Showing papers on "Turbofan published in 1974"

Cowling arrangement for a turbofan engine

Abstract: A cowling arrangement is provided for a turbofan engine of the variable pitch fan blade type wherein the aft portion of the fan cowling has the ability both to slide axially with respect to the main forward portion, providing an annular intake to increase reverse airflow during reverse pitch fan operation, and to vary radially so as to adjust exit area during normal operation at forward pitch.

Turbofan engine lubrication means

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 blades 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.

HYDES: A generalized hybrid computer program for studying turbojet or turbofan engine dynamics

Abstract: This report describes HYDES, a hybrid computer program capable of simulating one-spool turbojet, two-spool turbojet, or two-spool turbofan engine dynamics. HYDES is also capable of simulating two- or three-stream turbofans with or without mixing of the exhaust streams. The program is intended to reduce the time required for implementing dynamic engine simulations. HYDES was developed for running on the Lewis Research Center's Electronic Associates (EAI) 690 Hybrid Computing System and satisfies the 16384-word core-size and hybrid-interface limits of that machine. The program could be modified for running on other computing systems. The use of HYDES to simulate a single-spool turbojet and a two-spool, two-stream turbofan engine is demonstrated. The form of the required input data is shown and samples of output listings (teletype) and transient plots (x-y plotter) are provided. HYDES is shown to be capable of performing both steady-state design and off-design analyses and transient analyses.

Thrust control apparatus for obtaining maximum thrust reversal in minimum time upon landing of an aircraft

Abstract: The thrust control apparatus of the present invention is employed on an aircraft having a wing and a turbofan engine mounted on a strut extending downwardly and forwardly from the wing. The thrust control apparatus includes (a) a rearwardly opening turbine engine nozzle for directing primary turbine exhaust effluent rearwardly from the engine, (b) a fan and an annular fan duct surrounding the forward portion of the turbine engine, (c) a primary fan air duct being coupled to the annular fan air duct, extending upwardly and rearwardly from the annular fan duct, and terminating in a separate rearwardly opening fan air nozzle for directing the secondary fan effluent rearwardly from the engine, and (d) a first auxiliary duct being coupled to the primary fan air duct, extending upwardly therefrom, and terminating in an upwardly opening auxiliary fan air nozzle for directing fan air flowing through the first auxiliary duct upwardly in front of the aircraft wing. During cruise operation, a valve associated with the coupling between the primary duct and the first auxiliary duct is positioned to close the first auxiliary duct, allowing all of the fan effluent to be exhausted through the fan air nozzle. Upon approach to landing, the valve associated with the coupling of the primary duct and the first auxiliary duct is adjusted to a position where it bifurcates the fan effluent between the primary duct and the first auxiliary duct. At the same time the engine throttle is advanced, calling for the turbofan engine to generate near maximum r.p.m. A plurality of vanes in the first auxiliary nozzle directs the fan effluent flowing through the first auxiliary duct upwardly and rearwardly over the upper airfoil surface of the wing. Upon touchdown of the aircraft on the landing field, the valve associated with the coupling between the primary duct and the first auxiliary duct closes the primary duct diverting the entire flow of fan effluent through the first auxiliary duct. At the same time the plurality of vanes in the first auxiliary nozzle are shifted to direct the fan effluent upwardly and forwardly relative to the engine and the wing, thus reversing the flow direction of the fan effluent and providing a reverse thrust component to brake the aircraft.

Variable pitch turbofan engine and a method for operating same

Abstract: Variable geometry guide vanes are provided in a variable pitch turbofan assembly. A method is disclosed for reducing aerodynamically induced stresses in the variable pitch fan blades as the blades are changed between the forward and reverse pitch modes. The guide vane geometry is scheduled to change in a manner to control the flow into and out of the fan blades in order to establish a favorable aerodynamic environment during the transition between the forward and the reverse pitch modes.

Effects of forward velocity and acoustic treatment on inlet fan noise

Abstract: Flyover and static noise data from several engines are presented that show inlet fan noise measured in flight can be lower than that projected from static tests for some engines. The differences between flight and static measurements appear greatest when the fan fundamental tone due to rotor-stator interaction or to the rotor-alone field is below cutoff. Data from engine and fan tests involving inlet treatment on the walls only are presented that show the attenuation from this treatment is substantially larger than expected from previous theories or flow duct experience. Data showing noise shielding effects due to the location of the engine on the airplane are also presented. These observations suggest that multiringed inlets may not be necessary to achieve the desired noise reduction in many applications.

Engine mounting and boundary layer control fluid supply apparatus

Abstract: A midwing aircraft employs a unique configuration for mounting three high bypass turbofan engines. All three engines are mounted so that a portion thereof projects forwardly of the leading edge of the airfoil on which they are mounted and so that the chordal plane of the airfoil longitudinally bisects the engine. The exhaust from each of the engines is directed by two nozzles. Internal bifurcators split both the turbine exhaust and the fan exhaust from each of the engines evenly between the two nozzles. A pair of channels in each of the wing mounted engines intercepts a portion of the fan effluent and directs it rearwardly into boundary layer control supply plenums in the wing structure. Valve mechanisms for opening and closing the channels are mounted in the forward portions of the channels. Check valves are also provided in each of the channels to prevent backflow of fluid from the supply plenums into the channels. The engines are mounted on the airfoils by a pair of box beams that run along the interior longitudinal sides of each of the engine nacelles. The turbine portion of the turbofan engines is mounted to the inner sides of the box beams at a location forwardly of the leading edge of the airfoils. The box beams can be shrouded to serve as the fluid inlet channels for the fluid supply plenums. The rear portion of the box beams are removably affixed to ribs or flanges extending forwardly from the front main spar of the wing.

Relating Technology to Acquisition Costs: Aircraft Turbine Engines

Abstract: : The quantitative measure presented in the report is derived from a recent Rand study in which a technique was developed for assessing the date at which an aircraft turbine engine with a specified set of technical parameters should pass its 150-hr Model Qualification Test (MQT). The refined aircraft turbine engine TOA model is based on 26 U.S. military turbojet and turbofan engines developed and produced during the past 30 years. The model predicts the man-rated 150-hr MQT date as a function of certain of the engine's performance and design parameters. The parameters include maximum thrust of the engine at sea-level static conditions, weight, specific fuel consumption at military thrust at sea-level static, turbine inlet temperature, and a pressure term (the product of flight envelope maximum dynamic pressure and the overall pressure ratio of the engine). (Modified author abstract)

Low-Speed Aerodynamics of the Upper-Surface Blown Jet Flap

Abstract: Review of the results of recent wind-tunnel investigations conducted to provide fundamental aerodynamic information on the upper-surface blown jet-flap concept incorporating high-bypass-ratio turbofan engines. The results of the investigations have shown the concept to have aerodynamic performance generally comparable to that of other externally blown high-lift systems. Some of the more critical problem areas associated with this concept are covered, and solutions which have been found for these problems are discussed.

Summary of recent investigations of inlet flow distortion effect on engine stability

Abstract: A review is presented of recent experimental results, analytical procedures and test techniques employed to evaluate the effects of inlet flow distortion on the stability characteristics of representative afterburning turbofan and turbojet compression systems. Circumferential distortions of pressure and temperature, separately and in combination are considered. Resulting engine sensitivity measurements are compared with predictions based on simplified parallel compressor models and with several distortion descriptor parameters.

Real-time simulation of the TF30-P-3 turbofan engine using a hybrid computer

Abstract: A real-time, hybrid-computer simulation of the TF30-P-3 turbofan engine was developed. The simulation was primarily analog in nature but used the digital portion of the hybrid computer to perform bivariate function generation associated with the performance of the engine's rotating components. FORTRAN listings and analog patching diagrams are provided. The hybrid simulation was controlled by a digital computer programmed to simulate the engine's standard hydromechanical control. Both steady-state and dynamic data obtained from the digitally controlled engine simulation are presented. Hybrid simulation data are compared with data obtained from a digital simulation provided by the engine manufacturer. The comparisons indicate that the real-time hybrid simulation adequately matches the baseline digital simulation.

Preliminary static tests of a simulated upper-surface blown jet-flap configuration utilizing a full-size turbofan engine

Abstract: The investigation was conducted to evaluate the static turning performance and the pressure and temperature environment of an upper-surface-blown wing and flap utilizing a small turbofan engine. The tests involved modifications of the engine primary nozzle designed to alleviate high temperature problems on the wing and flaps and yet provide acceptable static turning performance over the desired range of flap deflections and thrust conditions.

The Rolls-Royce Rb 211 Turbofan Engine:

Abstract: The lecture gives a technical account of the Rolls-Royce RB 211 42 000 lb thrust turbofan engine now powering the Lockheed TriStar passenger transport.This engine was the result of extensive prelim...

Effects of nonuniform inflow on fan noise

Abstract: A prominant source of turbomachinery noise is due to high‐speed unsteady flows interacting with blades and vanes. In particular, atmospheric turbulence, cross‐wind effects, and the “ground vortex” apparent during most static test conditions can interact with the fan on turbofan engines to produce significant levels of noise. An analysis is presented that models this noise‐generating mechanism and is capable of predicting propagating noise, accepting as input various inlet turbulence structures, temperature fluctuations, and flow distortions. Because of the random uature of most inflow disturbances, a statistical approach was used to develop the model which is a modification and extension of a previous analysis presented by Mani [“Noise Due to Interaction of Inlet Turbulence with Isolated Stators and Rotors,” J.S.V. 19 (1971)]. The analysis shows that the level of fan blade passing tone and harmonics and their relative forward and rearward radiated intensities are critically dependent on both the inlet tur...

Calculation of the longitudinal aerodynamic characteristics of STOL aircraft with externally-blown jet-augmented flaps

Abstract: A theoretical investigation was made to develop methods for predicting the longitudinal aerodynamic characteristics of externally-blown, jet-augmented wing-flap combinations. A potential flow analysis was used to develop two models: a wing-flap lifting surface model and a high-bypass-ratio turbofan engine wake model. Use of these two models in sequence provides for calculation of the wing-flap load distribution including the influence of the engine wake. The method can accommodate multiple engines per wing panel and part-span flaps but is limited to the case where the flow and geometry of the configuration are symmetric about a vertical plane containing the wing root chord. Comparisons of predicted and measured lift and pitching moment on unswept and swept wings with one and two engines per panel and with various flap deflection angles indicate satisfactory prediction of lift and moment for flap deflections up to 30 to 40 degrees. At higher flap angles with and without power, the method begins to overpredict lift, due probably to the appearance of flow separation on the flaps.

Test Results of a VTOL Propulsion Concept Utilizing aTurbofan Powered Augmentor

Abstract: Several questions relevant to the feasibility of achieving successful VTOL flight with thrust augmenting ejector wings are answered by the present experimental study. Tests were performed with a large-scale turbofan powered augmentor that embodied many of the problems encountered in the design of real flight hardware. The apparatus consisted of four separate and parallel ejector channels in each of two wings. Results were compared with data from other laboratory experiments using a single channel ejector of similar geometry. Over-all performance levels of the large multichannel apparatus correlated well with the single-channel results. Minor interactions between the four ejector channels on each wing had no significant effect on the over-all level of thrust augmentation. However, the distribution of thrust was affected and should be considered in future aircraft system designs. Operating as an air pump, the turbofan engine was maintained in its safe operating regime throughout all test configurations. Nomenclature

Investigation of the stall-induced shock wave (hammershock) at the inlet to the engine

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.

NASA/GE quiet engine C acoustic test results

Abstract: The acoustic investigation and evaluation of the C propulsion turbofan engine are discussed. The engine was built as a part of the Quiet Engine Program. The objectives of the program are as follows: (1) to determine the noise levels produced turbofan bypass engines, (2) to demonstrate the technology and innovations which will reduce the production and radiation of noise in turbofan engines, and (3) to acquire experimental acoustic and aerodynamic data for high bypass turbofan engines to provide a better understanding of noise production mechanisms. The goals of the program called for a turbofan engine 15 to 20 PNdB quieter than currently available engines in the same thrust class.

Core engine noise control program. volume iii. prediction methods

Abstract: : Prediction methods for core engine noise were reviewed and either updated or new noise evaluation techniques formulated for low velocity coannular jets, combustors ('core' noise), Low pressure turbines, interaction between turbine tones and fan/core jet streams, obstructions in the flow passages and casing radiation. The development was based, to a large extent, on the analytical investigation and the model, component and engine tests evaluated during Phases 2 and 3 of this program. The results were cast in a general form, so as to be applicable to a wide variety of cycles, including present and future turbofan engines. The prediction methods were validated with measured acoustic data wherever possible.

Some comparisons of the flow characteristics of a turbofan compressor system with and without inlet pressure distortion

Abstract: The measured effects of a circumferential distortion in inlet total pressure on the fan, low, and high compressor of an afterburning turbofan engine are presented and discussed. Extensive inner-stage instrumentation, combined with a unique test technique offered an accurate means of measuring the shifts in flow, performance, and stall mechanisms within the compressor. These effects are compared at one speed to the corresponding effects measured with undistorted inlet flow. The results show the rate at which the distorted flow areas were attenuated and rotated, as well as the change in flow velocities that occurred at various points in the compressor. High response pressure traces indicated the location of stalls including the sequence of dynamic events from the onset and propagation of various stall-recovery events, to compressor surge, to the resulting hammershock.

Generalized dynamic engine simulation techniques for the digital computer

Abstract: Recently advanced simulation techniques have been developed for the digital computer and used as the basis for development of a generalized dynamic engine simulation computer program, called DYNGEN. This computer program can analyze the steady state and dynamic performance of many kinds of aircraft gas turbine engines. Without changes to the basic program, DYNGEN can analyze one- or two-spool turbofan engines. The user must supply appropriate component performance maps and design point information. Examples are presented to illustrate the capabilities of DYNGEN in the steady state and dynamic modes of operation. The analytical techniques used in DYNGEN are briefly discussed, and its accuracy is compared with a comparable simulation using the hybrid computer. The impact of DYNGEN and similar digital programs on future engine simulation philosophy is also discussed.

Forecast of jet engine exhaust emissions for future high altitude commercial aircraft

Abstract: Projected minimum levels of engine exhaust emissions that may be practicably achievable for future commercial aircraft operating at high altitude cruise conditions are presented. The forecasts are based on: (1) current knowledge of emission characteristics of combustors and augmentors; (2) the current status of combustion research in emission reduction technology; and (3) predictable trends in combustion systems and operating conditions as required for projected engine designs that are candidates for advanced subsonic or supersonic commercial aircraft. Results are presented for cruise conditions in terms of an emission index, g pollutant/kg fuel. Two sets of engine exhaust emission predictions are presented: the first, based on an independent NASA study and the second, based on the consensus of an ad hoc committee composed of industry, university, and government representatives. The consensus forecasts are in general agreement with the NASA forecasts.

Cruise performance of an isolated 1.15 pressure ratio turbofan propulsion system simulator at Mach numbers from 0.6 to 0.85

Abstract: An isolated 1.15 pressure ratio turbofan engine simulator was tested at Mach numbers from 0.6 to 0.85. At Mach 0.75 the net propulsive force of the fan and nacelle (excluding core thrust) was 73 percent of the ideal fan net thrust. Internal losses amounted to 7 percent, and external drag amounted to 20 percent of the ideal fan net thrust. External pressure and friction drag were about equal. The propulsive efficiency with a 90 percent efficient fan would have been 63 percent. For the aerodynamic characteristics of the nacelle that was tested, increasing the fan pressure ratio to approximately 1.35 would have resulted in a maximum propulsive efficiency of 67 percent.

Developmental design, fabrication, and test of acoustic suppressors for fans of high bypass turbofan engines

Abstract: An analysis procedure was developed for design of acoustically treated nacelles for high bypass turbofan engines. The plan was applied to the conceptual design of a nacelle for the quiet engine typical of a 707/DC-8 airplane installation. The resultant design was modified to a test nacelle design for the NASA Lewis quiet fan. The acoustic design goal was a 10 db reduction in effective perceived fan noise levels during takoff and approach. Detailed nacelle designs were subsequently developed for both the quiet engine and the quiet fan. The acoustic design goal for each nacelle was 15 db reductions in perceived fan noise levels from the inlet and fan duct. Acoustically treated nacelles were fabricated for the quiet engine and quiet fan for testing. Performance of selected inlet and fan duct lining configurations was experimentally evaluated in a flow duct. Results of the tests show that the linings perform as designed.

Terminal-Shock and Restart Control of a Mach 2.5, Mixed-Compression Inlet Coupled to a Turbofan Engine.

Abstract: Results of an experimental program conducted on a mixed-compression inlet coupled to a turbofan engine are presented. Open-loop frequency response data are presented that show the response of shock position (as measured by an average inlet static pressure) to sinusoidal airflow disturbances produced at the compressor face station. Also presented are results showing the effect of different passive terminations (a choke plate or a long duct) on the characteristics of the inlet. Transfer functions obtained by using experimental data are presented and compared to the experimental data. Closed-loop frequency response of shock position (with a proportional-plus-integral controller) is presented. In addition, transient data are presented that show the unstart-restart characteristics of the inlet.

Digital integrated control of a Mach 2.5 mixed-compression supersonic inlet and an augmented mixed-flow turbofan engine

Abstract: A digitally implemented integrated inlet-engine control system was designed and tested on a mixed-compression, axisymmetric, Mach 25, supersonic inlet with 45 percent internal supersonic area contraction and a TF30-P-3 augmented turbofan engine The control matched engine airflow to available inlet airflow By monitoring inlet terminal shock position and over-board bypass door command, the control adjusted engine speed so that in steady state, the shock would be at the desired location and the overboard bypass doors would be closed During engine-induced transients, such as augmentor light-off and cutoff, the inlet operating point was momentarily changed to a more supercritical point to minimize unstarts The digital control also provided automatic inlet restart A variable inlet throat bleed control, based on throat Mach number, provided additional inlet stability margin