Aircraft Propulsion Systems Research Articles

2020 vision: the prospects for large civil aircraft propulsion

AbstractThis paper will examine the prospects for propulsion systems for large civil transport aircraft over the next two decades, to the year 2020. This period is likely to see the market drivers for future propulsion system development change from the more traditional ones of fuel consumption and weight, to also include those that affect the impact of civil aviation on the environment, and the continuing pressure to reduce the cost of ownership of civil engines, namely, product unit cost, maintenance costs and reliability. Fifty years of civil aero-engine development are reviewed and trends showing the likely limits to the main engine performance parameters are provided. The paper concludes with consideration of a number of new civil aircraft and engine concepts that may emerge in the next 20 years

Steady Performance Measurements of a Turbofan Engine With Inlet Distortions Containing Co- and Counterrotating Swirl From an Intake Diffuser for Hypersonic Flight

The influence of distorted inlet flow on the steady and unsteady performance of a turbofan engine, which is a component of an air-breathing combined propulsion system for a hypersonic transport aircraft, is reported in this paper. The performance and stability of this propulsion system depend on the behavior of the turbofan engine. The complex shape of the intake duct causes inhomogeneous flow at the engine inlet plane, where total pressure and swirl distortions are present. The S-bend intakes are installed axisymmetrically left and right into the hypersonic aircraft, generating axisymmetric mirror-inverted flow patterns. Since all turbo engines of the propulsion system have the same direction of rotation, one distortion corresponds to a corotating swirl at the low pressure compressor (LPC) inlet while the mirror-inverted image counterpart represents a counterrotating swirl. Therefore the influence of the distortions on the performance and stability of the ‘CO’ and ‘COUNTER’ rotating turbo engine are different. The distortions were generated separately by an appropriate simulator at the inlet plane of a LARZAC 04 engine. The results of low-frequency measurements at different engine planes yield the relative variations of thrust and specific fuel consumption and hence the steady engine performance. High-frequency measurements were used to investigate the different influence of CO and COUNTER inlet distortions on the development of LPC instabilities.

An ecological exergy analysis for an irreversible Brayton engine with an external heat source

Brayton cycles have been used extensively in gas turbine power plants and aircraft propulsion systems. In this paper, an exergy analysis, based on an ecological optimization criterion, has been carried out for an irreversible Brayton engine with an external heat source. A cycle pressure ration is solved to yield optimum work done and reduced entropy production. Even though the work output and thermal efficiency are reduced by a certain amount, the ecological exergy analysis results in a better performance than that obtained with the maximum power (or work) output conditions.

Forward Flight Effects on Counterflow Thrust Vector Control of a Supersonic Jet

Introduction T HE beneŽ ts of active thrust vector control in high-performance Ž ghter aircraft, such as improved agility and maneuverability, are well established. Unfortunately, conventional thrust vectoring schemes, which rely on mechanical means to vector the jet thrust, have some associated drawbacks. They generally require complicated hardware, which can add to the aircraft weight; the dynamic performance of such systems is less than ideal; and there are heat transfer problems due to the hot exhaust jet impinging on the vectoring surface. Although recent advances have been made in improving mechanical systems, some of the mentioned issues remain a concern. In recent years, a  uidic-based thrust vectoring technique, counter ow thrust vector control (CFTVC), has been exploredwith promising results.2i4 These investigationshave convincingly demonstrated that CFTVC can be used to achieve single-axis pitch vectoring and multiaxis thrust vectoring for supersonic nozzles of various geometries and over a wide range of operating conditions. One of the primary advantages of CFTVC is the simplicity of hardware and excellent dynamic response. A comprehensive summary of these studies can be found in Refs. 2 and 4. The ultimate goal of our researchprogramis to developa CFTVC system that can be implemented in aircraft propulsion systems of the future. To this end one needs to consider real  ight effects, such as high jet exhaust temperatures and the in uence of forward  ight. Although high-temperatureeffects have been addressed to a limited extent in a previous investigation, almost nothing is known about forward  ight effects on CFTVC performance. In the present study, forward  ight effectsare simulatedby generatinga co owing stream around the periphery of the CFTVC system consisting of a rectangular Mach 1.4 jet. The in uence of the co owing stream on the system performance in terms of jet vector angle response is described in this Note.

Preliminary Design of Low Cost Propulsion Systems Using Next Generation Cost Modeling Techniques

At GE Aircraft Engines (GEAE), during the preliminary design process for aircraft propulsion systems, the designer has always been concerned about the cost implications of engine architecture and material requirements, which are driven by design specified engine thermodynamic operating conditions. The concern was not only about initial acquisition economics, but about maintenance costs associated with the propulsion life cycle as well as the development costs associated with design and certification of the power plant. The difficulty has been that there was no rapid, accurate cost estimating process to allow the designers ready access to the cost implications of design choices. Examination of cost models, both inside and outside the company, failed to locate a generic model which satisfied GEAE business needs. The technical challenge had been established and GEAE launched an initiative in the early 1990s to produce such a code. This paper presents trade studies considering engine cycle trades with cost as a key discriminator.

Cascade Optimization Strategy for Aircraft and Air-Breathing Propulsion System Concepts

Design optimization for subsonic and supersonic aircraft and for air-breathing propulsion engine concepts has been accomplished by soft-coupling the Flight Optimization System (FLOPS) and the NASA Engine Performance Program analyzer (NEPP), to the NASA Lewis multidisciplinary optimization tool COMETBOARDS. Aircraft and engine design problems, with their associated constraints and design variables, were cast as nonlinear optimization problems with aircraft weight and engine thrust as the respective merit functions. Because of the diversity of constraint types and the overall distortion of the design space, the most reliable single optimization algorithm available in COMETBOARDS could not produce a satisfactory feasible optimum solution. Some of COMETBOARDS' unique features, which include a cascade strategy, variable and constraint formulations, and scaling devised especially for difficult multidisciplinary applications, successfully optimized the performance of both aircraft and engines. The cascade method has two principal steps: In the first, the solution initiates from a user-specified design and optimizer, in the second, the optimum design obtained in the first step with some random perturbation is used to begin the next specified optimizer. The second step is repeated for a specified sequence of optimizers or until a successful solution of the problem is achieved. A successful solution should satisfy the specified convergence criteria and have several active constraints but no violated constraints. The cascade strategy available in the combined COMETBOARDS, FLOPS, and NEPP design tool converges to the same global optimum solution even when it starts from different design points. This reliable and robust design tool eliminates manual intervention in the design of aircraft and of air-breathing propulsion engines where it eases the cycle analysis procedures. The combined code is also much easier to use, which is an added benefit. This paper describes COMETBOARDS and its cascade strategy and illustrates the capability of the combined design tool through the optimization of a subsonic aircraft and a high-bypass-turbofan wave-rotor-topped engine.

High-Temperature Applications of Intermetallic Compounds

One of the greatest challenges currently facing the materials community is the need to develop a new generation of materials to replace Ni-based superalloys in the hot sections of gas-turbine engines for aircraft-propulsion systems. The present alloys, which have a Ni-based solid-solution matrix surrounding Ni3Al-based precipitates, are currently used at temperatures exceeding 1100°C, which is over 80% of the absolute melting temperature. Since Ni3Al melts at 1395°C and Ni at 1453°C, it is clear that significantly higher operating temperatures, with the attendant improvements in efficiency and thrust-to-weight ratio, can only be attained by the development of an entirely new materials system. This problem is a primary reason for the current high level of interest in high-temperature intermetallic compounds.The development of such a material system has important implications for national defense and for spin-offs to civilian technology, as well as for the economy and balance of payments. Obviously it would be a boon to any economy to have these new materials developed domestically, as was the case in the United States for the currently used single-crystal technology applied to Ni-based superalloys. As an example, the aerospace industry is one area where the United States is still the undisputed world leader, with net exports of $29 billion in 1989, twice that of any other U.S. industry.

Prediction method for broadband shock-associated noise from supersonic rectangular jets

Braodband shock associated noise is an important aircraft noise component of the proposed high-speed civil transport (HSCT) at take-offs and landings. For noise certification purpose one would, therefore, like to be able to predict as accurately as possible the intensity, directivity and spectral content of this noise component. The purpose of this work is to develop a semi-empirical prediction method for the broadband shock associated noise from supersonic rectangular jets. The complexity and quality of the noise prediction method are to be similar to those for circular jets. In this paper only the broadband shock associated noise of jets issued from rectangular nozzles with straight side walls is considered. Since many current aircraft propulsion systems have nozzle aspect ratios (at nozzle exit) in the range of 1 to 4, the present study has been confined to nozzles with aspect ratio less than 6. In developing the prediction method the essential physics of the problem are taken into consideration. Since the braodband shock associated noise generation mechanism is the same whether the jet is circular or round the present prediction method in a number of ways is quite similar to that for axisymmetric jets. Comparisons between predictions and measurements for jets with aspect ratio up to 6 will be reported. Efforts will be concentrated on the fly-over plane. However, side line angles and other directions will also be included.

Materials for the next generation of aircraft engineers

Researchers are today focusing their efforts on ambitious performance goals for turn‐of‐the‐century military and civil aircraft propulsion systems, objectives set by projects such as the High Speed Civil Transport. One such programme co‐ordinated by NASA and the DoD, the Integrated High‐Performance Turbine Engine Technology Initiative, or IHPTET, seeks to double thrust‐to‐weight ratios to 20:1 by the year 2003. Tomorrow's aircraft engines will undoubtedly run hotter and weigh less than their present‐day counterparts, and will depend on advanced materials. Metal‐matrix composites (MMCs) typically consisting of a titanium alloy matrix and ceramic reinforcement, are generally held as leading candidates because they are light and maintain their strength at higher operating temperatures.

Advanced Technology Programs for Small Turboshaft Engines: Past, Present, Future

This paper addresses approximately 15 years of advanced technology programs sponsored by the United States Army Aviation Applied Technology Directorate and its predecessor organizations and conducted by GE Aircraft Engines (GEAE). Included in these programs is the accomplishment of (1) the 1500 shp demonstrator (GE12), which led to the 1700, and (2) the 5000 shp Modern Technology Demonstrator Engine (MTDE/GE27). Also included are several advanced technology component programs that have been completed or are ongoing through the early 1990s. The goals for the next generation of tri-service small advanced gas generator demonstration programs are shown. A prediction is thus made of the advancements required to fulfill the aircraft propulsion system established by the DoD/NASA Integrated High-Performance Turbine Engine Technology (IHPTET) initiative through the year 2000.

Aircraft Propulsion Systems: Technology and Design. Edited by G. C. Oates. American Institute of Aeronautics and Astronautics, Inc., Washington, D.C.1989. 528 pp. Illustrated. $39.95 (AIAA Members), $49.95 (Non-Members).

Aircraft Propulsion Systems: Technology and Design. Edited by G. C. Oates. American Institute of Aeronautics and Astronautics, Inc., Washington, D.C.1989. 528 pp. Illustrated. 49.95 (Non-Members). - Volume 94 Issue 935

Evaluation of Control Techniques for Aircraft Propulsion Systems

This paper discusses the evaluation of modern controls for aircraft propulsion systems. Modern control techniques offer potential advantages over classical approaches. The benefits of multivariable optimization and guaranteed robustness are becoming increasingly attractive as aircraft become more highly integrated and complex. However, validation of modern control techniques has remained theoretical and applications have been restricted to the laboratory. To apply these techniques, the airframer must establish means to understand, evaluate, and verify them. Douglas has established an approach based on digital computer simulation facility to meet these ends. The major elements of this facility are: real-time dynamic system simulation; multivariable compensator generation; and hardware-in-the-loop closure. The facility is intended to serve as a stepping stone to flight test capability while retaining design and test flexibility. Features such as sensor synthesis and noise injection will ensure applicability to real-world implementation. This facility is being used in the evaluation of an integrated secondary system.

航空機およびスペースプレーン用エンジン

航空機およびスペースプレーン用エンジン

Sound generated from the interruption of a steady flow by a supersonically moving aerofoil

This paper examines a flow–aerofoil interaction problem that we believe is likely to be an important issue in advanced aircraft propulsion systems involving supersonic propellers. They are potentially noisy and it is important to identify the mechanism by which they generate noise so that they can be optimized for acceptable operation. One of the most potent sources of noise lies in the possibility that a second stage propeller blade cuts through the core of the tip vortex shed from a first stage blade. Then suddenly the streaming core flow must adjust to the boundary constraints of that second stage blade, and the adjustment will inevitably involve compressive waves that escape as sound. How strong these sound waves are, how long their life is and where they go to are important questions, the answers to some of which are obtained in this paper. We examine here what we think is a canonical problem and determine the level and directionality of the sound generated by the interruption of the axial vortex-core flow by a supersonic blade. The principal sound is launched in the Mach-wave direction, where the pressure pulse has an amplitude that decreases much more slowly than it would from spherical spreading. This pressure pulse can reach a distant observer with a very large amplitude, 160 dB or higher being typical. The peak sound pressures are found to be independent of blade speed at high supersonic tip velocity, while the energy radiated in the pulse, because of its reducing duration, attenuates as the supersonic speed increases. This aspect gives grounds for believing that the higher the speed, the quieter will be the stage interaction sound of a contrarotating supersonic propeller.

Potential application of advanced propulsion systems to civil aircraft

Introduction E has been a major factor in the development of airframes and powerplants. Wing design has progressed from the early empirical sections to today's fully-optimized aft-loaded supercritical sections. Civil turbine engines have progressed from turbojets through low-bypass-ratio turbofans to the current high-bypass-ratio turbofans. Propellers have advanced from fixed pitch to variable pitch and are now evolving from unswept single-rotation to counterrotation Propfans. All these evolutionary processes have been beneficial in increasing aircraft efficiency, but the task of integrating the powerplant with the airframe has become more and more complex. The last few years have seen a proliferation of proposals for aircraft propulsion systems which must be evaluated against aircraft requirements in order to arrive at the right choice of airframe/powerplant configuration. The choices made during the latter part of this decade will be crucial to the way in which civil transports evolve for service extending well into the next century. In view of the vast financial investment required for any new major aircraft development, aircraft companies tend to build upon what they know rather than innovate. Aircraft configurations develop along similar lines. The rear-engine jet installation of the Caravelle was the forerunner of the BAe 111, DC9, and Fokker F28/F100. The Trident engine configuration set the style for the Boeing 727. In more recent years, wing-mounted turbofans have dominated the civil market. There is remarkable similarity between the configurations of the Boeing 757 and 767 and the A300, A310, A320, and A330 family and further configurational similarity between the A340 and the Boeing 747. Only Douglas and Fokker have stayed with the rear-engined configuration. New developments in the propulsion scene may lead to reassessment of aircraft configurations in the 1990s. Even so, the majority of commercial aircraft in service at the end of the century will have wing-mounted engines. The major factors influencing aircraft development are safety, efficiency, economy, and noise. Safety must be paramount and, like community noise, is covered by legislation. Within these constraints, aircraft designers have the task of integrating aircraft and propulsion systems to create efficient, economic, and competitive aircraft.

Thermodynamics and Fluid Mechanics of Turbomachinery

During the last decade, rapid advances have been made in the area of flow analysis in the components of gas turbine engines. Improving the design methods of turbomachine blade rows and under- standing of the flow phenomena through them, has become one of the major research topics for aE'rodynamists. This increase of research efforts is due to the need of reducing the weight and fuel consumption of turbojet engines for the same thrust levels. One way of achieving this is to design more efficient components working at high local velocities. Design efforts can lead to desired results only if the details of flow through the blade rows are understood. It is also known that for aircraft propulsion systems development, time and cost can be reduced significantly if the perf ormance can be predicted with conf idence and enough precision. This* generally iK:eds sophisticated two or three dimensional computer codes that can give enough information for design and performance prediction. In the recent years, designers also started to use these sophisticated codes more and more with confidence, in connection with computer aided design and manufacturing techniques. On the other hand, the modelling and solution of flow and the meast

Polymer, metal, and ceramic matrix composites for advanced aircraft engine applications

Advanced aircraft engine research within NASA Lewis focuses on propulsion systems for subsonic, supersonic, and hypersonic aircraft. Each of these flight regimes requires different types of engines, but all require advanced materials to meet their goals of performance, thrust-to-weight ratio, and fuel efficiency. The high strength/weight and stiffness/weight properties of resin, metal, and ceramic matrix composites will play an increasingly key role in meeting these performance requirements. At NASA Lewis, research is ongoing to apply graphite/polyimide composites to engine components and to develop polymer matrices with higher operating temperature capabilities. Metal matrix composites, using magnesium, aluminum, titanium, and superalloy matrices, are being developed for application to static and rotating engine components, as well as for space applications, over a broad temperature range. Ceramic matrix composites are also being examined to increase the toughness and reliability of ceramics for application to high-temperature engine structures and components.

Fiber Optics for Propulsion Control Systems

The term “fiber optics” means the use of dielectric waveguides to transfer information. In aircraft systems with digital controls, fiber optics has advantages over wire systems because of its inherent immunity to electromagnetic noise (EMI) and electromagnetic pulses (EMP). It also offers a weight benefit when metallic conductors are replaced by optical fibers. To take full advantage of the benefits of optical waveguides, passive optical sensors are also being developed to eliminate the need for electrical power to the sensor. Fiber optics may also be used for controlling actuators on engine and airframe. In this application, the optical fibers, connectors, etc., will be subjected to high temperatures and vibrations. This paper discusses the use of fiber optics in aircraft propulsion systems, together with the optical sensors and optically controlled actuators being developed to take full advantage of the benefits which fiber optics offers. The requirements for sensors and actuators in advanced propulsion systems are identified. The benefits of using fiber optics in place of conventional wire systems are discussed as well as the environmental conditions under which the optical components must operate. Work being done under contract to NASA Lewis on optical and optically activated actuators sensors for propulsion control systems is presented.

Aircraft Engine Control Mode Analysis

This paper describes the control mode analysis procedure that is used to establish closed-loop control requirements for advanced aircraft propulsion systems. The procedure utilizes anticipated variations in engine component performance, engine deterioration, and control tolerances in a statistical analysis to establish corresponding variations in engine output performance and safety parameters. Potential closed-loop control configurations are evaluated by this process, compared, and the best configuration selected for implementation into control law and schedule designs. A byproduct of the analysis is the establishment of engine design and performance margins. The paper will describe typical engine variational models used in this process, the General Electric COMET program designed to automate the analysis, and typical mode study results based on a current augmented turbofan engine.

ECM in Aero Engine Component Machining

DIFFICULT to machine, high temperature materials have been introduced at an ever increasing rate into aircraft propulsion systems over the last twenty five years. Over the same period, the aircraft industry has had an ‘on‐off’ affair with electrochemical machining (ECM).