General Electric (Sweden)

The consumption of engine life characterized by low EGT margin, expended life-limited parts, and slow engine accelerations is the principal cause of aircraft engine removal. Life extending control results from a conscious effort on the part of control system designers to extend the life of an engine by modifying the control logic or control hardware to influence one or more of these life-consuming factors. General Electric Aircraft Engines and NASA Glenn Research Center are currently engaged in a collaborative research programme to investigate control technologies applicable to extending on-wing life of aircraft engines. A trade study of potential schemes that may have a positive impact on engine life has been performed, and the results of this study are used to narrow the focus of further research under this programme.

A unified robust multivariable approach to propulsion control design has been developed at NASA Glenn Research Center. The critical elements of this unified approach are: a robust H/sub /spl infin// control synthesis formulation; a simplified controller scheduling scheme; and a new approach to the synthesis of integrator windup protection gains for multivariable controllers. This paper presents results from an application of these technologies to control design for linear models of an advanced turbofan engine. The objectives of the study were to transfer technology to industry and to identify areas of further development for the technology. The technology elements and industrial development of tools to implement the steps are described with respect to their application to a GE variable-cycle turbofan engine. A set of three-input/three-output three-state linear engine models was used over a range of power levels covering engine operation from idle to maximum unaugmented power. Results from simulation evaluation are discussed and insight is provided into how the design parameter choices affect the results.

The quality of laser-drilled holes is significantly influenced by the laser peak power, pulse format, and wavelength. Three advanced materials are used to demonstrate the importance of choosing the correct laser parameters for a specific material. The materials are: (1) intermetallic single crystal nickel aluminide (NiAl) alloy; (2) N5, a single crystal nickel-based superalloy; and (3) a silicon carbide (SiC) ceramic matrix composite (CMC). The laser peak power is varied in terms of the pulse duration and format. For low peak powers, long pulse format (pulse lengths on the order of ms), conventional and also shaped-pulse (burst) commercial rod Nd:YAG laser systems were used. For high peak powers, a short pulse format was adopted for the laser used, namely a cw-pumped Q-switched or modelocked/Q-switched Nd:YAG oscillator followed by a cw-pumped multipass amplifier using a face-pumped, total internal reflection Nd:YAG slab as the gain medium. Finally, a KrF excimer laser operating at a 248 nm wavelength was used. The excimer wavelength was chosen to be close to the Nd:YAG fourth harmonic.

An innovative inlet total pressure distortion measurement rake has been designed and developed for the F/A-18 A/B/C/D aircraft inlet. The design was conceived by NASA and General Electric Aircraft Engines personnel. This rake has been flight qualified and flown in the F/A-18 High Alpha Research Vehicle at NASA Dryden Flight Research Center, Edwards, California. The eight-legged, one-piece, wagon wheel design of the rake was developed at a reduced cost and offered reduced installation time compared to traditional designs. The rake features 40 dual-measurement ports for low- and high-frequency pressure measurements with the high-frequency transducer mounted at the port. This high-frequency transducer offers direct absolute pressure measurements from low to high frequencies of interest, thereby allowing the rake to be used during highly dynamic aircraft maneuvers. Outstanding structural characteristics are inherent to the design through its construction and use of lightweight materials.

An analytical model is developed for predicting the onset of supersonic stall bending flutter in axial flow compressors. The analysis is based on a modified two dimensional, compressible, unsteady actuator disk theory. It is applied to a rotor blade row by considering a cascade of airfoils whose geometry and dynamic response coincide with those of a rotor blade element at 85 percent of the span height (measured from the hub). The rotor blades are assumed to be unshrouded (i.e., free standing) and to vibrate in their first flexural mode. The effects of shock waves and flow separation are included in the model through quasi-steady, empirical, rotor total-pressure-loss and deviation-angle correlations. The actuator disk model predicts the unsteady aerodynamic force acting on the cascade blading as a function of the steady flow field entering the cascade and the geometry and dynamic response of the cascade. Calculations show that the present model predicts the existence of a bending flutter mode at supersonic inlet Mach numbers. This flutter mode is suppressed by increasing the reduced frequency of the system or by reducing the steady state aerodynamic loading on the cascade. The validity of the model for predicting flutter is demonstrated by correlating the measured flutter boundary of a high speed fan stage with its predicted boundary. This correlation uses a level of damping for the blade row (i.e., the log decrement of the rotor system) that is estimated from the experimental flutter data. The predicted flutter boundary is shown to be in good agreement with the measured boundary.

The laser‐flash technique for thermal diffusivity determinations was modified to handle thicker samples (up to 1.3 cm). The modification consisted of substituting an ir source for the laser and using step heating. Thus measurements can be made on representative samples of large‐grained heterogeneous materials. Experimental measurements were made on a carbon magnesite brick, and the concept was verified using finite‐element models.

We have previously described the drilling of advanced materials such as intermetallics, superalloys, and composites using an Nd:YAG laser operating at the fundamental wavelength of 1.064 μm [1]. We have now extended these studies to the second harmonic wavelength of 532 nm of a high peak power Nd:YAG laser. The results show that drilling using the shorter wavelength further reduces undesired thermal effects such as recast layers and heat affected zones. A comparison of these results with those obtained at the fundamental wavelength is reported.

A high integrity dual alloy disk (DAD) process was demonstrated under Navy contract funding (NOO140-89-C-WC14).

<div class="htmlview paragraph">The measurement of the smoking characteristics of jet engines and jet engine components is necessary to evaluate the relative merits of proposed methods of smoke reduction, identify sources, and estimate the visibility of the exhaust plume. Several techniques have been employed by the General Electric Co. to collect data over a wide range of environment.</div> <div class="htmlview paragraph">Techniques evaluated included optical systems, quantitative gravimetric system, and soiled tape methods. Many of the soiled tape methods of measuring smoke are compared, and a calculation procedure is described for making a direct comparison of any two soiled tape methods.</div> <div class="htmlview paragraph">The soiled tape method used by General Electric to measure jet engine smoke is described in detail. The measurement system utilizes a GE spot meter which filters the smoke through Whatman paper and produces a smoke number that is based upon the diffuse reflection from the filtrate produced by filtering 0.3 cu ft of smoke through a square inch of filter paper.</div>

The vapor pressure of liquid sodium sulfate in the range 954 to 1204 C (1750 to 2200 F) has been measured by the transpiration method in air. The results are much lower than those extrapolated into this temperature range from previously published results but are believed considerably more reliable on the basis of excellent conformance to Trouton's rule. The results are expressed by the equation: 1n Pmm=20.54(±1.27)−36540(±1760)/T°K

A stress intensity factor solution for a surface crack in a finite solid subjected to an arbitrary stress field is presented. The solution was developed based on the superposition principle, the weight function technique, and a referenced finite body correction factor. An additional surface factor is identified when the solution is applied to the reduction of data from tests on surface flaw specimens. Verification of the solution is first made by comparison with published results for problems with non-uniform stresses. The examples include a surface crack under pure bending load and a corner crack at a circular hole. Another assessment was achieved by verifying the solution against the test results of ASTM round-robin test data for cracked fastener holes. Good correlation was obtained on all aspects of experimental observations such as the backtracked stress intensity factors, the measured residual lives, and the observed variation in crack aspect ratio. It has been further demonstrated, from Air Force supported test programs, that the solution is accurate in predicting crack propagation behavior and residual life for subcomponent specimens under complex loadings. The test specimens are made of four different superalloys in various shapes of geometric discontinuities. The test conditions include various combinations of temperature, stress level, mean stress, and cycle profiles. The results have shown that the great majority of the measured life/predicted life ratios are within a factor of 1.5. It has also been demonstrated that the capability of the methodology is independent of the stress levels, specimen types, materials, and cycle profiles used in the study.

GE Aircraft Engines (GEAE) has worked with various vendors since 1992 to develop laser shock processing (LSP). GEAE launched production on the stage one fan blades for the F101 / B1 Bomber and F110/F16 Falcon engines in 1996 and has, with the US Air Force, nearly completely retrofitted the USAF fleet. Initial applications were driven by critical performance and flight safety issues. The laser equipment was expensive to procure and maintain and required a highly skilled maintenance staff for daily setup and process maintenance. GEAE launched a three year program to investigate alternative laser technologies in order to robust the equipment and enable the use of commercially available laser technologies. The result is the fourth generation laser system. The fourth generation laser system has enabled GEAE to apply LSP to smaller, inexpensive aircraft engine components such as compressor airfoils. With minimal added cost, GEAE is able to apply LSP to compressor airfoils and double the permissible damage allowable before an engine requires repair. This paper will discuss the development of the fourth generation laser and the application to thin compressor airfoils along with other opportunities for cost effective laser shock processing.

We previously described drilling of advanced materials (intermetallics, superalloys, and composites) at the Nd:YAG laser fundamental wavelength and the excimer laser ultraviolet wavelength [ICALEO’95]. We now report further studies at the second harmonic wavelength of a high peak power Nd:YAG laser. The results show that drilling at the shorter wavelength further reduced the undesired thermal effects such as recast layers and heat affected zones (HAZ). A comparison is made with the previous results at the fundamental wavelength.

By the mid-eighties, GE Corporate Research and Development (CRD) had successfully designed high brightness slab geometry lasers for military applications. A subsequent chain of events led to GE Aircraft Engines (GEAE) support of CRD development of an industrial quality slab or face pumped laser (FPL) system. The goal was a 500 Watt Nd:YAG laser system with brightness exceeding conventional rod laser systems. The system was to operate at commercial rod drilling laser parameters, eg. millisecond pulse durations, tens of joules per pulse, repetition rates up to 40 Hertz and beyond.

True rejuvenation of fatigue damaged material is not practiced in the aerospace power plant industry. Lack of knowledge on fatigue damage accumulation and lack of confidence in restoration processing have been the major barriers to its use. However, repair of fatigue damaged hardware is practiced widely in engine overhaul shops. Effectively, the three prime methods of: (1) removal of distressed metal, (2) replacement of the distressed area, or (3) repair welding can restore components to original condition. The unique ways in which these three methods are applied in jet engine overhaul are reviewed in sufficient detail to provide an appreciation of the techniques and provide information as to how they may be extended to other structures that sustain fatigue damage.

US critical infrastructure is increasingly the target of cyberattacks, where disturbances could cause considerable damage and disruption. To help provide a new layer of cyber-physical protection for one key energy delivery system, natural gas pipelines, GE Vernova Advanced Research along with partners Florida State University and Intel Corporation created an innovative technology called "Resilient Energy Delivery and Control Systems" (REDCS). This cybersecurity package helps detect anomalies caused by cyberattacks, isolate the subsystem being impacted by the attack, and provide functions that can allow for resiliency – giving better situational awareness to the operators and cybersecurity specialists or in the future perform closed loop control for continued operation while compromised.

When using a laser process for the creation of holes to be used in film cooling applications, the mass flow rate is a critical factor in judging hole quality. In the present study, an experimental investigation was undertaken to identify the importance of laser drilling process parameters on the hole airflow. The total mass flow rate through a hole is a function of the aerodynamic losses resulting from both frictional effects and geometric features of the hole inlet and exit. Optimum aerodynamic performance depends upon the proper selection of laser drilling process parameters. Using a four parameter, two level test matrix, process boundaries were examined. These parameters included laser power, laser beam focus, laser beam aperture, and workpiece thickness. Laser beam focus was determined to be the most effective individual parameter, followed by workpiece thickness. Laser beam aperture was the least effective parameter. Interactions between laser beam focus, workpiece thickness, and laser power were found to produce the largest change in the hole flow rate. Flow rate variations among three sample sets were also significant.

Abstract A computer simulation study was conducted to investigate modifications of a current test plan for evaluating rolling contact fatigue life of experimental materials, so as to improve the use of testing resources and to produce more reliable data. The simulations revealed that a slight modification of the test plan, using available test rigs, could result in greater precision with fewer tests and a shorter average test duration.