Showing papers on "Turbofan published in 1984"

Fuel savings potential of the NASA Advanced Turboprop Program

Abstract: The NASA Advanced Turboprop (ATP) Program is directed at developing new technology for highly loaded, multibladed propellers for use at Mach 0.65 to 0.85 and at altitudes compatible with the air transport system requirements. Advanced turboprop engines offer the potential of 15 to 30 percent savings in aircraft block fuel relative to advanced turbofan engines (50 to 60 percent savings over today's turbofan fleet). The concept, propulsive efficiency gains, block fuel savings and other benefits, and the program objectives through a systems approach are described. Current program status and major accomplishments in both single rotation and counter rotation propeller technology are addressed. The overall program from scale model wind tunnel tests to large scale flight tests on testbed aircraft is discussed.

Finite Element-Integral Acoustic Simulation of JT15D Turbofan Engine

Abstract: An iterative finite element integral technique is used to predict the sound field radiated from the JT15D turbofan inlet. The sound field is divided into two regions: the sound field within and near the inlet which is computed using the finite element method and the radiation field beyond the inlet which is calculated using an integral solution technique. The velocity potential formulation of the acoustic wave equation was employed in the program. For some single mode JT15D data, the theory and experiment are in good agreement for the far field radiation pattern as well as suppressor attenuation. Also, the computer program is used to simulate flight effects that cannot be performed on a ground static test stand.

Circulation control technology applied to propulsive high lift systems

Abstract: Technology developed for the Circulation Control Wing high-lift system has been extended to augment lift by entraining and redirecting engine thrust. Ejecting a thin jet sheet tangentially over a small curved deflecting surface adjacent to the slipstream of a turbofan engine causes the slipstream to flow around that deflecting surface. The angle of deflection is controlled pneumatically by varying the momentum of the thin jet sheet. The downward momentum of the slipstream enhances wing lift. This concept of pneumatically deflecting the slipstream has been applied to an upper surface blowing high-lift system and to a thrust deflecting system. The capability of the pneumatic upper surface blowing system was demonstrated in a series of investigations using a wind tunnel model and the NASA Quiet Short-haul Research Aircraft (QSRA). Full-scale thrust deflections greater than 90 deg were achieved. This mechanically simple system can provide increased maneuverability, heavy lift or overload capability, or short takeoff and landing performance.

Tone Generation by Rotor-Downstream Strut Interaction

Abstract: A JT15D fan stage was acoustically tested in the NASA Lewis anechoic chamber as part of the joint Lewis/Langley Research Center investigation of flight simulation techniques and flight effects using the JT15D engine as a common test vehicle. Suspected rotor-downstream support strut interaction was confirmed through the use of simulated support struts, which were tested at three axial rotor-strut spacings. Tests were also per- formed with the struts removed. Inlet boundary layer suction in conjunction with an inflow control device was also explored. The removal of the boundary layer reduced the fan fundamental tone levels, suggesting that the mounting and mating of such a device to the nacelle requires careful attention. With the same inflow control device installed, good acoustic agreement was shown between the engine on an outdoor test stand and the fan in the anechoic chamber. HE development of effective inflow control devices (ICD's) makes it possible to study noise generation mechanisms, such as rotor-stator interaction, with reduced masking effects of inflow disturbances. Modern turbofan engines are often designed with blade/vane numbers selected to prevent propagation of the fundamental rotor-stator in- teraction tone. However, less consideration has been given to possible rotor interactions with engine support struts. These struts are either located downstream of the stator row or are integrated into the stator as large cross-section vanes.! This paper presents results for a JT15D fan stage which was acoustically tested in the NASA Lewis Research Center anechoic chamber2 as part of a joint NASA Lewis/Langley investigation of flight simulation techniques and flight effects using the JT15D-1 engine as a common test vehicle.3"7 The engines used in these studies were instrumented with blade and vane pressure transducers to assist in isolating noise generation mechanisms. Although the primary goal of this study was to evaluate inflow control techniques, the results revealed that for the JT15D-1 engine in particular speed ranges the fundamental tone was controlled by the presence of six engine support struts located downstream of the stator. Blade pressure results showing a strong six per revolution disturbance pointed to these struts as the probable noise source. The interaction between the 28-blade rotor of the JT15D and the six support struts would result in a m-22 acoustic spinning mode having 22 circumferential lobes. This mode was shown to exist in the inlet duct of a JT15D engine when the results from two pressure sensors located in the duct so as to allow spining mode identification by signal phase relationship were used.3 However, it was not possible to alter the support struts in the engine to establish the behavior of this apparent noise source. Downstream support struts were not required for the JT15D fan installation in the anechoic chamber. Six simulated support struts were fabricated and installed in the test fan stage to simulate the actual engine support strut installation. These simulated struts were located at three axial spacings from the stator trailing edge. Thus, in the present study results were obtained for the spacing effect of downstream support struts as well as for fan stage alone with no downstream struts.

HYTESS: A hypothetical turbofan engine simplified simulation

Abstract: A users manual for a hypothetical turbofan engine simplified simulation is presented. This digital simulation exists as FORTRAN source code. The program is self-contained and was developed to offer those interested in engine dynamics and controls research an efficient, realistic, and easily used engine simulation. The engine is modeled using a state space formulation. Matrix elements within the linear state space structure are nonlinear functions of various engine variables.

Multivariable control for the F-100 engine using the LQG/LTR methodology

Abstract: The design of a multivariable feedback control system for the Pratt and Whitney F-100 turbofan jet engine is a challenging task for control engineers. This paper employs a linearized model of the F-100 engine to demonstrate the use of the newly developed Linear Quadratic Gaussian/Loop Transfer Recovery (LQG/LTR) design methodology, which adopts an integrated frequency-domain and time-domain approach to multivariable feedback control synthesis so as to meet stability-robustness, command-following, and disturbance-rejection specifications.

The design and development of a low emissions transply combustor for the civil Spey engine

Abstract: : This paper describes the design and development of a low emissions tubo-annular combustor now entering service in the Spey aero gas turbine engine. The combustors, ten of which form the tubo-annular combustion system, are constructed from an advanced cooling material known as Transply. Use of this pseudo transpiration cooling material enables a significant saving to be made in using the wall cooling air. This air is used in optimising the primary zone and intermediate zone stoichiometry which, combined with an aerodynamic curved vane swirler, results in substantial reduction of emission levels. A number of significant durability problems have been overcome to meet the rigorous demands of aero-engine operation. The paper outlines the development process, starting with the constraints imposed by an existing engine design and describing the rig and engine test programme leading to a full definition of the aero-thermodynamics of the developed combustor.

Effect of combined pressure and temperature distortion orientation on high-bypass-ratio turbofan engine stability

Abstract: Total-temperature, static-pressure and total-pressure distributions were measured in the inlet duct upstream of the engine inlet and within the fan and compressor of a YTF34 turbofan engine. Free-stream and boundary layer yaw angle variations were measured between a rotable screen assembly and the engine inlet. Total pressure distortions were generated using three 180 deg extent screens and total temperature distortions were generated using a rotatable hydrogen burner. Reynolds number index upstream of the rotatable screen assembly was maintained at 0.5 (based on the undistorted sectors at station 1, the inlet flow measuring station). The engine mechanical fan speed at sea level condition was rated at 7005 rpm. The engine was tested at a corrected fan speed of 90 percent of rated condition. Yaw angle increased between the rotatable screen assembly and the engine inlet. The largest variation in free-stream and boundary layer yaw angle occurs when the combined distortions are 180 deg out-of-phase. Static-pressure distortion increased exponentially as flow approached the engine. Total-pressure distortions were attenuated between the engine inlet and the compressor exit. Total-temperature distortion persisted through the compressor for all four combined distortions investigated.

Energy efficient engine program contributions to aircraft fuel conservation

Abstract: Significant advances in high bypass turbofan technologies that enhance fuel efficiency have been demonstrated in the NASA Energy Efficient Engine Program. This highly successful second propulsion element of the NASA Aircraft Energy Efficiency Program included major contract efforts with both General Electric and Pratt & Whitney. Major results of these efforts will be presented including highlights from the NASA/General Electric E3 research turbofan engine test. Direct application of all the E3 technologies could result in fuel savings of over 18% compared to the CF6-50 and JT9D-7. Application of the E3 technologies to new and derivative engines such as the CF6-80C and PW 2037, as well as others, will be discussed. Significant portions of the fuel savings benefit for these new products can be directly related to the E3 technology program. Finally, results of a study looking at far term advanced turbofan engines will be briefly described. The study shows that substantial additional fuel savings over E3 are possible with additional turbofan technology programs.

Measurement and prediction of Energy Efficient Engine noise

Abstract: The NASA/GE Energy Efficient Engine (E3) static noise levels were measured in an acoustic arena on the Integrated Core and Low Spool Test System. These measured levels were scaled to the appropriate size to power four study aircraft and were projected to flight for evaluation of noise levels relative to FAR36, Stage III limits. As a result of these evaluations, it is predicted that the NASA/GE E3 engine with a wide spacing cut-on blade/vane ratio fan and a forced mixer nozzle can meet FAR36 Stage III limits with sufficient design margin.

Test-engine and inlet performance of an aircraft used for investigating flight effects on fan noise

Abstract: As part of the NASA Flight Effects on Fan Noise Program, a Grumman OV-1B Mohawk aircraft was modified to carry a modified and instrumented Pratt & Whitney JT15D-1 turbofan engine. Onboard flight data, together with simultaneously measured farfield acoustic data, comprise a flight data base to which JT15D-1 static and wind-tunnel data are compared. The overall objective is to improve the ability to use ground-based facilities for the prediction of flight inlet radiated noise. This report describes the hardware and presents performance results for the research engine.

Effect of variable inlet guide vanes on the operating characteristics of a tilt nacelle inlet/powered fan model

Abstract: The effects of a variable inlet guide vane (VIGV) assembly on the operating characteristics of a V/STOL inlet and on the performance of a 20-in. (0.508-m) diameter fan engine were investigated. The data indicate that the VIGVs are effective thrust modulators over a wide range of free-stream velocities, nacelle angles of attack, and fan speeds. The thrust modulation ranges, including choking limits, fan stall limits, and inlet separation boundaries are presented. The presence of the VIGV assembly causes significant losses in inlet angle-of-attack capability and generally increases the blade stress levels at all limit conditions except at high angle of attack and high free-stream velocity. Reducing the fan nozzle exit area limited the positive VIGV actuation range and consequently decreased the range of thrust modulation at all limit conditions except at both high free-stream velocity and high angle of attack conditions.

Altitude testing of a flight weight, self-cooled, 2D thrust vectoring exhaust nozzle

Abstract: The Augmented Deflector Exhaust Nozzle (ADEN) was tested in PSL-3 at NASA-Lewis Research Center using an F404 engine. The ADEN is a flight weight Single Expansion Ramp Nozzle with thrust vectoring, an internal cooling system utilizing the available engine fan flow, and a variable area throat controlled by the engine control system. Test conditions included dry and max A/B operation at nozzle pressure ratios from 2.0 to 15.0. High nozzle pressure loading was simulated to verify structural integrity at near maximum design pressure. Nozzle settings covered the full range in throat area and + or - 15 deg deflection angle. Test results demonstrated expected aerodynamic performance, cooling system effectiveness, control system stability, and mechanical integrity.

Study of stator-vane fluctuating pressures in a turbofan engine for static and flight tests

Abstract: As part of a program to study the fan noise generated from turbofan engines, fluctuating surface pressures induced by fan-rotor wakes were measured on core- and bypass-stator outlet guide vanes of a modified JT15D-1 engine. Tests were conducted with the engine operating on an outdoor test stand and in flight. The amplitudes of pressures measured at fan-rotor blade-passage fundamental frequencies were generally higher and appeared less stable for the static tests than for the flight tests. Fluctuating pressures measured at the blade-passage frequency of the high-speed core compressor were interpreted to be acoustic; however, disturbance trace velocities for either the convected rotor wakes or acoustic pressures were difficult to interpret because of the complex environment.

Effects of inlet distortion on a static pressure probe mounted on the engine hub in an F-15 airplane

Abstract: Problems encountered in obtaining good engine face pressure data were studied. A single static measurement located upstream of the engine hub in the stream flow was found to provide a pressure signal suitable for engine control. Two identical probes for measuring fan inlet static (PS2) pressure were designed and mounted on the hub of the left F100-PW-100 turbofan engine installed in the F-15 test aircraft for flight evaluation. The probe is used as a static pressure sensor for a digital engine control system.

Applications of finite element and wave envelope element approximations to turbofan engine noise radiation including flight effects

Abstract: The problem of acoustic radiation from turbofan engine inlets in flow has not lent itself fully to analysis by numerical means because of the large domains and high frequencies involved. The current work has extended the use of finite elements and wave envelope elements, elements which simulate decay and wavelike behaviour in their interpolation functions, from the no-flow case in which they have been proven, to cases incorporating mean flow. By employing an irrotational mean flow assumption, the acoustics problem has been posed in an axisymmetric formulation in terms of acoustic velocity potential, thus minimizing computer solution storage requirements. The results obtained from the numerical procedures agree well with known analytical solutions, static experimental jet engines inflow data, and also with flight test results.

Low frequency noise in a quiet, clean, general aviation turbofan engine

Abstract: A quiet, clean, general aviation, turbofan engine was instrumented to measure the fluctuating pressures in the combustor, turbine exit duct, engine nozzle and the far field. Both a separate flow nozzle and an internal mixer nozzle were tested. The fluctuating pressure data are presented in overall pressure and power levels and in spectral plots. The combustor data are compared to recent theory and found to be in excellent agreement. The results indicate that microphone correction procedures for elevated mean pressures are questionable. Ordinary coherence function analysis suggests the presence of an additional low frequency noise source downstream of the turbine that is due to the turbine itself. Low frequency narrowband data and coherence function analysis are presented.

Studies of convertible turboshaft-turbofan engines for high speed rotorcraft

Abstract: Rotary wing aircraft require auxiliary thrust to fly at speeds higher than current helicopters. One approach is to use the turboshaft engine to drive both the vehicle rotor and a variable geometry fan which allows independent variation of shp and thrust. Various convertible engine configurations including variable pitch fans, variable inlet guide vane fans, and clutched fans are described and their suitability for two types of aircraft is examined. One is a 225 knot U.S. Army combat rotorcraft in which the rotor operates in high-speed flight. The variable inlet guide vane fan with or without a clutch is shown to be a viable approach. The second aircraft is a 400 knot X-wing commercial transport in which the rotor is stopped in flight. The variable inlet guide vane fan and prop/shaft systems are shown to be competitive.

General Aviation Synthesis Program

Abstract: Program performs preliminary design of fixed-wing aircraft. Emphasis placed on fixed wing aircraft with propulsion systems varying from single piston engine with fixed-pitch propeller through twin turbo-prop/turbofan systems used in business or transport aircraft. GASP written in FORTRAN IV.

A solution for aero-acoustic induced vibrations originating in a turbofan engine test cell

Abstract: Simp1 e proof-of-concept, aero-acoustic scale model tests were conducted to identify practical solutions for reducing exhaust jet noise emanating from a General Electric turbofan test facility at Strother, Kansas. The exhaust stack flow characteristics were believed to be responsible for unacceptable vibrations of a lightweight roof of an adjacent building. Scale model configurations of exhaust stack flow modifiers were chosen based both on anticipated aero-acoustic effectiveness and full scale ease of implementation. Several of the test schemes exhibited noise reduction characteristics deemed acceptable. At the low frequencies of interest, reductions of greater than 20 dB in sound pressure levels were measured. Full scale implementation of a scheme that is both aero-acoustically effective and simple in mechanical concept has been carried out at Strother, Kansas. Prel iminary sound pressure 1 evel and resultant building vibration data indicate that a satisfactory solution has been found.

Analysis of the effect on combustor noise measurements of acoustic waves reflected by the turbine and combustor inlet

Abstract: Spectral analyses of static pressure fluctuations measured in turbine engine combustors at low engine speed show good agreement with theory. At idle speed the high pressure turbine is unchoked. Above idle speed the turbine chokes and a significant change in the shape of the measured combustor pressure spectrum is observed. A simplified theoretical model of the acoustic pressure generated in the combustor due to the turbulence-flame front interaction did not account for acoustic waves reflected from the turbine. By retaining this simplified combustion noise source model and adding a partial reflecting plane at the turbine and combustor inlet, a simple theoretical model was developed that reproduces the undulations in the combustor fluctuating pressure spectra. Plots of the theoretical combustor fluctuating pressure spectra are compared to the measured pressure spectra obtained from the CF6-50 turbofan engine over a range of engine operating speeds. The simplified combustion noise theory when modified by a simple turbine reflecting plane adequately accounts for the changes in measured combustor pressure spectra. It is further concluded that the shape of the pressure spectra downstream of the turbine, neglecting noise generated by the turbine itself, will be the combustion noise spectra unchanged except for the level reduction due to the energy blocked by the turbine.

TF34 convertible engine control system design

Abstract: The characteristics of the TF34 convertible engine, capable of producing shaft power, thrust, or a combination of both, is investigated with respect to the control system design, development, bench testing, and the anticipated transient response during engine testing at NASA. The modifications to the prototype standard TF34-GE-400 turbofan, made primarily in the fan section, consist of the variable inlet guide vanes and variable exit guide vanes. The control system was designed using classical frequency domain techniques and was based on the anticipated convertible/VTOL airframe requirements. The engine has been run in the fan mode and in the shaft mode, exhibiting a response of 0.14 second to a 5-percent thrust change.

Experimental Performance Evaluation of Ventilated Mixers- A New Mixer Concept for High-Bypass Turbofan Engines

Abstract: The experimental performance data and analysis from a dual cold/hot flow nozzle test on two ventilated mixer models is presented The test measurements include total axial nozzle thrust, surface static pressures, and rake surveys of total pressure and total temperature taken at the charging station, the mixing plane, and the nozzle exit plane The mixer models were designed and developed using computational techniques A special numerically controlled manufacturing technique was used in fabricating the mixer hardware Ventilation slots through the lobe walls were machined to inhibit separation by energizing the boundary layer in the primary flow The analyses of the test results on ventilated mixers, as compared to the corresponding unventilated mixers, indicate that the ventilation concept results in a significant reduction in total mixer pressure loss, decrease in jet noise, and increase in mixing effectiveness The characteristics of mixer ventilation and its impact on a current technology turbofan engine is also investigated

Flight testing the digital electronic engine control in the F-15 airplane

Abstract: The digital electronic engine control (DEEC) is a full-authority digital engine control developed for the F100-PW-100 turbofan engine which was flight tested on an F-15 aircraft. The DEEC hardware and software throughout the F-15 flight envelope was evaluated. Real-time data reduction and data display systems were implemented. New test techniques and stronger coordination between the propulsion test engineer and pilot were developed which produced efficient use of test time, reduced pilot work load, and greatly improved quality data. The engine pressure ratio (EPR) control mode is demonstrated. It is found that the nonaugmented throttle transients and engine performance are satisfactory.

Energy Efficient Engine: Control system component performance report

Abstract: An Energy Efficient Engine (E3) program was established to develop technology for improving the energy efficiency of future commercial transport aircraft engines. As part of this program, General Electric designed and tested a new engine. The design, fabrication, bench and engine testing of the Full Authority Digital Electronic Control (FADEC) system used for controlling the E3 Demonstrator Engine is described. The system design was based on many of the proven concepts and component designs used on the General Electric family of engines. One significant difference is the use of the FADEC in place of hydromechanical computation currently used.

Computer study of a jet flap ASTVOL 'Harrier'

Abstract: A study of the costs/benefits trade-off was conducted for an Advanced Supersonic Short Takeoff and Vertical Landing (ASTOVL) aircraft incorporating a jet flap. The data used were the theory of jet flaps and high aspect ratio nozzles, experience with a V/STOL aircraft study performed for NASA Ames Research Center in February 1982, and a high performance aircraft-synthesis program (ACSYNT). The methodology was to accurately model the supersonic Harrier V/STOL aircraft design on ACSYNT, and then modify the design by both adding high aspect-ratio nozzles in place of the rear (core-flow) nozzles on the Pegasus-type turbofan engine, and integrating these nozzles on each wing's trailing edge, thus creating a jet flap. The predicted performance advantages (increase in maximum lift coefficient with flap deflection and horizontal thrust recovery) were traded off against the disadvantages (additional weight and thrust loss due to ducting) on two representative missions.

Supersonic STOVL aircraft with turbine bypass/turbo-compressor engines

Abstract: Three propulsion systems for a Mach 2 STOVL fighter were compared. The three propulsion systems are: (1) turbine bypass engine with a turbocompressor used for STOVL only; (2) turbine bypass engine with a turbocompressor for both STOVL and thrust during forward flight; and (3) mixed flow afterburning turbofan with a remote burner lift system. In the first system, the main engines have afterburners and the turbocompressors use after burning during STOVL. In the second system, the turbine bypass engines are dry and the turbocompressors have afterburners. The mission used in the study is a deck launched intercept mission. It is indicated that large improvements in combat time are possible when the turbocompressors are used for both left and thrust for forward flight.