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RESEARCH PAPERS

J. Eng. Gas Turbines Power. 1988;110(1):1-7. doi:10.1115/1.3240080.

Large-scale equations of state for steam used for generating tables are unsuitable for inclusion infinite difference flow calculation computer codes. Such codes, which are in common use in the turbomachinery industry, may require 106 property evaluations before convergence is achieved. This paper describes a simple equation of state for superheated and two-phase property calculations for use in these circumstances. Computational efficiency is excellent and accuracy over the range of application is comparable to that of the large-scale equations. Further advantages are that complete thermodynamic consistency is maintained and the equation can be differentiated analytically for direct substitution into the gas dynamic equations where required. A truncated virial form is used to represent superheated properties and a new empirical correlation for the third virial coefficient of steam is presented.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):8-16. doi:10.1115/1.3240092.

A simple steam-injected gas turbine cycle equipped with an exhaust heat recovery section is analyzed. The heat recovery section consists of a waste heat boiler, which produces the steam to be injected into the combustion chamber, and a self-production demineralized water plant based on a distillation process. This plant supplies the pure water needed in the mixed steam-gas cycle. Desalination plant requirements are investigated and heat consumption for producing distilled water is given. Overall steam-gas turbine cycle performance and feasibility of desalting plants are investigated in a firing temperature range from 1000.°C to 1400.°C for various compressor pressure and steam-to-air injection ratios. An example is reported.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):17-22. doi:10.1115/1.3240079.

It is generally accepted that development time scales for civil and military aero-engines can exceed those of the airframe they will power. It is now essential to ensure that relevant engine technologies are conceived and proven ahead of commitment to full-scale engine development if future military and civil propulsion requirements are to be met in an affordable way. The scope and scale of UK demonstrator activity has been greatly expanded in recent years in recognition of this need, principally through increased government funding. This paper discusses the principles underlying technology demonstration including the circumstances pertaining in the UK, concluding that a comprehensive program of technology demonstration conducted in a step-by-step fashion and properly integrated with transition to full-scale engineering development will produce significant financial and operational benefits.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):23-27. doi:10.1115/1.3240081.

KLM Royal Dutch Airlines has been using the General Electric ground-based engine monitoring (GEM) system for the CF6-50 and CF6-80 engines for several years. During the last year, various additional elements of the monitoring system have been introduced to the maintenance departments and are currently operational. This paper describes the introduction and the application of the GEM system within KLM’s organization. Also some attention is given to the (potential) benefits that are related to the use of this system, as well as to KLM’s engine monitoring plans for the near future.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):28-32. doi:10.1115/1.3240082.

Advanced integrated flight and propulsion control systems may require the use of optic technology to provide enhanced electromagnetic immunity and reduced weight. Immunity to electromagnetic interference and pulses is required for integrated systems where flight and propulsion control systems communicate with each other and diverse systems located throughout a composite aircraft. Weight reduction is crucial to the complex engine control systems required for advanced engines incorporating diagnostics, variable geometry and vectoring/reversing exhaust nozzles. A team of Pratt & Whitney, McDonnell Aircraft, Hamilton Standard, and United Technologies Research Center have developed the conceptual design of an optic engine control system, under a contract from NASA Lewis, entitled Fiber Optic Control System Integration (FOCSI). FOCSI is a triservice/NASA joint program designed to provide the optic technology requirements for advanced fighter/attack aircraft.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):33-40. doi:10.1115/1.3240083.

The technique of controlling engine acceleration has made possible gas turbine controls with simple hydromechanics and a minimal number of inputs into the electronics. This paper describes a control and electrical power generation system developed for an unmanned aircraft gas turbine, and the results obtained from the development engine running carried out with it.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):41-44. doi:10.1115/1.3240084.

Compressor rotors and turbine rotors are subject to centrifugal and thermal loads. These loads increase proportionally with tip speed, pressure ratio, and gas temperature. On the other hand, the rotor weight must be lessened to improve rotor dynamics and restrict bearing load. Thus, an optimum design technique is required, which offers the lightest possible wheel shape under the stress limit restriction. This paper introduces an optimum design system developed for turbomachinery rotors, and discusses several application results. The sequential linear programming method is used in the optimizing process, and centrifugal and thermal stress analyses of variable thickness rotating wheels are performed using Donath’s method. This system’s validity is confirmed by application to uniform-strength rotating disk problems and comparison with analytical results. This optimum design program is then applied to the design of axial flow compressor wheels.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):45-50. doi:10.1115/1.3240085.

The vibratory responses of blades in gas turbine engines vary because of mistuning. An approach is developed for calculating the statistical distribution of peak resonant stresses in engine blading. It is used to predict the vibratory response of an un-shrouded fan stage. The results of the calculation compare favorably with test data for the lower frequency modes. The procedure can be used to predict fleet durability and offers a practical engineering approach for dealing with stage mistuning.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):51-57. doi:10.1115/1.3240086.

The effect of fluid inertia on the synchronous steady-state operation of a centrally preloaded single mass flexible rotor supported in squeeze film bearing dampers is examined theoretically. For a model representative of some aircraft engine applications, frequency response curves are presented exhibiting the effect of fluid inertia on rotor excursion amplitudes and imbalance transmissibilities for both pressurized and unpressurized short open-ended squeeze film damper supports. It is shown that a significant reduction in amplitude response and transmitted force is possible for dampers operating at moderately large squeeze film Reynolds numbers. Furthermore, for unpressurized dampers the possibilities of bistable operation and jump phenomena are shown to be reduced and virtually disappear at sufficiently large operating Reynolds numbers.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):58-62. doi:10.1115/1.3240087.

Closed-form expressions are sought which will allow the rapid and accurate calculation of pressure variation, flow velocities, and flow friction losses in crank-driven Stirling cycle machines. The compression and expansion spaces of the Stirling machine are assumed to be isothermal and their volumes are assumed to vary sinusoidally. It is further assumed that the cyclic pressure variation of the working fluid and the flow velocities within the passages of the machine can be represented by sinusoids. Closed-form expressions are deduced for the amplitude and phase of these variations. Using the expressions so deduced, formulae are derived for frictional losses in the three heat exchangers, taking into account the variation in mass flow rate over the cycle and the difference in amplitude of mass flow between the two ends of the regenerator. By comparing these expressions with calculations based on the assumption of an average flow rate over the cycle, it is shown that the latter method leads to flow losses being underestimated by more than 50 percent. It is recommended that the formulae deduced here be used for first-stage design work.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):63-69. doi:10.1115/1.3240088.

Leakage flow and heat transfer of scaled-up stepped labyrinth seals were investigated experimentally and numerically. The experiments were conducted in a test rig under steady conditions. For different geometries and pressure ratios a finite element program was used to determine the temperature distribution and subsequently the heat transfer coefficients. In verifying the experimental results, the flow field of the seals was calculated numerically by a finite difference program. Heat transfer coefficients were derived utilizing the well-known analogies between heat transfer and wall friction.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):70-77. doi:10.1115/1.3240089.

Flow visualization and heat transfer measurements have been made in a cavity comprising two nonplane disks of 762 mm diameter and a peripheral shroud, all of which could be rotated up to 2000 rpm. “Cobs,” made from a lightweight foam material and shaped to model the geometry of turbine disks, were attached to the center of each disk. Cooling air at flow rates up to 0.1 kg/s entered the cavity through the center of the “upstream” disk and left via holes in the shroud. The flow structure was found to be similar to that observed in earlier tests for the plane-disk case: a source region, Ekman layers, sink layer, and interior core were observed by flow visualization. Providing the source region did not fill the entire cavity, solutions of the turbulent integral boundary-layer equations provided a reasonable approximation to the Nusselt numbers measured on the heated “downstream” disk.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):78-85. doi:10.1115/1.3240090.

Typically cooling air must be metered into cavities bordering turbine disks to offset cavity air temperature rise due to windage generated by air drag from rotating and stationary surfaces and the ingestion of hot mainstream gas. Being able to estimate the minimum amount of cooling air required to purge turbine rim cavities accurately is important toward providing optimum turbine cycle performance and hardware durability. Presented is an overview of a method used to model windage rise and ingestion on a macroscopic scale. Comparisons of model results to engine test data are included.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):86-93. doi:10.1115/1.3240091.

The dynamics of spray drop interaction within the turbulent wake of a bluff body were investigated using the Aerometrics Phase Doppler Particle Analyzer, which determines both drop size and velocity. Detailed measurements obtained included spray drop size, axial and radial velocity, angle of trajectory, and size-velocity correlations. The gas-phase flow field was also ascertained via the behavior of the smallest drops. Results showed dramatic differences in drop behavior when interacting with turbulence for the various size classes. Small drops were recirculated in a pair of toroidal vortices located behind the bluff body, whereas the larger drops followed the general direction of the spray cone angle. This was documented via backlit photography. Local changes in number density were produced as a result of lateral convection and streamwise accelerations and decelerations of various drop size classes. The spray field interaction illustrated by these data effectively reveals the complexity associated with the development of the spray and casts some doubts toward attempting to describe sprays via simple integral quantities such as the Sauter mean diameter.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):94-99. doi:10.1115/1.3240093.

Empirical formulae are presented by means of which the specific heat, mean molecular weight, density, and specific heat ratio of aviation fuel-air and diesel fuel-air systems can be calculated as functions of pressure, temperature, equivalence ratio, and hydrogen-to-carbon atomic ratio of the fuel. The formulae have been developed by fitting the data from a detailed chemical equilibrium code to a functional expression. Comparisons of the results from the proposed formulae with the results obtained from a chemical equilibrium code have shown that the mean absolute error in predicted specific heat is 0.8 percent, and that for molecular weight is 0.25 percent. These formulae provide a very fast and easy means of predicting the thermodynamic properties of combustion gases as compared to detailed equilibrium calculations, and they are also valid for a wide range of complex hydrocarbon mixtures and pure hydrocarbons as well as aviation and diesel fuels.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):100-104. doi:10.1115/1.3240071.

A novel method for predicting aviation fuel combustion performance has been developed in which the sooting point of a premixed flame is detected automatically. Comparisons with full-scale combustor data confirm that the technique is a more realistic index of combustion quality than Smoke Point or hydrogen content.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):105-110. doi:10.1115/1.3240072.

The performance characteristics of prefilming airblast atomizers depend largely on the shear stresses in each of the two air supply channels. As an extension of previously reported results, experiments were conducted using an atomizer model with separately controlled air ducts and typical prototype nozzles. It was shown that the quality of atomization can be limited due to internal droplet formation. However, the velocity profiles of the atomization air and the properties of the liquid are the dominant parameters that determine the drop-size distribution generated at the atomization edge. The shear flow at the nozzle exit and the recirculation zone depend largely on the swirl or counterswirl of the exiting air. Correlations have been obtained between the spray characteristics and the relevant parameters.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):111-116. doi:10.1115/1.3240073.

A 380-kW (1.3 million Btu/hr) two-burner level, tangentially fired, pilot-scale facility was used to characterize a dry-calcium-based sorbent SO2 capture technique combined with an offset auxiliary air low-NOx burner. Baseline tests showed that the facility properly simulates full-scale temperatures and emission levels. Dry sorbent SO2 test results suggest that for enhanced sorbent SO2 capture, injection should take place away from the burner zone where temperatures are lower, and that the time sorbent particles spend in the optimal temperature range should be extended as much as possible through sorbent injection methods and temperature profile modification.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):117-126. doi:10.1115/1.3240074.

A numerical furnace model (FURMO) was developed to model steady-state, three-dimensional pulverized-fuel combustion in practical furnace geometries. This model is based on a fundamental description of various interacting processes which occur during combustion: turbulent flow, heterogeneous and homogeneous chemical reaction, and heat transfer. The detailed analysis achieved by the method is useful for evaluating furnace performance and in the interpretation of laboratory, intermediate, and utility test data. In this paper, three-dimensional pulverized coal combustion is investigated for a 560 MW utility boiler. Numerical results for flow, heat transfer, and chemistry are presented. Contour maps are exhibited to describe these complex three-dimensional interactions. Model sensitivity is evaluated for changes in slag layer thickness, particle size distribution, and devolatilization and char oxidation rates.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):127-131. doi:10.1115/1.3240075.

For future advanced steam turbines of 4500 psi and 1100°F, a high-temperature rotor is one of the most important components to be developed. We estimated that the usable temperature limit of existing 12Cr steel was approximately 1075°F, and then developed improved 12Cr steels. Prototype rotors were made from three types of developed steels, and were put to various evaluation tests. All three steels had creep-rupture strength exceeding that of existing 12Cr steels and were satisfactory in quality and in the other mechanical properties.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):132-141. doi:10.1115/1.3240076.

Extensive use has been made by the gas turbine industry of centrispun castings of certain highly alloyed heat resisting steels. The paper outlines the main features of the centrispinning process and discusses the advantages that one could expect, not only in mechanical properties, but also in cost and the casting to shape in refractory molds. Results of mechanical tests on sections cut from representative castings are given and show the high order of the tensile strength to be expected.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):142-149. doi:10.1115/1.3240077.

The hot corrosion resistance of several protective coatings that had been applied to MAR-M-509 nozzle guide vanes and exposed in a utility gas turbine has been evaluated. The coatings included basic aluminide, rhodium-aluminide, platinum-rhodium-aluminide, and palladium-aluminide diffusion coatings, and cobalt-chromium-aluminum-yttrium (CoCrAlY) and ceramic overlay coatings. A combination of metallographic examination of vane cross sections and energy dispersive X-ray analysis (EDS) was employed in the evaluation. The results showed that none of the coatings was totally resistant to corrosive attack. The CoCrAlY and platinum-rhodium-aluminide coatings exhibited the greatest resistance to hot corrosion. The CoCrAlY coated vanes were, however, susceptible to thermal fatigue cracking. Except for the poor performance of the palladium-aluminide coating, the precious metal aluminides offered the best protection against corrosion. Hot isostatically pressing coatings was not found to be beneficial, and in one case appeared detrimental.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(1):150-154. doi:10.1115/1.3240078.

Nickel and cobalt-base superalloy blades and vanes in the hot sections of all gas turbines are coated to enhance resistance to hot corrosion. Pack cementation aluminizing, invented in 1911, is the most widely used coating process. Corrosion resistance of aluminide coatings can be increased by modification with chromium, platinum, or silicon. Chromium diffusion coatings can be used at lower temperatures. Formation and degradation mechanisms are reasonably well understood and large-scale manufacturing processes for these coatings are gradually being automated. Pack cementation and related diffusion coatings serve well for most aircraft engine applications. The trend for industrial and marine engines is more toward the use of overlay coatings because of the greater ease of designing these to meet a wide variety of corrosion conditions.

Commentary by Dr. Valentin Fuster

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