bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of Manufacturing Variability on the Aerodynamic Performance of a Centrifugal Compressor Stage With Curvilinear Blades
Authors: Panizza A. , Valente R. , Rubino D. , Tapinassi L.
Published: September 2016

The goal of the present study is to quantify the uncertainty in the aerodynamic performance of a centrifugal compressor stage with curvilinear impeller blades, due to impeller manufacturing variability. Impellers with curvilinear element blades allow a greater control of secondary flows with respect to impellers having ruled blades. High flow coefficient impellers for centrifugal compressors exhibit larger secondary flow than medium or low flow coefficient impellers, due to the stronger curvature of the flow path and the larger blade height for the same external diameter. Thus curvilinear blade impellers allow to improve the efficiency and range of high flow coefficient centrifugal compressor stages. As the design of these impellers is more complex than the design of ruled blade impellers, it is important to estimate the impact of the impeller manufacturing variability on the performance of the full stage. Sampling methods are often used in uncertainty propagation studies. However, sampling based approaches require a very large number of samples to have an accurate estimate of the performance uncertainty. 3D steady RANS computations are necessary to capture the impact of the geometric variability of the curvilinear blade impeller, on the stage performance. Thus, sampling methods would require an excessive computational time. In this work, the Polynomial Chaos Expansion (PCE) method with arbitrary probability distributions, implemented in DAKOTA, is used to reduce the number of runs required for the uncertainty quantification study. Manufacturing measurement data are been used to derive the histograms of the main impeller design parameters. From these histograms, numerically-generated orthogonal polynomials are computed for each parameter using a discretized Stieltjes procedure. Stochastic expansion methods such as PCE suffer from the curse of dimensionality, i.e., an exponential increase in the number of runs as the number of uncertain parameters increases. To mitigate the curse of dimensionality, sparse grids are used, which allow a drastic reduction of the number of runs. The results of the study show that the performance variability is small, thus our design with curvilinear element blades is robust with respect to impeller manufacturing variability. Using Sobol indices, we also rank the design parameters according to their impact on the performance variability.
Analysis of Fan Stage Design Attributes for Boundary Layer Ingestion
Authors: Hall D. K. , Greitzer E. M. , Tan C. S.
Published: September 2016

This paper describes a new conceptual framework for three-dimensional turbomachinery flow analysis and its use to assess fan stage attributes for mitigating adverse effects of inlet distortion due to boundary layer ingestion (BLI). A non-axisymmetric throughflow method has been developed to describe the fan flow field with inlet distortion. In this the turbomachinery is modeled using momentum and energy source distributions that are determined as a function of local flow conditions and a specified blade camber surface geometry. Comparison with higher-fidelity computational and experimental results shows that the method captures the principal flow redistribution and distortion transfer effects associated with BLI. Distortion response is assessed for a range of (i) rotor spanwise work profiles, (ii) rotor-stator spacings, and (iii) non-axisymmetric stator geometries. For the parameters examined, changes in axisymmetric design result in trades between rotor and stator distortions, or between different radial sections of a given blade row with marginal overall gain. Of the approaches examined, non-axisymmetric stator exit flow angle distributions were found to provide the greatest reduction in rotor flow distortion and thus may offer the most potential for mitigating decreases in performance due to BLI inlet distortion.
Thermodynamic Evaluation of Pulse Detonation Combustion for Gas Turbine Power Cycles
Authors: Gray J. A. T. , Vinkeloe J. , Moeck J. , Paschereit C. O. , Stathopoulos P. , Berndt P. , Klein R.
Published: September 2016

Constant-volume (pressure-gain) combustion cycles show much promise for further increasing the efficiency of modern gas turbines, which in the last decades have begun to reach the boundaries of modern technology in terms of pressure and temperature, as well as the ever more stringent demands on reducing exhaust gas emissions. The thermodynamic model of the gas turbine consists of a compressor with a polytropic efficiency of 90%, a combustor modeled as either a pulse detonation combustor (PDC) or as an isobaric homogeneous reactor, and a turbine, the efficiency of which is calculated using suitable turbine operational maps. A simulation is conducted using the one-dimensional reacting Euler equations to obtain the unsteady PDC outlet parameters for use as turbine inlet conditions. The efficiencies for the Fickett–Jacobs and Joule cycles are then compared. The Fickett–Jacobs cycle shows promise at relatively low compressor pressure ratios, whereas the importance of the harvesting of exhaust gas kinetic energy for the cycle performance is highlighted.
Linearized Euler Equations for the Prediction of Linear High-Frequency Stability in Gas Turbine Combustors
Authors: Schulze Moritz , Hummel Tobias , Klarmann Noah , Berger Frederik , Schuermans Bruno , Sattelmayer Thomas
Published: September 2016

A novel methodology for linear stability analysis of high-frequency thermoacoustic oscillations in gas turbine combustors is presented. The methodology is based on the linearized Euler equations, which yield a high-fidelity description of acoustic wave propagation and damping in complex, non-uniform, reactive mean flow environments, such as encountered in gas turbine combustion chambers. Specifically, this work introduces three novelties to the community: (1) Linear stability analysis on the basis of linearized Euler equations. (2) Explicit consideration of three-dimensional, acoustic oscillations at screech level frequencies, particularly the first transversal mode. (3) Handling of non-compact flame coupling with LEE, that is, the spatially varying coupling dynamics between perturbation and unsteady flame response due to small acoustic wavelengths. Two different configurations of an experimental model combustor in terms of thermal power and mass flow rates are subject of the analysis. Linear flame driving is modeled by prescribing the unsteady heat release source term of the linearized Euler equations by local flame transfer functions, which are retrieved from first principles. The required steady state flow field is numerically obtained via CFD, which is based on an extended Flamelet-Generated Manifold combustion model, taking into account heat transfer to the environment. The model is therefore highly suitable for such types of combustors. The configurations are simulated, and thermoacoustically characterized in terms of eigenfrequencies and growth rates associated with the first transversal mode. The findings are validated against experimentally observed thermoacoustic stability characteristics. On the basis of the results, new insights into the acoustic field are discussed.
Flow Survey of a Forward Curved Blades Centrifugal Fan for HVAC Applications
Authors: Breviario Fabio , Brivio Dario , Cardillo Lucio , Corsini Alessandro , Delibra Giovanni
Published: September 2016

The advancements in fan technology are nowadays animated by two major drivers: the legal requirements that impose minimum fan efficiency grades for fans sold within European Union (and soon US and Asia), and the market request for better air performance and lower sound emissions.

Within HVAC (Heating, Ventilating and Air Conditioning) applications, centrifugal fans with forward curved blades are widely used due to the higher total pressure rise capability and lower acoustic emissions with respect to more efficient backward curved blades. However the continuous rise of minimum fan efficiency grades pushes the manufacturers to develop a new generation of forward curved centrifugal fans, improving previous design. Here the challenge is not only on aerodynamics, but in the overall production process, as squirrel cage fans are characterised by a cost-effective consolidated technology, based on simple blade geometries and easy series manufacturing. For example, the blades usually have circular camber lines, as results of cut cylinders. Thus, once the number of blades and the angle at the leading edge are selected, the chord and the deflection capability are constrained as well.

These concurring aspects led industry to include in the design process new tools, in particular CFD, to analyse the flow features of the current generation of fans in order to understand which phenomena are to be either controlled or exploited to increase efficiency and total pressure rise.

Here we present a numerical investigation on a forward curved blade centrifugal fan for HVAC applications, to highlight the flow features inside the impeller and in the critical region of coupling with the volute. The analysis was carried out with OpenFOAM, an open-source library for CFD. Computations were performed with the frozen rotor approach and validated against available experimental data.
Reduced Order Models for Blisks With Small and Large Mistuning and Friction Dampers
Authors: Tang Weihan , Baek Seunghun , Epureanu Bogdan I.
Published: September 2016

In operation, rotating bladed disks (blisks) are often subject to high levels of dynamic loading, resulting in large amplitudes of forced vibrations especially at resonance. Moreover, variations in structural properties of individual sectors, referred to as mistuning, can lead to strain energy localization and can amplify forced responses. To prevent damages caused by high cycle fatigue, various frictional damping sources are introduced to dissipate vibration energy. Due to the nonlinear behavior of frictional contacts, conventional methods to study the dynamics of the blisk-damper systems are based often on numerical time integration, which is time-consuming and can be computationally prohibitive due to the large sizes of commercial blisk models. Existing techniques for model reduction either rely heavily on cyclic symmetry of the blisk-damper system, or are based on component mode synthesis (CMS). However, in the presence of mistuning, cyclic symmetry no longer exists. Also, mistuning is random and best studied statistically. Repetitive CMS condensation for a large amount of random mistuning patterns can lead to a computationally formidable task.

This paper presents a reduced-order modeling technique to efficiently capture the nonlinear dynamic responses of blisk-damper systems with both small perturbations in blade material properties (small mistuning), and significant changes in the blisk geometries (large mistuning). The reduced-order models (ROMs) are formed by projecting the blisk-damper systems onto a novel mode basis that mimics the contact behavior. This mode basis contains normal mode shapes of the mistuned blisk-damper systems with either sliding or sticking conditions enforced on the contact surfaces. These mode shapes are computed through the N-PRIME method, a technique recently developed by the authors to efficiently obtain mode shapes for blisks with simultaneous large and small mistuning. The resulting modal nonlinear equations of motion are solved by a hybrid frequency/time (HFT) domain method with continuation. In the HFT method, the contact status and friction forces are determined in the time domain by a quasi-two-dimensional contact model at each contact point, whereas the modal equations of motion are solved in the frequency domain according to a harmonic balance formulation. The forced responses computed by the proposed ROMs are validated for two systems with distinct mistuning patterns. A statistical analysis is performed to study the effectiveness of the frictional dampers under random mistuning patterns.
Review of Coal-to-Synthetic Natural Gas (SNG) Production Methods and Modeling of SNG Production in an Entrained-Flow Gasifer
Authors: Lu Xijia , Wang Ting
Published: September 2016

In this paper, the coal-to-synthetic natural gas (SNG) technologies have been reviewed. Steam-oxygen gasification, hydrogasification, and catalytic steam gasification are the three major gasification processes used in coal-to-SNG production. So far, only the steam-oxygen gasification process is commercially proven by installing a catalytic methanation reactor downstream of the gasification process after syngas is produced, cleaned, and shifted to achieve an appropriate H2/CO ratio for methanation reaction. This process is expensive, less efficient, and time consuming. Ideally, it will be more effective and economic if methanation could be completed in an once-through entrained-flow gasifier. Technically, this idea is challenging because an effective gasification process is typically operated in a high-pressure and high-temperature condition, which is not favorable for methanation reaction, which is exothermic. To investigate this idea, a computational model is established and a sensitivity study of methanation reactions with and without catalysts are conducted in this study.

In modeling the methanation process in a gasifier, correct information of the reaction rates is extremely important. Most of known methanation reaction rates are tightly linked to the catalysts used. Since the non-catalytic reaction rates for methanation are not known in a gasifer and the issues are compounded by the fact that inherent minerals in coal ashes can also affect the methanation kinetics, modeling of methanation in an entrained-flow gasifier becomes very challenging. Considering these issues, instead of trying to obtain the correct methnation reaction rate, this study attempts to use computational model as a convenient tool to investigate the sensitivity of methane production under a wide range methanation reaction rates with and without catalysts. From this sensitivity study, it can be learned that the concept of implementing direct methanation in a once-through entrained-flow gasifier may not be attractive due to competitions of other reactions in a high-temperature environment. The production of SNG is limited to about 18% (vol) with catalytic reaction with a pre-exponential factor A in the order of 107. A further increase of the value of A to 1011 doesn’t result in more production of SNG. This SNG production limit could be caused by the high-temperature and short residence time (3–4 seconds) in the entraind-flow gasifier.
Advanced High Temperature Erosion Tunnel for Testing TBC and New Turbine Blade Materials
Authors: Shin Dongyun , Hamed Awatef
Published: September 2016

Current elevated turbine inlet temperatures were made possible by the development of blade thermal barrier coatings (TBCs). However the effectiveness of these coatings could be compromised by erosive particles ingested into the engine with the incoming air or generated by the combustion of heavy and synthetic fuels. Reliable test facilities are essential to characterize their erosion resistance in increased test temperatures. This paper provides a detailed description of an advanced high temperature erosion tunnel capable of testing at temperature of 1370 °C (2500 °F) that has been recently constructed and installed in the University of Cincinnati Gas Turbine Erosion Lab. The paper also presents an overview of both theoretical and experimental investigations dealing with the new high temperature erosion tunnel design optimization and validation with comparisons to our legacy erosion tunnels. Results are presented for tested standard plasma sprayed 7 wt% Yttria stabilized Zirconia (7YSZ) TBC coated samples’ erosion rates at different temperatures, particle impact velocities and impingement angles.
Leakage Degradation of Straight Labyrinth Seal due to Wear of Round Tooth Tip and Acute Trapezoidal Rub-Groove
Authors: Dogu Yahya , Sertçakan Mustafa C. , Gezer Koray , Kocagül Mustafa , Arıcan Ercan , Ozmusul Murat S.
Published: September 2016

In this paper, labyrinth seal leakage is numerically quantified for an acute trapezoidal rub-groove accompanied with a rounded tooth, as a function of rub-groove sizes and tooth-groove axial positions. Analyses parameters include clearance, pressure ratio, number of teeth, and rotor speed.

Labyrinth seals wear during engine transients. Radial incursion and axial movement of the rotor-stator pair cause the labyrinth teeth to rub against the unworn stator surface. The labyrinth teeth and/or stator wear depending on their material hardness. Wear damage in the form of material loss or deformation permanently increases seal clearance, and thus, leakage. This leakage is known to be dependent on the shape and geometry of the worn tooth and the stator rub groove.

There are two types of reported tooth tip wear. These can be approximated as a mushroom shape and a round shape. The stator rub-groove shapes can be approximately simulated in five forms: rectangle, trapezoid (isosceles and acute), triangle, and ellipse.

In this paper, the acute trapezoidal rub-groove shape is specifically chosen, since it is the most similar to the most commonly observed rub-groove form. The tooth tip is considered to be rounded, because the tooth tip wears smoothly and a round shape forms during rub-groove formation. To compare the unworn tooth, the flat stator is also analyzed as a reference case. All analyzed parameters for geometric dimensions (groove width, depth, wall angle, tooth-groove axial position,) and operating conditions (flow direction, clearance, pressure ratio, number of teeth, rotor speed) are analyzed in their practical ranges.

CFD analyses are carried out by employing a compressible turbulent flow solver in a 2-D axi-symmetrical coordinate system. CFD analyses show that the rounded tooth leaks more than an unworn sharp-edged tooth, due to the formation of a smooth and streamlined flow around the rounded geometry. This smooth flow yields less flow separation, flow disturbance, and less of vena contract a effect. The geometric dimensions of the acute trapezoidal rub-groove (width, depth, wall angle) significantly affect leakage. The effects of clearance, pressure ratio, number of teeth, and rotor speed on the leakage are also quantified. Analyses results are separately evaluated for each parameter.
Labyrinth Seal Leakage Degradation due to Various Types of Wear
Authors: Dogu Yahya , Sertçakan Mustafa C. , Gezer Koray , Kocagül Mustafa , Arıcan Ercan , Ozmusul Murat S.
Published: September 2016

This paper systematically presents a complete leakage comparison for various types of wear experienced by labyrinth seals. Labyrinth seals used in turbine engines are designed to work at a clearance during steady-state engine operations. The tooth tip rubs the stator and wears either itself or the stator surface during transient operations, depending on the material properties of the tooth and stator. Any type of wear that increases clearance or deforms the tooth tip will cause permanent and unpredictable leakage degradation. This negatively affects the engine’s overall efficiency, durability, and life.

The teeth have been reported to wear into a mushroom profile or into a rounded profile. A rub-groove on the opposing surface may form in several shapes. Based on a literature survey, five rub-groove shapes are considered in this work. They are: rectangle, trapezoid (isosceles and acute), triangle, and ellipse. In this work, leakage degradation due to wear is numerically quantified for both mushroomed and rounded tooth wear profiles. It also includes analyses on rounded teeth with the formation of five rub-groove shapes. All parameters are analyzed at various operating conditions (clearance, pressure ratio, number of teeth, rotor speed).

CFD analyses are carried out by employing compressible turbulent flow in a 2-D axi-symmetrical coordinate system. CFD analyses show that the following tooth-wear conditions affect leakage from least to greatest: unworn, rounded, and mushroomed. These are for an unworn flat stator. It is also observed that rub-groove shapes considerably affect the leakage depending on the clearance. Leakage increases with the following groove profiles: triangular, rectangular, acute trapezoidal, isosceles trapezoidal, and elliptical. The results show that any type of labyrinth seal wear has significant effects on leakage. Therefore, leakage degradation due to wear should be considered during the engine design phase.
E-Class Late Fuel Staging Technology Delivers Flexibility Leap
Authors: Romoser Carey E. , Harper James , Wilson Matthew B. , Simons Derrick W. , Citeno Joseph V. , Lal Mihir
Published: September 2016

The latest in GE heavy duty gas turbine combustion technology is now available on Frame 7E/EA and 9E machines. Late Fuel Staging (LFS) delivers innovative flexibility, providing value to customers in turndown, efficiency, emissions, and operability. Until now, these machines were characterized by a compliant load range from ∼60% to 100%. Late Fuel Staging delivers additional turndown to ∼35% through physics-based understanding, advanced modeling, and state-of-the-art testing.
Non-Axisymmetric Endwall Profile Optimization of a High-Pressure Transonic Turbine Using Approximation Model
Authors: Kim Inkyom , Kim Jinuk , Cho Jinsoo , Kang Young-Seok
Published: September 2016

Secondary loss of low aspect ratio turbines takes as much as 50% of the total loss. Non-axisymmetric endwall profile optimization was conducted for the nozzle hub and shroud of a 1-stage high-pressure transonic turbine. The endwalls of the hub and the shroud were individually optimized using an approximation model. Kriging model was used for response surface generation and the optimum solution was searched using Genetic Algorithm with stage efficiency as the objective function.

Optimized endwall profiles reduced nozzle losses and shocks, thereby improving stage efficiency. The shroud endwall profile showed higher performance, because it influenced the flow over the whole span, whereas the influence of the hub endwall profile was limited close to the hub.

The stage efficiency was improved by 0.39%p when both the hub and the shroud endwall profiles were applied. However, the mass flow rate exceeded the design limit and the efficiency had no benefit to the single shroud endwall profile, showing the limitations of individually optimized endwall profiles.
Optimal Arrangement of the Film Cooling Holes Considering the Manufacturing Tolerance for High Pressure Turbine Nozzle
Authors: Lee Sanga , Rhee Dong-Ho , Yee Kwanjung
Published: September 2016

In spite of a myriad of researches on the optimal shape of film cooling holes, only a few attempts have been made to optimize the hole arrangement for film cooling so far. Moreover, although the general scale of film cooling hole is so small that manufacturing tolerance has substantial effects on the cooling performance of turbine, the researches on this issue are even scarcer. If it is possible to obtain optimal hole arrangement which not only improve the film cooling performance but also is robust to the manufacturing tolerance, then overall cooling performance of a turbine would become more reliable and useful from the practical point of view. To this end, the present study proposed a robust design optimization procedure which takes the manufacturing uncertainties into account. The procedure was subsequently applied to the film cooling holes on high pressure turbine nozzle pressure side to obtain the robust array shape under the uncertainty of the manufacturing tolerance. First, the array of the holes was parameterized by 5 design variables using the newly suggested shape functions, and 2 representative factors were considered for the manufacturing tolerance of the film cooling hole. Probabilistic process that consists of Kriging surrogate model and Monte Carlo Simulation with descriptive sampling method was coupled with the design optimization process using Genetic Algorithm. Through this, film cooling hole array which shows the high performance, yet robust to the manufacturing tolerance was obtained, and the effects of the manufacturing tolerance on the cooling performance was carefully investigated. As a result, the region where the film cooling effectiveness is noticeable, as well as the maximum width of the variation of the film cooling effectiveness were reduced through optimization, and it is also confirmed that the tolerance of the holes near the leading edge is more influential to the cooling performance because the film cooling effectiveness is more sensitive to the manufacturing tolerance of the leading edge than that of the trailing edge.
Combined Cycle Engine Cascades Achieving High Efficiency
Authors: Schroder Andy , Turner Mark G. , Roberts Rory A.
Published: September 2016

Two combined cycle engine cascade concepts are presented in this paper. The first uses a traditional open loop gas turbine engine (Brayton cycle) with a combustor as the topping cycle and a series of supercritical carbon dioxide (S–CO2) engines as intermediate cycles and a bottoming cycle. A global optimization of the engine design parameters was conducted to maximize the combined efficiency of all of the engines. A combined cycle efficiency of 65.0% is predicted. The second combined cycle configuration utilizes a fuel cell inside of the topping cycle in addition to a combustor. The fuel cell utilizes methane fuel. The waste heat from the fuel cell is used to heat the high pressure air. A combustor is also used to burn the excess fuel not usable by the fuel cell. After being heated, the high pressure, high temperature air expands through a turbine to atmospheric pressure. The low pressure, intermediate temperature exhaust air is then used to power a cascade of supercritical carbon dioxide engines. A combined efficiency of 73.1% using the fuel lower heating value is predicted with this combined fuel cell and heat engine device. Details of thermodynamics as well as the (S–CO2) engines are given.
A Noise Assessment Framework for Subsonic Aircraft and Engines
Authors: Ali Fakhre , Ellbrant Lars , Elmdahl David , Grönstedt Tomas
Published: September 2016

This paper proposes a preliminary subsonic aircraft and engine noise assessment framework, capable of computing the aircraft total noise level at all three certification points (i.e. Approach, Lateral, and Flyover) defined by the International Civil Aviation Organisation. The proposed framework is numerically integrated to account for the complete aircraft noise sources (i.e. the fuselage, wings, landing gear, as well as noise sources resulting from the engine component level, (i.e. fan, compressor, combustor, turbine, and jet). The developed framework is based on a wide-range of empirical and semi-empirical correlations collected from the public domain literature. The fidelity of the framework also caters for flight effects such as atmospheric attenuation, spherical spreading, Doppler shift, lateral attenuation, retarded time and ground reflection. A conversion between the sound pressure level SPL [SPLdB] to effective perceived noise level EPNL [EPNdB] is also included to allow for a consistent comparison with the certification procedure. Through the successful deployment of the proposed framework a generic aircraft model, representative of a modern commercial carrier aircraft has been investigated, operating under representative operational conditions. The sound pressure level corresponding to various aircraft and engine component have been thoroughly investigated and verified with trends acquired based on the theory. Furthermore, the predictions made by the framework corresponding to the aforementioned three certification points have also been verified against the noise level measurements provided by the International Civil Aviation Organization. The results acquired exhibit good correlation against the verification data for total noise levels at the microphones. Furthermore, a component level comparison is also presented which exhibit good agreement with verification data. The deployed methodology can essentially be regarded as an enabling technology to support the effective and efficient implementation of framework(s) (i.e. Technoeconomic, Environmental and Risk Assessment) targeted to evaluate the existing and advanced aircraft and engine architectures in terms of operational performance and environmental impact.
An Energy Based Fouling Model for Gas Turbines: EBFOG
Authors: Casari Nicola , Pinelli Michele , Suman Alessio , di Mare Luca , Montomoli Francesco
Published: September 2016

Fouling is a major problem in gas turbines for aero-propulsion. The aerodynamics and heat load of the blades are severely affected by this phenomenon with local geometrical variations due to deposition and erosion. Currently two major models are available in literature for the evaluation of fouling effects in CFD: the first one is based on a critical threshold for the viscosity, whereas the second is characterized by the normal velocity to the surface. Both models aim to define a likelihood coefficient which estimates the probability a particle has to stick to a surface, known as sticking coefficient. However current models lack of generality being application specific.

This work presents an innovative model for the estimation of the sticking probability. The fouling effect is defined as function of particle velocity, temperature and size through an energy based approach. Expressing the energy involved in the impact through an Arrhenius’ type equation a general formulation for the sticking coefficient is obtained. The method, named EBFOG (Energy Based FOulinG), is the first “energy” based model presented in the open literature that can account any common deposition effect in gas turbines.

The EBFOG model is implemented into a Lagrangian tracking procedure, coupled to a full three-dimensional CFD solver. Particles are tracked inside the domain and the velocity, size and temperature of each ones are calculated. The local geometry of the blade is modified accordingly to the deposition rate, the mesh is modified and the CFD solver updates the flow field.

The application of this model to particle deposition in high pressure turbine vanes is investigated showing the flexibility of the proposed methodology. Such model is particular important in aircraft engines where the effect of fouling for the turbine, in particular the reduction of the HP nozzle throat area, influences heavily the performance: the energy based approach is thus used to quantify the area modification and estimate the variation of the compressor performance. The compressor map as a function of the operating hours in a severe environment can be in this way predicted to estimate, for example, the time that an engine can fly in a cloud of volcanic ashes. For this reason the impact of the fouling on the throat area of the nozzle is quantified for different conditions.
Effect of Preheating on Flame Structure of a Swirl Stabilized Combustor With Porous Insert to Control Thermoacoustics
Authors: Depperschmidt Daniel L. , Kornegay John A. , Allen James C. , Agrawal Ajay K.
Published: September 2016

Lean premixed (LPM) combustion is a common strategy in the turbine industry for power generation to reduce emissions of nitric oxides and other pollutants. LPM combustion tends to produce thermoacoustic instabilities under specific conditions. Previously we have shown that an appropriately designed ring-shaped porous insert located on the dump plane can mitigate thermoacoustic instabilities in LPM swirl-stabilized combustion for a range of operating conditions, and explained results based on time-resolved flowfield measurements. In this study, experiments are conducted at higher inlet air temperatures than used before, and the flame structure in the combustor without and with porous insert is investigated for the first time using time-resolved OH planar laser-induced fluorescence technique operated at 10 kHz. Large pressure oscillations in the fuel-air mixing tube demonstrate the existence of thermoacoustic instabilities without the porous insert. The pressure oscillations diminish with the porous insert, which is attributed to the changes in the flow field and flame structure.
Flameless Oxidation Combustor Development for a Sequential Combustion Hybrid Turbofan Engine
Authors: Levy Y. , Erenburg V. , Sherbaum V. , Gaissinski I.
Published: September 2016

A promising method of reducing NOx emissions in combustion systems is the Flameless oxidation (FO), which is based on significant dilution of the oxygen concentration in the reactant stream and elevating its temperature to above auto ignition level.

The present work is aimed at developing an FO based combustor for a sequential combustion turbofan engine, where the primary combustor is fuelled with H2 and the secondary combustor with hydrocarbon (jet or bio-jet) fuel. The work was performed within the framework of the European project AHEAD (www.ahead-euproject.eu). Being situated between the high pressure and the low pressure turbines, the inlet conditions to the FO combustor are non-conventional.

CHEMKIN simulations revealed the theoretical feasibility of a combustion system to operate in the FO mode of combustion under the specific Take off and Cruise operating conditions. Several design iterations were conducted to find an appropriate geometrical configuration that would allow for such a system to operate in a stable manner. The design iterations were followed by intensive CFD simulations (FLUENT) and a final design was a achieved where the predictions indicated nearly uniform internal temperature distribution with low mass fraction of CO (14.4ppm) and NOx (0.5 ppm) at the exhaust.

A separate experimental verification study was performed and confirmed the ability of the CFD model to predict the behaviour of such a combustion configuration within the hybrid turbofan engine and its results will be published elsewhere.
Foreign Object Damage and Fatigue After Impact Simulations on Flat and Curved Hi Nicalon and Hi Nicalon Type S (MI SiC) Specimens at Room and 1200°C Using Building Block Approach
Authors: Abdi Frank , Godines Cody , Morscher Gregory N. , Choi Sung , Villa Montero Marc , Han Zipeng , Presby Michael
Published: September 2016

SiC-based ceramic matrix composites (CMC) in turbine engine applications must sustain fatigue residual life after foreign object impacts that might occur in services. Experiments, nondestructive evaluations (NDE), and simulations have illustrated good correlations between impact energy and foreign object damage (FOD) and fatigue life after impact at room and 1200°C temperatures. Flat and curved five-harness satin (5HS) woven CMCs specimens, consisting of Hi-Nicalon Type S (Goodrich) and Hi-Nicalon (Rolls Royce) in MI SiC matrix, were tested and simulated. Tests measured electrical resistivity (ER), acoustic emission (AE), and microscopy. Simulations used a building block validation strategy and the Multi-Scale Progressive Failure Analysis (MS-PFA) method. Simulations complemented experiments in understanding and predicting the damage states, of impact, and fatigue residual strength after impact of CMCs to form a more complete understanding of the damage mechanisms involved in such events. The GENOA software developed by Alpha STAR Corporation [1, 2, 3] is capable of Durability and Damage Tolerance (D&DT), life, and reliability predictions by means of multi-scale progressive failure analysis (damage and fracture evolution). In general, CMCs are modeled using effective fiber, matrix, and interface constitutive behaviors, from which the lamina stiffness, strengths, and the strain rate effect can be derived. Similarly, the fatigue strength and stiffness degradation, and the effect of defects in a matrix micro crack density, voids, as well as fibers waviness, and damages after impact can be characterized. The final simulation is static loading and impact on a generic CMC SiC/SiC (Sylramic MI 5HS) blade which is to be used in future blade optimization based on minimizing damage incurred.

The GENOA software platform supports FAA recommended ASTM standard Building-Block Validation Strategy with reduced tests conducting: 1) Material Calibration and Qualification, and 2) FEM Verification, Validation, and 3) Blind Predictions (Accreditation). The simulation and test comparisons performed included the damage size for both the CMC (fracture) and the steel impactor (plastic deformation), rebound velocities, SN curves for fatigue of pristine and impacted specimens at room and high temperatures. All simulations showed good correlation. The MS-PFA tool demonstrated a great potential for CMC post FOD fatigue life for part certification supported with reduced tests.
Using a Tracer Gas to Quantify Sealing Effectiveness for Engine Realistic Rim Seals
Authors: Clark Kenneth , Barringer Michael , Thole Karen , Clum Carey , Hiester Paul , Memory Curtis , Robak Christopher
Published: September 2016

As overall pressure ratios increase in gas turbine engines, both the main gas path and cooling temperatures increase leading to component durability concerns. At the same time effective use of the secondary air for both cooling and sealing becomes increasingly important in terms of engine efficiency. To fully optimize these competing requirements, experiments at engine-relevant conditions are required to validate new designs and computational tools. A test turbine has been commissioned in the Steady Thermal Aero Research Turbine (START) lab. The test turbine was designed to be a 1.5 stage turbine operating under continuous flow simulating engine-relevant conditions including Reynolds and Mach numbers with hardware true to engine scale. The first phase of research conducted using the test turbine, which was configured for a half-stage (vane only), was to study hot gas ingestion through turbine rim seals.

This paper presents a series of facility benchmarks as well as validation experiments conducted to study ingestion using a tracer gas to quantify the performance of rim seals and purge flows. Sensitivity studies included concentration levels and sampling flow rates in flow regimes that ranged from stagnant to compressible depending upon the area of interest. The sensitivity studies included a range of purge and leakage flow conditions for several locations in the rim seal and cavity areas. Results indicate reasonable sampling methods were used to achieve isokinetic sampling conditions.
Effects of Purge Jet Momentum on Sealing Effectiveness
Authors: Clark Kenneth , Barringer Michael , Thole Karen , Clum Carey , Hiester Paul , Memory Curtis , Robak Christopher
Published: September 2016

Driven by the need for higher cycle efficiencies, overall pressure ratios for gas turbine engines continue to be pushed higher thereby resulting in increasing gas temperatures. Secondary air, bled from the compressor, is used to cool turbine components and seal the cavities between stages from the hot main gas path. This paper compares a range of purge flows and two different purge hole configurations for introducing the purge flow into the rim cavities. In addition, the mate face gap leakage between vanes is investigated. For this particular study, stationary vanes at engine relevant Mach and Reynolds numbers were used with a static rim seal and rim cavity to remove rotational effects and isolate gas path effects. Sealing effectiveness measurements, deduced from the use of CO2 as a flow tracer, indicate that the effectiveness levels on the stator and rotor side of the cavity depend on the mass and momentum flux ratios of the purge jets relative to the swirl velocity. For a given purge flow rate, fewer purge holes resulted in better sealing than the case with a larger number of holes.
Flow Characteristics of a Novel Centrifugal Compressor Design
Authors: Mishra Shashank , Abdallah Shaaban , Turner Mark
Published: September 2016

Multistage axial compressor has an advantage of lower stage loading as compared to a single stage. Several stages with low pressure ratio are linked together which allows for multiplication of pressure to generate high pressure ratio in an axial compressor. Since each stage has low pressure ratio they operate at a higher efficiency and the efficiency of multi-stage axial compressor as a whole is very high. Although, single stage centrifugal compressor has higher pressure ratio compared with an axial compressor but multistage centrifugal compressors are not as efficient because the flow has to be turned from radial at outlet to axial at inlet for each stage. The present study explores the advantages of extending the axial compressor efficient flow path that consist of rotor stator stages to the centrifugal compressor stage. In this invention, two rotating rows of blades are mounted on the same impeller disk, separated by a stator blade row attached to the casing. A certain amount of turning can be achieved through a single stage centrifugal compressor before flow starts separating, thus dividing it into multiple stages would be advantageous as it would allow for more flow turning. Also the individual stage now operate with low pressure ratio and high efficiency resulting into an overall increase in pressure ratio and efficiency. The baseline is derived from the NASA low speed centrifugal compressor design which is a 55 degree backward swept impeller. Flow characteristics of the novel multistage design are compared with a single stage centrifugal compressor. The flow path of the baseline and multi-stage compressor are created using 3DBGB tool and DAKOTA is used to optimize the performance of baseline as well novel design. The optimization techniques used are Genetic algorithm followed by Numerical Gradient method. The optimization resulted into improvements in incidence and geometry which significantly improved the performance over baseline compressor design. The multistage compressor is more efficient with a higher pressure ratio compared with the base line design for the same work input and initial conditions.
Numerical Analysis of Transonic Compressor With Various Tip Clearance Gap
Authors: Sakuma Yasunori , Watanabe Toshinori , Himeno Takehiro
Published: September 2016

Computational analysis has been conducted on the NASA Rotor 37 transonic compressor with various tip clearance gap heights. Using steady rotor-only analysis, the change in overall performance, basic flow characteristics, and near-casing phenomena have been carefully observed. The results have clarified that the peak efficiency of the compressor decreases almost linearly with the increase in gap height. Meanwhile, the stall margin was prone to deterioration in cases of significantly small or significantly large clearance gaps. The peak stall margin was attained when the gap was set to 75% of the original height. Focusing on the flow structures, the tip leakage flow and tip leakage vortex seemed to be dominant loss sources in the case of a large tip clearance gap. On the other hand, trailing edge separation at the blade tip was the major loss source in case of a small tip clearance gap. The difference in the near-casing flow structure also determined the onset process of numerical instability. In case of a large tip clearance gap, the advance of the interface between the main flow and tip leakage flow seemed to cause an accumulation of blockage in the region near the casing, possibly triggering the tip-initiated stall. In the case of a small tip clearance gap, interaction among the wall separation, blade tip trailing edge separation, and shockwave /boundary layer interaction was significant. These phenomena appeared to play a major role in the onset of numerical instability in the blade tip region.
Influence of Residence Time on Fuel Spray Sauter Mean Diameter (SMD) and Emissions Using Biodiesel and its Blends in a Low NOx Gas Turbine Combustor
Authors: Altaher Mohamed A. , Li Hu , Andrews Gordon E.
Published: September 2016

Biodiesels have advantages of low carbon footprint, reduced toxic emissions, improved energy supply security and sustainability and therefore attracted attentions in both industrial and aero gas turbines sectors. Industrial gas turbine applications are more practical biodiesels due to low temperature waxing and flow problems at altitude for aero gas turbine applications. This paper investigated the use of biodiesels in a low NOx radial swirler, as used in some industrial low NOx gas turbines. A waste cooking oil derived methyl ester biodiesel (WME) was tested on a radial swirler industrial low NOx gas turbine combustor under atmospheric pressure, 600K air inlet temperature and reference Mach number of 0.017&0.023. The pure WME, its blends with kerosene (B20 and B50) and pure kerosene were tested for gaseous emissions and lean extinction as a function of equivalence ratio for both Mach numbers. Sauter Mean Diameter (SMD) of the fuel spray droplets was calculated. The results showed that the WME and its blends had lower CO, UHC emissions and higher NOx emissions than the kerosene. The weak extinction limits were determined for all fuels and B100 has the lowest value. The higher air velocity (at Mach = 0.023) resulted in smaller SMDs which improved the mixing and atomizing of fuels and thus led to reductions in NOx emissions.
A Combined Power Plant Fueled by Syngas Produced in a Downdraft Gasifier
Authors: Fortunato Bernardo , Camporeale Sergio Mario , Torresi Marco , Fornarelli Francesco , Brunetti Gianluigi , Pantaleo Antonio Marco
Published: September 2016

In this paper different gas-steam combined-cycles fueled by syngas produced in a local downdraft gasifier, are analyzed. At first, the downdraft gasifier model is briefly described, where waste biomass is transformed into syngas, which can be used more efficiently than the original solid biomass to generate useful power, and can be transported much more easily. The gasifier model is able to estimate, with good approximation, the composition of the produced syngas, taking separately into account the biomass drying and the pyrolysis, oxidation and reduction processes. The gasifier operates at ambient pressure using air as gasification agent and biomass as input. Among others, pomace has been considered, since, in Italy (where the plant is supposed to be located) there are many regions, like Apulia, where this biomass is largely available. Three different plant configurations have been proposed and compared in terms of overall performance. The first two, named REXC (Regenerative cycle with EXternal Combustor) and CR (Conventional Regenerative cycle), burn the syngas in an internal combustor, whereas the third one, named SyEXC (Syngas External Combustion), considers an externally fired configuration for the syngas combustion.

In the REXC cycle, a secondary external combustion system, fed by cellulosic biomass, is connected to a heat exchanger in order to increase the air temperature, as in a regenerative cycle. The combustion products pass through a primary heat exchanger placed in the external combustion system, heating the compressed air, which flows into the primary internal combustion chamber, where a defined quantity of syngas reacts with the compressed air. The turbine exhaust gas (TEG), before going back into the external combustion, partially transfers its enthalpy content to a Heat Recovery Steam Generator (HRSG) of a bottoming Rankine cycle.

The second plant configuration (CR cycle) is characterized by a main internal combustor fueled by the produced syngas and implements a conventional regenerative process. The TEG is reheated by an externally fired combustion before flowing in the HRSG of a bottoming Rankine cycle.

The last plant configuration (SyEXC) differs from the CR one only for the main externally fired gas turbine fueled by syngas, thus avoiding any costly cleanup operation and cooling.