bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Mistuning Identification Method Based on the Subset of Nominal System Modes Method
Authors: Waldherr Christian U. , Buchwald Patrick , Vogt Damian M.
Published: November 2019

The mistuning problem of quasi periodic structures is subject of numerous scientific investigations for more than 50 years. Researchers developed reduced order models to reduce the computational costs of mistuning investigations including finite element models. One question which has also high practical relevance is the identification of mistuning based on modal properties. In the present work, a new identification method based on the Subset of Nominal System Modes method (SNM) is presented. The input data for the identification procedure consists solely of the mistuned natural frequencies of the investigated mode family as well as of the corresponding mistuned mode shapes in the form of one degree of freedom per sector. The reduction basis consists of the tuned mode shapes of the investigated mode family. Furthermore, the proposed identification method allows for the inclusion of centrifugal effects like stress stiffening and spin softening without additional computational effort. From this point of view the presented method is also appropriate to handle centrifugal effects in reduced order models using a minimum set of input data compared to existing methods. The powerfulness of the new identification method is demonstrated on the example of an axial compressor blisk. Finite element calculations including geometrical mistuning provide the data base for the identification procedure. The correct functioning of the identification method including measurement noise is also validated to show the applicability to a case of application where real measurement data is available.
Development and Analysis of an Integrated Mild-Partial Gasification Combined (IMPGC) Cycle: Part 2 — Comparison With Other Power Generation Systems
Authors: Long Henry A. , Wang Ting
Published: November 2019

The baseline Integrated Mild-Partial Gasification Combined (IMPGC) Cycle model developed in Part 1 is compared with other established power system designs, including the likes of subcritical and ultra-supercritical (USC) Rankine cycle systems, Natural Gas Combined Cycle (NGCC) systems, and Integrated Gasification Combined Cycle (IGCC) systems. A comprehensive comparison and analysis of the pros and cons, the thermodynamic performance, and environmental impact of each system are performed. The results show that, with a very conservative approach, IMPGC consistently outperforms all other forms of coal-based power, being outclassed only (expectedly) by NGCC. IMPGC is more efficient than the standard subcritical Rankine cycle by nine percentage points, more than a USC Rankine cycle by nearly four points, and more than IGCC by seven points.
Modeling Thermally Grown Oxides in Thermal Barrier Coatings Using Koch Fractal
Authors: Warren Peter , Haldar Sandip , Raghavan Seetha , Ghosh Ranajay
Published: November 2019

Growth of the Thermally Grown Oxide (TGO) between the bond coat and thermal barrier coating (TBC) during service is one of the most common causes of failure within thermal barrier coating (TBC) systems. Initially this oxide will provide protection from oxidation for the substrate, but stress build up will contribute to delamination of the topcoat. Research has been carried out over the stresses caused by this TGO growth, and how to best mitigate these induced stresses. The interface topography plays a critical role for air plasma sprayed (APS) TBCs in development of stress profiles across the TGO/TBC interface [1, 2]. The APS TBCs fail by cracking in the TBC close to the TGO-TBC interface. Most models treat TGO as a sinusoidal wavelength interface. However, most TGO surfaces have been experimentally observed to have fractal like patterns at the interfacial region of the bondcoat and topcoat. Fractals provide us a better understanding of interactions at rough interfaces between two materials adhered to one another. In this work, we model the topography of the TGO using a Koch fractal. We find the geometry selected to model the TGO layer has a direct effect on the stress generation and creep strain during simulation.
A Comparison of Tip Gap Loss Sensitivity for Shrouded vs. Unshrouded Turbine Rotors
Authors: Banks William V. , Ameri Ali A. , Boyle Robert J. , Bons Jeffrey P.
Published: November 2019

A numerical study was conducted to evaluate the loss sensitivity of shrouded vs. unshrouded turbine rotor blades. Accuracy is demonstrated with a series of grid independence studies. Application of the methods is performed through various studies related to the effects of shrouding a High-Pressure Turbine (HPT) rotor blade for a NASA-specified N+3 timeframe single-aisle aircraft engine at takeoff conditions. Flat, Recessed, and Shrouded rotor configurations are evaluated at tip clearances from 0.25% to 4% of blade span. Mach # distributions, near-tip blade loading, and other flow characteristics are examined. Plots of stage efficiency vs. tip clearance are presented, with trends compared to available experimental data. It is shown that for the imposed boundary conditions, the addition of a shroud improves stage efficiency and significantly reduces sensitivity to tip clearance at higher clearance fractions. A casing recess is also shown to slightly increase sensitivity to tip clearance for tip clearances greater than 0.5%. Total pressure loss profiles vs. blade span are also compared, providing insight into the mechanisms behind the performance of the three configurations.
Design, Optimization and Analysis of Supersonic Radial Turbines
Authors: Inhestern Lukas Benjamin , Braun James , Paniagua Guillermo , Serrano Cruz José Ramón
Published: November 2019

New compact engine architectures such as pressure gain combustion require ad-hoc turbomachinery to ensure an adequate range of operation with high performance. A critical factor for supersonic turbines is to ensure the starting of the flow passages, which limits the flow turning and airfoil thickness. Radial outflow turbines inherently increase the cross section along the flow path, which holds great potential for high turning of supersonic flow with a low stage number and guarantees a compact design. First the preliminary design space is described. Afterwards a differential evolution multi-objective optimization with 12 geometrical design parameters is deducted. With the design tool AutoBlade 10.1, 768 geometries were generated and hub, shroud, and blade camber line were designed by means of Bezier curves. Outlet radius, passage height, and axial location of the outlet were design variables as well. Structured meshes with around 3.7 million cells per passage were generated. Steady three dimensional Reynolds averaged Navier Stokes (RANS) simulations, enclosed by the k-omega SST turbulence model were solved by the commercial solver CFD++. The geometry was optimized towards low entropy and high power output. To prove the functionality of the new turbine concept and optimization, a full wheel unsteady RANS simulation of the optimized geometry exposed to a nozzled rotating detonation combustor (RDC) has been performed and the advantageous flow patterns of the optimization were also observed during transient operation.
Time-Accurate Evaluation of Film Cooling Jet Characteristics for Plenum and Crossflow Coolant Supplies
Authors: Sperling Spencer J. , Mathison Randall M.
Published: November 2019

Gas turbine film cooling creates complicated and highly unsteady flow structures. This study seeks to examine the unsteady characteristics created by different film hole inlet geometries using a fast-response pressure sensitive paint (PSP) technique able to capture time-accurate measurements at 2000 frames per second, resolving frequencies up to 1000 Hz. Time accurate and time-averaged measurements are used to evaluate the performance of a plenum-style inlet and a crossflow-style inlet in varying turbulence environments over a flat plate. The results of this study are intended to begin the process of breaking down widely accepted time-averaged film effectiveness contours into the cumulative effects of smaller oscillating cooling jets. Jet behaviors observed in this study include a sweeping oscillation, unsteady attachment and separation from the plate, and time accurate and time average flow bias.

The behavior and performance of higher blowing ratio, separated film cooling jets depend heavily on the momentum flux ratio. Crossflow fed cooling holes show bias to the upstream side of the cooling hole with respect to the internal crossflow direction. Plenum fed cooling holes outperform crossflow fed cooling holes, and the difference increases with increasing momentum flux ratio. Cooling hole inlet geometry and momentum flux ratio affect the core of the jet, and freestream turbulence affects the periphery of the jet. Fluctuating frequencies of plenum fed and crossflow fed cooling holes were seen to be influenced by the turbulent velocity fluctuation frequency. The resulting mode shapes showed dominant side-to-side fluctuations for higher turbulence environments and a separation and reattachment motion for lower turbulence environments.
Carbon Monoxide Emission Measurements From a Supercritical CO2 Combustor Rig Using a Mid-Infrared Laser Absorption Diagnostic
Authors: Anderson James P. , Camou Alejandro , Petersen Eric L. , Harris Mark , Cusano David M.
Published: November 2019

A rugged, mid-infrared (IR) CO laser absorption diagnostic has been developed to monitor the amount of CO produced by a high-pressure CH4-O2 combustor test rig operating at supercritical CO2 conditions (30 MPa and 1150°C). The laser system operates at the fundamental absorption band, ν″ = 0, R(12), of CO near 4.5 μm. The mid-IR diagnostic was constructed from a tunable quantum cascade laser (QCL), an absorption cell with two window ports for monitoring CO exhaust concentration, and two IR photodetectors. Temperature and pressure sensors were mounted near the absorption cell to monitor exhaust flow conditions, and the operational wavelength of the laser was determined by a calibration process using a known mixture of CO and N2. Environmental conditions at the remote outdoor test facility posed significant difficulties in the data acquisition process for the IR diagnostic. Fluctuating environmental temperatures proved to be problematic when operating cryogenic photodetectors and stabilizing a QCL designed to operate with an internal temperature of −15°C. Improvements to the IR system included elimination of problematic stagnation regions via a new absorption cell design and an increase in the CO detection limit. During steady state conditions, the mid-IR diagnostic measured the CO concentration to within ± 80.6 ppm. The IR diagnostic was shown to have superior CO detection response time and the ability to resolve features not detected by other CO detector counterparts.
Pre-Test Evaluation of Probe Configuration Errors
Authors: Gillespie John , Frohnapfel Dustin , O’Brien Walter
Published: November 2019

Rake probes are commonly used in turbomachinery applications to measure distorted inlet flows, including both pressure and swirl distortions. An especially common configuration is the 40 probe rake array, consisting of eight identical arms equally spaced circumferentially around the inlet, each arm having five sensing locations spaced along centers of equal area. By measuring many locations simultaneously, rake probes have the advantage of expedited data collection when compared to traversing probes. However, this reduction in test time comes at the cost of rigid geometry with limited measurement locations. As a result, it is possible for rake probes to miss or exaggerate significant areas of the flow profile, such as large gradients or small features, based on the fixed location of the probe and the particular details of the distortion. The purpose of this paper is to demonstrate a procedure that can be used to evaluate the ability of any desired probe configuration (40 probe rake or otherwise) to sufficiently and accurately measure a non-uniform flow profile. Results of this procedure for a range of profiles and probe configurations are also presented.

In order to accurately determine the impact of discrete sampling on the results, two broad sets of data were generated numerically and analyzed. The first set consists of four fundamental total pressure distortions: once-per-rev circumferential, twice-per-rev circumferential, hub radial, and tip radial. The second set consists of three realistic turbofan distortion patterns: two analytic (though not fundamental) profiles, and one generated from S-duct computational results.

For all investigated patterns, Radial Distortion Intensity and Circumferential Distortion Intensity are calculated in the manner described by ARP 1420, a guideline issued by the S-16 Turbine Engine Inlet Flow Distortion Committee for measuring total pressure distortions in turbomachinery. Additionally, interpolated total pressure contours are generated for each measurement configuration. These were then used to make point-to-point comparisons between the actual and estimated data. While total pressure distortion was used as the variable of interest for the majority of this paper, the conclusions may be applied to swirl, temperature, or any other flow property measured using a probe rake or traversing probe.
Multi Objective Optimization of Flexible Supercritical CO2 Coal-Fired Power Plants
Authors: Alfani Dario , Astolfi Marco , Binotti Marco , Campanari Stefano , Casella Francesco , Silva Paolo
Published: November 2019

Coal-fired power plants play a major role in large scale power generation by producing about 41% and 25% of the electricity in the world and in the EU, respectively. In the context of EU’s climate and energy policy (EU Reference Scenario 2016) and with a view to decarbonizing the electricity sector, the share of non-programmable renewable energies will soar in future years both in and outside the EU. As result, the role of fossil-fuel plants including coal-fired plants is expected to evolve, leading to a paradigm shift for their design and operation, which will move from constant base-load operation to increasingly variable power production for the integration of intermittent renewable energy sources. In the present work, developed within the EU project sCO2-Flex, the design and analysis of a coal-fired plant implementing a 100 MWel recompressed sCO2 power cycle is assessed, with particular focus on the trade-off between system performance and flexibility. The effects of the different design assumptions on the overall components’ sizing and system performance are investigated and a methodology to quantify the thermal inertia and the system flexibility based on the calculation of heat exchangers surfaces, volumes and masses (boiler tube walls and convective pass, recuperators and gas cooler heat rejection unit) is then presented. Finally, the cycle optimization is repeated with the aim to find the optimal trade-off between plant efficiency and thermal inertia, eventually providing a number of promising designs for next generation sCO2 fossil fuel power plants.
Design and Manufacturing of a Metal 3D Printed kW Scale Axial Turboexpander
Authors: Novotny Vaclav , Vitvarova Monika , Kolovratnik Michal , Stunova Barbora Bryksi , Vodicka Vaclav , Spale Jan , Zikmund Petr , Drasnar Martin , Schastlivtseva Elizaveta
Published: November 2019

Greater expansion of distributed power and process systems based on thermodynamic cycles with single to hundred kW scale power output is limited mainly there are not available cost-effective expanders.

Turboexpanders have a perspective of high efficiency and flexibility concerning operating parameters even for the micro applications. However, they suffer from a high manufacturing cost and lead time in the development of traditional technologies (such as casting and machining processes).

Additive manufacturing provides a possibility to overcome some of the issues. Manufacturing parts with complicated shapes by this technology, combining multiple components into a single part or rapid production by 3D printing for development purposes are among the prospective features with this potential. On the other hand, the 3D printing processes come with certain limitations which need to be overcome.

This paper shows a design and manufacturing process of a 3 kW axial impulse air turbine working with isenthalpic drop 30 kJ/kg. Several samples to verify printing options and the turbine itself has been manufactured from stainless steel by the DMLS additive manufacturing method. Manufactured are two turbine variations regarding blade size and 3D printer settings while maintaining their specific dimensions. The turboexpanders testing method and rig is outlined. As the surface quality is an issue, several methods of post-processing of 3D printed stator and rotor blading to modify surface quality are suggested. Detailed experimental investigation is however subject of future work.
A Study on the Leakage and Rotordynamic Coefficients of a Long-Smooth Seal With Laminar-Two-Phase, Mainly-Oil Mixtures
Authors: Zhang Min , Childs Dara W. , Tran Dung L. , Shrestha Hari
Published: November 2019

This paper conducts a comprehensive study on the effects of the air presence in the oil on the leakage and rotordynamic coefficients of a long-smooth seal (inner diameter D = 89.306 mm, radial clearance Cr = 0.140 mm, and length-diameter ratio L/D = 0.65) under laminar-two-phase flow conditions. The mixture consists of air and silicone oil with inlet GVF (gas volume fraction) up to 10%.

Tests are performed at inlet temperature Ti = 39.4 °C, exit pressure Pe = 6.9 bars, pressure drop PD = 31 and 37.9 bars, and rotor speed ω = 5, 7.5, and 10 krpm. The test seal is always concentric with the rotor, and no intentional fluid pre-rotation is provided at the seal inlet.

The complex dynamic stiffness coefficients Hij of the test seal are measured and fitted by the frequency-independent direct stiffness K, cross-coupled stiffness k, direct damping C, cross-coupled damping c, direct virtual-mass M, and cross-coupled virtual-mass mq coefficients.

Under laminar flow conditions, increasing inlet GVF has negligible effects on K, k, C, and effective damping Ceff, while it decreases c and M. These trends are correctly predicted by San Andrés’s bulk-flow model with laminar flow friction formula. As inlet GVF increases, measured leakage flow rate ṁ increases slightly. In general, the predictions of K, k, C, c, Ceff, and ṁ are reasonably close to measurements.
Influence of Temperature Distribution on Radial Growth of Compressor Discs
Authors: Luberti Dario , Tang Hui , Scobie James A. , Pountney Oliver J. , Owen J. Michael , Lock Gary D.
Published: November 2019

For the next generation of aero-engines, manufacturers are planning to increase the overall compressor pressure ratio from existing values around 50:1 to values of 70:1. The requirement to control the tight clearances between the blade tips and the casing over all engine-operating conditions is a challenge for the engine designer attempting to minimise tip-clearances losses. Accurate prediction of the tip clearance requires an accurate prediction of the radial growth of the compressor rotor, which depends on the temperature distribution of the disc. The flow in the rotating cavities between adjacent discs is buoyancy-driven, which creates a conjugate heat transfer problem: the disc temperature depends on the radial distribution of Nusselt number, which in turn depends on the radial distribution of disc temperature.

This paper focuses on calculating the radial growth of a simplified compressor disc in isolation from the other components. Calculations were performed using one-dimensional (1D) theoretical and two-dimensional finite-element computations (2D FEA) for overall pressure ratios (OPR) of 50:1, 60:1 and 70:1. At each pressure ratio, calculations were conducted for five different temperature distributions; the distribution based on an experimentally-validated buoyancy model was used as the datum case, and results from this were compared with those from linear, quadratic, cubic and quartic power laws.

The results show that the assumed distribution of disc temperature has a significant effect on the calculated disc growth, whereas the pressure ratio has only a relatively small effect. The good agreement between the growth calculated by the 1D theoretical model and the FEA suggests that the 1D model should be useful for design purposes.
An Evidence Based Process Facilitating Engineering Education and Innovation in the Field of Turbomachinery
Authors: Otto Marcel , Kapat Jayanta S. , Phelps Robin , O’Neal Thomas , Gramatikas George
Published: November 2019

A confluence of disruptive trends in the energy industry is creating an imperative for providers as well as all companies throughout the value-chain to innovate. Due to the physical and intellectual proximity of universities to cutting edge technology development universities are at the epicenter for the next generation of energy innovation and innovators. However, through traditional disciplinary coursework and research activities, today’s engineering faculty and students do not gain the skills to be effective innovators and advance their inventions from the lab to the market. As a result, new methods of education and training is required to meet the energy innovation imperative.

The National Science Foundation Innovation Corps (I-Corps) program, which aims to develop critical innovator skills while aiding in the process of developing innovations that have potential to solve a market-based problems. The program is an intense workshop with the goal to develop a scalable business model around the invention by “getting out of the building” and conducting more than 100 interviews with potential customers and other key stakeholders to test hypotheses related to problems and value propositions. The evidence from those interviews is used to validate or invalidate hypotheses about the business model.

The present paper examines the I-Corps program as an evidence-based process to facilitate engineering education and innovation in the field of turbomachinery. Utilizing a case study approach, we analyze the experiences of PDCC Technologies, a university based startup trying to commercialize a high temperature material as a potential component of gas turbine engines. The journey through the program including key “aha” moments and lessons learned is retold based on the specific example. The paper concludes with a summary of value for students and faculty and remarks on the improvement of the engineering program itself.
Heat Transfer Coefficient Augmentation for a Shaped Film Cooling Hole at a Range of Compound Angles
Authors: Haydt Shane , Lynch Stephen
Published: November 2019

Shaped film cooling holes are used to efficiently deliver coolant to the surface of a gas turbine part to keep metal temperatures low. The ultimate goal of film cooling is to reduce the heat flux into a component, relative to a case with no coolant injection. This reduction in heat flux is primarily achieved via a lower driving temperature at the wall for convection, represented by the adiabatic effectiveness. Another important consideration, however, is how the disturbance to the flowfield and thermal field caused by the injection of coolant augments the heat transfer coefficient. The present study examines the spatially-resolved heat transfer coefficient augmentation for a shaped film cooling hole at a range of compound angles, using a constant heat flux foil and IR thermography. Results show that the heat transfer coefficient increases with compound angle and with blowing ratio. Due to the unique asymmetric flowfield of a compound angle hole, a significant amount of augmentation occurs to the side of the film cooling jet, where very little coolant is present. This causes local regions of increased heat flux, which is counter to the goal of film cooling. Heat transfer results are compared with adiabatic effectiveness and flowfield measurements from a previous study.
Advantages and Experience of Using SSS (Synchro-Self-Shifting) Clutches in Hybrid Propulsion Such As CODELOG or CODELAG Naval Marine Systems
Authors: Hendry Morgan L. , Bellamy Nicholas
Published: November 2019

Hybrid marine ship propulsion systems are currently being used, and many more are being considered worldwide, including for commercial ships as well as for navies worldwide. These hybrid propulsion systems offer extended ship range and potentially quiet operation with propulsion on propeller shaft line electric motors. When high power and / or speed may be required, the main engines or turbines can be quickly started, and propeller shaft line clutches provide quick and reliable transition from or back to the electric motors.

In the naval marine sector, several ship programs currently use “Combined Diesel Electric or Gas Turbine” (CODELOG) or “Combined Diesel Electric and Gas Turbine” (CODELAG) propulsion. Some utilize Synchronous Self-Shifting Clutches, and some utilize other types of non-automatic friction clutches. Many navies worldwide are considering this type of hybrid propulsion, but variations in machinery arrangements and components can result in significant differences in fuel efficiency, weight, space, first time cost, ship performance, and propulsion machinery lifecycle maintenance with associated cost.

Therefore, serious investigation of the alternatives early in the ship design phase is important and accessing the experience of these existing systems with these components is vital, before settling on a machinery arrangement and its components for a future ship program.

As the old cliché says, “The Devil is in the Details!” Like any system, the success, the reliability, and the ultimate capability often come down to design details and the components chosen. Naval ships are designed to operate, even when damaged or when control or oil supply systems fail. Simplicity and the ability to improvise is often the key to mission success or failure. Synchronous Self-Shifting Clutches, or SSS Clutches, have proven to be “fit and forget” in these propulsion systems, have performed without fail in battle conditions, and this paper will describe the systems, explore the alternatives for propulsion clutches, provide advantages and disadvantages, and will provide experience of SSS Clutches in hybrid propulsion systems.
Impact of Fuel Composition on Gas Turbine Engine Performance
Authors: Burnes Dan , Camou Alejandro
Published: November 2019

An industrial gas turbine can run on a wide variety of fuels to produce power. Depending on the fuel composition and resulting properties, specifically the hydrogen-carbon ratio, the available output power, operability, and emissions of the engine can vary significantly. This study is an examination of how different fuels can affect the output characteristics of Solar Turbines Incorporated industrial engines, and highlights the benefits of using fuels with higher hydrogen-carbon ratios including higher power, higher efficiency, and lower carbon emissions. This study also highlights critical combustion operability issues that need to be considered such as autoignition, flashback, blowout and combustion instabilities that become more prominent when varying the hydrogen-carbon ratio significantly. Our intent is to provide a clear and concise reference to edify the reader examining attributes of fuels with different properties and how natural gas is superior to other fossil fuels with lower hydrogen carbon ratios in terms of carbon emissions, power, and efficiency.
Performance Comparison of Internal and External Reforming for Hybrid SOFC-GT Applications by Using 1D Real-Time Fuel Cell Mode
Authors: Chen Hao , Yang Chen , Zhou Nana , Harun Nor Farida , Tucker David
Published: November 2019

Solid oxide fuel cells integrated with gas turbine (SOFC-GT) systems are considered among the most promising power generation units, not only because of the high efficiency, low emissions and carbon capture ability, but also the flexibility to use different kinds of fuels such as natural gas, syngas and biogas directly. In the case of natural gas, Previous researches have demonstrated that solid oxide fuel cells possess the ability to utilize natural gas directly by reforming it inside the anode because of the high operating temperature. But the major problem of internal reforming is that it increases the temperature gradient at the leading edge of fuel cell which may lead to high thermal stress and damage the cells. On the other side, external reforming requires an additional reformer outside of fuel cell, which may increase the investment costs. Also, the amount of air needed to cool the fuel cell is doubled, compared with internal reforming. A full comparison between internal reforming and external reforming of the pressurized SOFC is needed for the hybrids application.

In this paper, a real time equilibrium reformer model based on minimization of Gibbs free energy was built to couple with 1D real time solid oxide fuel cell model. An internal on-anode reforming SOFC stack configuration for hybrid SOFC-GT system application was compared with external reforming configurations with 800K, 900K and 1000K reforming temperatures. The results show that internal reforming provides better performance of SOFC stack in the case of high fuel utilization. However, the external reforming showed a higher stack efficiency and smaller stack size compared with on-anode reforming when keeping a relatively lower SOFC stack fuel utilization, necessarily for high hybrid efficiency. Results indicated that external and internal reforming of fuel needs to be optimized depending on different design conditions of the entire hybrid system in terms of efficiency and investment cost. This paper shows that the hybrid system provides the opportunities for thermal integration on performance and efficiency improvement over fuel cell anode reforming.
A Bayesian Framework for Estimation of Strain Life Lower Bounds and its Application to IN617
Authors: Dourado Arinan , Irmak Firat , Viana Felipe A. C. , Gordon Ali P.
Published: November 2019

The practice of applying strain-life relationships to model materials subjected to low cycle fatigue conditions has been widely-accepted for the past seventy years. The Coffin-Manson rule employs a double, two-parameter power law equation to correlate cycles to failure to strain range (or vice versa). Plastic strain range dominates low life, while elastic strain dominates high life. In some settings with well-established materials, copious amounts of test data are available. The median response and the Coffin-Manson parameters are determined through regression. Scatter in both strain amplitude and fatigue life values are a consequence of material and specimen variation, test technician attributes or more. Recent initiatives have endeavored to transition deterministic approaches over to probabilistic analogies. Confidence bands, lower ones in particular, are useful for understanding reliability curves and implementing reliability-based design and optimization. In settings with accelerated product development schedules, intentionally sparse sets of test data are used to play “what if” scenarios in the context of life prediction. We propose a non-stationary variance to model deviations from the Coffin-Manson rule and use Bayesian statistical methods to estimate model parameter uncertainties. The proposed approach is applied to the calibration of strain-life parameters of the candidate material Inconel 617, a Ni-base alloy used is combustion equipment. When compared with constant variance (such as in traditional regression), the results show an improved characterization of the confidence bounds for fatigue life. This is important as it indicates that the methodology can be used to manage the number of coupon test to achieve an acceptable convergence.
Auto Ignition Study of Methane and Bio Alcohol Fuel Blends
Authors: Zheng Xuan , Jouzdani Shirin , Akih-Kumgeh Benjamin
Published: November 2019

Methane (CH4) and bio alcohols have different ignition properties. These have been extensively studied and the resulting experimental data have been used to validate chemical kinetic models. Methane is the main component of natural gas, which is of interest because of its relative availability and lower emissions compared to other hydrocarbon fuels. Given growing interest in fuel-flexible systems, there can be situations in which the combustion properties of natural gas need to be modified by adding biofuels, such as bio alcohols. This can occur in dual fuel internal combustion engines or gas turbines with dual fuel capabilities. The combustion behavior of such blends can be understood by studying the auto ignition properties in fundamental combustion experiments. Studies of the ignition of such blends are very limited in the literature.

In this work, the auto ignition of methane and bio alcohol fuel blends is investigated using a shock tube facility. The chosen bio alcohols are ethanol (C2H5OH) and n-propanol (NC3H7OH). Experiments are carried out at 3 atm and 10 atm for stoichiometric and lean mixtures of fuel, oxygen, and argon. The ignition delay times of the pure fuels are first established at conditions of constant oxygen concentration and comparable pressures. The ignition delay times of blends with 50% methane are then measured. The pyrolysis kinetics of the blends is further explored by measuring CO formation during pyrolysis of the alcohol and methane-alcohol blends. The resulting experimental data are compared with the predictions of selected chemical kinetic models to establish the ability of these models to predict the disproportionate enhancement of methane ignition by the added alcohol.
Governing Parameters Influencing CMAS Adhesion and Infiltration Into Environmental/Thermal Barrier Coatings in Gas Turbine Engines
Authors: Ghoshal Anindya , Walock Michael J. , Murugan Muthuvel , Mock Clara , Bravo Luis , Pepi Marc , Nieto Andy , Wright Andrew , Luo Jian , Jain Nishan , Flatau Alison , Fehrenbacher Larry
Published: November 2019

Sand particulate ingestion into modern gas turbine engines for fixed wing and vertical lift aircraft is a significant challenge for both military and civilian missions. ARL as part of a DoD funded Laboratory University Collaborative Initiative (LUCI) and Vannevar Bush Fellowship at UCSD are investigating the governing parameters that primarily influences the CMAS adhesion kinetics and infiltration on the standard Yttria Stabilized Zirconia (YSZ) as part of metallic single crystal Nickel superalloys TBC and SiC/SiC CMC T/EBCs. Current research shows various parameters including CMAS viscosity, porosity, adhesion strength, contact angle (wettability factor), geological factors affecting sand formation, coating and structural substrate roughness and surface temperature, internal flow Reynolds number, temperature, pressure, Mach number, boundary layer and bleed air, coating process (columnar vs splat morphology), tortuosity factor et al affects the CMAS adhesion and infiltration. This paper is a summary of our current research to identify and study the governing parameters that affects the CMAS formation, adhesion and infiltration and the underlying interfaces between CMAS and T/EBC, bond coat and the structural substrate. This work is aligned with Army Modernization Priority Future Vertical Lift and PEO Aviation Advanced Turbine Engine (ATE) Program.
Design and Numeric Simulation of a Thermoacoustic Bi-Directional Turbine Test Rig
Authors: Liu Dongdong , Chen Yanyan , Dai Wei , Luo Ercang
Published: November 2019

As a new type of acoustic-electric conversion method, bi-directional impulse turbine provides great potential for developing large scale and economic thermoacoustic power generators. A test rig for turbine tests in acoustic fields, which are provided through two reciprocating pistons, has been introduced. A three-dimensional numerical model has been used to simulate the whole system. The fundamental characteristics of the turbine in oscillating flow are analyzed. Impact of acoustic field features on the turbine performance has been studied. The results show that the performance is sensitive to the acoustic field. For the test rig, a typical result is that with a shaft power of 187 W, the turbine can reach an efficiency around 32%.
Towards a Better Understanding of Crack Growth in Nickel-Cast Alloys Under Creep-Fatigue and Thermo-Mechanical Fatigue Conditions
Authors: Kraemer Karl Michael , Mueller Falk , Kontermann Christian , Oechsner Matthias
Published: November 2019

To ensure the feasibility of gas turbines, despite rising commodity prices and emission restrictions, an enhancement of both their efficiency and flexibility is necessary. The consequential higher loading of components at high temperature conditions calls for an increased use of damage tolerant design approaches. To still guarantee a safe operation, a sound understanding and reliable estimations for crack growth under service conditions is indispensable. In this paper, the results from several projects in this field conducted at the TU Darmstadt and involved partners are summarized to identify and describe the various influences on crack growth under creep-fatigue and thermo-mechanical fatigue (TMF) loading. The activation of damage mechanisms under TMF loading and interactions between them are dependent of the temperature cycle and the respective load phasing. Depending on the type of loading (force- vs. strain-control), contrary influences of the phase shift on the TMF crack growth rates are found. This can partially be attributed to the differences in mean stress evolution. Crack initiation and propagation under creep-fatigue and TMF conditions are also often connected with significant scattering of initiation sites and crack growth rates. One reason for this non-uniform behaviour is the interaction of geometric discontinuities with the microstructure. To investigate the role of the local grain structure for crack initiation and propagation, in-situ observation techniques for crack tip movement and local strain fields were applied. Harsh gradients in the local deformation behaviour were identified as origins of secondary crack initiation. To describe crack growth under creep-fatigue and TMF conditions, the linear accumulation model “O.C.F.” was developed. It is based on the contributions of fatigue, creep and oxidation to crack growth per load cycle. This model is capable to reproduce the effects of time-dependent damage, different load ratios and TMF phase shifts, as well as component geometry. Substantial advantages of this method are its independence from empiric correction factors to assess changing load cycle forms and the possibility to give analytic estimations without the need of extensive data processing. The model is currently validated for three nickel cast alloys, also including single crystalline (SX) and directionally solidified (DS) cast variants, different creep-fatigue and TMF loading scenarios and crack geometries. The model’s linear formulation allows assessing the dominant driver of crack growth at each stage of an experiment. These predictions are compared with fractographic investigations and in-situ observations of crack paths to identify the mechanisms of crack growth under different TMF load cycle forms.
2-Stage Air Filtration for Gas Turbine Naval Applications
Authors: de Arcangelis Gianluca
Published: November 2019

Traditional air filtration systems for Gas Turbine Naval applications consist of 3 stages: 1st vane separator + pocket filter + 2nd vane separator. The 2nd vane separator is required to drain out droplets formed by the traditional pocket filter during its coalescing function.

Further to technological advancements in the water repellency of filter media, as well as leak-free techniques, it is now possible to implement a pocket filter that avoids leaching water droplets downstream. This enables the elimination of the 3rd stage vane separator in the air filtration system. The result is a suitable 2-stage air filtration system.

The elimination of the 3rd stage vane separator provides the obvious following advantages:

• Reduced pressure drop

• Reduced weight

• Reduced foot-print

• Reduced cost

Latest technological advancements in water repellency and high efficiency melt-blown media also allow the attainment of higher performance such as:

• Increased efficiency against water droplet and salt in wet state

• Increased efficiency against dry salt and dust

This results in higher cleanliness of the Gas Turbines with benefits in terms of compressor fouling, compressor blades corrosion and turbine blades hot erosion.

Higher performance also results in simplified maintenance as technicians need only focus on the replacement of the elements as opposed to the cleaning and overhauling of the intake duct.

The paper goes through the engineering challenges of evolving from a 3-stage to 2-stage filtration system.

The paper provides data from testing at independent laboratories with results that back the claims. Furthermore, reference is made to Offshore Oil & Gas installations and testing that have proven successful with independently measured data.
Considerations for Using Additive Manufacturing Technology in Centrifugal Compressor Research
Authors: Meier Matthew A. , Gooding William J. , Fabian John , Key Nicole
Published: November 2019

An additive manufactured (AM) vaned diffuser for use in a centrifugal compressor research facility was designed and implemented. Utilizing an AM process to manufacture the diffuser reduces the long lead time that is associated with conventionally manufactured diffusers, and it increases the instrumentation capabilities within the flow path. Several AM techniques and a variety of plastic and metal materials were evaluated for this application. A high-temperature, stereolithography (SL) resin was chosen because of the tight dimensional tolerances maintained by the SL process. Utilizing a high-temperature plastic also results in manufacturing costs that are significantly less than using a metal material. Samples of the chosen material were subjected to mechanical testing to investigate the effects of build direction (BD) and to verify its properties in the high-temperature compressor environment. To fit within the manufacturing space of an SL machine, the AM diffuser consists of seven radially symmetric sections that are assembled to form a complete flow path. Considerations for modifying the research facility to allow for this unique installation are presented. Precision measurements of the AM components were obtained to compare printed and modeled geometry, and they demonstrate close alignment of flow path dimensions.
Thermal Development of an Impinging Jet Using Planar Laser Induced Fluorescence (PLIF)
Authors: Wright Lesley M. , Seitz Sara
Published: November 2019

Planar Laser Induced Fluorescence (PLIF) has been demonstrated to investigate a round jet impinging on a flat surface. Detailed thermal field distributions have been obtained near the flat target surface to characterize the wall jet development ensuing from the stagnation point. While PLIF has been demonstrated for combustion applications to measure concentration gradients within a mixture, its application for temperature field measurements is less established. Therefore, the technique was applied to a simple, cylindrical impinging jet. The jet Reynolds number varied with Rejet = 5,000–15,000 while the jet–to–target surface spacing varied from H / D = 4–10. The cooling jet (Tjet ∼ 300 K) impinged on a flat, heated surface. The PLIF technique was able to capture the free jet structure and jet development along the target surface. With a short impingement length (H / D = 4), the potential core of the jet strikes the target surface. The thermal gradients captured during the experiments demonstrate the fully turbulent nature of the impinging jet with H / D = 10. The thermal boundary development along the target surface is clearly captured using this fluorescence method. The near wall temperature gradients acquired with the PLIF method have been used to calculate heat transfer coefficients on the heated surface, and these values compare favorably to those measured using a well-established steady state, heat transfer method. The PLIF technique has been demonstrated for this fundamental impingement setup, and it has proven to be applicable to more complex heat transfer and cooling applications.
Intraguild aggressiveness between an alien and a native predatory mite
Authors: L.A. Escudero-Colomar , E. Creus , A. Chorąży , A. Walzer
Published: November 2019

The predatory mite Amblydromalus limonicus, non-native in Europe, can be used legally in several European countries as greenhouse biocontrol agent against thrips species, although this species is also able to feed on whiteflies and gall mites. The first record of the unintended occurrence of A. limonicus in apple orchards in Europe comes from Catalonia (Spain), where A. limonicus is well established in the native predatory mite community since 2011. The dominant species in this community is Amblyseius andersoni, which has a similar life-style as A. limonicus (large, aggressive predator with broad diet range) making intraguild (IG) interactions between the two predators likely. Thus, we tested the IG aggressiveness of native and alien female predators, when provided with IG prey (larvae). Alien females of A. limonicus proved to be highly aggressive IG predators against native larvae of A. andersoni, which were attacked earlier and more frequently than alien larvae by the native predator. Nearly all attacks by the alien predator resulted in the death of native IG prey, whereas about 10% of the alien intraguild prey escaped the attacks of the native predator. Additionally, native IG prey is smaller than alien prey, which should facilitate the overwhelming by the alien predator. We argue that the strong aggressive intraguild behavior of A. limonicus is contributing to its establishment success in the native predatory mite community.
Influence of the player on the dynamics of the electric guitar
Authors: Le Carrou Jean-Loic , Paté Arthur , Chomette Baptiste
Published: November 2019

The sound of the electric guitar is strongly dependent on the string vibration. Where a mode of the structure coincides with a mode of the fretted string, coupling between the string and structure occurs at that “deadspot.” The coupling significantly lowers decay time, leading to the name [Paté, Le Carrou, and Fabre (2014). J. Acoust. Soc. Am. 135(5), 3045–3055]. But how the guitarist affects the dynamic behavior of the structure by grasping the neck, holding the instrument with the strap, or laying the instrument on his/her thigh remains to be investigated. This is the aim of the paper. Two methods are proposed to identify the modal parameters of the electric guitar structure, either by a classical modal analysis in simulated playing configuration, or by an operational modal analysis in real playing configuration. For this latter method, modal parameters are identified from dynamic measurements performed when each string is plucked. Both methods are compared and allow one to quantify the modal frequency modification and the added modal damping, which depend on the player's body-part in contact with the structure and on the modal shape considered. Consequences of these modal parameters on the modeled sound show that the player can increase the decay time close to a deadspot.