bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow and Heat Transfer Computations in a Rotating Cavity With Tangential Seal Air Flow
Authors: Tekriwal Prabhat
Published: December 2014

Axi-symmetric and three-dimensional CFD models for a rotating open interdisk cavity have been developed to predict flow, heat transfer, windage power loss and cavity air temperatures as a part of the rotor thermomechanical analysis and design life study. The cavity has a tangential (axial and circumferential) seal air flow above it. The rotational Reynolds number is 4.8 × 106 and the non-dimensional seal flow rate is 9.8 × 104. Measured wall temperatures are used as boundary conditions in the model. The axi-symmetric model smears the cavity bolts as 360° continuous rings and therefore ignores the bolts pumping effect. The windage loss calculation from the axi-symmetric model is in good agreement with the experimental data in the literature. The heat transfer coefficient values from the axi-symmetric and three-dimensional models are comparable in most of the regions apart from near the bolts. Also, the three-dimensional model simulates the bolt pumping effects and yields a much higher windage loss value, which in turn raises the cavity air temperature. It is concluded that a three-dimensional model is necessary for an accurate heat transfer analysis.
Conversion of Liquid to Gaseous Fuel for Prevaporised Premixed Combustion in Gas Turbines
Authors: Wang Y. , Reh L. , Pennell D. , Winkler D. , Döbbeling K.
Published: December 2014

Stationary gas turbines for power generation are increasingly being equipped with low emission burners. By applying lean premixed combustion techniques for gaseous fuels both NOx and CO emissions can be reduced to extremely low levels (NOx emissions <25vppm, CO emissions <10vppm). Likewise, if analogous premix techniques can be applied to liquid fuels (diesel oil, Oil No.2, etc.) in gas-fired burners, similar low level emissions when burning oils are possible. For gas turbines which operate with liquid fuel or in dual fuel operation, VPL (Vaporised Premixed Lean)-combustion is essential for obtaining minimal NOx-emissions. An option is to vaporise the liquid fuel in a separate fuel vaporiser and subsequently supply the fuel vapour to the natural gas fuel injection system; this has not been investigated for gas turbine combustion in the past.

This paper presents experimental results of atmospheric and high-pressure combustion tests using research premix burners running on vaporised liquid fuel. The following processes were investigated:

• evaporation and partial decomposition of the liquid fuel (Oil No.2);

• utilisation of low pressure exhaust gases to externally heat the high pressure fuel vaporiser;

• operation of ABB premix-burners (EV burners) with vaporised Oil No.2;

• combustion characteristics at pressures up to 25bar.

Atmospheric VPL-combustion tests using Oil No.2 in ABB EV-burners under simulated gas turbine conditions have successfully produced emissions of NOx below 20vppm and of CO below 10vppm (corrected to 15% O2). 5vppm of these NOx values result from fuel bound nitrogen. Little dependence of these emissions on combustion pressure bas been observed. The techniques employed also ensured combustion with a stable non luminous (blue) flame during transition from gaseous to vaporised fuel. Additionally, no soot accumulation was detectable during combustion.
Computation of Two-Phase Flows in Low-NOx Combustor Premix Ducts Utilizing Fuel Film Evaporation
Authors: Rosskamp Heiko , Willmann Michael , Wittig Sigmar
Published: December 2014

For aircraft gas turbines as well as for industrial gas turbines current and future developments aim at the implementation of lean premixed-prevaporized (LPP) combustor techniques. For the development and optimization of these combustors powerful CFD-codes are required. A new code developed at the Institut für Thermische Strömungsmaschinen (ITS), University of Karlsruhe, provides detailed information on the gas flow as well as on the propagation and evaporation characteristics of liquid wall films inside combustors. The flow characteristics of the gas phase are predicted using a Finite-Volume 3D-Navier-Stokes code with k-ε turbulence modeling. To calculate the evaporation characteristics of a propagating wall film, a two-dimensional wall film model based on the boundary layer equations is proposed.

The present paper comprises a comparison between calculations and experiments for the verification of the code and a detailed study on the evaporation characteristics of fuel films. The results obtained allow judgement to be made on the risk of coke formation on the prefilming surface and suggest that in some operating points a LPP combustor can be operated utilizing solely film evaporation. In addition, the computer code developed also accounts for many familiar types of shear driven film flows such as internal prefilming air blast atomizer flows for example.
Gas Fuel Conditioning System Design Considerations for Utility Gas Turbines
Authors: Wilkes Colin , Dean Anthony J.
Published: December 2014

This paper describes considerations that must be addressed when designing a gas fuel clean up system to meet utility gas turbine fuel specifications. Each gas turbine manufacturer has a gas fuel specification that must be met in order to protect the equipment from the effects of burning poor quality gas fuel. With the introduction of advanced technology combustion systems and strict emission requirements, it has become increasingly important that clean, dry gas fuel be provided at the inlet to the gas turbine control system in order to maintain the equipment in proper working order. The ASME gas fuel standard B133.7M is representative of a specification that meets or exceeds most manufacturer’s requirements. This specification calls for superheating to avoid the condensation of moisture or hydrocarbon liquids and includes limits on particulate concentration and size. Issues relating to the fuel quality are discussed, including calculation and measurements of dew points, gas sampling and analysis and relative location of cleanup equipment required to meet this specification.
Computation of Unsteady Flows Around Oscillating Blades Using Linear and Nonlinear Harmonic Euler Methods
Authors: Ning Wei , He Li
Published: December 2014

An quasi three-dimensional time-linearized Euler method has been developed to compute unsteady flows around oscillating blades. In the baseline method, unsteady flow is decomposed into a steady flow plus a linear harmonically varying unsteady flow. Both the steady flow equations and the unsteady perturbation equations are solved using a pseudo time-marching method. Based upon this method, a novel nonlinear harmonic Euler method has been developed. Due to the nonlinearity of the aerodynamic governing equations, time-averaging generates extra “unsteady stress” terms. These nonlinear effects are included by a strongly coupled approach between the perturbation equations and the time-averaged equations. Numerical results demonstrate that nonlinear effects are very effectively modelled by the nonlinear harmonic method.
Shock Analysis for a Homopolar, Permanent Magnet Bias Magnetic Bearing System
Authors: Hawkins Lawrence A.
Published: December 2014

A transient, nonlinear analysis was developed and used to study the effect of shock machine testing on a gas turbine simulator supported by homopolar, permanent magnet bias magnetic bearings. The magnetic bearing nonlinearities modeled included saturation effects, clearance effects, and integrator and current limits. Free vertical travel of the shock machine anvil table supporting the simulator was also modeled. The magnetic bearing model was coupled to characteristic matrix based models of the rotor and support system and integrated to produce a time simulation of system performance. The results indicate saturation of the magnetic bearing for brief periods following impacts significant enough to exceed design load capacity, followed by recovery to stable operation in less than a second. The analysis was used to evaluate sizing for the magnetic bearing and backup bearing systems and to evaluate the control system strategy.
Rotordynamic Impact of Swirl Brakes on Labyrinth Seals With Smooth or Honeycomb Stators
Authors: Kwanka K.
Published: December 2014

The flow through labyrinth seals of turbomachinery generates forces which can cause self-excited vibrations of the rotor above the stability limit. The stability limit is reached at a specific rotating speed or power. The continuous growth in of power density and rotating speed necessitates an exact prediction of the stability limit of turbomachinery.

Usually the seal forces are described with dynamic coefficients. A new, easy-to-handle identification procedure uses the stability behavior of a flexible rotor to determine the dynamic coefficients. Systematic measurements with a great number of labyrinth seal geometries lead to reasonable results and demonstrate the accuracy and sensitivity of the procedure. A comparison of the various methods used to minimize the excitation indicates which seal is more stable and will thus improve the dynamic behavior of the rotor.
A Numerical Study of Flutter in a Transonic Fan
Authors: Isomura Kousuke , Giles Michael B.
Published: December 2014

The bending mode flutter of a modern transonic fan has been studied using a quasi-3D viscous unsteady CFD code. The type of flutter in this research is that of a highly loaded blade with a tip relative Mach number just above unity, commonly referred to as transonic stall flutter. This type of flutter is often encountered in modern wide chord fans without a part span shroud.

The CFD simulation uses an upwinding scheme with Roe’s 3rd-order flux differencing, and Johnson and King’s turbulence model with the later modification due to Johnson and Coakley. A dynamic transition point model is developed using the en method and Schubauer and Klebanoff’s experimental data.

The calculations of the flow in this fan reveal that the source of the flutter of IHI transonic fan is an oscillation of the passage shock, rather than a stall. As the blade loading increases, the passage shock moves forward. Just before the passage shock unstarts, the stability of the passage shock decreases, and a small blade vibration causes the shock to oscillate with a large amplitude between unstarted and started positions. The dominant component of the blade excitation force is due to the foot of the oscillating passage shock on the blade pressure surface.
Crack Initiation in a Coated and an Uncoated Nickel-Base Superalloy Under TMF Conditions
Authors: Johnson Peter K. , Arana María , Ostolaza Koldo M. , Bressers Johan
Published: December 2014

A thermomechanical fatigue (TMF) cycle, intended to represent aero-engine blade working conditions, was selected for carrying out tests on uncoated and aluminide coated SRR99 samples until test piece failure. Optical images of the surface of test pieces were collected during testing to monitor surface crack initiation and accompanying transformations. Using these images, surface changes were quantified as a function of time. Post test, each sample was taken through an incremental polishing procedure to allow damage in the tested material to be studied as a function of depth, using optical microscope based quantitative metallography and scanning electron microscopy (SEM). The relationship between the observed surface changes and the damage built-up subsurface was examined. Differences in damage density on the surface and subsurface planes between coated and uncoated samples could accommodate the observed life reductions.
Theory and Methodology of Optimally Measuring Vibratory Strains in Closely Spaced Modes
Authors: Yang M.-T. , Griffin J. H.
Published: December 2014

Stress ratios are traditionally used to infer maximum stresses in blades from strain measurements. This method may not be applicable to all the modes of modern low aspect ratio (LAR) blades since LAR blades often have high frequency “tip” modes which are so closely spaced that slight changes in structural properties can cause significant mode shape changes.

In this paper, it is first shown that the actual tip modes of a LAR blade can be well approximated as linear combinations of the “nominal” modes. The stress field of the blade can then be estimated by calculating the modal content from multiple strain measurements. However, since placement and gage inaccuracies can introduce significant errors in the calculation, it is necessary to find the optimal gage placement which minimizes the error in estimated stresses. An error estimate using “norms” and an efficient optimization method are developed for this purpose.
Aspects of Vane Film Cooling With High Turbulence: Part I — Heat Transfer
Authors: Ames Forrest E.
Published: December 2014

A four vane subsonic cascade was used to investigate the influence of film injection on vane heat transfer distributions in the presence of high turbulence. The influence of high turbulence on vane film cooling effectiveness and boundary layer development was also examined in part II of this paper. A high level, large scale inlet turbulence was generated for this study with a mock combustor (12 %) and was used to contrast results with a low level (1 %) of inlet turbulence. The three geometries chosen to study in this investigation were one row and two staggered rows of downstream cooling on both the suction and pressure surfaces in addition to a showerhead array. Film cooling was found to have only a moderate influence on the heat transfer coefficients downstream from arrays on the suction surface where the boundary layer was turbulent. However, film cooling was found to have a substantial influence on heat transfer downstream from arrays in laminar regions of the vane such as the pressure surface, the stagnation region, and the near suction surface. Generally, heat transfer augmentation was found to scale on velocity ratio. In relative terms, the augmentation in the laminar regions for the low turbulence case was found to be higher than the augmentation for the high turbulence case. The absolute levels of heat transfer were always found to be the highest for the high turbulence case.
Developing Centrifugal Compressor Train Optimization Models for Performance Evaluation
Authors: Summers Steven M.
Published: December 2014

Recent advances in numerical optimization software now allow problems arising in the evaluation of complex centrifugal compressor train performance to be readily solved by machinery users. Analyses of compressor operations often requires consideration of multiple non-linear constraints involving pressure, temperature, flow rate, composition and power. Based on these constraints, the operational boundaries of the machinery must be evaluated. Frequently operating points of greatest interest exist where one of the operational variables, such as flow rate, is maximized subject to operational constraints. A methodology is proposed which can be used to apply commercially available optimization software to problems of this type. A review of gas equation of state relationships needed to determine thermodynamic properties is provided, as well as methods for calculating compressor discharge pressure based on polytropic head and efficiency. Recycle control is considered and a model is proposed.
The Effect of Turbulence on the Heat Transfer in Closed Gas-Filled Rotating Annuli
Authors: Bohn Dieter , Gier Jochen
Published: December 2014

Higher turbine inlet temperatures are a common measure for increasing the thermal efficiency of modern gas turbines. This development not only leads to the need for more efficient turbine blade cooling but also to the requirement of a more profound knowledge of the mechanically and thermally stressed parts of the rotor. For determining thermal stresses from the temperature distribution in the rotor of a gas turbine, one has to encounter the convective transfer in rotor cavities. In the special case of an entirely closed gas-filled rotating annulus the convective flow is governed by a strong natural convection.

Owen and other researchers have found, that the presence of turbulence and its inclusion in the modeling of the flow causes significant differences in the flow development in rotating annuli with throughflow like e.g. different vortex structures. However, in closed rotating annuli there is still a lack of knowledge concerning the influence of turbulence. Based on previous work, in this paper the influence of turbulenceon the flow structure and on the heat transfer is investigated.

The flow is investigated numerically with a three-dimensional Navier-Stokes solver, based on a pressure correction scheme. To account for the turbulence, a low-Reynolds-number k-ε-model is employed. The results are compared with experiments performed at the Institute of Steam and Gas Turbines. The computations demonstrate that turbulence has a considerable influence on the overall heat transfer as well as on the local heat transfer distribution. Three-dimensional effects are discussed by comparing the three-dimensional calculation with a two-dimensional calculation of the same configuration and are found to have some impact.
Characterization of Oscillations During Premix Gas Turbine Combustion
Authors: Richards George A. , Janus Michael C.
Published: December 2014

The use of premix combustion in stationary gas turbines can produce very low levels of NOx emissions. This benefit is widely recognized, but turbine developers routinely encounter problems with combustion oscillations during the testing of new pre mix combustors. Because of the associated pressure fluctuations, combustion oscillations must be eliminated in a final combustor design. Eliminating these oscillations is often time-consuming and costly because there is no single approach to solve an oscillation problem.

Previous investigations of combustion stability have focused on rocket applications, industrial furnaces, and some aeroengine gas turbines. Comparatively little published data is available for premised combustion at conditions typical of an industrial gas turbine.

In this paper, we report experimental observations of oscillations produced by a fuel nozzle typical of industrial gas turbines. Tests are conducted in a specially designed combustor, capable of providing the acoustic feedback needed to study oscillations. Tests results are presented for pressures up to 10 atmospheres, and with inlet air temperatures to 588 K (600 F) burning natural gas fuel.

Based on theoretical considerations, it is expected that oscillations can be characterized by a nozzle reference velocity, with operating pressure playing a smaller role. This expectation is compared to observed data, showing both the benefits and limitations of characterizing the combustor oscillating behavior in terms of a reference velocity rather than other engine operating parameters. This approach to characterizing oscillations is then used to evaluate how geometric changes to the fuel nozzle will affect the boundary between stable and oscillating combustion.
Comparative Rotating Stall and Surge Characteristic of a Centrifugal Compressor With Three Different Types of Diffusers
Authors: Engeda Abraham
Published: December 2014

The diffuser system of a centrifugal compressor comes basically in two general categories either as vaneless or vaned diffuser. Vaned diffusers can further be subdivided into two depending on channel geometry as straight channel or curved channel, or depending on solidity. Three different diffuser types: a vaneless, conventional vaned and a low solidity vaned were tested in the present study. All diffusers were tested downstream of the same impeller. All the diffusers had the same diffuser exit radius to impeller tip radius ratio.

The influence of each type of diffuser on the performance and stall characteristics of the inducer and impeller as a whole was studied. In addition, diffuser stall characteristics of each type diffuser were also studied. The type of diffuser had no significant effect on inducer and impeller stall. The inducer was more stable with the conventional vaned diffuser configuration. Rotating Stall was detected with the vaneless diffuser configuration at the onset of surge. Four stall cells rotated in the same direction as the impeller at 122 Hz.

Numerous works have been documented on rotating stall and surge for centrifugal compressors. Prediction of the inception of rotating stall and surge for a specific geometry and operation is not yet fully possible. Therefore, experimental results and correlations are still of great importance.
Blade Film Cooling by Underexpanded Transonic Jet Layers
Authors: Gehrer Arno , Woisetschläger Jakob , Jericha Herbert
Published: December 2014

The evolution of increasing turbine inlet temperature has led to the necessity of full-coverage film cooling for the first turbine vane and blade. A new approach using high speed wall jets for blade cooling has been proposed by the authors. In this paper a 2-D upwind-biased Navier-Stokes code is used to calculate the aerodynamic behaviour of these surface coolant jets in a linear cascade. Special emphasis is put on the investigation of the coolant flow around the leading edge. Various numerical results concerning the leading edge flow are presented in detail, showing a strong tendency of these jets to bend towards convex surfaces. Finally, Schlieren pictures taken at the Institute’s transonic cascade on a 140mm chord length blade are presented for comparison.
Controlled-Endwall-Flow Blading for Multistage Axial Compressor Rotor
Authors: Inoue M. , Kuroumaru M. , Furukawa M. , Kinoue Y. , Tanino T. , Maeda S. , Okuno K.
Published: December 2014

This research aims to develop an advanced technology of highly loaded axial compressor stages with high efficiency and sufficient surge margin. To improve endwall boundary layer flows which lead to energy loss and instability at an operation of low flow rate, the Controlled-Endwall-Flow (CEF) rotor blades were designed and tested in the low speed rotating cascade facility of Kyushu University. The CEF rotor blades have three distinctive features: the leading-edge sweep near hub and casing wall, the leading-edge bend near the casing, and the same exit metal angle of blade evaluated by a conventional design method. Mechanical strength of the blade was verified by a numerical simulation at a high speed condition. The baseline rotor blades were designed under the same design condition and tested to compare with the CEF rotor. The results showed that the maximum stage efficiency of the CEF rotor was higher by 0.7 percent and the increase in surge margin was more than 20 percent in comparison with the baseline rotor. The results of both internal flow survey and 3D Navier-Stokes analysis showed that improvement of the overall stage performance resulted from activation of the endwall boundary layers, and suggested that further improvement might be expected by combination of end-bend stator blades and a highly loaded axial compressor stage could be developed by use of the CEF rotor.
Progress on the ICR Engine Development
Authors: Bowen Thomas L.
Published: December 2014

Since 1992, advanced development of an intercooled recuperated (ICR) gas turbine engine for naval ship propulsion has been progressing under a U.S. Navy contract. This paper summarizes progress on the ICR engine development. An overview of the program plan is presented including discussion of significant changes made since contract award. The engine development status is discussed including the significant accomplishments, the recovery from an initial recuperator failure, and the remaining development work.
A Steam-Augmented Gas Turbine With Reheat Combustor for Surface Ships
Authors: Urbach Herman B. , Knauss Donald T. , Garman Richard W. , Gupta Ashwani K. , Sexton Michael R.
Published: December 2014

The steam-augmented gas turbine (SAGT) differs from commercial steam-injected gas turbines where steam flow may be considerably less than 15% of air flow. SAGT combustors may operate near stoichiometric combustion conditions with steam flow as high as 50% of air flow, thus achieving specific powers exceeding 555 hp-sec/lb.

A previous simulation study of the steam-augmented gas turbine, which did not include compressor and turbine maps, examined the applicability of the concept in the Navy’s DDG-51-class ship environment. In this re-examination, component maps were employed to establish credible off-design engine performance, and to confirm estimates of overall ship fuel requirements based solely on anticipated component efficiencies. Also, the present simulation employs a heat-exchanger sub-program fully integrated into the main software program. The re-examination has led to several revisions and refinements of previous conclusions, which are discussed in the text.

The SAGT engine concept described herein, dispenses with intercoolers, but adds a low-pressure reheat combustor. The low-pressure combustor flame temperature exceeds 2700° F, which analyses show to be stable. Exhaust gas temperatures are not permitted to fall below 450° F, and the heat recovery steam generator is designed to hold feedwater temperatures close to 300° F to avoid the gas-side acid dewpoint.

At the most efficient operating points, the efficiency of this new reheat SAGT engine exceeds 44.5% with a 2200° F turbine inlet temperature, at an ambient 100°-F temperature. Moreover, it exhibits a 23% reduction in overall system volume. Simulation data show that the maximum efficiency of the SAGT engine peaks at engine powers required for cruising speeds, in contrast to the efficiency of the LM2500, which peaks at full-throttle. Since Navy ships operate near cruise conditions for the majority of their mission time, a SAGT plant uses 29% less fuel than the baseline LM2500 plant. Moreover, employing conservative cost estimates, the SAGT plant is quite competitive on a first-acquisition cost basis with gas turbines currently in the fleet.
An Experimental Study of the Effect of Wake Passing on Turbine Blade Film Cooling
Authors: Heidmann James D. , Lucci Barbara L. , Reshotko Eli
Published: December 2014

The effect of wake passing on the showerhead film cooling performance of a turbine blade has been investigated experimentally. The experiments were performed in an annular turbine cascade with an upstream rotating row of cylindrical rods. Nickel thin-film gauges were used to determine local film effectiveness and Nusselt number values for various injectants, blowing ratios, and Strouhal numbers. Results indicated a reduction in film effectiveness with increasing Strouhal number, as well as the expected increase in film effectiveness with blowing ratio. An equation was developed to correlate the span-average film effectiveness data. The primary effect of wake unsteadiness was found to be correlated by a streamwise-constant decrement of 0.094·St. Steady computations were found to be in excellent agreement with experimental Nusselt numbers, but to overpredict experimental film effectiveness values. This is likely due to the inability to match actual hole exit velocity profiles and the absence of a credible turbulence model for film cooling.
Bidirectional Brush Seals
Authors: Hendricks Robert C. , Wilson Jack , Wu Tom , Flower Ralph
Published: December 2014

Presented is a study of the use of a set of I.D./O.D. bidirectional brush seals to reduce the leakage losses in a wave rotor. Relative to the baseline configuration, data indicate the use of brush seals enhanced wave rotor efficiency from 36 to 45 percent at low leakages (small rotor endwall gap spacings) and from 15 to 33 percent at high leakages (larger endwall gap spacings). These brush seals are capable of sealing positive or negative pressure drops with respect to the axial direction.

Surface tribology for these tests suggested little evidence of grooving although the bristles did wear-in and the rotor surface appeared polished.
Computation of 3-D Compressible Flow From a Rectangular Nozzle With Delta Tabs
Authors: Reddy Dhanireddy R. , Steffen Christopher J. , Zaman Khairul B. M. Q.
Published: December 2014

A three-dimensional viscous flow analysis is performed using a time-marching Reynolds-averaged Navier-Stokes code for a 3:1 rectangular nozzle with two delta tabs located at the nozzle exit plane to enhance mixing. Two flow configurations, a subsonic jet case and a supersonic jet case using the same tab configuration which were previously studied experimentally, are computed and compared with the experimental data. The experimental data include streamwise velocity and vorticity distributions for the subsonic case, and Mach number distributions for the supersonic case, at various axial locations downstream of the nozzle exit. The computational results show very good agreement with the experimental data. In addition, the effect of compressibility on vorticity dynamics are examined by comparing the vorticity contours of the subsonic jet case with those of the supersonic jet case which were not measured in the experiment.
Multicriteria Optimization of Time Control Laws of Short Take-Off and Vertical Landing Aircraft Power Plant
Authors: Egorov I. N. , Kretinin G. V. , Leshchenko I. A.
Published: December 2014

A multicriteria optimization methodology has been discussed to determine time control laws of advanced aircraft gas turbine engines of complex structure. The resulting optimum control laws ensure top improvement of several defined power plant effectiveness criteria in the system of aircraft at transient work modes. The power plant work quality increase effect is attained due to its work process adaptation for numerous requirements from the side of the aircraft.

The proposed methodology effectiveness has been shown by the example of optimizing problem solving to determine time control laws of variable elements of short take-off and vertical landing aircraft power plant.
Variable Flow Turbofan Engine for an HSCT Application
Authors: Converse George L. , Dunbar Donald K. , Miller Marlen L. , Hoskins Paul D. , Jones Scott M.
Published: December 2014

A variable flow fan aircraft propulsion system offers the potential for achieving a low specific thrust with high flow and low jet velocity requirement as specified for takeoff, side-line noise, initial climb, and a high specific thrust requirement for climb and acceleration to supersonic cruise. These requirements are conflicting. To achieve this, the operating envelope of a variable flow fan has to be expanded over existing turbofan engines. The variable flow fan concept (i.e., the Variable Fan Exit or “VFX”) can efficiently operate beyond the usual fan (or compressor) stall operating line using novel methods of designing and scheduling the fan geometry as a function of flight Mach Number, fan pressure ratio and corrected speed. Fan geometry is altered by using variable inlet guide vanes (IGV’s), variable stators, and variable outlet guide vanes (OGV’s).
Numerical Prediction of the Dynamic Behaviour of Premixed Flames Using Systematically Reduced Multi-Step Reaction Mechanisms
Authors: Bohn Dieter , Li Yuhong , Matouschek Gero , Krüger Uwe
Published: December 2014

Environmental compatibility requires low emission burners for both gas turbine power plants and jet engines. In the past, significant progress has been made in the development of low NOx and CO burners by introducing lean premixed techniques. Unfortunately these burners often have a more pronounced tendency than conventional burner designs to produce combustion driven oscillations. The oscillations may be excited to such an extent that strong pulsation may occur, and this is associated with a risk of engine failure.

In order to describe the acoustical behaviour of the complete burner system, it is crucial to determine the unit function response of the flame itself. Using a new method which was presented in 1996 by Bohn et al. [1] the dynamic flame behaviour can be predicted by means of a full Navier-Stokes-simulation of the complex combustion process for both the steady-state and transient case.

The authors have successfully used this method to obtain the frequency response of turbulent diffusion flames which are mainly controlled by the mixing process. Chemical kinetics become dominant for premixed flames. Therefore, the combustion process of a premixed methane-air mixture is modelled using a systematically reduced 6-step reaction mechanism which takes account of a set of 25 elementary reactions. This reduced mechanism was implemented in the 3D-Navier-Stokes solver in order to perform a combined flow and combustion computation.

The dynamic combustion process of a laminar premixed methane flame in a matrix burner configuration has been investigated. At first, the steady-state combustion process was simulated using the code described above. The results are compared with experimental data. Very good agreement over a wide range of equivalence ratios has been found for quantities such as laminar burning velocity or adiabatic flame temperature. The steady state results are then used as an operating point from which the transient flame behaviour after a sudden jump in the mass flow at the burner inlet has been obtained. Finally, these data lead to the unit function response which can be transferred into frequency space by a Laplace transformation.

The frequency response of the premixed methane flame obtained by a Navier-Stokes simulation has been compared with both experimental as well as analytical solutions. It must be stressed that a pure delay time element which is often used as an analytical formulation is not suitable to describe the dynamic flame behaviour in detail. The frequency response shows the characteristics of a higher order delay time element with several important details.

Parametric studies on the influence of equivalence ratio and the flow pattern of the internal burner fluid flow which are of interest for gas turbine applications, show the importance of the detailed knowledge of the dynamic flame behaviour for the stability analysis of a gas turbine combustor.
Aerodynamics of Turbine Rim-Seal Ingestion
Authors: Hills Nicholas J. , Green Tony , Turner Alan B. , Chew John W.
Published: December 2014

This paper describes the theoretical modelling of the flow in a rotor-stator wheelspace with ingestion through the rim-seal. The predictions are compared with experimental measurements of pressure taken for an axial clearance rim-seal downstream of a set of nozzle guide vanes. The mainstream pressure asymmetry caused by the guide vanes was measured in the absence of coolant flow. Using this data, three-dimensional CFD calculations were carried out, providing both predictions of the cavity pressures and insight into the flow mechanisms involved. The CFD predictions gave good agreement with experiment at low coolant flow rates. However, at high coolant flow rates, disagreement with the experimental results is evident, suggesting that the interaction between the coolant flow and the mainstream flow through the nozzle guide vanes could no longer be ignored.
A Detailed Analysis of Film Cooling Physics: Part II — Compound–Angle Injection With Cylindrical Holes
Authors: McGovern Kevin T. , Leylek James H.
Published: December 2014

Detailed analyses of computational simulations with comparisons to experimental data were performed to identify and explain the dominant flow mechanisms responsible for film cooling performance with compound angle injection, Φ, of 45°, 60°, and 90°. A novel vorticity and momentum based approach was implemented to document how the symmetric, counter–rotating vortex structure typically found in the crossflow region in streamwise injection cases, becomes asymmetric with increasing Φ. This asymmetry eventually leads to a large, single vortex system at Φ = 90° and fundamentally alters the interaction of the coolant jet and hot crossflow. The vortex structure dominates the film cooling performance in compound angle injection cases by enhancing the mixing of the coolant and crossflow in the near wall region, and also by enhancing the lateral spreading of the coolant. The simulations consist of fully–elliptic and fully–coupled solutions for field results in the supply plenum, film–hole, and crossflow regions and includes surface results for adiabatic effectiveness η and heat transfer coefficient h. Realistic geometries with length–to–diameter ratio of 4.0 and pitch–to–diameter ratio of 3.0 allowed for accurate capturing of the strong three–way coupling of flow in this multi–region flowfield. The cooling configurations implemented in this study exactly matched experimental work used for validation purposes and were represented by high quality computational grid meshes using a multi–block, unstructured grid topology. Blowing ratios of 1.25 and 1.88, and density ratio of 1.6 were used to simulate realistic operating conditions and to match the experiments used for validation. Predicted results for η and h show good agreement with experimental data.
A Detailed Analysis of Film Cooling Physics: Part III — Streamwise Injection With Shaped Holes
Authors: Hyams Daniel G. , Leylek James H.
Published: December 2014

The physics of the film cooling process for shaped, streamwise-injected, inclined jets is studied for blowing ratio (M = 1.25, 1.88), density ratio (DR = 1.6), and length-to-diameter ratio (L/D = 4) parameters typical of gas turbine operations. A previously documented computational methodology is applied for the study of five distinct film cooling configurations: (1) cylindrical film hole (reference case); (2) forward-diffused film hole; (3) laterally-diffused film hole; (4) inlet shaped film hole, and (5) cusp-shaped film hole. The effects of various film hole geometries on both flow and thermal field characteristics is isolated, and the dominant mechanisms responsible for differences in these characteristics are documented. Special consideration is given to explaining crucial flow mechanisms from a vorticity point of view. It is found that vorticity analysis of the flow exiting the film hole can aid substantially in explaining the flow behavior downstream of the film hole. Results indicate that changes in the film hole shape can significantly alter the distribution of the exit-plane variables, therefore strongly affecting the downstream behavior of the film.

Computational solutions of the steady, Reynolds-averaged Navier-Stokes equations are obtained using an unstructured/adaptive, fully implicit, pressure-correction solver. Turbulence closure is obtained via the high Reynolds number k-ε model with generalized wall functions. Detailed field results as well as surface phenomena involving adiabatic film effectiveness (η) and heat transfer coefficient (h) are presented. When possible, computational results are validated against corresponding experimental cases from data found in the open literature. Detailed comparisons are made between surface and field results of the film hole shapes investigated in this work; design criteria for optimizing downstream heat transfer characteristics are then suggested.
Stall Inception and the Prospects for Active Control in Four High Speed Compressors
Authors: Day I. J. , Breuer T. , Escuret J. , Cherrett M. , Wilson A.
Published: December 2014

As part of a European collaborative project, four high speed compressors were tested to investigate the generic features of stall inception in aero-engine type compressors. Tests were run over the full speed range to identify the design and operating parameters which influence the stalling process. A study of data analysis techniques was also conducted in the hope of establishing early warning of stall. The work presented here is intended to relate the physical happenings in the compressor to the signals that would be received by an active stall control system. The measurements show a surprising range of stall related disturbances and suggest that spike-type stall inception is a feature of low speed operation while modal activity is clearest in the mid speed range. High frequency disturbances were detected at both ends of the speed range and non-rotating stall, a new phenomenon, was detected in three out of the four compressors. The variety of the stalling patterns, and the ineffectiveness of the stall warning procedures, suggests that the ultimate goal of a flightworthy active control system remains some way off.
LDV Study of Developing Flows Through a Smooth Duct With a 180 Deg Straight-Corner Turn
Authors: Liou Tong-Miin , Chen Chung-Chu
Published: December 2014

In view of lacking in velocity field data for the flow through turbine blade internal cooling passages, laser Doppler velocimetry measurements are presented for the flow development in a two-pass smooth rectangular duct of 1.1 aspect ratio with a 180 deg straight-corner turn with and without duct rotation. The test duct had a curvature axis normal to the rotational axis. The Reynolds number based on the bulk mean velocity and hydraulic diameter was 1.4 × 104 and the rotation numbers were 0 and 0.082. Characteristics, such as the upstream and downstream extents of the sharp-turn effect on the main flow profile, curvature induced Dean vortices inside the turn, turning geometry-induced separating bubble immediately downstream of the turn, and the resulting double-peak mean velocity profiles in the second pass are used to describe the developing mean flow for the case without rotation. High turbulence levels and significantly more non-uniform flow after the sharp turn in the front part of the second pass explain previously reported work showing higher but non-uniform heat transfer after that turn. Rotating the duct augments and shifts the peaks of the streamwise mean velocity and turbulence intensity profiles towards the trailing and leading walls of the first and second passes, respectively. In addition, the duct rotation skews the separating bubble and reduces its size to about 75% of its stationary counterpart.
Thermodynamic Analysis of Closed Loop Cooled Cycles
Authors: Watson Darren T. , Ritchey Ian
Published: December 2014

Closed loop steam cooling schemes have been proposed by a number of manufacturers for advanced Combined Cycle Gas Turbine (CCGT) power plant (see for example Corman (1996) and Briesch et al. (1994)) asserting that thermal efficiencies in excess of 60% (LHV) are achievable combined with significant improvements of ∼15% in specific power (see Corman (1995)). In understanding the efficiency advantage however, the relative performance of each cooling system (subject to the same practical constraints and technology levels) is a better indicator then the absolute value.

Assessment of the performance of such novel schemes generally involves a detailed numerical analysis of an integrated cycle which may often prevent validation of the results or obscure an understanding of the physical basis for the claimed improvements. Here, to overcome this, a group of simplified expressions are defined for the variation of each cycles efficiency due to cooling which show where the differences come from. These expressions are based simply on a calculation of the marginal increase in heat rejected, to the environment from the cycle, due to an increase in the level of cooling. After these relationships are validated using detailed heat balance calculations they are used to compare the main cooling options, namely open loop air, closed loop air and closed loop steam when subject to the same practical constraints and assumptions. Based on these results it is proposed that the relative advantage of closed loop cooling may not be as significant as previously thought. Furthermore, it is shown that the closed loop cooling efficiency gain is heavily dependent on the performance and reliability of substantial Thermal Barrier Coatings (TBCs).

Finally, although the majority of recent interest in closed loop cooling schemes has focused upon CCGT plant, there are other systems where the benefits of closed loop steam cooling appear to be greater, in particular cycles involving steam injected gas turbines. Such a cycle is analysed here with a number of advanced cooling options.
Research of a High Thrust-to-Weight Ratio Small Turbofan Engine
Authors: Akagi Masahiro , Shinomiya Masashi , Sakaki Junichi , Sugai Shunji
Published: December 2014

The 3rd Research Center of the Technical Research and Development Institute (TRDI) of Japan Defense Agency (JDA) and Ishikawajima-Harima Heavy Industries Co., Ltd. (IHI) developed and tested the demonstrator of a high thrust-to-weight ratio small turbofan engine with an afterburner called “XF3-400”, the purpose of which is to establish engine technologies for the future supersonic aircraft for JDA.

The development program started in 1981 and the first engine test was carried out in 1992. All the engine tests planned completed in March 1995 successfully.

This paper reports the design, development and test results of the XF3-400 engine above.
Environmental Degradation of Gas Turbine Materials in Steam
Authors: Patel Y. , Tamboli D. , Desai V. H. , Cheruvu N. S.
Published: December 2014

Steam has been proposed as an efficient cooling medium for the hot section components in the advanced gas turbines replacing compressed air for more efficient cooling allowing the turbine to operate at higher efficiency. To evaluate the effect of steam on oxidation and corrosion of hot section materials, three superalloys (X-45, Inconel-617 and IN-738LC) were exposed to steam at 840°C. Steam environments used were (a) steam generated from deionized water, (b) steam generated from deionized water with 5ppm each of NaCl and Na2SO4 and (c) steam generated from deionized water with 50 ppm each of NaCl and Na2SO4. The respective exposure times were 3900, 2950, and 1450 hours. IN-738LC showed severe internal oxidation in steam. In contaminated steam the hot corrosion damage was maximum in Inconel-617. X-45 showed less oxidation damage than IN-738LC and less hot corrosion than Inconel-617.
Computation of Leading-Edge Film Cooling With Injection Through Rows of Compound-Angle Holes
Authors: Lin Y.-L. , Stephens M. A. , Shih T. I-P.
Published: December 2014

Computations were performed to investigate the three-dimensional flow and heat transfer about a semi-cylindrical leading edge with a flat afterbody that is cooled by film-cooling jets, injected through three staggered rows of compound-angle holes with one row along the stagnation line and two rows along ±25°. Results are presented for the surface adiabatic effectiveness, temperature distribution, velocity vector field, turbulent kinetic energy, and surface pressure. These results show the interactions between the mainstream hot gas and the cooling jets, and how those interactions affect surface adiabatic effectiveness. The computed results were compared with experimental data generated under a blind test, and reasonably good agreements were obtained.

This computational study is based on the ensemble-averaged conservation equations of mass, momentum (compressible Navier-Stokes), and energy closed by a low Reynolds number k-ω turbulence model. Solutions were generated by a cell-centered finite-volume method that uses second-order accurate flux-difference splitting of Roe on a multiblock structured grid system. In the computations, the flow is resolved not just in the region about the leading edge, but also inside the film-cooling holes and in the plenum where the cooling flow emerges.