GE Aviation Research Articles

Practice Summary: GE Optimizes for Aircraft Engine Overhaul Scheduling and Shop Assignment

We present an optimization-based decision support system to generate optimal aircraft engine maintenance schedules that reflect qualitative and quantitative trade-offs from customer, business, and shop perspectives. The approach is currently implemented at GE Aviation Services for global overhaul network induction planning for all commercial product lines.

AM for aerospace repair

GE Aviation's facility in Singapore is reportedly the first to offer metal 3D printing for engine component repair. This article discusses the benefits of using the process.

Data Driven Tools and Methods for Microtexture Classification and Dwell Fatigue Life Prediction in Dual Phase Titanium Alloys

Microtexture has been linked to large reductions in cold dwell fatigue (CDF) life of specific dual phase titanium alloy aeroengine components. A recently completed Metals Affordability Initiative (MAI) funded program led by Pratt & Whitney (P&W) and includes ATI Forged Products, Boeing, GE Aviation, Rolls Royce (RR), Arconic, Titanium Metals Corporation (TIMET), PCC-Wyman Gordon (PCC-WG), Scientific Forming Technologies (SFTC), Materials Resources LLC (MRL) and The Ohio State University (OSU) has developed improved techniques for the characterization of microtexured regions (MTR) in titanium billet and forgings, and integrated computational materials engineering (ICME). These methods are aimed at developing and integrating process and property modeling tools for the prediction of microtexture and fatigue life in titanium components. These characterization and fatigue life prediction tools have near-term application off ramps that will enable use for process and product development and quality control. Key results for two widely used alloys, Ti-6242 and Ti-64, will be reviewed in this paper.

Scaled Demonstration of Fluid Insert Noise Reduction for Tactical Fighter Aircraft Engines

This paper summarizes a university-industry cooperative project to develop a new method of noise reduction applicable to tactical fighter aircraft engines. There is an acute need for reduction of the noise produced during takeoff in aircraft carriers. This paper describes the fluid insert noise reduction technology, also referred to as “distributed blowing.” The method involves injection of air through the divergent wall of a converging–diverging nozzle to generate fluid inserts. Substantial noise reductions in small-scale experiments have been achieved for mixing noise in the maximum noise emission direction and in broadband shock-associated noise. This paper describes the extension of the methodology to moderate-scale experiments conducted in industry. Changes to the original small-scale design for use in the industry-scale model experiments are described. The experiments were conducted in the GE Aviation Cell 41 Laboratory, and noise reductions were achieved that were very similar to those obtained in the small-scale experiments. Changes to the operating parameters produced noise reductions that in some cases exceeded comparable small-scale results. Scaling the moderate-scale experiments to a full-scale aircraft produces reductions in the A-weighted spectral peak that exceed 7 dB in the direction of maximum noise emission.

Future proofing

GE Aviation has upgraded its testing facilities to deal with the challenges of next-generation engine development

Integration and evaluation of aircraft power plant production and operational data

The paper focuses on identification of the limits of data collection based on data analyses in GE Aviation Czech, Ltd. to improve current system for data collection pertaining non-conforming products which are collected during the process of the product reconciliation. The paper contains a description of non-conformity product, data collection as well as their analysis and evaluation. Paper describes development of conceptual model of data integration about non-conformity products regarding aircraft power plant production and operation data, by the means of UFO upper level ontology. It shows the importance for building a system for collecting and evaluating data about non-conformity products in GE Aviation Czech, Ltd.

Praxair Surface Technologies & GE Aviation Collaborate for the Development of Specialized Coatings

Praxair Surface Technologies & GE Aviation Collaborate for the Development of Specialized Coatings

Progress in Additive Manufacturing

Additive manufacturing (AM) is among the fastest growing and most talked about manufacturing technologies on the planet. It is providing diverse opportunities for new product design and manufacturing. At GE, efforts such as the additively produced LEAP engine fuel nozzle and low-pressure turbine blade manufacturing are examples of how GE Aviation is leveraging these technologies in innovative ways. These are just a few illustrations of how AM is changing the manufacturing landscape and many others are described in the articles that follow. This rapid growth and investment poses several questions for the minerals, metals, and materials community: What exactly is ‘‘additive manufacturing?’’ Why has it captured the manufacturing industry imagination? How can the TMS community of materials and process technologists and leaders contribute to its growth and implementation? At its core, AM is a suite of technologies that ‘‘build’’ components using digital model data. The ASTM Committee F42 on AM Technologies has defined seven different process routes as being part of the field of AM. Each process has its own unique benefits and challenges that derive from the thermal and chemical processing cycle and the resulting microstructure. Any discussion of the technology needs to take into account the details of the resulting materials microstructure, surface roughness, and ability to maintain engineering tolerances, as well as implementation details about reliability and cost, and potential supply chain issues. The industrial excitement around this suite of processes is being driven by its capacity for empowering designers to focus on designing components for functionality rather than limitations of conventional processes such as casting, brazing, or forming processes. Furthermore, it is now enabling a whole new paradigm of rapid testing and product introduction wherein functional metal prototypes can be used for testing of individual components and manufacturing assembly processes (e.g., joining, forming, or machining). Using AM means product development cycles do not have to rely on traditional methods for manufacturing metallic prototypes, which can take months to produce. This leads to the key question: How can the minerals, metals, and materials community contribute to responsible, accelerated growth given the context of where the field is today? The key to industrial implementation for manufacturing technologies is a thorough understanding of the synergistic interaction of materials and processes. For AM, there are currently only a handful of materials and processes that are well understood, such as the previously mentioned laser powder-bed fusion of cobalt chrome and electron beam powder-bed fusion of titanium aluminide. To realize the full potential of AM, further maturation of the processing-structure-properties linkages will be required in a broader set of metal alloys and for many more processing approaches. When that happens, AM adoption will accelerate as industrial designers become empowered to select tailored material and process combinations that drive performance improvement for demanding applications. This special topic, Progress in AM, strives to meet that challenge by presenting a collection of articles that cover a broad spectrum of material systems and AM processing approaches including original research topics and application reviews. To download any of the articles, follow the URL: http://link.spring er.com/journal/11837/67/3/page/1 to the table of contents page for the March 2015 issue (Vol. 67, No. 3). In ‘‘Metallurgical and Mechanical Evaluation of 4340 Steel Produced by Direct Metal Laser Sintering,’’ by Elias Jelis, Matthew Clemente, Stacey Kerwien, Nuggehalli M. Ravindra, and Michael R. Hespos, the authors present new work on the Edward D. Herderick is the guest editor for the Process Technology and Modeling Committee of the TMS Materials Processing & Manufacturing Division, and coordinator of the topic Progress in Additive Manufacturing in this issue. JOM, Vol. 67, No. 3, 2015

Silver Thick Film Based Insulated Metal Substrates for High Temperature Power Applications

Thick film technology is normally applied to ceramic substrates such as Al2O3 and AlN, where conductor thicknesses for Au and Ag-Pd based thick film materials are <20μm for signal processing. For power devices applications, thicker deposits are required to increase the current carrying capacity and thick print Cu and Ag materials have been developed for ceramic substrates. For power applications, this technology still requires attachment of the ceramic substrate to a heat sink, that may be made of aluminium or copper, which needs a thermal interface material. In printed circuit board technology, insulated metal substrates have been developed for power module assembly to eliminate the thermal interface material, where the copper conductor circuit is attached and isolated from the integral heatsink, through an organic based dielectric based on epoxy adhesive material. The organic based material limits the operating temperature of the substrate to around 175°C. This paper covers the development of a thick film based approach to producing insulated metal substrates that can operate at higher temperatures than an organic based dielectric system. Thick film dielectric materials have been developed for direct deposition onto aluminium substrates with firing temperatures of around 500°C, combined with a silver based thick film material, which is used as the conductor to the power devices. SiC die attach to the silver based thick film material has been evaluated using a silver sinter die attach material which provides a mono-metallic die attach system. Samples have been temperature cycled from −40°C to +250°C for over 100 cycles without deterioration and the results are compared with Cu/Si3N4 substrates, which have shown issues with cracking and delamination for the equivalent thermal cycling regime. This work has been carried out under the Innovate UK supported project HITEC, led by Prodrive and involving the University of Warwick, Ricardo, TT Electronics - Semelab, GE Aviation Systems – Newmarket, Diamond Hard Surfaces and GaN Systems.

Assessment of MEMS Vibration Energy Harvesting for High Temperature Sensing Applications

Distributed electronics for improving the accuracy of sensing in harsh high temperature environments, such as aero-engine and down-well is a growing field, where reduced power input requirements in cabling and batteries is viewed a key enabler for accelerating the adoption of high temperature electronics. Although batteries are available that can operate up to 200°C, they offer limited life at high temperatures and are bulky, increasing the costs of deployment and maintenance. Cabling also adds weight and takes up space in limited access applications. Energy harvesting in-situ offers the opportunity to make a step change in the design of high temperature electronics modules and in expanding their possible range of applications; for example, in sensor systems for combustor and turbine monitoring in aero-engines. This paper covers an assessment of MEMS vibration energy harvesting technology for high temperature sensing applications. MEMS devices based on the principle of parametric resonance, using AlN on Silicon have been designed and fabricated, along with sourcing of high temperature components for rectification, impedance matching and energy storage. The MEMS devices have been packaged into ceramic chip carriers and measured for energy output from a random vibration profile representative of an aerospace application. The measured output from the MEMS vibration energy harvester is capable of providing sufficient power to be of interest for autonomous sensing applications. This paper reports on the performance of the MEMS vibration energy harvesting devices and their associated circuitry at room temperature and at temperatures of up to 150°C. The challenges remaining to develop robust energy harvesting devices that could be applied in aero-engine, down-well and other high temperature applications are described. This work has been carried out under the Innovate UK supported project HI-VIBE, in a collaboration between GE Aviation Systems – Newmarket and the University of Cambridge.

Performance and Reliability of SiC dies, Die attach and Substrates for High Temperature Power Applications up to 300°C

The recent commercial availability of silicon carbide power semiconductor devices are theoretically capable of operating at temperatures well beyond the limits of silicon devices and have generated an interest in developing high temperature capable packaging solutions to match. In this work, the performance and reliability of a number of commercially available silicon carbide power MOSFET dies from multiple vendors was determined for die temperatures up to 350°C. Although these results have demonstrated a number of aging effects and very high on-state resistances at high temperatures, it appears that these devices can perform reliably even in air atmospheres for 100 hours or more at 350°C. In addition, commercially available DBC type ceramic-based substrates have been evaluated for their thermal cycling performance and candidate high temperature capable die attach materials including silver sinter paste and tin and gold-tin pre-form based transient liquid phase types have also been evaluated. These results have demonstrated that the active metal brazed substrates, both copper and aluminium variants, in conjunction with the silicon carbide dies and silver sinter die attach may serve as the basis for high temperature power modules, and may be operated reliably in thermal cycled applications and in air atmospheres up to 300°C. Due to large threshold voltage shift of the SiC MOSFETs at these temperatures, it may be necessary to implement a negative gate bias capability. This work has been carried out under the Innovate UK supported project HITEC, led by Prodrive and also including The University of Warwick, GE Aviation Systems, Ricardo, TT Electronics Semelab, Diamond Hard Surfaces and GaN Systems.

Dynamic Response of a Metal and a CMC Turbine Blade During a Controlled Rub Event Using a Segmented Shroud

Ceramic matrix composites (CMCs) provide several benefits over metal blades including weight and increased temperature capability, and have the potential for increased engine performance by reduction of the cooling flow bled from the compressor and by allowing engines to run at higher turbine inlet temperatures. These CMC blades must be capable of surviving fatigue (high cycle and low cycle), creep, impact, and any tip rub events due to the engine missions or maneuvers that temporarily close blade tip/shroud clearances. As part of a cooperative research program between GE Aviation and the Ohio State University Gas Turbine Laboratory, OSU GTL, the response of a CMC stage 1 low-pressure turbine blade has been compared with the response of an equivalent metal turbine blade using the OSU GTL large spin-pit facility (LSPF) as the test vehicle. Load cells mounted on the casing wall, strain gages mounted on the airfoils, and other instrumentation are used to assess blade tip rub interactions with a 120-deg sector of a representative turbine stationary casing. The intent of this paper is to present the dynamic response of both the CMC and the metal blades with the turbine disk operating at design speed and with representative incursion rates and depths. Casing wear and blade tip wear are both characterized for several types of rub conditions including a light, medium, and heavy rub at room temperature. For each condition, the rub primary dynamic modes have been evaluated, and the corresponding blade tip loads have been calculated. The preliminary results suggest that a CMC blade has similar abilities to a metal blade during a rub event.

Process Compensated Resonance Testing: Whole Body Surface NDT for Ceramic Balls

Process Compensated Resonance Testing (PCRT) is a non-destructive evaluation method for ceramic balls using measured resonance frequencies of parts to detect surface and internal flaws. It offers fast, accurate and affordable defect detection for ceramic rolling elements for hybrid bearings. PCRT has demonstrated capabilities for bulk property/internal defect detection, process monitoring, material property characterization, and surface defect detection. In co-inspection comparison, PCRT demonstrated superior defect detection and/or throughput versus visual, FPI (Fluorescent Penetrant Inspection) and UT (Ultrasonic Testing). Vibrant’s automated ball testing system tests more than 75 balls per hour with no ball-to-ball contact. This research is funded in part by the US Navy and AFRL (Airforce Research Laboratory) with support of Vibrant’s Industrial partners at Honeywell, Rolls-Royce Corporation, GE Aviation, Winsted Precision Ball and Barden Precision Bearing.

Avian Avoidance and Aviation

This article presents an overview of the current state of dealing with jet engine bird ingestion. At Turbo Expo ‘13 in San Antonio, Dr. Aspi Wadia of GE Aviation and Dr. Lee S. Langston (author of this paper) co-chaired a three-hour panel, ‘Jet Engine Bird Ingestion – Current Issues and Ways Forward.’ The leadoff panelist was Capt. Paul Eschenfelder, a retired Delta Airlines pilot, now with Embry-Riddle Aeronautical University, who gave an overall review of recent bird strike accidents around the world. Panelist John Dalton, who is a Technical Fellow in Airplane Safety Engineering for Boeing, gave the airframe original equipment manufacturer (OEM) history and his views on the bird strike problem. The panel’s fourth member was Dr. Nicholas Carter who is the Director of Finance for the World Birdstrike Association (WBA). Carter explained the role of the WBA, which is the international body that represents all states and countries in issues related to bird hazards at airfields and airports.

Design and Assembly of High Temperature Distributed Aero-engine Control System Demonstrator

This paper covers the development of a distributed high temperature electronics demonstrator for integration with sensor elements to provide digital outputs that can be used by the FADEC (Full Authority Digital Electronic Control) system or the EHMS (Engine Health Monitoring System) on an aircraft engine. This distributed electronics demonstrator eliminates the need for the FADEC or EHMS to process the sensor signal, which will assist in making the overall system more accurate and efficient in processing only digital signals. This will offer weight savings in cables, harnesses and connector pin reduction. The design concept was to take the output from several on-engine sensors, carry out the signal conditioning, multiplexing, analogue to digital conversion and data transmission through a serial data bus. The unit has to meet the environmental requirements of DO-160 with the need to operate at 200°C, with short term operation at temperatures up to 250°C. The work undertaken has been to design an ASIC based on 1.0μm Silicon on Insulator (SOI) device technology incorporating sensor signal conditioning electronics for sensors including resistance temperature probes, strain gauges, thermocouples, torque and frequency inputs. The ASIC contains analogue multiplexers, temperature stable voltage band-gap reference and bias circuits, ADC, BIST, core logic, DIN inputs and two parallel ARINC 429 serial databuses. The ASIC was tested and showed to be functional up to a maximum temperature of 275°C. The ASIC has been integrated with other high temperature components including voltage regulators, a crystal oscillator, precision resistors, silicon capacitors within a hermetic hybrid package. The hybrid circuit has been assembled within a stainless steel enclosure with high temperature connectors. The high temperature electronics demonstrator has been shown to operate from −40°C to +250°C. This work has been carried out under the EU Clean Sky HIGHTECS project with the Project being led by Turbomeca (Fr) and carried out by GE Aviation Systems (UK), GE Research – Munich (D) and Oxford University (UK).

Trends in Automotive Packaging

The long-term trend in automobiles has been increasing electronics content over time. This trend is expected to continue and drives diverse functional, form factor, and reliability requirements. These requirements, in turn, are leading to changes in the package types selected and the performance specifications of the packages used for automotive electronics. Several examples will be given. This abstract covers the development of a distributed high temperature electronics demonstrator for integration with sensor elements to provide digital outputs that can be used by the FADEC (Full Authority Digital Electronic Control) system or the EHMS (Engine Health Monitoring System) on an aircraft engine. This distributed electronics demonstrator eliminates the need for the FADEC or EHMS to process the sensor signal, which will assist in making the overall system more accurate and efficient in processing only digital signals. This will offer weight savings in cables, harnesses and connector pin reduction. The design concept was to take the output from several on-engine sensors, carry out the signal conditioning, multiplexing, analogue to digital conversion and data transmission through a serial data bus. The unit has to meet the environmental requirements of DO-160 with the need to operate at 200°C, with short term operation at temperatures up to 250°C. The work undertaken has been to design an ASIC based on 1.0 μm Silicon on Insulator (SOI) device technology incorporating sensor signal conditioning electronics for sensors including resistance temperature probes, strain gauges, thermocouples, torque and frequency inputs. The ASIC contains analogue multiplexers, temperature stable voltage band-gap reference and bias circuits, ADC, BIST, core logic, DIN inputs and two parallel ARINC 429 serial databuses. The ASIC was tested and showed to be functional up to a maximum temperature of 275°C. The ASIC has been integrated with other high temperature components including voltage regulators, a crystal oscillator, precision resistors, silicon capacitors within a hermetic hybrid package. The hybrid circuit has been assembled within a stainless steel enclosure with high temperature connectors. The high temperature electronics demonstrator has been demonstrated operating from −40°C to +250°C. This work has been carried out under the EU Clean Sky HIGHTECS project with the Project being led by Turbomeca (Fr) and carried out by GE Aviation Systems (UK), GE Research – Munich (D) and Oxford University (UK).

Acoustic measurements of models of military style supersonic nozzle jets

Modern military aircraft jet engines are designed with variable-geometry nozzles to provide optimal thrust in different operating conditions, depending on the flight envelope. However, acoustic measurements for such nozzles are scarce, due to the cost involved in making full-scale measurements and the lack of details about the exact geometries of these nozzles. Thus the present effort at Pennsylvania State University (PSU) in partnership with GE Aviation and the NASA Glenn Research Center is aiming to study and characterize the acoustic field produced by supersonic jets issuing from converging-diverging military style nozzles, and to identify and test promising noise reduction techniques. An equally important objective is to develop methodology for using data obtained from small- and moderate-scale experiments to reliably predict the full-scale engine noise. The experimental results presented show reasonable agreement between small-scale and medium-scale jets, as well as between heated jets and heat-simulated ones.

Practice Summary: Flight Trajectory Optimization

We developed and implemented a novel algorithm to control the trajectory of an aircraft flight to reduce the costs it incurs. Our algorithm computes the values for the parameters to be entered into the aircraft’s flight management system to minimize the fuel and schedule-adherence costs incurred on the flight. We implemented it in a prototype software system that is currently in use at GE Aviation Services.

Effects of Different Microstructure on Resistance of EA4T Railway Axle Steel of Equal Strength to Fatigue Crack Growth

Fatigue crack growth (FCG) rates in an EA4T railway axle steel heat treated by two different methods in near threshold and stable regions of growth were evaluated. Quite significant differences were observed, when the obtained results were compared with those published in the literature. Participation of the laboratory in an Exova (GE Aviation) FCG measurement qualification round robin programme with very good results practically excluded errors in the experimental methodology used. Strength of the two different evaluated series of the experimental material was equivalent. Nevertheless, there were substantial differences in fatigue crack growth rates, about 5-times in stable FCG region and even more than 10-times in the near threshold region, when oil quenching and air hardening treatments were compared. The differences were explained by different microstructures of the two groups of materials. Some minor differences between the character of the FCG curve in the threshold region evaluated using SEN(B) and M(T) specimens, published in the literature, are discussed considering crack closure phenomenon.

Numerical and Experimental Comparison of a Tandem and Single Vane Deswirler Used in an Aero Engine Centrifugal Compressor

Abstract The present work is part of the research project at the Institute of Jet Propulsion and Turbomachinery at the RWTH Aachen University in collaboration with GE Aviation. The subject is the numerical and experimental analysis of two blading strategies used in the diffusion system of an aero engine centrifugal compressor. The transonic centrifugal compressor investigated contains a close-coupled impeller and passage diffuser, followed by a deswirler system. The deswirler redirects the flow towards the combustion chamber, while decreasing swirl and recovering pressure. It is characterized by a high aerodynamic loading, due to a moderate inlet Mach number of 0.35, in combination with a required flow redirection of 70 deg in circumferential and 135 deg in meridional direction. For this purpose, two different blading strategies are investigated, both retaining the same meridional flow path and integral chord length. The first design is a tandem configuration with 30 vanes in the first row and 60 vanes in the second row. In principal, this approach benefits from the small wetted surface, the short and thereby stable boundary layers as well as the positive blade interaction due to the close alignment. The second design contains one row of 75 vanes. The higher solidity is needed to compensate for the longer boundary layers. The two deswirlers investigated are compared to a less compact baseline deswirler with simple prismatic vanes. Experimental and numerical data shows that both new configurations have very similar stage efficiency. The single row design shows a higher static pressure recovery, resulting in a +0.2%-points total-to-static isentropic efficiency increase compared to the tandem design. Detailed flow analysis in the deswirler system shows different characteristics in terms of losses, loss mechanisms and pressure build-up. Due to the required high turning, both designs suffer from flow separation. Nevertheless, the single row design shows its robustness under the impact of 3D flow, whereas the tandem suffers from end wall induced losses. The results show that the classical mechanisms making a tandem favorable for high flow turning in 2D flow are counteracted by 3D flow mechanisms caused by the spanwise pressure gradient. The low aspect ratio even increases the effect of 3D end wall mechanisms. These results, combined with a higher manufacturing effort, show that a tandem configuration is not necessarily the superior design for highly 3D flow conditions.