Military Jet Engines Research Articles

Old and New

As prime movers go, gas turbines are virtually brand new, compared to, say, wind and water turbines which have been around for millennia. But they have also reached a considerable level of maturity. Gas turbines now dominate both the world’s aircraft propulsion and a good portion of electric power generation. The fortunes of the industry are not uniform, however. The commercial jet engine market is robust and growing; the military jet engine, electric power, and other markets have been relatively flat or declining. But those are the sectors where the possibilities lie. They aren’t new, but they have the potential for renewal. This study delves deeper into the current status and trends in theworldwide gas turbine market.

Application of time reversal analysis to military jet aircraft noise

The source mechanisms of jet noise are not fully understood and different analysis methods can provide insight. Time reversal (TR) is a robust data processing method that has been used in myriad contexts to localize and characterize sources from measured data, but has not extensively been applied to jet noise. It is applied here in the context of an installed full-scale military jet engine. Recently, measurements of an F-22A were taken using linear and planar microphone arrays at various engine conditions near the jet plume [Wall et al., Noise Control Eng. J. 60, 421–434 (2012)]. TR provides source imaging information as broadband and narrowband jet noise recordings are reversed and back propagated to the source region. These reconstruction estimates provide information on dominant source regions as a function of frequency and highlight directional features attributed to large-scale structures in the downstream jet direction. They also highlight the utility of TR analysis as being complementary to beamforming and other array methods. [Work supported by ONR.]

Empirical Tests of Wireless Sensor Network in Jet Engine Including Characterization of Radio Wave Propagation and Fading

This letter describes how to replace a wired telemetry system for structural health monitoring (SHM) in jet engines with a wireless sensor network (WSN). With a WSN, the time required for engine preparation can be reduced from several months to only a few weeks. The WSN is tested in a military jet engine used in the Swedish jet fighter JAS 39 Gripen. Also, the wave propagation is characterized in the real engine and a half-scale engine with both linear- and circular-polarized antennas. The measurements are analyzed by using K-factor and path loss. Finally, the complete system is tested in a full-scale test with a running engine. The intended WSN will operate in the 2.45-GHz ISM band. The K-factor for the real engine ranges from about 2 to 8 and for the half-scale engine from about 1 to 15. The use of circularly polarized antennas does not always reduce the fading. The complete system measured the bit error rate (BER) and temperature. The performed tests were successful, and the BER were 2.8%-10.5% during the test. The practical test also showed the possibility of using a WSN as a monitoring system in jet engines.

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.

Effect of change in role of an aircraft on engine life

AbstractNew aircraft require years of development from concept to realisation and can be prone to delays. Consequently, military operators take existing fleets and operate them in a different role. The objective of this study is to examine the effect of operating a typical low bypass military fast jet engine, originally designed for a European theatre, in a hot and harsh climate. The specific purpose is to determine the effect on the high-pressure turbine blade life and the life- cycle cost of the engine.A mission profile and respective performance conditions were analysed and modelled using an in-house performance tool. The flow conditions were simulated using ANSYS® FLUENT. A conjugated heat transfer solution was adopted to determine the blade metal temperature. The blade was modelled physically in 3D using SIMULIA® ABAQUS FEA software. The stresses were derived and used to calculate the temperature coupled low cycle fatigue and creep life.A deterioration case was also studied to evaluate the effect of sand and dust ingestion. There was a significant life reduction of approximately 50% due to creep. The reduction in life was inversely proportional to the life cycle cost of the engine depending on the operating conditions. The results were compared with similar engines and summarised in the context of airworthiness regulations and component integrity.

Developing the Modeling Recommendation Matrix: Model‐Assisted Communication at Volvo Aero

AbstractVolvo Aero Norway (VAN) is a manufacturing company specializing in the production of high precision aerospace components for both commercial and military jet engines. VAN has, as a high‐end production company, a highly diverse set of stakeholders in their employees, customers and suppliers. It is therefore a definite need for VAN to have personnel that can communicate efficiently between stakeholders to be able to complete projects and optimize production in order to sustain their competitive position.Using systems modeling is a known technique to aid communication, raise understanding and create debate surrounding any given system of interest. By measuring the value, in regards to the aforementioned effects of modeling, of the work being performed at VAN we can discuss the usefulness of modeling‐based communication. We will examine the connection between a stakeholder's distance to a given system and the optimal level of modeling detail and novelty.In this paper, we will discuss model effectiveness based on balancing impact factors based on stakeholder's system proximity. We will classify and evaluate models in a 2D‐Matrix and present recorded trends at VAN.

On the Scaling of Small, Heat Simulated Jet Noise Measurements to Moderate Size Exhaust Jets

Modern military aircraft jet engines are designed with variable geometry nozzles to provide optimum thrust in different operating conditions, depending on the flight envelope. However, the 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 geometry of these nozzles. Thus the present effort at The Pennsylvania State University and the NASA Glenn Research Center in partnership with GE Aviation is aiming to study and characterize the acoustic field produced by supersonic jets issuing from converging-diverging military style nozzles. An equally important objective is to validate methodology for using data obtained from small and moderate scale experiments to reliably predict the most important components of full scale engine noise. The experimental results presented show reasonable agreement between small scale and moderate scale jet acoustic data, as well as between heated jets and heat-simulated ones. Unresolved issues however are identified that are currently receiving our attention, in particular the effect of the small bypass ratio airflow. Future activities will identify and test promising noise reduction techniques in an effort to predict how well such concepts will work with full scale engines in flight conditions.

Air Race

This article presents an overview of the existence and use of gas turbines in the past, present, and future. The article uses the data provided by Forecast International of Newtown, Conn., which covers both aviation and nonaviation gas turbine markets. The gas turbine has proven to be an example of technological evolution, where improvements in efficiency and reliability continue to amass, 70 years after its invention. Advanced technology developed in military jet engines has often migrated to commercial jet engines and nonaviation gas turbines, and improved their performance. Gas turbine combined-cycle power plants come in all sizes. The largest combined-cycle gas turbines are the H class machines made by GE and Siemens. Given the world’s current focus on sustainable or renewable energy, how do natural gas-fired gas turbines fit in? In some instances, renewable energy, such as solar or wind, just would not be practical without assistance from gas turbines. As power production moves tentatively into a low-carbon future, or as people look for more fuel-efficient ways to cross continents, it’s a sure bet that gas turbines will be there.

Bespoke vibration analysis for military jet engines

Bespoke vibration analysis for military jet engines

Fatigue of air supply manifold support rod in military jet engines

Bending fatigue failure occurred in a support rod linking the bleed air supply manifold to the diffuser case in a military jet engine. Other rods were subsequently found cracked. The rods were wrought Inconel 718, operating at approximately 550 °C. The bending was caused by relative movements of two expansion sleeves held together by the rods. Accommodative swiveling of the spherically rounded ends of the rods in the mating seatings of the inner sleeves was prevented by contact pressure, fretting, and binding. The main reason for binding was decomposition of the antigalling compound applied to the contact surfaces. Fractographic analysis and oxidation interference colors enabled interpretation of the cracking history of the broken rod. Elementary stress and fracture mechanics calculations indicated that the maximum fatigue stress was below the stress needed to “unlock” the spherically rounded rod end from its seating.

Risk factors of jet fuel combustion products

Air travel is increasing and airports are being newly built or enlarged. Concern is rising about the exposure to toxic combustion products in the population living in the vicinity of large airports. Jet fuels are well characterized regarding their physical and chemical properties. Health effects of fuel vapors and liquid fuel are described after occupational exposure and in animal studies. Rather less is known about combustion products of jet fuels and exposure to those. Aircraft emissions vary with the engine type, the engine load and the fuel. Among jet aircrafts there are differences between civil and military jet engines and their fuels. Combustion of jet fuel results in CO 2, H 2O, CO, C, NO x , particles and a great number of organic compounds. Among the emitted hydrocarbons (HCs), no compound (indicator) characteristic for jet engines could be detected so far. Jet engines do not seem to be a source of halogenated compounds or heavy metals. They contain, however, various toxicologically relevant compounds including carcinogenic substances. A comparison between organic compounds in the emissions of jet engines and diesel vehicle engines revealed no major differences in the composition. Risk factors of jet engine fuel exhaust can only be named in context of exposure data. Using available monitoring data, the possibilities and limitations for a risk assessment approach for the population living around large airports are presented. The analysis of such data shows that there is an impact on the air quality of the adjacent communities, but this impact does not result in levels higher than those in a typical urban environment.

Characterizing the Source of Fugitive Middle Distillate Fuels—A Case Study Involving Railroad Diesel Fuel, Mandan, North Dakota

Middle distillate fuels are used in civilian and military jet engines, on-road (truck and bus) and off-road diesel (diesel-electric locomotives, heavy equipment, and farm machinery) engines, marine diesel engines, nonaviation gas turbines, and domestic and commercial furnaces. As such, these fuels are common environmental contaminants that may arise from multiple sources. The considerable liability associated with these fugitive fuels requires that their source(s) be defensibly determined. In this paper we describe the “chemical fingerprinting” features of middle distillate fuels that can be used in assessments of their source(s) in the environment. A case study in which railroad (off-road) diesel fuel #2 could be distinguished from nonrailroad fuels (e.g., on-road diesel fuel #2, fuel oil #2, and/or fuel oil #1) in Mandan, North Dakota, is presented.

Sensor Fault Detection for Gas Turbines with Knowledge Based Methods

The gas path analysis is a useful tool for modeling jet engines and stationary gas turbines, respectively Such models can be used for diagnosis that means that measurement values as inputs deliver state variables as outputs from the model The measurement values are not fault free. They are disturbed by noise and by systematic sensor errors Therefore algorithms have to be implemented which filter the noise and compensate the systematic sensor errors In alternation to the model based procedures the diagnosis problem can also be solved by knowledge based methods using an expert system. Such an expert system is developed on the basis of uncrisp rules from fuzzy logic and is presented in this paper. It is an efficient tool especially for detecting the localization of systematic sensor errors. The amounts of these errors then can be found by model based methods, The diagnosis software package is applied on military and civilian jet engines on teststands and it is used in power plants for stationary gas turbines.

Knowledge based sensor fault detection for gas turbines under consideration of model based methods

The gas path analysis is a useful tool for modeling jet engines and stationary gas turbines, respectively. Such models are used for diagnosis that means that measurement values as inputs deliver state variables as outputs from the model. The measurement values are not fault free. They are disturbed by noise and by systematic sensor errors. Therefore algorithms have to be implemented which filter and compensate these errors; furthermore the modeling is not exact. Thereby the algorithms must be extended and adapted to this case. In alternation to the model based procedures the diagnosis problem can also be solved by knowledge based methods using an expert system. Such an expert system is developed and presented in this paper. It is an efficient tool — also in connection with the model based procedures — for detecting faults in the states of the engine and faults in the sensors as well. The diagnosis software package is applied on military and civilian jet engines and it is used in power plants for stationary gas turbines.