to guarantee robustness against non-linear frictional forces and modelling error. The control scheme ensures that the absolute value of the sliding function decreases when it is outside the sliding boundary layer and the steady state value of the sliding function is bounded by the sliding boundary layer. Application of the scheme to a hydraulic servosystem has shown that adaptively estimated frictional forces compare favourably with those obtained from direct measurement. A significant reduction in tracking error is achieved through the use of non-linear friction compensation.
Comparisons of H∞ control and generalized predictive control for a laser scanner system
Authors: Ordys A W , Stoustrup J , Smillie I
Published: October 2002

This paper describes tests performed on a laser scanner system to assess the feasibility of H∞ control and generalized predictive control design techniques in achieving a required performance in a trajectory following problem. The two methods are compared with respect to achieved scan times, tracking errors and overshooting. The results are illustrated on a simulation example.
Robust output feedback pole assignment using genetic algorithm
Authors: Lam J , Tam H K
Published: October 2002

In this paper, the problems of output feedback robust approximate pole assignment (OFRAPA) and robust output feedback stabilization (ROFS) are considered. The idea is to search for an optimal output feedback gain matrix such that objective functions defined via appropriate robustness measures and pole assignment constraints can be optimized using a genetic algorithm (GA). The nature of the GA renders it suitable for optimizing non-smooth objectives such as that involving computation of the spectral condition number or the real stability radius. Furthermore, constraints on the elements of the feedback gain matrix can be catered for naturally in the GA parameter encoding procedure.
Design of a reduced-rule self-organizing fuzzy logic controller for water hydraulic applications
Authors: Jones E , Dobson A , Roskilly A P
Published: October 2002

The use of self-organizing fuzzy logic controllers (SOFLCs) in high-speed multi-variable systems has been largely limited by the high number of rules generated, and by the application specific nature of the learning process. This paper concerns the development of a more generically applicable form of an SOFLC that uses a limited rule base of predetermined size, resulting in improved generalization properties and a reduction in the processing time. A simulation study on a four-valve water hydraulic actuator for a subsea robotic arm shows how this method can be applied to system modelling, the resulting 48-rule fuzzy model then providing the necessary process model for training the SOFLC. Using this fuzzy model the SOFLC was able to tune a set of 12 rules to control the actuator and then to adapt these rules to compensate for a simulated leak of hydraulic fluid.
Multi-objective optimal-tuning proportional-integral controller design for the ALSTOM gasifier problem
Authors: Liu G P , Dixon R , Daley S
Published: October 2002

This paper presents a proportional-integral (PI) controller design approach using multi-objective optimization which addresses the ALSTOM benchmark challenge on gasifier control. The non-linear gasifier has been linearized about three operating points. The design aim is to satisfy a set of specifications on the system outputs, inputs and input rates when a step disturbance is applied to the system. The parameters of the multiple-input multiple-output (MIMO) PI controller are selected to satisfy a set of multi-objective performance criteria, which are formulated from the system specifications. Simulation results are presented which demonstrate the performance of the controller at the three operating points.
Multi-objective optimization approach to the ALSTOM gasifier problem
Authors: Griffin I A , Schroder P , Chipperfield A J , Fleming P J
Published: October 2002

A control system design procedure based on the optimization of multiple objectives is used to realize the control design specifications of the linear gasification plant models. A multi-objective genetic algorithm (MOGA) is used in conjunction with an H∞ loop-shaping design procedure (LSDP) in order to satisfy the requirements of this critical system. The H∞ LSDP is used to guarantee the stability and robustness of the controller while its associated weighting matrix parameters are selected using the multi-objective search method in order to achieve performance requirements. A controller emerges which is stable but unable to completely meet some of the control objectives. Despite this shortcoming, the study is an excellent vehicle for introduction to an effective H∞ loop-shaping procedure. Further work, beyond the scope of this challenge has subsequently produced an improved controller design.
H∞ control system for a four-high stand rolling mill
Authors: Lisini G G , Toni P , Valigi M C
Published: October 2002

In steelworks the demand for a higher product quality level has improved the rolling mill process by means of a proper work roll speed control system. Firstly this paper proposes a lumped-parameter hot-rolling mill model. The rolling mill examined is reversible and equipped with an independent speed control system for each work roll (two single-input single-output systems). Therefore, the same revolution speed, essential for a high-quality process, can only be ensured by equal set point values. Nevertheless, during the process, different disturbance load torques cause speed differences and, even if they are not noticeable, rolled section defects cannot be avoided. The second part of the paper shows that it is possible to design a proper H∞ controller, to change the two independent control systems into a more complex multiple-input multiple-output system that will obtain decidedly better performances. Simulation examples have shown improvements.
Numerical approach for axisymmetric piezoceramic geometries towards fluid control applications
Authors: Peelamedu S M , Kosaraju C B , Dukkipati R V , Naganathan N G
Published: October 2002

Piezoceramics have been increasingly popular and utilized for the purpose of micro-actuation. The choice of material internal poling directions for such geometries depends upon the type of actuation desired in each application. There are no generalized analysis procedures that have been developed to be able to predict the response of such actuator geometries. In this work, a finite element model has been developed to analyse axisymmetric piezoceramic actuators with arbitrary internal poling. The finite element methodology is verified by demonstrating favourable agreement between the numerical results obtained in this study with the results published for an inkjet printer application. In addition, the design of a piezoceramic nozzle is investigated with both single-layer and stacked axisymmetric piezoceramic geometries. Such piezoceramic nozzles and orifices can be effectively employed in various sensitive fluid control applications.