Showing papers on "Turbofan published in 1978"

Aircraft Gas Turbine Engine Technology

Abstract: Aircraft Gas Turbine Engine Technology provides a comprehensive, easy-to-understand treatment of the background, development, and applications of the gas turbine engine it its various forms, such as turobjet, turbofan, turboprop, and turboshaft powerplants Designed primarily as a resource for technicians preparing for the FAA aircraft powerplant mechanic certification, Aircraft Gas Turbine Engine Technology also may be used a reference The text also discusses the changing maintenance and overhaul procedures and philosophies and the role of fuel metering in engine operation

Partial span inlet guide vane for cross-connected engines

Abstract: A pair of turbofan engines are cross connected such that during normal-mode operation horsepower can be shared by the respective cores, and when one engine core becomes inoperative the fan of that engine can be driven by the turbine of the operative engine to thereby maintain a substantial thrust output. In order to balance the respective thrust outputs, variable inlet guide vanes are controlled to decrease the fan mass flow in the operative engine and increase the fan mass flow in the inoperative engine. The variable inlet guide vanes are so constructed as to only partially span the fan duct so as to not appreciably affect the airflow to the core when the inlet guide vane angle setting is altered to allow the core to thereby retain a high level of supercharging during this operational period of maximum power demand.

Integrated control system for a gas turbine engine

Abstract: An integrated control system for a gas turbine engine of the turbofan type receives signals from a plurality of engine sensors and from the engine operator and generates control signals therefrom. A first control signal regulates the fan exhaust nozzle area in order to control inlet throat Mach number to maintain a low level of engine noise. Additional control signals regulate fuel flow to control engine thrust and fan pitch to control fan speed. A plurality of schedules are utilized to maintain a predetermined relationship between the controlled parameters and a number of fixed and calculated limits can override the control signals to prevent unsatisfactory engine performance.

Exhaust nozzle control and core engine fuel control for turbofan engine

Abstract: An exhaust nozzle control and core engine fuel control for a turbofan engine serving to optimize thrust during steady state and transient operation modes of a turbofan engine of the mixed flow type by adjusting or trimming the exhaust nozzle area as a function of fan pressure ratio and fan rotor speed and by adjusting or trimming the core engine fuel flow as a function of fan rotor speed and or turbine inlet temperature. The control serves to enhance stability by assuring airflow in the engine and its inlet is within a given value avoiding inlet buzz and high distortion to the engine and avoiding even transient operation in conditions that might cause compressor flow instability or stall. Fuel flow is adjusted or trimmed as a function of fan rotor speed or turbine inlet temperature limits depending on which is calling for the least amount of fuel.

Propulsion system for a V/STOL airplane

Abstract: A propulsion system for an airplane to permit it to achieve vertical and/or short take-offs and landings. The propulsion system is integrated into a wing/nacelle unit and includes a thrust vectoring system. A separate flow turbofan engine is mounted in each wing/nacelle unit. A system of three flaps is located at the rear of each wing/nacelle unit for deflecting the turbofan engine exhaust downward, rearward, or any angle in between. These three flaps are arranged to provide a main thrust nozzle in the horizontal flight position without any additional flaps between them. One flap is located at the wing/nacelle upper surface trailing edge. Two slots are provided at the leading edge of this flap. The upper forward most slot is provided as an exit nozzle for the engine turbine exhaust, which is shrouded from the fan exhaust. The second of these two slots removes a portion of the high energy fan exhaust from the fan discharge duct and ejects it over the flap upper surface. The other two flaps are positioned such that, in the horizontal position they are both aligned with the wing/nacelle lower surface and in the vertical position, one is aligned with the wing/nacelle lower surface and the other is aligned with the wing/nacelle upper surface. When the flaps are in the vertical position, the aft most slot in the upper flap and a slot formed between the upper flap and the lower aft flap provide a means of improving the turning efficiency of the fan exhaust stream.

Numerical modeling of three-dimensional flows in turbofan engine exhaust nozzles

Abstract: An experimental and numerical study was conducted to investigate the use of three-dimensi onal viscous analysis for the design of internal mixers for jet noise suppression. Three flows, a full-scale free mixer, a fullscale lobed mixer, and a model-scale lobed mixer, were selected for study. Details of the experiments, turbulence modeling, and the determination of initial flow properties from engine operating properties are described together with a discussion of the usefulness of the analysis for mixing design. Overall the results are encouraging and, at least for the flows considered here, numerical analysis appears to compare favorably with model-scale tests as a simulation of the full-scale flow.

External gas turbine engine cooling for clearance control

Abstract: An active clearance control (ACC) for a turbofan engine is disclosed herein where the cross section of the external spray bars are fabricated in square or substantially square configurations.

Jet noise source modification due to forward flight

Abstract: XTENSIVE use of noise-absorbi ng materials in the inlet and exhaust ducting of modern high bypass ratio turbo fan engines has reduced the noise generated by fans, compressors, turbines, and burners to the level that the jet noise (noise generated in the exhaust plume by mixing the high velocity jet with the ambient air) is an important part of the total noise signature of current aircraft. The characteristics of jet noise from turbojet and turbofan engines have been well documented under static conditions. However, aircraft noise certification limits must be satisfied under actual aircraft flyover conditions during takeoff and approach operations. Thus, it is important that methods be developed to more accurately predict the jet noise under flight conditions. The effect of flight on jet noise of a circular jet exhaust has been simulated by testing in wind tunnels.1'2 Noise measurements obtained in wind tunnel tests show that the jet exhaust noise of nozzles operating subsonically is reduced in flight from the static levels at all measurement angles. However, noise measurements obtained from some flyover tests3 have shown less noise reduction than the results of the wind tunnei tests. In order to help resolve the differences in wind tunnel and flyover results, it is necessary to understand the effects of flight on the fundamental mechanisms of jet noise generation. Measuring the changes caused by flight in the aerodynamic parameters responsible for noise generation and relating these changes to the measured noise reductions caused by flight will provide a more basic understanding of the effect of flight on jet noise than is currently available. This understanding will allow eventual improvements in our ability to develop more accurate in-flight predictions. The noise reduction in flight is generally attributed to changes in the strength of the acoustic sources distributed throughout the jet shear layer. The acoustic source strength at a point in the jet shear layer is determined from the local aerodynamic flow properties. The mean and turbulence flow quantitites needed to determine the acoustic source strength are mean velocity, mixing layer growth, turbulence intensity, integral length scale, eddy convection velocity, and integral

Prop-fan propulsion - Its status and potential

Abstract: Studies have established that advanced turboprop (prop-fan) equipped aircraft will reduce fuel consumption by 15 to 30 percent compared to aircraft equipped with high-bypass turbofan engines of equivalent technology. A reduction in direct operating costs of approximately 10 percent has been identified for commercial aircraft as well as approximately 20 percent lower gross weight airplane for long endurance military missions. The prop-fan propulsion system is being investigated as part of the NASA Aircraft Energy Efficiency program which includes both analytical studies and experimental tests. The experimental work encompasses performance and acoustic wind tunnel tests on several prop-fan models. The prop-fan technology status is reviewed in the major areas of performance, installed effects, cabin noise, blade structure and maintenance cost. Also, further activities required to complete the technical validation of prop-fans are described.

Energy Efficient Engine Preliminary Design and Integration Studies

Abstract: The technology and configurational requirements of an all new 1990's energy efficient turbofan engine having a twin spool arrangement with a directly coupled fan and low-pressure turbine, a mixed exhaust nacelle, and a high 38.6:1 overall pressure ratio were studied. Major advanced technology design features required to provide the overall benefits were a high pressure ratio compression system, a thermally actuated advanced clearance control system, lightweight shroudless fan blades, a low maintenance cost one-stage high pressure turbine, a short efficient mixer and structurally integrated engine and nacelle. A conceptual design analysis was followed by integration and performance analyses of geared and direct-drive fan engines with separate or mixed exhaust nacelles to refine previously designed engine cycles. Preliminary design and more detailed engine-aircraft integration analysis were then conducted on the more promising configurations. Engine and aircraft sizing, fuel burned, and airframe noise studies on projected 1990's domestic and international aircraft produced sufficient definition of configurational and advanced technology requirements to allow immediate initiation of component technology development.

Aerodynamic design and performance testing of an advanced 30 deg swept, eight bladed propeller at Mach numbers from 0.2 to 0.85

Abstract: The increased emphasis on fuel conservation in the world has stimulated a series of studies of both conventional and unconventional propulsion systems for commercial aircraft. Preliminary results from these studies indicate that a fuel saving of from 15 to 28 percent may be realized by the use of an advanced high speed turboprop. The turboprop must be capable of high efficiency at Mach 0.8 above 10.68 km (35,000 ft) altitude if it is to compete with turbofan powered commercial aircraft. An advanced turboprop concept was wind tunnel tested. The model included such concepts as an aerodynamically integrated propeller/nacelle, blade sweep and power (disk) loadings approximately three times higher than conventional propeller designs. The aerodynamic design for the model is discussed. Test results are presented which indicate propeller net efficiencies near 80 percent were obtained at high disk loadings at Mach 0.8.

Design of a multivariable controller for a high-order turbofan engine model by Zakian's method of inequalities

Abstract: The method of inequalities is used to design a simple multivariable controller for the regulation of the net thrust level, total airflow and inlet temperature of a 24th-order plant which consists of an F100 turbofan engine and actuators These results reveal some of the inherent difficulties associated with the control of the plant

Noise suppressing turbofan nozzles and method

Abstract: Noise perceived below a turbofan is reduced by providing a thicker fan flow below the turbofan primary exhaust flow than is present in conventional turbofans having generally circular and concentric fan and exhaust flows. To thicken the fan flow, the exhaust nozzle is offset upward in the fan nozzle, or the exhaust nozzle discharge end is canted to offset the exhaust flow upward, or the exhaust nozzle is flattened to a generally rectangular or an elliptical shape having a major horizontal axis. In any of these cases, the thickness of the fan flow below the primary exhaust flow is increased and less noise is perceived below the turbofan than if circular concentric fan and exhaust flows were produced. In one embodiment a noise-suppressing thickened fan flow is used in combination with a conventional noise-suppressing multilobe or multitube mixing nozzle to further reduce noise perceived below the turbofan.

Future large civil turbofans and powerplants

Abstract: Design evolution and development of the three-shaft RB 211 type of engine is capable of reducing the installed cruise fuel consumption by 15% compared with current levels, i.e., with fan, compressor, and turbine efficiencies that have already been experimentally demonstrated. This performance improvement translates to a reduction in aircraft direct operating cost of 6% to 8%. A further reduction in cruise fuel consumption could be obtained by combining higher specific air flow in an engine with components that are on average 2% more efficient than currently demonstrated. This can be achieved in a configuration of geared fan engine which gives a cruise fuel consumption of 20% to 22% lower than current levels, depending upon the installation losses of the larger nacelle.

Multivariable quadratic synthesis of an advanced turbofan engine controller

Abstract: A digital controller for an advanced turbofan engine utilizing multivariate feedback is described. The theoretical background of locally linearized control synthesis is reviewed briefly. The application of linear quadratic regulator techniques to the practical control problem is presented. The design procedure has been applied to the F100 turbofan engine, and details of the structure of this system are explained. Selected results from simulations of the engine and controller are utilized to illustrate the operation of the system. It is shown that the general multivariable design procedure will produce practical and implementable controllers for modern, high-performance turbine engines.

Partial swirl augmentor for a turbofan engine

Abstract: A partial swirl augmentor for a turbofan engine having an annular duct for directing hot gases into the augmentor combustion chamber Located within the combustion chamber is a piloted vee-gutter flameholder system which has a circumferential pilot located at the outer edge of the swirlng hot turbine exhaust gas stream As a result thereof, the partial swirl augmentor can attain state-of-the art engine after burning thrust levels with an increased altitude blow-out limit

Acoustic evaluation of a novel swept-rotor fan

Abstract: Inlet noise and aerodynamic performance are presented for a high tip speed fan designed with rotor blade leading edge sweep that gives a subsonic component of inlet Mach number normal to the edge at all radii. The intent of the design was to minimize the generation of rotor leading edge shock waves thereby minimizing multiple pure tone noise. Sound power level and spectral comparisons are made with several high-speed fans of conventional design. Results show multiple pure tone noise at levels below those of some of the other fans and this noise was initiated at a higher tip speed. Aerodynamic performance of the fan did not meet design goals for this first build which applied conventional design procedures to the swept fan geometry.

Supersonic through-flow fan engines for supersonic cruise aircraft

Abstract: Engine performance, weight and mission studies were carried out for supersonic through flow fan engine concepts. The mission used was a Mach 2.32 cruise mission. The advantages of supersonic through flow fan engines were evaluated in terms of mission range comparisons between the supersonic through flow fan engines and a more conventional turbofan engine. The specific fuel consumption of the supersonic through flow fan engines was 12 percent lower than the more conventional turbofan. The aircraft mission range was increased by 20 percent with the supersonic fan engines compared to the conventional turbofan.

Engine thrust control system

Abstract: A control system and method for utilizing the rotational speed of the high-speed spool in a multi-spool turbofan engine to stabilize changes in engine operation which affect the thrust output of the engine. Signals representing the actual rotational speed of the high-speed spool, the actual value of the selected engine pressures which provide an accurate measure of engine thrust, and a commanded value of the selected engine pressures are processed; and an error signal is provided in response to these three signals which is a function of all three signals. The error signal is then used to control the rate of fuel flow to the engine which, in turn, controls engine thrust. In one embodiment the error signal is a function of the rotational speed of the high-speed spool and the actual and commanded values of engine pressure ratio, and in another embodiment the error signal is a function of the rotational speed of the high-speed spool and the actual and commanded values of integrated engine pressure ratio.

Turbofan engine having core supercharging stage

Abstract: A turbofan configuration for a gas turbine engine is disclosed. Various construction details which improve engine performance by supercharging working medium gases to the engine core are discussed. Engines configured in accordance with the present invention include an island splitter which is disposed across the fan flow path. The island splitter is spaced apart from the core engine case. A supercharging, compression stage is driven commonly with the fan stage and extends outwardly into proximity with the core case.

Turbofan augmentor flameholder

Abstract: A turbofan augmentor flameholder having a hollow ring-like structure of annular configuration concentric with the center line of a turbine of a turbofan engine. The ring-like structure has protruding therefrom in the radial direction a first group of hollow gutters extending in a direction toward the center line of the turbine and a second group of hollow gutters extending from the ring-like structure in a direction away from the center line and toward the outer casing of the turbofan engine. The second group of gutters have a vee-shaped angular configurated portion in a direction toward the turbine. The angular configurated portion gradually increases in angle along the gutter in the radial direction as a direct function of its distance from the ring-like structure. Such a relationship provides optimum efficiency for the dispersion of hot exhaust gases from the turbine to the flameholder for gas turbofan engine augmentation.

Advanced Fault Detection and Isolation Methods for Aircraft Turbine Engines.

Abstract: : Aircraft engine diagnostic methods are reviewed. The role of computer-aided diagnostic procedures for current and future engines is discussed from the aspects of performance monitoring, trending, and fault detection/isolation. Development of advanced maximum likelihood or regression algorithms for each of these is presented. A methodology is developed for applying these algorithms to models derived from engine test stand or flight data. Specific computational results are given for a high performance turbofan engine. (Author)

Acoustic tests of duct-burning turbofan jet noise simulation: Comprehensive data report. Volume 1, section 1: Model scale data

Abstract: Model scale data on a 12.2 m (40 ft) arc are presented which were obtained in the hot, static acoustic tests on eleven nozzle designs suitable for use on duct-burning turbofan engines.

Acoustic evaluation of a novel swept-rotor fan. [noise reduction in turbofan engines

Abstract: Inlet noise and aerodynamic performance are presented for a high tip speed fan designed with rotor blade leading edge sweep that gives a subsonic component of inlet Mach number normal to the edge at all radii. The intent of the design was to minimize the generation of rotor leading edge shock waves thereby minimizing multiple pure tone noise. Sound power level and spectral comparisons are made with several high-speed fans of conventional design. Results showed multiple pure tone noise at levels below those of some of the other fans and this noise was initiated at a higher tip speed. Aerodynamic performance of the fan did not meet design goals for this first build which applied conventional design procedures to the swept fan geometry.

Ground Effects on Lift for Turbofan Powered-Lift STOL Aircraft

Abstract: Early studies of turbofan powered-lift STOL concepts indicated that a basic problem of aircraft which incorporate such concepts would be a serious adverse ground effect on lift. Experience to date with actual powered-lift STOL aircraft, however, has not borne out this concern. This apparent disagreement is examined and recent research data are used to help explain some of the differences observed. Analysis indicates that most of the disagreement can be attributed to the use of wind tunnel data that were not directly applicable to the airplane because the model did not properly represent some of the design features and operating conditions of the airplane.

DYGABCD: A program for calculating linear A, B, C, and D matrices from a nonlinear dynamic engine simulation

Abstract: A digital computer program, DYGABCD, was developed that generates linearized, dynamic models of simulated turbofan and turbojet engines. DYGABCD is based on an earlier computer program, DYNGEN, that is capable of calculating simulated nonlinear steady-state and transient performance of one- and two-spool turbojet engines or two- and three-spool turbofan engines. Most control design techniques require linear system descriptions. For multiple-input/multiple-output systems such as turbine engines, state space matrix descriptions of the system are often desirable. DYGABCD computes the state space matrices commonly referred to as the A, B, C, and D matrices required for a linear system description. The report discusses the analytical approach and provides a users manual, FORTRAN listings, and a sample case.

Procedures for generation and reduction of linear models of a turbofan engine

Abstract: A real time hybrid simulation of the Pratt & Whitney F100-PW-F100 turbofan engine was used for linear-model generation. The linear models were used to analyze the effect of disturbances about an operating point on the dynamic performance of the engine. A procedure that disturbs, samples, and records the state and control variables was developed. For large systems, such as the F100 engine, the state vector is large and may contain high-frequency information not required for control. This, reducing the full-state to a reduced-order model may be a practicable approach to simplifying the control design. A reduction technique was developed to generate reduced-order models. Selected linear and nonlinear output responses to exhaust-nozzle area and main-burner fuel flow disturbances are presented for comparison.

Altitude calibration of an F100, S/N P680063, turbofan engine

Abstract: An airflow and thrust calibration of an F100 engine was conducted in coordination with a flight test program to study airframe-propulsion system integration characteristics of turbofan-powered high-performance aircraft. The tests were conducted with and without augmentation for a variety of simulated flight conditions with emphasis on the transonic regime. Test results for all conditions are presented in terms of corrected airflow and corrected gross thrust as functions of corrected fan speed for nonaugmented power and an augmented thrust ratio as a function of fuel-air ratio for augmented power. Comparisons of measured and predicted data are presented along with the results of an uncertainty analysis for both corrected airflow and gross thrust.

Low speed test of a high-bypass-ratio propulsion system with an asymmetric inlet designed for a tilt-nacelle V/STOL airplane

Abstract: A large scale model of a lift/cruise fan inlet designed for a tilt nacelle V/STOL airplane was tested with a high bypass ratio turbofan. Testing was conducted at low freestream velocities with inlet angles of attack ranging from 0 deg to 120 deg. The operating limits for the nacelle were found to be related to inlet boundary layer separation. Small separations originating in the inlet diffuser cause little or no performance degradation. However, at sufficiently severe freestream conditions the separation changes abruptly to a lip separation. This change is associated with a significant reduction in nacelle net thrust as well as a sharp increase in fan blade vibratory stresses. Consequently, the onset of lip separation is regarded as the nacelle operating limit. The test verified that the asymmetric inlet design will provide high performance and stable operation at the design forward speed and angle of attack conditions. At some of these, however, operation near the lower end of the design inlet airflow range is not feasible due to the occurrence of lip separation.