Showing papers on "Turbofan published in 1992"

Variable specific thrust turbofan engine

Abstract: An aircraft turbofan engine and method of operation effect variable specific thrust. The engine includes a fan disposed in a fan casing and a booster compressor disposed in a first flow splitter and powered by a core engine. A second flow splitter is disposed inside the fan casing and defines fan outer and inner ducts. The booster compressor includes at least one stage of rotor blades each having a shroud and an integral rotor flade extending radially outwardly therefrom into the fan inner duct. The fan outer duct includes a variable area first exhaust nozzle disposed at an aft end of the fan casing and is positionable in a first position to permit shifting of a portion of the fan air from the outer duct to the inner duct for flow between the flades to vary specific thrust of the engine.

Turbofan engine having a contrarotating low-pressure compressor

Abstract: A turbofan engine includes two oppositely rotating fan rotors which are arranged upstream of the core engine, and has a booster with two contra-rotating coaxial rotors. The radially exterior booster rotor is arranged between the rearward fan rotor and the low-pressure turbine in a torque-transmitting manner. The gearless construction permits an almost uniform loading of the low-pressure shafts.

Thrust reverser for a turbofan engine

Abstract: A thrust reverser for a turbofan engine is disclosed in which the pressure of the gases passing through the cold flow air duct act on a downstream segment of the thrust reverser door so that the door is normally biased toward its closed, forward thrust position. This positively eliminates any possibility of the thrust reverser door inadvertently opening into its reverse thrust position. The thrust reverser according to the present invention is thus self-closing regardless of the position and/or functioning of the typical closing and locking mechanisms. The thrust reverser door assembly has internal and external doors separately pivotally attached to the turbofan housing so as to each be movable between closed, forward thrust positions, and opened, reverse thrust positions. A single actuating mechanism may be utilized to move both of the internal and external doors between their respective closed and opened positions.

Models for Predicting the Performance of Brayton-Cycle Engines

Abstract: The performance of gas-turbine engines is the result of choices of type of cycle for the application, cycle temperature ratio, pressure ratio, cooling flows and component losses. The output is usually given as efficiency versus specific power. The type of efficiency of interest (thermal, propulsive, specific thrust, overall efficiency) must be specified. This paper presents a set of computer programs for the performance prediction of shaft-power and jet-propulsion cycles, such as simple, regenerative, intercooled-regenerative, turbojet and turbofan cycles. Each cycle is constructed using individual component modules. Realistic default assumptions are made by the programs, or other values can be specified by the user for component efficiencies as functions of pressure ratio, cooling mass-flow rate as a function of cooling technology levels, and various other cycle losses. The programs can be used to predict design point and off-design point operation using appropriate component efficiencies. The effect of various cycle choices on overall performance are discussed.Copyright © 1992 by ASME

Separable fan strut for a gas turbofan powerplant

Abstract: A method and apparatus which facilitate separation of a gas turbofan powerplant into modules for shipping, maintenance and repair is disclosed Various construction details are developed which provide means for mounting a fan cowling to an engine core in a manner which permits transference of operational loads from the fan cowling to the engine core and separation of the fan cowling from the engine core In one embodiment, a fan cowling (46) is attached to an engine core (18) by a plurality of radially extending through struts (64) The through struts include a bolted joint (72) which permits separation of a powerplant (12) into a first module and a second module For this embodiment, a method for varying between an assembled and disassembled condition is comprised of manipulating the joints between an engaged and disengaged position and axially moving the separate modules along a longitudinal centerline (14)

Pressure based close loop thrust control in a turbofan engine

Abstract: Fuel flow and nozzle area are controlled by a multi-variable control. A requested fan speed is compared with measured fan speed, producing an error signal which is translated in a proportional-integral inner control loop into a requested compressor pressure signal that represents an acceptable rate of change in compressor pressure for difference between requested and measured fan speed. The error signal is compared with measured compressor pressure; the difference being used in a multi-variable control to adjust fuel flow and turbine exhaust area to achieve the requested compressor pressure.

Propulsion system for a V/STOL aircraft

Abstract: The invention is a propulsion system for powering an aircraft in both vertical and horizontal flight modes. In detail, the invention comprises a gas-driven ducted lift fan mounted in the aircraft for providing thrust in the vertical flight mode. A turbofan engine is mounted in the aircraft that comprises a fan section for providing thrust in the horizontal flight mode and a turboshaft engine having an output drive shaft coupled to the fan section for driving same. A gas transfer duct is mounted in the aircraft having a first end adapted to receive exhaust air from the fan section and a second end coupled to the lift fan. A turbocompressor is mounted in the transfer duct and a combustor is mounted in the transfer duct between the turbocompressor and the lift fan, the combustor for receiving and burning fuel and providing combustion gases for driving the ducted left fan. A shafting system couples the turbocompressor to the output shaft of the turboshaft engine. A decoupling system is connected to the shafting system for decoupling the turbocompressor from the output shaft of the turboshaft engine.

Turbofan engine with means to smooth intake air

Abstract: A turbojet fan engine is disclosed having a fan or prop fan which blows air into a secondary channel and an external shroud for the turbine and the secondary channel, in which the front end of the shroud is formed with an inlet lip and the rear end of the shroud is formed in a nozzle-like, pointed manner and at least one end of the shroud is changed, with respect to its effective profile geometry, by means of air under pressure which is taken from the engine and blown out at the appropriate end of the shroud.

Aircraft gas turbine engine backbone deflection control

Abstract: A gas turbine engine backbone deflection control apparatus to counter the effects of backbone bending due to gust, thrust. and maneuver loads by introducing a controlled backbone counter-bending moment by applying controlled tensioning forces only between axially spaced apart frames connected by the backbone. One embodiment of the invention, for a high bypass ratio turbofan engine, provides a hydraulically powered actuator to produce tensioning forces in cables connected between a fan frame and a turbine frame and the actuator is controlled by the engines digital electronic control system using input signals generated by inlet moment load sensors and/or blade tip clearance sensors.

Subsonic flight test evaluation of a performance seeking control algorithm on an F-15 airplane

Abstract: The subsonic flight test evaluation phase of the NASA F-15 (powered by F 100 engines) performance seeking control program was completed for single-engine operation at part- and military-power settings. The subsonic performance seeking control algorithm optimizes the quasi-steady-state performance of the propulsion system for three modes of operation. The minimum fuel flow mode minimizes fuel consumption. The minimum thrust mode maximizes thrust at military power. Decreases in thrust-specific fuel consumption of 1 to 2 percent were measured in the minimum fuel flow mode; these fuel savings are significant, especially for supersonic cruise aircraft. Decreases of up to approximately 100 degree R in fan turbine inlet temperature were measured in the minimum temperature mode. Temperature reductions of this magnitude would more than double turbine life if inlet temperature was the only life factor. Measured thrust increases of up to approximately 15 percent in the maximum thrust mode cause substantial increases in aircraft acceleration. The system dynamics of the closed-loop algorithm operation were good. The subsonic flight phase has validated the performance seeking control technology, which can significantly benefit the next generation of fighter and transport aircraft.

Subsonic flight test evaluation of a propulsion system parameter estimation process for the F100 engine

Abstract: Integrated engine-airframe optimal control technology may significantly improve aircraft performance. This technology requires a reliable and accurate parameter estimator to predict unmeasured variables. To develop this technology base, NASA Dryden Flight Research Facility (Edwards, CA), McDonnell Aircraft Company (St. Louis, MO), and Pratt & Whitney (West Palm Beach, FL) have developed and flight-tested an adaptive performance seeking control system which optimizes the quasi-steady-state performance of the F-15 propulsion system. This paper presents flight and ground test evaluations of the propulsion system parameter estimation process used by the performance seeking control system. The estimator consists of a compact propulsion system model and an extended Kalman filter. The extended Laman filter estimates five engine component deviation parameters from measured inputs. The compact model uses measurements and Kalman-filter estimates as inputs to predict unmeasured propulsion parameters such as net propulsive force and fan stall margin. The ability to track trends and estimate absolute values of propulsion system parameters was demonstrated. For example, thrust stand results show a good correlation, especially in trends, between the performance seeking control estimated and measured thrust.

Fanjet with booster compressor

Abstract: A turbofan engine (1) with a fan rotor (3) directly (17) driven by the low pressure turbine (16) by way of a shaft, has a low pressure compressor (5) (booster) with two contra-rotating booster rotors (18a, b). One booster rotor (18) is directly connected to the fan rotor (3), the other is driven by way of a planetary gearing (6), which is coupled to the shaft (17). Since only approximately half the booster power has to be transmitted by the gearing (6), the gearing (6) can be kept small, the cost of cooling thereby remaining correspondingly low.

Optimization of a Multistage Axial Compressor in a Gas Turbine Engine System

Abstract: The work presents a procedure to determine the design parameters of multistage axial compressor (MAC) rows, the parameters optimum from the point of view to assure the best integrated indices of gas turbine engine (GTE) both at the design and off-design operation mode.Effectiveness of the proposed approach has been demonstrated with regards to solving the problems of optimum contouring by the radius of 7 rows of 4-stage fan included in a two-shaft turbofan. For the examples under consideration respective problems of non-linear programming have been set whose dimensionality reached up to 63 of the design parameters of fan blade rows.It is shown, that the requirement to provide the best engine characteristics, integrated matching both GTE component parts (in our case these are compressor blade rows) and integrated characteristics of components included in an engine is of more importance than assuring the highest efficiency of separate components under consideration.Copyright © 1992 by ASME

Far-field noise and internal modes from a ducted propeller at simulated aircraft takeoff conditions

Abstract: The ducted propeller offers structural and acoustic benefits typical of conventional turbofan engines while retaining much of the aeroacoustic benefits of the unducted propeller. A model Advanced Ducted Propeller (ADP) was tested in the NASA Lewis Low-Speed Anechoic Wind Tunnel at a simulated takeoff velocity of Mach 0.2. The ADP model was designed and manufactured by the Pratt and Whitney Division of United Technologies. The 16-blade rotor ADP was tested with 22- and 40-vane stators to achieve cut-on and cut-off criterion with respect to propagation of the fundamental rotor-stator interaction tone. Additional test parameters included three inlet lengths, three nozzle sizes, two spinner configurations, and two rotor rub strip configurations. The model was tested over a range of rotor blade setting angles and propeller axis angles-of-attack. Acoustic data were taken with a sideline translating microphone probe and with a unique inlet microphone probe which identified inlet rotating acoustic modes. The beneficial acoustic effects of cut-off were clearly demonstrated. A 5 dB fundamental tone reduction was associated with the long inlet and 40-vane sector, which may relate to inlet duct geometry. The fundamental tone level was essentially unaffected by propeller axis angle-of-attack at rotor speeds of at least 96 percent design.

Turbine bypass engines

Abstract: A supersonic aircraft engine, either turbojet or turbofan, having a compressor, a diffuser, a combustion chamber, a turbine, and a nozzle passageway, and a turbine bypass passageway for bypassing compressor exit flow around the turbine. The bypass passageway comprises a plurality of supply pipes, and a flow control valve is mounted in each of the plurality of supply pipes. Under given flight conditions, a predetermined number of these flow control valves are fully closed, while the remaining flow control valves are opened as necessary for the given flight condition to obtain a desired rate of turbine bypass flow. The turbine bypass flow is supersonically mixed with the turbine exit flow during transonic acceleration or discharged externally of the engine housing. The turbine bypass flow is primarily composed of boundary layer air flowing along the inner and outer walls of the diffuser.

Effects of bleed air extraction of thrust levels on the F404-GE-400 turbofan engine

Abstract: A ground test was performed to determine the effects of compressor bleed flow extraction on the performance of F404-GE-400 afterburning turbofan engines. The two engines were installed in the F/A-18 High Alpha Research Vehicle at the NASA Dryden Flight Research Facility. A specialized bleed ducting system was installed onto the aircraft to control and measure engine bleed airflow while the aircraft was tied down to a thrust measuring stand. The test was conducted on each engine and at various power settings. The bleed air extraction levels analyzed included flow rates above the manufacturer's maximum specification limit. The measured relationship between thrust and bleed flow extraction was shown to be essentially linear at all power settings with an increase in bleed flow causing a corresponding decrease in thrust. A comparison with the F404-GE-400 steady-state engine simulation showed the estimation to be within +/- 1 percent of measured thrust losses for large increases in bleed flow rate.

Thrust stand evaluation of engine performance improvement algorithms in an F-15 airplane

Abstract: An investigation is underway to determine the benefits of a new propulsion system optimization algorithm in an F-15 airplane. The performance seeking control (PSC) algorithm optimizes the quasi-steady-state performance of an F100 derivative turbofan engine for several modes of operation. The PSC algorithm uses an onboard software engine model that calculates thrust, stall margin, and other unmeasured variables for use in the optimization. As part of the PSC test program, the F-15 aircraft was operated on a horizontal thrust stand. Thrust was measured with highly accurate load cells. The measured thrust was compared to onboard model estimates and to results from posttest performance programs. Thrust changes using the various PSC modes were recorded. Those results were compared to benefits using the less complex highly integrated digital electronic control (HIDEC) algorithm. The PSC maximum thrust mode increased intermediate power thrust by 10 percent. The PSC engine model did very well at estimating measured thrust and closely followed the transients during optimization. Quantitative results from the evaluation of the algorithms and performance calculation models are included with emphasis on measured thrust results. The report presents a description of the PSC system and a discussion of factors affecting the accuracy of the thrust stand load measurements.

Thrust reverser for a high-bypass ratio turbofan engine

Abstract: A thrust reverser for a turbofan engine having a very high bypass ratio is disclosed having a plurality of baffles pivotally attached to a gas turbine engine housing so as to extend into a cold flow air stream emanating from the turbofan exit The baffles are pivotally attached to the gas turbine engine housing and may be moved into extended, thrust reversing positions in which some of the baffles form a greater angle with the gas turbine engine housing than the remainder of the baffles By moving the baffles located generally on opposite upper and lower portions of the gas turbine engine housing to the greater angles, the requisite thrust reversing force may be developed while at the same time minimizing the overall vertical dimension of the engine housing so as to provide the maximum amount of ground clearance for the turbofan engine Secondary baffles are provided between the main baffles to close open spaces between the main baffles Due to the orientation of the baffles in their extended, thrust reversing positions, the transverse configuration of the baffles is generally oval

Oblique wing supersonic transport concepts

Abstract: The economic and technical features of two SST concepts that offer the potential of reducing the impact of the environmental constraints on the aircraft design and performance are presented. The potential economic performance of these aircraft is referenced to equivalent passenger size subsonic designs employing consistent design guidelines and assumptions. Total operating cost and airline return on investment are utilized for the economic comparisons.

Installation Effects of Wing-Mounted Turbofan Nacelle-Pylons on a 1/17-Scale, Twin-Engine, Low-Wing Transport Model

Abstract: A twin-engine, low-wing transport model, with a supercritical wing of aspect ratio 10.8 designed for a cruise Mach number of 0.77 and a lift coefficient of 0.55, was tested in the Langley 16-Foot Transonic Tunnel. The purpose of this test was to compare the wing-nacelle interference effects of flow-through nacelles simulating superfan engines (very high bypass ratio (BPR ~ 18) turbofan engines) with the wing-nacelle interference effects of current-technology turbofan engines (BPR ~ 6). Forces and moments on the complete model were measured with a strain-gage balance, and extensive external static-pressure measurements (383 orifice locations) were made on the wing, nacelles, and pylons of the model. Data were taken at Mach numbers from 0.50 to 0.80 and at model angles of attack from -4 degrees to 8 degrees. Test results indicate that flow-through nacelles with a very high bypass ratio can be installed on a low-wing transport model with a lower installation drag penalty than for a conventional turbofan nacelle at a design cruise Mach number of 0.77 and lift coefficient of 0.55.

A Comparison of the Measured and Predicted Flowfield in a Modern Fan-Bypass Configuration

Abstract: A 3-D viscous Navier-Stokes flow solver was used to predict core and bypass rotor performance and radial flow characteristics of a 4.6:1 bypass ratio, single stage fan. The 3-D flow solver can handle several blade rows simultaneously and has the capability to include a downstream splitter. Results of the analysis are compared with experimental data obtained during rig testing of a modern high bypass single stage turbofan in which rotor performance for both bypass and core streams was measured.Copyright © 1992 by ASME

Computational fluid dynamics based three-dimensional turbofan inlet/fan cowl analysis system

Abstract: A three-dimensional turbofan inlet/fan cowl analysis system based on computational fluid dynamics (CFD) has been developed. This system was established to aid nacelle designers in the efficient assessment of their design concepts by providing for immediate evaluation of design changes without extensive reliance on wind tunnel testing. A reliable CFD flow solver, user-friendly grid generator, and postprocessing software are included in the system. The system is easy to use by designers who are not particularly familiar with CFD. Validation and applicability studies have been performed using several different inlet/fan cowl configurations at on-design and off-design engine operating conditions. This work demonstrates that an Euler-based CFD code integrated with automatic grid generation and postprocessing can reduce the development cycle time in the inlet/fan cowl design process.

Design of a hybrid laminar flow control nacelle

Abstract: Consideration is given to the potential application of hybrid-laminar-flow control to the external surface of a modern, high-bypass-ratio (HBR) turbofan engine nacelle. With the advent of advanced ultra-HBR fans (with bypass ratios of 10-15), the wetted areas of these nacelles approach 10 percent of the total wetted area of future commercial transports. A hybrid-laminar-flow-control pressure distribution is specified and the corresponding nacelle geometry is computed utilizing a predictor/corrector design method. Linear stability calculations are conducted to provide predictions of the extent of the laminar boundary layer. Performance studies on an advanced twin-engine transport configuration are presented to determine potential benefits in terms of reduced fuel consumption.

Propulsion and aerodynamic analysis of the Beta II two-stage-to-orbit vehicle

Abstract: A study of a revised version of the Beta II two-stage-to-orbit vehicle has been undertaken. The goal of the study was to modify and refine critical components of the NASA/Boeing/Wright Laboratory Beta II booster design to better define a successful baseline vehicle that can provide routine access to space. The vehicle geometry was modified and corresponding aerodynamics were predicted. The propulsion system was improved by refining the nacelle design which included incorporating a variable capture area inlet, replacing the five High Speed Civil Transport derived turbine bypass turbojet engines with four variable cycle turbofan engines per nacelle, and removing the bypass duct system. The ramjet performance was adjusted for the change in airflow due to the variable capture area inlet. The second stage wing-body orbiter design was not modified for this study. The total Beta II takeoff weight which resulted was approximately 1.0 million pounds.

Performance benefits of adaptive in-flight propulsion system optimization

Abstract: The communication throughput and data-processing capacities of integrated flight/propulsion control systems allow engine operating schedules to be adjusted in-flight, on the basis of adaptive optimization algorithms which identify engine component performance variations due to manufacturing, wear, and damage. A quantification is presently made of the performance benefits accruing to adaptive in-flight optimization, via comparisons of fuel consumption and turbine temperature data for variable geometry and component match optimized cases with conventional cases. A low-bypass mixed-flow turbofan and a high-bypass nonmixed turbofan are thus treated. 6 refs.

Spinning mode analysis of the acoustic field generated by a turboshaft engine

Abstract: The spinning mode analysis of a ducted acoustic field is a powerful means for advancing the understanding of noise sources in turbofan or turboshaft engines, and it is also the main information needed to predict the far-field directivity radiated by the inlet or the nozzle. Tests were made with a circular array of fixed microphones in a nozzle cross section of a Turbomeca TM 333 turboshaft engine to determine the modal characteristics of its acoustic field. The main difficulty in data processing comes from the high background noise due to the very turbulent internal flow. A conventional method based on the angular Fourier transform of the cross-spectral matrix may therefore be inadequate. Several improvements are discussed and validated by numerical simulations, such as the use of a three-signal coherence technique to reduce the output noise. A further gain is achieved by the reduction of the estimate bias due to the finite number of statistical averages. The experimental TM 333 wave-number spectra are presented in the last section at several frequencies, corresponding to the broadband combustion noise and to the tones emitted by the high-pressure turbine and the free turbine. The observed spinning modes are explained by taking into account the nozzle cut-off properties and the radiation mechanisms of transonic rotors.

Commercial turbofan engine exhaust nozzle flow analyses using PAB3D

Abstract: Recent developments of a three-dimensional (PAB3D) code have paved the way for a computational investigation of complex aircraft aerodynamic components. The PAB3D code was developed for solving the simplified Reynolds Averaged Navier-Stokes equations in a three-dimensional multiblock/multizone structured mesh domain. The present analysis was applied to commercial turbofan exhaust flow systems. Solution sensitivity to grid density is presented. Laminar flow solutions were developed for all grids and two-equation k-epsilon solutions were developed for selected grids. Static pressure distributions, mass flow and thrust quantities were calculated for on-design engine operating conditions. Good agreement between predicted surface static pressures and experimental data was observed at different locations. Mass flow was predicted within 0.2 percent of experimental data. Thrust forces were typically within 0.4 percent of experimental data.

Effects of chemical equilibrium on turbine engine performance for various fuels and combustor temperatures

Abstract: A study was performed to quantify the differences in turbine engine performance with and without the chemical dissociation effects for various fuel types over a range of combustor temperatures. Both turbojet and turbofan engines were studied with hydrocarbon fuels and cryogenic, nonhydrocarbon fuels. Results of the study indicate that accuracy of engine performance decreases when nonhydrocarbon fuels are used, especially at high temperatures where chemical dissociation becomes more significant. For instance, the deviation in net thrust for liquid hydrogen fuel can become as high as 20 percent at 4160 R. This study reveals that computer central processing unit (CPU) time increases significantly when dissociation effects are included in the cycle analysis.