bluuebunny/crossref_metadata_2025 huggingface dataset:
Fuel and Combustion System Capabilities of GE’s F and HA Class Gas Turbines
Authors: Goldmeer Jeffrey , York William , Glaser Paul
Published: August 2017

The world is currently undergoing a shift in the power industry with an increase in the amount of electrical power being generated from natural gas. This is being driven, in part, by the increase in availability of natural gas derived from shale gas and the reduction in global natural gas prices. In parallel, there is a second trend; a shift of new gas turbines installations to higher efficiency F and HA-class gas turbine combined cycle platforms. Supporting these industry trends, GE’s DLN 2.6+ combustion system, which is available for the 7F, 9F, 7HA, and 9HA gas turbines offers a high degree of operational and fuel flexibility. The latest evolution of this combustion technology for GE’s 7F gas turbines has been commissioned on 25 units, including new units and upgrades to existing turbines. The increased fuel and operational flexibility of this system is aided by GE’s advanced control systems that includes a high fidelity digital twin. This paper details recent developments of the DLN 2.6+ combustion system as well as validation examples for both the DLN 2.6+ and the digital twin controls system.
A Study of Source Term Model for Full Coverage Film Cooling Simulation
Authors: Zhang Yufang , Wang Ke
Published: August 2017

Full-coverage film cooling, based on use of closely spaced inclined small diameter cylindrical holes, is considered as a very efficient cooling approach for modern combustion chambers. However, a CFD-based thermal analysis of such components is very expensive if mesh is generated in numerous cooling holes. In order to reduce the computational cost, several models have been developed by researchers. Among them, source term model is one of the most potential models. In this model, a film cooling hole is replaced by a mass source and a mass sink in the fluid domain, and an energy sink is used to simulate the convective cooling inside hole.

In this paper, the source term model was used for RANS simulation of a multi-perforated plate case, and the effect of grid setup was analyzed. It has been concluded that the height of first prism layer has an important effect on the numerical results, whereas effect of maximum grid size on coupled walls is relatively small. Then, the source term model was used for numerical simulations of a single dome combustor case. Numerical results of flow split and pressure losses in non-reacting case agreed well with experimental results. In reacting case, a good agreement between numerical and experimental results, including liner temperature and pressure loss, was also obtained.
Time-Resolved Three-Component PIV Investigation of Flashback in Stratified Flames
Authors: Ranjan Rakesh , Clemens Noel
Published: August 2017

Flashback of stratified swirl flames in a model combustor with an axial swirler and a centerbody were investigated at 1 atm and 3 atm. The global equivalence ratio for the flashback conditions is kept at 0.63 and 0.85 for atmospheric and elevated pressure experiments respectively. The bulk velocity of the fuel-air mixture during the flashback is set to 2.5 m/s for all experiments. Stratification in the flow is achieved by injecting methane through the fuel-ports on the swirler vanes. The nature of stratification is assessed by conducting planar laser induced fluorescence (PLIF) experiments in non-reacting flows. Acetone was used as fuel tracer which allowed the calculation of spatial distribution of equivalence ratio in the mixing tube. The ensemble-averaged distribution confirmed the radial stratification in the mixing tube. Instantaneous PLIF measurements showed intermittent presence of fuel rich structures close to the center-body. For flashback experiments, time-resolved three-component PIV and simultaneous chemiluminescence imaging at 4kHz were applied to investigate the interaction between the flame and the stratified flow. The global behavior of flashback was characterized by a large flame tongue swirling around the center-body during upstream propagation. The flame tongue stopped propagating at an intermediate location and kept swirling around the center-body. A comparison with fully premixed flashback showed that the stratified flame was more wrinkled and the radial extent of stratified flame brush was larger than the fully premixed cases. Reacting flow experiments at elevated pressure showed highly wrinkled flame surface due to the presence of turbulence and local variation in equivalence ratio.
Probabilistic Fracture Mechanics for Heavy Duty Gas Turbine Rotor Forgings
Authors: Kadau Kai , Gravett Phillip W. , Amann Christian
Published: August 2017

We developed and successfully applied a direct simulation Monte-Carlo scheme to quantify the risk of fracture for heavy duty rotors commonly used in the energy sector. The developed Probabilistic Fracture Mechanics high-performance computing methodology and code ProbFM routinely assesses relevant modes of operation for a component by performing billions of individual fracture mechanics simulations. The methodology can be used for new design and life-optimization of components, as well as for the risk of failure quantification of in service rotors and their re-qualifications in conjunction with non-destructive examination techniques, such as ultrasonic testing. The developed probabilistic scheme integrates material data, ultra-sonic testing information, duty-cycle data, and finite element analysis in order to determine the risk of failure. The methodology provides an integrative and robust measure of the fitness for service and allows for a save and reliable operation management of heavy duty rotating equipment.
The Influence of Lubricant Supply Conditions and Bearing Configuration on the Performance of (Semi) Floating Ring Bearing Systems for Turbochargers
Authors: San Andrés Luis , Yu Feng , Gjika Kostandin
Published: August 2017

Engine oil lubricated (semi) floating ring bearing (S)FRB systems in passenger vehicle turbochargers (TC) operate at temperatures well above ambient and must withstand large temperature gradients that can lead to severe thermo-mechanical induced stresses. Physical modeling of the thermal energy flow paths and an effective thermal management strategy are paramount to determine safe operating conditions ensuring the TC component mechanical integrity and the robustness of its bearing system. On occasion, the selection of one particular bearing parameter to improve a certain performance characteristic could be detrimental to other performance characteristics of a TC system. The paper details a thermohydrodynamic model to predict the hydrodynamic pressure and temperature fields and the distribution of thermal energy flows in the bearing system. The impact of the lubricant supply conditions (pressure and temperature), bearing film clearances, oil supply grooves on the ring ID surface are quantified. Lubricating a (S)FRB with either a low oil temperature or a high supply pressure increases (shear induced) heat flow. A lube high supply pressure or a large clearance allow for more flow through the inner film working towards drawing more heat flow from the hot journal, yet raises the shear drag power as the oil viscosity remains high. Nonetheless, the peak temperature of the inner film is not influenced much by the changes on the way the oil is supplied into the film as the thermal energy displaced from the hot shaft into the film is overwhelming. Adding axial grooves on the inner side of the (S)FRB improves its dynamic stability, albeit increasing the drawn oil flow as well as the drag power and heat flow from the shaft. The predictive model allows to identify a compromise between different parameters of groove designs thus enabling a bearing system with a low power consumption.
Large-Eddy Simulation of Roughened NACA65 Compressor Cascade
Authors: Joo Jongwook , Medic Gorazd , Sharma Om
Published: August 2017

Large eddy simulations over a NACA65 compressor cascade with roughness were performed for multiple roughness heights. The experiments show flow separation as airfoil roughness is increased. In LES computations, surface roughness was represented by regularly arranged discrete elements using guidelines from Schlichting. Results from wall-resolved LES indicate that specifying an equivalent sandgrain roughness height larger than the one in experiments is required to reproduce the same effects observed in experiments. This highlights the persisting uncertainty with matching the experimental roughness geometry in LES computations, pointing towards surface imaging and digitization as a potential solution. Some initial analysis of flow physics has been conducted with the aim of guiding the RANS modeling for roughness.
Assessment of Biofuels/Jet A-1 Blends to Meet Cold Start and Altitude Relight Requirements
Authors: Jean Joël , Fossi Alain , deChamplain Alain , Paquet Bernard
Published: August 2017

The certification of new fuels for aircraft applications requires preliminary extensive investigations for the most critical combustion phases. Especially, cold start and altitude relight of an aircraft gas turbine and thus its operating envelope could potentially be affected by the use of new fuels. To assess such effects, a test rig is designed using two different air-assist pressure atomizers. The ignition envelopes for seven different blends with a minimum of 50% Jet A-1 are compared to that of pure Jet A-1. Variation in combustor aerodynamics is accounted for by considering various pressure drops across the combustion chamber, and the ignition envelope is retrieved by finding the minimum and maximum fuel-air ratios leading to a successful ignition event. Effects of fuel physical properties, pressure and temperature which are critical factors for a successful ignition event are also investigated. To simulate cold start and altitude relight, a heat exchanger is used to cool air and fuel, while a bleed valve mounted between the combustor and a steam ejector is used to regulate the operating pressure. Globally, cold start for temperatures ranging from 10°C to −40°C, and the altitude relight for operating altitudes ranging from 4 572 m to 10 668 m, show that the lean limit for the seven blends of fuels are in some cases as good as, and for the other cases better than the pure Jet A-1. Some discrepancies are noted for altitude relight at 9 161 m and 10 688 m, for some biofuels with a minimum of 50% Jet A-1, suggesting a need of real engine testing before final approval. Apart from these isolate cases, almost all the biofuel blends with a minimum of 50% Jet A-1 are truly “drop-in” fuels and should qualify for aviation use since they do not present any negative impact on the typical engine components used in the test program. Furthermore, ASTM D1655 requirements are also achieved for all test conditions. Biofuel blends with less than 50% Jet A-1 are found to always be better than the biofuel blends with minimum of 50% Jet A-1 and, it is recommended to modify ASTM D1655 to include them as acceptable “drop-in” fuels.
Development and Evaluation of Foreign Object Damage Resistant Ceramic Matrix Composites
Authors: Iwano Craig , Sullivan Brian , Hoo Fatt Michelle
Published: August 2017

Under a Phase II Navy SBIR program, Materials Research & Design (MR&D) performed an integrated analytical, fabrication and experimental program in order to develop foreign object damage (FOD) resistant silicon carbide (SiC) fiber-based ceramic matrix composites (CMCs), specifically 2D tape SiC/SiC. MR&D believes strongly that the most efficient approach towards the development of FOD-resistant CMCs is to develop a mathematical simulation of the impact event which can be correlated to measured responses and observed failures. Once correlated with available test data, the developed math model was used as part of an Integrated Computational Materials Engineering (ICME) approach to analytically investigate modifications to baseline CMC material in an attempt to identify which properties best influenced FOD resistance. The best candidate material modifications were then selected for fabrication and experimental validation. When considering all of the numerical and empirical data (visible damage, rebound velocity (energy absorption), strain data, NDE inspection and residual strength testing), all of the MR&D-proposed material modifications demonstrated improved FOD resistance when compared to the baseline CMC material.
Economic Viability of On-Line Compressor Washing for Different Rated Capacity
Authors: Musa Gali , Igie Uyioghosa , Pilidis Pericles , Gowon Sule
Published: August 2017

On-line compressor washing has shown to relatively improve engine performance by decelerating the rate of engine degradation due to fouling during operation. There is a number of influencing parameters that determine the economic benefit, some of which includes the frequency of washing, the effectiveness of washing liquid and the size of the engine or power output produced.

This study, unlike others, explores the cost-benefit analysis, focusing on the viability of compressor washing for various gas turbine engines or rated capacities, ranging from a 5MW single machine to a 300MW unit. Fouling degradation trend obtained from actual machine operation have been implemented and the application of different washing frequencies and recoveries of lost power shows the significantly higher return on investment for the larger engines in comparison to the smaller engines. This is partly due to the fact that the washing equipment cost, though increases with engine size, does not increase proportionally. Another contributing factor is the cost penalty per MW when the same level of degradation is implemented for all the engines.

Some of the key aspects captured in this study are the capital and maintenance cost used, that relates to the different engine sizes, therefore ensuring a more indicative basis for comparing the viability of the different engines. This also includes the estimation of washing liquid utilised based on their respective typical mass flows.

When the number of engines increases to 4 for a given operations, the return on investment increases by a factor of 3.5. This is possible as one wash unit can be applied to more than one engine within proximity. Higher return on investment is achieved when more than one relatively small engine is used to obtain a higher total power output. This is about 1.7 times higher for four 63MW engines versus one 255MW, as relatively cheaper washing equipment is implemented for the same total operational capacity. The study also shows that on-line washing is not always viable for electric power generation. This is observed for smaller light-duty engines, especially in situations when the level of fouling is relatively low.
Direct Fired Oxy-Fuel Combustor for sCO2 Power Cycles: 1MW Scale Design and Preliminary Bench Top Testing
Authors: Delimont Jacob , McClung Aaron , Portnoff Marc
Published: August 2017

Direct fired oxy-fuel combustion as a heat source for supercritical carbon dioxide (sCO2) power cycles is a promising method for providing the needed thermal energy input. The method of combustion has the potential to provide efficient power generation with integrated carbon capture at up to 99% of generated CO2. One of the highest efficiency power cycles being considered for sCO2 cycles in the recompression cycle. In the recompression sCO2 power cycle, the amount of energy recovered from the recuperation is roughly five times the energy added via the combustor. Because of this high degree of recuperation in sCO2 power cycles, the inlet temperature of the combustor is much higher than a more traditional combustor design. This elevated combustor temperature leads to some unique design challenges and approaches which are quite different from a traditional combustion system. A combustor designed for these conditions has never been built, and thus the design of the combustor discussed in this paper started from a clean slate.

This necessitates a large degree of fundamental research which might not be necessary for a more well understood traditional combustor design process. Building on previous thermodynamic and chemical kinetics studies, a reduced order reaction kinetics model was used with ANSYS CFX software to explore various auto-ignition type combustor geometries. A discussion of some geometries and the modelling techniques used is presented. Various injector configurations were examined and metrics were used to compare the various configurations. By utilizing the CFD flow field results, a preliminary design for a 1MW-class oxy-fuel combustor was developed.

In the past, little experimental research has been conducted on combustion within carbon dioxide at pressures above 200 bar. In order to confirm the validity of the auto-ignition style combustor a small bench top test rig was constructed to test the oxy-fuel combustion at the full pressure and temperature. This system was designed to validate some of the fundamental properties of the combustion. This includes a gas sampling system and a measurement of auto-ignition delay. Preliminary, data from a bench top scale, sCO2 oxy-fuel combustor experiment will be presented.

The results from this work will enable future development of sCO2 power cycles which enable 99% carbon capture, while maintaining overall cycle efficiency which is competitive with natural gas combined cycle power plants.
Technology Demonstration of a Splittered Transonic Rotor With a Downstream Variable Geometry Tandem Stator
Authors: Bauinger Sabine , Gannon Anthony J. , Hobson Garth V. , Terrell Aaron D.
Published: August 2017

This paper presents the experimental results of an advanced concept transonic compressor stage with a splittered rotor and a downstream variable geometry tandem stator. Two blisks make up the stator, with the first containing the upstream blades and the second the downstream. The downstream row is fixed while the upstream row is able to rotate about the machine axis. This was found to be a very simple and robust method of adjusting the geometry as it had only one moving part in contrast to the complex mechanisms required to move individual blades within a traditional row. Five different relative positions between the forward and aft blade rows were experimentally investigated in order to find the ideal stator positions for different operating conditions of an engine. It was found that the peak efficiency, maximum flow rate and maximum flow range of the entire stage could be adjusted by moving the single upstream stator blisk. This variable tandem stator configuration could thus eliminate the need for inlet guide vanes (IGV’s) with variable flaps in the first compressor stage, which are typically found in many military engines. This removal of a blade row could lead to lighter and less complex engine. The variable stator concept may also be applicable to the high pressure stages during startup where a high mass flow rate would reduce the need for bleed systems. Results over a wide speed range from subsonic to transonic are presented and the geometry is available upon request as a test case.
Turbine Shroud Heat Transfer and Cooling With Blade Rotation: Part I — Forward, Backward and Lateral Injection
Authors: Tamunobere Onieluan , Acharya Sumanta
Published: August 2017

This is the first in a two-part series of an experimental film cooling study on a gas turbine shroud with a blade rotation speed of 1200 RPM. In this part of the study, the effect of forward, backward and lateral injection on the shroud heat transfer and cooling behavior is investigated. The shroud with a staggered hole arrangement and a hole pitch to diameter ratio of 4.0, consists of holes angled at 45° to the surface. Four hole configurations using inline and lateral coolant injection methods are utilized in this study. The first configuration consists of streamwise and forward facing holes inclined at 45 degrees to the surface (ϕ = 0°). The second configuration consists of backward facing holes also inclined at 45 degrees to the surface (ϕ = 180°). The third and fourth configurations consist of lateral injection with a surface angle of 45 degrees in the direction of blade rotation (ϕ = 90°) and opposite the direction of blade rotation (ϕ = 270°), respectively. The heat transfer coefficient is reported for the no-coolant case and measurements of the heat transfer coefficient and film cooling effectiveness are reported for each configuration at nominal blowing ratios of 0.5, 1.0, 1.5 and 2.0 using liquid crystal thermography. The results show that in-line injection performs better than lateral injection at low blowing ratios and the reverse is true at higher blowing ratios. Backward injection does show higher laterally averaged effectiveness with increased spreading in the vicinity of the coolant holes than forward injection. With a compact coolant hole arrangement, this results in higher area averaged effectiveness for backward injection than forward injection. With increased lateral spreading of the coolant in the hole region, lateral injection results in higher peak effectiveness values than inline injection. Nevertheless, lateral injection does not have the axial penetration of inline injection and as such leaves regions of the shroud downstream of the coolant holes vulnerable.
LPC Blade and Non-Axisymmetric Hub Profiling Optimization Using Multi-Fidelity Non-Intrusive POD Surrogates
Authors: Benamara Tariq , Breitkopf Piotr , Lepot Ingrid , Sainvitu Caroline
Published: August 2017

The present contribution proposes a Reduced Order Model based multi-fidelity optimization methodology for the design of highly loaded blades in low pressure compressors. Environmental, as well as, economical limitations applied to engine manufacturers make the design of modern turbofans an extremely complex task. A smart compromise has to be found to guarantee both a high efficiency and a high average stage loading imposed for mass reduction constraints, while satisfying stability requirements.

The design of compressor blades, usually involves at the same time a dedicated parametrization set-up in highdimensional space and high-fidelity simulations capturing, at least, efficiency and stability as most impacting phenomena. Despite recent advances in the high-performance computing area, introducing high-fidelity simulations into automated optimization, or even surrogate assisted optimization, loops still stands as a endeavor for engineers. In this framework, the proposed methodology is based on multi-fidelity surrogate models capable of representing the physics at hand in reduced spaces inferred from both precise, albeit costly, high-fidelity simulations and abundant, yet less accurate lower-fidelity data. Finally, we investigate the coupling of the proposed hierarchised multi-fidelity non-intrusive Proper Orthogonal Decomposition based surrogates with an evolutionary algorithm to reduce the number of high-fidelity simulation calls towards the targeted optimum.
Turbine Shroud Heat Transfer and Cooling With Blade Rotation: Part II — Effect of Trenched Holes With Forward, Backward and Lateral Injection
Authors: Tamunobere Onieluan , Acharya Sumanta
Published: August 2017

This is the second in a two part series investigating heat transfer and film cooling on a gas turbine shroud with a blade rotation speed of 1200 RPM. In this paper, the effect of coolant injection on a shroud using forward, backward and laterally oriented holes embedded in trenches is studied. Four injection configurations (θ = 45° and ϕ = 0°, 90°, 180°, 270°), each with cooling holes arranged in four rows in a staggered pattern are tested. Each row of cooling holes is embedded in a trench with a trench width of 3 hole diameters and a trench depth of 0.75 hole diameter. For each configuration, detailed heat transfer coefficient and film cooling effectiveness measurements are reported for nominal blowing ratios of 0.5, 1.0, 1.5 and 2.0. The results show that trenching increases the local film cooling effectiveness in and immediately around the trenches in all configurations studied. Trenching the coolant holes also does have varying effects on the heat transfer coefficients based on the direction of coolant injection. Generally, trenching does increase the heat transfer coefficient when compared to both the no-coolant and baseline injection cases especially in the entrenched region. Trenching does provide the best results for forward injection where the reduced jet momentum results in a more two dimensional and better lateral coolant spread when compared to the baseline case. With the increased lateral coolant spread does come an increase in the overall film cooling effectiveness but also a corresponding increase in the heat transfer coefficients in the near-trench region as it acts as a turbulence promoter. Embedding backward facing holes in trenches does result in higher local film cooling effectiveness in and around the trenches. However, trenching does decreases the persistence and penetration of the coolant coverage in the streamwise direction. Trenching also results in higher than baseline heat transfer values for backward injection. Trenching also does improve the cooling effectiveness in the trenches for both lateral injection methods.
A Dynamic Model for the Evaluation of Aircraft Engine Icing Detection and Control-Based Mitigation Strategies
Authors: Simon Donald L. , Rinehart Aidan W. , Jones Scott M.
Published: August 2017

Aircraft flying in regions of high ice crystal concentrations are susceptible to the buildup of ice within the compression system of their gas turbine engines. This ice buildup can restrict engine airflow and cause an uncommanded loss of thrust, also known as engine rollback, which poses a potential safety hazard. The aviation community is conducting research to understand this phenomena, and to identify avoidance and mitigation strategies to address the concern. To support this research, a dynamic turbofan engine model has been created to enable the development and evaluation of engine icing detection and control-based mitigation strategies. This model captures the dynamic engine response due to high ice water ingestion and the buildup of ice blockage in the engine’s low pressure compressor. It includes a fuel control system allowing engine closed-loop control effects during engine icing events to be emulated. The model also includes bleed air valve and horsepower extraction actuators that, when modulated, change overall engine operating performance. This system-level model has been developed and compared against test data acquired from an aircraft turbofan engine undergoing engine icing studies in an altitude test facility and also against outputs from the manufacturer’s customer deck. This paper will describe the model and show results of its dynamic response under open-loop and closed-loop control operating scenarios in the presence of ice blockage buildup compared against engine test cell data. Planned follow-on use of the model for the development and evaluation of icing detection and control-based mitigation strategies will also be discussed. The intent is to combine the model and control mitigation logic with an engine icing risk calculation tool capable of predicting the risk of engine icing based on current operating conditions. Upon detection of an operating region of risk for engine icing events, the control mitigation logic will seek to change the engine’s operating point to a region of lower risk through the modulation of available control actuators while maintaining the desired engine thrust output. Follow-on work will assess the feasibility and effectiveness of such control-based mitigation strategies.
Real Time Conditioning Monitoring for Failure Prediction
Authors: Franco-Piña J. Alejandro , Contreras Luis , Jauregui Juan C.
Published: August 2017

Nowadays, the growth in the diameter of the rotors and the power capacity of the machinery require the application of constant monitoring to predict failures and reduce maintenance activities. These activities prevent emergency stops and failures that require the replacement of components; however, these operations involve a high cost.

The system presented in this paper integrates a fast data processing method that can analyze monitoring signals in real-time. The overall system includes a set of sensors for the measurement of acceleration, angular velocity, temperature, voltage, electrical current, and oil quality. The system presented is able to produce a frequency spectrum with a length of 8192 points. The FFT module was implemented in a FPGA (Field Programmable Gate Array) and it generates in real time, the frequency spectrum. This system adjusts the dominant frequencies to the wind turbine velocity.
Novel Curvature-Based Airfoil Parameterization for Wind Turbine Application and Optimization
Authors: Balasubramanian Karthik , Turner Mark G. , Siddappaji Kiran
Published: August 2017

The direct proportionality of streamline curvature to the pressure gradient normal to it causes the dependence of surface pressure loading on geometry curvature. This allows for the use of geometry curvature as a direct and aerodynamically meaningful interface to modify and improve performance of wind turbine sections. A novel blade parameterization technique driven by specification of meanline second derivative and a thickness distribution is presented. This technique is implemented as T-Blade3 which is an already existing in-house open-executable. The second derivative which is indicative of curvature, is used, enabling exploration of a large design space with minimal number of parameters due to the use of B-spline control points, capable of producing smooth curves with only a few points. New thickness and curvature control capabilities have been added to TBlade3 for isolated and wind turbine airfoils. The parameterization ensures curvature and slope of curvature continuity on the airfoil surface which are critical to smooth surface pressure distribution. Consequently, losses due to unintentional pressure spikes are minimized and likelihood of separation reduced. As a demonstration of the parameterization capability, Multi-Objective optimization is carried out to maximize wind turbine efficiency. This is achieved through an optimization tool-chain that minimizes a weighted sum of the drag-to-lift ratios over a range of angles of attack and sectional Reynolds numbers using a Genetic Algorithm. This allows for radial Reynolds number variation and ensures efficiency of wind turbine blade with twist incorporated. The tool-chain uses XFOIL to evaluate drag polars. This is implemented in MATLAB and Python in serial and in parallel with the US Department of Energy optimization system, DAKOTA. The Python and DAKOTA versions of the code are fully open-source. The NREL S809 horizontal axis wind turbine laminar-flow airfoil which is 21% thick has been used as a benchmark for comparison. Hence, the optimization is carried out with the same thickness-to-chord ratio. Drag coefficient improvement ranging from 17% to 55% for Cl between 0.3 and 1 was achieved.
The Effect of External Casing Impingement Cooling Manifold Standoff Distance on Casing Contraction for Thermal Control of Blade Tip Clearance
Authors: Choi Myeonggeun , Gillespie David R. H. , Lewis Leo V.
Published: August 2017

Thermal closure of the engine casing is widely used to minimize undesirable blade tip leakage flows thus improving jet engine performance. This may be achieved using an impingement cooling scheme on the external casing wall, provided by manifolds attached to the outside of the engine. The assembly tolerance of these components leads to variation in the standoff distance between the manifold and the casing and its effects on casing contraction must be understood to allow build tolerance to be specified.

For cooling arrangements with promising performance, the variation in closure with standoff distance of z/d = 1–6 were investigated. A cooling manifold, typical of that adopted by several engine companies, incorporating three different arrays of short cooling holes (chosen from previous study by Choi et al. (2016)) and thermal control dummy flanges were considered. A series of heat transfer tests using a transient liquid crystal technique were undertaken to measure spatially resolved heat transfer coefficient of a baseline sparse jet array. The experimental heat transfer results validated the extensive numerical predictions using RANS realizable k-epsilon turbulence model. The associated casing contraction was inferred from a finite element analysis using these distributions as the external casing thermal boundary condition. The flow in the system can be modulated to match the closure at different engine operating conditions, the relationship between thermal closure and coolant mass flow rates, inferred from the averaged jet Reynolds numbers assuming uniform distribution between cooling holes was predicted. Typical contractions of 0.5–2.2mm are achieved from the 0.02–0.35kg/s of the current casing cooling flows.

The variation in heat transfer coefficient observed with standoff distance is much lower for the sparse array investigated compared to a previous designs employing arrays typical of blade cooling configurations. The reason for this is explained through interrogation of the local flow field and resultant heat transfer coefficient. This implies acceptable control of the circumferential uniformity of case cooling can be achieved with relatively large assembly tolerance of the manifold relative to the casing.
Numerical Examination of Lock-In Hypothesis of Non-Synchronous Vibration in an Axial Compressor
Authors: Gan Jiaye , Im Hong-Sik , Zha Ge-Cheng
Published: August 2017

This paper examines the lock-in hypothesis of non-synchronous vibration (NSV) in a high speed multistage axial compressor. The unsteady Reynolds-averaged Navier-Stokes (URANS) equations and modal approach based structural dynamic equations are solved. A low diffusion E-CUSP approximate Riemann solver with a 3rd order WENO scheme for the inviscid fluxes and a 2nd order central differencing for the viscous terms are employed. The structural vibration of the blades are solved by a set of modal equations that are fully coupled with the flow equation. The rigid blade simulations are conducted to examine the main driver of NSV. A 1/7th annulus sector of IGV-rotor-stator is used with a time shifted phase lag BC at circumferential boundaries. A dominant excitation frequency caused by the traveling tip vortices are captured. The excitation frequency is not on the engine order. The simulation is then switched to fluid structure interaction that allows the blades to vibrate freely under the flow excitations. The matching of aerodynamic forcing frequency with the structure response frequency seems indicating that the NSV of this compressor is a limit cycle oscillation (LCO) excited by aerodynamic forcing, not caused by flow frequency/phase locked to structural frequency. The rotating speed is varied within a RPM range, in which the rig test detected the NSV. The unsteady flows with rigid blades are simulated first at several RPMs. The simulation indicates that the structure response follows the frequency of the flow excitations existing in the rigid blades. At least under the simulated conditions, the NSV does not appear to be a lock-in phenomenon, which has the flow frequency lock-in to the structure natural frequency.
Experimental and Computational Characterization of Flow Rates in a Multiple-Passage Gas Turbine Combustor Swirler
Authors: Erdmann Timothy J. , Burrus David L. , Briones Alejandro M. , Stouffer Scott D. , Rankin Brent A. , Caswell Andrew W.
Published: August 2017

One of the challenges of gas turbine combustor research is to accurately measure and model air mass flow rates through complex air injection schemes. Accurate measurements and computations of air mass flow rates are necessary for determining air and fuel distributions, which influence a range of combustor operation and performance characteristics. Experimental and computational studies were performed on a representative gas turbine combustor swirler. The swirler geometry consists of four component flows: two co-rotating annular axial swirls, one radial swirl, and cooling on the periphery of the swirler. The purpose of this study is to compare measured and computed air mass flow rates in a realistic swirler with a complex geometry and to quantify the magnitude of the interaction effects between air passages. The measurements of the air mass flow rates were performed using a calibrated air flow stand. The computations were performed using commercial Computational Fluid Dynamics (CFD) tools. Comparisons between measured and computed air mass flow rates show good agreement for the individual and total flow configurations. Significant interaction effects among the swirling flows are observed when all of the air passages are open. The radial swirl mass flow rate decreases by 2.7% and the outer axial swirl mass flow rate increases by 3.8% when the individual component flow configuration is compared to the total flow configuration. The computed mass flow rates demonstrate that the interactions among the swirl flows create a significant change in mass flow distribution within the swirler.
Absolute and Convective Instabilities of a Separated Boundary Layer Near the Leading Edge of an Aerofoil
Authors: Sarkar S. , Jadhav K. S.
Published: August 2017

Present work describes the stability analysis of a separated boundary layer over a constant thickness aerofoil subjected to an impulse at the boundary for varying angles of attack (α1) and tail flap deflections (β1), where, the Reynolds number (Rec) based on chord is 1.6 × 105 and the inlet free-stream turbulence (fst) being 1.2%. The features of the boundary layer are investigated through flow field measurement by a planar particle image velocimetry (PIV) and hotwire anemometer. The response to the impulse can grow either in space and time. The Orr-Sommerfield (O-S) equation has been solved, where the mean velocity field is obtained from the experiment. Criteria following Huerre and Monkewitz [1] are used here to decide the type of instability. It has been observed that the separated boundary layer near the leading edge is absolutely unstable for low angles of attack, whereas, it is convectively unstable for higher angles of attack, when the Kelvin-Helmholtz instability is bypassed. Further, it shows a convective instability for flap angles of ±30 deg.
The Increasing Complexity of Hot Corrosion
Authors: Shifler David A.
Published: August 2017

It has been conjectured that if sulfur in fuel is removed, engine materials will cease to experience attack from hot corrosion, since this sulfur has been viewed as the primary cause of hot corrosion and sulfidation. Historically, hot corrosion has been defined as an accelerated degradation process that generally involves deposition of corrosive species (e.g., sulfates) from the surrounding environment (e.g., combustion gas) onto the surface of hot components, resulting in destruction of the protective oxide scale. Most papers in the literature, since the 1970s, consider sodium sulfate salt as the single specie contributing to hot corrosion.

Recent Navy standards for Navy F-76 and similar fuels have dropped the sulfur content down to 15 parts per million (ppm). Most observers believe that the removal of sulfur will end hot corrosion events in the Fleet. However, the deposit chemistry influencing hot corrosion is known to be much more complex consisting of multiple sulfates and silicates. Sulfur species may still enter the combustion chamber via ship’s air intake, which may include seawater entrained in the air. In addition to sodium sulfate, seawater contains magnesium, calcium and potassium salts, and atmospheric contaminants that may contribute to hot corrosion. This paper will cover some of the revised understanding of hot corrosion and consider other possible contaminants that could further complicate a full understanding of hot corrosion.
Elimination of the male reproductive tract in the female embryo is promoted by COUP-TFII in mice
Authors: Zhao Fei , Franco Heather L. , Rodriguez Karina F. , Brown Paula R. , Tsai Ming-Jer , Tsai Sophia Y. , Yao Humphrey H.-C.
Published: August 2017

The makings of the reproductive tract

Every embryo, regardless of its sex, contains both male and female primitive reproductive tracts before sexual differentiation. To establish a sex-specific reproductive system, female embryos need to remove the components of male tracts. The general consensus contends that removal of the male tracts occurs by default, a passive outcome owing to a lack of testis-derived androgens. Working in mice, Zhao
et al.
discovered that this process instead was actively promoted by the transcription factor COUP-TFII (see the Perspective by Swain). Without the action of this factor, embryos retained male reproductive tracts, independently of androgen action. These findings unveil unexpected mechanisms underlying the sexually dimorphic establishment of reproductive tracts.

Science
, this issue p.
717
; see also p.
648
Zones, spots, and planetary-scale waves beating in brown dwarf atmospheres
Authors: Apai D. , Karalidi T. , Marley M. S. , Yang H. , Flateau D. , Metchev S. , Cowan N. B. , Buenzli E. , Burgasser A. J. , Radigan J. , Artigau E. , Lowrance P.
Published: August 2017

Beating bands in substellar atmospheres

Brown dwarfs are objects with masses that are between those of large planets and small stars. They share many features with gas giant planets, particularly conditions in their atmospheres. Apai
et al.
analyzed how the infrared brightness of three brown dwarfs changes over time. Several perplexing features can be explained if bands of clouds rotating within their atmospheres generate beat patterns. Such bands are seen in optical images of Jupiter but best match infrared images of Neptune. The results shed light on the atmospheric physics of brown dwarfs and gas giant planets around the Sun and other stars.

Science
, this issue p.
683
Collaborative environmental governance: Achieving collective action in social-ecological systems
Authors: Bodin Örjan
Published: August 2017

Collaborative governance

By its nature, environmental governance requires collaboration. However, studies have shown that various types of stakeholders often lack the willingness to deliberate and contribute to jointly negotiated solutions to common environmental problems. Bodin reviews studies and cases that elucidate when, if, and how collaboration can be effective and what kind of environmental problems are most fruitfully addressed in this way. The piece provides general conclusions about the benefits and constraints of collaborative approaches to environmental management and governance and points out that there remain substantial knowledge gaps and key areas where more research is needed.

Science
, this issue p.
eaan1114
A pathology atlas of the human cancer transcriptome
Authors: Uhlen Mathias , Zhang Cheng , Lee Sunjae , Sjöstedt Evelina , Fagerberg Linn , Bidkhori Gholamreza , Benfeitas Rui , Arif Muhammad , Liu Zhengtao , Edfors Fredrik , Sanli Kemal , von Feilitzen Kalle , Oksvold Per , Lundberg Emma , Hober Sophia , Nilsson Peter , Mattsson Johanna , Schwenk Jochen M. , Brunnström Hans , Glimelius Bengt , Sjöblom Tobias , Edqvist Per-Henrik , Djureinovic Dijana , Micke Patrick , Lindskog Cecilia , Mardinoglu Adil , Ponten Fredrik
Published: August 2017

Modeling the cancer transcriptome

Recent initiatives such as The Cancer Genome Atlas have mapped the genome-wide effect of individual genes on tumor growth. By unraveling genomic alterations in tumors, molecular subtypes of cancers have been identified, which is improving patient diagnostics and treatment. Uhlen
et al.
developed a computer-based modeling approach to examine different cancer types in nearly 8000 patients. They provide an open-access resource for exploring how the expression of specific genes influences patient survival in 17 different types of cancer. More than 900,000 patient survival profiles are available, including for tumors of colon, prostate, lung, and breast origin. This interactive data set can also be used to generate personalized patient models to predict how metabolic changes can influence tumor growth.

Science
, this issue p.
eaan2507
Ectopic calcification in pseudoxanthoma elasticum responds to inhibition of tissue-nonspecific alkaline phosphatase
Authors: Ziegler Shira G. , Ferreira Carlos R. , MacFarlane Elena Gallo , Riddle Ryan C. , Tomlinson Ryan E. , Chew Emily Y. , Martin Ludovic , Ma Chen-Ting , Sergienko Eduard , Pinkerton Anthony B. , Millán José Luis , Gahl William A. , Dietz Harry C.
Published: August 2017

Ectopic calcification in PXE integrates both local and systemic perturbations of extracellular ATP metabolism and can be attenuated with a TNAP inhibitor.
VP4- and VP7-specific antibodies mediate heterotypic immunity to rotavirus in humans
Authors: Nair Nitya , Feng Ningguo , Blum Lisa K. , Sanyal Mrinmoy , Ding Siyuan , Jiang Baoming , Sen Adrish , Morton John M. , He Xiao-Song , Robinson William H. , Greenberg Harry B.
Published: August 2017

Individual human VP4- and VP7-binding monoclonal antibodies mediate serotype cross-reactive neutralizing immunity to rotaviruses.
Modeling human brain development
Authors: Chung Kwanghun
Published: August 2017

Human forebrain spheroids enable in vitro observation of region-specific neural migration and circuit formation during brain development.
Immunity at the forefront of the brain: A new genetic model of FTD
Authors: Morris Jill K.
Published: August 2017

Functional characterization of a genetic variant linked to frontotemporal dementia in a murine model reveals deficits in cerebral immune response and metabolism.
Impact of Poxvirus Vector Priming, Protein Coadministration, and Vaccine Intervals on HIV gp120 Vaccine-Elicited Antibody Magnitude and Function in Infant Macaques
Authors: Phillips Bonnie , Fouda Genevieve G. , Eudailey Josh , Pollara Justin , Curtis Alan D. , Kunz Erika , Dennis Maria , Shen Xiaoying , Bay Camden , Hudgens Michael , Pickup David , Alam S. Munir , Ardeshir Amir , Kozlowski Pamela A. , Van Rompay Koen K. A. , Ferrari Guido , Moody M. Anthony , Permar Sallie , De Paris Kristina
Published: August 2017

Despite success in reducing vertical HIV transmission by maternal antiretroviral therapy, several obstacles limit its efficacy during breastfeeding, and breast-milk transmission is now the dominant mode of mother-to-child transmission (MTCT) of HIV in infants. Thus, a pediatric vaccine is needed to eradicate oral HIV infections in newborns and infants. Utilizing the infant rhesus macaque model, we compared 3 different vaccine regimens: (i) HIV envelope (Env) protein only, (ii) poxvirus vector (modified vaccinia virus Ankara [MVA])-HIV Env prime and HIV Env boost, and (iii) coadministration of HIV Env and MVA-HIV Env at all time points. The vaccines were administered with an accelerated, 3-week-interval regimen starting at birth for early induction of highly functional HIV Env-specific antibodies. We also tested whether an extended, 6-week immunization interval using the same vaccine regimen as in the coadministration group would enhance the quality of antibody responses. We found that pediatric HIV vaccines administered at birth are effective in inducing HIV Env-specific plasma IgG. The vaccine regimen consisting of only HIV Env protein induced the highest levels of variable region 1 and 2 (V1V2)-specific antibodies and tier 1 neutralizing antibodies, whereas the extended-interval regimen induced both persistent Env-specific systemic IgG and mucosal IgA responses. Antibody-dependent cell-mediated cytotoxicity (ADCC) antibodies in plasma were elicited by all vaccine regimens. These data suggest that infant immunizations beginning at birth are effective for the induction of functional HIV Env-specific antibodies that could potentially protect against breast milk transmission of HIV and set the stage for immunity prior to sexual debut.