Showing papers on "Turbofan published in 1973"

Multi-mission tandem propulsion system

Abstract: A multi-mission tandem propulsion system is provided for an aircraft which must operate efficiently at both supersonic and subsonic speeds while generating low noise levels during takeoff, accelerated climb to altitude, approach to landing, and landing. The propulsion system includes a forward turbofan engine coaxially spaced apart from an aft turbojet engine wherein both engines may be selectively controlled to provide overall maximum efficiency during all modes of operation.

Turbofan engine having counterrotating compressor and turbine elements and unique fan disposition

Abstract: A turbofan engine is provided with a compressor and a turbine, all of the bladed stages of the turbine and substantially all of the bladed stages of the compressor being rotor stages. Adjacent rotor stages within the compressor and the turbine are relatively counterrotating. The engine has three independently rotatable shafts connecting respectively three sets of bladed stages of the turbine with three sets of bladed stages of the compressor to form three engine spools. A bladed fan occupying an annular duct substantially surrounding the compressor is driven by the intermediate of the three spools and is disposed near the axial center of the compressor. A quarterstage inlet fan, disposed within the duct upstream of the first fan, is driven by the radially innermost shaft, and has a predetermined length such as to maintain a substantial torque balance between the counterrotating rotors at a preselected rotary velocity of the innermost shaft.

Self-trimming control for turbofan engines

Abstract: A twin spool turbofan engine control is designed which maintains engine thrust and stall margin at nominal levels as the operating characteristics of the engine high spool deteriorates with operating hours, increased altitude or increased power extraction. An electronic supervisory control monitors the high rotor speed and the fan turbine inlet temperature relationships for all engine power settings from intermediate to maximum, and the electronic supervisory control schedules are adjusted based upon shifts in the relationships. In one embodiment the fuel flow to the engine is trimmed in response to a desired fan turbine inlet temperature schedule determined as a function of engine inlet temperature and main burner pressure, the schedule being modified in response to the difference between operating high rotor speed and a reference rotor speed which in turn is a function of engine inlet temperature. In another embodiment the engine fuel flow is trimmed in response to a high rotor speed schedule determined as a function of engine inlet temperature and biased by the difference between a sensed fan turbine inlet temperature and a reference fan turbine inlet temperature. In both embodiments the area of a variable geometry nozzle in the engine is trimmed to modify the fan airflow.

A computer program for calculating design and off-design performance for turbojet and turbofan engines

Abstract: Program uses component performance maps to enable user to do analytical engine cycle calculations. Through scaling procedure, each of the component maps can be used to represent a family of maps. Either convergent or convergent-divergent nozzles may be used.

Surge indicator for turbine engines

Abstract: A pair of pressure transducers, one having a high response capability and the other a low response capability, are positioned in a turbofan or turbojet engine flow passage. The output from the high response transducer is passed through a notch filter to isolate the frequencies of interest. The output from the low response transducer is passed through a low pass filter to provide the absolute steady-state pressure level. The ratio of the high frequency pressure signal within the frequency range of interest to the steady-state pressure signal is calculated and compared to a reference ratio signal. If the calculated pressure ratio signal exceeds the reference ratio signal, the engine is approaching a surge condition, and a warning signal is generated which can be used for rescheduling of the engine away from stall. The apparatus may be used both to anticipate surge and to sense the actual occurrence of a surge condition. The invention herein described was made in the course of or under a contract with the Department of the Air Force.

Abating exhaust noises in jet engines

Abstract: A noise abating improvement for jet engines including the provision of apparatus in the primary flow stream of gas turbine engines such as turbojet, turbofan, turboprop, and other jet engines such as ram jets, scram jets and hybrid jet engines, or in either the primary and/or secondary flow streams of turbofan engines or the like, for imparting to the exhaust gases a component rotation or swirl about the engine''s longitudinal axis. The rotary component in the exhaust gases has the effect of substantially suppressing the build up on sound energy normally produced by an axial flow exhaust system.

Thrust control apparatus for a jet propulsion engine and actuating mechanism therefor

Abstract: An aircraft, employing upper surface blowing to augment and supplement aerodynamic lift for short takeoff and landing (STOL) operation, has a turbofan jet propulsion engine cantilevered in a forward position on each wing In the STOL mode the engine exhaust is discharged rearwardly over the upper airfoil surface of the wing and is turned downwardly over extended trailing edge flaps by the Coanda effect to augment lift On approach for a short landing a portion of the fan air from the engine is diverted through vectoring channels and is directed downwardly and forwardly The diverted fan air by its rearward thrust component provides a subtractive effect on the forward drive thrust of the engine to reduce forward air speed while its upward thrust component compensates for the reduction in aerodynamic lift attending reduced forward air speed By selectively diverting a portion of the fan air the aircraft can achieve a steep angle of descent while maintaining a relatively low rate of descent The resulting glide path can be varied by altering the magnitude and angle of the diverted fan air stream as well as by engine power and flap setting variations An exhaust reversing door, incorporated in the engine exhaust nozzle, includes a lip door mounted at the rearward, upper portion thereof which throttles the rearward exhaust flow to maintain engine load matching when the vectoring channels are opened Actuating linkage for operating the lip door is connected between fixed engine structure and the lip door in such a manner so as not to interfere with the operation of the reversing door

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

Abstract: An investigation has been conducted to determine the aerodynamic characteristics of a large-scale subsonic jet transport model with an upper surface blowing flap system that would augment lift. The model had a 25 deg swept wing of aspect ratio 7.89 and two turbofan engines with the engine centerline located at 0.256 of the wing semispan. The lift of the flap system was augmented by turbofan exhaust impingement on the Coanda surface. Results were obtained for several flap deflections and engine nozzle configurations at jet momentum coefficients from 0 to 4.0. Three-component longitudinal data are presented with two engines operating. Limited longitudinal and lateral data are presented with an engine out. In addition, limited exhaust and flap pressure data are presented.

Digital computer simulation of the dynamic response of a twin-spool turbofan with mixed exhausts

Abstract: The dynamic behaviour of gas turbines is of great practical importance, but unfortunately it cannot be investigated experimentally until late in the development programme when the mechanical integrity of the engine has been established. In the case of aero engines there is a requirement for fast engine accelerations and all engine transients must be achieved with complete safety. Thrust response rates must be guaranteed by the engine manufacturer at a very early stage and clearly it would be of great value to study engine transient behaviour at the design stage; this should lead to a significant saving in development time and cost by decreasing the amount of test bed running required.

Development of Optimal Control Modes for Advanced Technology Propulsion Systems.

Abstract: : A nonlinear multivariable feedback controller was defined for the idle to military operating regime (9 to 100 percent thrust) of the Pratt and Whitney Aircraft F401 variable cycle turbofan engine. The analytical design involved linearizing the F401 engine dynamics about five steady-state operating points between idle and military thrust, applying linear optimal control synthesis methods at each point, and combining the five optimal linear controllers into a single nonlinear controller which has feedback gains that are scheduled with high compressor speed. Variable fan, compressor and exhaust geometries as well as main burner fuel flow are coordinated by the controller to achieve rapid engine dynamic response.

Study of quiet turbofan STOL aircraft for short haul transportation

Abstract: Conceptual designs of Quiet Turbofan STOL Short-Haul Transport Aircraft for the mid-1980 time period are developed and analyzed to determine their technical, operational, and economic feasibility. A matrix of aircraft using various high-lift systems and design parameters are considered. Variations in aircraft characteristics, airport geometry and location, and operational techniques are analyzed systematically to determine their effects on the market, operating economics, and community acceptance. In these studies, the total systems approach is considered to be critically important in analyzing the potential of STOL aircraft to reduce noise pollution and alleviate the increasing air corridor and airport congestion.

Wind tunnel investigation of a large-scale 25 deg swept-wing jet transport model with an external blowing triple-slotted flap

Abstract: An investigation has been conducted to determine the aerodynamic characteristics of a large-scale subsonic jet transport model with an externally blown triple-slotted flap. The lift of the model was augmented by the turbofan engine exhaust impingement on the flap surface. The model had a 25 deg swept wing of aspect ratio 7.28 and four turbofan engines. The model was tested with two flap extents. One extended from 0.11 to 1.00 of the wing semispan, and the other extended from 0.11 to 0.75 of the wing semispan with a single-slotted aileron from 0.75 to 1.00 of the wing semispan. The results were obtained for several flap deflections with and without the horizontal tail at gross thrust coefficients from 0 to 4.0. Longitudinal and lateral data are presented with three and four engines operating.

Dual cycle aircraft turbine engine

Abstract: A method and apparatus applicable to jet engines for improving operating efficiency over broad ranges of flight conditions and for reducing engine noise output in take-off and landing by controlling the airflow entering and exiting the engines. A turbojet engine apparatus is described which operates efficiently at both subsonic and supersonic speeds and a method is described which enables a turbofan with an associated satellite turbojet or turbofan to operate more efficiently at both subsonic and supersonic speeds. In both cases, take-off and landing noise is reduced substantially. The apparatus consists essentially of arranging for two separate portions of an engine to act upon one airstream or, alternately, to operate on independent airstreams.

Noise and wake structure measurements in a subsonic tip speed fan

Abstract: The results of an experimental program are reported which show the effect of blade angle, tip speed, fan pressure ratio, and thrust on noise of a model fan of 0.457m (18 inches) diameter operating at subsonic tip speeds at pressure ratios between 1.06 and 1.15. The fan used in this study had 12 blades, 7 stator vanes, and a spacing between the rotor and stator of 1.85 blade chords. This fan was originally designed for aerodynamic testing and was considered a good performer. It was used in the noise test program as it incorporated features found to reduce noise in an earlier analytical parametric study. For a given pressure ratio the fan was shown to exhibit minimum noise at the blade angle and tip speed near that of maximum aerodynamic efficiency. Also, the noise level and spectrum character of this fan showed excellent correlation with scaled data of a similar larger diameter fan. Results of the program confirm the trends shown in the earlier analytical parametric study which showed that fan noise could be reduced for a given thrust and pressure ratio by increasing fan solidity, improving fan aerodynamic design, and operating the fan at an optimum subsonic tip speed. In addition to noise, the blade wake characteristics at the leading edge of the stator were measured in this program. At root and tip sections some difference between predicted and measured wakes was found. However comparisons between predicted and measured wakes at mid span locations was found to be good.

Geared Fan Engine Systems-Their Advantages and Potential Reliability

Abstract: Studies indicate that a reduction in aircraft noise is attainable through the use of high-bypassratio, low-fan-tip-speed turbofan propulsors. The weight and installation penalties associated with high-bypass-ratio, direct-drive engines could be reduced significantly by incorporating a small, high-speed turbine to drive the fan through a reduction gear system that is designed to current criteria as represented by the Allison T56 reduction gear planetary system. Operational experience with the T56 reduction gear indicates that the addition of a geared fan drive system will not compromise engine reliability.

Potential payoffs of variable geometry engines in fighter aircraft.

Abstract: The design and control characteristics of military aircraft engines are generally established to perform a specific design mission. For any such mission, there is one engine type which will produce the thrust levels and mission fuel requirements which minimize aircraft size. No single engine type can, however, optimally perform all missions. Variable geometry can improve engine performance at specific operating conditions. For missions which require significant operation at those operating conditions, variable geometry engines can be superior to fixed geometry designs. Using multitechnology computer techniques, aircraft sizing studies compared two advanced, fixed-geometry augmented engines (a turbojet and a turbofan), and an advanced, variable-geometry turbine, augmented turbojet. Sensitivities in takeoff gross weight are compared for a number of mission and aircraft performance elements. Results of the application of variable geometry engines to the various mission roles are summarized.

Acoustic characteristics of a large-scale wind tunnel model of an upper-surface blown flap transport having two engines

Abstract: The upper-surface blown (USB) flap as a powered-lift concept has evolved because of the potential acoustic shielding provided when turbofan engines are installed on a wing upper surface. The results from a wind tunnel investigation of a large-scale USB model powered by two JT15D-1 turbofan engines are-presented. The effects of coanda flap extent and deflection, forward speed, and exhaust nozzle configuration were investigated. To determine the wing shielding the acoustics of a single engine nacelle removed from the model were also measured. Effective shielding occurred in the aft underwing quadrant. In the forward quadrant the shielding of the high frequency noise was counteracted by an increase in the lower frequency wing-exhaust interaction noise. The fuselage provided shielding of the opposite engine noise such that the difference between single and double engine operation was 1.5 PNdB under the wing. The effects of coanda flap deflection and extent, angle of attack, and forward speed were small. Forward speed reduced the perceived noise level (PNL) by reducing the wing-exhaust interaction noise.

QCSEE task 2: Engine and installation preliminary design

Abstract: High-bypass turbofan engines with features required for commercial short haul powered lift transports were designed. Two engines were configured for each of the externally blown flap installations, under-the-wing and over-the-wing. Estimates of installed and uninstalled performance, noise, and weight were defined for each propulsion system.

An Altitude Test Facility for Large Turbofan Engines

Abstract: The altitude test facility at NGTE has been progressively developed over many years and now includes a test cell capable of testing large turbofan engines over a wide range of simulated flight conditions. The cell enables measurements to be made during rapid engine transients as well as at steady state conditions. Icing, freezing fog and tropical rain conditions can also be simulated. The cell is described and its basic test capability outlined. The methods used to measure the main engine performance parameters and the techniques for calibrating the measurement systems and defining their degrees of precision are described.

Wind tunnel tests of a 20 inch diameter 1.15 pressure ratio fan engine model

Abstract: Aerodynamic and acoustic measurements at a typical STOL aircraft takeoff and landing velocity demonstrated that a 1.35 inlet lip area contraction ratio was superior to a 1.26 ratio at high nacelle incidence angles. Reverse thrust, obtained with a variable pitch rotor, was lower at the landing velocity, and the noise level higher, than at the static condition. High speed tests showed that, for the design cruise Mach number of 0.75, internal losses and external drag were 27 percent of the ideal fan net thrust, and propulsive efficiency was estimated to be 59 percent for an 85 percent efficient fan stage.

The results of low-speed wind tunnel tests to investigate the effects of the NASA refan JT8D engine nacelles on the stability and control characteristics of the Boeing 727-200

Abstract: The results from two low-speed wind tunnel tests of the Boeing 727-200 airplane as configured with the NASA refan JT8D-109 turbofan engines are presented. The objective of these tests was to determine the effects of the refan installation on the low-speed stability and control characteristics of the 727 airplane. Four side nacelle locations were tested to insure that aerodynamic interactions of the nacelles and empennage would be optimized. The optimum location was judged to be the same as that of the production JT8D-9 engines; the current production engine mounts can be used for this location. Some small changes in the basic airplane characteristics are attributable to the refan nacelles. The flaps up longitudinal and lateral-directional stability are both slightly increased for low angles of attack and sideslip respectively. The longitudinal stability at stall is improved for both the flaps up and landing flap configurations. The high attitude characteristics of the basic airplane are not significantly altered by the refan nacelle installation. Directional control capability is not affected by the refan nacelles.

Application of finite difference techniques to noise propagation in jet engine ducts

Abstract: A finite difference formulation is presented for wave propagation in a rectangular two-dimensional duct without steady flow. The difference technique, which should be used in the study of acoustically treated inlet and exhausts ducts used in turbofan engines, can readily handle acoustical flow field complications such as axial variations in wall impedance and cross-section area. In the numerical analysis, the continuous acoustic field is lumped into a series of grid points in which the pressure and velocity at each grid point are separated into real and imaginary terms. An example calculation is also presented for the sound attenuation in a two-dimensional straight soft-walled suppressor.

The Influence of Engine Technology Advancements on Aircraft Economics

Abstract: A technology advancement in a new powerplant has both favorable and unfavorable effects. Increased bypass ratio and compression ratio, coupled with high turbine temperatures, improve performance but also increase engine price and maintenance cost. The factors that should be evaluated in choosing an engine for airline use are discussed. These factors are compared for two engines that might be considered for future 150 to 200 passenger airplanes: an all-new turbofan and a quiet derivative of an existing first generation turbofan. The results of the performance and cost evaluations of the example engines are reduced to common units so they can be combined.

Experimental Study of the Effect of Subsonic Exhaust Gas Diffusers on the Test Cell Wall and TF39 Cold-Flow Model Engine Exhaust Nozzle Plug and Core Engine Cowl Surface Pressures

Abstract: : An experimental investigation was conducted to determine the effects of exhaust gas collectors/subsonic diffusers on engine and test cell surface pressures during tests of high-bypass-ratio front-fan engines in ground test facilities. A one-tenth scale model of a TF39 turbofan engine installed in a one-tenth scale model of Propulsion Development Test Cell (J-1) was employed. Engine cowl and plug surface pressure data were recorded during model engine operation with cold air at five simulated power settings without exhaust collector, with exhaust collector, with exhaust collector equipped with a conventional subsonic diffuser, and with exhaust collector equipped with a segmented subsonic diffuser which separately diffused the fan and core engine exhaust jets.

Influence of Variable Turbine Geometry on Engine Installation Losses and Cycle Selection

Abstract: : The trend in military aircraft is toward increasing thrust loading for improved maneuverability coupled with a requirement for extended subsonic cruise range at low power settings. Conventional turbine engines designed to meet these requirements must operate over large ranges of airflow between maximum power and cruise. As a result, the inlets and nozzles designed for these engines cannot perform efficiently with the low airflow rates typical of subsonic cruise operation. Variable turbine geometry, however, offers a promising approach for obtaining both high thrust loading and efficient cruise performance by permitting large amounts of thrust modulation at constant airflow rates. As an example, the performance of a turbojet engine, which provides efficient high-thrust maneuvering and supersonic operation, can be improved by variable turbine geometry to the point where it is competitive with a fixed- turbine-geometry turbofan engine in the low-thrust subsonic cruise regime.

Multimission Aircraft Propulsion Simulator Initial Aero/Mechanical Test Results and Evaluation.

Abstract: : Initial aero/mechanical tests of the Multi-Mission Aircraft Propulsion Simulator were conducted in the AEDC R2C4 Test Cell of the engine test facility. A total of 38.1 hours of successful operation was completed. The simulator is designed with a compressor, turbine and mixer which result in the capability of simultaneously simulating scaled inlet airflow, nozzle pressure ratio and nozzle flow function which significantly improves scale model simulation. The simulator utilizes mass addition through a mixer from the spent turbine drive air to simulate heat addition. The physical size of the simulator represents a scale of from 6-10% of various aircraft engines thus, establishing the scale for installed performance aircraft models to be tested in wind tunnels. Aerodynamic and mechanical data obtained in this test included compressor and turbine mapping for compressor inlet pressures of 14.2, 12, and 6 psia. Also, one 180 deg. extent 1/rev distortion screen was tested where IDC ranged from 0.02 to .09. An analytical model has been developed to represent the simulator and a modification guide is included which gives procedures for modifying the mixer/nozzle to simulate other aircraft propulsion systems. Examples of typical aircraft engines which were simulated are included. Comprehensive mechanical data analysis and recommended follow-on development is included. (Author)