High Performance Jet Engines Research Articles

Assessing impact of near-ground meteorology on spectral variability in static jet aircraft noise measurements

ANSI/ASA standard S12.75 (2012) provides guidance on allowable meteorological conditions for acoustical measurements of installed high-performance jet engines. This paper investigates meteorological effects on acoustic data acquisition by analyzing recent measurements of a T-7A-installed GE F404 engine. During this measurement, the aircraft was run up six times at engine powers from idle to full afterburner, with test conditions following those prescribed by S12.75. However, far-field spectra show variability between runs, despite relatively uniform test conditions. Measurements of the vertical temperature gradient show a correlation between the gradient and spectral characteristics. This analysis suggests that local temperature profiles must be considered more carefully in future full-scale measurements. [Work supported by ONR Grant No. N00014-21-1-2069.]

Analysis of Radial Roller Bearing Rating Life in Complex Loading Conditions

Abstract An approach for accurate life analysis of radial roller bearings in complex loading conditions is presented. It employs ISO 16281 and accounts not only for external radial loads applied to the inner ring but also for (i) internal bearing clearance, (ii) flexibility of the bearing rings, (iii) rings out-of-roundness, (iv) inertia effects, (v) rolling elements profile, and (vi) rings misalignment. In the last decades, these factors have been becoming more and more important for modern high-performance jet engines, whose shafts are commonly hollow and the housing and the rings thicknesses may be of comparable magnitudes. To obtain the distribution of internal contact forces, an advanced static model of a bearing with deformable, potentially misaligned, rings is developed. The bending deformations of the rings are reproduced superimposing deformed shapes from each of the arising internal contact force applied individually. Bearing rollers are allowed to have non-cylindrical profile, and its geometry is approximated by means of slices each having constant diameter. A robust numerical scheme for solving the resultant set of equations with the aid of the barrier functions method is constructed. To increase even further the accuracy of rating life analysis, distributions of the contact stresses between the roller and the ring surfaces, obtained by solving numerically the problem of non-Hertzian interaction, are added to computations. A numerical benchmark test is presented to demonstrate the applicability of the developed approach. It shows how the aforementioned factors influence the bearing contact forces and its rating life.

Similarity spectral analysis of installed high-performance jet engine noise

Because the noise source mechanisms and radiation properties associated with high-thrust, tactical jet engines are not fully understood, full-scale measurements and analysis can shed significant insight. One method for examining spectral data is to compare them to empirical models for jet noise spectra. This paper compares measured near-field spectra from an installed F-404 engine with analytical similarity spectra for fine-scale mixing noise, large-scale mixing noise, and broadband-shock associated noise. This similarity spectral analysis enables us to determine spatial trends in overall level and peak frequency, and the relative importance of each type of noise radiation per location. This approach can be used to gain insights for different engine conditions as well as quickly compare to other aircraft.

Observations regarding the noise radiated from full-scale heated, supersonic jets

In this presentation, the characteristics of supersonic jet noise are reviewed. Observations from more than a decade’s worth of measurements of high-performance jet engines and large solid rocket motors are compared against each other and laboratory-scale findings. These include apparent source location and extent, directivity, spectral shape, relative importance of different noise components, and presence of nonlinear propagation effects.

(Invited) H. Russell Kunz: A Perspective on His Early Career

Fuel cell research at the Power Systems Group at Pratt & Whitney Aircraft rapidly expanded in 1962 when NASA awarded a contract to produce the fuel cells for the Apollo space program. At the time, Russ Kunz had already been at Pratt & Whitney for nine years, having been hired in 1953 straight out of college. Upon joining Pratt & Whitney, Russ was assigned to a team that had before his arrival been working to develop an advanced axial-flow turbojet engine, an activity with national security implications. This engine was to be used in two aircraft of strategic importance, an eight-engine long-range bomber and the world's first supersonic interceptor. The engine received the Air Force designation J57 and became the power plant used in both the B-52 Stratofortress bomber and the F-100 Super Sabre fighter, the latter of which became the first jet-powered aircraft able to sustain supersonic speed at low altitude and which set performance records that held for 10+ years. During his first nine years at Pratt & Whitney, Russ made significant contributions to the J57 that enabled subsequent versions to increasingly provide greater performance. Russ' involvement with the jet engine program ended when, in 1964, Pratt & Whitney moved its Power Systems Group from East Hartford, CT twelve miles north to a smaller facility in South Windsor, CT and Russ moved with it. It was at this facility where the fuel cells for every Apollo mission from 1966 to 1972 were produced. Work there continued with the transition to the Space Shuttle program from 1981 to 2011. During this period, Russ played a leading technical role. Although the fuel cell community may now remember Russ' for his more recent contributions, it was his earlier work on high-performance jet engines and power systems for the space program that embodied the technical challenges of a time when the future of aerospace technology was still being defined. This presentation will provide a brief overview of the contributions Russ made in his early career, within the context of the times, and the influence this work had on his family.

Isolation and testing of new single crystal superalloys using alloys-by-design method

Three new single crystal superalloys are isolated using theory-based computational modelling approaches, termed alloys-by-design methods. They are (i) an oxidation-resistant low Re-containing alloy with balanced properties, intended for general-purpose gas turbine applications; (ii) an alloy containing 5.6wt% Re and 2.6wt% Ru suitable for high performance jet engine applications, when creep resistance needs to be maximised without oxidation performance being excessively compromised and (iii) a cheap, corrosion-resistant alloy for power generation applications designed with ease-of-processing in mind. The new alloys have been manufactured using investment casting techniques, and their creep and oxidation behaviour evaluated. The robustness of the so-called alloys-by-design methods is demonstrated, although the predictions for microstructural stability need to be improved.

Occupational exposure to airborne particles and other pollutants in an aviation base

The occupational exposure to airborne particles and other pollutants in a high performance jet engine airport was investigated. Three spatial scales were considered: i) a downwind receptor site, ii) close to the airstrip, iii) personal monitoring.Particle number, surface area, mass concentrations and distributions were measured as well as inorganic and organic fractions, ionic fractions and Polycyclic Aromatic Hydrocarbons. Particle number distribution measured at a receptor site presents a mode of 80 nm and an average total concentration of 6.5 × 103 part. cm−3; the chemical analysis shows that all the elements may be attributed to long-range transport from the sea. Particle number concentrations in the proximity of the airstrip show short term peaks during the working day mainly related to takeoff, landing and pre-flight operations of jet engines. Personal exposure of workers highlights a median number concentration of 2.5 × 104 part. cm−3 and 1.7 × 104 part. cm−3 for crew chief and hangar operator.

Creep and fatigue interaction in the PWA1484 single crystal nickel-base alloy

While methods for modeling creep behavior of single crystal turbine airfoils are generally well developed, constant load creep does not fully represent the loading conditions present in a jet engine due to cyclic loading caused by the mission profile and throttle movements. As the aerospace industry seeks to become more accurate in physics-based modeling of materials that are used in turbine blades, creep–fatigue interaction must be incorporated into characterization of turbine blade materials. PWA1484, a second generation single crystal nickel-base superalloy that is used for turbine blades in many of today's high performance jet engines was tested in a creep–fatigue environment that is meant to simulate some conditions of the service environment of a jet engine. This research explores the behavior and microstructural evolution of samples of PWA1484 tested in a creep–fatigue environment at 871 °C in air. It was found that specimens subjected to prior fatigue loading exhibit a smaller region of primary creep that is proportional to the number of prior fatigue cycles, and an accelerated transition to a tertiary creep regime. However, specimens that are subject to a static load and allowed to creep to 2.5% creep strain exhibited an un-affected fatigue behavior. Post-test microstructural analysis revealed a coarsening of the gamma prime ( γ′) precipitates that was dependent on loading condition and time spent at elevated temperature.

Flashing flow of superheated jet fuel

Fuel stabilization technologies make it possible to utilize jet fuel to meet the heat sink capability demanded by the high performance jet engines in development. The resultant high fuel temperature creates the danger of vapor lock in the fuel line but also the possibility of utilizing the flash boiling to enhance the spray and mixing characteristics of an aero-engine combustor. To incorporate this new technology into the next generation aero-combustors, we need a quantitative understanding of the effects of this non-equilibrium, or flash vaporization of fuel in the Jet-A family on both the internal flow and the spray. We present the first attempt in simulating the flashing flow of a superheated JP8 fuel using a multi-dimensional transient code which incorporates a multi-component surrogate model to predict the JP8 properties in the superheated regime and resolves the finite flash vaporization rate under realistic flight conditions. Our numerical code was validated against available flashing flow data for water. Our simulations with superheated JP8 showed that, with respect to flow control and risk mitigation, flashing induced choking can occur even when the flow is subsonic – a consequence of the significant and rapid expansion of the two-phase fluid during the flashing process. This restriction on the flow rate, however, can be effectively controlled by adjusting the up-stream pressure. Our simulations also provided the initial conditions for the spray model. It showed that the spray core at the exit of the injector is non-uniform and is in the superheated state of varying degrees. A preliminary analysis of the flash vaporization time scale and the spray core breakup time indicated that the flashing phenomenon will play an important role in the spray breakup processes which will constitute our further works.

The Toxicity of Commercial Jet Oils

Jet oils are specialized synthetic oils used in high-performance jet engines. They have an appreciable hazard due to toxic ingredients, but are safe in use provided that maintenance personnel follow appropriate safety precautions and the oil stays in the engine. Aircraft engines that leak oil may expose others to the oils through uncontrolled exposure. Airplanes that use engines as a source of bleed air for cabin pressurization may have this source contaminated by the oil if an engine leaks. Examination of the ingredients of the oil indicates that at least two ingredients are hazardous: N-phenyl-1-naphthylamine (a skin sensitizer) and tricresyl phosphate (a neurotoxicant, if ortho-cresyl isomers are present). Publicly available information such as labels and MSDS understates the hazards of such ingredients and in the case of ortho-cresyl phosphates by several orders of magnitude.

Statistical Evaluation of Near-Field Sound Pressures Generated by the Exhaust of a High-Performance Jet Engine

The operation of modern, high-performance turbojet engines creates an environment that promotes rapid structural fatigue in many areas in jet aircraft. To facilitate the simulation of a valid test environment and, therefore, enable fatigue resistant structure to be readily developed, the characteristics of the near-field sound pressures created by the jet stream must be established. This study is concerned with the establishment of the level and the rate of occurrence of peak pressures in relation to the commonly measured rms level. A method is presented which enables the determination of these qualities from rms sound pressures recorded on magnetic tape. Also included are typical results obtained from near-field sound pressures generated by the jet exhaust of a General Electric CJ805 turbojet engine. Noted conclusions: (1) Occurrence of peak pressures does not follow a Rayleigh Distribution. (2) Peak pressure distribution is not altered by the physical position related to the jet stream nor does it appear to be a function of frequency. (3) A maximum ratio of peak to rms pressure is shown to exceed four, but a physical limit is not established.

Statistical Evaluation of Near Field Sound Pressures Generated by Exhaust of a High Performance Jet Engine

The operation of modern, high performance, turbojet engines creates an environment that promotes rapid structural fatigue in many areas in jet aircraft. To facilitate the simulation of a valid test environment and therefore enable fatigue resistant structure to be readily developed, the characteristics of the near field sound pressures created by the jet stream must be established. This study is concerned with the establishment of the level and the rate of occurrence of peak pressures in relation to the commonly measured rms level. A method is presented which enables the determination of these qualities from rms sound pressures recorded on magnetic tape. Also included are typical results obtained from near field sound pressures which were created by the jet exhaust of a General Electric CJ805 turbojet engine. Noted conclusions: (1) occurrence of peak pressures does not follow a Rayleigh distribution. (2) Peak pressure distribution is not altered by the physical position related to the jet stream nor does it appear to be a function of frequency. (3) A maximum ratio of peak to rms pressure is shown to exceed four, but a physical limit is not established.

High performance jet engine design dependent upon metallurgical ingenuity

High performance jet engine design dependent upon metallurgical ingenuity