bluuebunny/crossref_metadata_2025 huggingface dataset:
A Bayesian Quantile Regression Model for Insurance Company Costs Data
Authors: Sriram Karthik , Shi Peng , Ghosh Pulak
Published: March 2015

We examine the average cost function for property and casualty insurers. The cost function describes the relationship between a firm's minimum production cost and outputs. A comparison of cost functions could shed light on the relative cost efficiency of individual firms, which is of interest to many market participants and has been given extensive attention in the insurance industry. To identify and to compare the cost function, current practice is to assume a common functional form between costs and outputs across insurers and then to rank insurers according to the centre of the cost distribution. However, the assumption of a common cost–output relationship could be misleading because insurers tend to adopt different technologies that are reflected by the cost function in their production process. The centre-based comparison could also lead to biased inference especially when the cost distribution is skewed with a heavy tail. To address these issues, we model the average production cost of insurers by using a Bayesian quantile regression approach. Quantile regression enables the modelling of different quantiles of the cost distribution as opposed to just the centre. The Bayesian approach helps to estimate the cost-to-output functional relationship at a firm level by borrowing information across firms. In the analysis of US property–casualty insurers, we show that better insights into efficiency are gained by comparing different quantiles of the cost distribution.
Current Status of 300kW Industrial Ceramic Gas Turbine R&D in Japan
Authors: Honjo Kaoru , Hashimoto Ryosaku , Ogiyama Hisao
Published: March 2015

This paper gives an overview of the current status of Japan’s national industrial ceramic gas turbine (CGT) project.

The goals are 42% and higher thermal efficiency at the turbine inlet temperature (TIT) of 1350°C, and the emission from the exhaust gas should meet the regulatory values (for example, 70ppm for NOx). Also, ceramic material properties have the goals of 400 MPa for the minimum guaranteed strength at 1500°C, and 15 MPa m for the fracture toughness.

Currently, the basic metal gas turbine of TIT 900°C with all metallic components has already been fabricated and is running under some test conditions. The design of the basic ceramic gas turbine of TIT 1200°C has been completed and its manufacture is in progress. Research is addressing the production of large, complicated ceramic parts, and parts which have less deformation and defects can now be produced.
A Statistical Approach to the Experimental Evaluation of Transonic Turbine Airfoils in a Linear Cascade
Authors: Shelton M. L. , Gregory B. A. , Doughty R. L. , Kiss T. , Moses H. L.
Published: March 2015

In aircraft engine design (and in other applications), small improvements in turbine efficiency may be significant. Since analytical tools for predicting transonic turbine losses are still being developed, experimental efforts are required to evaluate various designs, calibrate design methods, and validate CFD analysts tools. However, these experimental efforts must be very accurate to measure the performance differences to the levels required by the highly competitive aircraft engine market. Due to the sensitivity of transonic and supersonic flow fields, it is often difficult to obtain the desired level of accuracy. In this paper, a statistical approach is applied to the experimental evaluation of transonic turbine airfoils in the VPI & SU transonic cascade facility in order to quantify the differences between three different transonic turbine airfoils. This study determines if the measured performance differences between the three different airfoils are statistically significant. This study also assesses the degree of confidence in the transonic cascade testing process at VPI & SU.
Lifting Surface Theory for Steady Aerodynamic Analysis of Ducted Counter Rotation Propfan
Authors: Kodama Hidekazu , Namba Masanobu
Published: March 2015

A lifting surface theory is developed to predict the steady performance for ducted counter rotation propfan with blade sweep. In solving the integral equation, the chordwise lifting pressures on the blade surfaces of front and rear rotors are expanded into a finite series at each radial collocation point, and the coefficients of the series are determined so that the blade surface flow tangency conditions for both rotors are satisfied at the corresponding number of control points. Calculations are carried out for the propfans with subsonic relative flows, and the effect of the number of blades on the total pressure rise is studied using a probable blade model. The interference effect between the rotors and the effect of blade sweep on the steady performance are also demonstrated.
The Influence of Adjustable Inlet Guide Vanes on the Performance of Multi-Stage Industrial Centrifugal Compressors
Authors: Lüdtke Klaus
Published: March 2015

Not only single-stage but also multi-stage centrifugal process compressors are often equipped with one row of adjustable Inlet guide vanes before the first stage.

The question, frequently asked by the rotating equipment purchaser is whether such an expensive component is justified for multi-stage centrifugal compressors, since it effects first stage head only. Does or does it not improve turn-down or power consumption in comparison with ordinary butterfly valva suction throttling? The paper examines if and to what degree the favorable turn-down and part-load power consumption of IGV-equipped single-stage machines can be transferred to multi-stage compressors.

An intuitive answer of-course is: the lower the number of stages, the more advantageous is the IGV-equipped compressor. There are however other influential parameters like molecular weight of the gas, Mach number, number of intercoolers and others.

In contrast to axial and integral gear compressors centrifugal single-shaft compressors cannot be equipped with adjustable IGV’s before each stage due to an extreme lack of interstage space dictated by rotordynamic requirements. The maximum number of IGV’s is two for back-to-back arranged centrifugal impellers.
Pressure Distributions in a Single and Two Versions of a Double Volute of a Centrifugal Pump
Authors: de Ojeda W. , Flack R. D. , Miner S. M.
Published: March 2015

Pressure measurements were recorded around the impeller and along the casing wall of a centrifugal pump, 0.60 (1583 US units) specific speed, assembled with a single volute/single discharge, and two versions of a double volute/single discharge. The latter comprised a splitter positioned in the second half of the discharge (i) midway between the impeller and casing, and (ii) along a spiral symmetric to the first–half casing section. The objective of such double volute casings is to reduce forces on the impeller and thus provide longer lives. Flow rates tested ranged from 20% to 105% of design. A repeated pattern consisted of pressure increasing from the first cutwater to the splitter leading edge at which the pressure drops and thereafter increases to the discharge. This pattern was noted at all flow rates with the symmetric volute geometry and only at flow rates higher than 60% for the centered splitter. By integration of the pressures static forces were found. Time averaged static forces ranged from 6.2 N at design to 33.0 N at 20% flow for the single volute. Both double volute configurations showed considerable thrust reduction throughout but for a few exceptions. Reductions ranged from 26% at 30% flow to 62% at 90% flow for the center splitter, and from 52% reduction at 20% flow to 72% at 80% flow for the symmetric splitter. For comparison of performance of the different configurations, at flow rates above 85% of design the head was 8% and 9% less for the double volutes than for the single volutes. At flows below 40% of design the head was 3% and 4% higher for the double volutes than for the single volute.
Aerodynamic Performance of a Transonic Low Aspect Ratio Turbine Nozzle
Authors: Moustapha S. H. , Carscallen W. E. , McGeachy J. D.
Published: March 2015

This paper presents detailed information on the three-dimensional flow field in a realistic turbine nozzle with an aspect ratio of 0.65 and a turning angle of 76 degrees. The nozzle has been tested in a large scale planar cascade over a range of exit Mach numbers from 0.3 to 1.3. The experimental results are presented in the form of nozzle passage Mach number distributions and spanwise distribution of losses and exit flow angle. Details of the flow field inside the nozzle passage are examined by means of surface flow visualization and Schtieren pictures. The performance of the nozzle is compared to the data obtained for the same nozzle tested in an annular cascade and a stage environment. Excellent agreement is found between the measured pressure distribution and the prediction of a 3D Euler flow solver.
Blade Loading and Shock Wave in a Transonic Circular Cascade Diffuser
Authors: Hayami H. , Nakamura T. , Sawae M. , Kawaguchi N.
Published: March 2015

Low-solidity circular cascade, conformally transformed from high-stagger linear cascade of double-circular-arc vanes with solidity 0.69, was tested as a part of diffuser systems of a transonic centrifugal compressor and the static pressures were measured around a vane of the cascade and on the side wall between cascade vanes in detail. The blade loading of cascade vane was discussed by integrating the pressure distribution around the vane. The experimental data for lift-coefficient of vane were almost on a single straight line with positive gradient against angle-of-attack over a wide range of inflow Mach number and inflow angle. The maximum lift-coefficient reached about 1.5 and the vane worked well to the surge condition of the compressor. The structure of shock wave was also discussed by drawing a contour map of flow Mach number between cascade vanes. The normal shock wave was observed on the suction surface of vane and it moved upstream along the suction surface with the decrease in inflow angle. The vane did not fall in stall even though the Mach number upstream of the shock wave was over 1.4.
Recess Vane Passive Stall Control
Authors: Ziabasharhagh M. , McKenzie A. B. , Elder R. L.
Published: March 2015

An experimental investigation has been carried out on the influence of a vaned recessed casing treatment on the stall margin improvement of axial flow fans with different hub to tip ratio, with and without inlet distortion.

The inlet distortion tests were conducted on a 0.5 hub to tip ratio fan and significant increases in the flow range with only small drops in operating efficiency were observed.

The clean flow tests were conducted on higher hub to tip ratio fans (0.7 and 0.9). In each case the stage characteristic was compared with the results obtained with a solid casing. Significant increases in the flow range, with only modest or no loss in operating efficiency, were observed for optimum configurations at both diameter ratios.
Influence of a Thermal Barrier Coating on the Performance of a Turboprop Engine
Authors: MacLeod J. D. , Laflamme J. C. G.
Published: March 2015

Under the sponsorship of the Canadian Department of National Defence, the Engine Laboratory of the National Research Council of Canada has evaluated the influence of applying a thermal barrier coating on the performance of a gas turbine engine. The effort is aimed at quantifying the performance effects of a particular ceramic coating on the first stage turbine vanes. The long term objective of the program is to both assess the relative change in engine performance and compare against the claimed benefits of higher possible turbine inlet temperatures, longer time in service and increased time between overhauls. The engine used for this evaluation was the Allison T56 turboprop with the first stage turbine nozzles coated with the Chromalloy RT-33 ceramic coating.

The issues addressed in testing this particular type of hot section coating were;

1) effect of coating thickness on nozzle effective flow area;

2) surface roughness influence on turbine efficiency;

This paper describes the project objectives, the experimental installation, and the results of the performance evaluations. Discussed are performance variations due to coating thickness and surface roughness on engine performance characteristics. As the performance changes were small, a rigorous measurement uncertainty analysis is included. The coating application process, and the affected overhaul procedures are examined. The results of the pre- and post-coating turbine testing are presented, with a discussion of the impact on engine performance.
Hot Corrosion Resistance of Thermal Barrier Coatings
Authors: Nagaraj B. A. , Maricdcchi A. F. , Wortman D. J. , Patton J. S. , Clarke R. L.
Published: March 2015

The hot corrosion resistance of yttria stabilized zirconia (YSZ) thermal barrier coatings was evaluated using an atmospheric burner rig. The coatings were deposited by plasma spraying and electron beam physical vapor deposition (EB-PVD). The tests were performed for up to 2000 hours at 1700°F and 1300°F. The test parameters were designed to simulate the deposit chemistry and corrosion microstructures observed in marine gas turbine engines. The YSZ coating performed very well in the tests, with no spallation and little bond coat corrosion.

Plasma sprayed YSZ coating was also evaluated by engine testing in a hot corrosive environment. Post test evaluation showed virtually no corrosion of the ceramic or the bond coat. Parts that were not ceramic coated had undergona severe corrosion. The results are discussed in terms of coating microstructures and the chemistry of the environment.
A System Dynamics Approach to Modeling Gas Turbine Combustor Wear
Authors: Bagepalli B. , Dinc S. , Imam I. , Barnes J. , Slocum C.
Published: March 2015

This paper deals with the development of the basic understanding of dynamic and wear problems of combustor systems. A system dynamic modeling approach has been developed using a general purpose dynamic/wear analysis program (Mechanism Analysis Program, MAP), and excellent validation has been achieved via laboratory tests. The objective is to develop a generic design/analysis tool, both, for quick evaluation of preliminary designs, and for detailed design studies to create improved/optimized combustor designs from a wear/life perspective.

Dynamic simulations of two different designs are run: Many worn field samples are available for one design, and laboratory test results for the other. The wear patterns on the former are matched very well by the analytical model. Excellent correlation, too, is obtained with the dynamic (accelerometer) measurements on the latter. It is, now, possible to isolate system dynamic causes (such as resonance) from material related ones (such as hardness) when designing for long life.
Viscous Flows in Centrifugal Compressor Diffusers at Transonic Mach Numbers
Authors: Teipel I. , Wiedermann A. , Evers W.
Published: March 2015

A numerical investigation of steady two- and three-dimensional flow fields in vaned diffusers of highly-loaded centrifugal compressors is described. The explicit MacCormack scheme was used to calculate inviscid and viscous effects because of the possibility of vectorization. Transonic Mach numbers are reached in the entrance of the diffuser and therefore time-dependent equations are solved. Two methods are employed to accelerate convergence of this explicit scheme. These techniques are (1) local time stepping and (2) applying a multigrid scheme. For the turbulent case an improved Baldwin-Lomax model given by Granville has been used.

The numerical procedure has been used to compute two-dimensional transonic flow fields of a centrifugal compressor diffuser at different impeller speeds. It is shown that the predicted pressure field is in reasonable agreement with experimental data. Different approaches for the evaluation of global loss figures have been compared with each other. In addition, an evaluation of the complete three-dimensional Navier-Stokes equations is presented. The vanes in the diffuser are twisted such that the flow field contains a strong three-dimensional effect. Again a comparison with experiments is carried out and the agreement is fairly good.
An Investigation of Post Stall Transients and Recoverability of Axial Compression Systems: Part II — Numerical Simulations
Authors: Jun Hu , Cai Tang Guo , Min Zhang Hui
Published: March 2015

Using the method developed in part I, the calculations of limited parameters, recovery behaviors from stalled flow, and the effect of compression system parameters on the recoverability from rotating stall have been carried out in the present paper. It is shown that the response mode of unstability, rotating stall, classic surge or deep surge, depends not only on the parameter B, but also on the compressor axisymmetrical characteristics and the final throttle setting or the stalled equilibrium operating point, and the critical combination values of (B*H/W) or, which determines whether ultimate oscillation is deep surge, or classic surge (or rotating stall), are very similar for different compressor axisymmetrical characteristic. The calculations of transient recovery behaviors from stalled flow, surge or rotating stall, are carried out to present that the method can be used to investigate these problems, and then the effect of system parameters on the recoverability is investigated to show that the parametre B, the compressor length to radius ratio lc, and the compressor duct parameter in all have little effect on the recoverability at the compression system, but the reciprocal time-lag parameter of blade passage a and compressor axisymmetrical characteristic have strong effect on it. It has been found that decreasing the value of [H/W] can decrease the recovery hysteresis from rotating stall and improves the recoverability of the compressor. The results are consistent with experience.
A Wide-Range Axial-Flow Compressor Stage Performance Model
Authors: Bloch Gregory S. , O’Brien Walter F.
Published: March 2015

Dynamic compression system response is a major concern in the operability of aircraft gas turbine engines. Multi-stage compression system computer models have been developed to predict compressor response to changing operating conditions. These models require a knowledge of the wide-range, steady-state operating characteristics as inputs, which has limited their use as predicting tools.

The full range of dynamic axial-flow compressor operation spans forward and reversed flow conditions. A model for predicting the wide flow range characteristics of axial-flow compressor stages was developed and applied to a 3-stage, low-speed compressor with very favorable results and to a 10-stage, high-speed compressor with mixed results.

Conclusions were made regarding the inception of stall and the effects associated with operating a stage in a multistage environment. It was also concluded that there are operating points of an isolated compressor stage that are not attainable when that stage is operated in a multi-stage environment.
Modified Surge in an Axial Flow Compressor
Authors: Půst Libor
Published: March 2015

This paper deals with an experimental study of the unsteady flow in a multistage axial-flow compressor with a high design flow coefficient (p = 1.2) at rpm lower than the design ones. A detailed description of the rotating stall during the so-called “modified surge” is given. In this surge type the rotating stall exists during all the surge cycle, in contradistinction of classic surge, when the rotating stall exists only in a part of the surge cycle.
Secondary Flows in a Transonic Cascade: Validation of a 3-D Navier-Stokes Code
Authors: Bassi F. , Savini M.
Published: March 2015

In this work is presented a finite volume full 3-D Navier-Stokes solver suitable for turbulent turbomachinery computations. The code is applied to the analysis of the secondary flow patterns in a transonic turbine cascade at three different isentropic outlet Mach numbers; namely 0.50, 1.02, 1.38. Detailed measurements obtained in four planes downstream of the trailing edge allow for comparison of losses, flow angles, vorticity and hence for a deep evaluation of the accuracy of the numerical results. Moreover the code is used to gain insight into the formation and the evolution of secondary flows inside the blade passage, into the generation of losses and into characteristic feature of these flows hard to detect experimentally. All the above mentioned aspects are examined and discussed as well as the influence of compressibility, giving thus a precise picture of secondary flows in the transonic regime.
An Investigation of Spanwise Mixing in Multistage Axial Flow Compressors
Authors: Li S.-M. , Chen M.-Z.
Published: March 2015

An equation system has been deduced for meridional throughflow fields of multistage axial flow compressors, presenting different kinds of spanwise mixing effects of the fields in a unified form. The spanwise mixing in compressors is caused by three kinds of effects, molecular motion, turbulent diffusion, and circumferential non–uniformities, the last of which includes secondary flow effects and others. This equation system thus unifies the two models for spanwise mixing analyses by Adkins & Smith (1981) and Gallimore & Cumpsty (1986). The turbulent diffusion in the two–dimensional (2–D) meridional fields is determined by complex three–dimensional (3–D) shear flows in compressors, rather than the 2–D shearing alone, so a turbulence model for 2–D meridional flow calculations is proposed on the basis of a simplified 3–D shearing structure in compressors. The circumferentially non–uniform correlation terms in the equation system have been modeled on the basis of Adkins and Smith (1981) secondary flow model and the experimental data for annular cascade wakes. The results obtained agree well with the experiments for five compressors. The results also show some improvement over the previous theories.
Simulation of the Secondary Air System of Aero Engines
Authors: Kutz K. J. , Speer T. M.
Published: March 2015

This paper describes a computer program for the simulation of secondary air systems. Typical flow system elements are presented, such as restrictors, tappings, seals, vortices, and coverplates. Two-phase flow as occuring in bearing chamber vent systems is briefly discussed. The algorithm is described for the solution of the resulting nonlinear equations. The validity of the simulation over the engine operation envelope is demonstrated by a comparison with test results.
Circulator Design/Technology Evolution for Gas-Cooled Nuclear Reactors
Authors: McDonald Colin F. , Marshall Ian R. , Donaldson John , Kapich Davdrin D.
Published: March 2015

The circulator is a key component in a gas-cooled nuclear power plant since it facilitates transfer of the reactor thermal energy (via the steam generator) to the electrical power conversion system. Circulator technology is well established and about 200 machines, which, in their simplest form, consist of an electrical motor driven compressor, have operated for many millions of hours worldwide in gas-cooled reactors. This paper covers the evolution of circulator design, technology and operating experience, with particular emphasis on how lessons learned over the last four decades (dominantly from the carbon dioxide cooled plants in the U.K.) are applicable to the helium cooled Modular High Temperature Gas-Cooled Reactor (MHTCR) which should see service in the U.S. at the turn of the next century. State-of-the-art technologies are covered in the areas of impeller selection, bearings, drive system, machine operation, and future trends are Identified.
Combined-Closed Gas Cycles for Terrestrial, Marine and Space Nuclear Power Systems
Authors: Tilliette Z. P.
Published: March 2015

Higher temperature nuclear heat sources are becoming available and more efficient energy conversion systems can be proposed, namely Brayton-Rankine combined cycles which are presently very successful in the terrestrial fossil power plants market. A combined gas-steam cycle adaptation to the now being developed high temperature gas-cooled reactor MHTGR is presented. In order to avoid serious problems associated with the direct cycle, the concept features a He/He heat exchanger and a steam generator heated in series. Consequences are a significant plant efficiency increase, a sufficiently low reactor inlet temperature, attractive operating conditions and a possible reduction of the reactor water ingress hazard.

Similar, judiciously simplified arrangements could be contemplated for possible future efficient marine nuclear power plants.

Cycle combinations could also offer new, suitable approaches of space power systems, particularly for Lunar or Martian bases. A bottoming gas cycle could be a dramatic booster of a topping static thermionic converter, provided that a significantly larger radiator area be acceptable. Combined Brayton-Rankine cycles are also possible candidates for Moon or Mars surface power systems. As a consequence, should a gas-cooled reactor be used as the heat source in a direct cycle arrangement, its design could be drastically simplified.
A Method to Improve Operation of the Gullfaks ‘A’ Gas Compression System
Authors: Bakken L. E. , Bradley T. M.
Published: March 2015

The Gullfaks ‘A’ Platform located in the Norwegian Sector of the North Sea, is designed to process 50,000 SM3/day of well head fluids to crude oil and gas product specifications. The present operating conditions of the process are different from the original design due to changes in feed stock. Furthermore, degradation of compressor performance due to fouling, wear and internal leakage has led to limited production flexibility. Field performance testing of the compressors has been carried out supplemented by computer based performance prediction. Based on this information, a dynamic simulation model of the process, tuned to actual plant operation, has been used to analyse the process behaviour. Modifications have been studied by dynamic process simulation before field implementation. These modifications have resulted in reduced operating and maintenance costs. Substantial decrease in compressor speed and load have led to reduced wear and maintenance. Operational and pollution tax savings are estimated at $1.5m/year.
Applications Using Dry Gas Seals to Control Axial Shaft Loads in Centrifugal Compressors
Authors: Bear C. C. , Gibson S. W.
Published: March 2015

Dry gas seal technology has developed significantly over the past two decades. In addition to advances in standard seal technologies, alternate configurations of dry gas seals within the compressor have provided compressor efficiency improvements among other benefits. This paper describes the innovative application of dry gas seals in the reduction and control of axial shaft forces in pipeline gas compressors.

By uniquely configuring the dry seals, the balance piston was removed from a beam type compressor, resulting in improvement of the compressor efficiency. In addition, the maximum axial forces in an overhung unit were substantially lowered, eliminating full pressure start-up problems, and allowing the practical installation of magnetic bearings. In both beam and overhung compressor applications, these dry seals combined with a control system reduce axial forces on the shaft to zero under most operating conditions.
Development of a Liquid-Fueled, Lean-Premixed Gas Turbine Combustor
Authors: Cowell L. H. , Smith K. O.
Published: March 2015

Development of a lean-premixed, liquid-fueled combustor is in progress to achieve ultra-low NOx emissions at typical gas turbine operating conditions. A filming fuel injector design was tested on a bench scale can combustor to evaluate critical design and operating parameters for low emissions performance. Testing was completed using No. 2 diesel. Key design variables tested include premixing length, swirler angle, injector centerbody diameter, and reduced liner cooling. NOx emissions below 12 ppmv at 9 bars pressure were measured. Corresponding CO levels were 50 ppmv. An optimized injector design was fabricated for testing in a 3 injector sector of an annular combustor. Operating parameters and test results are discussed in this paper.
Ignition and Exhaust Emission Characteristics of Spray Combustion in a Pre-Chamber Type Vortex Combustor
Authors: Ohkubo Youichirou , Nomura Yoshihiro , Idota Yoshinori , Gunji Yoshihisa
Published: March 2015

The lean ignition limit, the lean blowout limit and the exhaust emission characteristics of spray combustion have been investigated experimentally using a pre-chamber type vortex combustor developed for a 300KW large-bus gas turbine engine. It has been verified that these depend on the spray characteristics of the fuel injector and the air flow pattern or the distribution of air in the chamber.

Ignition succeeds through three processes. The first step is the formation of a flame kernel near the sparking ignitor, the second step is the propagation of the flame kernel into a flame holding region, and the last step is the formation of a rotating flame in that region. The lean blowout limit of the rotating flame depends on the air flow pattern in the pre-chamber when the air temperature in the combustor inlet is under 470K, while a constant fuel-air ratio of less than 0.001 is maintained at 470K and above. With no or a little secondary air, the NOx emission index does not increase in proportion to the fuel-air ratio, because both the gas temperature and residence time decrease due to the radiative heat loss caused by soot formation and reduction of a recirculation region in the main-chamber.

These phenomena were evaluated with 3 dimensional numerical simulations taking account of spray combustion, soot formation, the extended-Zeldovich thermal NO formation and radiative heat loss.
Calculation of Three-Dimensional Unsteady Flows in Turbomachinery Using the Linearized Harmonic Euler Equations
Authors: Hall Kenneth C. , Lorence Christopher B.
Published: March 2015

An efficient three-dimensional Euler analysis of unsteady flows in turbomachinery is presented. The unsteady flow is modelled as the sum of a steady or mean flow field plus a harmonically varying small perturbation flow. The linearized Euler equations, which describe the small perturbation unsteady flow, are found to be linear, variable coefficient differential equations whose coefficients depend on the mean flow. A pseudo-time time-marching finite-volume Lax-Wendroff scheme is used to discretize and solve the linearized equations for the unknown perturbation flow quantities. Local time stepping and multiple-grid acceleration techniques are used to speed convergence. For unsteady flow problems involving blade motion, a harmonically deforming computational grid which conforms to the motion of the vibrating blades is used to eliminate large error-producing extrapolation terms that would otherwise appear in the airfoil surface boundary conditions and in the evaluation of the unsteady surface pressure. Results are presented for both linear and annular cascade geometries, and for the latter, both rotating and nonrotating blade rows.
Experimental and Theoretical Investigation of a Research Atomizer/Combustion Chamber Configuration
Authors: Hassa C. , Blümcke E. , Brandt M. , Eickhoff H.
Published: March 2015

A research airblast atomizer/combustion chamber configuration has been built for the validation of a mathematical model of two phase flows in gas turbine combustors. The inlet boundary conditions of the gas flow were measured within the nozzle by Laser-Two-Focus-Velocimetry. Starting velocities and mass fluxes for the droplet sizes of the spray were measured by Phase-Doppler-Anemometry at a plane 7mm downstream of the atomizer lip. Gas- and drop velocities were measured consecutively in the confined swirling isothermal flow throughout the combustor and were compared with the results of a newly developed mathematical model of spray dispersion.

The spray shows the general structure of an axial acceleration of all dropsizes and a following dispersion of the droplets and radial separation by centrifugal forces according to their size. Measured and calculated drop velocities for 10, 30 and 50μm drops compare well, except for some differences, which can be explained by deficiencies of the gas flow calculation. Mass flux and volumetric mean diameter profiles are also correctly reproduced.
Evaluation of Simple Aluminide and Platinum Modified Aluminide Coatings on High Pressure Turbine Blades After Factory Engine Testing-Round II
Authors: Connor Jeffrey A.
Published: March 2015

This paper presents results of factory engine testing of simple aluminide and platinum modified aluminide coatings. Simple aluminide coatings were produced using pack cementation processes. Platinum modified aluminide coatings were produced using three aluminiding processes; pack cementation, above-the-pack or out-of-contact processing, and chemical vapor deposition. These coatings were evaluated on both directionally solidified and single crystal nickel base superalloy turbine blades. These high pressure turbine blades were tested in a commercial high bypass turbofan engine operating predominantly in a high temperature oxidation environment. Included in this paper are discussions of coatings phase stability, coating growth due to diffusion during engine operation, comparison of coating performance and assessment of remaining coating life after engine testing.
Low Leakage Fiber Metal Seals
Authors: Jarrabet G. P. , Lu L.
Published: March 2015

To improve compressor efficiency, gas turbine engine manufacturers have focused on the need for impermeable low leakage rub strip seal materials. Rub strips are used for clearance control between rotating and stationary components in gas turbine engine compressors and turbines. Fiber metal materials are used in many clearance control seal applications and offer suitable rub characteristics, erosion resistance and temperature capability. The excellent abradability characteristics are related to the seal’s high pore volume of many small but interconnected and open pores. A ceramic foam compositing process was developed for incorporating a closed cell foam into the fiber metal structure. This composite seal material achieves the low leakage needs of advanced engines. The properties of abradability, erosion resistance, oxidation resistance, and low weight inherent in fiber metal compressor seals are maintained. The seals are fabricated by brazing preformed rub strips to backing rings and final machining. Seal fabrication uses conventional processing. The low leakage composite rub strip is an innovative approach to improving compressor efficiency that offers a combination of desirable properties in a seal material.
Phasing the Construction of an IGCC Plant for Fuel Flexibility
Authors: Dechamps P. J. , Mathieu Ph.
Published: March 2015

The Integrated Coal Gasification in Combined Cycle technique allows a come back to coal: starting with a Combined Cycle plant, it is possible to add gasification units several years later and hence to switch from natural gas to coal. However, the price to pay will be capital cost but also a loss of performances of the resulting plant compared to a genuine Integrated Coal Gasification in Combined Cycle.

In this paper, we investigate the phasing option starting with a new Combined Cycle plant, optimized on natural gas operation, and ending with an Integrated Coal Gasification in Combined Cycle plant. We calculate the performances of the resulting plants with four types of gasifiers based on Texaco, Shell, Dow and British-Gas-Lurgi processes. We then compare the performances of these four plants with the performances of new Integrated Coal Gasification in Combined Cycle plants, optimized on coal operation and fully integrated, comprising the same four gasifiers. We finally compare the loss of performances in the four cases and recommend the selection of a gasifier type for such a phasing strategy.
Excitation of Blade Vibration due to Surge of Centrifugal Compressors
Authors: Jin D. , Haupt U. , Hasemann H. , Rautenberg M.
Published: March 2015

Centrifugal compressor surge at high rotational speed and reduced blade thickness can produce dangerous excitation effects which have numerous resulted in problems in the past. This paper presents an investigation of blade excitation during surge in a high performance single stage centrifugal compressor with various impeller and diffuser geometry. The blade vibration was measured using blade mounted strain gages. The flow characteristics during surge as the cause of blade excitation were simultaneously determined by fast response dynamic pressure transducers. The experiments have been performed using a radial and a backswept impeller, as well as a vanless and vaned diffusers. The rotational speed of the compressor was varied from 5,000 to 14,500 rpm. The characteristics of unsteady flow during surge, such as, the flow pattern of rotating stall and the non-periodic pressure fluctuation during surge were studied in detail. The experimental results demonstrated that, in addition to the excitation of rotating stall during surge, strong non-periodic pressure fluctuations at the beginning and the end of the surge induced dangerous blade excitations in all compressor configurations. The maximum strain values of blade vibration for all compressor versions at different rotational speeds of the compressor were measured to estimate the danger of blade excitation during surge. The results showed that the blade excitation during compressor surge with vaned diffusers is stronger than the excitation with a vanless diffuser and that the blade excitation with a radial impeller is stronger than the excitation with a backswept impeller.
Unsteady Pressure Measurements on the Rotor of a Model Turbine Stage in a Transient Flow Facility
Authors: Dietz A. J. , Ainsworth R. W.
Published: March 2015

This paper describes unsteady pressure measurements made on the mid span suction and pressure surfaces of a rotating turbine blade in a transient facility. The measurements were made at the engine representative conditions for this turbine using high spatial density surface mounted semi-conductor transducers. This high spatial density, coupled with the wide bandwidth capability of the sensors and data acquisition system, has enabled analyses of unsteady wave propagation effects (both in magnitude and phase) to be carried out. This paper significantly adds to the body of data available at engine representative conditions, particularly in terms of compressibility.

Distinctions are drawn between events which are propagating at free stream velocities and those which move at local acoustic velocities. Comparisons are made with theories which have been previously expounded, and some inconsistencies are outlined.
Turbine Blade Vibration Monitoring System
Authors: Kawashima T. , Iinuma H. , Wakatsuki T. , Minagawa N.
Published: March 2015

This paper describes a development and an evaluation of an optical blade vibration monitoring system applicable to gas turbine engine high pressure turbine blading.

The system uses high intensity He-Ne lasers, optical fibers and associated electronics, and can monitor rotor blade vibration under engine running conditions. With a combined water and air probe cooling system, it can be used for monitoring turbine blade vibration at 1300 degree C range gas temperature.

The system was applied to actual gas turbine engines and has demonstrated it’s effectiveness as a useful tool for gas turbine blade vibration evaluation.
Stability of a Pretwisted Blade With Nonconstant Rotating Speed
Authors: Yang S. M. , Tsao S. M.
Published: March 2015

An analytical model is presented to investigate the vibration and stability of a pretwisted blade under nonconstant rotating speed. Two coupled bending displacements in flapwise and edgewise directions are considered. The time-dependent rotating speed leads to nonautonomous systems in which parametric resonance can occur. Six parametric instabilities, including primary and combination resonances, are predicted by using multiple scale method. These instability predictions are compared with those from numerical results of a more detail model. Among all instabilities, the combination resonance when perturbed frequency near twice of the fundamental frequency is found to be most critical and sensitive to system parameters.
Aerodesign and Performance Analysis of a Radial Transonic Impeller for a 9:1 Pressure Ratio Compressor
Authors: Colantuoni S. , Colella A.
Published: March 2015

The aerodynamic design of a centrifugal compressor for technologically advanced small aeroengines requires more and more the use of sophisticated computational tools in order to meet the goals successfully at minimum cost development.

The objective of the present work is the description of the procedure adopted to design a transonic impeller having 1.31 relative Mach number at the inducer tip, 45° back-swept exit blade angle, and a tip speed of 636 m/s.

The optimization of the blade shape has been done analyzing the aerodynamic flowfield by extensive use of a quasi-3d code and a fully 3D Euler solver based on a time-marching approach and a finite volume discretization.

Testing has been done on the impeller-only configuration, using a compressor rig that simulates a real engine hardware, i.e. having an S-shape air-intake. The overall performance of the impeller are presented and discussed.
Heat Transfer and Turbulence in a Turbulated Blade Cooling Circuit
Authors: Abuaf N. , Kercher D. M.
Published: March 2015

The aero-thermal performance of a typical turbine blade three-pass turbulated cooling circuit geometry was investigated in a 10X plexiglas test model. The model closely duplicated the blade’s leading edge, midchord and trailing edge cooling passage geometries. Steady state heat transfer coefficient distributions along the blade pressure side wall (convex surface) of the cooling circuit passages were measured with a thin-foil heater and a liquid crystal temperature sensor assembly. The heat transfer experiments were conducted on rib-roughened channels with staggered turbulators along the convex and concave surfaces of the cooling passages. Mid-channel axial velocity and turbulence intensity measurements were taken by hot wire anemometry at each passage end of the three-pass cooling circuit to characterize and relate the local thermal performance to the turbulence intensity levels. The near-atmospheric experimental data are compared with results of a Computational Fluid Dynamics (CFD) analysis at the operating internal environment for a IX rotating model of the blade cooling circuit and other turbulator channel geometry heat transfer data investigations. The comparison between the measurements and analysis is encouraging. Differences with other heat transfer data appear reasonably understood and explainable.
Heat Transfer in Serpentine Flow Passages With Rotation
Authors: Mochizuki S. , Takamura J. , Yamawaki S. , Yang Wen-Jei
Published: March 2015

Heat transfer characteristics of a three-pass serpentine flow passage with rotation is experimentally studied. The walls of the square flow passage are plated with thin stainless-steel foils through which electrical current is applied to generate heat. The local heat transfer performance on the four side walls of the three straight flow passages and two turning elbows are determined for both stationary and rotating cases. The through flow Reynolds, Rayleigh (centrifugal type) and Rotation numbers are varied. It is revealed that three-dimensional flow structures cause the heat transfer rate at the bends to be substantially higher than at the straight flow passages. This mechanism is revealed by means of a flow visualization experiment for non-rotating case. Along the first straight flow passage, the heat transfer rate is increased on the trailing surface but is reduced on the leading surface, due to the action of secondary streams induced by the Coriolis force. At low Reynolds numbers, the local heat transfer performance is primarily a function of buoyancy-force. In the higher Reynolds number range, however, the circumferential average Nusselt number is only a weak function of the Rayleigh and Rotation numbers.
An Experimental Study of Film Cooling in a Rotating Transonic Turbine
Authors: Abhari Reza S. , Epstein A. H.
Published: March 2015

Time-resolved measurements of heat transfer on a fully cooled transonic turbine stage have been taken in a short duration turbine test facility which simulates full engine non-dimensional conditions. The time average of this data is compared to uncooled rotor data and cooled linear cascade measurements made on the same profile. The film cooling reduces the time-averaged heat transfer compared to the uncooled rotor on the blade suction surface by as much as 60%, but has relatively little effect on the pressure surface. The suction surface rotor heat transfer is lower than that measured in the cascade. The results are similar over the central 3/4 of the span implying that the flow here is mainly two-dimensional. The film cooling is shown to be much less effective at high blowing ratios than at low ones. Time-resolved measurements reveal that the cooling, when effective, both reduced the d.c. level of heat transfer and changed the shape of the unsteady waveform. Unsteady blowing is shown to be a principal driver of film cooling fluctuations, and a linear model is shown to do a good job in predicting the unsteady heat transfer. The unsteadiness results in a 12% decrease in heat transfer on the suction surface and a 5% increase on the pressure surface.
Reliability Measurements for Gas Turbine Warranty Situations
Authors: Ekstrom Thomas E.
Published: March 2015

Reliability performance is currently receiving significant attention in the bid requests for new gas turbine generating units. Reliability guarantees backed by liquidated damages clauses are becoming the rule rather than the exception. But the power generation industry does not have a universally accepted set of reliability measurements and the more commonly used measurements are not sufficiently refined for the warranty situation.

This paper is intended to provide the guidance, structure and refinement needed for meaningful reliability warranties.

Four key areas of reliability measurement: starting reliability, running reliability, availability and equivalent availability are separately addressed. And within each of these areas there is the flexibility, the methodology and the need to adapt the measurement system to the varied operating regimes and philosophies encountered such as: peaking vs. continuous service, attended vs. unattended sites, different levels of maintenance intensity, chargeable vs. non-chargeable outage events and emotional/political/optical acceptability (i.e., 3% Forced Outage Factor vs. 40% Forced Outage Rate). Warranty structuring rationale and suggested contract language are provided to address such needs as a rigorous and explicit operating log, certification of data, measurement accuracy, statistical confidence, assurance of readiness and risk assessment.

The suggestions presented herein have been constructed with logic and fairness. This paper will be beneficial to all Architect Engineers, Utilities, Independent Power Producers and OEM’s that become involved with the structuring of reliability warranties.