bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Validation of an Innovative Metallic Tile Holder System for a Ceramic Combustor Liner
Authors: Becchi Riccardo , Burberi Emanuele , Facchini Bruno , Tarchi Lorenzo , Abba Luca
Published: September 2016

In gas turbine, the enhancement of durability and the increase of reliability represent essential requirements. These issues become even more critical for components subjected to high thermal loads, as the combustion chamber, and go in parallel with the desire for higher efficiency, which resulted in a reduced amount of air that the cooling systems designers have available for the combustor liner.

This work presents the results of an experimental campaign aimed to evaluate the performance on a portion of the combustion chamber liner of the latest Ansaldo Energia AE64.3A+ gas turbine. In this configuration ceramic tiles replace the previous metallic heat shields, reducing coolant consumption up to 40%.

The designed test article is made up of two ceramic bricks, held on the shells by means of air cooled metallic tile holders, and is installed in a dedicated plenum chamber where is run over by an air flow from several angles of incidence in order to simulate some realistic turbine conditions.

A preliminary numerical study is conducted to estimate the test article surface pressure distributions in order to evaluate the mainstream flow impact on the tile holder cooling system behaviour. A novel application of Pressure Sensitive Paint (PSP) technique is applied to evaluate the air seal cooling of the brick holder system, essential to prevent hot gas ingestion. Furthermore, infrared (IR) thermography measurements on the liner are performed using an hot mainstream flow and reproducing typical cooling flow conditions. During the tests, several thermocouples, allocated on most critic brick holder components, continuously check the metal temperature.
Numerical Evaluation of the Unsteady Flow in a Centrifugal Compressor With Vaned Diffuser via URANS Approach
Authors: Zamiri Ali , Lee Byung Ju , Chung Jin Taek
Published: September 2016

The three dimensional, compressible, unsteady Navier-Stokes equations are solved to investigate the flow field of a centrifugal compressor with high compression ratio. Computational domain is consisted of an inlet bell and impeller with splitter blades followed by a two dimensional wedge vaned diffuser. The numerical method is validated by comparing the computational results with the experiments in terms of pressure ratio and compressor efficiency. The present study focuses on the unsteady pressure fluctuations and entropy production within the impeller and diffuser passages at the compressor design point. It is shown that the interaction between the impeller and diffuser blades leads to unsteadiness at the interface region and a pulsating behavior within the diffuser passages. Pressure waves with different convective velocities, generated by the impeller-diffuser interaction and pseudo-periodic unsteady separation bubbles, are captured in time/space domain along the diffuser blade surfaces. The pressure fluctuation spectra captured at the impeller-diffuser interface is evaluated to analyze the noise characteristics of the centrifugal compressor as a main source of blade passing frequency noise.
Performance Investigation of Cycle-Integrated Parallel Hybrid Turboshafts
Authors: Vratny Patrick C. , Kaiser Sascha , Seitz Arne , Donnerhack Stefan
Published: September 2016

Motivated by the long term target settings for research and innovation in Europe and in North America, initial investigations of parallel hybrid electric power plant systems have indicated significant fuel reduction potentials for short range air transport. While an electric motor assists the gas turbine in suppling mechanical power to the gas turbine within the classical parallel hybrid topology, in the present paper, a more sophisticated variant, namely the Cycle-Integrated Parallel Hybrid (CIPH) is considered. More specifically, the design and performance implications of a CIPH power plant architecture are investigated with regard to an advanced turboshaft (TS) engine application for helicopters. For this purpose, an array of compressor stages of the baseline TS power plant are decoupled from the turbine section, and are driven mechanically independently by means of electric motors. The baseline power plant of the investigated concept is derived for a 12-ton-helicopter accommodating 19 passengers on a 450nm mission. It consists of an axi-centrifugal compressor powered by the high pressure turbine as well as a free low pressure (power) turbine delivering a maximum shaft power of 3300 kW. For the presented CIPH concept, the axial compressor section is electrified with the help of linear electric motors mounted at the blade tips. Due to typical design characteristics of electric motors, counter rotating stages are considered most appropriate for the targeted TS power plant application. The electric motor power supply is realized through a Power Management And Distribution system featuring proper levels of redundancy. For the electrical energy storage, advanced battery technology is taken into account. Hybrid electric Energy and Propulsion Systems (EPS) can be characterized meaningfully by the degree of power hybridization, HP, being defined as the ratio of the installed electric power to the total power. For the presented CIPH application, a best and balanced HP of 19.7% has been identified. In typical part load operation, this may lead to relative Power Specific Fuel Consumption (PSFC) improvements of up to 45% and overall efficiency has been almost doubled compared to the TS reference. With the implementation of electric power within the cycle, additional degrees of freedom for power plant operation and control can be established. At vehicular level, a retrofitted version of the reference helicopter equipped with the CIPH TS propulsion system faces more than 50% reduced range, but simultaneously reduces total energy consumption (fuel plus electrical) by 28% and CO2 by 42% compared to the reference vehicle at identical reduced range.
Aerodynamic Loading Distribution Effects on Off-Design Performance of Highly Loaded LP Turbine Cascades Under Steady and Unsteady Incoming Flows
Authors: Berrino Marco , Simoni Daniele , Ubaldi Marina , Zunino Pietro , Bertini Francesco
Published: September 2016

The present work is part of a continuous cooperation between GE AvioAero and the University of Genova aimed at understanding the detailed flow physics of efficient highly loaded LPT blades for aeroengine applications. In this paper the effects of the aerodynamic loading distribution on the performances of three different cascades with the same Zweifel number have been experimentally investigated under steady and unsteady incoming flow conditions. Measurements have been carried out for several Reynolds numbers (in the range 70000<Re<300000) with an incidence angle variation of ±9°, in order to cover the typical realistic LP aeroengine turbine working range on design and off-design conditions.

Profile aerodynamic loadings and total pressure loss coefficients have been evaluated for the different cases. Efficiency data clearly highlight that at nominal incidence an aft loaded cascade provides the lowest profile losses when the boundary layer is attached to the wall, as it occurs in the unsteady case or at high Reynolds numbers. Only at the lowest Reynolds number in the steady case, a front loaded profile is preferable since it helps to prevent a laminar boundary layer separation. Moreover, the aft loaded profile has also shown a better robustness to incidence angle variation, both for the steady and the unsteady inflow conditions. Indeed, the growth of profile losses with incidence is weaker for the aft loaded cascade with respect to the front and the mid loaded ones. However, irrespective of the loading distribution the loss trend vs incidence angle has been found to be completely different between the steady and the unsteady operations.

Results in the paper give a clear overview of the impact of the loading distribution on profile losses as a function of Reynolds number, as well as a detailed view of the influence due to the loading characteristics on incidence robustness under the realistic unsteady inflow case.
Aerothermal Investigation on the Flow and Heat Transfer in a Helically Corrugated Cooling Channel
Authors: Mayo Ignacio , Cernat Bogdan C. , Virgilio Marco , Pappa Alessio , Arts Tony
Published: September 2016

The detailed flow field and heat transfer were experimentally investigated in a channel with a circular cross section and equipped with a helical rib of low blockage ratio. Stereoscopic Particle Image Velocimetry (S-PIV) was applied in order to measure the three components of the mean and turbulent velocities in the symmetry plane of the channel. Additionally, steady-state Liquid Crystal Thermography (LCT) and Infrared Thermography (IRT) were employed in order to study the convective heat transfer coefficient on the wall. Measurements were carried out more than six pitches downstream of the rib origin, presenting periodic velocity and heat transfer fields from this location on. The resulting velocity and heat transfer fields show similarities with those present in channels of plane walls, such as low momentum and heat transfer areas upstream and downstream of the obstacle, and high kinetic energy and heat transfer a few rib heights downstream of the obstacle. On the other hand, the shape of the rib induces a swirling motion with the same sense as the rib. The azimuthal mean velocity is negligible in the core of the pipe, but it shows considerable levels close to the wall.
Three-Dimensional Aerodynamic Optimization of a Multi-Stage Axial Compressor
Authors: Ning Tao , Gu Chun-wei , Li Xiao-tang , Liu Tai-qiu
Published: September 2016

An optimization method combined of a genetic algorithm, an artificial neural network, a CFD solver and a blade generator, is developed in this research and applied in the three-dimensional blading design of a newly designed highly-loaded 5-stage axial compressor. The adaptive probabilities of crossover and mutation, non-uniform mutation operator and elitism operator are employed to improve the convergence of the genetic algorithm. Considering both the optimization efficiency and effectiveness, a mixture of high-fidelity multistage CFD method and approximate surrogate model of the feed-forward ANN is used to evaluate the fitness. In particular, the database is updated dynamically and used to re-train the surrogate model of ANN for improving the accuracy for predicting. The last stator of the compressor is optimized at the near stall operating point. The tip bow with relative bow height Hb and bow angle αb are treated as design parameters. The adiabatic efficiency as well as the penalty of mass flow and total pressure ratio constitute the objective functions to be maximized. The optimum (Hb = 0.881, αb = 14.7°) obtains 0.4% adiabatic efficiency increase for the whole compressor at the optimized operating point. The detailed aerodynamic is compared between the baseline and optimized stator, and the mechanism is analyzed. The optimized version obtains 5.1% increase in stall margin and maintains the efficiency at the design point.
Analysis of Heavy Duty Gas Turbine Stator-Rotor Cavity Through 3D CFD-1D Fluid Network — Field Measurements Combined Approach
Authors: Bavassano Francesco , Mantero Marco , Gasnier Thibault , Ronconi Emanuele
Published: September 2016

An effective design and development of the Secondary Air System of a heavy-duty gas turbine is crucial for many purposes, such as cooling and sealing air supply, pre-swirling features, leakages control, casings and rotor thermal state assessment and rotor axial thrust management. All of these features directly impact on the performances and integrity of the whole machine and accordingly require advanced design approaches.

The first stage stator-rotor turbine cavity of Ansaldo E-Class heavy-duty gas turbine AE94.2 underwent design modifications to adjust its internal pressure and consequently lower the global rotor axial load acting on the thrust bearing. This goal had to be reached while maintaining safety against hot gas ingestion from the turbine section main flow into the cavity, thus preserving the GT integrity.

A multi-purpose analysis was then carried out on the cavity Secondary Air System. This involved steady 3D CFD calculations with a computational domain comprising the first turbine stage and the corresponding stator-rotor wheelspace. A combined use of CFD and SASAC, the in-house Ansaldo 1D fluid network code, finally led to an upgraded design of the cavity. Two field measurement campaigns were subsequently carried out on an AE94.2 GT to validate both the baseline configuration and the upgraded one, by means of 6 pressure and temperature sensors in the cavity and 12 load cells/thermocouples on the thrust bearing.

The CFD model and results are presented, the fluid network tuning is discussed and the experimental setup and main outcomes of the two field campaigns are reported. Constant references to the definitive literature are made, with an effort to correlate at best research and industrial practice.

These integrated activities allowed to perform a reliable verification against hot gas ingestion into the stator-rotor cavity and to successfully develop an effective solution, which reduced the GT rotor residual axial thrust by up to 25% less.
Multistage Axial Compressor Flow Field Predictions Using CFD and Through-Flow Calculations
Authors: Banjac Milan , Petrovic Milan V. , Wiedermann Alexander
Published: September 2016

A comparison between two different methods for aerodynamic calculation of multistage axial compressors is presented. Results obtained using classical 2D through-flow calculations were compared with CFD results for several test cases, including various subsonic and supersonic multistage axial compressors with different geometric configurations and stage operating parameters. Calculated flow fields were compared in terms of overall compressor performances, individual blade row operation parameters and spanwise distributions of different flow variables. Nominal and off-design compressor operating conditions were analyzed and all the results were compared with experimental data. Accuracy, advantages and differences between individual methods are discussed.
Numerical Application of Double Modal Synthesis to an Industrial Mistuned Clustered Stator Vane and Experimental Validation
Authors: Philippe Jonathan , Thouverez Fabrice , Blanc Laurent , Gruin Marion
Published: September 2016

Bladed disks are subjected to dynamically fluctuating high-pressure loads. To ensure their robust design, current models must be continuously improved to take phenomena such as mistuning into account. Geometric and material dispersions imply some mistuning effects, which result in both the loss of cyclic symmetry properties and a vibratory response amplification in frequency ranges of high modal density. These conditions complicate the prediction of vibratory behavior, causing high modal density and extreme sensitivity to mistuning. It becomes thus even more essential to maintain structural strength and prevent fatigue. In a first section, a substructuring method has been adopted to reduce finite elements models. It has been applied on an industrial stator vane model. This reduction method is a double modal synthesis based on Craig-Bampton method coupled to a static modes basis reduction through a second modal synthesis. This method yields excellent results and allows dividing computation costs roughly by a five hundred factor. Thanks to an appropriate choice of substructures it is then possible to generate thousands of mistuning configurations and compute them. Thus, 50,000 mistuning draws have been performed, covering a range of 5% maximum variation of blades and platforms Young modulus with a significant statistical meaning. A virtual modal characterization of the industrial stator vane has finally been made in a context of statistical treatment. In a second section, a modal identification has been performed on an industrial stator vane. The part has been subjected to white noise excitation and frequency response functions vibrations have been obtained through scanning vibrometer measurements. The numerical model has then been adjusted, matching whole system modes as they are less or not subjected to misutning. Experimental results have finally been compared to the readjusted statistical modal characterization previously computed. What stands out from this comparison is that most modal frequencies of the industrial stator vane used for experimental analyses are in the envelope predicted by statistical calculation.
Development of a Fast Response Aerodynamic Pressure Probe Based on a Waveguide Approach
Authors: Fioravanti Andrea , Lenzi Giulio , Ferrara Giovanni , Ferrari Lorenzo
Published: September 2016

Currently fast response aerodynamic probes are widely used for advanced experimental investigations in turbomachinery applications. The most common configuration is a virtual three hole probe. This solution is a good compromise between probe dimension and accuracy. Several authors have attempted to extend the capabilities of these probes in terms of bandwidth and operating conditions. Even though differences exist between the solutions in the literature, all of the designs involve the positioning of a dynamic pressure sensor close to the measurement point. In general terms, the higher the frequency response, the more the sensor is exposed to the flow. This physical constraint puts a limit on the probe applicability since the measurement conditions have to comply with the maximum allowed operating conditions of the sensor. In other applications, when the conditions are particularly harsh and a direct measurement is not possible, a waveguide probe is commonly used to estimate the local pressure. In this device the sensor is connected to the measurement point through a transmitting duct which guarantees that the sensor is operating in a less critical condition. Generally, the measurement is performed through a pressure tap and particular attention must be paid to the probe design in order to have an acceptable frequency response function. In this study, the authors conceived, developed and tested a probe which combines the concept of a fast response aerodynamic pressure probe with that of a waveguide probe. Such a device exploits the benefits of having the sensor far from the harsh conditions while maintaining the capability to perform an accurate flow measurement.
An Optimization of Swirl Recovery Vane for Fokker 29 Propeller Using Design of Experiment Method
Authors: Yangang Wang , Nanshu Chen , Qingxi Li , Eitelberg Georg
Published: September 2016

Compared with the single propeller, a propeller with Swirl Recovery Vanes (SRV) has great advantages in recovering the residual swirl, which leads to an improvement both in thrust and propulsion efficiency. Based on the preliminary design of the SRV for Fokker F29 propeller, Design of Experiment (DoE) method was employed to optimize and further improve the performance of SRV in the present study. Firstly, orthogonal experiment was adopted to identify the most significant factors for affecting thrust. Secondly, steepest ascent method was used to search for the optimum range of target factors by using climbing experiment and factorial experiment. Finally, center composite experiment was adopted to find the optimal solution. As a result, the thrust of the optimized SRV has increased significantly by 11.78% at the design point, which leads to a 0.66% increment of total efficiency of propeller and SRV propulsion system, and even more increment at low rotation speed (2.10%). Besides, compared with the original SRV, the optimized SRV geometry improves the flow characteristics at the tip region of the vane. The tip vortex and swirl kinetic energy have been weakened distinctly, and the thrust coefficient distribution along the spanwise tends to be more uniform.
Twin Shaft Gas Turbine Variable Area Turbine Nozzle: Analytical Modeling and Optimization of Kinematic Chain
Authors: Colantoni Simone , Tripoli Girolamo , Gorte Devidasa Pai , Franchini Francesco , Rossetti Fabio , Spagnolo Marco
Published: September 2016

Some of twin shaft gas turbines models of GE are equipped with Variable Area Turbine Nozzle (VATN), also called Nozzle Guide Vane (NGV) as the first stator stage of Low Pressure Turbine (LPT). By varying the throat area, VATN controls the energy split between the High Pressure Turbine (HPT) and Low Pressure Turbine, allowing higher operational flexibility and higher efficiency at partial load/speed. This flexibility is an important requirement for gas turbine in mechanical drive applications.

This paper is focused on the design, development and optimization of a numerical Finite Element (FE) model of the kinematic chain implemented to actuate the variable area turbine nozzles, in order to evaluate the required force as input to size and design the actuator. The kinematic chain is composed of an arrangement of linkage components that transfer the load provided by the actuator to the VATN and achieve a desired rotation of VATN airfoil around its axis. The load provided by actuator has to balance the aerodynamic load taking into account the contribution of friction developed inside the kinematic chain. The FE model has been specifically developed to evaluate the effects of different parameters, such as manufacturing tolerances and assembly clearances, in terms of total actuation force requirement, stress/life of the components and friction distribution.

The additional scope of the detailed FE model is to represent an analytical validation criterion of the results obtained through a simplified spreadsheet-based tool which aims to be a reliable and quick responding system both for new product design phase and for implemented fleet issues resolution.
Emissions of a Wet Premixed Flame of Natural Gas and a Mixture With Hydrogen at High Pressure
Authors: Stathopoulos P. , Kuhn P. , Wendler J. , Tanneberger T. , Terhaar S. , Paschereit C. O. , Schmalhofer C. , Griebel P. , Aigner M.
Published: September 2016

It is generally accepted that combustion of hydrogen and natural gas mixtures will become more prevalent in the near future, to allow for a further penetration of renewables in the European power generation system. The current work aims at the demonstration of the advantages of steam dilution, when highly reactive combustible mixtures are used in a swirl-stabilized combustor. To this end, high-pressure experiments have been conducted with a generic swirl-stabilized combustor featuring axial air injection to increase flashback safety. The experiments have been conducted with two fuel mixtures, at various pressure levels up to 9 bar and at four levels of steam dilution up to 25% steam-to-air mass flow ratio. Natural gas has been used as a reference fuel, whereas a mixture of natural gas and hydrogen (10% hydrogen by mass) represented an upper limit of hydrogen concentration in a natural gas network with hydrogen enrichment. The results of the emissions measurements are presented along with a reactor network model. The latter is applied as a means to qualitatively understand the chemical processes responsible for the observed emissions and their trends with increasing pressure and steam injection.
An Experimental and Numerical Investigation of the Effect of Combustor-Nozzle Platform Misalignment on Endwall Heat Transfer at Transonic High Turbulence Conditions
Authors: Arisi A. , Mayo D. , Li Z. , Ng W. F. , Moon H. K. , Zhang L.
Published: September 2016

A detailed experimental and numerical study has been conducted to investigate the endwall heat transfer characteristics on a nozzle platform that has been misaligned with the combustor exit, resulting in a backward facing step at the nozzle inlet. The study was carried out under transonic engine representative conditions with an exit Mach number of 0.85 (Reexit = 1.5 × 106), and an inlet turbulence intensity of 16%. A transient infrared thermography technique coupled with endwall static pressure ports, were used to map the endwall surface heat transfer and aerodynamic characteristics respectively. A numerical study was also conducted by solving the steady state Reynolds Averaged Navier Stokes (RANS) equations using the commercial CFD solver ANSYS Fluent v.15. The numerical results were then validated by comparing to experiment data and good agreement was observed. The results reveal that the classical endwall secondary flows (endwall crossflows, horseshoe and passage vortices) are weakened and a unique auxiliary vortex system develops within the passage and interacts with the weakened horseshoe vortex. It is observed that heat transfer in the first half of the passage endwall is heavily influenced by this auxiliary vortex system. Heat transfer augmentation of between 15% and 40% was also observed throughout the NGV endwall. Furthermore, the auxiliary vortex system results in a delayed cross-passage migration of the horseshoe vortex which consequently results in large lateral gradient in heat transfer downstream of the throat.
Identification of Thermodynamic Combined Cycle Design Parameters Using Multi Objective and Multi Variable Optimisation Methodologies to Achieve 65% Combined Cycle Power Plant Net Efficient
Authors: Baykal Sevket , Rufli Peter , Bolliger Raffaele , Fusaro Francesco , Kujawski Hubert
Published: September 2016

Clean and cost-effective power generation is the key factor to cope with imposed challenges of competing technologies in the energy market. Improvements in thermal power generation efficiency will significantly contribute to the goals of reducing emissions and cost of electricity, thereby increasing their competitiveness. However, targeted high efficiency levels (e.g., 65% combined cycle power plant net efficiency) cannot be achieved with today’s technology. One of the main difficulties is the appropriate distribution of technology challenges among various combined cycle equipment. Optimization of the early phases of innovation in the product development for future technologies is key for their sustainability and increased likelihood of economic success. For this purpose a combined cycle power plant initial design methodology was developed with the help of the Original Equipment Manufacturers, OEMs. As the main advantage, this approach is able to combine current OEM’s state of the art in product technology with an educated guess for near future technology development. The application of the developed methodology is done on the exploration of the design parameters of new technologies to achieve 65% combined cycle power plant net efficiency. The results highlight the interdependence of the topping and bottoming cycle thermodynamic performance parameters and a large number of potential designs achieving 65% efficiency was identified. The technical realization of found thermodynamic performance parameters would be evaluated later in terms of their technological challenge and economic viability. In this respect the integrative combined cycle power plant optimization methodology is the key to analyze existing limitations and explore new technologies in order to constantly increase the value for power plant customers.
Multi-Disciplinary Analyses for the Design of a High Pressure Turbine Blade Tip
Authors: Caloni Stefano , Shahpar Shahrokh
Published: September 2016

The design of a high pressure turbine blade is a challenging task requiring multiple disciplines to be solved simultaneously. Most recently, conjugate analyses are being developed to tackle such a problem; they are able to resolve both the fluid dynamics in a turbine passage and the thermal distribution in the solid part of the component. In this paper, the in-house Hydra CFD solver is used to analyse a high pressure shroudless turbine blade for a modern jet engine. The turbine is internally cooled and a Thermal Barrier Coating (TBC) is applied on the aerofoil surface. The coupling technique used at the interface in the presence of the TBC is described. The flow features at the tip of the turbine blade are the main focus of this study. Four different tip configurations are analysed. A flat tip and a squealer tip are chosen as reference designs; however the effects of opening the Trailing Edge (TE) on the Suction Side (SS) and the Pressure Side (PS) are also investigated. Both a cooled and an uncooled configuration of the turbine blade are analysed and the effect of the cooling flow on the over tip leakage is studied. Finally, conjugate analyses for the cooled turbine blades are used to predict the temperature reached by the different tip designs. The design with an opened TE on the SS shows a significant aerodynamic improvement over the others without increasing the temperature the tip has to withstand in operation.
Reduced Order Models of Blisks With Small Geometric Mistuning
Authors: Baek Seunghun , Zhao Yixin , Epureanu Bogdan
Published: September 2016

A technique for generating reduced order models (ROMs) of bladed disks with small geometric mistuning is proposed. Discrepancies in structural properties (mistuning) from blade to blade can cause a significant increase in the maximum vibratory stress. The effects of mistuning have been studied over the past few decades. Many researchers have studied the dynamic behavior of mistuned bladed disks by using ROMs. Many of these techniques rely on the fact that the modes of a mistuned system can be approximated by a linear combination of modes of the corresponding tuned system. Also, the tuned system modes have been modeled in component mode mistuning by using modal participation factors of cantilevered blade modes. Such techniques assume that mistuning can be well modeled as variations in blade alone frequencies. However, since geometric deformations contain stiffness and mass variations, mistuning can no longer be captured by cantilevered blade modes alone. To address this, a new technique is presented for generating ROMs of bladed disks with small geometric mistuning which may be a more general case of mistuning in practice.
A Research on Waste-Gated Turbine Performance Under Unsteady Flow Condition
Authors: Deng Q. , Burke R. D. , Zhang Q. , Pohorelsky Ludek
Published: September 2016

Turbochargers are key components of engine air-paths that must be carefully considered during the development process. The combination of fluid, mechanical and thermal phenomenon make the turbocharger a highly dynamic and non-linear modelling challenge. The aim of this study is to quantify the dynamic response of the turbocharger system across a frequency spectrum from 0.003Hz to 500Hz, i.e. for exhaust gas pulsation in steady state, load steps and cold start drive cycles, to validate the assumption of quasi-steady assumptions for particular modelling problems.

A waste-gated turbine was modelled using the dual orifice approach, a lumped capacitance heat transfer model and novel, physics-based pneumatic actuator mechanism model. Each sub-model has been validated individually against experimental measurements. The turbine inlet pressure and temperature and the waste-gate actuator pressure were perturbed across the full frequency range both individually and simultaneously in separate numerical investigations. The dynamic responses of turbine housing temperature, turbocharger rotor speed, waste-gate opening, mass flow and gas temperatures/pressures were all investigated.

The mass flow parameter exhibits significant dynamic behaviour above 100Hz, illustrating that the quasi-steady assumption is invalid in this frequency range. The waste-gate actuator system showed quasi-steady behaviour below 10Hz, while the mechanical inertia of the turbine attenuated fluctuations in shaft speed for frequencies between 0.1–10Hz. The thermal inertia of the turbocharger housing meant that housing temperature variations were supressed at frequencies above 0.01Hz.

The results have been used to illustrate the importance of model parameters for three transient simulation scenarios (cold start, load step and pulsating exhaust flow).
Exergoeconomic Analysis of a Combined Cycle of Three Levels of Pressure
Authors: Torres González Edgar Vicente , Lugo-Leyte Raúl , Salazar-Pereyra Martín , Toledo Velázquez Miguel , Lugo-Méndez Helen Denise , Torres Aldaco Alejandro
Published: September 2016

This paper presents an exergoeconomic analysis of the combined cycle power plant Tuxpan II located in Mexico. The plant is composed of two identical modules conformed by two gas turbines generating the required work and releasing the hot exhaust gases in two heat recovery steam generators. These components generate steam at three different pressure levels, used to produce additional work in one steam turbine. The productive structure of the considered system is used to visualize the cost formation process as well as the productive interaction between their components. The exergoeconomic analysis is pursued by 1) carrying out a systematic approach, based on the Fuel-Product methodology, in each component of the system; and 2) generating a set of equations, which allows compute the exergetic and exergoeconomic costs of each flow. The thermal and exergetic efficiency of the two gas turbines delivering 278.4 MW are 35.16% and 41.90% respectively. The computed thermal efficiency of the steam cycle providing 80.96 MW is 43.79%. The combined cycle power plant generates 359.36 MW with a thermal and exergetic efficiency of 47.27% and 54.10% respectively.
Optimizing Surge Margin and Efficiency of a Transonic Compressor
Authors: Goinis Georgios , Nicke Eberhard
Published: September 2016

It has been shown in several cases that casing treatments can improve the surge margin of a compressor. The question that is often left unanswered when designing and optimizing a casing treatment for a given compressor stage is whether the casing treatment can still improve the performance and surge margin when used on an aerodynamically improved rotor.

The current work includes the influence of the rotor geometry and casing geometry in the analysis. Several optimizations with equal objectives, to improve surge margin and efficiency, were performed. First the different components were optimized separately. The possible impact of optimizing the rotor, the casing geometry and the casing treatment on surge margin and efficiency are compared in terms of global performance and aerodynamic effects. It is then analyzed how combinations of optimized geometries perform. Of particular interest is how the circumferential grooves perform when used in combination with the optimized blade geometry.

The optimizations were performed using state of the art CFD and optimization procedures. Constraints on boundary conditions, mass flow rates and stresses were applied in order not to change the behavior of the compressor at design point significantly or to deteriorate the structural mechanics.
Fault Detection Using Reduced Rank Linear Engine Models
Authors: Allen Cody W. , Holcomb Chad M. , de Oliveira Mauricio
Published: September 2016

In diagnostic applications, data acquired from a unit in operation is often compared to predictions generated from a reference model. The equipment condition is often assessed via residual analysis, which compares the running data to model predictions. Often, the reference model may take the form of a high-fidelity, first principles physics model. Here, we seek to capture the dominant features of the turbine engine, using parameters typically instrumented in field applications using reduced rank linear models that are trained on data generated from the high fidelity design models. The reduced rank linear models are well suited to diagnostic applications. Specifically, a modified Principle Component Regression is applied to the reference data to obtain our reduced rank model. We then use real measurement data input into the reduced rank model to produce predictions and correspondingly, residuals whose statistical properties can characterized with respect to the high-fidelity model. This requires characterization of the expected measurement errors which are user input. The model is capable of working with a complete or reduced set of measurements. In the case of the redundant measurements, we can perform an analysis on the fidelity of the measurements. We show how to calculate a measure of agreement between a given set of measurements and the underlying model. Departures of the given, real data from the models predictions indicate possible faults in the operating variables. In addition, if a certain sensor is suspected of being fouled, we can leverage the ability of the model to predict with a reduced set of inputs and then compare the new predictions measure of agreement with the underlying model.
Uncertainty Quantification of Thermocouple Air Temperature Measurement in Highly Radiative Environment: Application to Turbofan Engine Compartment
Authors: Sommerer Y. , Drouin V. , Nicolas X. , Trouette B.
Published: September 2016

This paper focuses on thermocouple air temperature measurement uncertainty due to the radiative fluxes present in the engine compartment where engine case skin temperature can exceed 900 K. To really measure air temperature, the convective heat flux in the thermocouple bead must be predominant. This is why heat shields are used in order to reduce the radiative heat flux on the bead. However, in engine compartment, the heat shield orientation must be optimized since numerous hot walls surround the thermocouple.

In order to evaluate the impact of badly oriented heat shields and to provide a data bank for numerical simulation validations, a heated wind tunnel has been used. It has been shown that the uncertainty on the thermocouple temperature can reach dozens of degrees depending on the air speed and the heat shield orientation. Furthermore a specific 3D thermocouple model has been build and validated by comparison with the lab measurements. Then this thermocouple 3D model has been integrated in the whole engine compartment aero-thermal model in order to quantify the uncertainty of the thermocouple air temperature measurement in the real engine environment.
Stability Analysis of Multiharmonic Nonlinear Vibrations for Large Models of Gas-Turbine Engine Structures With Friction and Gaps
Authors: Petrov E. P.
Published: September 2016

An efficient method is proposed for the multiharmonic frequency domain analysis of the stability for nonlinear periodic forced vibrations in gas-turbine engine structures and turbomachines with friction, gaps and other types of nonlinear contact interfaces. The method allows using large-scale finite element models for structural components together with detailed description of nonlinear interactions at contact interfaces between these components. The highly accurate reduced models are applied in the assessment of stability of periodic regimes for large-scale model of gas-turbine structures. An approach is proposed for the highly-accurate calculation of motion of a structure after it is perturbed from the periodic nonlinear forced response.

Efficiency of the developed approach is demonstrated on a set of test cases including simple models and large-scale realistic bladed disc models with different types of nonlinearities: friction, gaps and cubic nonlinear springs.
Detailed Investigation of RANS and LES Predictions of Loss Generation in an Axial Compressor Cascade at Off Design Incidences
Authors: Leggett John , Priebe Stephan , Sandberg Richard , Michelassi Vittorio , Shabbir Aamir
Published: September 2016

In the design of modern jet engines the need for accurate loss prediction techniques is ever present. The most common tool currently in use is Reynolds Averaged Navier-Stokes model which provides good estimation at design conditions but can struggle with off design conditions. With accuracy being such an important requirement, an alternative method such as Large Eddy Simulation presents an opportunity to improve and assess the off design performance.

Although still limited by computational resources, the use of Large Eddy Simulations in conjunction with more detailed loss analysis methods forms a powerful tool for assessing and improving current Reynolds Averaged Navier-Stokes techniques. The simulations performed here are an incidence sweep at off-design conditions with free stream turbulence. The results of the two methodologies are compared with the use of loss breakdown analysis and the best practice of applying the loss breakdown technique to compressors is outlined.
Film Cooling Performance Improvement With Optimized Hole Arrangement on Pressure Side Surface of Nozzle Guide Vane: Part I — Optimization and Numerical Investigation
Authors: Lee Sanga , Rhee Dong-Ho , Cha Bong Jun , Yee Kwanjung
Published: September 2016

Although a plethora of high-performance film cooling hole configurations have been suggested, they are too complicated to manufacture and extremely difficult to maintain their original shapes during turbine operation. Thus, it is assumed that there is little room for further performance improvement by optimizing a single hole shape. However, optimization researches on the arrangement of the film cooling holes are still insufficient, so investigation of the possibility of the optimal hole array for improving film cooling performance is worth pursuing. In this study, to improve the film cooling performance of the pressure side surface of the nozzle guide vane, not a single film cooling hole shape, but an arrangement of the holes was considered. First, the optimum hole arrangements were determined by numerical optimization strategy, which contains newly suggested hole arrangement parameterization method and Efficient Global Optimization (EGO) method. Each array of the holes was parameterized by the shape function which consists of 5 design variables. This shape function is able to represent more general array shapes than the existing turbine film cooling hole array shape regardless of how many holes are included in a row. EGO method based on Kriging model is applied with Genetic Algorithm (GA), which yields superior optimization efficiency with minimum number of sampling points. Each sampling point obtained their fitness function by analyzing the nozzle with various array shape. Through this, the group of optimum hole arrangements, which greatly reduce the average wall temperature and the temperature deviation of the nozzle surface simultaneously were obtained. From the results, it is confirmed that the superior cooling performance was achieved when the array has smaller hole distances at the hub rather than at the shroud and when the array is disposed on the upstream position rather than on the downstream position. These optimization results were validated against experimental data, and it will be discussed in PART II.
Effect of Incoming Wakes on the Stator Performance in a Single-Stage Low Speed Axial Flow Compressor Operating at Design and Near Stall Conditions
Authors: Pallot Guillaume , Kato Dai , Kanameda Wataru , Ohta Yutaka
Published: September 2016

Unsteady flow phenomena can significantly influence the performance of turbomachines. The convection of the wake coming from a rotor into a downstream stator is one of these phenomena. In the case of compressors, when the rotor wake is transported through a downstream stator, it undergoes viscous mixing and stretching (Smith 1966), which are two mechanisms responsible for its attenuation. The flow field of a low speed single-stage compressor comprising a rotor and a downstream stator is computed using unsteady CFD simulations at design and near stall conditions. Simulations results are compared to steady and unsteady data obtained from yawmeter and hotwire measurements at both rotor and stator exit. The study focuses on the rotor wake attenuation and the related unsteady total pressure loss generated in the stator passage. The loss due to viscous mixing of the rotor wake is calculated analytically using a wake dissipation model. Based on experimental, numerical and analytical results, a break-down of the unsteady total pressure losses is performed for the two operating conditions. Unsteady total pressure losses are classified into two categories. The first category is the loss generated by viscous mixing of the rotor wake and the second one the loss generated by the interactions between the rotor wake and the stator pressure and suction surfaces boundary layers (interaction loss). Results show that the interactions between the rotor wake and the stator surfaces boundary layers play an important part in the unsteady loss generation process and that the contribution of this interaction loss increases from design to near stall condition.
Investigation of Single Jet Combustor Using Flamelet Generated Manifold Combustion Model and Detailed Chemistry
Authors: Patil Sunil , Cooper Judy , Orsino Stefano , Meadows Joseph , Valdes Richard , Laster Walter R.
Published: September 2016

Numerical simulation results of a single jet premixed combustion system at atmospheric pressure are compared against comprehensive particle image velocimetry (PIV) flow measurements and Raman scattering temperature measurements for natural gas and hydrogen fuels. The simulations were performed on hexahedral meshes with 1–5 million elements. RANS calculations were carried with the k-ε realizable turbulence model. Combustion was modeled using the Flamelet Generated Manifold model (FGM) and detailed chemistry. Both the flame position and flame liftoff predicted by the FGM were in reasonable agreement with experiments for both fuels and showed little sensitivity to heat transfer or radiation modeling. The detailed chemistry calculation predicts the temperature gradients along the jet centerline accurately and compares very closely with the Raman scattering measurements. The much closer agreement of the jet axial velocity and temperature profiles with experimental values, coupled with the significantly protracted presence of intermediates in the detailed chemistry predictions, indicates that the impact of nonequilibrium intermediates on very lean natural gas flames is significant.
Foreign Object Damage in an Oxide/Oxide Ceramic Matrix Composite (CMC) Under Prescribed Tensile Loading
Authors: Kedir Nesredin , Faucett David , Sanchez Luis , Choi Sung R.
Published: September 2016

Foreign object damage (FOD) behavior of an N720/alumina oxide/oxide ceramic matrix composite (CMC) was characterized at ambient temperature by using spherical projectiles impacted at velocities ranging from 100 to 350 m/s. The CMC targets were subject to ballistic impact at a normal incidence angle while being loaded under different levels of tensile loading in order to simulate conditions of rotating aeroengine airfoils. The impact damage of frontal and back surfaces was assessed with respect to impact velocity and load factor. Subsequent post-impact residual strength was also estimated to determine quantitatively the severity of impact damage. Impact force was predicted based on the principles of energy conservation.