Pratt & Whitney (United States)

When creating designed experiments, it is not always possible to run the experiment at the exact settings required to maintain orthogonal effects. However, this is not measurement error when precise measurements of the settings can be made once the experiment begins. A comparison is made for a 15-run Box–Behnken design using both the intended design settings and the actual design settings. Variance inflation factors are used to measure the induced collinearity in the effects. Two cutoff values are suggested for use to determine when an effect's variance inflation factor is too large to keep that effect in the model.

The purpose of this paper is to introduce the new ASME measurement uncertainty methodology which is the basis for two new ASME/ANSI standards and the ASME short course of the same name. Some background and history that led to the selection of this methodology are discussed as well as its application in current SAE, ISA, JANNAF, NRC, USAF, NATO, and ISO Standards documents and short courses. This ASME methodology is rapidly becoming the national and international standard.

The oxidation of alloys in 0.1 atm of oxygen has been studied at temperatures of 1000°, 1100°, and 1200°C. Twenty‐one alloys with varying chromium [2–30 weight per cent (w/o)] and aluminum (1–9 w/o) contents were examined. It was found that all of the alloys initially underwent a period of transient oxidation before steady‐state conditions were established. The transient period of oxidation usually did not exceed 1 hr and was characterized by rapid conversion of thin surface layers of the alloys to oxides with the subsequent formation of continuous layers of one of the following oxides: , , or . Steady‐state conditions were established with the formation of these continuous oxide layers, and oxidation occurred by three different mechanisms which were characterized by the growth of an external layer of over a subscale of and Al2O3, the growth of an external layer of over an subscale or the growth of a continuous, external layer of .

We present further calculations of the three-dimensional mode patterns and power outputs from a highpower gas-dynamic laser, including a nonuniform flowing, saturable gain medium plus index inhomogeneities (shocks) inside the laser. The calculations are carried out using a plane-wave or k-space expansion together with the fast Fourier transform. A new expanding-beam coordinate transform converts all diverging or converging sections of the resonator mode into equivalent collimated beam sections. The resulting FFT propagation code is significantly faster than earlier propagation codes using other eigenmode expansions.

The resonant response of a turbine airfoil attenuated through use of a Coulomb damper is analyzed. Parameters that control the damper’s effectiveness are identified and characteristics of an optimized system are described. The results of the analysis are confirmed by laboratory tests.

Complex fluid flows are encountered widely in nature, in living beings and in engineering practice. These flows often involve both geometric and dynamic complexity and present problems that are difficult to analyse because of their wide range of length and time scales, as well as their geometric configuration. This book describes some newly developed computational techniques and modelling strategies for analysing and predicting complex transport phenomena. It summarizes advances in the context of a pressure-based algorithm. Among methods discussed are discretization schemes for treating convection and pressure, parallel computing, multigrid methods, and composite, multiblock techniques. With respect to physical modelling, the book addresses issues of turbulence closure and multiscale, multiphase transport from an engineering viewpoint. Both fundamental and practical issues are considered, along with the relative merits of competing approaches. The final chapter is devoted to practical applications that illustrate the advantages of various numerical and physical tools. Numerous examples are given throughout the text. Mechanical, aerospace, chemical and materials engineers can use the techniques presented in this book to tackle important, practical problems more effectively.

Over the last several years, the development of coherent anti-Stokes Raman spectroscopy (CARS) has progressed through simple flames of increasing complexity to practical application in internal combustion engines, simulations of gas turbine combustors, and a variety of other devices. Here, the first application of CARS to an actual afterburning jet engine is described. The CARS instrument constructed is capable of completely remote operation and permits instantaneous thermometry at a 20-Hz rate. Its design and operation as well as sample exhaust measurements will be presented.

The present study evaluates an innovative approach for enhancement of surface heat transfer in a channel using concavities, rather than protruding elements. Serving as a vortex generator, a concavity is expected to promote turbulent mixing in the flow bulk and enhance the heat transfer. Using a transient liquid crystal imaging system, local heat transfer distribution on the surface roughened by an staggered array based on two different shapes of concavities, i.e. hemispheric and tear-drop shaped, have been obtained, analyzed and compared. The results reveal that both concavity configurations induce a heat transfer enhancement similar to that of continuous rib turbulators, about 2.5 times their smooth counterparts 10,000 ≤ Re ≤ 50,000. In addition, both concavity arrays reveal remarkably low pressure losses that are nearly one-half the magnitudes incurred with protruding elements. In turbine cooling applications, the concavity approach is particularly attractive in reducing system weight and ease of manufacturing.

Local rates of heat transfer on the endwall, suction, and pressure surfaces of a large scale turbine blade cascade were measured for two inlet boundary layer thicknesses and for a Reynolds number typical of gas turbine engine operation. The accuracy and spatial resolution of the measurements were sufficient to reveal local variations of heat transfer associated with distinct flow regimes and with regions of strong three-dimensional flow. Pertinent results of surface flow visualization and pressure measurements are included. The dominant role of the passage vortex, which develops from the singular separation of the inlet boundary layer, in determining heat transfer at the endwall and at certain regions of the airfoil surface is illustrated. Heat transfer on the passage surfaces is discussed and measurements at airfoil midspan are compared with current finite difference prediction methods.

The experiment of Champagne, Harris & Corrsin in generating and studying a nearly homogeneous turbulent shear flow has been extended to larger values of the dimensionless downstream time or strain by the use of a larger mean velocity gradient in the same wind tunnel. The system appears to reach an asymptotic state in which scales and turbulent energy grow monotonically. Two-point covariances and tensor structure of one-point ‘Reynolds stress’ and ‘pressure/strain-rate covariance’ agree with the earlier case. However, the linear intercomponent energy exchange hypothesis due to Rotta, very roughly confirmed by the earlier experiment, is contradicted by the present data.

Condition monitoring of engine gas generators plays an essential role in airline fleet management. Adaptive diagnostic systems are becoming available that interpret measured data, furnish diagnosis of problems, provide a prognosis of engine health for planning purposes, and rank engines for scheduled maintenance. More than four hundred operations worldwide currently use versions of the first or second generation diagnostic tools. Development of a third generation system is underway which will provide additional system enhancements and combine the functions of the existing tools. Proposed enhancements include the use of artificial intelligence to automate, improve the quality of the analysis, provide timely alerts, and the use of an Internet link for collaboration. One objective of these enhancements is to have the intelligent system do more of the analysis and decision making, while continuing to support the depth of analysis currently available at experienced operations. This paper presents recent developments in technology and strategies in engine condition monitoring including: (1) application of statistical analysis and artificial neural network filters to improve data quality, (2) neural networks for trend change detection, and classification to diagnose performance change, and (3) expert systems to diagnose, provide alerts and to rank maintenance action recommendations.

The current interest in tough, high‐temperature materials has motivated fiber coating development for brittle‐matrix composites with brittle reinforcements. Such coatings are needed for controlled interface debonding and frictional sliding. The system investigated in this study was sapphire fiber‐reinforced alumina. This system is thermochemically stable for severe use conditions, exhibits little thermal expansion mismatch, and utilizes the excellent strength and creep resistance of sapphire reinforcements. Porous oxide and refractory metal coatings which satisfy requirements for toughness improvement in these composites were identified by employing a variety of newly developed mechanical testing techniques for determining the interfacial fracture energies and sliding resistances.

The growth of nickel‐aluminum spinel, NiAl 2 O 4 , in diffusion couples of polycrystalline Al 2 O 3 and NiO was investigated between 1200° and 1500°C. The growth kinetics for the spinel layer obeyed a parabolic rate law in this temperature range. Marker experiments showed that the spinel layer formed by counterdiffusion of nickel and aluminum ions. Comparison of experimental and theoretical values of the parabolic rate constants suggests that the diffusion of aluminum ions through the spinel layer is rate controlling.

How can we make an alloy to fit a specific materials requirement? The oldest method of alloy fabrication, casting, has two inherent limitations: Phases with high melting points are difficult to melt; and the cooling of the alloys from the melt is slow, so that alloy segregation and phase separation have time to occur. The other traditional method, powder metallurgy, has helped with the second of these problems: Allowing the homogeneous melt to be cooled in tiny droplets makes it possible at least to limit segregation to the scale of the resulting powder particles.

This review addresses recent literature on turbine passage aerodynamics and endwall heat transfer; articles that describe the endwall flow and cooling problems are summarized, recent activity on improving endwall aerothermal design is discussed, improved cooling schemes are proposed, and methods for managing secondary flows to allow more effective cooling are suggested. Much attention is given to aerodynamic losses associated with secondary flows developed near the endwalls. The endwall region flowfield is influenced by the stagnation zones established as the endwall approach flow boundary layer meets the airfoil leading edges, by the curvature of the passages, by the steps and gaps on the endwall surface ahead of and within the passage, by the leakage and coolant flows introduced through the endwall surface ahead of and within the passage, by the tip leakage flows between the blades and shroud in the rotor endwall region, and by many more effects. Recent combustor redesigns have flattened the turbine inlet temperature profile and have raised the turbine inlet temperatures. This, coupled with a continued need to improve engine durability and availability, has spurred strong interest in thermal control of the turbine endwall regions. Thus, much of the literature presented herein is focused on endwall cooling and, in particular, the effects of near-endwall secondary flows on endwall cooling.

The afterburner on a modern aircraft gas turbine engine provides significant thrust augmentation critical to the performance and mission of tactical aircraft. Higher exhaust temperatures and survivability requirements for advanced aircraft have resulted in new constraints on the augmentor design which dramatically changes the design architecture. Many of the design methods established for afterburners over the past 50 years are insufficient for the augmentor configurations being developed today. This paper will describe some of the fundamental technical challenges being faced by augmentor designers, and will outline critical needs in terms of fundamental combustion sciences and engineering that needs to be acquired to support new design methods for advanced augmentors.

The physical characteristics of surface roughness observed on first-stage high-pressure turbine vanes that had been in service for a long period were investigated in this study. Profilometry measurements were utilized to provide details of the surface roughness formed by deposits of foreign materials on different parts of the turbine vane. Typical measures of surface roughness such as centerline average roughness values were shown to be inadequate for characterizing roughness effects. Using a roughness shape parameter originally derived from regular roughness arrays, the turbine airfoil roughness was characterized in terms of equivalent sand-grain roughness in order to develop an appropriate simulation of the surface for laboratory experiments. Two rough surface test plates were designed and fabricated. These test plates were evaluated experimentally to quantify the heat transfer rate for flow conditions similar to that which occurs on the turbine airfoil. Although the roughness levels on the two test plates were different by a factor of two, both surfaces caused similar 50 percent increases in heat transfer rates relative to a smooth surface. The effects of high free-stream turbulence, with turbulence levels from 10 to 17 percent, were also investigated. Combined free-stream turbulence and surface roughness effects were found to be additive, resulting in as much as a 100 percent increase in heat transfer rate.

An anomaly in the absorption of ultrasonic waves has been found in some very pure superconductors and and has been investigated in detail in superconducting lead. It consists in a strong dependence of the absorption on the amplitude of the ultrasonic waves. The amplitude dependence is only weakly present in the normal state. The effect is found to be strongly temperature-dependent, decreases as impurities are added to the crystal, and exhibits little or no change with frequency. Deformation and annealing have a pronounced effect on the anomaly. It appears that these characteristics can be understood in terms of a model, which is proposed here, based on the assumption of a strong interaction between the conduction electrons and the dislocations in the metal crystal. The presence of weakly pinned dislocations and their motion in the field of the sound wave is assumed. In the normal state, this motion is highly damped by the conduction electrons, and therefore, the dislocations cannot contribute much to the ultrasonic absorption. In the superconducting region, this damping decreases with the same temperature dependence as the ultrasonic absorption by the electrons. The dislocations become more free to move and therefore can cause an (amplitude-dependent) absorption by themselves. The mechanism for this absorption is thought to be dislocation unpinning similar to that discussed, for example, by Granato and L\"ucke.

This paper describes the results of an industry effo rt to test Bio-derived Synthetic Paraffinic Kerosene (Bio-SPK) from natural plant oils. The program included the identification and sourcing of sustainable feedstocks, the use of a new fuel processing method, nu merous fuel tests, engine operability, performance and emissions tests, and flight testing in three Boeing aircraft models. The Bio-SPK blended fuels have potential to reduce life cycle CO2 emissions and be compatible with current aircraft, systems, and infrastructure.

This paper describes the results of a study to determine the performance improvements achievable by circumferentially indexing successive rows of turbine stator airfoils. An experimental/analytical investigation has been completed that indicates significant stage efficiency increases can be attained through application of this airfoil clocking concept. A series of tests was conducted at the National Aeronautics and Space Administration’s (NASA) Marshall Space Flight Center (MSFC) to experimentally investigate stator wake clocking effects on the performance of the Space Shuttle Main Engine Alternate Fuel Turbopump Turbine Test Article. Extensive time-accurate Computational Fluid Dynamics (CFD) simulations have been completed for the test configurations. The CFD results provide insight into the performance improvement mechanism. Part one of this paper describes details of the test facility, rig geometry, instrumentation, and aerodynamic operating parameters. Results of turbine testing at the aerodynamic design point are presented for six circumferential positions of the first stage stator, along with a description of the initial CFD analyses performed for the test article. It should be noted that first vane positions 1 and 6 produced identical first to second vane indexing. Results obtained from off-design testing of the “best” and “worst” stator clocking positions, and testing over a range of Reynolds numbers are also presented. Part two of this paper describes the numerical simulations performed in support of the experimental test program described in part one. Time-accurate Navier–Stokes flow analyses have been completed for the five different turbine stator positions tested. Details of the computational procedure and results are presented. Analysis results include predictions of instantaneous and time-average midspan airfoil and turbine performance, as well as gas conditions throughout the flow field. An initial understanding of the turbine performance improvement mechanism is described.