bluuebunny/crossref_metadata_2025 huggingface dataset:
Trailing Edge Cooling of Gas Turbine Airfoil Using Blockages With Straight and Inclined Holes
Authors: Siw Sin Chien , Chyu Minking K. , Alvin Mary Anne
Published: September 2014

This paper describes the detailed experimental studies of heat transfer enhancement and pressure loss characteristics internal cooling passages using single, double and triple blockages equipped with straight and inclined holes. The blockage consist of 7 holes with the diameter, D = 6.35mm, which is 0.5 of the height of the channel. Three different hole inclination angles ranging from 0°, 15° and 30° from the horizontal plane are explored. The case with straight holes (0°) is considered as baseline case, while the cases with inclined holes are introduced to enhance heat transfer performance. The transient liquid crystal technique is employed to deduce the heat transfer coefficient on the internal cooling channel, while the pressure loss of the entire channel is measured using pressure taps connected to the digital manometer. Numerical analysis is later performed using ANSYS CFX, based on the shear stress turbulence (SST) model to provide detailed insights about the flow field in the channel, which explains the heat transfer phenomena caused by varying the hole inclination angle. The heat transfer performance of the blockages is higher than conventional configuration using vortex generators, i.e., pin-fins by approximately two folds, while accompanied by much higher pressure loss. The proposed inclined holes array exhibits more effective impingement effects resulted in a substantial cooling performance compared to the baseline case by approximately 50%. This design can be applicable to the trailing edge of gas turbine airfoils, which can provide high heat transfer rate and pressure loss from repeated significant area contractions.
Visualization of Different Flashback Mechanisms for H2/CH4 Mixtures in a Variable-Swirl Burner
Authors: Sayad Parisa , Schönborn Alessandro , Li Mao , Klingmann Jens
Published: September 2014

Flame flashback from the combustion chamber to the premixing section is a major operability issue when using high H2 content fuels in lean premixed combustors. Depending on the flow-field in the combustor, flashback can be triggered by different mechanisms. In this work, three flashback mechanisms of H2/CH4 mixtures were visualized in an atmospheric variable swirl burner using high speed OH* chemiluminescence imaging. The H2 mole fraction of the tested fuel mixtures varied between 0.1 and 0.9. The flow-field in the combustor was varied by changing the swirl number from 0.0 to 0.66 and the total air mass-flow rate from 75 to 200 SLPM (standard liters per minute). The following three types of flashback mechanism were observed: Flashback caused by combustion induced vortex breakdown occurred at swirl numbers ≥ 0.53 for all of the tested fuel mixtures. Flashback in the boundary layer and flashback due to autoignition were observed at low swirl numbers and low total air mass-flow rates. The temporal and spatial propagation of the flame in the optical section of the premixing tube during flashback was studied and flashback speed for different mechanisms was estimated. The flame propagation speed during flashback was significantly different for the different mechanisms.
Application of Complex Demodulation for Pseudo-Key-Phasor Recovery From Fast-Response Pressure Measurements
Authors: Ilott Jordan W. , Allan W. D. E. , Asghar Asad
Published: September 2014

When digitizing the output of fast-response pressure transducers installed on rotating machinery, it is often desirable to use a phase-synchronized method. The mechanical design of many turbomachines, particularly those not originally designed for a research application, can make it difficult to install the physical key-phasor needed to acquire phase-synchronized measurements.

A method of phase-synchronization using a pseudo-key-phasor is presented in this paper. The technique applies complex demodulation to recover a pseudo-key-phasor signal from the blade-passing signal recorded in sampled data. The recovered pseudo-key-phasor is then used to digitally resample the data at a constant phase angle, removing the effect of small rotor speed variations. Example applications of this technique to vibration measurements can be found in the literature; however, examples of application to rotor pressure measurement were not.

The technique has been applied to fast-response pressure measurements taken on the shroud of a high speed centrifugal compressor. It was found that this technique was able to remove the effect of rotor speed variations from data sampled with equal time intervals, making them suitable for phase averaging.
Aircraft Engine Electrical Power Generation With a SOFC Combustor
Authors: Roberts Rory A. , Therkelsen Peter
Published: September 2014

Next generation aircraft will require more onboard electrical power generation capacity as systems previously powered by engine bleed and hydraulics are electrified and new electricity based technologies are integrated. Increasing the amount of electrical power generated from aircraft main engines reduces thrust capacity and thrust specific fuel consumption (TSFC), but could increase specific fuel consumption (SFC). An alternative cycle with very high conversion efficiencies is proposed for electrical power production on aircraft. The unique cycle, termed a SOFC combustor, integrates a Solid Oxide Fuel Cell (SOFC) with existing onboard combustion based engines. The SOFC combustor produces direct current (DC) electrical power and provides high temperature exhaust for use in the expansion process of the aircraft engine. The SOFC combustor utilizes compressed air from the engine’s compressor and vaporized fuel to produce DC current. Fuel and air not utilized by the fuel cell are converted to thermal products by an aerodynamically stabilized combustion system capable of adapting to fuel/air and pressure variations. Hot products from the combustion system are returned to the main engines for use as thrust or mechanical shaft work. System level results will be presented for overall impact to aircraft engine specific fuel consumption.
Effects of TBC Thickness on an Internally and Film Cooled Model Turbine Vane
Authors: Stewart William R. , Kistenmacher David A. , Bogard David G.
Published: September 2014

Previous tests simulating the effects of TBC (thermal barrier coating) on an internally and film cooled model turbine vane showed that the insulating effects of TBC dominate over variations in film cooling geometry and blowing ratio. In this study overall and external effectiveness were measured using a matched Biot number model vane simulating a TBC of thickness 0.6d, where d is the film cooing hole diameter. This was a 35% reduction in thermal resistance from previous tests. Overall effectiveness measurements were taken for an internal cooling only configuration, as well as for three rows of showerhead holes with a single row of holes on the pressure side of the vane. This pressure side row of holes was tested both as round holes and as round holes embedded in a realistic trench with a depth of 0.6 hole diameters. Even in the case of this thinner TBC, the insulating effects dominate over film cooling. In addition, using measurements of the convective heat transfer coefficient above the vane surface, and the thermal conductivities of the vane wall and simulated TBC material, the overall effectiveness of the thin TBC thickness can be predicted from the thick TBC data, for an internal cooling only configuration.
Heat Transfer and Friction Studies in a Tilted and Rib-Roughened Trailing-Edge Cooling Cavity With and Without the Trailing-Edge Cooling Holes
Authors: Taslim Mohammad , Halabi Joseph S.
Published: September 2014

Local and average heat transfer coefficients and friction factors were measured in a test section simulating the trailing edge cooling cavity of a turbine airfoil. The test rig with a trapezoidal cross sectional area was rib-roughened on two opposite sides of the trapezoid (airfoil pressure and suction sides) with tapered ribs to conform to the cooling cavity shape and had a 22-degree tilt in the flow direction upstream of the ribs that affected the heat transfer coefficients on the two rib-roughened surfaces. The radial cooling flow traveled from the airfoil root to the tip while exiting through 22 cooling holes along the airfoil trailing edge. Two rib geometries, with and without the presence of the trailing-edge cooling holes, were examined. The numerical model contained the entire trailing-edge channel, ribs and trailing-edge cooling holes to simulate exactly the tested geometry. A pressure-correction based, multi-block, multi-grid, unstructured/adaptive commercial software was used in this investigation. Realizable k–ε turbulence model in conjunction with enhanced wall treatment approach for the near wall regions, was used for turbulence closure. The applied thermal boundary conditions to the CFD models matched the test boundary conditions. Comparisons are made between the experimental and numerical results.
Dynamic Modeling and Control System Definition for a Micro-CSP Plant Coupled With Thermal Storage Unit
Authors: Ireland Melissa K. , Orosz Matthew S. , Brisson J. G. , Desideri Adriano , Quoilin Sylvain
Published: September 2014

Organic Rankine cycle (ORC) systems are gaining ground as a means of effectively providing sustainable energy. Coupling small-scale ORCs powered by scroll expander-generators with solar thermal collectors and storage can provide combined heat and power to underserved rural communities. Simulation of such systems is instrumental in optimizing their control strategy. However, most models developed so far operate at steady-state or focus either on ORC or on storage dynamics. In this work, a model for the dynamics of the solar ORC system is developed to evaluate the impact of variable heat sources and sinks, thermal storage, and the variable loads associated with distributed generation. This model is then used to assess control schemes that adjust operating conditions for daily environmental variation.
Effect of Blade Tip Modifications for Unducted Propulsors on Tip Vortex-Rotor Interaction Noise
Authors: Danner Florian , Kendall-Torry Christofer
Published: September 2014

Front rotor tip vortices impinging on a downstream blade row of an unducted propulsor induce distinct unsteadiness to blade loads with associated sound emissions. Since the region of unsteadiness is concentrated near the blade tips, reducing the rear rotor tip diameter represents a potential means for minimising interaction noise. A survey on the aeroacoustic effects resulting from a cropped rear rotor in combination with a front rotor blade tip modification is therefore presented. Analyses are based on data from computational fluid dynamics solutions with the Reynolds-averaged Navier-Stokes equations and direct acoustic predictions. The evaluation of polar directivities, blade surface pressure disturbances and details of the unsteady flow field provide insight into the underlying phenomena. Results show that an arbitrary reduction of the rear rotor tip diameter does not necessarily decrease noise radiation and that winglet-like structures applied to the front rotor blade tips are capable of reducing acoustic emissions due to tip vortex-rotor interactions.
Advanced 0-D Performance Modelling of Counter Rotating Propellers for Multi-Disciplinary Preliminary Design Assessments of Open Rotors
Authors: Bellocq Pablo , Sethi Vishal , Capodanno Stefano , Patin Alexis , Rodriguez Lucas Fernando
Published: September 2014

Due to their high propulsive efficiency, Counter Rotating Open Rotors (CRORs) have the potential to significantly reduce fuel consumption and emissions relative to conventional high bypass ratio turbofans. However, this novel engine architecture presents many design and operational challenges both at engine and aircraft level.

The assessment of the impact of the main low pressure preliminary design and control parameters of CRORs on mission fuel burn, certification noise and emissions is necessary at preliminary design stages in order to identify optimum design regions. These assessments may also aid the development process when compromises need to be performed as a consequence of design, operational or regulatory constraints.

The required preliminary design simulation tools should ideally be 0-D or 1-D (for computational purposes) and should capture the impact of the independent variation of the main low pressure system design and control variables such as: the number of blades, diameter and rotational speed of each propeller, the spacing between the propellers and the torque ratio of the gearbox or the counter rotating turbine amongst others. From a performance point of view, counter rotating propellers have historically been modelled as single propellers. Such a performance model does not provide the required flexibility for a detailed design and control study.

This paper presents a novel 0-D performance model for Counter Rotating Propellers (CRPs) based on the classical low speed performance model for individual propellers and the interactions between them. This model also incorporates a compressibility correction which is applied to both propellers. The proposed model is verified with publicly available wind tunnel test data from NASA.

The novel 0-D counter rotating propeller performance model is used to produce a performance model of a geared Open Rotor engine with a 10% clipped propeller. This engine model is first used to study the impact of the control of the propellers on the cruise fuel consumption. Subsequently, the engine performance model is integrated in a multi-disciplinary simulation platform to study the impact of the control of the propellers on the certification noise.

The results of this case study show that 1–2% SFC savings at cruise are possible and an optimal control schedule is identified. It is also concluded that significant certification noise reductions are possible through an adequate control of the rotational speeds of the propellers.
A Remotely Operated Aeroelastically Unstable LPT Cascade for Turbomachinery Aeromechanics Education and Training: Remote Flutter Lab
Authors: Monaco Lucio , Vogt Damian M. , Bergmans John , Fransson Torsten H.
Published: September 2014

The use of advanced pedagogical methodologies in connection with advanced use of modern information technology (ICT) for delivery enables new ways of communicating, of exchanging knowledge, and of learning that are gaining increasing relevance in our society. Remote laboratory exercises offer the possibility to enhance learning for students in different technical areas, especially to the ones not having physical access to laboratory facilities and thus spreading knowledge in a world-wide perspective. A new “Remote Flutter Laboratory” has been developed to introduce aeromechanics engineering students and professionals to aeroelastic phenomena in turbomachinery. The laboratory is world-wide unique in the sense that it allows global access for learners anywhere and anytime to a facility dedicated to what is both a complex and relevant area for gas turbine design and operation. The core of the system consists of an aeroelastically unstable turbine blade row that exhibits self-excited and self-sustained flutter at specific operating conditions. Steady and unsteady blade loading and motion data are simultaneously acquired on five neighboring suspended blades and the whole system allows for a distant-based operation and monitoring of the rig as well as for automatic data-retrieval.

This paper focuses on the development of the “Remote Flutter Laboratory” exercise as a hands-on learning platform for online and distant-based education and training in turbomachinery aeromechanics enabling familiarization with the concept of critical reduced frequency and of flutter phenomena. This laboratory set-up can easily be used “as is” directly by any turbomachinery teacher in the world, free of charge and independent upon time and location with the intended learning outcomes as specified in the lab, but it can also very easily be adapted to other intended learning outcomes that a teacher might want to highlight in a specific course. As such it is also a base for a turbomachinery repository of advanced remote laboratories of global uniqueness and access. The present work documents also the pioneer implementation of the LabSocket System for the remote operation of a wind tunnel test facility from any Internet-enabled computer, tablet or smartphone with no end-user software or plug-in installation.
Axial Bladeless Turbine Suitable for High Supersonic Flows
Authors: Vinha N. , Paniagua G. , Sousa J. , Saracoğlu B.
Published: September 2014

The development of future propulsion systems, targeting superior efficiencies with ultra compact designs, may rely on the extraction of power from high supersonic flows. In conventional supersonic turbines operating under such extreme flow conditions, the presence of airfoils induces important flow perturbations that originate severe aerodynamic losses while restricting the operating range due to starting issues. These limitations represent design opportunities for bladeless turbines.

The present paper documents for the first time in the open literature an axial bladeless turbine concept, able to extract mechanical power from high supersonic flows through an annular channel. The tangential drag force exerted by the viscous supersonic flow on the rotating inner and outer endwalls produce power, with enhanced simplicity, coolability, manufacturability, and maintainability. Reynolds Averaged Navier-Stokes simulations allowed the detailed evaluation of the aerodynamic performance of the bladeless configuration. The present unconventional axial turbine concept becomes an exceptional design choice when one seeks to extract certain amount of power from supersonic flows with minimum pressure losses.
Visualization and Time Resolved PIV Measurements of the Flow in the Tip Region of a Subsonic Compressor Rotor
Authors: Tan David , Li Yuanchao , Wilkes Ian , Miorini Rinaldo L. , Katz Joseph
Published: September 2014

A new optically index matched facility has been constructed to investigate tip flows in compressor-like settings. The blades of the one and a half stage have the same geometry, but lower aspect ratio as the inlet guide vanes and the first stage of the LSAC facility at NASA Glenn. With transparent blades and casings, the new setup enables unobstructed velocity measurements at any point within the tip region, and is designed to facilitate direct measurements of effects of casing treatments on the flow structure. We start with a smooth endwall casing. High speed movies of cavitation and time-resolved PIV measurements have been used to characterize the location, trajectory, and behavior of the Tip Leakage Vortex (TLV) for two flow rates, the lower one representing pre-stall conditions. Results of both methods show consistent trends. As the flow rate is reduced, TLV rollup occurs further upstream, and its initial orientation becomes more circumferential. At pre-stall conditions, the TLV is initially aligned slightly upstream of the rotor passage, and subsequently forced downstream. Within the passage, the TLV breaks up into a large number of vortex fragments, which occupy a broad area. Consequently, the cavitation in the TLV core disappears. With decreasing flow rate, this phenomenon becomes more abrupt, occurs further upstream, and the fragments occupy a larger area.
High Speed Visualization and PIV Measurements in the Near Field of Spray Produced by Flow-Blurring Atomization
Authors: Jiang Lulin , Agrawal Ajay K. , Taylor Robert P.
Published: September 2014

Clean and stable combustion of alternative liquid fuels, such as biodiesel, straight vegetable oil and glycerol has been achieved in past studies by using a novel flow blurring (FB) injector without fuel pre-processing or combustor hardware modification. FB injector employs aerodynamic principle to form two phase flow immediately upstream of the injector exit. Explosion of air bubbles at the injector exit atomizes the liquid into a fine spray. In this study, the flow field in the near field of the FB injector is investigated by high-speed visualization and time-resolved Particle Image Velocimetry (PIV) techniques. Experiments are performed using water and air for air to liquid mass ratio (ALR) of 2. Flow visualization at the injector exit focused on field of view with the dimension of 2.3 mm × 1.4 mm, spatial resolution of 7.16 μm per pixel, exposure time of 1 μs, and image acquisition rate of 100 k frames per second (fps). Image sequence illustrates fine spray of FB atomization in the near field and the break-down process of larger droplets appearing occasionally. Time-resolved PIV technique is applied to quantify the injector near field. Plots of instantaneous, mean, root-mean-square velocities and turbulence kinetic energy are presented to reveal the droplet characteristics and secondary atomization process. Results show that the majority of the liquid is atomized into fine droplets at the injector exit. The droplet velocity increases in the flow direction and decreases from the center to the periphery of the spray. This result is consistent with the size of the droplets, i.e., the larger droplets move slowly while the finer droplets move faster as they follow the atomizing air flow.
Effects of Area Ratio and Mean Rise Angle on the Aerodynamics of Inter-Turbine Ducts
Authors: Zhang Yanfeng , Hu Shuzhen , Mahallati Ali , Zhang Xue-Feng , Vlasic Edward
Published: September 2014

The present work, a continuation of a series of investigations on the aerodynamics of aggressive inter-turbine ducts (ITD), is aimed at providing detailed understanding of the flow physics and loss mechanisms in four different ITD geometries. A systematic experimental and computational study was carried out for varying duct mean rise angles and outlet-to-inlet area ratio while keeping the duct length-to-inlet height ratio, Reynolds number and inlet swirl constant in all four geometries. The flow structures within the ITDs were found to be dominated by the counter-rotating vortices and boundary layer separation in both the casing and hub regions. The duct mean rise angle determined the severity of adverse pressure gradient in the casing’s first bend whereas the duct area ratio mainly governed the second bend’s static pressure rise. The combination of upstream wake flow and the first bend’s adverse pressure gradient caused the boundary layer to separate and intensify the strength of counter-rotating vortices. At high mean rise angle, the separation became stronger at the casing’s first bend and moved farther upstream. At high area ratios, a 2-D separation appeared on the casing. Pressure loss penalties increased significantly with increasing duct mean rise angle and area ratio.
A Comparison of Two Fan Stage Designs With Different Rotor Leading Edge Sweep
Authors: Gunaraj John , Hanson David , Hayes Jeffrey , Lorzel Heath , Nolcheff Nick , Repp Russ
Published: September 2014

Two modern single-stage fans have been designed to meet the same set of performance objectives. The most significant difference between the two designs is the fan rotor leading edge sweep. The baseline rotor has a moderately aft swept leading edge while the redesigned rotor has a more complex sweep distribution, including moderate forward sweep in the tip region. Each stage consists of the fan rotor, full span stator, and split mid-frame, and is designed for a medium bypass ratio turbofan application. The stator and the mid-frame are identical for the two configurations. The primary purpose of this study is to validate the CFD methodology, in this case a steady ANSYS-CFX approach, to predict the fan stage performance at the operating point at two tested speeds and also to predict the stalling throttle condition. Numerical predictions and engine test results are presented and show good agreement. These predicted results are compared with high quality test data including thorough measurements of total pressure and total temperature at both the rotor and stator exits allowing for a detailed understanding and comparison of the individual blade row performance. The analytical model identifies the key performance trends, including an increase in flow capacity and stability margin with equivalent stage pressure ratio and efficiency for the redesigned fan relative to the baseline.
Heat Transfer in Rotating Two-Pass Channel With Bleed Holes on Tip Surface
Authors: Sohn Ho-Seong , Yun Namgeon , Park Jun Su , Cho Hyung Hee , Kim Kyung Min , Kim Beom Soo , Jang Byung Moon
Published: September 2014

Effusion flow from a blade tip region, not only protect the blade tip directly against hot gas but also influence the cooling performance of the internal cooling passage. The present study investigated the heat/mass transfer of a rotating two-passage rectangular duct using three different types of effusion hole arrays on the internal tip surface. The duct inlet was 80 mm × 16 mm, and the hydraulic diameter was 26.67 mm. The Reynolds number, which is based on the hydraulic diameter, was 10,000. The mass flow rate of the effusion flow was 10% of the total inlet mass flow. The naphthalene sublimation method was used to determine the local heat/mass transfer coefficient. The results indicated that effusion flow enhanced the heat transfer on the tip surface: they decreased the recirculation flow and counter-rotating flow in the turning region of the internal passage. The effusion holes enhanced the local heat transfer around holes due to local secondary flows such as tripping flows. The rotating channel had a different heat transfer distribution compared to the stationary channel due to Coriolis and centrifugal forces.
Mode Transition and Intermittency in an Acoustically Uncoupled Lean Premixed Swirl-Stabilized Combustor
Authors: LaBry Zachary A. , Taamallah Soufien , Kewlani Gaurav , Shanbhogue Santosh J. , Ghoniem Ahmed F.
Published: September 2014

The prediction of dynamic instability remains an open and important issue in the development of gas turbine systems, particularly those constrained by emissions limitations. The existence and characteristics of dynamic instability are known to be functions of combustor geometry, flow conditions, and combustion parameters, but the form of dependence is not well understood. By modifying the acoustic boundary conditions, changes in flame and flow structure due to inlet parameters can be studied independent of the acoustic modes with which they couple. This paper examines the effect of equivalence ratio on the flame macrostructure — the relationship between the turbulent flame brush and the dominant flow structures — in an acoustically uncoupled environment. The flame brush is measured using CH* chemiluminescence, and the flow is interrogated using two-dimensional particle image velocimetry. We examine a range of equivalence ratios spanning three distinct macrostructures. The first macrostructure (ϕ = 0.550) is characterized by a diffuse flame brush confined to the interior of the inner recirculation zone. We observe a conical flame in the inner shear layer, continuing along the wall shear layer in the second macrostructure (ϕ = 0.600). The third macrostructure exhibits the same flame brush as the second, with an additional flame brush in the outer shear layer (ϕ = 0.650). Between the second and third macrostructures, we observe a regime in which the flame brush transitions intermittently between the two structures. We use dynamic mode decomposition on the PIV data to show that this transition event, which we call flickering, is linked to vorticity generated by the intermittent expansion of the outer recirculation zone as the flame jumps in and out of the outer shear layer. In a companion paper, we show how the macrostructures described in this paper are linked with dynamic instability [1].
Test Results of 40MW-Class Advanced Humid Air Turbine and Exhaust Gas Water Recovery System
Authors: Takeda Takuya , Araki Hidefumi , Iwai Yasushi , Morisaki Tetsuro , Sato Kazuhiko
Published: September 2014

Operational flexibility, such as faster start-up time or faster load change rate, and higher thermal efficiency, have become more and more important for recent thermal power systems. The advanced humid air turbine (AHAT) system has been studied to improve operational flexibility and thermal efficiency of gas turbine power generation systems. A 40MW-class AHAT test facility was built and the rated output was achieved. Through operations at the facility, it has been verified for the first time that the key components of the medium-class gas turbines, such as an axial compressor and multi-can combustor, can be applied to the AHAT system. The cold start-up time from ignition to rated power was about 60 min, which is approximately one-third that of a conventional gas turbine combined cycle (GTCC) plant. NOx emissions were 24ppm (at 16% O2) when the humidity of combustion air was approximately a half that of present commercial AHAT plants, and NOx emissions in a future commercial AHAT system were thought to be less than 10ppm. A water recovery system which recovers water from a part of the exhaust gas of the 40MW-class test facility was built and test operations were made from June 2013. In this paper, water recovery test results as well as the 40MW-class gas turbine test results are shown.
Oil Free 8 kW High-Speed and High Specific Power Turbogenerator
Authors: Heshmat Hooshang , Walton James F. , Hunsberger Andrew
Published: September 2014

In the paper the authors will present the design and preliminary test results for a high specific power (i.e., kW/kg) fully integrated and completely oil-free gas turbine driven electric generating system that operates with commercially available heavy fuel. The oil-free, high-speed micro-turboalternator system achieves high specific power through operating speeds to 180,000 rpm and the use of compliant foil bearings, high performance compressor and turbine and a permanent magnet alternator. The high operating temperatures and speeds require that oil-free compliant foil bearings be used and that the alternator section be isolated from the turbine engine portion of the system. The selected modular design approach, including compressor and turbine aerodynamic design, system thermal management issues and the corresponding impact on rotor bearing system dynamics, will all be presented. The paper concludes with a presentation of preliminary testing results showing stable full speed operation and peak power generated. Data obtained compares well with design predictions both from a rotordynamic and with regard to the cycle efficiency and performance. Conclusions regarding the ability to scale the technology to even smaller systems will also be presented.
Experimental and Numerical Performance Characterization of a Transonic Compressor Rotor Operating Behind an Inlet-Guide Vane With Variable Flap Angles
Authors: Hobson Garth V. , Gannon Anthony , Holmes Wendell , McCormick Michael , Capece Vincent
Published: September 2014

The performance of a modern, forward-swept, transonic compressor rotor has been characterized operating behind an inlet-guide (IGV) vane section that has variable flaps. Testing was performed at both transonic and subsonic rotor tip speeds in an attempt to determine the off-design performance of the rotor at various flap angle settings of the IGV’s. Measurements at moderate flap angles (+20° and −10°) have been determined up to 90% speed (27,000 rpm) of the drive turbine maximum capability. Extremely high flap angles, in excess of +55°, were tested down into the low speed range. For this study the negative flap angles produced counterswirl and the positive flap angles produced swirl in the same direction as the rotation of the rotor.

A rigorous definition of the mass-averaged efficiency is presented. Performance predictions were carried out using ANSYS-CFX on a single passage model consisting of both the IGV and the rotor. Reasonable comparisons with a medium mesh resolution were obatined when compared to experiment.
Forced Response Analysis of Steam Turbine Inlet Flow Control Valves
Authors: Chakrabarti Suryarghya , Potdar Yogesh , Baik Sanghum , Welch David , Forte Guido
Published: September 2014

This work presents a comparison of two forced response methodologies implemented in commercial finite element software Ansys for describing the dynamic structural response of a steam turbine combined stop and control valve assembly in realistic operation conditions. The first method employs one-way coupling where the pressure field of a selected acoustic mode from an acoustic modal analysis on the valve cavity is scaled based on a pressure probe measurement and mapped onto the structure followed by a harmonic forced response analysis at the structure natural frequency. This method is called the decoupled model — it is fast and conservative as it assumes the acoustic and the structure modes to coincide providing a worst-case forced response estimate. The second method employs two-way coupling between acoustics and structure vibration. It takes five to ten times longer to run than the decoupled model because of the presence of non-symmetric system matrices and must be run multiple times with inputs spanning the operating condition range. However, the coupled model provides the opportunity for a more optimal design as it does not assume the acoustic and structure modes to line up. For the valve geometry studied in this work the effect of two-way coupling seems significant in some conditions where it can cause changes of up to 50% in the forced response.
Correspondence Between Uncoupled Flame Macrostructures and Thermoacoustic Instability in Premixed Swirl-Stabilized Combustion
Authors: Taamallah Soufien , LaBry Zachary A. , Shanbhogue Santosh J. , Ghoniem Ahmed F.
Published: September 2014

In this paper, we conduct an experimental investigation of a confined premixed swirl-stabilized dump combustor similar to those found in modern gas turbines. We operate the combustor with premixed methane-air in the lean range of equivalence ratio ϕ ∈ [0.5–0.75]. First, we observe different dynamic modes in the lean operating range, as the equivalence ratio is raised, confirming observations made previously in a similar combustor geometry but with a different fuel [1]. Next we examine the correspondence between dynamic mode transitions and changes in the mean flame configuration or macrostructure. We show that each dynamic mode is associated with a specific flame macrostructure. By modifying the combustor length without changing the underlying flow, the resonant frequencies of the geometry are altered allowing for decoupling the heat release fluctuations and the acoustic field, in a certain range of equivalence ratio. Mean flame configurations in the modified (short) combustor and for the same range of equivalence ratio are examined. It is found that not only the same sequence of flame configurations is observed in both combustors (long and short) but also that the set of equivalence ratio where transitions in the flame configuration occur is closely related to the onset of thermo-acoustic instabilities. For both combustor lengths, the flame structure changes at similar equivalence ratio whether thermo-acoustic coupling is allowed or not, suggesting that the flame configuration holds the key to understanding the onset of self-excited thermo-acoustic instability in this range. Finally, we focus on the flame configuration transition that was correlated with the onset of the first dynamically unstable mode ϕ ∈ [0.61–0.64]. Our analysis of this transition in the short, uncoupled combustor shows that it is associated with an intermittent appearance of a flame in the outer recirculation zone (ORZ). The spectral analysis of this “ORZ flame flickering” — based on flame chemiluminescence data — shows the presence of unsteady events occurring at two distinct frequency ranges. A broad band at low frequency in the range ∼[1 Hz – 10 Hz] and a narrow band centered around 28 Hz.
Slow Crack Growth of a Pyroceram Glass Ceramic Under Static Fatigue Loading: Commonality of Slow Crack Growth in Advanced Ceramics
Authors: Choi Sung R. , Faucett D. Calvin , Skelley Brenna
Published: September 2014

An extensive experimental work for Pyroceram™ 9606 glass-ceramic was conducted to determine static fatigue at ambient temperature in distilled water. This work was an extension and companion of the previous work conducted in dynamic fatigue. Four different applied stresses ranging from 120 to 170 MPa was incorporated with a total of 20–23 test specimens used at each of four applied stresses. The slow crack growth parameters n and D were found to be n = 19 and D = 45 with a coefficient of correlation of rcoef = 0.9653. The Weibull modulus of time to failure was in a range of msf = 1.6 to 1.9 with an average of msf = 1.7±0.2. A life prediction using the previously-determined dynamic fatigue data was in excellent agreement with the static fatigue data. The life prediction approach was also applied to advanced monolithic ceramics and ceramic matrix composites based on their dynamic and static fatigue data determined at elevated temperatures. All of these results indicated that a SCG mechanism governed by a power-law crack-growth formulation was operative, a commonality of slow crack growth in these materials systems.
Numerical Analysis of the Use of Vegetable Oil-Tars Mixtures From Syngas Scrubbing in a Microturbine Combustor
Authors: Laranci Paolo , Bidini Gianni , D’Alessandro Bruno , Fantozzi Francesco
Published: September 2014

TARs are a mixture of heavy and light hydrocarbons produced from pyrolysis and gasification of biomass and waste, as condensable volatiles in the syngas. Given their relatively low dew point, they are usually removed from syngas to avoid condensation and fouling of engines and equipment. Vegetable oil scrubbing compared to water scrubbing yields oil tar mixtures which is a renewable fuel and may be useful successfully to power a gas turbine. The feasibility of burning TAR, blended vegetable oil, in a combustor of a turbine is investigated. Computational simulations with a CFD software were performed to analyze evaporation and combustion processes of vegetable oil-tars mixture compared with pure vegetable oil and diesel, in terms of residence time, temperature distributions, inlet turbine conditions.

The results show difficulties in evaporation of both vegetable oil and vegetable oil-tar mixture compared to diesel, with consequences in the combustion in terms of temperature distributions and higher NOx emissions. Preheating of vegetable oil and vegetable oil-tar mixture improves their evaporation approaching the results to those of the diesel case.
Rotordynamic Validation of an Ultra High Speed Multistage Centrifugal Compressor Stacked Rotor
Authors: Vannini Giuseppe
Published: September 2014

The author’s company is currently developing some centrifugal compressor prototypes where the traditional rotor design based on shrunk on wheels and spacers is not suitable due to the specific service requirements (e.g. high peripheral speed or high temperature). For instance the development of a new centrifugal compressor technology aimed to reduce the number of compressor units needed to fulfill a given service is ongoing. In order to accomplish this challenging target a very high rotational speed is required together with special “high pressure ratio” centrifugal stages. The rotor mechanical configuration which has been selected here is a stacked configuration where each centrifugal wheel is integral with the relevant shaft portion. The several shaft portions are mated together through high precision toothed connections (Hirth couplings) and the assembly is secured through a pre-stretched tie-rod.

This rotor stacked configuration is not typical for the most of the industrial centrifugal compressors (a solid shaft with shrink fitted impellers is the common solution, as anticipated) but it is allowed by API standards [1], and it is referenced in Turbomachinery technical literature [2].

The rotordynamics of this special prototype is very challenging since it deals with a seven piece stacked rotor running supercritical. An extensive validation program was required in addition to careful design. This is the specific subject of the present paper which will cover the main following items: validation of the “rotor alone” rotordynamic modelization through comparison with the relevant ping test results, selection of special high speed journal bearings, and overview of the low and high speed balancing process. All these steps together finally allowed the author’s company to fully demonstrate the soundness of this stacked rotor technology for application in High Pressure Ratio Compression service.
Model Validation for Identification of Damage Dynamics
Authors: Madden Ryan J. , Sawicki Jerzy T. , Pesch Alexander H.
Published: September 2014

Robust control techniques have allowed engineers to create more descriptive models by including uncertainty in the form of additive noise and plant perturbations. As a result, the complete model set is robust to any discrepancies between the mathematical model and actual system. Experimental unfalsification of the model set leads to the guarantee that the model and uncertainties are able to recreate all experimental data points. In this work, such a robust control relevant model validation technique is applied to structural health monitoring in order to 1) detect the presence of damage and 2) identify the damage dynamics when used in conjunction with model-based identification. Additionally, the robust control relevant model validation technique allows for a novel quality measure of the identified damage dynamics. Feasibility of the method is demonstrated experimentally on a rotordynamic crack detection test rig with the detection and identification of a change in structure. Further insight is gained from application of the method to seeded damage on a rotor levitated on active magnetic bearings in the form of a local reduction in stiffness.
Kinetics of Pyrolysis of Mesquite Fuel: Comparison of Different Methods
Authors: Chen Wei , Thanapal Siva Sankar , Annamalai Kalyan , Ranjan Devesh , Lawrence Ben , Ansley Robert James
Published: September 2014

Recently Torrefaction processes are used to improve the quality of fuels. Upper limit on torrefaction temperature can be determined using the maximum volatile release method (MVR) in deducing the kinetics of pyrolysis. The single reaction model (SRM), parallel reaction model (PRM also known as distributed reaction model) and three component models (TCM for hemicellulose, cellulose and lignin) of pyrolysis are briefly reviewed. The MVR method uses the maximum volatile release rate conditions for extracting the kinetics of pyrolysis. Thermogravimetric (TGA) and Differential Thermal (DTA) analyses for mesquite biomass were performed in a thermo-gravimetric instrument and particularly the pyrolysis data of the mesquite samples from MVR are compared with those of SRM and PRM. The focus of current paper is on the extraction of kinetics data (activation energies and pre-exponential factors) from various methods: MVR for the SRM (called as SRM-MVR), PRM and SRM-CA and on the comparison of experimental data with model predictions from SRM-MVR, SRM-CA and PRM for mesquite fuel. It was found that the SRM-CA displays the largest error to predict the mass loss, and SRM-MVR generated less error than SRM-CA even though the kinetics data for SRM-MVR were extracted using a single point. The predicted pyrolysis behavior from the PRM exhibits the best agreement for the whole domain of pyrolysis but peak point which is of importance in torrefaction process is not predicted well. Particularly the kinetics data generated with SRM-MVR is useful in estimating the upper limit on temperature of torrefaction for biomass fuels.
Pursuit of the common good
Authors: Dasgupta Partha , Ramanathan Veerabhadran
Published: September 2014

Religious institutions may mobilize public opinion and action
Tracking antibiotic resistance
Authors: Beatson Scott A. , Walker Mark J.
Published: September 2014

Sequencing plasmids can reveal the transmission of resistance among bacteria from patients in a clinical setting
Harmful mutations can fly under the radar
Authors: Servick Kelly
Published: September 2014

With more sensitive genetic tests, researchers are hunting the roots of disease in the human “mosaic.”
Play it again, Uncle Sam
Authors: Mervis Jeffrey
Published: September 2014

Prominent academics recommend growth in federal basic research budget that matches previous golden era
A systems approach to the modern microbiome world: Investigating host-microbiota symbiosis
Authors: Paliy Oleg , Belkaid Yasmine
Published: September 2014

Microorganisms living in or on the body of a healthy human adult outnumber human cells by 10 to one. A large number of the 100 trillion microbes that compose the majority of life on Earth have coevolved a close relationship with the mammalian immune system. Therefore, by solely limiting research to either the host or bacteria, only half of the information required in microbiome studies is being seen. The symbiotic relationship of the host and resident microbiota must remain in delicate harmony to maintain a healthy body. Disruption of the microbial community can lead to an imbalance in homeostasis of the immune cells including Th17, T regulatory, and innate lymphoid cells, which can influence susceptibility of the host to a variety of health disorders including rheumatoid arthritis, obesity, inflammatory bowel disease, Crohn’s disease, diabetes, and ulcerative colitis, among others. As the number of microbiome studies grow, it is becoming increasingly clear that the host and microbiota do not operate alone. To understand the complete story, the interaction between the host and bacterial systems needs to be considered through a more holistic, systematic approach. This webinar will discuss just such an approach, examining the problem from the perspective of both the host and microbiome.
Stimulation of Innate Immunity byIn VivoCyclic di-GMP Synthesis Using Adenovirus
Authors: Koestler Benjamin J. , Seregin Sergey S. , Rastall David P. W. , Aldhamen Yasser A. , Godbehere Sarah , Amalfitano Andrea , Waters Christopher M.
Published: September 2014

The bacterial second messenger cyclic di-GMP (c-di-GMP) stimulates inflammation by initiating innate immune cell recruitment and triggering the release of proinflammatory cytokines and chemokines. These properties make c-di-GMP a promising candidate for use as a vaccine adjuvant, and numerous studies have demonstrated that administration of purified c-di-GMP with different antigens increases protection against infection in animal models. Here, we have developed a novel approach to produce c-di-GMP inside host cells as an adjuvant to exploit a host-pathogen interaction and initiate an innate immune response. We have demonstrated that c-di-GMP can be synthesizedin vivoby transducing a diguanylate cyclase (DGC) gene into mammalian cells using an adenovirus serotype 5 (Ad5) vector. Expression of DGC led to the production of c-di-GMPin vitroandin vivo, and this was able to alter proinflammatory gene expression in murine tissues and increase the secretion of numerous cytokines and chemokines when administered to animals. Furthermore, coexpression of DGC modestly increased T-cell responses to aClostridium difficileantigen expressed from an adenovirus vaccine, although no significant differences in antibody titers were observed. This adenovirus c-di-GMP delivery system offers a novel method to administer c-di-GMP as an adjuvant to stimulate innate immunity during vaccination.