[Show abstract][Hide abstract] ABSTRACT: The estimated life of gas turbines is expected to diminish over time when compared to the manufacturers’ estimated life, particularly when used as a back-up to Renewable Energy Sources (RES). As RES are been introduced into the grid, the gas turbines used in conjunction with them are operated in “Load-Following” modes to these RES which includes wind, thermal, solar, etc. As back-up plants, the start/stop and power settings are expected to be dictated by the response to grid requirements and need to compensate for the load shortfall attributable to unpredictable nature of RES. This mode of operation results in Gas turbine high pressure turbine blades experiencing low cycle fatigue and creep life failure over time. It is therefore of great importance to estimate the life consumed during this mode of operation to enable appropriate maintenance planning/repair action. In order to estimate the life consumed during adverse/cyclic operating regimes, a tool has been developed wherein different scenarios can be simulated and analyzed to obtain engine life consumption factors. The tool is capable of estimating life consumption based on seasonal power demand. For the purpose of study, an aero derivative power plant of 100MW power output was used as a reference engine. The paper provides an in-depth analysis of the study undertaken and it arrives at the conclusion that the operation of engine during summer contributes to a higher degree of LCF and creep life consumption in comparison to operations during other seasons.
[Show abstract][Hide abstract] ABSTRACT: The life cycle estimation of power plants is important for gas turbine operators. With the introduction of wind energy into the grid, gas turbine operators now operate their plants in load-following modes as back-ups to the renewable energy sources which include wind, solar, etc. The motive behind this study is to look at how much life is consumed when an intercooled power plant with 100MW power output is used in conjunction with wind energy. This operation causes fluctuations because the wind energy is unpredictable and overtime causes adverse effects on the life of the plant – The High Pressure Turbine Blades. Such fluctuations give
rise to low cycle fatigue and creep failure of the blades depending on the operating regime used. A performance based model that is capable of estimating the life consumed of an intercooled power plant has been developed. The model has the capability of estimating the life consumed based on seasonal power demands and operations. An in-depth comparison was undertaken on the life consumed during the seasons of operation and arrives at the conclusion that during summer, the creep and Low cycle life is
consumed higher than the rest periods. A comparison was also made to determine the life consumed between load-following and stop/start operating scenarios. It was also observed that daily creep life consumption in summer was higher than the winter period in-spite of having lower average daily operating hours in a start-Stop operating scenario.
Journal of Propulsion and Power 08/2015; · 0.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The paper presents a methodology for estimating the fatigue life of rolling-element bearing under irregular loading conditions. This method overcomes the limitations encountered by rolling-element bearing lifing models based on a constant bearing load assumption, when used in applications where bearing load varies over time with also changes in rotational speed. To include these irregular loading effects, a load-slice averaging methodology is applied to the loading history; in which the loading history is assumed to be composed of many thin slices of loading conditions. The operating conditions within each loading slice are averaged, and with the aid of linear damage rule and Lundberg-Palmgren load-life correlation for rolling-element bearings, each loading slice fatigue damage contribution is determined. The cumulative loading slice fatigue damage is used to estimate rolling-element bearing life. This approach can also be used as a tool for real-time life prognosis of rolling-element bearings. The method is demonstrated with simulated loading histories acting on a Cooper split cylindrical roller bearing and life prediction comparison is made between several approximate closed form bearing life expressions for different types of loading.
The Twelfth International Conference on Condition Monitoring and Machinery Failure Prevention Technologies CM2015 / MFPT2015, Oxford, UK; 06/2015
[Show abstract][Hide abstract] ABSTRACT: In this work, the Techno-economic Environmental Risk Analysis framework, a multi-disciplinary optimisation tool developed by Cranfield University, is utilised in conjunction with an in-house optimiser to carry out aircraft engine cycle optimisation processes. The central point here is the evaluation of the capabilities of the in-house optimiser for performing this type of optimisation processes. Simplifying hypotheses are thus considered when both defining the aircraft flight trajectory and modelling the different engine configurations analysed. Accordingly, several optimum engine cycles minimising separately three objective functions, (i) specific fuel consumption in cruise (ii) fuel burned, and (iii) oxides of nitrogen emitted, are determined. The cycle optimisation processes carried out yield results reflecting the general trends expected when optimising according to these objective functions. It follows then that the in-house optimiser is suitable for carrying out gas turbine power plant optimisation processes. It is expected that this optimiser be utilised in future for both optimising the preliminary design of gas turbine engines and determining optimum and “greener” aircraft engine cycles.
Journal of Aerospace Technology and Management 05/2015; 7(2):143-156. DOI:10.5028/jatm.v7i2.406
[Show abstract][Hide abstract] ABSTRACT: The aim of this paper is to assess and compare techno-economic viability of large-scale simple cycle (SC) and advanced cycles aero-derivative industrial gas turbines combined-heat-and-power (ADIGT-CHP) generation in the petrochemical industry in terms of net present value (NPV), internal rate of return (IRR), and simple-payback-period (SPBP). To achieve this, a techno-economic assessment method was applied using a case study of a large-scale Refinery CHP. Parameters of technical performance of the ADIGT-CHP such as fuel flow, power output, emissions, heat recovery, and steam flow, in conjunction with various cost elements were made inputs in an economic module utilising a 20 years life-cycle. Economic principles were applied to predict the NPV, IRR, and SPBP of the three ADIGT-CHP cycles over conventional case (Grid electricity plus on-site boiler). The advanced cycles considered are intercooled (IC) cycle and intercooled-recuperated (ICR) cycle. The result shows that all three ADIGT–CHP cycles exhibit positive NPV, good payback-period and internal-rate-of-return, which is an indication that all are viable, though the SC ADIGT–CHP was found to be more profitable than the others. The percentage savings in operational cost of SC, IC, and ICR cycle ADIGT–CHP over the conventional case were obtained as 21.1%, 20.5%, and 19.7% respectively. More so, SC ADIGT–CHP was found to exhibit higher CHP efficiency and steam flow than IC and ICR cycles. This sort of assessment would aid decision makers to make good choice of large-scale ADIGT-CHP cycle option in the petrochemical industry.
[Show abstract][Hide abstract] ABSTRACT: This paper presents the development of a mathematical model for the implementation of flexible rotor blade dynamics in real-time helicopter aeromechanics applications. A Lagrangian approach is formulated for the rapid estimation of natural vibration characteristics of nonuniform rotor blades. A matrix/vector formulation is proposed for the treatment of elastic blade kinematics in the time-domain. In order to overcome the classical hurdles of time-accurate simulation and establish applicability in real-time, a novel, second-order accurate, finite-difference scheme is employed for the numerical discretisation of elastic blade motion. The proposed rotor dynamics model is coupled with a finite-state induced flow and an unsteady blade element aerodynamics model. The combined formulation is implemented in a helicopter flight mechanics simulation code. The integrated approach is deployed in order to investigate rotor blade resonant frequencies, trim control angles, oscillatory blade loads and induced vibration for a hingeless and an articulated helicopter rotor. Extensive comparisons are carried out with wind tunnel and flight test measurements, and non-real-time comprehensive analysis methods. Good agreement with measured data is exhibited considering primarily the low-frequency harmonic components of oscillatory loading. It is shown that, the developed methodology can be utilised for real-time simulation on a typical computer with sufficient modelling fidelity for accurate estimation of oscillatory blade loads.
[Show abstract][Hide abstract] ABSTRACT: A large variety of promising power and propulsion system concepts are being proposed to reduce carbon dioxide and other emissions. However, the best candidate to pursue is difficult to select and it is imperative that major investments are correctly targeted to deliver environmentally friendly, economical and reliable solutions. To conceive and assess gas turbine engines with minimum environmental impact and lowest cost of ownership in a variety of emission legislation scenarios and emissions taxation policies, a tool based on a techno-economic and environmental risk assessment methodology is required. A tool based on this approach has been developed by the authors. The core of the tool is a detailed and rigorous thermodynamic representation of power plants, around which other modules can be coupled (that model different disciplines such as aircraft performance, economics, emissions, noise, weight and cost) resulting in a multidisciplinary framework. This approach can be used for efficient and cost-effective design space exploration in the civil aviation, power generation, marine, and oil and gas fields. In the present work, a conceptual intercooled core aeroengine design was assessed with component technologies consistent with 2020 entry into service via a multidisciplinary optimisation approach. Such an approach is necessary to assess the trade-off between asset life, operating costs and technical specification. This paper examines the influence of fuel consumption, engine weight and direct operating costs with respect to extending the engine life. The principal modes of failure such as creep, fatigue and oxidation, are considered in the engine life estimation. Multidisciplinary optimisation, comprising the main engine design parameters, was carried out with maximum time between overhaul as the objective function. The trade-off between minimum block fuel burn and maximum engine life was examined; the results were compared against the initial engine design and an assessment was made to identify the design changes required for obtaining an improved engine design in terms of direct operating costs. The results obtained from the study demonstrate that an engine optimised for maximum time between overhaul requires a lower overall pressure ratio and specific thrust but this comes at the cost of lower thermal efficiency and higher engine production costs.
Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering 10/2014; 228(13):2424-2438. DOI:10.1177/0954410013518509 · 0.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Industrial gas turbines are susceptible to compressor fouling, which is the deposition and accretion of airborne particles or contaminants on the compressor blades. This paper demonstrates the blade aerodynamic effects of fouling through experimental compressor cascade tests and the accompanied engine performance degradation using TURBOMATCH, an in-house gas turbine performance software. Similarly, on-line compressor washing is implemented taking into account typical operating conditions comparable with industry high pressure washing. The fouling study shows the changes in the individual stage maps of the compressor in this condition, the impact of degradation during part-load, influence of control variables, and the identification of key parameters to ascertain fouling levels. Applying demineralized water for 10 min, with a liquid-to-air ratio of 0.2%, the aerodynamic performance of the blade is shown to improve, however most of the cleaning effect occurred in the first 5 min. The most effectively washed part of the blade was the pressure side, in which most of the particles deposited during the accelerated fouling. The simulation of fouled and washed engine conditions indicates 30% recovery of the lost power due to washing.
Journal of Turbomachinery 10/2014; 136(10):101001. DOI:10.1115/1.4027747 · 0.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper presents a mathematical model for the simulation of rotor blade flexibility in real-time helicopter flight dynamics applications that also employs sufficient modeling fidelity for prediction of structural blade loads. A matrix/vector-based formulation is developed for the
treatment of elastic blade kinematics in the time domain. A novel, second-order-accurate, finite-difference scheme is employed for the approximation of the blade motion derivatives. The proposed method is coupled with a finite-state induced-flow model, a dynamic wake distortion model, and
an unsteady blade element aerodynamics model. The integrated approach is deployed to investigate trim controls, stability and control derivatives, nonlinear control response characteristics, and structural blade loads for a hingeless rotor helicopter. It is shown that the developed methodology
exhibits modeling accuracy comparable to that of non-real-time comprehensive rotorcraft codes. The proposed method is suitable for real-time flight simulation, with sufficient fidelity for simultaneous prediction of oscillatory blade loads.
Journal of the American Helicopter Society 10/2014; 59(4). DOI:10.4050/JAHS.59.042006 · 0.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Purpose - The performance benefits of boundary layer ingestion (BLI) in the case of air vehicles powered by distributed propulsors have been documented and explored extensively by numerous studies. Therefore, it is well known that increased inlet flow distortion due to BLI can dramatically reduce these benefits. In this context, a methodology that enables the assessment of different propulsion architectures, whilst accounting for these aerodynamic integration issues, is studied in this paper. Design/methodology/approach - To calculate the effects of BLI-induced distortion, parametric and parallel compressor approaches have been implemented into the propulsion system analysis. The propulsion architectures study introduces the concept of thrust split between propulsors and main engines and also examines an alternative propulsor configuration. In the system analysis, optimum configurations are defined using thrust-specific fuel consumption as figure of merit. Findings - For determined operating conditions, the system analysis found an optimum configuration for 65 per cent of thrust delivered by the propulsor array, which was attributed mainly to the influence of the propulsor's intake losses. An alternative propulsor design, which used the ejector pump effect to re-energize the boundary layer, and avoiding the detrimental effects of BLI are also cited in this work. Originality/value - To summarize, this paper contributes with a general review of the research that has been undertaken to tackle the aforementioned aerodynamic integration issues and, in this way, make viable the implementation of distributed propulsion systems with BLI.
[Show abstract][Hide abstract] ABSTRACT: This paper presents a numerical formulation targeting the rapid estimation of natural vibration characteristics of helicopter rotor blades. The proposed method is based on application of Lagrange’s equation of motion to the kinematics of blade flap/lag bending and torsion. Modal properties obtained from Bernoulli-Euler beam and classical torsional vibration theory, are utilised as assumed deformation functions in order to estimate the time variations of strain and kinetic energy for each degree of freedom. Integral expressions are derived, describing the generalised centrifugal force and torsional moment acting on the blade in terms of normal coordinates, for flap/lag transverse displacement and torsional deformation. Closed form expressions are provided for the direct analysis of hingeless, freely-hinged and spring-hinged articulated rotor blades. Results are presented in terms of natural frequencies and mode shapes for two small-scale rotor blade models. Extensive comparisons are carried out with experimental measurements and nonlinear finite element analysis. Predictions of resonant frequencies are also presented for two full-scale rotor blade models and the results are compared with established multi-body dynamics analysis methods. It is shown that, the proposed approach exhibits excellent numerical behaviour with low computational cost and definitive convergence characteristics. The comparisons suggest very good and in some cases excellent accuracy levels, especially considering the method’s simplicity, computational efficiency, and ease of implementation.
[Show abstract][Hide abstract] ABSTRACT: A significant problem encountered in the gas turbine industry with fuel products is the degradation of fuel and fuel systems by micro-organisms, which are largely bacteria, embedded in biofilms. These micro-organisms cause system fouling and other degradatory effects, extending often to sudden failure of components with cost implications. Current methods of assessment are only postimpact evaluation and do not necessarily quantify the effects of fuel degradation on engine performance and emission. Therefore, effective models that allow predictive condition monitoring are required for engine's fuel system reliability, especially with readily biodegradable biofuels. The aim of this paper is to introduce the concept of biofouling in gas turbines and the development of a biomathematical model with potentials to predict the extent and assess the effects of microbial growth in fuel systems. The tool takes into account mass balance stoichiometry equations of major biological processes in fuel biofouling. Further development, optimization, and integration with existing Cranfield in-house simulation tools will be carried out to assess the overall engine performance and emission characteristics. This new tool is important for engineering design decision, optimization processes, and analysis of microbial fuel degradation in gas turbine fuels and fuel systems.
Journal of Engineering for Gas Turbines and Power 06/2014; 136(6). DOI:10.1115/1.4026367 · 0.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The aero-thermodynamic effects of water ingestion on an axial flow compressor performance are presented in this article. Under adverse weather conditions, gas turbine engine performance deteriorates and in extreme cases, this performance deterioration may result in flameout or shutdown of the engine, which means that serious incidents or possibly accidents may occur. When the water droplets enter into the engine they break up into smaller droplets which may bounce, coalesce or splash onto the compressor blades. They also form a liquid film whose motion is influenced by inertia forces, blade friction, aerodynamic drag and pressure gradient. The water liquid film has considerable effects on blade’s geometric characteristics. Apart from the change in its profile due to thickness increase, air shear force and water droplets momentum cause waves in water film’s surface introducing a kind of ‘roughness’ on blade’s surface. The current work focuses on the aero-thermodynamic effects. Its methodology is based on computational fluid dynamics, which is used to solve the flow field of the computational domain. The model consists of an extended inlet, an inlet guide vane, a
rotor and a stator blade. Several cases with water ingestion are solved, varying the parameter of water mass and engine rotational speed, simulating adverse weather conditions. On the rotor blade, the water film height and speed are calculated at the equilibrium condition. This condition is achieved when the water mass which flows out of the blade surface equals with this which impacts on it. Taking into account the film thickness at each computational node of the blade surface, the blade’s geometry is changed. Furthermore, an equivalent roughness is introduced and the effects on compressor’s performance are calculated. It is found that deterioration is more pronounced in low rotational speed. For 4% water/air, compressor’s isentropic efficiency deteriorates 8.5% for idle speed and 1.6% for full speed. For the same water mass, mass flow capacity deteriorates 2.4% at idle speed while the change is small for full speed.
Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering 03/2014; 228(3):411-423. DOI:10.1177/0954410012474421 · 0.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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 satisfactory 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.
Journal of Aerospace Technology and Management 01/2014; 6(1):29-42. DOI:10.5028/jatm.v6i1.288
[Show abstract][Hide abstract] ABSTRACT: This paper considers comparative assessment of simple and advanced cycle small-scale aero-derivative industrial gas turbines derived from helicopter engines. More particularly, investigation was made of technical performance of the small-scale aero-derivative engine cycles based on existing and projected cycles for applications in industrial power generation, combined heat and power concept, rotating equipment driving, and/or allied processes. The investigation was done by carrying out preliminary design and performance simulation of a simple cycle (baseline) two-spool small-scale aero-derivative turboshaft engine model, and some advanced counterpart aero-derivative configurations. The advanced configurations consist of recuperated and intercooled/recuperated engine cycles of same nominal power rating of 1.567 MW. The baseline model was derived from the conversion of an existing helicopter engine model. In doing so, design point and off-design point performances of the engine models were established. In comparing their performances, it was observed that to a large extent, the advanced engine cycles showed superior performance in terms of thermal efficiency, and specific fuel consumption. In numerical terms, thermal efficiencies of recuperated engine cycle, and intercooled/recuperated engine cycles, over the simple cycle at DP increased by 13.5%, and 14.5% respectively, whereas specific fuel consumption of these cycles over simple cycle at DP decreased by 12.5%, and 13% respectively. This research relied on open access public literature for data.
[Show abstract][Hide abstract] ABSTRACT: The liquefaction of natural gas is an energy intensive process and accounts for a considerable portion of the costs in the liquefied natural gas (LNG) value chain. Within this, the selection of the driver for running the gas compressor is one of the most important decisions and indeed the plant may well be designed around the driver, so one can appreciate the importance of driver selection. This paper forms part of a series of papers focusing on the research collaboration between Shell Global Solutions and Cranfield University, looking at the equipment selection of gas turbines in LNG service. The paper is a broad summary of the LNG Technoeconomic and Environmental Risk Analysis (TERA) tool created for equipment selection and looks at all the important factors affecting selection, including thermodynamic performance simulation of the gas turbines, lifing of hot gas path components, risk analysis, emissions, maintenance scheduling, and economic aspects. Moreover, the paper looks at comparisons between heavy duty industrial frame engines and two artificial design variants representing potential engine uprates. The focus is to provide a quantitative and multidisciplinary approach to equipment selection. The paper is not aimed to produce absolute accurate results (e.g., in terms of engine life prediction or emissions), but useful and realistic trends for the comparison of different driver solutions. The process technology is simulated based on the Shell DMR technology and single isolated trains are simulated with two engines in each train. The final analysis is normalized per tonne of LNG produced to better compare the technologies.
Journal of Engineering for Gas Turbines and Power 11/2013; 136(2):022001. DOI:10.1115/1.4025474 · 0.80 Impact Factor