A dynamic convergence control scheme for the solution of the radial equilibrium equation in through-flow analyses

One of the most frequently encountered numerical problems in scientific analyses is the solution of non-linear equations. Often the analysis of complex phenomena falls beyond the range of applicability of the numerical methods available in the public domain, and demands the design of dedicated algorithms that will approximate, to a specified precision, the mathematical solution of specific problems. These algorithms can be developed from scratch or through the amalgamation of existing techniques. The accurate solution of the full radial equilibrium equation (REE) in streamline curvature (SLC) through-flow analyses presents such a case. This article discusses the development, validation, and application of an 'intelligent' dynamic convergence control (DCC) algorithm for the fast, accurate, and robust numerical solution of the non-linear equations of motion for two-dimensional flow fields. The algorithm was developed to eliminate the large extent of user intervention, usually required by standard numerical methods. The DCC algorithm was integrated into a turbomachinery design and performance simulation software tool and was tested rigorously, particularly at compressor operating regimes traditionally exhibiting convergence difficulties (i.e. far off-design conditions). Typical error histories and comparisons of simulated results against experimental are presented in this article for a particular case study. For all case studies examined, it was found that the algorithm could successfully 'guide' the solution down to the specified error tolerance, at the expense of a slightly slower iteration process (compared to a conventional Newton-Raphson scheme). This hybrid DCC algorithm can also find use in many other engineering and scientific applications that require the robust solution of mathematical problems by numerical instead of analytical means

Degradation Effects on Combined Cycle Power Plant Performance, Part 1: Gas Turbine Cycle Component Degradation Effects,’’

This is the second paper exploring the effects of the degradation of different components on combined cycle gas turbine (CCGT

Degradation Effects on Combined Cycle Power Plant Performance, Part II:

This paper describes the effects of degradation of the main gas path components of the gas turbine topping cycle on the combined cycle gas turbine (CCGT

Integrated electrical and mechanical modelling of integrated-full-electric-propulsion systems

Integrated Full Electric Propulsion (IFEP) systems are the subject of much interest at present. Current research is focused on analysing and improving aspects of subsystem and system performance. However, there is a great need to look more widely at the `multi-physics' problem of characterising the dynamic interactions between the electrical and mechanical systems. This paper will discuss the changing nature of modelling and simulation to aid research into IFEP systems, outlining the alternative angle taken by the Advanced Marine Electrical Propulsion Systems (AMEPS) project to characterise and investigate electrical-mechanical system interactions. The paper will describe this approach and highlight the unique challenges associated with the problem, discussing the suitable methods that will be adopted to address these challenges. Finally, an overview of the present and future research opportunities facilitated via the AMEPS project will be presented

Theoretical optimal trajectories for reducing the environmental impact of commercial aircraft operations

This work describes initial results obtained from an ongoing research involving the development of optimization algorithms which are capable of performing multi-disciplinary aircraft trajectory optimization processes. A short description of both the rationale behind the initial selection of a suitable optimization technique and the status of the optimization algorithms is firstly presented. The optimization algorithms developed are subsequently utilized to analyze different case studies involving one or more flight phases present in actual aircraft flight profiles. Several optimization processes focusing on the minimization of total flight time, fuel burned and oxides of nitrogen (NOx) emissions are carried out and their results are presented and discussed. When compared with others obtained using commercially available optimizers, results of these optimization processes show atisfactory level of accuracy (average discrepancies ~2%). It is expected that these optimization algorithms can be utilized in future to efficiently compute realistic, optimal and ‘greener’ aircraft trajectories, thereby minimizing the environmental impact of commercial aircraft operations

An experimental and numerical investigation of the effect of aero gas turbine test facility aspect ratio on thrust measurement

This work describes the outcome of research program investigating thrust measurements in enclosed test facility for modern aero gas turbine engines. Literature work, experimental work and a description of Computational fluid dynamics simulation system have been developed to improve the accuracy of test bed thrust measurement. The key parameters covered in the research include test house size in relation to engine size. The effect of the distance of engine to detuner on the thrust correction factor was also investigated. The rule of loss mechanism within the test facility to include intake momentum drag, cradle drag, base drag, recirculation on loss and intake exhaust losses loss. The thrust correction factor prediction technique available in the open literature are compared with the result given by this research and conclusion are drawn. CFD predictions show that the biggest difference with experimental data is only 1 % in TCF for the largest test cell size. For the smallest test cell this difference increases to only 2%. These results in terms of accuracy are lower than what would normally be expected for general CFD work. The major contributions to thrust measurement technology include the following: 1. The research was able to ascertain that as engine size increases it will become more risky to rely on test bed results as giving an accurate prediction of static thrust. 2. The work has enabled confident prediction that test bed results can give test bed static thrust compared to free air testing with an accuracy of one half of 1%. 3. Using Fluent it has been possible to reproduce a comparable comparison with test bed results. This will give the user of the research a higher level of confidence in predicting thrust measurements for test beds whose size is small in comparison with engine size. 4. It is of course an ambition for all those working in the field to eliminate engine testing. However this is unachievable ambition. This research has shown the way to improve CFD prediction towards achieving this ambition. Finally detailed recommendations are given for continuation for this research program.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Sub-idle modelling of gas turbines : altitude relight and windmilling

Gas turbine sub-idle performance modelling is still in an early development stage and this research aims to provide and improve present techniques, for modelling of windmilling and transient windmilling relights, through to groundstart simulations. Engine ATF data was studied and used to align models created within this research for low and high bypass engines, and compare these models simulation results. Methods for the extrapolation of component characteristics are improved and performed in linearised parameter form, and the most efficient approach discussed. The mixer behaviour is analysed and recommendations of off-design mixer behaviour representation in a sub-idle model are proposed and performed within the modelling. Combustion at sub-idle conditions is investigated with regards to the loading parameter definition, and also its representation for the influence of evaporation rate being limiting to overall combustion efficiency. A method is proposed on extrapolating and representation of the combustion characteristic. Compressor behaviour and the blade torques at locked rotor and windmilling conditions are studied using 3D CFD, producing insight and discussion on CFD suitability and what it can offer at these operating conditions. From the CFD studies generic loss coefficients were created for all compressor blades, from which a zero speed is created for the whole compressor, from a theoretical stage stacking calculation. This zero-speed curve is shown to allow interpolation of component characteristics to the sub-idle region, improving the definition and a predictive approach. A windmilling conditions cascade test rig is proposed, designed and built for validating the CFD loss coefficients. The findings and discussions within this thesis provide useful reference material on this complicated and little documented area of research. The modelling and methods proposed, provide great advancement of the research area, along with further integration of the Cranfield UTC in performance with Rolls-Royce.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Dealing with missing data for prognostic purposes

© 2016 IEEE. Centrifugal compressors are considered one of the most critical components in oil industry, making the minimisation of their downtime and the maximisation of their availability a major target. Maintenance is thought to be a key aspect towards achieving this goal, leading to various maintenance schemes being proposed over the years. Condition based maintenance and prognostics and health management (CBM/PHM), which is relying on the concepts of diagnostics and prognostics, has been gaining ground over the last years due to its ability of being able to plan the maintenance schedule in advance. The successful application of this policy is heavily dependent on the quality of data used and a major issue affecting it, is that of missing data. Missing data's presence may compromise the information contained within a set, thus having a significant effect on the conclusions that can be drawn from the data, as there might be bias or misleading results. Consequently, it is important to address this matter. A number of methodologies to recover the data, called imputation techniques, have been proposed. This paper reviews the most widely used techniques and presents a case study with the use of actual industrial centrifugal compressor data, in order to identify the most suitable ones

Reciprocating compressor prognostics of an instantaneous failure mode utilising temperature only measurements

Reciprocating compressors are critical components in the oil and gas sector, though their maintenance cost is known to be relatively high. Compressor valves are the weakest component, being the most frequent failure mode, accounting for almost half the maintenance cost. One of the major targets in industry is minimisation of downtime and cost, while maximising availability and safety of a machine, with maintenance considered a key aspect in achieving this objective. The concept of Condition Based Maintenance and Prognostics and Health Management (CBM/PHM) which is founded on the diagnostics and prognostics principles, is a step towards this direction as it offers a proactive means for scheduling maintenance. Despite the fact that diagnostics is an established area for reciprocating compressors, to date there is limited information in the open literature regarding prognostics, especially given the nature of failures can be instantaneous. This work presents an analysis of prognostic performance of several methods (multiple linear regression, polynomial regression, K-Nearest Neighbours Regression (KNNR)), in relation to their accuracy and variability, using actual temperature only valve failure data, an instantaneous failure mode, from an operating industrial compressor. Furthermore, a variation for Remaining Useful Life (RUL) estimation based on KNNR, along with an ensemble technique merging the results of all aforementioned methods are proposed. Prior to analysis, principal components analysis and statistical process control were employed to create !! and ! metrics, which were proposed to be used as health indicators reflecting degradation process of the valve failure mode and are proposed to be used for direct RUL estimation for the first time. Results demonstrated that even when RUL is relatively short due to instantaneous nature of failure mode, it is feasible to perform good RUL estimates using the proposed techniques

The effect of upstream duct boundary layer growth and compressor blade lean angle variation on an axial compressor performance

The compressor of a gas turbine engine is extremely vulnerable on upstream duct- induced flow non-uniformities whether the duct is an engine intake or an interconnecting duct. This is justified by its position being literally an extension of the duct flow path, coupled to the fact that it operates under adverse pressure gradients. In particular, this study focuses on performance deviations between installed and uninstalled compressors. Test results acquired from a test bed installation will differ from those recorded when the compressor operates as an integral part of an engine. The upstream duct, whether an engine intake or an inter-stage duct, will affect the flow-field pattern ingested into the compressor. The case study presented here aims mostly at qualifying the effect of boundary layer growth along the upstream duct wall on compressor performance. Additionally, the compressor performance response on blade lean angle variation is also addressed, with the aim of acquiring an understanding as to how compressor blade lean angle changes interact with intake-induced flow non-uniformities. Such studies are usually conducted as part of the preliminary design phase. Consequently, experimental performance investigation is excluded at this stage of development, and therefore, computer-aided simulation techniques are used if not the only option for compressor performance prediction. Given the fact that many such design parameters need to be assessed under the time pressure exerted by the tight compressor development programme, the compressor flow simulation technique needs to provide reliable results while consuming the least possible computational time. Such a low computational time compressor flow simulation method, among others, is the two-dimensional streamline curvature (SLC) method, being also applied within the frame of reference of the current study. The paper is introduced by a brief discussion on SLC method. Then, a reference is made to the radial equilibrium equation, which is the mathematical basis of SOCRATES, a turbomachinery flow simulation tool that was used in this study. Subsequently, the influence of the upstream duct on the compressor inlet radial flow distribution is being addressed, with the aim of adjusting the compressor blade inlet lean angle, in order to minimize compressor performance deterioration. The paper concludes with a discussion of the results