bluuebunny/crossref_metadata_2025 huggingface dataset:
A Biogas Fuelled Micro Gas Turbine: Energetic Performance and Environmental Impact Analysis
Authors: Chiariello Fabio , Reale Fabrizio , Calabria Raffaela , Massoli Patrizio
Published: November 2019

The use of biogas in micro gas turbines (MGTs) generally requires invasive structural modifications to fuel compression units, control valves and combustor. Costs associated with the modifications significantly reduce the benefits of a rational and sustainable exploitation of energy resources of lower value as the biogas.

In order to overcome this aspect, in a recent paper the authors proposed a dual fuel approach, identifying a structurally non-invasive and cost-effective technical solution to increase the CO2 concentration in the fuel and to extend the operation domain of the MGT when low calorific value fuels are used. In that study, it has been evaluated, implemented and tested an innovative management strategy of fuel feeding and combustion. Experimental preliminary tests validated the idea of a new supply strategy for exceeding the current limits of biogas exploitation as MGT fuel.

With this approach the MGT operating domain has been extended, increasing more than twice the CO2 concentration limit than experimentally validated limit available in literature.

In this study the authors present a more extensive investigation concerning the energetic performance and the environmental impact of a 100 kWe MGT Turbec T100 when fuelled with a mixture of natural gas and carbon dioxide (synthesis biogas) in the dual fuel approach, by varying CO2 concentration in the fuel at part load condition.

The data acquired by an extensive experimental campaign, in terms of thermodynamic parameters and gaseous exhaust emissions, are presented and compared with the results of numerical simulations.

A 3D CFD analysis of the combustion process is also presented. Initial and boundary conditions of the numerical approach were obtained from a previous validated 0D thermodynamic matching model.

The synergistic activity between numerical modeling and experimental work allows to analyze and explain the overall behavior of the micro gas turbine in the dual fuel mode with biogas fuel.

The study shows that the micro gas turbine can stably operate in a dual fuel mode until the CO2 content rises above 25%.
Effects of Swirl on the Stabilization of Non-Premixed Oxygen Enriched Flames Above Coaxial Injectors
Authors: Degeneve A. , Mirat C. , Caudal J. , Vicquelin R. , Schuller T.
Published: November 2019

An experimental study is carried out to analyze effects of swirl on the structure and stabilization of methane non-premixed oxygen-enriched flames above a co-axial injector in which the two streams are eventually swirled. The mean position of the flame and the liftoff height above the injector lips are investigated with OH* chemiluminescence images. The oxygen enrichement, the momentum flux ratio between the two co-flows, the swirl level inside the central jet and the swirl level in the annular jet are varied over a large range of operating conditions. It is found that, in the absence of swirl in the central stream, the flame is always attached to the lips of the internal injection tube. As the inner swirl level increases, the flame front located at the lips of the internal injection tube disappears. When the annular swirl level is high enough to create a central recirculating bubble, the flame detaches from the nozzle rim and remains lifted at a finite distance above the injector. Increasing the oxygen concentration shifts this transition to smaller momentum flux ratios and smaller annular swirl levels. The lift-off distance can be finely tuned and depends on the inner and outer swirl levels, and on the momentum flux ratio between the two coaxial streams. It is shown that this feature neither depends on the confinement of the injector nor on the thermal stress exerted by the hot burnt gases on the injector back plane. About 1000 configurations were investigated that could be classified into only four distinct stabilization modes, in which the flame structure was shown to follow a similar pathway when the momentum flux ratio between the two streams, the swirl level in the central and external streams and the quarl angle of the annular stream are varied. It is finally shown how these limits are altered when the oxygen concentration in the annular oxidizer stream is varied from air to oxygen-enriched operation.
A Re-Design Study Based on a High Pressure Cyclonic Combustor Operated With Liquid Fuel
Authors: Grimm Felix , Enderle Benedict , Kislat Oliver , Izadi Saeed , Zanger Jan , Kutne Peter , Aigner Manfred
Published: November 2019

Computational Fluid Dynamics are widely used as a design tool for a variety of thermo-fluid systems. Advantages of those numerical approaches are clearly the fairly detailed degree of valuable data at low computational costs, when RANS (Reynolds Averaged Navier Stokes) methods are used in the system design process.

In this work, a combustion system operated at elevated pressure conditions is re-designed with CFD RANS methods. The combustor is operated with liquid fuel and is positioned between an upstream recuperation and a downstream turbine section. System design is carried out on the basis of a commercially available C30 configuration from the Capstone® Turbine Corporation. The micro turbine produces 30kW of electrical power and is therefore highly suited for micro gas turbine related applications.

In the design process, as presented in the paper, several modifications are carried out. The system recuperation is changed, thus inflow modifications are given. Recuperation was explicitly simulated and is used as a combustor inflow boundary condition. The system is then analyzed and modified in terms of air splits in order to achieve certain combustion characteristics. Optimization is carried out for combustor air splits and turbine inlet temperature profile conditions are significantly improved. Reacting multi-phase simulations are used in order to characterize flow field and combustion. Further on, conjugated heat transfer is taken into account in order to characterize temperature distribution in the combustor. Additionally, combustor residence times are determined. It is demonstrated that the pursued methods and procedures are computationally cheap but at the same time highly suited and sufficient for thorough combustion system development.
Experimental and Numerical Investigation on the Influence of Thermally Induced Stress Gradients on Fatigue Life of the Nickel-Base Alloy Mar-M247
Authors: Thiele Marcus , Eckmann Stefan , Huang Min , Gampe Uwe , Fischer Kathrin A. , Schlesinger Michael
Published: November 2019

Today’s and future parameters of stationary gas turbines and aircraft engines require intensive and highly efficient cooling of hot gas path components. High temperature and thermally induced stress gradients with impact on fatigue life are the consequence. Thermally induced stress gradients differ from geometrically induced stress gradients with respect to stress mechanics by the independence from external loads and material mechanics by the influence of temperature on material properties and strength. Regarding the contribution and evaluation on damage, the latter characteristic feature in turbomachinery is currently not fully understood.

Therefore, a test facility has been designed, set up, and reported in GT2018-76519 for the investigation of the influence of stationary temperature, and thus thermally induced stress gradients, on the damage evolution of cooled high-temperature components. To achieve high temperature and thermally induced stress gradients, large heat fluxes are required. A unique radiation heating has been developed allowing very high heat fluxes of q̇ ≥ 1.5 MW/m2 for testing of hollow cylindrical specimens.

The conventional cast nickel-base alloy Mar-M247 has been chosen to study the influence of thermally induced stress gradients on fatigue life. The low-cycle fatigue testing of the hollow cylindrical specimens has been conducted both with and without superimposed stationary temperature gradients. In addition, Complex Low-Cycle Fatigue (CLCF) tests with symmetric and nonsymmetric loading conditions have been performed to provide the necessary database for the adaptation of a viscoplastic deformation model. To calculate the local stress-strain field and service life of the test specimens, linear elastic and viscoplastic finite element studies have been performed and were assessed by means of a fracture mechanics-based lifetime model.

The test results show the considerable influence of the temperature gradient on the low-cycle fatigue life for the investigated material. Both the radial temperature variation over the specimen wall with a hot outer surface and a cooled inner surface as well as the thermally induced stresses are stated to be the main drivers for the change in low-cycle fatigue life. The test results enhance the understanding of fatigue-damage mechanisms under local unsteady conditions and can be used as a basis for improved service life predictions.
Combined Experimental and Numerical Investigation of the Aero-Thermal Performance of a Rotor Blade Cascade With Platform Cooling
Authors: Barigozzi G. , Perdichizzi A. , Pestelli L. , Abram R.
Published: November 2019

This paper reports the results of a combined experimental and numerical investigation carried out to support the design of a film cooling system for a rotor blade platform. A 7 blade cascade of a high-pressure-rotor stage of a heavy-duty gas turbine has been tested in a low speed wind tunnel. Tests have been carried out at a low Mach number (Ma2is = 0.27) with a relatively high inlet turbulence intensity level of about 7.6% at the leading edge plane. The same cascade model was also numerically tested by means of a 3D RANS approach. Cascade flow and heat transfer behavior was first experimentally assessed without coolant injection and used to validate the numerical approach. These data were also used to design the platform cooling scheme based on shaped holes that was then tested for variable injection rates. The thermal behavior was measured by using the Binary PSP technique, so to obtain film cooling effectiveness distributions over the passage. RANS 3D CFD simulations were also run on the same cooled model and testing conditions, allowing to critically assess the prediction capability of the selected numerical approach and of the design process.
An Enhanced Gas Turbine Engine Laboratory: A Learning Platform Supporting an Undergraduate Engineering Curriculum
Authors: Bellocchio Andrew T. , Benson Michael J. , Van Poppel Bret P. , Norberg Seth A. , Benz Ryan
Published: November 2019

A gas turbine engine has supported the U.S. Military Academy’s mechanical engineering program for nearly three decades. Recent, substantial enhancements to the engine, controls, and data acquisition systems greatly increased the student experience by leveraging its broad capabilities beyond the original laboratory learning objectives. In this way, the laboratory served as a learning platform for more than just instruction on gas turbine fundamentals and the Brayton cycle.

The engine is a refurbished auxiliary power unit from Pratt & Whitney Aeropower, installed in the Embrauer 120 and similar to a unit installed on a U.S. Army helicopter. Whereas the original laboratory experience permitted students to test the engine at three different loads applied by a water brake dynamometer, the revised experience allowed for a broader range of test conditions. The original laboratory included single point measurements of three temperatures and two pressures, along with the fuel flow rate, dynamometer torque, and engine speed. The revised laboratory allowed the user to vary bleed air and engine loads across an operational envelope at a user-specified acquisition rate. The improved data acquisition system used LabVIEW™ and included multiple state sensors for pressure, temperature, fuel flow, bleed air, and dynamometer performance, thereby enabling a more complete analysis by accounting for the energy transported by bleed airflow and absorbed by the water brake. Students then quantified the uncertainty in their measurements and analysis. The new emphasis on uncertainty quantification, part of a program-level initiative, challenged students’ notion of “substitute and solve” while also familiarizing them with large, experimental data sets.

The re-envisioned laboratory raised the students’ level in the cognitive domain and served as their premier engine experience. Rather than merely observing engine adjustments across a small range of conditions, students designed their own laboratory experience. With the updated approach, students viewed a graphic of the turbine’s laboratory operating range and chose the key variables of interest — selecting data points within the laboratory operating range — and then justified their selections. The enhanced experience added analysis of flow exergy and exergetic efficiency. The exercise also challenged students to hypothesize why actual turbine performance was less than predicted and determine sources of error and uncertainty. Moreover, the new laboratory offers opportunities to expand the turbine engine’s utility from supporting a single thermal-fluids course to a multidisciplinary learning platform. Concluding remarks address concepts for augmenting course instruction in other courses within the curriculum, including heat transfer, mechanical vibrations, and dynamic modeling and controls.
Experimental Study of the Precessing Vortex Core Impact on the Liquid Fuel Spray in a Gas Turbine Model Combustor
Authors: Renaud Antoine , Ducruix Sébastien , Zimmer Laurent
Published: November 2019

Despite being good candidates for the reduction of pollutant emissions from gas turbines, burners operating in Lean Premixed Prevaporized regimes often face stability issues and can be sensitive to perturbations. The swirling flow used to aero-dynamically stabilize the flame can also lead to the appearance of a large-scale coherent flow structure known as the Precessing Vortex Core (PVC). In the present study, a swirl-stabilized combustor fed with liquid dodecane is studied at a globally lean operating condition with the help of high-speed diagnostics and Dynamic Mode Decomposition (DMD) as the main post-processing method. It is shown that the trace of a PVC originating inside the injector is still present in the fuel spray at the entrance of the chamber even though the aerodynamical structure itself is not detectable anymore. The perturbation of the fuel spray is then transmitted to the flame through local equivalence ratio fluctuations. It is observed that the PVC trace on the spray and thus on the flame can be suppressed by air flow modulations generated by a siren device. The suppression of this trace is shown to come from a decay of the aerodynamical structure itself rather than by a change in fuel mixing or vaporization. Analysis of the characteristic frequency of the PVC shows a frequency spread indicating a loss of coherence of the structure with the high amplitude air flow rate fluctuations.
Semiconductor Nano and Micro Membrane Based Pressure Sensors for Wide Bandwidth Measurements
Authors: Kang Y. , Sibold R. , Homer M. , Gladwin L. , Claus R. , Ng W. , Ruan H.
Published: November 2019

Semiconductor nanoµ membranes (NMMs) are gaining acceptance in the semiconductor industry as the benefits they provide become key enablers in scaling and performance enhancements of electronic devices. These tailored-modulus conformal NMM sensor skins with integrated interconnect elements and electronic devices can be applied to new or existing wind tunnel models for full spectrum pressure monitoring. The material is resistant to normal fluids and solvents, can potentially operate over a wide temperature range, and is capable of withstanding erosion. Experimental data presented in this paper demonstrates that: 1) silicon NMMs may be used as single pressure sensor transducers and elements in sensor arrays, and 2) the arrays may be instrumented to map pressure over the surfaces of test articles over a range of Reynolds numbers, temperature and other environmental conditions. Of most importance, we have 1) shown that the small-feature-size sensor elements are highly sensitive to pressure (frequency response from DC up to 5MHz), 2) developed several types of sensor packages for the demonstration of pressure sensing with a miniature probe tip, and 3) confirmed operation in wind tunnel and shock tube tests over 100 times up to Mach 4.2 on several test articles.
Visualization of Supercritical Carbon Dioxide Flow Through a Converging-Diverging Nozzle
Authors: Lim Chang Hyeon , Pathikonda Gokul , Pidaparti Sandeep , Ranjan Devesh
Published: November 2019

Supercritical carbon dioxide (sCO2) power cycles have the potential to offer a higher plant efficiency than the traditional Rankine superheated/supercritical steam cycle or Helium Brayton cycles. The most attractive characteristic of sCO2 is that the fluid density is high near the critical point, allowing compressors to consume less power than conventional gas Brayton cycles and maintain a smaller turbomachinery size. Despite these advantages, there still exist unsolved challenges in design and operation of sCO2 compressors near the critical point. Drastic changes in fluid properties near the critical point and the high compressibility of the fluid pose several challenges. Operating a sCO2 compressor near the critical point has potential to produce two phase flow, which can be detrimental to turbomachinery performance. To mimic the expanding regions of compressor blades, flow through a converging-diverging nozzle is investigated. Pressure profiles along the nozzle are recorded and presented for operating conditions near the critical point. Using high speed shadowgraph images, onset and growth of condensation is captured along the nozzle. Pressure profiles were calculated using a one-dimensional homogeneous equilibrium model and compared with experimental data.
Sweeping Jet Film Cooling at High Blowing Ratio on a Turbine Vane
Authors: Hossain Mohammad A. , Ameri Ali , Gregory James W. , Bons Jeffrey P.
Published: November 2019

Experimental and numerical investigations were conducted to study the effects of high blowing ratios and high freestream turbulence on sweeping jet film cooling. Experiments were conducted on a nozzle guide vane suction surface in a low-speed linear cascade. Experiments were performed at blowing ratios of 0.5–3.5 and freestream turbulence of 0.6% and 14.3%. Infrared thermography was used to estimate the adiabatic cooling effectiveness. Thermal field and boundary layer measurement were conducted at a cross-plane (x/D = 12) downstream of the hole exit. Results were compared with a baseline 777-shaped hole and showed that sweeping jet hole has a better cooling performance at high blowing ratios. The Thermal field data revealed that the coolant separates from the surface at high blowing ratios for the 777-shaped hole while the coolant remains attached for the sweeping jet hole. Boundary layer measurement further confirmed that due to the sweeping action of the jet, the jet momentum of the sweeping jet hole is much lower than that of a 777-shaped hole. Thus the coolant remains closer to the wall even at high blowing ratios. Large Eddy Simulations (LES) were performed for both sweeping jet and the 777-shaped hole to evaluate the interaction between the coolant and the freestream at the near hole regions. Results showed that 777-shaped hole has a strong jetting action at high blowing ratio that originates inside the hole breakout edges thus causing the jet to blow off from the surface. In contrast, the sweeping jet hole does not show this behavior due to its internal geometry and the sweeping action of the jet.
A Modular Transonic Turbine Cascade for Cooled Rotor Metal Effectiveness Investigations
Authors: Parker James A. , Romero Ed , Povey Thomas
Published: November 2019

The Metal Effectiveness Rotor Cooling (MERC) facility at the University of Oxford is a new blow-down linear cascade tunnel developed for aerothermal research of turbine rotor blade and rotor platform cooling systems. A high level of engine similarity is achieved with matched Mach numbers, Reynolds numbers, coolant-to-mainstream pressure ratios, and Biot number (using DMLS components of appropriate conductivity). The modular working section includes five blade passages, including platform and fir tree root geometries, and engine representative hub seals. The facility is designed to allow high accuracy IR camera measurement of the blade and platform surfaces (for metal effectiveness measurements) and downstream area traverse measurements. Detailed traverse measurements are possible in a single run, because of the long run time of the facility (up to 5 minutes).

The facility is being used for development and optimisation research of novel blade and platform cooling systems, with an emphasis on overall thermal performance of parts (metal effectiveness). Modular cassettes allow the blade components to be rapidly interchanged, and for variations to the designs of the front and rear hub seals. The engine representative seals and coolant feed paths allow for all engine leakage flows to be replicated in the experiment. This is important, because they are influential in determining the platform cooling flow structure (character and extent of secondary flow) and overall metal effectiveness result. Coolant supplied to each of the hub seals, and blade shank pocket can be independently varied to achieve required mass flows and pressure ratios. Rotor blades are typically manufactured using DMLS, allowing fast development and optimisation of fully-featured cooling systems at significantly reduced cost compared to traditional casting techniques.

To demonstrate the capability of the new facility, we present full-surface metal-effectiveness measurements of the rotor blade platforms (post-processed using high-accuracy infrared thermography techniques separately developed at the University of Oxford.)

The purpose of this paper is to outline the capabilities of the facility, describe the prior work and research context which led to its development, and to demonstrate the accuracy of the measurement techniques employed by presenting typical measured data. An argument is made for the importance of including realistic hub seal leakage paths in experiments investigating platform cooling flows by illustrating their significant impact on overall cooling performance. The MERC facility is a response to the need to develop more advanced rotor platform cooling schemes for future engines.
Numerical Investigation of Circumferential Groove Casing Treatment on a Low Speed Contra-Rotating Fan
Authors: Heinrich Martin , Khaleghi Hossein , Friebe Christian
Published: November 2019

This study is aimed at understanding the effects of circumferential groove casing treatment on the performance of a low speed contra-rotating fan. Three dimensional, transient simulations are carried out using the open source CFD library Open-FOAM. The numerical results are validated with experiments for the smooth casing, which show a good agreement. Three treated casing configurations are investigated: 1) grooves at the top of the first rotor, 2) grooves at the top of the second rotor, and 3) grooves at the top of both rotors. Two operating points are simulated for all configurations. Flow inside the grooves is highly dominated by the main and blade passage flows. Grooves increase fan performance at near-stall flow conditions by up to 3 % and reduce pressure fluctuations significantly. Furthermore, they have a larger impact on fan performance when placed on top of the first rotor compared to placing them on top of the second rotor.
Aerodynamic and Structural Design of a Centrifugal Fan for an Air Cushion Vehicle
Authors: Cameron B. H. , Grald E. W. , Conboy T. M. , Passow C. H. , Kattamis N. T. , George Daniel , Bray Joseph , Cole Robert E.
Published: November 2019

A methodology is presented for the re-design of a large centrifugal impeller used for the lift fan on an air cushion vehicle. The design is driven by stringent requirements for aerodynamic and structural performance. It is also desired to minimize the fan’s life cycle cost, by reducing both the manufacturing cost and on-going maintenance burden. Improving the fan efficiency will increase the vehicle’s endurance and range, and minimizing life cycle cost will reduce the overall operational expenses. The lift fan assembly has a double-inlet impeller and an offset double-discharge volute. The new impeller design provides increased air flow with similar aerodynamic efficiency when compared to the prior design. To reduce the manufacturing cost, the new fan blade design can be produced by an aluminum extrusion process. The manufacturing process dictates that the blade cross-section be two-dimensional across the entire span, which poses structural challenges for attachment of the blades to the shroud and center disk. Analysis of the aerodynamic and structural performance of the lift fan was carried out using computational fluid dynamics (CFD) and structural finite element analysis (FEA) models. The fabrication of full-scale lift fan components is described. Plans for final assembly and for conducting full-scale, full-power aerodynamic testing will also be explained.
Design Considerations for Ceramic Matrix Composite High Pressure Turbine Blades
Authors: Boyle Robert J. , Parikh Ankur H. , Nagpal Vinod K.
Published: November 2019

Issues associated with using SiC/SiC Ceramic Matrix Composite (CMC) materials for High Pressure Turbine (HPT) rotor blades are explored. SiC/SiC materials have higher temperature capability than current HPT superalloys. The strength versus temperature characteristics of SiC/SiC CMCs differs from that of superalloys. Stress analyses were done for a NASA specified notional single aisle aircraft engine blade to be available in the N+3 time frame, (beyond 2030). Stacking, the relative position of hub and tip sections, depends on both pressure and centrifugal forces, and material density. The effect of blade stacking on blade stresses is examined. The change in stresses as the rotation rate varies is examined. The change in engine weight, and thus fuel consumption, due to changes in engine size as the rpm changes is discussed. SiC/SiC CMC materials are generally not isotropic. The effect on stresses and strains of a directional variation in Young’s modulus is examined. Shrouding metallic HPT rotor blades is not common. Shrouding SiC/SiC CMC rotor blades may be feasible due to the lower density, and thus lower centrifugal loads, of SiC/SiC blades. The increase in stresses due to shrouding a SiC/SiC blade is discussed.
Analyzing the Potential for Erosion in a Supercritical CO2 Turbine Nozzle With Large Eddy Simulation
Authors: Finn Justin R. , Doğan Ömer N.
Published: November 2019

Large eddy simulation of supercritical CO2 flow carrying solid oxide particles through a radial turbine nozzle has been conducted at a Reynolds number of 0.5 × 106. The three-dimensional geometry corresponds to the nozzle where erosion damage was observed by Fleming and Kruizenga [1]. The turbulent flow through the passage was approximated as incompressible, and the spatially filtered Navier-Stokes equations were solved on an unstructured grid. One way coupled, porous, oxide particles (30μm diameter, 2500 kg ṁ m−3) were continuously injected upstream of the passage and tracked in a Lagrangian manner as they were carried through the domain by the turbulent flow. Statistics of mean particle concentration and particle-nozzle impacts were collected to identify regions along the passage prone to erosion damage. For this condition, the particles became highly concentrated as they passed along the pressure side of the nozzle. High impact velocities and oblique collision angles near the trailing edge led to relatively high predicted rates of erosion, near the location where damage was observed in the laboratory. Extrapolation of simulation results to proposed operational Reynolds numbers suggests that very small particles, with diameter < 10μm, could cause high velocity impacts and eventual degradation.
A Method for Rotordynamic Force Prediction of a Centrifugal Compressor Impeller Front Cavity Using a Transient Whirling CFD Technique
Authors: Hoopes Kevin , Moore J. Jeffrey , Rimpel Aaron , Kulhanek Chris , Venkataraman Balaji
Published: November 2019

In order to improve the rotordynamic stability predictions of centrifugal compressor impeller front cavities, a method for modeling the eye seal and shroud cavity using transient, moving wall, CFD simulation is presented. This method allows for the extraction of the rotordynamic coefficients from the eye seal and impeller front cavity using a single model. This paper presents the details of the method as well as a set of typical results at various different whirling frequencies for a centrifugal impeller front cavity. Along with the CFD derived rotordynamic coefficients, predictions using correlations from the literature are also presented for comparison.
Effect of Microporosity on Damage Initiation in Ceramic Matrix Composites
Authors: Gururaja Suhasini , Nagaraja Abhilash
Published: November 2019

Ceramic matrix composites (CMC) are a subclass of composite materials consisting of reinforced ceramics. They retain the advantages of ceramics such as lower density and better refractory properties but exhibit better damage tolerance compared to monolithic ceramics. This combination of properties make CMCs an ideal candidate for use in high temperature sections of gas turbines. However, modeling the damage mechanisms in CMCs is complex due to the heterogeneous microstructure and the presence of processing induced defects such as matrix porosity. The effect of matrix pore location and orientation on damage initiation in CMCs is of interest in the present work.

CMCs fabricated by various fabrication processes exhibit matrix pores at different length scales. Microporosities exist within fiber bundles in CMCs have a significant effect on microscale damage initiation and forms the focus of the current study. In a previous work by the authors, a two step numerical homogenization approach has been developed to model statistical distribution of matrix pores and to obtain the effective mechanical properties of CMCs in the presence of matrix porosity. A variation of that approach has been adopted to model matrix pores and investigate the severity of pores with respect to their location and orientation. CMC microstructure at the microscale has been modeled as a repeating unit cell (RUC) consisting of fiber, interphase and matrix. Ellipsoidal pores are modeled in the matrix with pore distance from the interphase-matrix interface and pore orientation with respect to the loading direction as parameters. Periodic boundary conditions (PBCs) are specified on the RUC by means of constraint equations. The effect of the pore on the local stress fields and its contribution to matrix damage is studied.
The STEP 10 MWe sCO2 Pilot Plant Demonstration
Authors: Marion John , Kutin Mike , McClung Aaron , Mortzheim Jason , Ames Robin
Published: November 2019

A team led by Gas Technology Institute (GTI), Southwest Research Institute® (SwRI®) and General Electric Global Research (GE-GR), along with the University of Wisconsin and Natural Resources Canada (NRCan), is actively executing a project called “STEP” [Supercritical Transformational Electric Power project], to design, construct, commission, and operate an integrated and reconfigurable 10 MWe sCO2 [supercritical CO2] Pilot Plant Test Facility located at SwRI’s San Antonio, Texas campus. The $119 million project is funded $84 million by the US DOE’s National Energy Technology Laboratory (NETL Award Number DE-FE0028979) and $35 million cost share by the team, component suppliers and others interested in sCO2 technology. This project is a significant step toward sCO2 cycle based power generation commercialization and will inform the performance, operability, and scale-up to commercial facilities.

Supercritical CO2 (sCO2) power cycles are Brayton cycles that utilize supercritical CO2 working fluid to convert heat into power. They offer the potential for higher system efficiencies than other energy conversion technologies such as steam Rankine or organic Rankine cycles, especially when operating at elevated temperatures. sCO2 power cycles are being considered for a wide range of applications including fossil-fired systems, waste heat recovery, concentrated solar power, and nuclear.

The pilot plant design, procurement, fabrication, and construction are ongoing at the time of this publication. By the end of this 6-year project, the operability of the sCO2 power cycle will be demonstrated and documented starting with facility commissioning as a simple closed recuperated cycle configuration initially operating at a 500°C (932°F) turbine inlet temperature and progressing to a recompression closed Brayton cycle technology (RCBC) configuration operating at 715°C (1319 °F).
3D Heat Transfer Assessment of Full-Scale Inlet Vanes With Surface-Optimized Film Cooling: Part 1 — Experimental Results
Authors: Anthony R. J. , Clark J. P. , Finnegan J. , Johnson J. J.
Published: November 2019

Full-scale annular experimental evaluation of two different high pressure turbine first stage vane cooling designs was carried out using high frequency surface heat-flux measurements in the Turbine Research Facility at the Air Force Research Laboratory. A baseline film cooling geometry was tested simultaneously with a genetically optimized vane aimed to improve efficiency and part life. Part 1 of this two-part paper describes the experimental instrumentation, test facility, and surface heat flux measurements used to evaluate both cooling schemes. Part 2 of this paper describes the result of companion conjugate heat transfer posttest predictions, and gives numerical background on the design and modelling of both film cooling geometries.

Time-resolved surface heat flux data is captured at multiple airfoil span and chord locations for each cooling design. Area based assessment of surface flux data verifies the genetic optimization redistributes excessive cooling away from midspan areas to improve efficiency. Results further reveal key discrepancies between design intent and real hardware behavior. Elevated heat flux above intent in some areas led to investigation of backflow margin and unsteady hot gas ingestion at certain film holes. Analysis shows areas toward the vane inner and outer endwalls of the aft pressure side were more sensitive to reduced aft cavity backflow margin. In addition, temporal analysis shows film cooled heat flux having large high frequency fluctuations that can vary across nearly the full range of film cooling effectiveness at some locations. Velocity and acceleration of these large unsteady heat flux events moving near the endwall of the vane pressure side is reported for the first time. The temporal nature of the unsteady 3-D film cooling features are a large factor in determining average local heat flux levels. This study determined this effect to be particularly important in areas on real hardware along the HPT vane pressure side endwalls towards the trailing edge, where numerical assumptions are often challenged. Better understanding of the physics of the highly unsteady 3D film cooled flow features occurring in real hardware is necessary to accurately predict distress progression in localized areas, prevent unforeseen part failures, and enable improvements to turbine engine efficiency. The results of this two-part paper are relevant to engines in extended service today.
The Role of Mean Flame Anchoring on the Stability Characteristics of Syngas, Synthesis Natural Gas, and Hydrogen Fuels in a Turbulent Non-Premixed Bluff-Body Combustor
Authors: Baraiya Nikhil Ashokbhai , Chakravarthy Satynarayanan R.
Published: November 2019

A lab-scale bluff body combustor is mapped for its stability and flame dynamics of non-premixed flames. The characteristics are observed across variations in the fuel composition, as well as in the inlet flow rate. The combustor is seen to exhibit markedly different dynamics for each of the varied fuel compositions. This behavior is explained on the basis of mean flame stabilization behavior and on the combined effects of the fuel-jet momentum flux and global equivalence ratio. It is seen that the H2 flames primarily act as a pilot source for secondary combustion of either CO or CH4. Further, it is seen that, the high momentum flux associated with H2-CO mixtures result in combustion near the wall and outside the bluff-body shear layers at low inlet flow rates. Whereas, at high inlet flow rates, the mean heat release rate is seen to stabilize closer to the injection holes as well as extend to near the bluff-body shear layer. This marked difference in flame stabilization is seen to have a drastic effect on the nature of oscillations inside the chamber. This is contrasted to H2-CH4 (synthesis natural gas) flames that exhibit stabilization inside the bluff-body wake at high inlet flow rate. The difference between H2-CH4 and H2-CO flames with regards to combustion dynamics is then explained as a result of the flame stabilization behavior, which is seen to be different across the varied fuel compositions. While H2-CH4 flame exhibits the well-known large wake structures responsible for combustion instability, H2-CO flame exhibits no such structures, owing to their stabilization point. Further analysis using pressure fixed phase instants reveal the difference in nature of combustion dynamics across the tested fuel compositions and are justified using the spatial Rayleigh index map.
Investigation on Effect of Inlet Flow Turbulence on the Combustion Instability Using Simultaneous PIV and CH* Chemiluminescence in a Backward Facing Step Combustor
Authors: Pancharia Pankaj , Ramanan Vikram , Nagarajan Baladandayuthapani , Chakravarthy S. R.
Published: November 2019

The present study investigates the role of inlet turbulence intensity on the stability characteristics of a lab scale backward facing step combustor (BFS). Turbulence generator placed upstream of the flame holder is used to vary the turbulence levels. The present study utilizes simultaneous chemiluminescence, particle image velocimetry (PIV) and unsteady pressure fluctuation measurement are done in a time-resolved manner to study the role of inlet turbulence intensity on the flame-flow dynamics and identify different modes of combustion instability as a result of the same. The bifurcation plot with airflow rate, in terms of step-based Reynolds number (Re) as the control parameter, indicates a counterintuitive picture, whereby higher turbulence intensity postpones the onset of instability. The finding has been reported in the past by Nagarajan et. al [30], with the present work extending it. It is shown that the flow-flame structures at high (∼1000 Pa) and very high (>4000 Pa), conditions, the dynamics are significantly different across the same turbulence intensity at different equivalence ratio as well as at different turbulence intensities for the same equivalence ratio. Analysis of the flame-flow dynamics reveals the role of the extent of vortex initiated by acoustics and its orientation in forming an unsteady loop, whereby the vortex span and strength aids the flame to propagate upstream of the step, and the flame in-turn being responsible to sustain the large-scale vortex. This phenomenon is distinct from the conventional vortex sustained combustion instability, whereby the vortex is of the lower span and does not influence the upstream flow. The role of inlet turbulence intensity is seen to be more pronounced in the extent of the flame propagating upward, which then completes the fore-mentioned loop.
Development of a Gas Turbine Concept for Electric Power Generation in a Commercial Hybrid Electric Aircraft
Authors: Schneider Michael , Dickhoff Jens , Kusterer Karsten , Visser Wilfried , Stumpf Eike , Hofmann Jan-Philipp , Bohn Dieter
Published: November 2019

Civil aviation is growing 4.7% per annum. Alternative propulsion systems are necessary to reduce emissions causing global warming. The electrification of aircraft propulsion systems has the potential to use renewable energy and reduce the environmental footprint of aviation.

At present, full electric flight appears to be feasible for small aircraft only, due to the power density of batteries which is approximately 45-times lower than that of kerosene. Hybrid electric concepts may present a bridging technology towards more electrified aviation for short/mid-range aircraft. The hybrid concept combines the benefits of electrical power with conventional turboshaft engine technology.

Within the framework of the ‘HyFly’ project (supported by the German Luftfahrtforschungsprogramm LuFo V-3), a hybrid electric concept for a short/mid-range 19 PAX aircraft is studied. In this paper the results of a preliminary design exercise of the gas turbine used in this concept is presented.

Conventional aircraft gas turbines deliver maximum power only at take-off for a short period of time. At this power setting temperature and stress levels are at the extreme and dominate overall engine life consumption. In the HyFly concept, the gas turbine inlet temperature is kept constant during the entire flight. The engine is not driven into the extreme take-off power setting, resulting in a significant increase of engine life. The constant power setting also offers the opportunity to optimize efficiency especially around the base load point. For take-off and an emergency power rating, extra power is provided by batteries.

In this paper, a survey of existing engine technology is presented considering suitability for the concept. The impact of improvement of component efficiencies, increase in cycle pressure ratio and turbine inlet temperature, relative to the state-of-the-art, is analyzed using a B&B-AGEMA in-house gas turbine simulation tool. In addition, a weight model is presented for preliminary estimation of engine mass. Finally, requirements for the individual gas turbine sub-component design and performance are defined. This will build the basis for further component design.
CO Time-Histories During Oxy-Methane Combustion in a CO2 Environment
Authors: Pryor Owen M. , Ninnemann Erik , Vasu Subith
Published: November 2019

Carbon monoxide time-histories and ignition delay times were measured in carbon dioxide diluted methane mixtures behind reflected shockwaves. Experiments were performed around 2 atm for a temperature range between 1650–2000 K. The experiments were performed for a mixture of XCH4 = 0.5%, XO2 = 1.0%, XCO2 = 8.5%, XAr = 90.0%. The mixture was chosen to minimize energy release during the experiment and a minimum of 2 ms was recorded for all experiments. The carbon monoxide time-histories were measured using a tunable diode laser absorption spectroscopy technique and measuring the absorbance at two different wavelengths to isolate the impact of carbon monoxide on the absorbance. Carbon monoxide was measured at a wavelength of 4886.94 nm while the interfering species was measured at 4891.17 nm. Each experiment was performed twice, with the pressure and temperature before combustion being matched to within the experimental uncertainty of the two experiments. The ignition delay times were measured using OH* radical emission to determine the time-scales of the experiments. All experiments were compared to detailed chemical kinetic mechanisms that can be found in the literature. The experimental results show that the detailed mechanisms from the literature were able to accurately predict the general profile of the carbon monoxide time-histories but under-predicted maximum concentration of CO being formed at these conditions.
Role of sulfur in catalyzing fluorine atom fast etching of silicon with smooth surface morphology
Authors: Arora Priyanka , Nguyen Tam , Chawla Aseem , Nam Sang-Ki , Donnelly Vincent M.
Published: November 2019

Chemical reaction probabilities, defined as the number of silicon atoms removed per incident fluorine atom, have been investigated in mixtures of NF3 and SF6 plasmas in an inductively-coupled plasma reactor. Fluorine atom densities were measured by optical emission actinometry, and isotropic etching rates were measured by the degree of undercutting of SiO2-masked silicon by cross-sectional scanning electron microscopy. In addition, atomic force microscopy was used to examine surface morphology of etched Si surfaces. The F atom reaction probabilities derived from isotropic etching rates indicate an ∼30-fold higher reaction probability in SF6 plasmas compared with values in NF3 plasmas. Surfaces etched in SF6 plasmas were much smoother than those etched in NF3 plasmas. The addition of only 10% SF6 to an NF3 plasma produced a much higher reaction probability (∼5-fold) than in a pure NF3 plasma. This surprising enhancement of reaction probabilities for F with Si in SF6 plasmas is further investigated, based on the mechanism of adsorbed sulfur acting as a catalyst to greatly enhance the etching rate of Si. Dilute sulfur solutions in isopropyl alcohol were allowed to evaporate on the masked Si samples, depositing sulfur in relatively high concentrations near mask edges in ∼2 μm diameter periodic “strings of beads.” The sulfur-dosed sample etched several times faster at the center of each bead than a sample not exposed to sulfur that was placed side by side. The catalytic effect of sulfur is ascribed to an enhanced F sticking coefficient and/or decreased desorption rate on a surface covered with sulfur.
Temporary hearing threshold shift in harbor seals (Phoca vitulina) due to a one-sixth-octave noise band centered at 16 kHz
Authors: Kastelein Ronald A. , Helder-Hoek Lean , Cornelisse Suzanne , Huijser Léonie A. E. , Terhune John M.
Published: November 2019

Temporary hearing threshold shifts (TTSs) were investigated in two adult female harbor seals after exposure for 60 min to a continuous one-sixth-octave noise band centered at 16 kHz (the fatiguing sound) at sound pressure levels of 128–149 dB re 1 μPa, resulting in sound exposure levels (SELs) of 164–185 dB re 1 μPa2s. TTSs were quantified at the center frequency of the fatiguing sound (16 kHz) and at half an octave above that frequency (22.4 kHz) by means of a psychoacoustic hearing test method. Susceptibility to TTS was similar in both animals when measured 8–12 and 12–16 min after cessation of the fatiguing sound. TTS increased with increasing SEL at both frequencies, but above an SEL of 174 dB re 1 μPa2s, TTS was greater at 22.4 kHz than at 16 kHz for the same SELs. Recovery was rapid: the greatest TTS, measured at 22.4 kHz 1–4 min after cessation of the sound, was 17 dB, but dropped to 3 dB in 1 h, and hearing recovered fully within 2 h. The affected hearing frequency should be considered when estimating ecological impacts of anthropogenic sound on seals. Between 2.5 and 16 kHz the species appears equally susceptible to TTS.
Academic Bullying: Taking the Hallway Chats to the Level of Formalized Policy
Authors: Meaney Karen S. , Armstrong Sonya L.
Published: November 2019

Bullying in any context adversely affects individuals and organizations. Although bullying is typically conceived of as an issue specific to children in schoolyards, adult bullying is widespread, and the literature on workplace bullying continues to emerge as a scholarly focus. More specifically, academic bullying in higher-education institutions has been identified as an area of particular interest. Considerable literature exists that addresses definitions, characteristics, and effects of faculty bullying; however, the literature is scant regarding effective practice and policy that explicitly aim to prevent academic bullying. Furthermore, although this is a topic often discussed informally on university campuses, it does not appear to be addressed explicitly in formalized institutional policies. In this manuscript, the authors provide the findings of the initial stages of a content analysis aimed at exploring extant policy at public doctoral-granting universities. Implications and recommendations for policy development based on the results of this policy review are provided.