The Gas Turbine Cycle

Thrust vectoring is a requirement for fifth generation fighters, giving them super-maneuverability capabilities, allowing them to execute tactical maneuvers that are not possible using conventional aerodynamic mechanisms. The most widely used and successful method for achieving this is by using gimbaled engines or nozzles. The complexities involved in this method, have encouraged future engine designers to explore different avenues for achieving thrust vectoring, one of which is fluidic thrust vectoring. In fluidic thrust vectoring, jet deflection is achieved by fluid injection at various locations on the nozzle. During thrust vectoring operations, the engine performance is affected. This is primarily due to the change in effective nozzle area. When a nozzle is gimbaled, as is the method used in currently operational thrust vectored engines, or during fluidic thrust vectoring operations, there is a change in effective nozzle area. This impacts the engine mass flow rate, thus affecting the engine operation. The change in performance is similar to that of an engine fitted with a variable area nozzle. In this study, we attempted to retrofit a thrust vectoring nozzle to an existing engine designed for a fourth-generation fighter aircraft, in order to give it fifth-generation fighter aircraft capabilities. A Twin spool mixed flow turbofan engine with a convergent nozzle is selected and its performance is simulated using Gasturb 13. The baseline engine consists of a low pressure spool, high pressure spool, combustion chamber and convergent-divergent nozzle. For the sake of simplicity, the convergent-divergent nozzle is replaced with a convergent nozzle, with no loss in thrust at design point. The design point is arrived at based on engine data available in open literature. Following this, offdesign performance is simulated, for studying the effect of thrust vectoring operations, which are modeled as a nozzle area change. Suitably scaled generic maps provided in Gasturb are used for off-design simulations. The effect of nozzle area change on engine performance is studied at sea level static conditions. The nozzle area is decreased by a maximum of 15%, in steps of 1%. During thrust vectoring operations, there is a significant change in bypass ratio and fan surge margin, with the other performance parameters being relatively constant. Following this, simulations are conducted at different flight conditions to understand the effect of nozzle area change for different flight regimes. A total of seven different flight conditions are selected to understand the operational envelope of thrust vectoring operation. It is found that at all flight conditions, thrust vectoring has a significant influence on bypass ratio and fan surge margin. While for most conditions, there is an improvement in fan surge margin, there are two conditions where fan surge margin decreases substantially.

Automatic design optimization is highly sensitive to problem formulation. The choice of objective function, constraints and design parameters can dramatically impact on the computational cost of optimization and the quality of the resulting design. The best formulation varies from one application to another. A design engineer will usually not know the best formulation in advance. To address this problem, we have developed a system that supports interactive formulation, testing and reformulation of design optimization strategies. Our system includes an executable, data-flow language for representing optimization strategies. The language allows an engineer to define multiple stages of optimization, each using different approximations of the objective and constraints or different abstractions of the design space. We have also developed a set of transformations that reformulate strategies represented in our language. The transformations can approximate objective and constraint functions, abstract or reparameterize search spaces, or divide an optimization process into multiple stages. The system is applicable in principle to any design problem that can be expressed in terms of constrained optimization; however, we expect the system to be most useful when the design artifact is governed by algebraic and ordinary differential equations. We have tested the system on problems of racing yacht design and jet engine nozzle design. We report experimental results demonstrating that our reformulation techniques can significantly improve the performance of automatic design optimization. Our research demonstrates the viability of a reformulation methodology that combines symbolic program transformation with numerical experimentation. It is an important first step in a research program aimed at automating the entire strategy formulation process.

The centrifugal impellers are used in a wide variety of turbo-machineries, ranging from low pressure fans for cooling of electric motor to high pressure ratio gas turbine compressors, from tiny cryo-cooler compressors to large industrial petrochemical compressor stations. The relative flow in centrifugal impeller is very complex due to different fluid dynamics phenomenon and their interactions. It is subjected to the complex secondary flows and significant separation of the boundary layers, which result in non-uniformity of outlet flow both in tangential direction (e.g. “ jet-wake” flow) and axial direction. By the development of experimental and computational techniques the considerable progress in understanding of complex flow effects in impeller is made. The wide-spread use of reactive impellers with backswept blades in all state-of-the-art designs of compressors has resulted in significant improvements of aero and thermodynamics characteristics of impeller (e.g. distribution of outlet flow velocities). The increasingly present appearance in the several recent years of calculations by means of verified and validated users software based on the engineering numerical methods enables an increasingly wide replacement of time-consuming experimental investigations (i.e. of physical modelling), which give a limited number of data of integral character, by mathematical modelling which gives a large number of data over a short time, enabling not only integral but also structural analysis. This results in rapid and significant improvements of aero and thermodynamics characteristics and in the end in energy conversion efficiency. The aim of the paper is to apply expert knowledge in carrying out numerical modelling of the flow in centrifugal compressor by means of users software. The algorithm is presented on the comparison of aero and thermodynamics characteristics of centrifugal compressors with reactive impellers with backswept normal and “ S” shape blades. The comparison shows that the compressor with impeller with “ S” shape blades has better aero and thermodynamics characteristics and thus also the energy conversion efficiency. Since there are experimental measurements of aero and thermodynamics characteristics of the numerically investigated compressors in literature, the verification and validation of the users software have been performed simultaneously. Also the alternating modelling of the flow and change of impeller blades geometry with the aim of improving the aero and thermodynamics characteristics up to attaining of maximum possible efficiency of energy conversion presents the algorithm of geometry optimisation of the impeller design with backswept blades.

Jet engines are critical assets in aircraft, and their availability is crucial in the modern aircraft industry. Therefore, their maintenance scheduling is one of the major tasks an airline has to make during an engine’s lifetime. A proper engine maintenance schedule can significantly reduce maintenance costs without compromising the aircraft's reliability and safety. Different maintenance scheduling approaches have been used for jet engines, such as corrective, preventive, and predictive maintenance strategies. Regarding the safety demands in aircraft industries, preventive maintenance is a frequent maintenance method for jet engines. However, preventive maintenance schedules are often use fixed maintenance intervals, which is usually suboptimal. This paper focuses on minimizing a jet engine's overall maintenance cost by optimizing its preventive maintenance schedule based on an engine’s comprehensive reliability model. A hierarchical optimization framework including the golden section search and genetic algorithms is applied to find the optimal set of preventive maintenance number and their times and the components to be replaced at those times during the jet engine's overall lifetime. The Monte Carlo simulation is used to estimate the engine’s failure times using their lifetime distributions from the reliability model. The estimated failure times are then used to determine the engine's overall corrective and preventive maintenance costs during its lifetime. Finally, an optimal preventive maintenance schedule is proposed for an RB 211 jet engine using the presented method. In the end, comparing the proposed method's overall maintenance cost with two other maintenance methods demonstrates the proposed schedule's effectiveness. The method presented in this paper is generic, and it can be used for other similar engineering systems.

Virtual prototyping is introduced and the future development trends of Virtual Prototyping for Flight Control System are summarized. For analyzing redundancy Flight Control Computer Systems (FCCS) of Boeing, Airbus series and BUAA civil aircraft scheme, a VP testing platform for FCCS of civil aircraft is proposed. This platform is based on COTS products, modular components and user interactive interface. It can produce virtual prototypes of dissimilar redundancy FCCSs of Boeing 777, Airbus A340 and BUAA civil aircraft scheme. This platform is open and expandable, supporting concurrent multidisciplinary design.

In an effort to support the Air Force's new F-22 Fighter aircraft with its dual F119-PW-100 jet engines, a new approach has been taken to realize the benefits of automated jet engine testing. This paper describes an automated test approach that is currently under development and will be used by the Air Force to test the F119 jet engine; It also identifies; the equipment, methods and techniques that are being employed to accomplish this task.

Off-design performance of micro-scale solar Brayton cycle

Japanese research activities on jet engines began in the 1940s and progressed as far as the test flight of the Ne-20 jet engine. All work was discontinued, however, at the end of World War II. After seven years, production of jet engines was permitted to resume, as the major defense equipment mainly under licenses with European and American manufacturers. Efforts were subsequently continued to develop more advanced technologies, which were then applied to design and manufacture the civil and military engines. Full-scale development of superalloys and other engine materials began in Japan as a part of multiple national programs aimed at developing new gas turbines. A number of original materials and process technologies have been studied. This paper addresses the current and future material technologies in Japan. Business Overview It is generally predicted that the number of airline passengers throughout the world will grow at a rate of about 5% per year until 2020. Demand is expected to grow rapidly especially in the Asia-Pacific region. The aero-engine industry in Japan has grown considerably in the last half century. Total production in fiscal 2001 was worth approximately $23 million, about twice the amount sold in fiscal 1985. Japanese production accounts for several percent of the total world market; it is equivalent to about one-ninth of the American production, and equal to the production of Germany or Canada. Despite the lingering affects of the war in Iraq and SARS, the long-term prospects for the aero-engine industry are strong, making it an exception to the general malaise that currently afflicts so many other Japanese industries. The nature of the business has changed drastically in recent years, as well. Although the field of defense retains its historical importance, it accounts for a decreasing share of total aero-engine sales, declining from 75% in the 1980s to about 60% today. In the past several years, it has been predicted that civil engines will eventually outsell those for military use. The other major change has been the expansion of related maintenance and service sectors, and the increased provision of component production services to the major manufacturers in the US and Europe. Generally speaking, maintenance and service industries are increasingly being localized, and production is becoming more specialized throughout the world. In the future, Japanese manufacturers expect to develop their own next-generation engines, one for patrol planes for defense, and one for small regional planes (50-seat class) for the civil market.

This chapter reflects on the previous chapters to present a civil aircraft perspective to clearance. It briefly describes the common areas and differences between the clearance of flight control laws (FCLs) of civil transport aircraft and fighter aircraft. It evaluates and discusses the applicability of the presented FCL clearance techniques for civil aircraft and gives some recommendations for future research.

A recent strategy carried out by the aircraft industry to reduce the total cost of the new generation fighters has consisted in the development of a single airframe with different technical and operational specifications. This strategy has been designed to reduce costs in the Research, Design and Development phase with the ultimate objective of reducing the final unit price per aircraft. This is the case of the F-35 Lightning II, where three versions, with significant differences among them, are produced simultaneously based on a single airframe. Whereas this strategy seems to be useful to cut down pre-production sunk costs, their effects on production costs remain to be studied. This paper shows that this strategy can imply larger costs in the production phase by reducing learning acquisition and hence, the total effect on the final unit price of the aircraft is indeterminate. Learning curves are estimated based on the flyaway cost for the latest three fighter aircraft models: The A/F-18E/F Super Hornet, the F-22A Raptor, and the F-35A Lightning II. We find that learning rates for the F-35A are significantly lower (an estimated learning rate of around 9%) than for the other two models (around 14%).

The passenger air transport industry is highly dependent on the external environment and a number of other factors. In turn, passenger air transport, their level and development affect the civil (commercial) aircraft industry, which is the subject of this work. Such an unexpected external factor as the pandemic was no exception. COVID-19 has had an impact on the entire world economy, as evidenced by many processes and their statistical indicators. The recovery of both the global economy and the civil aircraft industry after the opening of borders and the resumption of transportation will take a long time and will change the current trends in the industry. Each entity involved in the industry will have to restructure its activities. The purpose of this paper is to identify the main future trends in the development of the industry based on a comparative analysis of the industry state before the pandemic and today. The authors will also present their forecast for the development of the global civil aircraft industry in the medium term. As a result of the research, the authors came to the following conclusions. Before the pandemic, the market was characterized by a duopolistic structure (Boeing and Airbus); the development of the industry depends directly on the trends of the world economy; market demand is mainly formed in the Asia-Pacific region; the growth of demand for narrow-body aircraft models is strengthening; the role of first-tier suppliers in the production of aircraft is expanding. According to authors’ opinion, the pandemic will bring some new features to market trends: there will be a reduction in demand for new aircraft and, consequently, a reduction in production volumes; the tendency to switch to less spacious aircraft will become more clear; there will be a faster industry recovery of the in the countries with developed domestic traffic, and there will be an increase in demand for regional aircraft.KeywordsCivil aircraft industryCOVID-19AirbusBoeingEmbraerBombardierSukhoiSuperjetJEL CodeL93

RECENT discussions in Parliament have brought into the open a number of problems in the aircraft industry about which many people have been worried for some time. There is concern, among other things, about the organization of the industry, the degree of real control which the Government, through the Ministry of Supply, has over it; the ways of formulating specifications for new civil aircraft, and the distribution of resources within the industry.

The strip producibility, good fabricability, and excellent mechanical properties of β alloys make them useful for a variety of fabricated sheet metal structures on aircraft. TIMETAL 15-3 is currently used for environmental control system ducting on the Boeing 777 and, more recently, has been used on the Airbus A380. For applications that require exposure to higher temperatures, such as the exhaust assemblies, TIMETAL 21S is now used on the Boeing 777, Airbus A340, and various other civil and military aircraft.

An evaluation of additive manufacturing technologies in future aero engine design is carried out using the compressor of an engine. Parts in a compressor are identified which have the potential of increasing the performance of the engine if redesigned with the design freedom of additive manufacturing. Typical problems in compressor design as the necessity of weight reduction or integrating new function into existing components to further increase the performance of the engine are addressed. Concepts of redesigned parts in the compressor are developed and further investigated on their potential to further improve the current engine design. The studies are carried out using commercial FEM-tools. In the first concept which is briefly covered in this paper a hollow compressor blade is investigated. A cavity is inserted into a rotor blade with the purpose of decreasing the weight of the blade and to manipulate the Eigen modes of the blade. The geometry and the position of the cavity is varied in order to find a solution for both weight saving and Eigen mode alteration. Further structures in the blade are used to influence the Eigen modes of the blade specifically in a certain range. In the second concept auxetic structures are inserted into a double-walled compressor casing. The focus of this concept is on the tip clearance behavior of the casing. Since the rotor disc design is determined by strength requirements the tip clearance has to be set by the casing. The geometrical parameters of the auxetic structure is investigated with the purpose of developing a passive tip clearance control system. Elements which influence the radial expansion of the casing are identified with the aim of generating a modular system for future compressor casing developments. So the casing elements are adaptable to the radial expansion of a certain rotor. An improved tip clearance behaviour in relevant operating points is achieved. In the last concept a casing with casing treatments is redesigned with the focus of improving the mechanical behaviour of the casing mainly the thermal behaviour and the vibrational behaviour of the casing treatment itself. This paper presents concepts for future aero engine design using the freedom in design offered by additive manufacturing technologies. The focus of this paper is on the evaluation of the potential of additive manufacturing technologies on future aero engine design. The advantages for the overall engine performance as well as identified challenges are also discussed using the mentioned design examples.

<div class="section abstract"><div class="htmlview paragraph">This paper builds upon recent publication (SAE Technical Paper 2011-01-1388, 2011, doi:10.4271/2011-01-1388) and outlines the on-going development of an advanced simulator for virtual engine mapping and optimization of engine performance, combustion and emissions characteristics.</div><div class="htmlview paragraph">The model is further advanced through development of new sub-models for turbulent mixing, multiple injection events, variable injection pressures, engine breathing and gas exchange, as well as particulates formation and oxidation. The result is a simulator which offers engine design and performance data typically associated with 1D thermodynamic engine cycle simulations but with the "physics-based" model robustness usually associated with 3D CFD methods. This combination then enables efficient optimization of engine design with respect to engine performance, combustion characteristics and exhaust gas emissions.</div><div class="htmlview paragraph">As a demonstration, a detailed method to parameterize (calibrate) the advanced PDF-based model is presented followed by application to three case studies: 1) a concept study of a heavy-duty diesel engine, examining the impact of increased injection pressure and lower compression ratio to meet engine design constraints and Stage IV/Tier 4 exhaust gas emission limits for both NO<sub>x</sub> and PM, 2) examining the performance of both the proposed model and 3D-CFD to simulate heat release and exhaust gas emissions in a HSDI diesel engine, 3) performance of the model over a full load-speed map in terms of combustion and NO<sub>x</sub> emissions. The results demonstrate the robustness of the model compared to experimental observations and equivalent performance compared to more human resource and CPU cost-intensive 3D-CFD simulations.</div></div>