Showing papers on "Turbofan published in 1999"

Advanced Turbofan Duct Liner Concepts

Abstract: The Advanced Subsonic Technology Noise Reduction Program goal is to reduce aircraft noise by 10 EPNdB by the year 2000, relative to 1992 technology. The improvement goal for nacelle attenuation is 25 percent relative to 1992 technology by 1997 and 50 percent by 2000. The Advanced Turbofan Duct Liner Concepts Task work by Boeing presented in this document was in support of these goals. The basis for the technical approach was a Boeing study conducted in 1993-94 under NASA/FAA contract NAS1-19349, Task 6, investigating broadband acoustic liner concepts. As a result of this work, it was recommended that linear double layer, linear and perforate triple layer, parallel element, and bulk absorber liners be further investigated to improve nacelle attenuations. NASA LaRC also suggested that "adaptive" liner concepts that would allow "in-situ" acoustic impedance control also be considered. As a result, bias flow and high-temperature liner concepts were also added to the investigation. The major conclusion from the above studies is that improvements in nacelle liner average acoustic impedance characteristics alone will not result in 25 percent increased nacelle noise reduction realtive to 1992 technology. Nacelle design advancements currently being developed by Boeing are expected to add 20-40 percent more acoustic lining to hardwall regions in current inlets, which is predicted to result in and additional 40-80 percent attenuation improvement. Similar advancements are expected to allow 10-30 percent more acoustic lining in current fan ducts with 10-30 percent more attenuation expected. In addition, Boeing is currently developing a scarf inlet concept which is expected to give an additional 40-80 percent attenuation improvement for equivalent lining areas.

Turbofan engine including fans with reduced speed

Abstract: An impeller is directly driven by an output shaft of a core engine. The airflow produced by the impeller rotates an air turbine and a fan disposed integrally with the air turbine. The impeller and the air turbine form a fluid coupling which serves also as a speed reducing mechanism. The rotational speed of the fan can be reduced to be lower than that of the output shaft while retaining efficiency of the core engine. The outer diameter of the fan can be increased, raising a bypass ratio.

Integrated fan-core twin spool counter-rotating turbofan gas turbine engine

Abstract: A twin spool counter-rotating turbofan gas turbine engine having a counter-rotating fan module integrated with the high pressure compressor and driven by a counter-rotating turbine utilizing only two drive shafts. The two drive shafts are aerodynamically coupled and rotate in opposite directions relative to each other with or without the use of a gearbox. The integration between the fan module and high pressure compressor allows the fan blade rows to operate at the same mechanical speed of the high pressure compressor blade rows. An afterburner module may be added to the present invention to provide thrust augmentation.

Bayesian belief networks for fault identification in aircraft gas turbine engines

Abstract: Describes the methodology for usage of Bayesian belief networks (BBNs) in fault detection for aircraft gas turbine engines. First, the basic theory of BBNs is discussed, followed by a discussion on the application of this theory to a specific engine. In particular, the selection of faults and the means by which operating regions for the BBN system are chosen are analyzed. This methodology is then illustrated using the GE CFM56-7 turbofan engine as an example.

Vertical take-off and landing vehicle configured as a compound autogyro

Abstract: A compound autogyro has a unique system of rotor blade retraction and vectored thrust. Redundant thrust systems provide for emergency conditions. Located in the upper mast are twin gas lines leading to a hub section of the rotor. In the hub, they divide the mass flow into two additional gas lines reaching to the tip ends of rigid rotor blades. A revolving, upper section of the rotor mast is attached to a lower, non-rotating section by a spherical bearing. Directly beneath this attach bearing is a distribution plenum, which receives the mass flow from each of three or four turbofan engines. To achieve high levels of propulsion, the turbofans are equipped with vectoring vanes that direct the mass flow to a plenum or, in the alternative, out a jet pipe for conventional flight. Another set of vectoring vanes can direct the mass flow downwardly, in case of a serious failure upon takeoff.

Air intake and blowing device

Abstract: An air intake and blowing device, comprising a blowing fan (11) such as a turbo fan capable of blowing air in all directions which is installed inside a main casing (2) provided with an air intake port (5) and an air blowing port (9) enclosing the air intake port (5), the air blowing port (9) being provided with a vortex flow creating member which creates a spiral blowing vortex air flow to form a spirally swirl-blowing air flow, and air surrounded by the blowing air flow being formed in a stable tornado flow and sucked strongly into the air intake port (5).

Single vs. Two Stage High Pressure Turbine Design of Modern Aero Engines

Abstract: In this paper, the two-stage shrouded HPT engine configuration rated at 22000 lbs thrust is used as the baseline from which a single stage HPT unshrouded design is systematically derived to evaluate the potential weight and cost advantage. The baseline thermodynamic cycle at the rated thrust level was modified in order to optimize the turbine inlet temperature, overall pressure ratio, and core flow with a single stage HPT and deliver competitive performance. The comparative study, although preliminary in depth, has led to the advantages and disadvantages associated with an unshrouded single versus a two-stage shrouded HPT design. The results compare design configuration, secondary air system, weight, safety, life, specific fuel consumption (SFC), and future thrust growth capability. The main advantages of the single stage application are reductions in cost and complexity of design, lower turbine gas temperature, and ease of maintenance. The main disadvantages are in reduced turbine polytropic/isentropic efficiency for HPC pressure ratio greater than 9, increased SFC, higher rim speed, higher HPT exit Mach number, higher bypass ratio to achieve the desired thrust level, and possibly higher weight. A quantitative statement on the reduction of engine cost/weight is premature until a detailed design and the associated cost-benefit is performed. The paper concludes by recommending that the design philosophy of the modern unmixed turbofan engine (single or two-stage HPT) leads to a balance between the selected turbine gas temperature versus the by-pass ratio in order to minimize cost and maximize the thrust-to-weight ratio and the cycle efficiency. In either ease, the expected high reliability and reduced engine cost/weight in the context of future thrust-growth capability need to be demonstrated by proven technology which seem to favor the two-stage HPT configuration.Copyright © 1999 by ASME

Fan noise reduction from turbofan engines using adaptive herschel-quincke tubes

Abstract: An array of adaptive or fixed Herschel-Quincke tubes (1) aligned in a circumferential or helical array about an inlet (38) of a turbofan engine. The array of tubes effectively divide the acoustic energy generated by the engine. One of the energy components propagates within the tubes while the other propagates within the engine compartment. The acoustic energy within the tubes is reintroduced into the engine compartment to cancel the acoustic energy remaining in the engine as it propagates from the fan (36) towards the inlet and the outlet (34) openings.

Fan case for turbofan engine having a fan decoupler

Abstract: A fan case for a turbofan engine having a fan including plurality of fan blades mounted to a rotor disk and a decoupler that fails in response to a predetermined load includes a substantially annular shell. The shell has a forward section, an intermediate section, and an aft section. The fan case further includes an aft facing step formed at the forward end of the intermediate section to prevent blade fragments from being ejected forward. The intermediate section is axially aligned with the fan and has a large inside diameter. The intermediate section thus defines an annular space around the fan blades that is sufficiently large to allow the fan to orbit when the decoupler fails. The intermediate section and the aft section are aligned radially to allow blade fragments to be ejected aft, avoiding additional secondary blade damage.

Integrated fan/low pressure compressor rotor for gas turbine engine

Abstract: This invention concerns a turbofan gas turbine engine with an integrated fan and low pressure compressor rotor which is mounted to a forward end of the shaft immediately upstream of a one piece engine support structure (20). The fan blade portion (30) and compressor blade portion (31) have aerodynamically aligned lateral airfoil surfaces and platforms enabling a single integrated rotor to replace prior art separate blades thereby simplifying the engine design and reducing the axial length of the engine.

Method and apparatus for a fan noise controller

Abstract: A fan system, such as a turbofan, marine propeller, or a cooling fan, includes a fan noise control system for reducing noise generated by the fan system. The noise control system may be configured to reduce either broadband noise, blade-passage noise, or both. In particular, the fan noise control system suitably includes a pre-swirl generator configured to provide a layer of fluid upstream from the fan blades. The layer swirls in the direction of the fan's rotation, reducing the angular velocity differential between the fan blades and the incident fluid. In addition, the fan noise control system may also include a fluid seal generator configured to create a fluid barrier between the fan blade tips and the interior surface of the fluid flow channel. The fluid seal inhibits leakage flow between the fan blade tips and the interior surface as well as the formation of blade vortices. By minimizing the blade wake and the blade tip vortices without adding solid surfaces, noise tends to diminish.

The History of North American Small Gas Turbine Aircraft Engines

Abstract: The Small Turbine Engine Definitions Setting the Stage Evolution of the Small Turbine Engine Industry Teledyne CAE Lycoming General Electric Small Aircraft Engines Williams International Pratt and Whitney Canada Allison Garrett (Allied Signal Engines) Conclusion Appendix - History of Contemporary Miniature Turbojet Engines.

Active flow control to reduce fan blade vibration and noise

Abstract: An experimental investigation is conducted to reduce the unsteady stator-rotor interaction in a turbofan simulator using active flow control. The fan rotor of a l/lCscale turbofan propulsion simulator is subjected to circumferentially periodic inlet flow distortions, generated by four stators that support a centerbody in the inlet mounted onto the simulator. These wakes are re-energized by injecting air from the trailing edge of each stator through discrete blowing holes. The flow rate through each blowing hole is controlled by individual MEMS (Micro-Electra-Mechanical-System) based microvalve. The microvalve actuation signal voltage is generated by a PID (Proportional Integral and Derivative) controller and is a function of the wake velocity defect. Far-field Sound Pressure Level (SPL) at the Blade Passing Frequency (BPF) without and with blowing is measured in an anechoic chamber. The experiments are performed for two simulator speeds of 29,500 ‘pm and 40,000 rpm. Wake reenergization produces significant reductions in the BPF tone at both speeds. The sound power level at the BPF calculated from measured far-field directivity shows that source power is reduced by at least half The feasibility and advantage of active control is demonstrated by the ability of the system to respond to changes in the inlet flow velocity.

Active control of inlet noise from a turbofan engine using inlet wavenumber sensors

Abstract: In this paper, active control of the inlet noise from a turbofan engine is experimentally investigated with inlet-mounted sensors and actuators. The experimental work is carried out on a running JTlSD turbofan jet engine in a test stand at Virginia Tech. The control inputs were supplied by twelve acoustic sources equipped with neodymium iron cobalt magnets mounted in a single circumferential array upstream of the fan. An inlet sensing technique using an axial array of microphones mounted in the inlet and processed to observe axial wavenumbers traveling down the inlet was used to generate the error signals. The concept of combining active and passive control components together with a hybrid passive-active inlet is also investigated experimentally. The results show that the combination of active and passive control techniques is an effective means of reducing radiated noise from turbofan engines. The wavenumber sensing scheme is shown to be an effective technique for reducing the radiation towards particular directions in the far field when implemented on a passively-lined inlet.

Comparative Analysis of the Windmilling Performance of Turbojet and Tbrbofan Engines

Abstract: The windmilling performance of turbojet and turbofan (TF) engines is investigated numerically by means of a performance synthesis program. Different types of TF engines are taken into consideration, including mixed and unmixed exhaust configurations and configurations with and without a booster compressor on the low-pressure shaft. Furthermore, different design bypass ratios are investigated. The free windmilling performance is calculated for various ram pressure ratios, and, in addition, power input and offtake on the high-pressure shaft are considered. The calculated results indicate a rather strong dependency, not only on the design bypass ratio, but also on the engine type. For example, the internal drag and the maximum power offtake for a given ram pressure ratio differ considerably when comparing mixed and unmixed exhaust configurations. However, for the relight capability, the design bypass ratio is identified as the most important parameter. Nevertheless, the results of this investigation make evident that the rather widespread procedure to present the windmilling performance of engines dependent on ram pressure ratio and design bypass ratio is insufficient.

Intake Engine Interactions of a Modern Large Turbofan Engine

Abstract: An engine experiment has been carried out to investigate Fan Stability and response to ambient wind conditions during static high power running of a modern large turbofan engine. This paper describes the experiment and the conclusions.Intermittently the inlet would separate and drive the fan into stall from which it did not recover when the inlet cleared up: on high working lines one inlet separation could stall the fan; on lower working lines the inlet separation / fan flow / bypass duct pressure would develop a divergent 10Hz oscillation which could eventually stall the fan. The interaction of the stalled fan with the turbine and mixed nozzle would then raise the fan running line above the stall dropout level thus locking the fan into stall even when the inlet cleared up. A one dimensional dynamic model of the engine was created that would exhibit similar behaviour to the engine when a delay was introduced between the inlet loss and fan face loss. The engine never showed steady operation with the inlet separated.Copyright © 1999 by ASME

Active control of fan tones radiated from turbofan engines. ii. in-duct error sensors

Abstract: This paper continues an earlier companion paper in which the results of active control computer simulations aimed at assessing the potential for reducing the fan tones radiated from the inlet of turbofan engines were presented. The earlier study found that good levels of reductions in the sound power transmitted and sound pressure radiated towards the sidelines could be obtained by using error sensors located in the radiated far field. The present paper is also concerned with these control objectives, but with the important difference that the error sensors are located on the duct wall. The error sensor array described in this paper is comprised of a number of axial line array of discrete sensors uniformly distributed around the duct wall. By applying the appropriate phase delay between the sensor signals in a single axial array and summing, an estimate of the mode amplitudes versus axial propagation angle can be obtained. This in-duct pressure measurement can be related to the far-field radiation pattern. Practical issues are also addressed such as the influence on the array’s performance of the in-duct boundary layer and interference from cut-off modes. The basis for the technique is the close relationship between the in-duct ray–mode angles and those of the far-field peak pressure lobe of the radiated field.

Turbofan engine construction

Abstract: A turbofan engine construction has a stator portion coupled to and centra disposed within a rigid casing. A rotor portion is disposed between the rigid casing and the stator portion for rotation about the stator portion. A portion of fluids entering the turbofan are heated between the stator and rotor portions prior to expulsion thereof. The remainder of the fluids entering the turbofan pass unheated through the stator portion prior to expulsion. As a result, the heated fluids are expelled annularly about the unheated fluids.

Transportation propulsion system

Abstract: A gas turbine engine (8) has a plurality of gas generators (28, 30, 32, 34) which generate and cool pressurized gas streams (38, 40) that are combined in a high efficiency topping cycle in a wave rotor convertor (36) The output of the wave rotor convertor (36) drives a single power turbine (24) Each gas generator may comprise an aircraft-type turbofan engine (28B, 30B) An electric generator (48) is selectively driven by each gas generator (28, 30, 32, 34)

Broadband noise radiation models for aircraft engines

Abstract: Far-field noise radiation models are presented for broadband random noise radiation from an aircraft engine. Models include radiation from the fan inlet and aft duct, and the engine core duct. Turbomachinery broadband noise generation models which define the acoustic power generation in the duct as distributed among the duct modes or as a mode cut-off ratio distribution can be used as input. In this paper simple acoustic power distributions have been assumed to demonstrate the far-field radiation field. The inlet radiation model includes the influence of the bellmouth used in static tests or the inlet lip used for wind-tunnel or flight tests. The aft duct models include the effect of the nozzle area change and the jet slip layer on the propagation and radiation of the internally generated broadband noise. Acoustic power has been conserved and the far-field pressure properly evaluated even for the difftcult aft radiation cases where the radiation angle is drastically altered by the shear layer. A new termination transmission loss model is also presented which is valid for the inlet and the aft ducts. The noise radiation models are intended to be approximate but adequate representations where very rapid calculations are needed for many modes. The broadband random noise radiation models developed here are intended to be reasonably accurate and provide extremely fast computational capability. This speed is required since extremely large numbers of duct modes can propagate in modem turbofan engines at the high frequencies usually encountered with turbomachinery broadband noise. The noise radiation models are intended to be used in conjunction with noise source models which predict the broadband noise generation in the engine ducts in terms of the duct modes or other convenient modal representation such as the modal cut-off ratio power

The Methodology of Stochastic Optimization of Parameters and Control Laws for the Aircraft Gas-Turbine Engines Flow Passage Components

Abstract: This paper presents the main theses of stochastic approach to the multimeasure parameters and control laws optimization for the aircraft gas-turbine engines. The methodology allows us to optimize the engines taking into account the technological deflections which inevitably take place in the process of manufacturing of the engine’s components as well as engine’s control deflections. The stochastic optimization is able to find highly robust solutions, stable to inaccuracies in technological processes.The effectiveness of the methodology is shown by example of optimization problem solution to find the control laws for the flow passage controllable elements of the 4-th generation aircraft mixed-flow turbofan engine. The use of information about the existing and advanced production technology levels during the optimization process, including some components manufacturing accuracy, allows us to considerably increase the probability of optimum solution implementation in practice. In real engine there are some components manufacturing deflections as well as control accuracy deflections. It results a certain engine’s performance deviation. An engine optimization classic deterministic approach can not take into account this circumstance, so the probability of an optimum design implementation is too low.Copyright © 1999 by ASME

System for active flutter control

Abstract: A system (300) for controlling aeromechanical instability or flutter in turbofan engines (200) having fan blades (202, 204, 208, 210, 212, 214, 216) employs a sensor (310), such as an off-blade static pressure sensor (12) or proximity detector (310) mounted on a turbofan engine (200) at an inlet of a rotor of the engine for generating a signal to detect resonance of the turbofan blades at frequencies associated with flutter. A controller (330) is coupled to the sensor (310) for generating by spatial Fourier decomposition from the sensor signal a command signal comprising a real time amplitude component and a spatial phase of disturbances of a predetermined nodal diameter and coincident with a natural frequency of resonance of a predetermined structural mode of the fan blades (202, 204, ..., 216) in the stationary frame. An actuator (342), such as a bleed valve or acoustic speaker (342), is mounted on the turbofan engine (200) for damping flutter dynamics in response to the amplitude of the command signal.

Thrust-vectoring turbofan jet-engine analysis

Abstract: Engine thrust vectoring (TV) is an emerging new technology for future military and civil aircraft in which the Technion has made significant contributions. Rapidly deflecting engine jets to maneuver the aircraft with or without conventional aerodynamic flight control (CAFC) significantly enhances the flight safety, agility, and combat kill-ratio capabilities of fighter aircraft in the near term and enhances the safety of civil transport jets in the long term. There are yet no realistic predictions of engine dynamic responses to yaw-pitch-roll TV commands in the public domain. Hence, the primary aim of this work is to provide such a first. The results obtained comprise, therefore, a required fundamental step for advanced aircraft/TV implementation. The selection of this work focuses on the Lockheed-Martin TV F-16/F-100 research study conducted at the Technion. A unique TV-engine computer algorithm has been developed that expands the conventional steady-state modeling capabilities of onand off-design as well as the conventional transients (via throttle changes) to create realistic dynamic TV-engine simulations at various altitudes and Mach numbers. This work has been expanded to include predictions for TV in civil aircraft (via a fixed geometry nozzle) under the same conditions. It is concluded that the military TV configuration, as expected, produces no variations in engine performance while providing TV flight control benefits. It is also demonstrated that under the same dynamic conditions, the civil configuration provides an increase in thrust, enhancing the benefits available from TV in the civil domain.

Inverse adaptive neuro-control of a turbo-fan engine

Abstract: Neural Networks have been successfully used for implementing control architectures for different applications. In this work we examine neural network augmented inverse adaptive control of a turbo-fan engine. This implementation is classified as a level one intelligent control where changes in the system during the course of its operation can be corrected with an adaptive controller. The inverse control architecture presented uses a neural network to augment an existing proportional-integral (PI) controller to accommodate engine changes. The present architecture is implemented on a linear model as well as on a nonlinear engine model that was provided by General Electric. The non-linear engine model used for the simulation is a XTE46 turbo-fan engine. The model simulates a changed engine by changing the flow and efficiency scalars of the various components of the engine, namely, the fan, the compressor, and the turbines. Results of using the inverse adaptive neurocontrol show excellent command following abilities even in the presence of big engine changes.

Advanced modeling of active control of fan noise for ultra high bypass turbofan engines

Abstract: An advanced model of active control of fan noise for ultra high bypass turbofan engines has been developed. This model is based on a boundary integral equation method and simulates the propagation, radiation and control of the noise generated by an engine fan surrounded by a duct of finite length and cylindrical shape, placed in a uniform flow. Control sources, modeled by point monopoles placed along the wall of the engine inlet or outlet duct, inject anti-noise into the duct to destructively interfere with the sound field generated by the fan. The duct inner wall can be lined or rigid. Unlike current methods, reflection from the duct openings is taken into account, as well as the presence of the evanescent modes. Forward, as well as backward (i.e., from the rear of the engine), external radiation is computed. The development of analytical expressions for the sound field resulting from both the fan loading noise and the control sources is presented. Two fan models are described. The first model uses spinning line sources with radially distributed strength to model the loading force that the fan blades exert on the medium. The second model uses radial arrays of spinning point dipoles to simulate the generation of fan modes of specific modal amplitudes. It is shown that these fan models can provide a reasonable approximation of actual engine fan noise in the instance when the modal amplitude of the propagating modes or the loading force distribution on the fan blades, is known.

Flow field investigations on a wing installed Couter Rotating Ultra- high-bypass Fan engine simulator in the low speed wind tunnel DNW-LST

Abstract: For a better understanding of jet interference from wing mounted turbofan engines and for improved CFD modelling more detailed flow field studies and reliable test data are required. With this objective, within the framework of the DLR-NLR co-operation, flow field investigations have been carried out in the Low Speed Wind Tunnel LST 3x2.25 m² of the DNW (German Dutch Wind tunnels) on a twin-jet transport aircraft half model (ALVAST). The half model was tested in cruise configuration (clean wing without flaps) without and with a wing mounted engine simulator . Two types of engine simulators were used: a Through Flow Nacelle (TFN) and a turbo-powered Counter Rotating Ultra-high-bypass Fan (CRUF). All tests have been carried out at wind tunnel speed V0=60 m/s (Mach number M0=0.18). The flow fields behind the wing and engine simulators (TFN and CRUF) were investigated using a rake equipped with total pressure probes and a rake equipped with directional probes. In this way time-averaged flow field planes perpendicular to the tunnel flow were obtained. Non-intrusive flow field measurements were carried out using the Particle Image Velocimetry (PIV) technique. This technique was used to investigate the stream-wise development of the turbo-powered CRUF inlet and fan exhaust flow and the velocity flow field near wing and pylon. Information about both the unsteady and the time-averaged flow field was obtained. The measurement techniques proved to be successful for engine/airframe interference studies. The two techniques are complementary and the results correspond well with each other. Furthermore a useful database has become available for further improvement of the CFD modelling. CFD computations have already been made for the cruise configuration without engine simulator, which correspond reasonably well with the five-hole rake measurements

The Gas Turbine Heat Cycle and its Influence on Fuel Efficiency and Emissions

Abstract: This paper discusses the application fo heat exchangers to aircraft engines. At first the thermodynamic cycles with and without heat recovery and intercooling will be compared in a parameter study and the most suitable heat cycle for aircraft application will be selected. Next, heat exchangers of different kind and geometry and their off-design behaviour will be described. One of them will be selected for an intercooled and recuperated (ICR) aircraft engine. The results of an engine performance simulation program for this engine will be presented, the simulation will cover several operating points at sea level static (SLS) and in flight. The data base of the simulation corresponds to real engines and heat exchangers and therefore represents todays' technology. The results of the simulation will be compared with data of a modern high-bypass turbofan, which has been simulated by the same program. Finally the behaviour of the intercooled, recuperative and the conventional engine on a flight mission will be compared, which has beein calculated by a flight performance program coupled with the engine simulation program. The results will be summarised and evaluated regarding fuel consumption, NOx and soot production as well as weight assumptions.

Industry perspective on jet noise—Prediction and reduction requirements

Abstract: Spectacular growth of airline passenger traffic, nearly tenfold since 1970, has been fueled by a steady trend toward lower cost airfares made possible by technological achievements in airframe and aircraft engine design. Of all the advancements in aircraft design, none has been more important than that of the high bypass ratio (HBPR) turbofan engine, first introduced in 1969 on the Boeing 747. Since then, HBPR turbomachinery noise technology has kept pace with other engine refinements, allowing newer aircraft to meet increasingly stringent community noise requirements. Even more advanced turbomachinery and nacelle noise technology is now at hand as a result of government/industry efforts in both Europe and the United States. Engines with substantially lower fan noise will be introduced. Jet noise will remain the major obstacle to further noise reduction. Since the majority of new commercial aircraft over the next 20 years will be powered by HBPR engines, research in jet noise must be a major priority. This paper examines the needs for jet noise reduction across the range of commercial aircraft types, and suggests technology development efforts including CFD tools for jet characterization, active flow control, installation effects, and novel suppression devices. This paper also discusses challenges in jet noise technology for supersonic airliners.

Sound diffraction by the splitter of a turbofan engine

Abstract: 3