Browsing by Author "Ramsden, K. W."
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Item Open Access Cascade Testing and CFD Applied to Gas Turbine Performance Improvement with Compressor Cleaning(Cranfield University, 2010-03) Gannan, Aiad; Ramsden, K. W.With the growing interest in life cycle costs for heavy-duty gas turbines, equipment operators are investigating the trade off between performance improvements and associated maintenance costs. One of the key factors leading to performance degradation during plant operation is compressor fouling especially in harsh environments. These results from the adherence of dust or sand particles mixed with small oil droplets to compressor blade surfaces. The result is a reduction in compressor pressure ratio and an overall loss in mass flow, compressor efficiency and, therefore, overall power output. To restore this power loss, an increased fuel flow rate with the consequent higher firing temperature (TET) is necessary. This will seriously reduce the creep life of the HP turbine blades. The research described here is divided into three sections: The first section focuses on the simulation and diagnostic analyses of a typical clean and fouled industrial gas turbine. The analysis tool is a performance code (Turbomatch) developed at Cranfield University. The performance degradation was based on the following engine which is currently operating in the Libyan Desert, using field data available from the company. A single shaft industrial gas turbine (11 MW) engine The study comprised a simulation of the "clean" engine performance of a typical small gas turbine used for power generation. The study also examined the economic impact of compressor fouling on operating costs due to increased fuel flow rate and the reduced creep life of the HP turbine. Additionally, the study included an economical analysis of various types of compressor online washing techniques. The real engine data of a Sulzer Type 7 gas turbine (11MW) have been collected from a Libyan oil field over a period of four months without compressor washing. Corrected to standard ambient conditions the results are then compared with the clean engine performance. A case study shows that as a result of compressor fouling, the compressor efficiency decreases about 2.5%, and Heat Rate increases by 7% and power output falls by 10%. Consequently, the cost of power losses in a one year period is around $600,000. The second section involves high fidelity CFD (two dimensional and three dimensional) simulations of the fouling mechanism of the ninth stage of an axial compressor. This HP9 stage was tested in No. 3 Compressor Test Facility at Rolls-Royce. The comparison between the experimental data and the ANSYS CFX is shown in chapter 4. This research contains a description of the numerical analyses carried out on the HP9 test case to include the effects of variable amounts of roughness both in terms of spatial distribution and equivalent grain size. The examination of the effects of adding roughness to selected regions of the rotor blade suction side has shown the relative importance of the leading edge end on the blade suction side over other regions of the blade. The relative impact was quantified in terms of the wake velocity defect, magnitude and wake width. However when the radial distribution is considered the differences between clan and roughened blades is less apparent excepting for the case where the entire suction side of the blade is roughened. The pressure distribution around the blades was also examined. This part of the work has shown the benefits of flow analysis using CFD in a very small region of the flow field. In this case close the analysis is confined to the leading edge and trailing edge of a compressor blade. It also demonstrates clearly the disadvantages of fouling in reducing pressure rise through increases of total pressure loss and therefore reduced efficiency. It has been established that the leading edge and the concave surfaces of the rotor blade are the most sensitive regions to the fouling. It is emphasised that experimental verification of this trend would be very difficult to achieve with a cascade rig because both rotor and stator would need static pressure tapings very close to one another at the leading edge of the blade. This would be extremely difficult to achieve in practice. In the third section experimental work has been undertaken on a cascade facility in the Gas Turbine Laboratory. This details measurements of the cascade the pressure losses as a result of increasing levels of fouling on the blades. In addition, further experiments are undertaken to recover performance loss due to fouling through a washing technique. This has facilitated a rigorous estimation of the magnitude of compressor stage inefficiency caused by fouling. By observing the actual distribution of fouling in a typical compressor, it is now possible to estimate more accurately the overall impact of the fouled performance on overall compressor efficiency. Furthermore an experimental study has been carried out based on a need in practice for online compressor washing; an investigation was undertaken by using a different spray nozzle pressure. The detergent used for the washing experiments was a water based cleaner diluted with demineralised water in a ratio of 1: 4. The fouled compressor efficiency after cleaning with the current project washing scheme has been improved by 2.2%.Item Open Access An experimental and computational analysis of compressor cascades with varying surface roughness(Cranfield University, 2009-03) Fouflias, Dimitrios; Ramsden, K. W.This thesis presents a CFD and experimental analysis associated with the parameter compressor fouling and a CFD analysis associated with the parameter on-line compressor washing of industrial gas turbines. On-line compressor washing is very popular and quite effective in the industrial gas turbine operational scheme. Many companies apply on-line washing with the engine running at normal speed so as to avoid downtime periods for off-line cleanings that could cause significant economic drawbacks. At this thesis vital parameters affecting compressor cleaning of an industrial gas turbine were examined and combined in such a way so as to provide adequate coverage of the frontal inlet guide vane area which is critical for effective cleaning. The parameters investigated were water injection nozzle position, inclination with respect to the engine centerline, injection velocity and nozzle spray angles. However, before applying compressor washing, compressor fouling comes into consideration. For this purpose a compressor cascade tunnel (test rig) was designed and come into operation in order to examine different levels of fouling. The cascade test rig involved as well a washing kit for future cleaning of the cascade blades. This work related to the cascade design released a lot of information about designing suction type compressor cascade test rigs by analysing the flow inside the cascade rig computationally and three-dimensionally via CFD tools. The results in terms of the quality of flow obtained for the current test rig were also compared with modified versions of the test rig, one which involved a bigger plenum area behind the cascade test section and one involving the current rig running in a blowing type mode. The CFD results coming out from the compressor cascade tunnel for the different fouling levels, were analysed in terms of mass flow capacity and polytropic efficiency reduction due to fouling by using Howell’s theory (1945) and they were used as inputs for running performance simulation in terms of an industrial gas turbine engine using the performance simulation code Turbomatch. Therefore, a correlation between cascade fouling and real engine uniformly stage spread fouling was achieved. At high levels fouling where the 254 microns roughness height takes place, the nondimensional air mass flow reduction can reach levels of 1.6% and the drop in compressor efficiency can touch the value of 5%. The CFD results obtained after running all the simulation scheme for the different roughness levels, were compared to the actual experimental results coming from running the compressor cascade rig with the same fouling scheme of roughness. Applying Howell’s theory (1945), the fouled cascade was correlated to a uniformly fouled stage and a real industrial gas turbine. This time input in the Turbomatch code was the percentage deterioration in compressor efficiency calculated from correlated cascade data. This deterioration reaches a high level of 11 % when the fouling particle size is 254 microns.Item Open Access Fluid flow analysis using the boundary element method(1993-05) Carneiro, Helder Fernando De Franca Mendes; Ramsden, K. W.An Attempt at development of theory and computer program for the solution of potential and viscous flow problems using the Boundary Element Methods is introduced in this work. A program for potential flow analysis of cascades is developed and properly validated. Theory and programs for boundary element analysis of viscous flow using vorticity-velocity formulation and pressure-velocity formulation along with the penalty function approach were developed. Many tests were carried out on the programs, and case studies of Poiseuille, Couette and driven-cavity flows were analysed and results were compared with existing solutions. The developed vorticity-velocity algortithms converge well for low Reynolds number, but the program based on the penalty function approach has limited success only for cases without domain integrations.Item Open Access The influence of swirler design parameters on the aerodynamics of downstream recirculation region(Cranfield University, 1976-05) Kilik, Erol; Lefebvre, A. H.; Ramsden, K. W.The influence of swirler design parameters namely, vane shape (flat or curved), vane outlet angle, aspect ratio and space-to-chord ratio (number of vanes), on the pressure drop-mass flow characteristics and the size and turbulence characteristics of the downstream recirculation region has been determined experimentally. A five-hole spherical pressure probe and hot-wire anemometry have been used for the investigation. A technique for simple and reasonably accurate interpretation of the signals from the hot-wire anemometer has been formulated. Its performance has been tested at first in round jets for which experimental turbulence data are already available for comparison purposes. The method has been applied subsequently to swirling flows issuing from the swirlers; the mean and turbulence characteristics of the flow fields have been determined in this way. In addition to these, the turbulent viscosities Ĭrr, Ĭrz, Ĭrθ and Ĭθθ have been calculated. Also, detailed accounts of the previous experimental work on swirling flows and of some finite difference procedures for the computation of weakly and strongly swirling flows have been given. It has been shown that the hot-wire formulation developed provides a simple, economic and efficient procedure for the measurement of the turbulence quantities in swirling flows. The results have shown that curved vane type swirlers operate more efficiently than flat vane types such that a larger recirculation region and a stronger shear zone are induced at a lower pressure drop. The pressure drop through both the flat and curved vane type swirlers increases with increasing vane angle, decreasing aspect ratio and decreasing space-to-chord ratio. The size of the downstream recirculation region, the reverse mass flow and the decay rates of the axial and swirl velocities increase with increasing vane angle and decreasing aspect ratio in the case of curved vane type swirlers. The effect of the space-to-chord ratio has not been found very significant in the cases of I6 and I2 vanes for the vane angle of 60° and the aspect ratio 0.4. Higher turbulence and stronger shear zones can be obtained in swirling flows with increasing vane angle, decreasing aspect ratio and decreasing space-to-chord ratios. Turbulence is anisotropic in strongly swirling jets issuing from vane type swirlers. The most dominant stresses are in turn ww, uw, and uu; all the other stresses are smaller. In parallel to the anisotropy in the stresses, the turbulent viscosities are also anisotropic; the turbulent viscosity Ĭθθ has shown domination among the four viscosities which have been calculated. Ĭrr values have shown too much scatter. For these reasons, curved vane type swirlers should prove much more efficient than flat vane types in the application to combustion process.Item Open Access A multimedia computational aid to gas turbine design teaching(Cranfield University, 1995-10) Ramsden, K. W.; Pilidis, PericlesThe ambitions of the teacher to fully prepare engineering students for the working environment are usually limited by the length of the lecture course. Consequently, few opportunities exist in the learning process for the student to gain experience in both design and design-optimisation. This document describes a suite of integrated personal computer based programmes designed to illustrate many important aspects of gas turbine component design and overall performance estimation for use both inside and outside the classroom. Accordingly, the objectives of the programmes are to provide a broad understanding of the whole engine and its major components by enabling the following: o a rapid and in depth method for the assessment of design point, off design and deteriorated performance principles for a wide range of gas turbine types and applications. a demonstration of the needs and implications of performance compromise arising from design constraints. a demonstration of how the design and performance limitations imposed by one component influence others. a demonstration of the design compromises required by the interactions between the disciplines of aerodynamics, thermodynamics and mechanical integrity. O O O When used in conjunction with a programme of lectures, tutorials, case studies, and computer based workshops, the new software enables a rapid and in depth understanding of gas turbine performance and component design. ln addition, the programme suite has extensive general application to gas turbine overall performance assessment and to the preliminary design of compressors and turbines.Item Open Access Optimization of centrifugal pumps operation for least cost and maximum availability(Cranfield University, 2008-04) Abdulnabi, I. O. N.; Ramsden, K. W.There are five M.O.L. Centrifugal pumps “Main Oil Line” in Ghani oil field for transporting crude oil from Ghani oil field to Joffra oil field at a distance of about 81.25 miles (130Km) then from Joffra oil field to Ras Lanuf Terminal at a distance of about 84.40 miles (135Km). The five centrifugal pumps do not all have the same specifications. Three of these pumps have the same power (255 Kw) and are working with five impellers but the other two pumps have the same power (150 Kw) and are working with six impellers. The efficiency and the head are the same for each pump. So the total power in the pumping system is (1,065 Kw). Usually two out of five centrifugal pumps are operational the other three pumps are on standby in case of failure of one or more pumps. These pumps are 24 years old and subjected to routine maintenance. This project presents a study to optimize the existing pumping system in order to make the capital cost less. The main change will be in pumping station design mainly to decrease the number of the existing centrifugal pumps with less cost and to meet Veba Oil Operations (VOO) requirements. As mentioned, the system is required to transport 45,000 BPD (298 m3/h), during the expected life of the project, which is through the pumping system from Ghani oil field to Joffra oil field then to Ras Lanuf Terminal. This study offers different pump design to evaluate and select the optimum design according to the lowest cost, highest reliability and availability.Item Open Access The Potential of Liquid Hydrogen for long range aircraft propulsion(Cranfield University, 2009-04) Verstraete, Dries; Ramsden, K. W.The growth of aviation needed to cater for the needs of society might be undermined by restrictions resulting from the environmental implications of air traffic. Hydrogen could provide an excellent alternative to ensure a sustainable future for aviation. Several challenges remain to be addressed though before its adoption can become reality. The liquid hydrogen tanks are one of the areas where considerable research is needed. Further insight into unusual restrictions on aircraft classes that would be thought of as ideal candidates for hydrogen is also required. Hydrogen fueled very large long range transport aircraft for instance suffer from the 80 m airport box constraint which leads to a strong decrease in performance compared to other aircraft classes. In this work 3 main tools are developed to look into some of these issues. An aircraft conceptual design tool has been set up to allow a comparison between kerosene and hydrogen on a common and hence fair basis. An engine performance assessment routine is also developed to allow the coupling of the design of engine and aircraft as one integrated system. As the link between both subsystems is the liquid hydrogen tank, a detailed design method for the tanks has also been created. With these tools it has been shown that the gravimetric efficiency for large transport aircraft varies by only a few percent for a wide range of fuel masses and aircraft diameters with values in the order of 76to 80%. The performance of the long range transport aircraft itself however varies strongly from one class to another. For aircraft with a passenger load around 400 passengers, takeoff weight reductions around 25% can be obtained for similar operating empty weights and fuel weights of about 30% of the equivalent kerosene fuel weight. For 550 passenger aircraft however, the takeoff weight reduction reduces strongly due to the need for a triple deck fuselage and the resulting increase in fuselage mass. Whereas for the first category of aircraft, a 3 to 6 times higher fuel price per energy content can be afforded for similar direct operating costs, this cost advantage is reduced by about a third for the 550 passenger aircraft. A twin fuselage configuration alleviates the geometrical restrictions and restores the potential for an aircraft family but does not yield strong weight reductions. In a subsequent study, the implications of unconventional engine cycles as well as drag reduction resulting from natural laminar flow through surface cooling should be assessed using the developed set of tools as this will reveal the full potential of hydrogen as an aviation fuel.Item Open Access Streamline curvature computational programme for axial compressor performance prediction(Cranfield University, 1987-09) Barbosa, J. R.; Ramsden, K. W.Accurate prediction of overall performance is vital if the extremely high design and development costs of modern high speed compressors are to be minimised. This fact, which is not novel, has led to the development of many computer programmes for such prediction. However, the most useful of these are proprietary. Some of those that are accessible in the open literature are of limited application to high performance axial compressors. This is mainly because they cannot reliably handle the transonic flows which characterise modern designs; nor are they generally easy to use from an interactive stand point. Accordingly, this report describes the origination of a streamline curvature programme for compressor performance prediction which attempts to bridge the gap in the existing literature base. The correlations used allow the package to be applied to more recent compressors at the highest level of the technology. In general, the programme is both interactive and fully modular. The former makes it easy for the user to access the programme quickly and effectively whilst the latter facilitates the use, for example, of alternative loss and deviation models to those prescribed within the programme. A further important feature of this new programme is its flexibility. For example, it can be used in three modes: firstly, as an analysis programme for performance prediction of compressors of known geometry; secondly, as a design/development tool to assess the likely performance changes occasioned by the introduction of geometrical variations in both blading and annulus shape; thirdly, as a straight design programme for new compressors provided a project analysis has been carried out beforehand. In the first two modes of operation, the programme requires details of standard blading, annulus geometry, design mass flow and pressure ratio. In the third, the user is free to prescribe his own blade shapes. The combined features described were introduced to make the package an ideal teaching tool. In this respect it should be emphasised that the complete novice to axial compressor design and performance assessment would experience difficulties using the package. However, the user who has some background, perhaps through lectures or in an appropriate industrial environment would quickly become adept. Against this background, whilst the programme is very interactive, it cannot claim, in its own right, to be an Expert System. The latter capability, however, can with some development easily be built in at a later stage. In order to minimise the time required accessing the programme, the report includes a comprehensive "user- guide". The validity of the prediction method is tested against an actual transonic compressor of known performance. The output is various and includes graphical presentation of all significant design/performance parameters throughout the compressor, including the compressor overall characteristic.Item Open Access Thrust and Flow Prediction in Gas Turbine Engine Indoor Sea-Level Test Cell Facilities(Cranfield University, 2006-02) Gullia, Alessandro; Ramsden, K. W.The principal aim of this research was to provide a detailed understanding of the performance of gas turbine engines inside indoor sea-level test beds. In particular the evaluation of both thrust correction factors and the estimation of the mass flow entering the test cell were at the core of the research. The project has been fully sponsored by Rolls-Royce pIc. Initially, their principal objective was to assess the relevance and accuracy of CFD when applied to thrust measurement inside indoor test beds with an intended outcome of minimising the use of expensive experimental measurements. The different system interfaces and accounting systems for in-flight conditions, available in the open literature have been developed and adapted for indoor environments. This has led to the definition of three different thrust correction equations using alternative definitions of thrust correction factor. Aero-dynamic principles have been applied for the derivation of one-dimensional relationships for the calculation of each thrust correction factor using generic engine-cell performance and dimensions. A one-dimensional analytical model has been developed to represent the enginedetuner ejector pump. This is able to characterise the engine-cell system performance and is used as the main tool for providing a matching procedure capable of predicting the cell entrainment ratio. By processing experimental data relevant to different engine-cell configurations through the ejector pump analytical model, a method for achieving the entrainment ratio control inside the cell has been identified. The CFD work has been concentrated into three main activities: • A quantitative extrapolation of the thrust correction factors including, the pre-entry force, the external and the total bellmouth force, the throat stream force, the intake momentum drag and the base drag. • The representation of the engine-detuner ejector performance for a variety of engine-cell configurations. • The modelling of the generic test cell components including the inlet stack, the cascade elbow, the exhaust stack & the blast basket. The outcomes of this research have been very successful in enhancing the validity of the thrust correction equations developed .. In particular, the use of a one-dimensional approach in their estimation has been shown to be fully justified. The work has also emphasised the value of CFD in supporting the derivation of the matching procedure for predicting and controlling cell entrainment ratio. Indeed, one of the strongest outcomes of this work has been the conclusion that both the engine-cell characteristic lines computed with the one-dimensional model and those computed with CFD for different cell configurations are almost identical. In addition, the use of CFD as a tool for the quantitative evaluation of the thrust correction factors has been established. Finally, the CFD results have facilitated an enhanced understanding of the complex flow structure inside indoor test cellsItem Open Access Turbine rotor blade erosion control with film cooling(Cranfield University, 1982-03) Al-Hassani, T. S. J.; Ramsden, K. W.Component erosion in gas turbines can be a serious problem. The erosive particles which may be sand, ingested into compressors in desert regions, or carbon shed from gas turbine combustors, contribute to significant blade life reduction. In extreme cases, both sand and carbon particles can cause surface build up on turbine blades reducing efficiency and block the small diameter cooling holes thereby reducing cooling effectiveness. A two-dimensional turbine cascade tunnel was designed and built incorporating perspex rotor blades which were eroded for a variety of parametric conditions. The aerodynamic performance of the turbine cascade tunnel is examined with respect to pressure losses and efficiency. The introduction of film cooling air in varying quantities and configurations in the leading edge region is shown to significantly reduce erosive wear. Maximum erosion was found to occur close to the stagnation point on the suction surface of the aerofoils. The test Reynolds number and particle trajectories were chosen to closely represent the entry conditions of an actual film cooled turbine which had experienced this type of erosive wear in operation.