1,721,012 research outputs found
Legibility of machine readable codes used for gas turbine part tracking
Full text linkGas turbines are comprised of many parts, which are often expensive and required to
survive a harsh environment for significant periods (with or without reconditioning). To
differentiate between parts, and facilitate keeping accurate historical records, they are
often given a unique identification number. However, manually recording and tracking
these is difficult. This has led to increased adoption of machine readable codes to help
reduce or eliminate many of the issues currently faced (mostly human error). The harsh
environment of a gas turbine means that typical methods of applying machine readable
codes, such as printed adhesive labels, are simply not durable enough. Direct part marking
(DPM) is necessary to ensure the desired longevity of the code over the part's useful life.
The research presented in this thesis was approached in two main phases. Firstly, the
author sought to investigate the technical solutions available for the elements required
of a part tracking system (encoding, marking and scanning). This included identifying
the characteristics of each and their compatibility with one other (across elements). In
conjunction with Alstom, criteria were identified that were used as a basis for comparison
so that the preferred technical solutions could be determined. The outcome of this process
was enhanced by the author developing a number of industrial contacts experienced in
implementing part tracking systems.
The second phase related to the legibility of the codes. The harsh environment of a
gas turbine results in surface degradation that may in turn reduce the legibility of any
machine readable codes present. To better understand why read failures occur, the author
_rst looked to the scanning process. Data Matrix symbols (marked via dot peen) require
the scanner to capture an image for processing. Image capture is typically achieved using
a charge-coupled device (CCD), each pixel of which induces a charge proportional to the
incident illumination. This illumination is received via reflection from the surface of the
part and hence the Data Matrix marked on it. Several surface features were identified that
govern the way in which the part surface will reflect light back to the scanner: surface
roughness, dot geometry and surface colour. These parameters are important because
they link the degradation mechanisms occurring { broadly categorised as deposition,
erosion or corrosion { with the scanning process. Whilst the degradation mechanisms
are distinctly different in their behaviour, their effect on surface reflectivity is common
in that they can all be characterised via the surface parameters identified. This was
deduced theoretically and so the author completed tests (utilising shot blasting to change
the surface roughness and oxidation to change its colour, independently) to show that
these surface parameters do indeed change with the introduction of surface degradation
and that there is a commensurate change in symbol legibility.
Based on the learning derived with respect to Data Matrix legibility, the author has
proposed a framework for developing a tool referred to as a Risk Matrix System. This
tool is intended to enhance the application of part tracking to gas turbine engines by
enabling symbol durability to be assessed based on the expected operating conditions.
The research presented is the first step in fully understanding the issues that affect the
legibility of symbols applied to gas turbine parts. The author's main contribution to
learning has been the identification of knowledge from various other sources applicable to
this situation and to present it in a coherent and complete manner. From this foundation,
others will be able to pursue relevant issues further; the author has made a number of
recommendations to this effect
Techno-economic analysis and predictive model for heavy-duty gas turbine, in relation to cooling air system degradation.
Full text linkModern gas turbines are featured with cooling air systems that allow them to operate at temperatures much higher than the melting points of most of their hot gas path components. When these systems degrade, creep life consumption is accelerated. If the risk is not assessed and managed in time, the engine could operate with high lifting risk. In the world of power industry, the operators are in most cases presented with two options when a lifting risk in their engine is identified. They can undertake a forced opening of the engine, against their existing planning of maintenance events, aiming to re-instate cooling air system’s functionality. Alternatively, they can derate the engine, by decreasing
firing temperature, to a level that will allow continuous operation until the next planned overhaul event.
The model presented in this work allows the operator to follow a third path. The operator can still manage effectively the lifting risk but also, critically, to do it in a commercially optimised way by taking into consideration electricity market conditions and the incentives that the market may present. This is important as this model fills a gap in the relevant research where the majority of the works are focused in managing lifting risks through a binary time-interval-reduction or firing- temperature-decrease approach.
The developed in this work tool uses a combination of performance modelling, analytical and computational methods, as well as Monte Carlo simulations. The cooling air system degradation is detected and assessed and the effect on cooling air temperature is determined with use of CFD. The impact on blades metal temperature is calculated with a combination of analytical model and Monte Carlo simulations. In a similar combination of analytical method and Monte Carlo, stress is calculated and together with OEM’s life expectancy, a creep life estimation model then is derived. The lifting risk is quantified and appropriate mitigation is proposed. The mitigation is in the form of a novel method, which uses market triggered factors to adjust dynamically engine’s firing temperature and define by this way engine’s performance. This hybrid approach results is an optimised operation in which the lifting risk is effectively managed, the original maintenance planning is respected and, critically, the commercial losses due to engine derate are significantly trimmed. The tool, with its risk-versus-value function, allows the operator to exercise a more or less conservative operation, following a case-by-case approach.PhD in Aerospac
Performance based diagnostics of a twin shaft aeroderivative gas turbine: water wash scheduling
Full text linkAeroderivative gas turbines are used all over the world for different applications
as Combined Heat and Power (CHP), Oil and Gas, ship propulsion and others.
They combine flexibility with high efficiencies, low weight and small footprint,
making them attractive where power density is paramount as off shore Oil and
Gas or ship propulsion. In Western Europe they are widely used in CHP small
and medium applications thanks to their maintainability and efficiency. Reliability,
Availability and Performance are key parameters when considering plant
operation and maintenance. The accurate diagnose of Performance is
fundamental for the plant economics and maintenance planning. There has been
a lot of work around units like the LM2500® , a gas generator with an
aerodynamically coupled gas turbine, but nothing has been found by the author
for the LM6000® .
Water wash, both on line or off line, is an important maintenance practice
impacting Reliability, Availability and Performance. This Thesis aims to select and
apply a suitable diagnostic technique to help establishing the schedule for off line
water wash on a specific model of this engine type. After a revision of Diagnostic
Methods Artificial Neural Network (ANN) has been chosen as diagnostic tool.
There was no WebEngine model available of the unit under study so the first step
of setting the tool has been creating it. The last step has been testing of ANN as
a suitable diagnostic tool. Several have been configured, trained and tested and
one has been chosen based on its slightly better response. Finally, conclusions
are discussed and recommendations for further work laid out
Application of probabilistic set-based design exploration on the energy management of a hybrid-electric aircraft
Full text linkThe energy management strategy of a hybrid-electric aircraft is coupled with the design of the propulsion system itself. A new design space exploration methodology based on Set-Based Design is introduced to analyse the effects of different strategies on the fuel consumption, NOx and take-off mass. Probabilities are used to evaluate and discard areas of the design space not capable of satisfying the constraints and requirements, saving computational time corresponding to an average of 75%. The study is carried on a 50-seater regional turboprop with a parallel hybrid-electric architecture. The strategies are modelled as piecewise linear functions of the degree of hybridisation and are applied to different mission phases to explore how the strategy complexity and the number of hybridised segments can influence the behaviour of the system. The results indicate that the complexity of the parametrisation does not affect the trade-off between fuel consumption and NOx emissions. On the contrary, a significant trade-off is identified on which phases are hybridised. That is, the least fuel consumption is obtained only by hybridising the longest mission phase, while less NOx emissions are generated if more phases are hybridised. Finally, the maximum take-off mass was investigated as a parameter, and the impact to the trade-off between the objectives was analysed. Three energy management strategies were suggested from these findings, which achieved a reduction to the fuel consumption of up to 10% and a reduction to NOx emissions of up to 15%.European Union funding: 87555
Integrated approach for stress based lifing of aero gas turbine blades
Full text linkIn order to analyse the turbine blade life, the damage due to the combined thermal and mechanical loads should be adequately accounted for. This is more challenging when detailed component geometry is limited. Therefore, a compromise between the level of geometric detail and the complexity of the lifing method to be implemented would be necessary. This thesis therefore focuses on how the life assessment of aero engine turbine blades can be done, considering the balance between available design inputs and adequate level of fidelity. Accordingly, the thesis contributes to developing a generic turbine blade lifing method that is based on the engine thermodynamic cycle; as well as integrating critical design/technological factors and operational parameters that influence the aero engine blade life. To this end, thermo-mechanical fatigue was identified as the critical damage phenomenon driving the life of the turbine blade.
The developed approach integrates software tools and numerical models created using the minimum design information typically available at the early design stages. Using finite element analysis of an idealised blade geometry, the approach captures relevant impacts of thermal gradients and thermal stresses that contribute to the Thermo-mechanical Fatigue damage on the gas turbine blade. The blade life is evaluated using the Neu/Sehitoglu Thermo-mechanical Fatigue model that considers damage accumulation due to fatigue, oxidation, and creep. The leading edge is examined as a critical part of the blade to estimate the damage severity for different design factors and operational parameters. The outputs of the research can be used to better understand how the environment and the operating conditions of the aircraft affect the blade life consumption and therefore what is the impact on the maintenance cost and the availability of the propulsion system. This research also finds that the environmental (oxidation) effect drives the blade life and the blade coolant side was the critical location. Furthermore, a parametric and sensitivity study of the Neu/Sehitoglu model parameters suggests that in addition to four previously reported parameters, the sensitivity of the phasing to oxidation damage would be critical to overall blade life
Boundary layer ingestion performance assessments with application to business jets.
Full text linkAdvancements in propulsion system performance are reliant on improvements in propulsive efficiency, through increases in turbofan bypass ratio. This requires larger nacelle diameters, which incur external aerodynamic penalties. Business jets cruise at high subsonic Mach numbers, and are therefore normally propelled by high specific thrust turbofans. The business jet may benefit from a BLI propulsion system, whereby the specific thrust may be reduced without incurring such heavy penalties in external drag rise. The aim of the research is to perform a design exploration study on BLI applied to
a business jet, with emphasis on external aerodynamics. Methods are developed to thoroughly analyse aerodynamic coupling between propulsor and airframe. A multi-physics, control-volume based approach led to the development of near-field momentum-based, far-field momentum-based and energy-based net-vehicle-force formulations. The former two, allowed for a set of thrust-force accounting systems to be defined. Energy-based methods, allowed for flow-field decompositions into different physical mechanisms. These include flow phenomena internal and external to the jet plume. The practical implications associated with applying these methods to RANS CFD solutions, is examined. This hinges around viscous stress tensor field continuity in the flow domain. It was found that the k — w SST turbulence model, along with a Green-Gauss Cell-Based gradient scheme, produced a continuous viscous stress tensor field. Having resolved this, the assessment methods were applied to solutions of non-propelled and propelled bodies. These methods were applied to control volumes having varying extents, which showed the far-field momentum-based method to be sensitive to spurious affects. The energy-based formulation, on the other hand, was observed to be relatively insensitive spurious affects. Good agreement (within 4%) was found between the forces predicted by all three methods over a non-propelled body. A very close agreement was observed between far-field momentum-based and energy-based results (within 1%) over the propelled body. However, much larger discrepancies were observed when compared against the near-field results. This was attributed to the increase in flow-field complexity, which now contained BL, shock and jet interaction regions. A design exploration study was performed by retrofitting a business jet with a fuselage concentric propulsor, powered by the baseline podded engines. A preliminary parametric study was first performed to gauge conditions favourable to BLI benefit. A ram drag approach to modelling BLI benefit was based on a flat plate analogy to obtain boundary layer profiles. Thrust-split, BLR, fan efficiency and intake pressure recoveries, were varied parametrically to asses potential benefits. An optimum SFC benefit between 5-7.5% was achieved at thrustsplits between 30-35%, when ingesting 65-90% of the BL thickness. This guided the the parametric CFD studies, where two tail-cone positions were examined. The first was placed at the top of the tail-cone, and the second positioned midway along the tail-cone. Benefits were only realised for the latter, where a 3-4% improvement in SFC was realised for a thrust-split around 20%, by ingesting 40% of the BL thickness. Energy breakdowns and decompositions were performed on all of the cases. One of the significant outcomes of this research was revealing that a significant proportion of the thrust force may be attributed to the isentropic expansion region within the jet plume's core.PhD in Aerospac
An evaluation of operation and creep life of stationary gas turbine engine
Full text linkDuring operation, gas turbine components undergo various types of timedependent
degradation due to high temperatures and mechanical loading. In
the case of stationary GT engines for mechanical power, creep failure
mechanism problems are a very common cause of mechanical failure that
significantly reduces component life. The magnitude of the adverse effect is
highly dependent on the operating conditions and design parameter of the
components. Against this background, the research programme was aimed at
achieving a better scientific understanding of the major reasons for creep
failure. This would allow mechanical equipment to keep running free creep
problem for longer. Therefore, the aim of this research was to develop an
analytical life model capable of assessing the influence of humidity on the
turbine blade heat transfer and cooling processes considering the engine
design parameters, operating conditions and working environment which, in
turn, affect blade creep life.
The whole cooled blade row is regarded as heat exchanger with convective/film
cooling and a thermal barrier coating. The approach is based on an engine
performance model, heat transfer models and the change of properties of moist
air as a function of water to air ratio (WAR). The changes of fluid properties due
to the presence of water vapour were not only considered through a variation of
the specific heat, the ratio of major specific heats and gas constant, but also
with the variation of density, Reynolds number, Nusselt number and other
related parameters. Cont/d
Aero-propulsive performance assessment approach to boundary layer ingestion aircraft
No full textA promising solution towards more sustainable and efficient aircraft propulsion
relies upon the ingestion of the boundary layer flow that develops around the
airframe. Amongst the plethora of concepts, the propulsive fuselage concept
appears to be the most pragmatic configuration, as a direct adoption of
conventional tube-and-wing aircraft, which has an additional propulsor integrated
around its tail. Nonetheless, there is a lack of consensus in the quantification and
interpretation of the performance of such vehicles. Long-established
momentum-based bookkeeping schemes break down as their underlying
assumptions do not hold true in highly-integrated airframe-propulsion systems.
Alternative approaches have been brought forth by considering holistically the
aircraft to evaluate its performance and decompose its aerodynamic forces.
Notably, energy- and exergy-based approaches improve one’s understanding on the
cause and effect of boundary layer ingestion mechanisms but require high
computational demands with dense grids. In sought of a universal approach,
energy- and momentum-based methods are used together in this work to quantify
the coupled aerodynamic performance of boundary layer ingestion aircraft. The
strengths of near-field momentum integrations are coupled with more informative
energy-based flow assessments. The design space of a propulsive fuselage aircraft is
explored via CFD after a reduction of its modelling to an axi-symmetric partial
assembly of the fuselage and propulsor. With variations in the thruster position
along the tail, its flow passage through the fan and pressure rise, and exhaust
design, best performance is achieved with a concept where the propulsor lies at
90% of the fuselage chord, for a fan hub radius of 30% of the fuselage radius, that
ingests around 43% of the boundary layer mass-flow, and applies a pressure rise of
1.29, to generate around a third of the total propulsive force requirement whilst
savings 11% of fuel relative to a short-to-medium range aircraft propelled by
state-of-the-art turbofans. The reasons for such savings are detailed with a
first-of-its-kind fully energetic flow decomposition which aims at attributing
boundary layer ingestion benefits to changes in propulsor design.PhD in Aerospac
A set-based design space exploration framework for hybrid-electric aicraft design
No full textEngineering design is characterised by uncertainty caused by a lack of experience and
information. The traditional approach focuses on iterating and refining an initial conceptual
design, which often is similar to the final one. Although this method serves well in
the case of evolutionary design, it is unsuitable for innovation. In fact, without a suitable
initial starting point, many rework iterations may be required to correct early inadequate
design decisions. In addition, it may be challenging to map the requirements directly onto
the design space.
This dissertation aims at developing a methodology to address this problem. The
developed framework starts from the hypothesis, and the knowledge to carry out the mapping
of requirements onto the input parameters is embedded in the simulation model, and
hence no additional rules are required. Instead, a probabilistic surrogate model based on
Gaussian processes is used in conjunction with Bayesian statistics to find and eliminate
unfeasible areas of the design space. This selection criterion is used in a set-based design
approach to explore pockets of the entire continuous design space. Finally, sets with a
sufficient likelihood of satisfying the requirements are searched with a local multidisciplinary
optimisation algorithm to recover the individual design points.
This process reduced the computational cost of the design space exploration by 80%
without sacrificing the number of alternative solutions. Thanks to the large amount of
data obtained, it was possible to produce new knowledge on hybrid-electric aircraft design.
Specifically, it was found that linear segments are sufficient for defining energy
management strategies, and the reduction of NOx emissions and fuel consumption are associated
with climb and cruise, respectively. Furthermore, when studying regional aircraft
operating missions, it was found that partial recharge is necessary to maintain the design
performance. However, this could reduce the duration of the battery. The battery ageing
rate correlates with the EMS’s demand for electrical energy. Finally, it was found that
the battery’s energy density is a determinant of the pack’s durability and the feasibility of
HE aircraft. The rate of improvement in emissions and fuel consumption is non-linear,
suggesting that investing in considerable technological improvements has better returns.
Indeed, the required technological level will not be available until the 2040s without an
exponential increment of the cell energy density.PhD in Aerospac
Turbine cooling and heat transfer modelling for gas turbine performance simulation
Full text linkThe successful design of cooling systems for gas turbine engines is a key factor to feasibility of new projects, as the trend for increasing turbine entry temperatures implies requirements for more sophisticated cooling methods. This work focuses on the prediction of cooling performance of turbines, starting from local heat transfer effects at the surface of blades and vanes and expanding to performance simulation of cooled high pressure turbines and engines. In this context, this thesis establishes a new method that investigates the following topics:
• The connection between the gas flow field around a cooled blade or vane and the prediction of cooling requirements of the setup.
• The connection between a detailed gas flow field around a cooled blade or vane and a preliminary estimation of its metal temperature.
• The effect that blade cooling requirements prediction has towards the performance simulation of a cooled turbine and the difference in results between turbine models of different axial resolution.
• A simulation platform that includes the aforementioned topics under a web-based gas turbine performance simulation program.
The first two objectives are tackled by developing a preliminary cooling design framework, which performs the needed convective and conductive heat transfer calculations between the gas and the blade, the blade and the coolant, and within the blade material. The method divides the geometry into a finite number of volumes, where heat transfer calculations are performed for steady-state conditions. One- and two-dimensional results show a good agreement with previous experimental work. The results suggest that chord resolution for blade heat transfer prediction is essential for a more accurate coolant temperature and mass flow rate prediction. In addition, conduction modelling has a dominant effect in heat transfer prediction of blades with steep temperature gradients.
The third objective is achieved by associating the coolant state before mixing with the main stream and the results in turbine performance. The coolant temperature and mass flow rate prediction have a significant impact on turbine work and thermodynamic efficiency, figures highlighted as well for different turbine axial resolution methods. The results suggest that as the coolant heats up through a blade or vane and eventually mixes with the main flow, it contributes significantly towards the predicted turbine work, affecting as well the overall engine performance results, such as specific fuel consumption and specific thrust. A multistage turbine model is most suitable for capturing these effects, but it requires a number of additional inputs.
Finally, the thesis suggests that a simulation framework such as the aforementioned, it can be of high usability and applicability if implemented on the cloud, rather than locally installed
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