bluuebunny/crossref_metadata_2025 huggingface dataset:
Stream Function Solution of Transonic Flow Along S2 Streamsurface of Axial Turbomachines
Authors: Zhao Xiaolu
Published: October 2009

Based on Wu’s general equations of 3-D turbomachine flow, expressed with respect to nonorthogonal curvilinear coordinates, the conservative stream-function formulations of transonic flow along S2 streamsurface have been discussed. The problem of mixed flow can be solved by the use of the artificial compressibility method, and the passage shock on the S2 streamsurface can be captured. The distribution of the fluid velocity from hub to shroud can be obtained directly by integrating the velocity gradient equation, after the principal equation has been solved, so that the difficulty of the nonuniqueness of density-mass flux relation is avoided. The density is determined after the velocity has been obtained. Two computer programs have been coded; one can be used to compute the hybrid or design problems, the other is suitable to compute the analysis problem. The former has been used to compute the transonic flow field along a mean S2 streamsurface in the DFLVR compressor rotor at design speed. The numerical results agree well with L2F measurement data.
On Thermodynamics of Gas-Turbine Cycles: Part 2—A Model for Expansion in Cooled Turbines
Authors: El-Masri M. A.
Published: October 2009

While raising turbine inlet temperature improves the efficiency of the gas-turbine cycle, the increasing turbine-cooling losses become a limiting factor. Detailed prediction of those losses is a complex process, thought to be possible only for specific designs and operating conditions. A general, albeit approximate, model is presented to quantify those cooling losses for different types of cooling technologies. It is based upon representing the turbine as an expansion path with continuous, rather than discrete, work extraction. This enables closed-form solutions to be found for the states along the expansion path as well as turbine work output. The formulation shows the key factor in determining the cooling losses is the parameter scaling the ratio of heat to work fluxes loading the machine surfaces. Solutions are given for three cases: internal air-cooling, transpiration air cooling, and internal liquid cooling. The first and second cases represent lower and upper bounds respectively for the performance of film-cooled machines. Irreversibilities arising from flow-path friction, heat transfer, cooling air throttling, and mixing of coolant and mainstream are quantified and compared. Sample calculations for the performance of open and combined cycles with cooled turbines are presented. The dependence and sensitivity of the results to the various loss mechanisms and assumptions is shown. Results in this paper pertain to Brayton-cycle gas turbines with the three types of cooling mentioned. Reheat gas turbines are more sensitive to cooling losses due to the larger number of high-temperature stages. Those are considered in Part 3.
A Numerical Modeling of Endwall and Tip-Clearance Flow of an Isolated Compressor Rotor
Authors: Hah C.
Published: October 2009

The current study is aimed at developing and appraising a numerical method for the development of endwall boundary layers through tip-clearances and their effect on the performance of an isolated compressor rotor. The Reynolds-averaged Navier-Stokes equation is solved for the entire flow field in elliptic form. The relative flow is computed on the generalized coordinates fixed on the rotor. Comparison between the numerical results and experimental data indicates that the complex three-dimensional viscous flow phenomena inside the tip region are properly predicted.
On Thermodynamics of Gas-Turbine Cycles: Part 3—Thermodynamic Potential and Limitations of Cooled Reheat-Gas-Turbine Combined Cycles
Authors: El-Masri M. A.
Published: October 2009

Reheat gas turbines have fundamental thermodynamic advantages in combined cycles. However, a larger proportion of the turbine expansion path is exposed to elevated temperatures, leading to increased cooling losses. Identifying cooling technologies which minimize those losses is crucial to realizing the full potential of reheat cycles. The strong role played by cooling losses in reheat cycles necessitates their inclusion in cycle optimization. To this end, the models for the thermodynamics of combined cycles and cooled turbines presented in Parts 1 and 2 of this paper have been extended where needed and applied to the analysis of a wide variety of cycles. The cooling methods considered range from established air-cooling technology to methods under current research and development such as air-transpiration, open-loop, and closed-loop water cooling. Two schemes thought worthy of longer-term consideration are also assessed. These are two-phase transpiration cooling and the regenerative thermosyphon. A variety of configurations are examined, ranging from Brayton-cycles to one or two-turbine reheats, with or without compressor intercooling. Both surface intercoolers and evaporative water-spray types are considered. The most attractive cycle configurations as well as the optimum pressure ratio and peak temperature are found to vary significantly with types of cooling technology. Based upon the results of the model, it appears that internal closed-loop liquid cooling offers the greatest potential for midterm development. Hybrid systems with internally liquid-cooled nozzles and traditional air-cooled rotors seem most attractive for the near term. These could be further improved by using steam rather than air for cooling the rotor.
Experimental Evaluation of Heavy Fan-High-Pressure Compressor Interaction in a Three-Shaft Engine: Part II—Analysis of Distortion and Fan Loading
Authors: Scha¨ffler A. , Miatt D. C.
Published: October 2009

Analysis of a severe rotating-stall phenomenon encountered in the fan core section of a three-shaft low bypass engine revealed interesting insight into the growth and circumferential extension of the stall cells immediately before surge of the high-pressure compressor was induced. The effect of a rotating distortion in contrast to the usually encountered stationary distortion is highlighted. The rotating distortion changes the time and hence the effectively felt distortion sector angle depending on a co- or contra-rotational arrangement of the distorting and the distorted compressor. The analysis shows that a contra-rotational arrangement provides a more stable and tolerant situation against that type of distortion. Analysis of the fan loading shows the static temperature rise coefficient to be the most descriptive for the fan rotor 1 hub section which initiated the rotating-stall mechanism.
Effect of Elevated Temperature and Pressure on Sprays From Simplex Swirl Atomizers
Authors: Dodge L. G. , Biaglow J. A.
Published: October 2009

The effects of air temperature and air pressure on spray quality of a moderately high capacity pressure swirl atomizer (127 kg/h MPa or 23.3 lbm/h psid) spraying jet-A and No. 2 diesel fuel have been examined. Drop-size distributions, in terms of both Sauter mean diameter (SMD) and the width of the distribution as given by the Rosin-Rammler N parameter, and cone angle as measured close to the nozzle (10-mm distance) have been determined over a variety of air conditions. A new correction procedure was developed to extend diffraction-based drop-size measurements in dense sprays from maximum optical opacities of 50% to maximum opacities of 96%, equivalent to an increase in spray density of a factor of five. Drop-size measurements are reported for a temperature range of room temperature (297K) to 589K and air pressures of atmospheric (101 kPa) to 597 kPa. Cone angle data are reported for temperatures to 589K and pressures to 1318 kPa. The maximum operating temperature was limited to the occurrence of autoignition. Close to the nozzle (25 mm), limited data suggest that the SMD’s were a strong function of air density, SMD ∼ ρ−0.53, but independent of air temperature (which affects air viscosity). The width of the distribution narrowed slightly with increasing density, N ∼ ρ0.15, at 25-mm distance. Trends of SMD and N are also shown as a function of distance from the nozzle at all conditions. These trends indicate some of the evaporation characteristics of fuel sprays. Pressure drop across the nozzle had an unusually large effect on SMD with SMD ∼ (ΔP)−0.86. At 10 mm from the nozzle exit, the cone angle of the nominal 80 deg cone angle nozzle was φ = 79.8–0.918 (ρ/ρ0) where ρ is the air density at the test condition and ρ0 the density at atmospheric conditions.
Investigation of a Tip Clearance Cascade in a Water Analogy Rig
Authors: Graham J. A. H.
Published: October 2009

The tip clearance flow region of high-pressure axial turbine blades for small gas turbine engines has been investigated in a water flow cascade. The blade model features variable clearance and variable endwall speeds. The cascade is scaled for Reynolds number and sized to give velocities suitable for visualization. Pressure profiles were measured on one blade, and correlated with the visualization. Unloading is found to be a major feature of the pressure field at both tip and midspan, and is intimately connected with scraping effects and the behavior of the clearance vortex. Some initial hot-film velocity measurements are also presented.
An Experimental Investigation Into Unsteady Blade Forces and Blade Losses in Axial Compressor Blade Cascade
Authors: Sugeng F. , Fiedler K.
Published: October 2009

The unsteady flow problem in the axial compressor has been simulated in wind-tunnels by means of high-speed rotating cylinders upstream of the blade row. To obtain the dynamic changes in the flow properties 20 high-response pressure transducers and 20 high-response hot-film, which are embedded at the surface of the selected blade, have been used in connection with a periodic sampling and averaging technique in digital data acquisition and reduction. The fluctuating forces and the fluctuating drags acting on the blade due to passing wakes shedding through the blade row are carried out.
Dynamic Response of a Centrifugal Blower to Periodic Flow Fluctuations
Authors: Abdel-Hamid A. N.
Published: October 2009

Experimental investigation of the dynamic response of a centrifugal blower to periodic flow rate modulations was carried out at different blower operating conditions. For modulation frequencies in the range of 0.0085–0.085 of the shaft rotation frequency, the fluctuating pressures at inlet, discharge, and across a flow orifice were simultaneously measured and analyzed in the time and frequency domains. Measurements of the amplitude and phase of the transfer function between the blower static pressure rise and the discharge flow rate fluctuations indicated that the quasi-steady approximation should be limited to frequencies lower than 0.02 of the shaft rotation frequency. For the same average flow rate, the static pressure rise progressively lagged the discharge flow rate fluctuations as the frequency was increased. The trend was similar to that of the inertia effects of a fluctuating flow in a pipe. For the same frequency these inertia effects increased as the average flow rate through the blower was decreased. Applications of the results to on-line measurements of the slope of the characteristic curve and improved dynamic modeling of centrifugal compressors and blowers are discussed.
A Distinction Between Different Types of Stall in a Centrifugal Compressor Stage
Authors: Ka¨mmer N. , Rautenberg M.
Published: October 2009

The flow at the stall line of a centrifugal compressor with vaneless diffuser was investigated at different speeds. A distinction between three kinds of stall phenomena could be made. One type of stall with regurgitation of fluid at the impeller inlet was of a nonperiodic character, whereas two different types of periodic stall appeared at higher speeds. The rotating nature of these two types of stall was verified from a comparison of signals of peripherally spaced pressure transducers. The low-frequency rotating stall exhibited features of diffuser generated stall and a lobe number of three was measured. From a detailed investigation of the high-frequency rotating stall, which included unsteady probe measurements upstream and downstream of the impeller, it can be shown that this type of rotating stall is generated in the impeller by a periodic breakdown of energy transfer from the rotor to the flow. This conclusion is supported by the distribution of shroud static pressures.
A Theory of Post-Stall Transients in Axial Compression Systems: Part II—Application
Authors: Greitzer E. M. , Moore F. K.
Published: October 2009

Using the theory developed in Part I, calculations have been carried out to show the evolution of the mass flow, pressure rise, and rotating-stall cell amplitude during compression system post-stall transients. In particular, it is shown that the unsteady growth or decay of the stall cell can have a significant effect on the instantaneous compressor pumping characteristic and hence on the overall system behavior. A limited parametric study is carried out to illustrate the impact of different system features on transient behavior. It is shown, for example, that the ultimate mode of system response, surge or stable rotating stall, depends not only on the B parameter, but also on the compressor length-to-radius ratio. Small values of the latter quantity tend to favor the occurrence of surge, as do large values of B. Based on the analytical and numerical results, some specific topics are suggested for future research on post-stall transients.
Through-Flow Modeling of Axial Turbomachinery
Authors: Dring R. P. , Joslyn H. D.
Published: October 2009

Through-flow analysis, which is at the heart of the aerodynamic design of turbomachinery, requires as aerodynamic input a row-by-row description of the airfoil loss, deviation, and blockage. Loss and deviation have been investigated extensively in both cascades and rotating rigs as well as in numerous two- and three-dimensional analytical studies. Blockage, however, has received far less attention. As defined herein, blockage is a measure of the departure of the flow field from the condition of axisymmetry which is assumed in the through-flow analysis. The full-span blockage distributions calculated from measured single-stage rotor wake data were used to provide the input to the through-flow analysis, along with the measured full-span distributions of loss and deviation. Measured and computed results are compared for the single-stage rotor operating with both thick and thin inlet hub and tip boundary layers. It is demonstrated that both the level and the spanwise and streamwise distributions of blockage have a strong impact on the computed rotor exit flow field.
A Unified Theory of Hybrid Problems for Fully Three-Dimensional Incompressible Rotor Flow Based on Variational Principles With Variable Domain
Authors: Liu Gao-lian
Published: October 2009

Making use of functional variations with variable domain and natural boundary conditions, this paper presents a unified theory of various hybrid problems (being a unification as well as a generalization of direct and inverse problems) for three-dimensional incompressible potential flow in a rotor blading. Three families of variational principles (VPs) have been established and provide a series of new rational ways for blade design and a sound theoretical basis for the finite element method (FEM). This theory can be extended to compressible and rotational flows and also constitutes an important part of the optimum design theory of bladings [8].
Growth of Secondary Flow Losses Downstream of a Turbine Blade Cascade
Authors: Chen L. D. , Dixon S. L.
Published: October 2009

Endwall total pressure losses downstream of a low-speed turbine cascade have been measured at several planes in order to determine the changes in secondary flow loss coefficients and the growth of the mixing loss with distance downstream. The results obtained are compared with various published secondary flow loss correlations in an attempt to explain some of the anomalies which presently exist. The paper includes some new correlations including one for the important gross secondary loss coefficient YSG with loading and aspect ratio parameters as well as the upstream boundary layer parameters.
The Influence of a Variable Normal Load on the Forced Vibration of a Frictionally Damped Structure
Authors: Menq C.-H. , Griffin J. H. , Bielak J.
Published: October 2009

An approximate procedure is developed for calculating the steady-state response of frictionally damped structures for which the normal load across the friction interface consists of a constant force and a force that varies linearly with the vibratory displacement. Such situations occur quite frequently in practice, as, for example; in the case of shrouded fan blades or in certain types of turbine-blade friction dampers. Depending on the magnitudes of the constant and the variable normal loads, the friction element will either stick, slip, or lift off at various intervals during a cycle of oscillation. The various possibilities are considered in the present study. Results from the approximate method are compared with “long-time” solutions obtained from a conventional transient analysis of the problem in order to assess the accuracy of the proposed procedure. As an application, the new method is then used to study the influence of the dynamic coupling on the optimization of the friction force in turbine blade dampers. Results show that the optimum friction force and the maximum amplitude of the response increase with dynamic coupling.
Influence of Friction Dampers on Torsional Blade Flutter
Authors: Sinha A. , Griffin J. H. , Kielb R. E.
Published: October 2009

This paper deals with the stabilizing effects of dry friction on torsional blade flutter. A lumped parameter model with single degree of freedom per blade has been used to represent the rotor stage. The well-known cascade theories for incompressible and supersonic flows have been used to determine the allowable increase in fluid velocity relative to the blade. It has been found that the effectiveness of friction dampers in controlling flutter can be substantial.
An Iwatsubo-Based Solution for Labyrinth Seals: Comparison to Experimental Results
Authors: Childs D. W. , Scharrer J. K.
Published: October 2009

The basic equations are derived for compressible flow in a labyrinth seal. The flow is assumed to be completely turbulent in the circumferential direction where the friction factor is determined by the Blasius relation. Linearized zeroth and first-order perturbation equations are developed for small motion about a centered position by an expansion in the eccentricity ratio. The zeroth-order pressure distribution is found by satisfying the leakage equation while the circumferential velocity distribution is determined by satisfying the momentum equation. The first-order equations are solved by a separation of variable solution. Integration of the resultant pressure distribution along and around the seal defines the reaction force developed by the seal and the corresponding dynamic coefficients. The results of this analysis are compared to published test results.
Effects of Fluid Inertia and Turbulence on the Force Coefficients for Squeeze Film Dampers
Authors: San Andre´s L. , Vance J. M.
Published: October 2009

The effects of fluid inertia and turbulence on the force coefficients of squeeze film dampers are investigated analytically. Both the convective and the temporal terms are included in the analysis of inertia effects. The analysis of turbulence is based on friction coefficients currently found in the literature for Poiseuille flow. The effect of fluid inertia on the magnitude of the radial direct inertia coefficient (i.e., to produce an apparent “added mass” at small eccentricity ratios, due to the temporal terms) is found to be completely reversed at large eccentricity ratios. The reversal is due entirely to the inclusion of the convective inertia terms in the analysis. Turbulence is found to produce a large effect on the direct damping coefficient at high eccentricity ratios. For the long or sealed squeeze film damper at high eccentricity ratios, the damping prediction with turbulence included is an order of magnitude higher than the laminar solution.
New Integration Techniques for Chemical Kinetic Rate Equations: Part II—Accuracy Comparison
Authors: Radhakrishnan K.
Published: October 2009

A comparison of the accuracy of several techniques recently developed for solving stiff differential equations is presented. The techniques examined include two general-purpose codes EPISODE and LSODE developed for an arbitrary system of ordinary differential equations, and three specialized codes CHEMEQ, CREK1D, and GCKP84 developed specifically to solve chemical kinetic rate equations. The accuracy comparisons are made by applying these solution procedures to two practical combustion kinetics problems. Both problems describe adiabatic, homogeneous, gas-phase chemical reactions at constant pressure, and include all three combustion regimes: induction, heat release, and equilibration. The comparisons show that LSODE is the most efficient code—in the sense that it requires the least computational work to attain a specified accuracy level—currently available for chemical kinetic rate equations. An important finding is that an iterative solution of the algebraic enthalpy conservation equation for the temperature can be more accurate and efficient than computing the temperature by integrating its time derivative.
Design of Combustor Cooling Slots for High Film Effectiveness: Part I—Film General Development
Authors: Sturgess G. J.
Published: October 2009

The metal liners of gas turbine engine combustors usually have to be provided with some form of thermal protection from the high temperatures of the reacting mixture of gases contained therein. For aircraft gas turbines, where weight is a factor, the protective medium is air. The air is most usually introduced by tangential injection as a discrete film at a number of axial stations along the combustor liner so that as the cooling potential of one film is depleted it is periodically renewed by another. Although invariably referred to as film cooling, the most important function of the film air is to act as a relatively cool barrier between the vulnerable liner and the reacting gases. The design margin for error is very small. Failure to design a cooling slot that provides a high film effectiveness can result in thermal damage to the liner. Manufacturing considerations almost always determine how a real slot design is reduced to practice. The resulting liners (inner and outer in the case of an annular combustor) contain no two slots that are exactly alike in aerodynamic behavior and, therefore, in film effectiveness performance. Phenomenological models of the film cooling process are invariably based on considerations of two-dimensional shear mixing. Empirical factors may be introduced to account for the differences in performance existing between two-dimensional film slots and real slots. However, such methods are not of much help in designing a slot configuration that will deliver good performance, for making comparative evaluations of competing designs, or in establishing the performance penalties associated with compromises made for manufacturing reasons. Heuristic arguments are used to derive a dimensionless grouping of internal geometric parameters that describe the lateral aerodynamic uniformity of the films produced by practical slots. It is assumed that the average film effectiveness is uniquely related to the film lateral uniformity. Experimental data from a number of different practical slot designs are examined in terms of this geometric mixing parameter, and film effectiveness is shown to depend on it over a wide range of axial distances and film blowing ratios. It is concluded that the geometric mixing parameter provides a means to differentiate good film cooling slot designs from poor ones.
Design of Combustor Cooling Slots for High Film Effectiveness: Part II—Film Initial Region
Authors: Sturgess G. J. , Pfeifer G. D.
Published: October 2009

A heuristically based geometric grouping has been used to relate the geometry of practical film cooling slots of gas turbine engine combustors to the circumferential uniformity of axial velocity in the film and the average film effectiveness. To be satisfactory, the cooling performance of a slot has been shown to require a low value of this group. A study of film development has been extended to the initial region of the film where cooling performance is at its maximum. It is demonstrated that such a region exists for both practical slots and idealized two-dimensional slots, but that the character of the initial region flow is completely different for practical slots and cannot be described by the same methods as can be used for two-dimensional slots.
Cold Flow and Combustion Experiments With a New Burner Air Distribution Concept
Authors: Johnson B. V. , Markowski S. J. , Craig H. M.
Published: October 2009

Experiments were conducted with a JT8D-engine sized can combustor modified such that all the combustion and dilution air entered through the burner front face from a single plenum through counter-rotating annular swirlers. Cold flow experiments were conducted to visualize and to develop a mixing and recirculation flow pattern within the combustor which contained annular and central recirculation cells and featured rapid mixing in the downstream section of the combustor. Laser velocimeter measurements, downstream of the air inlet configuration used in the combustion experiments, showed the largest velocity gradients in the radial direction were in the tangential velocity profile. Low-pressure combustion experiments were conducted with three flat spray fuel nozzle orientations and three air inlet geometries to determine the general air inlet and fuel injection characteristics required to produce acceptable combustion characteristics with the selected swirler configuration. The combustion experiments included emission, total pressure and total temperature measurements at the burner exit plane. Low emission levels and temperature pattern factors with relatively low burner pressure losses were demonstrated.
Flame Temperature Estimation of Conventional and Future Jet Fuels
Authors: Gu¨lder O¨. L.
Published: October 2009

An approximate formula is presented by means of which the adiabatic flame temperature of jet fuel-air systems can be calculated as functions of pressure, temperature, equivalence ratio, and hydrogen to carbon atomic ratio of the fuel. The formula has been developed by fitting of the data from a detailed chemical equilibrium code to a functional expression. Comparisons of the results from the proposed formula with the results obtained from a chemical equilibrium code have shown that the average error in estimated temperatures is around 0.4 percent, the maximum error being less than 0.8 percent. This formula provides a very fast and easy means of predicting flame temperatures as compared to thermodynamic equilibrium calculations, and it is also applicable to diesel fuels, gasolines, pure alkanes, and aromatics as well as jet fuels.
The Quantification and Improvement of the Thermal Stability of Aviation Turbine Fuel
Authors: Mills J. S. , Kendall D. R.
Published: October 2009

Studies of the propensity of aviation turbine fuels to lacquer engine oil-coolers that were described in an earlier paper have been extended to cover a wider range of fuels. Fuel performance was found to vary widely; some fuels were liable to lacquer oil-coolers to the extent of producing significant losses in efficiency at the most severe operating conditions currently encountered. Oxidation studies conducted in parallel with the rig investigations indicate that a fuel’s performance is strongly dependent on its tendency to initiate radical oxidation reactions. The relatively high initiation rate of less stable fuels is believed to be due in part to their trace content of metals that catalyze oxidation reactions. Accordingly, an approved metal deactivating additive has been examined as a means of improving the performance of such fuels.
USAF Toxicology Research on Petroleum and Shale-Derived Aviation Gas Turbine Fuels
Authors: Martone J. A.
Published: October 2009

As one of the nation’s largest users of aircraft turbine fuels, the USAF has interest in assuring the safe use of these hydrocarbons by its military and civilian workers. This concern stimulated research to define potential adverse health effects and develop criteria for safe exposure limits for military aviation fuels. The first inhalation exposure to JP-4, the primary fuel used in USAF aircraft, was conducted in 1973. Since this initial subchronic study, the USAF has conducted numerous subchronic and one-year oncogenic inhalation studies to establish health criteria for aviation fuels. This paper summarizes the status of studies to define the toxicity of petroleum and shale-derived aircraft turbine engine fuels and discusses the preliminary findings of toxic nephropathy and primary renal tumors observed in male Fischer 344 rats.
Evaluation of Fuel Preparation Systems for Lean Premixing-Prevaporizing Combustors
Authors: Dodds W. J. , Ekstedt E. E.
Published: October 2009

A series of tests was conducted to provide data for the design of premixing-prevaporizing fuel-air mixture preparation systems for aircraft gas turbine engine combustors. Fifteen configurations of four different fuel-air mixture preparation system design concepts were evaluated to determine fuel-air mixture uniformity at the system exit over a range of conditions representative of cruise operation for a modern commercial turbofan engine. Operating conditions, including pressure, temperature, fuel-air ratio, and velocity had no clear effect on mixture uniformity in systems which used low-pressure fuel injectors. However, performance of systems using pressure atomizing fuel nozzles and large-scale mixing devices was shown to be sensitive to operating conditions. Variations in system design variables were also evaluated and correlated. Mixture uniformity improved with increased system length, pressure drop, and number of fuel injection points per unit area. A premixing system compatible with the combustor envelope of a typical combustion system and capable of providing mixture nonuniformity (standard deviation/mean) below 15% over a typical range of cruise operating conditions was demonstrated.
Low-Temperature Hot Corrosion in Gas Turbines: A Review of Causes and Coatings Therefor
Authors: Goward G. W.
Published: October 2009

In about 1975 an apparently new form of hot corrosion attack of gas turbine airfoils was identified during low-power, low-metal-temperature operation of a marine gas turbine. The rate of this corrosion was substantially greater at about 700° C than that usually observed for sulfate-induced hot corrosion at 800° to 1000° C. The same type of hot corrosion has been subsequently reported to occur in ground-based gas turbines, and is similar in principle to fireside corrosion of boiler tubes. This paper presents a review of probable mechanisms of this so-called low-temperature hot corrosion, of test methods for its laboratory and rig simulation, and of coatings in use or in advanced development for protection of gas turbine airfoils operating in this corrosion regime.
Experimental and Analytical Investigation on the Variation of Spray Characteristics Along Radial Distance Downstream of a Pressure Swirl Atomizer
Authors: Zhao Y. H. , Li W. M. , Chin J. S.
Published: October 2009

The variation of spray characteristics (Sauter Mean Diameter and Rosin-Rammler drop-size distribution parameter) downstream of a pressure swirl atomizer along radial distance has been measured by laser light scattering technology. An analytical model has been developed that is capable of predicting the variation of spray characteristics along radial distance. A comparison between the prediction and experimental data shows excellent agreement. It shows that the spray model proposed, although relatively simple, is correct and can be used with some expansion and modification to predict more complicated spray systems.
Measurements of Entrainment by Acoustically Pulsed Axisymmetric Air Jets
Authors: Vermeulen P. J. , Ramesh V. , Yu Wai Keung
Published: October 2009

Direct measurements of entrainment by acoustically pulsed axisymmetric air jets flowing into surrounding air have been made for a range of orifice sizes, Strouhal numbers, and excitation powers. The entrainment was considerably increased, by up to 5.8 times at distances greater than 15 diameters axially downstream of the orifice exit plane. The entrainment of the excited jet varied linearly with downstream distance. The jet response varied nonlinearly with excitation strength, indicating that there may be a practical upper limit to the acoustic augmentation of entrainment. The response depends on Strouhal number and appears to be optimum at about 0.25.
An Improved Method for Accurate Prediction of Mass Flows Through Combustor Liner Holes
Authors: Adkins R. C. , Gueroui D.
Published: October 2009

A theory is devised for predicting the coefficients of discharge for some types of combustor liner holes and for calculating the local quantity of airflow into the liner. The resulting equations are tested against reliable empirical data and they show an agreement of better than 99 percent. The new correlation is particularly amenable to the preliminary design and development of combustors and could usefully be incorporated into numerical modeling techniques. The theory is also used to devise a simple but very accurate method of correlating experimental data that has advantages over many of the methods in current use.
Reliability Evaluation of Ceramic Rotor for Passenger-Car Turbochargers
Authors: Hamano Y. , Sagawa N. , Miyata H.
Published: October 2009

A performance advantage is expected when the rotors of turbochargers are made out of ceramics. In order to qualify as commercially produced engine components, ceramic rotors must demonstrate confirmed reliability because the operation conditions are severe and the behavior of ceramic components under such conditions is not well understood. By the progress of related technologies such as designing, shape-forming, and ceramics-to-metal joining, ceramic rotors having high enough reliability levels as confirmed by NDE methods are produced.
Analysis and Solution of a Nonsynchronous Vibration Problem in the Last Row Turbine Blade of a Large Industrial Combustion Turbine
Authors: Scalzo A. J. , Allen J. M. , Antos R. J.
Published: October 2009

This paper presents the analysis and corrective action taken to solve a flow-induced nonsynchronous vibration failure problem encountered in the last-stage rotating blade in a large industrial combustion turbine. A description of the fatigue failures and of temporary operation restrictions that precluded further failure is given. The results from a strain gage telemetry test are presented which show that failure was due to high vibratory stress excursions from fundamental mode vibration, which resulted from broad band buffeting excitations and very low aerodynamic damping at high levels of power and mass flow. From these data, design criteria were developed for designing a retrofittable blade that removed the operating restrictions. Telemetry test results (from the same turbine), which verified the new design, are also briefly presented and discussed. This investigation shows that the design of future high-performance exhaust end combustion turbine blading must take into account nonsynchronous excitation (buffeting) and the aeroelastic interaction between blade structure and flow, in addition to the synchronous excitations traditionally allowed for in the design process.
Experimental Rotordynamic Coefficient Results for Teeth-on-Rotor and Teeth-on-Stator Labyrinth Gas Seals
Authors: Childs D. W. , Scharrer J. K.
Published: October 2009

An experimental test facility is used to measure the rotordynamic coefficients of teeth-on-rotor and teeth-on-stator labyrinth gas seals. Direct damping coefficients are presented for these seals for the first time. The results are presented for the two seal configurations at identical operating conditions, and show that, in a rotordynamic sense, the teeth-on-stator seal is more stable than the teeth-on-rotor seal, for inlet tangential velocity in the direction of rotation.
Effect of Control Algorithms on Magnetic Journal Bearing Properties
Authors: Humphris R. R. , Kelm R. D. , Lewis D. W. , Allaire P. E.
Published: October 2009

Magnetic journal bearings are coming into increasing use in industry today. They are primarily used to replace either rolling element or fluid film bearings in rotating machinery. The major advantages are elimination of oil systems and associated seals, expected very long life, very low power losses, and great potential for vibration reduction. Disadvantages include lack of field experience, unknown reliability over a long time, high cost (so far primarily due to the small quantity being made for a given application), and advanced automatic control design required. This paper discusses the design of a magnetic journal bearing with four electromagnets arranged radially around a shaft to fully support a rotor. Each electromagnetic is connected to a controlling electronics circuit which regulates the current to the magnet. For the measurements presented here, only the top magnet was tested and the shaft was not rotating. Thus a single control algorithm was isolated from other effects. This paper compares two control algorithms with differing circuit band widths of 1.2 kHz and 50 kHz. The wider bandwidth algorithm produced approximately a sixfold increase in magnetic bearing stiffness and a much greater stable operating region compared to the lower bandwidth algorithm. Overall, the calculated effective stiffness and damping coefficients were within 20 to 30 percent of the measured values.
Numerical Simulations of Two-Stroke Cycle Engines Using Coal Fuels
Authors: Kishan S. , Bell S. R. , Caton J. A.
Published: October 2009

An analytical model of a two-stroke cycle, reciprocating, compression ignition engine was used to investigate the ignition and combustion characteristics of coal/water slurry fuels. The engine cycle simulation was based on a thermodynamic analysis of the cylinder contents and consisted of models for the injection, ignition, combustion, mixing, heat transfer, work, and scavenging processes. The thermodynamic analysis resulted in a set of first-order nonlinear, ordinary differential equations which were numerically integrated to obtain instantaneous cylinder gas, droplet, and particle conditions. The simulation results were first compared to experimental data from a large, slow-speed (120 rpm) engine using a coal/water slurry fuel. Complete validation of the model was not possible due to the lack of detailed experimental data, but comparisons are presented which indicate general agreement between measured and computed values. The model was then used to predict the performance of an engine representative of a locomotive medium-speed engine. Engine and fuel parameters were varied to study their effect on ignition and combustion of the coal/water slurry fuel and on the indicated engine performance. Increases in the inlet air temperature improved the ignition and combustion characteristics. Lower equivalence ratios or smaller particle sizes resulted in higher thermal efficiencies. Also, higher reactive coal led to increased cylinder pressures and higher thermal efficiencies due to faster burning rates.
Simulation of Subsonic Flow Through a Generic Labyrinth Seal
Authors: Rhode D. L. , Sobolik S. R.
Published: October 2009

A new method for predicting the leakage through labyrinth seals has been developed and is shown to provide realistic results which agree with measurements. It utilizes a finite-difference computer code which was developed in order to compute the pressure drop across a single cavity of the seal. This quantity is obtained at several leakage flow Mach numbers to be used subsequently in predicting the leakage rate. The model is widely applicable and does not require an estimate of the kinetic energy carry-over coefficient, whose value is often uncertain for many untested configurations. Detailed cavity distributions of basic flowfield quantities are also presented and examined. Specifically, the predicted results of four seal leakage mass flow rates at given cavity inlet pressure and temperature are compared, and important variations are examined. Also, realistic approximations of flow variable distributions within a single cavity are made from the included figures to assist in the development of analytical methods.
Multiaxial Life Prediction System for Turbine Components
Authors: Arvanitis S. T. , Symko Y. B. , Tadros R. N.
Published: October 2009

The objective of this paper is to present a complete three-dimensional life prediction system which was developed for turbine engine components. It will deal primarily with turbine blades and vanes which are subjected to hostile thermal and combustion environments under load which creates cyclic and/or steady multiaxial stress and strain fields. All of the above factors combined are detrimental to the service life of these components and need very careful consideration at the design stage. The developed multiaxial system for a mission includes evaluation of transient metal temperatures, corresponding elastic and inelastic strains, creep strains, and subsequently creep/fatigue lives. The calculations are performed using the ductility exhaustion method. The maximum principal normal strain ranges used in the life analysis are found by a developed procedure for a multiaxial system. The concept is based on analyzing all of the time steps computed in the mission, in order to develop the maximum principal normal strain range whose direction and magnitude is strictly a function of the component geometry and mission loading. The mission creep is then developed by maximizing a cumulative creep function. Directional consistency is maintained in accumulating creep/fatigue damage with respect to the incurred multiaxial stress and strain fields. Also the most damaging mission modes (creep or fatigue) will be separated. Further development in the model includes the capability of analytically obtaining the fatigue curve for any ratio R of minimum to maximum strain using baseline fatigue material properties (R = −1.0). Application of the model to an actual uncooled vane correlates well with test rig development experience.
A Comparison of the Predicted and Measured Thermodynamic Performance of a Gas Turbine Cogeneration System
Authors: Baughn J. W. , Kerwin R. A.
Published: October 2009

The thermodynamic performance of a gas turbine cogeneration system is predicted using a computer model. The predicted performance is compared to the actual performance, determined by measurements, in terms of various thermodynamic performance parameters which are defined and discussed in this paper. These parameters include the electric power output, fuel flow rate, steam production, electrical efficiency, steam efficiency, and total plant efficiency. Other derived parameters are the net heat rate, the power-to-heat ratio, and the fuel savings rate. This paper describes the cogeneration plant, the computer model, and the measurement techniques used to determine each of the necessary measurands. The predicted and the measured electric power compare well. The predicted fuel flow and steam production are less than measured. The results demonstrate that this type of comparison is needed if computer models are to be used successfully in the design and selection of cogeneration systems.
Part-Load Behavior of a Solar-Heated and Fossil-Fueled Gas Turbine Power Plant
Authors: Bammert K. , Lange H.
Published: October 2009

Solar energy can be converted effectively into electrical or mechanical energy. The radiant heat of the sun is collected by a parabolic dish, concentrated intensely, and reflected into a cavity receiver. Air flowing through tube panels in front of the receiver inner walls absorbs the radiant energy. Downstream of the receiver is a fossil-fired combustion chamber (hybrid construction). The fuel energy is converted at a higher utilization than in a straight fossil-fueled power plant. The overall efficiency of the hybrid plant rises with increasing turbine inlet temperature. The power delivered by the turbine serves to drive the compressor and the generator. A description of the thermodynamic design of the cycle is followed by statements on the performance characteristics of the individual components and by a description of the steady-state part-load behavior of the plant considering specific conditions such as variations in solar and fossil fuel-generated heat and fluctuating load on the power transmission grid.
Dynamic Behavior of a Solar-Heated Receiver of a Gas Turbine Plant
Authors: Bammert K. , Johanning J.
Published: October 2009

The mainly nonstationary operation of a solar-heated receiver can be simulated with sufficient accuracy only if data about the dynamic behavior are available. For this reason, the dynamic behavior of a solar cavity receiver with parabolic dish collector is investigated. The development of a mathematical simulation considering heat transfer and storage processes is presented and the procedure for a numerical solution is illustrated. The performance of the calculation method is finally demonstrated by simulating the passage of a cloud.
Wetness and Efficiency Measurements in L.P. Turbines With an Optical Probe As an Aid to Improving Performance
Authors: Walters P. T.
Published: October 2009

An absolute value for the wetness fraction in a partially condensed steam flow may be calculated from measurements of light transmission using the results of fundamental electromagnetic scattering theory. A probe is described that uses this principle for measuring radial wetness profiles in the final stages of L.P. turbines. Results are presented to show that the probe will provide reliable values for overall L.P. turbine efficiency and valuable diagnostic data on the performance of individual stages operating with wet or condensing flows.
Thermodynamic Evaluation of Gas Turbine Cogeneration Cycles: Part II—Complex Cycle Analysis
Authors: Rice I. G.
Published: October 2009

Complex open gas turbine cycles are analyzed by applying the heat balance method presented in Part I of this paper. Reheating, intercooling, regeneration, steam injection, and steam cooling are evaluated graphically to give a visual perspective of what takes place in terms of the overall heat balance when such complexities are introduced to the cycle. An example of a viable, new, intercooled regenerative cycle is given. A second example of a prototype reheat gas turbine is also included. The overall approach using the heat balance method can be applied to various cogeneration configurations when considering the more complex cycles of the future.
Acceleration Performance of Helicopter Engines
Authors: Maltby M. R.
Published: October 2009

The desirability of good acceleration behavior from helicopter gas turbine engines is discussed in the context of the increasing demand for helicopter maneuverability and safety. Features which result in improved engine handling qualities are discussed and reference is made to some analytical techniques which may be employed to assist in obtaining the best results.