Browsing by Author "Singh, Riti"
Now showing 1 - 10 of 10
Results Per Page
Sort Options
Item Open Access Advanced gas-path fault diagnostics for stationary gas turbines(Cranfield University, 2003) Ogaji, S. O. T.; Singh, RitiThe reliabilities of the gas-path components (compressor, burners and turbines) of a gas turbine (GT) are usually high when compared with those of other GT systems such as fuel supply and control. However, in the event of forced outage, downtimes are normally high, giving a relatively low availability. The purpose of condition monitoring and fault diagnostics is to detect, isolate and assess (i.e. estimate quantitatively the magnitude of) the faults within a system, which in this case is the gas turbine. An effective technique would provide a significant improvement in economic performance, reduce operational and maintenance costs, increase availability and improve the level of safety achieved. However, conventional analytical techniques such as gas-path analysis and its variants are limited in their applications to engine diagnostics due to several reasons that include their inability to:- operate effectively in the presence of noisy measurements; distinguish effectively sensor bias from component faults; preserve the nonlinearity in the gas-turbine parameter relationships; and the requirement for more sensors for achieving accurate diagnostics. The novelty of this research stems from its objective of overcoming most of these limitations and much more. In this thesis, we present the approach adopted in developing a diagnostic framework for the detection of faults in the gas-path of a gas turbine. The framework involves a large-scale integration of artificial neural networks (ANNs) designed and trained to detect, isolate and assess the faults in the gas-path components of the engine. Input to the diagnostic framework are engine measurements such as spool speeds, pressures, temperatures and fuel flow while outputs are either levels of changes in sensor(s) for the case of sensor fault(s) or the level of changes in efficiencies and flow capacities for the case of faulty components. The diagnostic framework has the capacity to assess both multiple component and multiple sensor faults over a range of operating points. In the case of component faults, the diagnostic system provides changes in efficiencies and flow capacities from which interpretations can be sought for the nature of the physical problem. The implication of this is that the diagnostic system covers a wide range of problems - both likely and unlikely-. The technique has been applied to several developed test cases, which are not only thermodynamically similar to operational engines, but also covers a range of engine configurations and operating conditions. The results obtained from the developed approach has been compared against those obtained from linear and nonlinear (recursive linear) gas-path analysis, as well as from the use of fuzzy logic. Analysis of the results demonstrates the promise of ANN applied to engine gas-path fault diagnostic activities. Finally, the limitations of this research and direction for future work are presented.Item Open Access Assessment of an energy-efficient aircraft concept from a techno-economic perspective(Elsevier, 2018-04-17) Goldberg, Chana; Nalianda, Devaiah; Sethi, Vishal; Pilidis, Pericles; Singh, Riti; Kyprianidis, KonstantinosAn increase in environmental awareness in both the aviation industry and the wider global setting has led to large bodies of research dedicated to developing more sustainable technology with a lower environmental impact and lower energy usage. The goal of reducing environmental impact has necessitated research into revolutionary new technologies that have the potential to be significantly more energy efficient than their predecessors. However, for innovative technologies in any industry, there is a risk that adoption will be prohibitively expensive for commercial application. It is therefore important to model the economic factors of the new technology or policy at an early stage of development. This research demonstrates the application of a Techno-economic Environmental Risk Assessment framework that may be used to identify the economic impact of an energy-efficient aircraft concept and the impact that environmental policy would have on the viability of the concept. The framework has been applied to a case study aircraft designed to achieve an energy saving of 60% in comparison to a baseline 2005 entry-into-service aircraft. The model compares the green aircraft concept to a baseline conventional aircraft using a sensitivity analysis of the aircraft direct operating cost to changes in acquisition and maintenance cost. The research illustrates an economically viable region for the technology. Cost margins are identified where the increase in operating cost due to expensive novel technology is counterbalanced by the reduction in cost resulting from low energy consumption. Viability was found to be closely linked to fuel price, with a low fuel price limiting the viability of energy-efficient aviation technology. In contrast, a change in environmental taxation policy was found to be beneficial, with the introduction of carbon taxation incentivising the use of an environmentally optimised aircraft.Item Open Access Distributed propulsion and future aerospace technologies(Cranfield University, 2007) Ameyugo, Gregorio; Singh, Riti; Bowman, Cliff; Taylor, MarkThis thesis describes an Engineering Doctorate project in Distributed Propulsion carried out from 2004 to 2007 at Cranfield University. Distributed propulsion is a propulsion system arrangement that consists in spreading the engine thrust along the aircraft span. This can be accomplished by distributing a series of driven fans or the engines themselves. The aim of this project is to determine the feasibility of distributed propulsion for civil aviation in the medium term (with small gas turbines) and long term (with driven fans) from a technical and economic perspective. The effect of distributed propulsion was assessed by creating a long-range subsonic airliner baseline with conventional technology for the small gas turbines study, and an equivalent blended wing body baseline for the driven fans study. Different distributed propulsion effects were modelled and integrated together to produce optimised baselines with different technological parameters. The feasibility of small gas turbine distributed propulsion was found to be limited by the excessive fuel consumption associated with small gas turbines. Although advanced heat exchanger technology could improve their performance, the resulting cost advantage might not be large enough to justify the development costs. The feasibility of distributed driven fans depends on the availability of superconductive elements, as electrical power transmission seems to be the only promising transmission method in the long run. If superconductive elements are applied, distributed driven fans could afford fuel burn reductions of more than 50% relative to current technology. As both distributed propulsion concepts rely on small propulsive units, their enabling technologies coincide with those required to develop future unmanned aerial vehicles. UAVs therefore represent the most appropriate technological avenue to develop technologies with the potential to become distributed propulsion enablers. Future work should therefore concentrate on improving engine performance and cost for unmanned aerial vehicles.Item Open Access Economic viability assessment of NASA's blended wing body N3-X aircraft(AIAA, 2017-07-12) Goldberg, Chana; Nalianda, Devaiah; Pilidis, Pericles; Singh, RitiNumerous novel aircraft concepts are under development that aim to achieve dramatic increases in efficiency and reductions in emissions in comparison to current aircraft. Research into these concepts typically focuses on performance aspects to establish whether the aircraft will be capable of meeting developmental goals. However, the final goal of such concepts is to progress to viable commercial products. Economic viability assessments are therefore an integral part of the development process to ensure a sustainable industry. The key question to address is whether a high efficiency aircraft concept can translate into an attractive product from an economic perspective. This research performed an economic viability assessment of NASA's N3-X aircraft, a blended wing body aircraft with a distributed boundary layer ingesting propulsion system. The sensitivity of the aircraft's direct operating cost to changes in acquisition price and maintenance cost was predicted to establish maximum cost margins for the aircraft. In a May 2017 fuel price scenario, the N3-X could be no more than 25% more expensive than the baseline aircraft to remain economically viable. Introducing a carbon tax or fuel price jump widens the margin for increased costs. Aircraft cost estimates for the aircraft predict an acquisition cost from 11{37% more expensive than the baseline. In combination with the direct operating cost sensitivity analysis, the N3-X is predicted to need to capture 30% of the aircraft market up to 2035.Item Open Access Methodology for the assessment of distributed propulsion configurations with boundary layer ingestion using the discretized miller approach(Praise Worthy Prize, 2017-06-30) Valencia, Esteban; Liu, Chengyuan; Nalianda, Devaiah; Panagiotis, Laskaridis; Gray, Iain; Singh, RitiThe growing global environmental awareness has motivated the search for more fuel-efficient aircraft propulsion systems. In this context, a configuration based on distributed propulsion with Boundary Layer Ingestion (BLI) has been found to present potential performance benefits. The concept has been documented and explored extensively during the last few years and various aerodynamic integration issues, such as: high levels of distortion and low intake pressure recovery; have been identified as factors that may be detrimental in realizing the technology full potential. Parametric and parallel compressor (PC) approaches have been used to assess the effect of these aerodynamic issues on propulsors fan performance. However, in the context of BLI, these tools are unable to assess the effects of combined radial and circumferential distortion that are present. In order to assess the combined distortion patterns and the effects of distortion at component and system levels, this study uses a novel method based on semi-empirical correlations denominated the Discretized Miller (DM) approach. This method was developed for BLI systems previously by the author, and it is now incorporated into the propulsor performance method to assess the effects of the combined radial and circumferential distortion patterns. The performance analysis, undertaken at a component and system level, aims to assess several propulsion architectures, using Thrust Specific Fuel Consumption (TSFC) as figure of merit. To define the suitability of the distributed propulsor array in this study, an airframe layout based on the N3-X aircraft concept and High Temperature Superconducting (HTS) electric motor capabilities were assumed. The key contribution of this study is to enable the introduction of the concept of thrust split between energy source and propulsion system in the system analysis, and thereby, allows the assessment of its effects on different propulsion system layouts, while considering the BLI induced distortion. The results obtained with this alternative performance method showed that BLI reduces the fan efficiency of a conventional fan by approximately 2%, whilst corroborating the TSFC trends observed in previous studies. The study also indicates that when sizing effects of propulsors and core-engines were neglected, a propulsion system configuration with 75% thrust split was found optimum.Item Open Access Multi-disciplinary investigation of a flap blown turboelectric distributed propulsion blended wing body aircraft.(2017-04) Tan, Jun Wei; Singh, Riti; Laskaridis, PanagiotisGrowing concerns about the rising costs of fuel as well as environmental issues have led to multiple innovative and futuristic aircraft concepts to tackle these issues. Turboelectric Distributed Propulsion (TeDP) and boundary layer ingestion are two such concepts. When applied to a conceptual aircraft such as the N3-X, it results in a blended wing body (BWB) aircraft with an array of fan propulsors mounted near the rear of the aircraft body and driven by superconducting motors powered by superconducting generators in the wing tip mounted turbogenerators. The elevator flaps of such a BWB aircraft are located at the trailing edge of the aircraft body. Coupled with the exhaust mass flow from the propulsor fan nozzles, it presents a chance to utilize flap blowing and/or thrust vectoring to further improve on the aircraft performance. By utilizing boundary layer ingestion, there can be expected 5-6% total fuel savings while flap blowing can further enhance the fuel savings to a total of 8-9%. However, integration issues such as intake pressure losses, deficiency in fan propulsor efficiency tends to mitigate the benefits derived. Furthermore, it is difficult to separate various design disciplines such as aerodynamics and propulsion in such a high integrated aircraft. Flap blowing further correlates to both disciplines. This dissertation addresses a broad overall design methodology that is both multi-disciplinary and multi-fidelity, addressing the above mentioned issues. Flap blowing can be seen to be a linkage between the often separate aerodynamics and propulsion design disciplines in an aircraft. The strip method code, designed to incorporate flap blowing into the preliminary design and analysis is presented in this study, showing its impact on aerodynamic performance, flight dynamic response and propulsion system design. Furthermore, other disciplines such as boundary layer ingestion, weight, and flight dynamics are considered and incorporated into the methodology. The main figure of merit used is the total fuel consumption of the aircraft and in addition, take-off distances are also studied and analysed. Take-off distances incorporating flap blowing and thrust vectoring demonstrated a reduction in distances between 25-30%. The reduction in take-off distance also led to the study on the potential of re-sizing the BWB outer wings to further reduce total fuel consumption and has shown great promise.Item Open Access Performance assessment of a boundary layer ingesting distributed propulsion system at off-design(AIAA, 2017-06-12) Goldberg, Chana; Nalianda, Devaiah; Pilidis, Pericles; Singh, Riti; Laskaridis, PanagiotisAs research on boundary layer ingesting aircraft concepts progresses, it becomes important to develop methods that may be used to model such propulsion systems not only at design point, but also over the full ight envelope. This research presents a methodology and framework for simulating the performance of boundary layer ingesting propulsion systems at o -design conditions. The method is intended for use as a preliminary design tool that may be used to explore the design space and identify design challenges or potential optimum con gurations. The method presented in this research enables the rapid analysis of novel BLI con gurations at a preliminary design stage. The method was applied to a case study of NASA's N3-X aircraft, a blended wing body concept with a distributed propulsor array ingesting the airframe boundary layer. The performance of two propulsor in the array was compare, one at the airframe centreline and one at the extreme edge of the array. Due to di erence in ow conditions, the centreline propulsor was shown to be more e cient at o -design than the end propulsor. However, this di erence in e ciency disappeared at sea level static where the boundary layer thickness is negligible and mass ow ratio is high. Di erence in thrust produce by the two propulsors was instead due their di erent sizes. Performance of the propulsor array as a whole was also presented both independently and including a link to a pair of turbogenerators to provide power. At o design, it was found that there was a discrepancy between the maximum power available from the turbogenerators at o -design operating points and that demanded by the propulsor array operating at 100% fan rotational speed. This discrepancy means that the propulsor array's performance is limited by the turbogenerators at o -design, particularly for low speed, low altitude operation.Item Open Access A physics-based maintenance cost methodology for commercial aircraft engines(Cranfield University, 2014-08) Stitt, Alice C.; Laskaridis, Panagiotis; Singh, RitiA need has been established in industry and academic publications to link an engine’s maintenance costs throughout its operational life to its design as well as its operations and operating conditions. The established correlations between engine operation, design and maintenance costs highlight the value of establishing a satisfactory measure of the relative damage due to different operating conditions (operational severity). The methodology developed in this research enables the exploration of the causal, physics-based relationships underlying the statistical correlations in the public domain and identifies areas for further investigation. This thesis describes a physics-based approach to exploring the interactions, for commercial aircraft, of engine design, operation and through life maintenance costs. Applying the “virtual-workshop” workscoping concept to model engine maintenance throughout the operating life captures the maintenance requirements at each shop visit and the impact of a given shop visit on the timing and requirements for subsequent visits. Comparisons can thus be made between the cost implications of alternative operating regimes, flight profiles and maintenance strategies, taking into account engine design, age, operation and severity. The workscoping model developed operates within a physics-based methodology developed collaboratively within the research group which encompasses engine performance, lifing and operational severity modelling. The tool-set of coupled models used in this research additionally includes the workscoping maintenance cost model developed and implements a simplified 3D turbine blade geometry, new lifing models and an additional lifing mechanism (Thermo-mechanical fatigue (TMF)). Case studies presented model the effects of different outside air temperatures, reduced thrust operations (derate), flight durations and maintenance decisions. The use of operational severity and exhaust gas temperature margin deterioration as physics based cost drivers, while commonly accepted, limit the comparability of the results to other engine-aircraft pairs as the definition of operational severity, its derivation and application vary widely. The use of a single operation severity per mission based on high pressure turbine blade life does not permit the maintenance to vary with the prevalent lifing mechanism type (cyclic / steady state).Item Open Access Theoretical optimal trajectories for reducing the environmental impact of commercial aircraft operations(Institute of Aeronautics and Space, 2014-03-01) Celis, Cesar; Sethi, Vishal; Zammit-Mangion, David; Singh, Riti; Pilidis, PericlesThis 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.Item Open Access Water injection on aircraft engines: a performance, emissions and economic study(ISABE, 2015-10-22) Mourouzidis, Christos; Igie, Uyioghosa; Pilidis, Pericles; Singh, RitiAlthough aviation based emissions are not the major sources of atmospheric pollution, their impact around the airport vicinity and the increase in air transport makes it a concern. Water injection on aircraft engines can reduce NOx emissions around the airports significantly. This has been demonstrated in research study by NASA Glenn Research Center in collaboration with Boeing Company. The aim of this study is to investigate the performance, emissions and economic aspects of water ingestion for medium and high bypass ratio jet engines using Cranfield University in-house gas turbine simulation software. British Airways was chosen as a representative airline to be used as case study in order to examine the effects of this technology. Performance and emissions models were developed for the most popular aircraft of the fleet, along with their engines. The simulations were focused on the take-off phase of the aircraft, injecting water in the low pressure compressor (LPC) and the combustor, for different water-toair ratios. The results were optimized in terms of fuel burn and verified against the respective results from the NASA study [1]. Finally, an economic model was developed in order to evaluate the monetary impact of these systems, from the point of view of an airliner with a specific number of aircraft in their fleet. The main outcomes of this study show that LPC water injection can provide more than 10% take-off thrust augmentation in a standard day when in hot days it can exceed 25%. Alternatively, the specific fuel consumption at take-off can reach a 10% reduction, for a fixed take-off thrust level. On the other hand, combustor water injection penalizes the engine performance in all cases. Additionally, depending on the point of injection and the water to air ratio, NOx emissions reduction ranges between 25%-85%. Finally, for the case study examined here, the value for the annual monetary benefit due to water injection can reach 599,654£, without taking into account the airport emission based fees. An investment of such sort could present a dynamic payback period of 7.5 years, assuming constant market interest of 8% and 10 years operational life of the equipment.