bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical and Experimental Investigation for Internal Cooling of Two Pass Gas Turbine Blades Channels Using Broken V Ribs
Authors: Kumar Sourabh , Amano R. S.
Published: September 2014

Improvements in the thermal efficiency of a gas turbine can be obtained by operating it at high inlet temperatures. This high inlet temperature develops high thermal stresses on the turbine blades in addition to improving the performance. Cooling methodologies are implemented inside the blades to withstand those high temperatures. Four different combinations of broken 60° V ribs in cooling channel are considered. The research work investigates and compares numerically and experimentally, internal cooling of channels with broken V ribs. Local heat transfer in a square duct roughened with 60° V broken ribs is investigated for three different Reynolds numbers. Aspect ratio of the channel is taken to be 1:1. The pitch of the rib is considered to be 10 times the width of the rib, which is 0.0635 m. The square cross section of the channel is 0.508 × 0.508 m2 with 0.6096 m length. This study provides information about the best configuration of a broken V rib in a cooling channel.
Quick Method for Aeroelastic and Finite Element Modeling of Wind Turbine Blades
Authors: Bennett Jeffrey , Bitsche Robert , Branner Kim , Kim Taeseong
Published: September 2014

In this paper a quick method for modeling composite wind turbine blades is developed for aeroelastic simulations and finite element analyses. The method reduces the time to model a wind turbine blade by automating the creation of a shell finite element model and running it through a cross-sectional analysis tool in order to obtain cross-sectional properties for the aeroelastic simulations. The method utilizes detailed user inputs of the structural layup and aerodynamic profile including ply thickness, orientation, material properties and airfoils to create the models. After the process is complete the user has two models of the same blade, one for performing a structural finite element model analysis and one for aeroelastic simulations. Here, the method is implemented and applied to reverse engineer a structural layup for the NREL 5MW reference blade. The model is verified by comparing natural frequencies to the reference blade. Further, the application to aeroelastic and structural evaluations is demonstrated. Aeroelastic analyses are performed, and predicted fatigue loads are presented. Extreme loads from the aeroelastic simulations are extracted and applied onto the blade for a structural evaluation of the blade strength. Results show that the structural properties and natural frequencies of the developed 5MW blade match well with the reference blade, however the structural analysis found excessive strain at 16% span in the spare caps that would cause the blade to fail.
Second Law Analysis of Integrated Solar Combined Cycle Power Plants
Authors: Gülen S. Can
Published: September 2014

Integrated Solar Combined Cycle (ISCC) is an operationally simple, clean electric power generation system that is economically more attractive vis-à-vis stand-alone Concentrating Solar Power (CSP) technology. The ISCC can be designed to achieve two primary goals: (1) replace natural gas combustion with solar thermal power at the same output rating to reduce fuel consumption and stack emissions and/or (2) replace supplementary (duct) firing in the Heat Recovery Steam Generator (HRSG) with “solar firing” to boost power generation on hot days.

Optimal ISCC design requires a seamless integration of the solar-thermal and fossil-thermal technologies to maximize the solar contribution to the overall system performance at the lowest possible size and cost. The current paper uses the exergy concept of the second law of thermodynamics to distill the quite complex optimization problem to its bare essentials. The goal is to provide the practitioners with physics-based, user-friendly guidelines to understand the key drivers and the interaction among them. Ultimately, such understanding is expected to help direct studies involving heavy use of time consuming system models in a focused manner and evaluate the results critically to arrive at feasible ISCC designs.
The Application of Flamelet-Generated Manifold in the Modeling of Stratified Premixed Cooled Flames
Authors: Donini Andrea , Bastiaans Robert J. M. , van Oijen Jeroen A. , de Goey L. Philip H.
Published: September 2014

CFD predictions of flame position, stability and emissions are essential in order to obtain optimized combustor designs in a cost efficient way. However, the numerical modeling of practical combustion systems is a very challenging task. As a matter of fact, the use of detailed reaction mechanisms is necessary for such reliable predictions. Unfortunately, the modeling of the full detail of practical combustion equipment is currently prohibited by the limitations in computing power, given the large number of species and reactions involved. The Flamelet-Generated Manifold (FGM) method reduces these computational costs by several orders of magnitude without loosing too much accuracy. Hereby FGM enables the application of reliable chemistry mechanisms in CFD simulations of combustion processes. In the present paper a computational analysis of partially premixed non-adiabatic flames is presented. In this scope, chemistry is reduced by the use of the FGM method. In the FGM technique the progress of the flame is generally described by a few control variables. For each control variable a transport equation is solved during run-time. The flamelet system is computed in a pre-processing stage, and a manifold with all the information about combustion is stored in a tabulated form.

This research applies the FGM chemistry reduction method to describe partially premixed flames in combination with heat loss, which is a relevant condition for stationary gas turbine combustors. In order to take this into account, in the present implementation the reaction evolution is described by the reaction progress variable, the heat loss is described by the enthalpy and the local equivalence ratio effect on the reaction is represented by the mixture fraction. A series of test simulations is performed for a two dimensional geometry, characterized by a distinctive stratified methane/air inlet, and compared with detailed chemistry simulations. The results indicate that detailed simulations are reproduced in an excellent way with FGM.
The Effects of Rotation and Mass Flow on Local Heat Transfer in Rotating Cavities With Axial Throughflow
Authors: Günther André , Uffrecht Wieland , Odenbach Stefan
Published: September 2014

This paper discusses experimental results from a two cavity test rig representative of the internal air system of a high pressure compressor. Thermal steady state measurements of the time-averaged, local heat fluxes based on surface temperatures on both sides of the mid disc are presented for the case of axial throughflow of cooling air. Additionally, measurements of the air temperature and the static pressure inside the cavities are given. Tests were carried out for a wide range of rotational Reynolds numbers up to 107 and axial Reynolds numbers up to 2×105 with a uniformly heated shroud. The method of heat flux determination and the approach to calculating the uncertainties are described and discussed. The local heat flux results from different rotational frequencies, and mass flows are compared and interpreted in terms of assumed flow structures. Using the results of air temperature and static pressure measurements, simple theoretical models of the density gradient and the mixing mass flow which radially enters the cavity, deliver deeper insight into the flow structure and its influence on the heat transfer.

The results show that the heat flux increases with increasing mass flow. The influence of rotation on the heat flux is weaker and more complex than the effect of mass flow. The flow can be separated into four parts, the existence and strength of which depend on the test conditions: rotating cavity flow, impinged flow and resultant secondary flow, instabilities due to a negative radial density gradient respective to the buoyancy-induced flow, and instabilities of the incoming jet. For the geometry with a small inlet gap tested here, the flow and heat transfer are dominated by the throughflow or rather by the secondary flow for Rossby numbers Roz > 1.5. The buoyancy-induced flow is negligible. For Rossby numbers Roz < 1.5, the rotation dominates the flow structure. Buoyancy-induced flow can increase radial mixing between the throughflow and the cavity flow as well as the heat transfer to and from the disc. However, at high rotational frequencies, the density gradient becomes positive due to the increase in pressure induced by the centrifugal force which reduces mixing and heat transfer to/from the disc. Therefore, the highest heat transfer at the disc is measured at medium rotational frequencies.
Time-Resolved Pressure Measurements at a Dual-Cavity Test Rig for Research on the Internal Air System of an Industrial Gas Turbine
Authors: Günther André , Uffrecht Wieland , Caspary Volker
Published: September 2014

This paper reports about time-resolved examination of the pressure in a dual-cavity test rig for research on the cooling air supply of industrial gas turbines. The test rig has stationary and telemetric instrumentation. Both systems are capable of time-resolved pressure measurement. The design of the test rig is based on a simplified geometry of the internal cavities of the high pressure turbine with receiver holes and simulates the restriction imposed by internal blade cooling flow circuits. The test rig consists of a rotor-stator cavity and a rotor-rotor cavity. The Stage One and Stage Two supplies are separated inside the rotor-stator cavity. The air enters axially without pre-swirl at the outer radius of the stator and leaves the rotor-stator cavity through three rotating, axially directed connecting holes at a radius that varies among the investigated cases. Therefore, different flow paths in the cavities are studied. The research is focused on the branched cooling air supply system, but the flow path can also be analyzed separately. The rim seal flow is not examined in the research work presented here.

Pressure fluctuations in the main gas path caused, for instance, by blade passing and combustor noise, are a well-known phenomenon and therefore the subject of current research, whereas experimental examinations of the pressure fluctuations in the internal air system of gas turbines are very rare. A detailed examination of the pressure in the internal air system is significant in light of the pressure difference between the main gas path and internal air system, which is the driving force for hot gas ingestion. In that sense, the difference between the average pressure on the main gas side to the average pressure in the internal air system is not enough to avoid hot gas ingestion.

Therefore, this paper focuses on pressure fluctuations in the internal cavities. The measurements of the pressure fluctuations in the rotor-stator cavity are presented for different operating conditions. The influence of the rotational speed, the mass flow rate, the flow path and the sensor position in the cavity on the time-resolved pressure is examined. Furthermore, time-resolved pressure measurements from the rotor-rotor cavity are presented. Variations of the axial gap size and the radial location of the connecting holes respective to the outlets of the rotor-stator cavity are described.
Film Cooling With Forward and Backward Injection for Cylindrical and Fan-Shaped Holes Using PSP Measurement Technique
Authors: Chen Andrew F. , Li Shiou-Jiuan , Han Je-Chin
Published: September 2014

A systematic study was performed to investigate the combined effects of hole geometry, blowing ratio, density ratio and free-stream turbulence intensity on flat plate film cooling with forward and backward injection. Detailed film cooling effectiveness distributions were obtained using the steady state pressure sensitive paint (PSP) technique. Four common film-hole geometries with forward injection were used in this study: simple angled cylindrical holes and fan-shaped holes, and compound angled (β = 45°) cylindrical holes and fan-shaped holes. Additional four film-hole geometries with backward injection were tested by reversing the injection direction from forward to backward to the mainstream. There are seven holes in a row on each plate and each hole is 4 mm in diameter. The hole length to diameter ratio is 7.5. The blowing ratio effect was studied at 10 different blowing ratios ranging from M = 0.3 to M = 2.0. The coolant to main stream density ratio (DR) effect was studied by using foreign gases with DR = 1 (N2), 1.5 (CO2), and 2 (15% SF6 + 85% Ar). The free stream turbulence intensity effect was tested at 0.5% and 6%. The results show higher density coolant provides higher effectiveness than lower density coolant, fan-shaped holes perform better than cylindrical holes, and compound angled holes are better than simple angled holes. In general, the results show the film cooling effectiveness with backward injection is greatly reduced for shaped holes as compared with the forward injection. However, significant improvements can be seen in both simple angled and compound angled cylindrical holes at higher blowing ratios and density ratio (DR = 2). Comparison was made between experimental data and empirical correlations for simple angled fan-shaped holes at engine representative density ratios. An improved correlation which covers a wider range of density ratios (DR = 1.0 to DR = 2.0) is proposed.
Small-Scale Wind Turbines Optimized for Class 2 Wind: A Wind Siting Survey and Annual Energy Production Analysis
Authors: Burdett Timothy A. , Van Treuren Kenneth W.
Published: September 2014

A crucial step in evaluating a potential location for a wind turbine, especially small-scale wind turbines, is a proper wind site survey. Eventually the wind site survey is used to calculate the annual energy production (AEP) of the wind turbine and determine if this location will be profitable. Generally, a wind classification of 3 or above is recommended for any wind turbine site, according to the U.S. Department of Energy. Wind Classes of 1–2 are not considered suitable; however, data suggests that a wind site with Class of 2 wind has the potential to be more cost effective than even the least expensive offshore wind and deserves consideration. Wind data usually exists at locations such as local airports; however, the height at which this data are taken is not representative of the heights at which wind turbines will be installed and thus, airport wind data should not be used. Also, with the variability in wind from location to location, the airport data are generally not near the potential site for the wind turbine and thus, are not useful. A local wind site survey generally entails a two year study of the site using a meteorological (MET) tower. Waco, TX is being studied for the application of small-scale wind turbines. Waco is in a Class 2 wind area; however, no proper wind survey had ever been accomplished. Such a study was undertaken using a MET tower of 100 ft with two anemometers at 100 ft, one anemometer at 75 ft and one anemometer at 50 ft. This paper will describe the potential of Class 2 wind as an energy source, the erection of the MET tower, collection of the data and analysis of the data for the potential of locating a small-scale wind turbine at the site. Techniques for analyzing data when two anemometers are present will be discussed. Focus will be on identifying invalid data with an emphasis on correcting this invalid data. The data from two anemometers was then used in a novel way to identify and correct the invalid data found at both the 75 ft and 50 ft elevations. A filtering technique has also been developed to help identify invalid data. Based on the results of the wind survey, it will be shown that it is feasible to purposely design wind turbine blades for Class 2 wind which will perform better than commercially available small-scale wind turbines.
Low Thermal Conductivity YSZ Thermal Barrier Coatings Made by the Solution Precursor Plasma Spray Process
Authors: Jordan E. H. , Jiang C. , Gell M. , Roth J.
Published: September 2014

The vast majority of thermal barrier coatings (TBCs) are made using 7 wt% yttria stabilized zirconia (7YSZ) due to its high thermal expansion coefficient, high fracture toughness, relatively low thermal conductivity and modest use of rare earth elements (Y). Lower thermal conductivity in TBCs is highly desirable because it would allow thinner coatings and/or improved thermal protection. By arranging the porosity in layers using the solution precursor plasma spray (SPPS) process it has been demonstrated that a 7YSZ coating with 15–23% porosity can be reproducibly fabricated having a thermal conductivity of about 0.6W/m·K, approximately half of the thermal conductivity of air plasma spray (APS) TBCs. Preliminary tests show that both cyclic furnace durability and erosion resistance are comparable to APS TBCs.
Material Property Determination of Vibration Fatigued DMLS and Cold-Rolled Nickel Alloys
Authors: Scott-Emuakpor Onome , George Tommy , Beck Joseph , Schwartz Jeremy , Holycross Casey , Shen M. H. Herman , Slater Joseph
Published: September 2014

An experimental procedure for qualifying material properties from cyclically worked parts was investigated in support of aging gas turbine engines and digital twin initiatives. For aging components, remanufacturing or repair efforts are necessary to sustain the life cycles of engines; and for digital twin, the virtual representation of a part requires accurate geometric and component material property measurement. Therefore, having an effective, non-destructive way to assess the material performance of parts is necessary. Since low cycle, low strain, mechanical testing is the ideal experimental approach for non-destructively assessing material properties, investigating the accuracy and trends of tensile properties of fatigue loaded parts was important. The fatigued parts used for this study were specimens tested according to the George Fatigue Method, and the materials observed were cold-rolled Inconel Alloys 625 and 718, and direct metal laser sintering (DMLS) Nickel Alloy 718. The tensile material properties were compared against pristine (non-fatigued) and published data. The comparison for the cold-rolled 625 and 718 results show an increase and a decrease, depending on rolling direction, of tensile strength due to the effects of fatigue cycles; however, the variation of the vibration affected tensile properties are all within one standard deviation of the pristine data. The comparisons of DMLS Nickel Alloys was conducted against two sets of alloys from different suppliers, and the results showed that the tensile properties are sensitive to DMLS manufacturing parameters and post-sintering processes. A digital twin related, nondestructive, material property determination technique is also discussed in this manuscript. The true alloy density was determined with the water displacement method, and elastic modulus is determined with an iterative Ritz method model. The modulus is under-predicted with this method, but suggestions for improving the model are discussed.
Simulation of Soot Volume Fraction and Size in High-Pressure Lifted Flames Using Detailed Reaction Mechanisms
Authors: Naik Chitralkumar V. , Puduppakkam Karthik V. , Meeks Ellen
Published: September 2014

A simulation study of high-pressure lifted flames in a constant-volume chamber has been conducted using detailed reaction mechanisms in CFD to investigate ignition times, flame lift-off lengths, soot production, and fuel effects. The fuels considered include n-heptane, a two-component surrogate fuel (SR), conventional U.S. No. 2 diesel (D2), and world-averaged jet fuel (Jet-A). Conditions for the flames are those of the experiments performed at Sandia National Laboratories; the n-heptane flame is labeled Spray H [Idicheria and Pickett, SAE 2005-01-3834], and the conditions for all other fuels studied are labeled Spray A [Kook and Pickett, SAE 2012-01-0678]. 3D CFD simulations have been performed using the FORTÉ CFD package. Complex fuels D2 and Jet-A have been modeled using multi-component surrogates. Detailed reaction mechanisms for fuel combustion and emissions formation have been used in the simulations. The size of the fuel mechanisms varied from 326 species to 1000 species for the different fuels. For soot predictions, two different models were used in the simulations: a detailed soot-surface mechanism and a seven-step phenomenological soot model. Both soot models were coupled with the fuel mechanism precursor predictions that included aromatics from benzene to pyrene. While using the detailed soot-surface mechanism, particulate (PM) size and number density were determined using the Method of Moments, which is implemented in the CFD software to calculate particle size distribution characteristics.

Results show excellent prediction of flame location and ignition for all fuels. Location and magnitude of soot fractions in the various flames show good agreement with the published data. Both the phenomenological soot model and the detailed soot-surface mechanism estimated comparable soot fractions in all flames. In addition, PM size information was predicted using the detailed soot-surface mechanism. Impacts of fuel, temperature, pressure, and oxygen concentrations on combustion and soot fractions have been captured by the simulations.
A Hybrid Semi-Empirical Model for Lean Blow-Out Limit Predictions of Aero-Engine Combustors
Authors: Hu Bin , Huang Yong , Xu Jianzhong
Published: September 2014

Lean blow-out (LBO) is critical to operational performance of combustion systems in propulsion and power generation. Current predictive tools for LBO are based on decades-old empirical correlations that have limited applicability for modern combustor designs. Based on Lefebvre’s model for LBO and flame volume concept, an FV (Flame Volume) model was proposed by Authors in early study. The FV model adds two key parameters of α and β that represent the fraction of dome air and dimensionless flame volume defined as the ratio of flame volume and combustor volume. Due to the flame volume is obtained from the experimental image, FV model could only be used in LBO analysis instead of predictions. In the present study, a hybrid FV model is proposed that combines the FV model with numerical simulation for LBO predictions. In the hybrid FV model, α and β are estimated from the numerical simulation result of the non-reacting flow in the combustor. Comparing with the experimental data for 11 combustors, the LBO fuel/air ratio obtained by hybrid FV model shows better agreement than that obtained by Lefebvre’s model. The maximum prediction uncertainties of hybrid FV model and Lefebvre’s model are about ±16% and ±48%, respectively. Moreover, the time cost of the LBO prediction using hybrid FV model for each case is about 6 hours with the computer equipment of CPU×12 and 24G memory, showing that the hybrid FV model is reliable and efficient to be used for the performance evaluation of the combustor, even the so called “paper combustors” in the primary design stage.
Three-Dimensional Velocity Measurements Around and Downstream of a Rotating Vertical Axis Wind Turbine
Authors: Ryan Kevin J. , Coletti Filippo , Dabiri John O. , Eaton John K.
Published: September 2014

Modern designs for straight-bladed vertical axis wind turbines (VAWTs) feature smaller individual footprints than conventional horizontal axis wind turbines (HAWTs), allowing closer spacing of turbines and potentially greater power extraction for the same wind farm footprint. However, the wakes of up-stream turbines could persist far enough to affect the performance of closely-spaced downstream turbines. In order to optimize the inter-turbine spacing and to investigate the potential for constructive aerodynamic interactions, the complex dynamics of VAWT wakes should be understood. The full three-component mean velocity field around and downstream of a scaled model of a rotating VAWT has been measured by Magnetic Resonance Velocimetry (MRV). The model turbine has an aspect ratio (height/diameter) of 1, and was operated in a water facility at subscale but still turbulent Reynolds number of 11,600 based on the turbine diameter. The main flow features including recirculation bubble sizes and strong vortex structures are believed to be representative of flow at full scale Reynolds number. To have kinematic similarity with a power-producing turbine, the model turbine was externally driven. Measurements were taken with the turbine stationary and while driven at tip speed ratios (TSRs) of 1.25 and 2.5, realistic values for VAWTs in operation. The MRV measurement produced three-dimensional velocity data with a resolution of 1/50 of the turbine diameter in all three directions. The flow is shown to be highly three dimensional and asymmetric for the entirety of the investigated region (up to 7 diameters downstream of the turbine). The higher TSR produced greater velocity defect and asymmetry in the near wake behind the turbine, but also showed faster wake recovery than the slower TSR and stationary cases. Wake recovery is affected by a counter-rotating vortex pair generated at the upwind-turning side of the turbine, which mixes faster fluid from the freestream in with the wake. The strength of vortices is shown to increase with TSR.
Operational Modal Analysis of Lateral Rotordynamic Modes of Rotating Machinery
Authors: Carden Eoin Peter , Morosi Stefano
Published: September 2014

The lateral rotordynamic response of turbomachinery is typically speed dependent due to hydrodynamic lubricated bearings, seals, gyroscopic and centrifugal effects, etc. Rotordynamic tools are used to predict the behavior of the machine during operation, however validating these results is challenging. Traditional experimental modal testing techniques rely on controlled and measured excitation together with measured responses. However, during operation this is unpractical, as the actual excitation force is rarely known.

Operational modal analysis (OMA) can identify the modal parameters of a system over its entire operational range from measurement of response due to some (unknown) excitation. OMA has proven successful on non-rotating structures, but has seldom been applied to rotating machinery.

Three case studies are presented demonstrating the use of OMA in identifying lateral rotors modes based on measurements from existing radial proximity probes during normal production undertaken as part of commissioning campaigns.

Challenges encountered in using and interpreting OMA results are discussed. The results show that proximity probe data acquired during normal operation may be used as input to OMA for the assessment of stability margins of rotating machinery, to produce experimentally derived Campbell diagrams and to identify backwards as well as forwards whirling modes.
Finite Element Approximation of Wave Propagation in Composite Material With Asymptotic Homogenization
Authors: Ebna Hai Bhuiyan Shameem Mahmood , Bause Markus
Published: September 2014

Advanced composite materials such as carbon fiber reinforced plastics are being applied to many aerospace or automotive structures in order to improve material performances and save weight. Most composites have strong, stiff fibres in a matrix which is weaker and less stiff. But these structures can be damaged due to fluid-structure interaction (FSI) oscillations or material fatigue. To design integrated structural health monitoring (SHM) systems in a lightweight structure, it is important to understand wave propagation phenomena in composite material, and the influence of the material properties of the structures. In non-destructive test (NDT), piezoelectric induced ultrasonic waves can be used for damage detection. In this work, we focus on mathematical modeling and numerical approximation of the propagation of time-harmonic elastic waves in a fiber-reinforced composite material. The fibers are assumed to be parallel to each other and statistically uniformly distributed. In this work we study higher order continuous finite element approximation of the elastic wave equation and the implementation is carried out by means of the FEM library deal.II. (Differential Equations Analysis Library)
Quick Aeromechanical Assessment of Turbine Blades Based on Shell Element Based Models
Authors: Chakrabarti Suryarghya , Wang Letian , Khan K. M. K. Genghis
Published: September 2014

A fast finite element model based tool has been developed to calculate the natural frequencies of fundamental modes of cooled gas turbine bladed disk assemblies during conceptual design. The tool uses shell elements to model the airfoil, shank, and disk, and achieves order of magnitude reduction in computation time allowing exploration of a wide design space at the preliminary design stages. The analysis includes prestress effects due to centrifugal loading and approximate temperature loading on the parts. Sensitivity studies are performed to understand the relative impact of design features such as airfoil internal geometry, bond coat, and thermal barrier coating on the system natural frequencies. Critical features are selected which need to be modeled to get an accurate natural frequency estimate. The results obtained are shown to be within 5% of the frequencies obtained from a full-fidelity finite element model. A case study performed on seven blade designs illustrates the use of this tool for quick aeromechanical assessment of a large number of designs.
Control Strategy for a Direct-Fired Fuel Cell Turbine Hybrid Power System
Authors: Pezzini Paolo , Tucker David , Traverso Alberto
Published: September 2014

A hardware-in-the-loop-simulation (HiLS) procedure for a direct-fired fuel cell turbine hybrid power system was evaluated for an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC), implemented through the Hybrid Performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behaviour. It is possible to model, test and evaluate the effects of different parameters on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and quantify risk mitigation strategies.

The previous implementation of emergency shut-down control strategies resulted in turbomachinery hardware failure. The primary linking event in these cases was compressor stall and surge resulting from the sudden loss of fuel during implementation of the standard double block and bleed strategy used during emergency failure. A new mitigation strategy involving automated ramps is proposed and described in detail to control the system from start-up to forced emergency shut-down. The control architecture shows how the virtual fuel cell model can be coupled to the real gas turbine safely, in all of stage of operations. The paper includes improvements to the emergency shutdown procedure, failure analyses, and the comparison of experimental data with previous results.
Three-Dimensional Structural Evaluation of a Gas Turbine Engine Rotor
Authors: Das Partha S.
Published: September 2014

Engine rotors are one of the most critical components of a heavy duty industrial gas turbine engine, as it transfers mechanical energy from rotor blades to a generator for the production of electrical energy. In general, these are larger bolted rotors with complex geometries, which make analytical modeling of the rotor to determine its static, transient or dynamic behaviors difficult. For this purpose, powerful numerical analysis approaches, such as, the finite element method, in conjunction with high performance computers are being used to analyze the current rotor systems.

The complexity in modeling bolted rotor behavior under various loadings, such as, airfoil, centrifugal and gravity loadings, including engine induced vibration is one of the main challenges of simulating the structural performance of an engine rotor. In addition, the internal structural temperature gradients that can be encountered in the transient state as a result of start-up and shutdown procedures are generally higher than those that occur in the steady-state and hence thermal shock is important factor to be considered relative to ordinary thermal stress. To address these issues, the current paper presents the steady-state & quasi-static analyses (to approximate transient responses) of two full 3-D industrial gas turbine engine rotors, SW501F & GE-7FA rotor, comprising of both compressor & turbine sections together. Full 3-D rotor analysis was carried out, since the 2-D axisymmetric model is inadequate to capture the complex geometries & out of plane behavior of the rotor. Both non-linear steady-state & transient analyses of a full gas turbine engine rotor was performed using the general purpose finite element analysis program ABAQUS.

The paper presents in detail the FEA modeling technique, overall behavior of the full rotor under various loadings, as well as, the critical locations in the rotor with respect to its strength and life. The identification of these critical locations is needed to help with the repair of the existing rotors and to improve and extend the operational/service life of these rotors.
Investigation of Flame Stabilization in a High-Pressure Multi-Jet Combustor by Laser Measurement Techniques
Authors: Lammel Oliver , Rödiger Tim , Stöhr Michael , Ax Holger , Kutne Peter , Severin Michael , Griebel Peter , Aigner Manfred
Published: September 2014

In this contribution, comprehensive optical and laser based measurements in a generic multi-jet combustor at gas turbine relevant conditions are presented. The flame position and shape, flow field, temperatures and species concentrations of turbulent premixed natural gas and hydrogen flames were investigated in a high-pressure test rig with optical access.

The needs of modern highly efficient gas turbine combustion systems, i.e., fuel flexibility, load flexibility with increased part load capability, and high turbine inlet temperatures, have to be addressed by novel or improved burner concepts. One promising design is the enhanced FLOX® burner, which can achieve low pollutant emissions in a very wide range of operating conditions. In principle, this kind of gas turbine combustor consists of several nozzles without swirl, which discharge axial high momentum jets through orifices arranged on a circle. The geometry provides a pronounced inner recirculation zone in the combustion chamber. Flame stabilization takes place in a shear layer around the jet flow, where fresh gas is mixed with hot exhaust gas. Flashback resistance is obtained through the absence of low velocity zones, which favors this concept for multi-fuel applications, e.g. fuels with medium to high hydrogen content.

The understanding of flame stabilization mechanisms of jet flames for different fuels is the key to identify and control the main parameters in the design process of combustors based on an enhanced FLOX® burner concept. Both experimental analysis and numerical simulations can contribute and complement each other in this task. They need a detailed and relevant data base, with well-known boundary conditions. For this purpose, a high-pressure burner assembly was designed with a generic 3-nozzle combustor in a rectangular combustion chamber with optical access. The nozzles are linearly arranged in z direction to allow for jet-jet interaction of the middle jet. This line is off-centered in y direction to develop a distinct recirculation zone. This arrangement approximates a sector of a full FLOX® gas turbine burner. The experiments were conducted at a pressure of 8 bar with preheated and premixed natural gas/air and hydrogen/air flows and jet velocities of 120 m/s.

For the visualization of the flame, OH* chemiluminescence imaging was performed. 1D laser Raman scattering was applied and evaluated on an average and single shot basis in order to simultaneously and quantitatively determine the major species concentrations, the mixture fraction and the temperature. Flow velocities were measured using particle image velocimetry at different section planes through the combustion chamber.
CFD Simulation of an Aeroengine Bearing Chamber Using an Enhanced Volume of Fluid (VOF) Method: An Evaluation Using Adaptive Meshing
Authors: Crouchez-Pillot Alexandre , Morvan Hervé P.
Published: September 2014

In aero engines, the rotating shafts are supported by a set of bearings, which are enclosed in bearing chambers. Cooling and lubrication oil escapes from the bearings and these chambers are designed to capture and recycle it. A good understanding of the oil behaviour inside bearing chambers is therefore desirable in order to limit the oil volume involved and minimize transmission losses whilst managing the engine core heat in the best possible manner.

This study is focused on the simulation of the oil behaviour inside such a chamber and special attention is given to the so-called KIT bearing chamber. The oil phase in the chamber can take different forms e.g. sprays, droplets, thin films or a combination of those. Assuming the oil we want to track remains dominantly as a film and large droplets/filaments, the Volume of Fluid (VOF) method is used in order to track the oil and the oil/air interface in the chamber, hereby investigating the feasibility and merits of such an approach and extending the earlier work carried out by the authors and colleagues. An Enhanced VOF approach coupled with level-set is used here unless stated otherwise. The simulated pump outlet condition, proposed by the University of Nottingham, is also employed in this study, to replicate an engine displacement pump.

Since the use of VOF requires a refined mesh in the oil region, an adaptive mesh approach based on the volume of fluid gradient is developed and validated to control the total cell count for some of the cases reported here and limit simulation costs. The Adaptive Mesh Approach (AMA) can allow a better resolution of critical interfaces, better compute the oil break-up (within the limitation of the physical models used) and then track the droplets and filaments. Therefore, not only the CPU time cost might be reduced compared to a fixed mesh approach but significant physical aspects of the problem should be better accounted for. In order to inform the set up and parameters used with this method, and appraise its value for the proposed application, the experimental study of Fabre is used before the approach is applied to the KIT chamber.

Good insight is obtained in terms of run time acceleration for such problem when combining the proposed VOF setup with adaptive meshing. Key set up parameters are quantified. The simulations carried out with the proposed set up are proving to be fairly robust and stable. Qualitative (physical) evidence is also encouraging and confirms the value of such an approach to the study of aeroengine bearing chambers.
Wireless Telemetric Data Acquisition and Real-Time Control for a High Measurement-Density Internal Heat Transfer Experiment
Authors: Habib Alexander J. , Barton Jeffery L. , Mathison Randall M. , Dunn Michael G.
Published: September 2014

This paper describes a wireless data transmission system for a large-scale rotating experiment to investigate the heat transfer in a three-passage serpentine test section. Patterned after the NASA HOST program, the current experiment extends the data set to larger aspect ratios including 1:2, 1:4 and 1:6. As with HOST, heat transfer is measured using the heated conducting segments technique, and the serpentine test section spins at rotation numbers representative of engine conditions. Rotating experiments are essential for capturing the representative operating conditions and complicated flow physics that must be understood to advance internal cooling technology for these high aspect ratio configurations.

There are challenges associated with controlling the operating parameters and collecting accurate data for high measurement-density rotating experiments. This experiment requires that 140 copper panels be held at a constant temperature by independently controlling and recording the power supplied to a separate heater on each panel. This means there must be 140 temperature measurements, 140 pairs of heater power leads, enough power to drive all of these heaters, and data recording capacity left over to measure fluid temperatures and pressures. Traditional methods of transferring rotating signals to the stationary frame of reference (such as slip rings) are widely implemented but have practical limitations in the quantity of transferrable signals and the electrical current capacity of the individual channels. Alternatively, wireless transmission techniques were first developed decades ago, but their practical use has been limited by onboard power delivery requirements and cost.

This paper describes the development of a new data transmission and control system that takes advantage of improvements in low-cost off-the-shelf electronics to create a battery powered and microprocessor controlled system for acquisition, storage, control, and wireless communication. These components are assembled to form an integral part of the rotating mechanical hardware. By handling high-fidelity microcircuit signal conditioning, data acquisition, feedback control, and data storage in the rotating frame and transmitting the results with two-way wireless communication, this system provides high measurement density and active feedback control that would have been impractical with a conventional slip-ring approach.

The design and construction of the wireless control system for one full sidewall of the three-serpentine passage is described in detail. Its capability and functionality is demonstrated with operational data. It will be demonstrated that while all of the components in this system are readily available, the unique combination of this technology opens up a new world of measurement capabilities.
ASME PTC-10 Performance Testing of Centrifugal Compressors — The Real Gas Calculation Method
Authors: Taher Matt
Published: September 2014

ASME PTC-10 (2009) provides a test procedure to determine the thermodynamic performance of centrifugal compressors for gases conforming to ideal gas laws and for real gases. It requires using real gas calculation methods where the compressibility values depart from the specified limits. ASME PTC-10 employs Schultz X and Y compressibility factors to calculate the polytropic exponent for real gas compression. Specific values of X and Y for the test gas at the test condition may be different from the values provided in ASME PTC-10 generalized charts. Therefore, special care should be taken to properly calculate X and Y factors for a test gas at specified conditions.

In this paper, Schultz compressibility factors X and Y are derived as functions of reduced properties. These functions can be used with any equation of state to precisely calculate X and Y values for any gas composition at the specified operating conditions. By using the proposed method, Schultz X and Y compressibility factors for propane are graphically represented covering a reduced pressure range of 0.1 to 3 and a reduced temperature range of 1.05 to 2. Also, the rate of change of polytropic exponents for propane over a wide range of pressures and temperatures is graphically demonstrated.
Prediction of the Aero-Acoustic Performance of Open Rotors
Authors: Van Zante Dale E. , Envia Edmane
Published: September 2014

The rising cost of jet fuel has renewed interest in contra-rotating open rotor propulsion systems. Contemporary design methods offer the potential to maintain the inherently high aerodynamic efficiency of open rotors while greatly reducing their noise output, something that was not feasible in the 1980’s designs. The primary source mechanisms of open rotor noise generation are thought to be the front rotor wake and tip vortex interacting with the aft rotor. In this paper, advanced measurement techniques and high-fidelity prediction tools are used to gain insight into the relative importance of the contributions to the open rotor noise signature of the front rotor wake and rotor tip vortex. The measurements include three-dimensional particle image velocimetry of the intra-rotor flowfield and the acoustic field of a model-scale open rotor. The predictions provide the unsteady flowfield and the associated acoustic field. The results suggest that while the front rotor tip vortex can have a significant influence on the blade passing tone noise produced by the aft rotor, the front rotor wake plays the decisive role in the generation of the interaction noise produced as a result of the unsteady aerodynamic interaction of the two rotors. At operating conditions typical of takeoff and landing operations, the interaction noise level is easily on par with that generated by the individual rotors, and in some cases is even higher. This suggests that a comprehensive approach to reducing open rotor noise should include techniques for mitigating the wake of the front rotor as well as eliminating the interaction of the front rotor tip vortex with the aft rotor blade tip.
Integrated “CFD - Acoustic” Computational Approach to the Simulation of Aircraft Fan Noise
Authors: Ferrante Piergiorgio , di Francescantonio Paolo , Hoffer Pierre-Alain , Vilmin Stéphane , Hirsch Charles
Published: September 2014

An innovative computational approach, integrating mesh generation, CFD simultaneous analysis of noise source and propagation, with acoustic radiation, is presented and applied to the simulation of the Advanced Noise Control Fan (ANCF) developed by NASA Glenn Research Center.

The tonal noise source and the sound propagation in the nacelle duct and in the nacelle near field are simultaneously predicted, starting from the engine geometry and parameters, with a single CFD analysis based on an efficient Nonlinear Harmonic (NLH) method. The sound radiation to the far field is computed with the Green’s function approach implemented in a BEM frequency domain solver of the convective Helmholtz equation.

The present method provides to a gain of close to two orders of magnitude compared to standard approaches, based on full unsteady flow simulations, followed by a near-field FEM based approach and a BEM method for the far-field noise propagation.

The final comparison between the numerical results and the measurements highlights the capability of the methodology to efficiently predict the unsteady flow field and the radiated sound field.
Numerical Study on Three-Dimensional Optimization of a Low-Speed Axial Compressor Rotor
Authors: Zhang Chenkai , Hu Jun , Wang Zhiqiang , Yin Chao , Yan Wei
Published: September 2014

This paper presents numerical optimization of a compressor rotor, to deepen the knowledge of endwall flow in the large-scale axial subsonic compressor, accordingly reduce its endwall loss and improve its aerodynamic performance. With numerical simulation and numerical optimization tools, three-dimensional stacking principle is optimized to improve the design operation point performance for the rotor. Results show that, hub region of the rotor cannot undertake large blade loading; compared to the prototype rotor, obvious aerodynamic performance improvements locate near the hub area, and a certain degree of positive dihedral in this region effectively helps to reduce its flow loss. The effect of “loaded leading edge and unloaded trailing edge” due to positive dihedral was shown, which suppresses flow separation near the trailing edge, consequently obviously reduces the flow loss and largely improves the rotor aerodynamic performance.