Showing papers on "Turbofan published in 1975"

Nacelle assembly and mounting structures for a turbofan jet propulsion engine

Abstract: A nacelle assembly including an inlet channel, an exterior cowl, a fan channel, and a turbine exhaust nozzle is directly mounted on a turbofan jet propulsion engine. The engine in turn is shock mounted directly on a strut, in turn affixed to an aircraft. A central portion of the outer cowl is hinged to open in a clam shell manner about hinges positioned adjacent the strut location to expose the fan casing and engine accessories for maintenance and removal. A rearward portion of the nacelle assembly is formed in two D-duct structures that are also hinged to open in a clam shell manner about hinges positioned adjacent the strut location. The D-duct structures include portions of the outer cowl and of the fan duct walls. When the D-duct structures are open, the turbine casing of the turbofan engine is exposed for maintenance, repair and removal. A pair of beams, affixed at one end to the aircraft fuselage, and enclosed by an aerodynamic fairing, constitute the mounting strut. The beams extend beyond the fairing into the nacelle and through a fan duct bifurcating structure. The forward of the two beams forks into a yoke-like structure that surrounds a portion of and is affixed by shock mounts to the exterior of the fan casing. The rear beam is also affixed to the turbine casing by a shock mount.

DYNGEN: A program for calculating steady-state and transient performance of turbojet and turbofan engines

Abstract: The DYNGEN, a digital computer program for analyzing the steady state and transient performance of turbojet and turbofan engines, is described The DYNGEN is based on earlier computer codes (SMOTE, GENENG, and GENENG 2) which are capable of calculating the steady state performance of turbojet and turbofan engines at design and off-design operating conditions The DYNGEN has the combined capabilities of GENENG and GENENG 2 for calculating steady state performance; to these the further capability for calculating transient performance was added The DYNGEN can be used to analyze one- and two-spool turbojet engines or two- and three-spool turbofan engines without modification to the basic program A modified Euler method is used by DYNGEN to solve the differential equations which model the dynamics of the engine This new method frees the programmer from having to minimize the number of equations which require iterative solution As a result, some of the approximations normally used in transient engine simulations can be eliminated This tends to produce better agreement when answers are compared with those from purely steady state simulations The modified Euler method also permits the user to specify large time steps (about 010 sec) to be used in the solution of the differential equations This saves computer execution time when long transients are run Examples of the use of the program are included, and program results are compared with those from an existing hybrid-computer simulation of a two-spool turbofan

Interim prediction method for fan and compressor source noise

Abstract: A method is presented for interim use in assessing the noise generated by fans and compressors in turbojet and turbofan engines. One-third octave band sound pressure levels consisting of broadband, discrete tone, and combination-tone noise components are predicted. Spectral distributions and directivity variations are specified. The method is based on that developed by other investigators with modifications derived from an analysis of full-scale, single-stage fan data. Comparisons of predicted and measured noise performance are presented, and requirements for improving the method are discussed.

Variable cycle gas turbine engines

Abstract: A design technique, method, and apparatus for varying the bypass ratio and modulating the flow of a gas turbine engine of the bypass type in order to achieve improved mixed mission performance The disclosed preferred embodiments each include a gas flow control system for management of core and bypass stream pressure comprising diverter valve means downstream of the core engine to selectively mix or separate the core and bypass exhaust streams The flow control system may also include variable geometry means for maintaining the engine inlet airflow at a matched design level at all flight velocities Each preferred embodiment thus may be converted from a high specific thrust mixed flow cycle at supersonic velocities to a lower specific thrust separated flow turbofan system at subsonic velocities with a high degree of flow variability in each mode of operation, wherein the engine inlet airflow may be maintained at a matched design level at all engine velocities To further improve flow flexibility and assist in maintaining the engine inlet airflow matched to a design level throughout a variable velocity range, the flow control system may include a split fan in conjunction with two concentric bypass ducts The disclosed variable cycle engine techniques, methods, and apparatus result in significantly reduced inlet and after-body drag levels and result in significantly improved installed fuel consumption for mixed mission aircraft

Split fan work gas turbine engine

Abstract: One or more of the aft stages of the fan section of a gas turbine engine are rotated by the high pressure turbine of a gas generator and the remainder of the fan stages are rotated by a low pressure turbine downstream of the gas generator. This arrangement divides the fan work between the low and high pressure turbines to permit more efficient utilization of the total available turbine capacity, reduction in low pressure turbine workload, increased aft fan stage pressure ratio capability and greater flow and pressure ratio modulation potential for a split fan engine. The invention has a wide range of application for various turbofan configurations including separated and/or mixed flow turbofan engines with separated or close coupled fan sections.

Turbofan engine with augmented combustion chamber using vorbix principle

Abstract: A mixed flow turbofan engine in which a portion of the core engine exhaust gases are passed into a pilot zone chamber where fuel is added thereto for vaporization therewith and wherein the fan air is passed over a series of vortex generators so that the vortex flow fan air and the vaporized fuel mixture will mix and combust rapidly in an augmentation combustion chamber.

Variable thrust nozzle for quiet turbofan engine and method of operating same

Abstract: An improved method of operating a gas turbine engine is presented wherein engine-generated noise is maintained at a reduced level during reduced thrust operation. Fan speed is maintained at a constant level while fan nozzle area is increased. This maintains high inlet Mach numbers for reduced forward noise propagation and also permits reduced nozzle exhaust velocity for reduced shear noise. In another embodiment, airflow is increased by means of a fan blade pitch change or speed increase while the fan nozzle area is increased, yielding both a net reduction in engine thrust and noise.

Common pod for housing a plurality of different turbofan jet propulsion engines

Abstract: A pod for mounting a turbofan jet propulsion engine on a strut is constructed so that a common cowl and portions of the fan air duct and turbine exhaust duct can accomodate a plurality of different turbofan engines that have substantially the same thrust rating but have variations in structural dimensions. The portions of the pod common to all such engines include an annular cowl, an inlet throat that merges into the forward end of the cowl to form an inlet highlight, a rearward portion of the outer fan duct wall, a rearward portion of the inner fan duct wall and a turbine nozzle. The common portions of the pod structure are designed about a common datum plane orthogonally oriented relative to the pod center line. The rear face of the turbine casing of each of the turbofan jet propulsion engines is positioned in this datum plane when mounted in the pod. An annular inlet adapter forms an inlet wall that couples the rearward edge of the inlet throat to the forward, peripheral portion of the engine fan casing. Outer and inner fan duct wall adapters couple the common outer and inner portions of the fan duct walls to the engine fan casing at the datum plane. A fan nozzle adapter ring is attached to the rear portion of the cowl and the outer fan duct wall to provide an appropriately dimensioned fan nozzle exit opening. The turbine outlet of at least one of the engines can be coupled directly to the common nozzle of the pod. An annular adapter ring is coupled between the forward edge of the common nozzle and the rearward face of the turbine engine outlet on those engines having a lesser longitudinal dimension.

Analysis of turbofan engine performance deterioration and proposed follow-on tests

Abstract: Data and engine parts on in-service JT3D and JT8D engines were analyzed and documented relative to engine deterioration. It is concluded that the fan-compressor system of these engines contributes to the long term engine deterioration. An engine test and instrumentation plan was formulated for a proposed follow-on program. The goal of this program is to verify the above conclusion and to attempt to identify more precisely which components of the fan-compressor system are at fault.

Philosophy, design, and evaluation of soft-mounted engine rotor systems

Abstract: Gas turbine engine rotors are conventionally supported by bearings mounted on relatively stiff supports. The resulting vibratory loads and deflections can be reduced significantly by judiciously soft-mounting the bearings through squirrel cages and/or squeeze films. In addition to minimizing loads and stresses in an engine, it is important that clearances during conditions of maneuvers, thermal bow, and rotor whirl due to unbalance (even under extraordinary conditions such as loss of blades) be controlled. For high-speed rotors, it becomes necessary to support the rotors on resiliently mounted bearings to achieve vibration-free, long-life, close-clearance engines. In this paper, the design philosophy, criteria, and methods of evaluation for soft-mounted turbine engine rotor systems used in General Electric aircraft engine design are described. A major constituent of this method is a computer program for system vibration and static analysis [VAST]. This program is capable of finding natural frequencies, normalized modes, and responses due to any distribution of exciting forces considering gyroscopic and shear-deflection effects. Aircraft mounting and excitations from the helicopter rotor are also included in the computer analysis. General Electric's T700 turboshaft engine, under development for the U.S. Army, serves to illustrate the squeeze film, softmounting concept of design. Results from tests of the T700 engine, Advanced Technology Axial Centrifugal Compressor (ATACC), T64 turboshaft, TF34 turbofan, and other engines are summarized verifying the advantages of soft-mounted rotor systems.

Method for reducing jet exhaust takeoff noise from a turbofan engine

Abstract: In a turbofan engine for jet aircraft the inner stream includes no noise suppression apparatus and the jet exhaust noise generated at takeoff is reduced by mechanically suppressing the jet exhaust noise of the outer stream and operating the engine at a bypass ratio, fan pressure ratio and gas generator power setting which yield a jet exhaust noise level from the suppressed outer stream which is louder than the jet exhaust noise level from the unsuppressed inner stream.

Investigation of the Stall Hammershock at the Engine Inlet

Abstract: The peak static pressures measured at the inlet to the engine during stall are presented for a turbojet and two turbofan engines. It is shown for one turbofan and the turbojet that the static pressure ratio across the hammershock does not exceed significantly the normal shock pressure ratio necessary to stop the flow. The second turbofan engine did not follow this rule. Possible reasons for the departure are discussed. For the two turbofan engines the influence of the stall method on the hammershock intensity has been investigated. Data related to the spatial distribution of pressure in the hammershock are also presented. Nomenclature a = speed of sound Cp = specific heat at constant pressure M = Mach number P - total pressure P = static pressure T = static temperature t = time

Thrust correlated engine pressure ratio indicator and method for turbofan engines with mixer-type nozzles

Abstract: A pneumatic computing device is disclosed for use with turbofan engines having mixer-type nozzles, in which both turbine and fan discharge pressures are tapped and pneumatically combined to derive a pressure equal to a weighted average thereof for application along with engine inlet pressure to a ratio-taking computing indicator instrument that registers an engine pressure ratio (EPR) from which the level of thrust developed by the engine can be accurately determined.

Design and evaluation of a sensor fail-operational control system for a digitally controlled turbofan engine

Abstract: A self-learning, sensor fail-operational, control system for the TF30-P-3 afterburning turbofan engine was designed and evaluated. The sensor fail-operational control system includes a digital computer program designed to operate in conjunction with the standard TF30-P-3 bill-of-materials control. Four engine measurements and two compressor face measurements are tested. If any engine measurements are found to have failed, they are replaced by values synthesized from computer-stored information. The control system was evaluated by using a realtime, nonlinear, hybrid computer engine simulation at sea level static condition, at a typical cruise condition, and at several extreme flight conditions. Results indicate that the addition of such a system can improve the reliability of an engine digital control system.

Wind tunnel investigation of a large-scale upper surface blown-flap model having four engines

Abstract: Investigations were conducted in the Ames 40- by 80-Foot Wind Tunnel to determine the aerodynamic characteristics of a large-scale subsonic jet transport model with an upper surface blown flap system. The model had a 25 deg swept wing of aspect ratio 7.28 and four turbofan engines. The lift of the flap system was augmented by turning the turbofan exhaust over the Coanda surface. Results were obtained for several flap deflections with several wing leading-edge configurations at jet momentum coefficients from 0 to 4.0. Three-component longitudinal data are presented with four engines operating. In addition, longitudinal and lateral data are presented with an engine out. The maximum lift and stall angle of the four engine model were lower than those obtained with a two engine model that was previously investigated. The addition of the outboard nacelles had an adverse effect on these values. Efforts to improve these values were successful. A maximum lift of 8.8 at an angle-of-attack of 27 deg was obtained with a jet thrust coefficient of 2 for the landing flap configuration.

Reverse pitch fan with divided splitter

Abstract: A gas turbofan engine including a variable pitch fan is provided with flow straightening means which are adapted to reduce fan exit swirl in the forward thrust mode. The flow straightening means are so arranged to produce low losses in the fluid entering a core engine during reverse thrust operation while allowing large supercharging of the core engine during forward thrust operation.

Technical Evaluation Report on Propulsion and Energetics Panel Meeting on Power Plant Controls for Aero Gas Turbine Engines (44th) held at Ustaoset Hoyfjellshotell, Norway on 9-13 September 1974.

Abstract: : The 44th Meeting of the Propulsion and Energetics Panel on 'Power Plant Controls for Aero Gas Turbine Engines' was held at Ustaoset Hoyfjellshotell, Norway, from 9-13 September 1974. The meeting had been organized to discuss advances and trends in the aero gas turbine engine controls together with appropriate techniques for the design of optimum controls. The meeting was divided into six sessions with a total of 29 papers. The first two sessions dealt with both steady state and transient performance of aero gas turbine engines in a general fashion to provide ground work for session three, where typical control requirements were discussed. The next two sessions were on control concepts and on simulation techniques, while the last session was devoted to control system hardware. This report gives a brief review of the papers presented and the conclusions to be drawn from them.

Application of real-time engine simulations to the development of propulsion system controls

Abstract: The development of digital controls for turbojet and turbofan engines is presented by the use of real-time computer simulations of the engines. The engine simulation provides a test-bed for evaluating new control laws and for checking and debugging control software and hardware prior to engine testing. The development and use of real-time, hybrid computer simulations of the Pratt and Whitney TF30-P-3 and F100-PW-100 augmented turbofans are described in support of a number of controls research programs at the Lewis Research Center. The role of engine simulations in solving the propulsion systems integration problem is also discussed.

Results of acoustic testing of the JT8D-109 refan engines

Abstract: A JT8D engine was modified to reduce jet noise levels by 6-8 PNdB at takeoff power without increasing fan generated noise levels. Designated the JT8D-109, the modified engines featured a larger single stage fan, and acoustic treatment in the fan discharge ducts. Noise levels were measured on an outdoor test facility for eight engine/acoustic treatment configurations. Compared to the baseline JT8D, the fully treated JT8D-109 showed reductions of 6 PNdB at takeoff, and 11 PNdB at a typical approach power setting.

Identification of Multivariable Gas Turbine Dynamics from Stochastic Input-Output Data.

Abstract: : Results directed toward the identification of multivariable gas turbine engine dynamics from stochastic input-output data are described. An identification algorithm based on modern state estimation theory was developed to identify the parameters of a linear time-invariant F100/F401 turbofan engine model. Unknown parameters of the F100/F401 model were introduced as auxiliary state variables thereby transforming the parameter identification problem to a nonlinear state estimation problem. The engine model was forced by commanded changes in main burner fuel flow and jet exhaust area. Gaussian noise was added to the commanded fuel flow to model metering valve uncertainties. Noise-corrupted measurements consisted of fan turbine inlet temperature, fan and compressor speeds, and main burner and afterburner pressures. The identification procedure was carried out at three steady-state design points between idle and military conditions.

Aerodynamic characteristics of a large-scale hybrid upper surface blown flap model having four engines

Abstract: Data are presented from an investigation of the aerodynamic characteristics of large-scale wind tunnel aircraft model that utilized a hybrid-upper surface blown flap to augment lift. The hybrid concept of this investigation used a portion of the turbofan exhaust air for blowing over the trailing edge flap to provide boundary layer control. The model, tested in the Ames 40- by 80-foot Wind Tunnel, had a 27.5 deg swept wing of aspect ratio 8 and 4 turbofan engines mounted on the upper surface of the wing. The lift of the model was augmented by turbofan exhaust impingement on the wind upper-surface and flap system. Results were obtained for three flap deflections, for some variation of engine nozzle configuration and for jet thrust coefficients from 0 to 3.0. Six-component longitudinal and lateral data are presented with four engine operation and with the critical engine out. In addition, a limited number of cross-plots of the data are presented. All of the tests were made with a downwash rake installed instead of a horizontal tail. Some of these downwash data are also presented.

Hybrid upper surface blown flap propulsive-lift concept for the Quiet Short-Haul Research Aircraft

Abstract: The hybrid upper surface blowing concept consists of wing-mounted turbofan engines with a major portion of the fan exhaust directed over the wing upper surface to provide high levels of propulsive lift, but with a portion of the fan airflow directed over selected portions of the airframe to provide boundary layer control. NASA-sponsored preliminary design studies identified the hybrid upper surface blowing concept as the best propulsive lift concept to be applied to the Quiet Short-Haul Research Aircraft (QSRA) that is planned as a flight facility to conduct flight research at low noise levels high approach lift coefficients, and steep approaches. Data from NASA in-house and NASA-sponsored small and large-scale wind tunnel tests of various configurations using this concept are presented.

Variable Cycle Engines for Advanced Supersonic Transports

Abstract: Variable Cycle Engines being studied for advanced commercial supersonic transports show potential for significant environmental and economic improvements relative to 1st generation SST engines. The two most promising concepts are: a Variable Stream Control Engine and a Variable Cycle Engine with a rear flow-control valve. Each concept utilizes variable components and separate burners to provide independent temperature and velocity control for two coannular flow streams. Unique fuel control techniques are combined with cycle characteristics that provide low fuel consumption, similar to a turbojet engine, for supersonic operation. This is accomplished while retaining the good subsonic performance features of a turbofan engine. A two-stream coannular nozzle shows potential to reduce jet noise to below FAR Part 36 without suppressors. Advanced burner concepts have the potential for significant reductions in exhaust emissions. In total, these unique engine concepts have the potential for significant overall improvements to the environmental and economic characteristics of advanced supersonic transports.

Experimental quiet engine program

Abstract: Full-scale low-tip-speed fans, a full-scale high-tip-speed fan, scale model versions of fans, and two full-scale high-bypass-ratio turbofan engines, were designed, fabricated, tested, and evaluated. Turbine noise suppression was investigated. Preliminary design studies of flight propulsion system concepts were used in application studies to determine acoustic-economic tradeoffs. Salient results are as follows: tradeoff evaluation of fan tip speed and blade loading; systematic data on source noise characteristics and suppression effectiveness; documentation of high- and low-fan-speed aerodynamic and acoustic technology; aerodynamic and acoustic evaluation of acoustic treatment configurations, casing tip bleed, serrated and variable pitch rotor blades, leaned outlet guide vanes, slotted tip casings, rotor blade shape modifications, and inlet noise suppression; systematic evaluation of aerodynamic and acoustic effects; flyover noise projections of engine test data; turbine noise suppression technology development; and tradeoff evaluation of preliminary design high-fan-speed and low-fan-speed flight engines.

Advanced supersonic propulsion system technology study, phase 2

Abstract: Variable cycle engines were identified, based on the mixed-flow low-bypass-ratio augmented turbofan cycle, which has shown excellent range capability in the AST airplane. The best mixed-flow augmented turbofan engine was selected based on range in the AST Baseline Airplane. Selected variable cycle engine features were added to this best conventional baseline engine, and the Dual-Cycle VCE and Double-Bypass VCE were defined. The conventional mixed-flow turbofan and the Double-Bypass VCE were on the subjects of engine preliminary design studies to determine mechanical feasibility, confirm weight and dimensional estimates, and identify the necessary technology considered not yet available. Critical engine components were studied and incorporated into the variable cycle engine design.

Wind tunnel investigation of a twin engine straight wing upper surface blown jet flap configuration

Abstract: An investigation was conducted in a full scale wind tunnel to determine the performance and aerodynamic characteristics of a twin engine, straight wing, upper surface blown jet flap configuration The model had two simulated high bypass ratio turbofan engines with rectangular nozzles exhausting onto the upper surface of the wing at the 35 percent chord station The model was tested with an aspect ratio 82 wing and with the wingtips removed to give an aspect ratio of 60

Propulsion systems technology

Abstract: The selection of components, control design, simulation, and tests are examined for designing supersonic propulsion systems. Inlet-engine combination under electronic control are shown. Design and test results from the integrated control for afterburning turbofan and supersonic cruise inlet are presented.