bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Turning Angle on the Loss Generation of LP Turbines
Authors: Torre Diego , Garcia-Valdecasas Guillermo , Cadrecha David
Published: August 2017

The effect of turning angle on the loss generation of Low Pressure (LP) Turbines has been investigated experimentally in a couple of turbine high-speed rigs. Both rigs consisted of a rotor-stator configuration. All the airfoils are high lift and high aspect ratio blades that are characteristic of state of the art LP Turbines.

Both rigs are identical with exception of the stator. Therefore, two sets of stators have been manufactured and tested. The aerodynamic shape of both stators has been designed in order to achieve the same spanwise distribution of Cp (Pressure coefficient) over the airfoil surface, each one to its corresponding turning angles. Exit angle in both stators is the same. Therefore the change in turning is obtained by a different inlet angle.

The aim of this experiment is to obtain the sensitivity of profile and endwall losses to turning angle by means of a back-to-back comparison between both sets of airfoils. Because the two sets of stators maintain the same pressure coefficient distribution, Reynolds number and Mach number, each one to its corresponding velocity triangles, one can state that the results are only affected by the turning angle.

Experimental results are presented and compared in terms of area average, radial pitchwise average distributions and exit plane contours of total pressure losses. CFD simulations for the two sets of stators are also presented and compared with the experimental results.
Analysis of a Turbine Bladed Disk With Structural and Aerodynamic Mistuning
Authors: Franz Dimitri , Salles Loic , Stapelfeldt Sina
Published: August 2017

In this paper the effects of mistuning on the flutter stability of a turbine blade are analysed. Two types of mistuning are considered, frequency mistuning and aerodynamic mistuning. The study concentrates on the the first family of modes (1F, first flap) as the blade fluttered in this mode during test. For the frequency mistuning analysis, the 1F frequency is varied around the annulus but the 1F mode shapes remain the same for all the blades. The mistuning analyses are performed by using a reduced order model (ROM) based on an eigenvalue analysis of the linearized modal aeroelastic system with the aerodynamic matrix calculated from the aerodynamic influence coefficients. The influence coefficients required for this algorithm are obtained from a three-dimensional, non-linear aeroelastic solver (AU3D) by shaking one blade in the datum (tuned) frequency and mode and recording aerodynamic forces on the other blades in the assembly. After the ROM is validated against the non-linear method for the tuned case, it is used for the mistuning and mis-staggering study as time-domain computations of such cases are very time consuming.

The results of this paper indicate that, frequency mistuning is always stabilizing but aerodynamic mistuning can be destabilizing under certain conditions. Moreover, it is shown that the effect of frequency mistuning is much higher than the one of aerodynamic asymmetries and that structural coupling limits the effects of mistuning.
Experimental Investigation of Self-Excited Combustion Instabilities in a Lean, Premixed, Gas Turbine Combustor at High Pressure
Authors: Buschhagen Timo , Gejji Rohan , Philo John , Tran Lucky , Portillo Bilbao J. Enrique , Slabaugh Carson D.
Published: August 2017

An experimental investigation of self-excited combustion instabilities in a high pressure, single-element, lean, premixed, natural gas dump-combustor is presented in this paper. The combustor is designed for optical access and is instrumented with high frequency pressure transducers at multiple axial locations. A parametric survey of operating conditions including inlet air temperature and equivalence ratio has been performed, which presents a wide range of peak to peak pressure fluctuations (p′) of the mean chamber pressure (pc). Two cases, Flame A and B with p′ /pc = 28% and p′/pc = 15% respectively, both presenting self-excited instabilities at the fundamental longitudinal (1L) mode of the combustion chamber, are discussed to study the coupling mechanism between flame-vortex interactions and the acoustic field in the chamber. OH*-chemiluminescence is used to obtain a map of global heat release distribution in the combustor. Phase conditioned analysis and Dynamic Mode Decomposition (DMD) analysis is performed, to highlight the contrasting mechanisms that lead to the two distinct instability regimes. Flame interactions with shear layer vortex structures just downstream of the dump plane during the compression phase of the acoustic cycle are found to augment the instability amplitude. Flame A engages strongly in this coupling, whereas Flame B is less affected and establishes a lower amplitude limit cycle.
Effect of Internal Crossflow Velocity on Film Cooling Effectiveness: Part II — Compound Angle Shaped Holes
Authors: McClintic John W. , Anderson Joshua B. , Bogard David G. , Dyson Thomas E. , Webster Zachary D.
Published: August 2017

In gas turbine engines, film cooling holes are commonly fed with an internal crossflow, the magnitude of which has been shown to have a notable effect on film cooling effectiveness. In Part I of this study, as well as in a few previous studies, the magnitude of internal crossflow velocity was shown to have a substantial effect on film cooling effectiveness of axial shaped holes. There is, however, almost no data available in the literature that shows how internal crossflow affects compound angle shaped film cooling holes. In Part II, film cooling effectiveness, heat transfer coefficient augmentation, and discharge coefficients were measured for a single row of compound angle shaped film cooling holes fed by internal crossflow flowing both in-line and counter to the span-wise direction of coolant injection. The crossflow-to-mainstream velocity ratio was varied from 0.2–0.6 and the injection velocity ratio was varied from 0.2–1.7. It was found that increasing the magnitude of the crossflow velocity generally caused degradation of the film cooling effectiveness, especially for in-line crossflow. An analysis of jet characteristic parameters demonstrated the importance of crossflow effects relative to the effect of varying the film cooling injection rate. Heat transfer coefficient augmentation was found to be primarily dependent on injection rate, although for in-line crossflow, increasing crossflow velocity significantly increased augmentation for certain conditions.
Fluid-Structure Interaction Study of Large and Light Axial Fan Blade
Authors: Castorrini A. , Corsini A. , Sheard A. G. , Rispoli F. , Lamperini M.
Published: August 2017

Numerical simulation tools are acquiring a crucial role in the virtual prototyping of new fan rotor blades. This, considering also the possibility in using new advanced materials, is opening the design capability to blades of longer, lighter and more slender structure.

On this perspective, the numerical tools must be improved in order to catch also the non-linear and coupling phenomena which were been treated until now using a weak coupling approach.

Here we present a fluid-structure interaction solver based on the finite element method, through its application to an existing fan blade. The study will show how, even in case of metal structure with little deformation, the coupling between fluid dynamics and structure dynamics can produce effects on both the fluid and the solid involved in the machine main process. The possibility to simulate directly both the aerodynamic and the effective structure response opens the way to improved design capabilities, avoiding time waste and costs due to long experimental testing campaign and over-dimensioned structures.
The Implementation of WikL: An Educational Wiki Supporting Collaborative Learning in Engineering University Courses
Authors: Zander Lisa , Tanneberger Tom , Peukert Juliane , Mensah Georg A.
Published: August 2017

A wiki called “WikL” is developed and employed at the Institut für Strömungsmechanik und Technische Akustik (ISTA) of Technische Universität Berlin to shift teacher focused lecturing to student focused learning in University engineering education. In this wiki, students create articles collaboratively which supports not only the gain of new knowledge but also the sharing and critical evaluation of this knowledge. This paper describes the various applications of the WikL in different classes and how it improves teaching. One of the advantages of the WikL is that it offers the possibility to link multiple courses over more than a single semester by giving access to other classes results that students might not have participated in before. For instance, it enables students that take a class on combustion to study topics of turbulence, if needed. Moreover, real measurement data taken in one course can be used to demonstrate the different effects of various analysis methods that are taught in another class. The wiki as a data and knowledge platform thus allows for cross-class teaching concepts. Though, the WikL is used with different learning concepts in the different classes, the underlying DokuWiki software allows for the customization of the WikL to meet course-specific requirements. In the future, the data and knowledge base of the WikL will grow with each semester providing a more and more valuable information platform for our students. The introduction of the WikL in more classes of our institution is intended.
A Numerical Investigation of the Effect of Inlet Preswirl Ratio on Rotordynamic Characteristics of Labyrinth Seal
Authors: Tsukuda Tomohiko , Hirano Toshio , Watson Cori , Morgan Neal R. , Weaver Brian K. , Wood Houston G.
Published: August 2017

Full three-dimensional CFD simulations are carried out using ANSYS CFX to obtain the detailed flow field and to estimate the rotordynamic coefficients of a labyrinth seal for various inlet swirl ratios.

Flow fields in the labyrinth seal with the eccentricity of the rotor are observed in detail and the detailed mechanisms that increase the destabilizing forces at high inlet swirl ratios are discussed based on the fluid governing equations associated with the flow fields. By evaluating the contributions from each term of the governing equation to cross coupled force, it is found that circumferential velocity and circumferential distribution of axial mass flow rate play key roles in generating cross coupled forces. In the case that circumferential velocity is high and decreases along the axial direction, all contributions from each term are positive cross coupled force. On the other hand, in the case that circumferential velocity is low and increases along the axial direction, one contribution is positive but the other is negative. Therefore, cross coupled force can be negative in the local chamber depending on the balance even if circumferential velocity is positive.

CFD predictions of cross coupled stiffness coefficients and direct damping coefficients show better agreement with experimental results than a bulk flow model does by considering the force on the rotor in the inlet region. Cross coupled stiffness coefficients derived from the force on the rotor in the seal section agree well with those of the bulk flow model.
Characterization and Optimization of Selective Laser Melting Materials Through Small Punch Testing
Authors: Torres Jonathan , Gordon Ali P.
Published: August 2017

With the heightened complexity of component design that may be achieved through AM comes an equally complex set of distinct material characteristics caused by the manufacturing method. To properly characterize new materials for use with selective laser melting (SLM), extensive material testing and analysis is necessary. Traditional testing techniques, however, are prohibitive due to the time and cost incurred. Miniaturized testing then becomes an attractive option for assessing material properties of SLM materials. The small punch test (SPT) has been developed for such purposes, where material is scarce or costly. Although lacking formal standardization, SPT has been successfully employed with various materials to assess several material properties and verified by traditional testing results. With the accompaniment of numerical simulations for use in the inverse method and determining correlation factors, several methods exist for equating SPT results with traditional stress-strain results. Additionally, the combination of SPT and SLM is relatively unexplored in literature, though studies have shown that SPT is sensitive to the types of structures and unique material characteristics present in SLM components. The present research therefore focuses primarily on the development and evaluation of a mechanical model of the SPT and its sensitivity to changes in material properties. The evolution of the SPT response with dependencies on the changing properties is then likened to the changes in SLM materials to make a case for the suitability of evaluating and optimizing SLM materials using SPT.
Characterization of Spark- and Laser-Ignition of Bio- and Natural Gas
Authors: Peters Nathan D. , Akih-Kumgeh Ben
Published: August 2017

This paper presents a comparative investigation of the early phase of combustion initiated by a focused pulsed laser beam and a conventional spark-discharge. The comparative approach is applied to the characterization of combustible mixtures of natural gas and biogas with varying CO2 content. Interferometry and Schlieren imaging are used to probe flame kernel formation and its subsequent transition to a self-sustained flame. The pressure rise in the chamber is also recorded by means of a fast-response piezo-electric pressure transducer. From these diagnostics, differences between the early phases of laser-induced and spark-ignition are revealed. Unlike in laser-induced ignition, spark-ignition features a delay in the transition from the early flame kernel to a self-sustained flame (attributed to heat loss), which leads to failed ignition for mixtures with high CO2 content. The role of CO2 as an ignition retardant is observed by comparing fuel/air mixtures with and without CO2.
Online Health Monitoring System Using Dynamic Structural Responses
Authors: Paspulati Amit K. , Veluru Krishna C. , Akki Kashinath
Published: August 2017

This paper discusses the methodology for detection of impending failures in gas turbine components. Gas turbine components when exposed to fatigue loading are prone to crack initiation and propagation (structural failure) during operation. Cracks when left undetected over the long duration of continuous engine operation may lead to failure of gas turbine components and unplanned shutdown. This paper presents the crack detection methodology proposed to be only used in older engines maintained by the service fleet. This is done by capturing the changes in physical characteristics of cracked gas turbine structures during engine operation. Monitoring the change in vibration characteristics is being proposed as an input in developing the health monitoring system. In verifying the proposed technique, static component such as flexible pipe is analytically evaluated and validated with field measurements.
Flame Dynamics Intermittency in the Bi-Stable Region Near a Subcritical Hopf Bifurcation
Authors: Ebi D. , Denisov A. , Bonciolini G. , Boujo E. , Noiray N.
Published: August 2017

We report experimental evidence of thermoacoustic bi-stability in a lab-scale turbulent combustor over a well-defined range of fuel-air equivalence ratios. Pressure oscillations are characterized by an intermittent behavior with “bursts”, i.e. sudden jumps between low and high amplitudes occurring at random time instants. The corresponding probability density functions of the acoustic pressure signal show clearly separated maxima when the burner is operated in the bi-stable region. A flame describing function, which links acoustic pressure to heat release rate fluctuations, is estimated at the modal frequency from simultaneously recorded flame chemiluminescence and acoustic pressure. The representation of its statistics is new and particularly informative. It shows that this describing function is characterized, in average, by a nearly constant gain and by a significant drift of the phase as function of the oscillation amplitude. This finding suggests that the bi-stability does not result from an amplitude-dependent balance between flame gain and acoustic damping, but rather from the non-constant phase difference between the acoustic pressure and the coherent fluctuations of heat release rate.
Fractal Characteristics of Combustion Noise
Authors: Saurabh Aditya , Imran Hassan , Nawroth Holger , Paschereit Christian Oliver , Kabiraj Lipika
Published: August 2017

Fractal analysis is undertaken to characterize flame surface fluctuations on an unconfined turbulent premixed flame and the resulting far-field acoustics fluctuations. Results indicate that combustion noise is monofractal and is characterized by an anti-correlated structure with a Hurst exponent less than 0.5. The anti-correlated nature was identified in the pressure fluctuations as well as flame surface fluctuations for small time scales. Additionally, results suggest that flame surface fluctuations are multifractal for large time scales. The calculated Hurst exponent increases noticeably with the equivalence ratio and decreases slightly with Reynolds number for the investigated operating conditions. Variation in the Hurst exponent for combustion noise data is compared with a case study of synthetic fluctuations comprised of linear combinations of white and 1/f2 noise. These results provide a more detailed characterization of the temporal structure of flame surface fluctuations and resulting noise emission from turbulent premixed flames than is presently known.
Thermochemical Mechanism Optimization for Accurate Predictions of CH Concentrations in Premixed Flames of C1-C3 Alkane Fuels
Authors: Versailles Philippe , Watson Graeme M. G. , Durocher Antoine , Bourque Gilles , Bergthorson Jeffrey M.
Published: August 2017

Increasingly stringent regulations on NOx emissions are enforced by governments owing to their contribution in the formation of ozone, smog, fine aerosols, acid rains and nutrient pollution of surface water, which affect human health and environment. The design of high-efficiency, low-emission combustors achieving these ever-decreasing emission standards requires thermochemical mechanisms of sufficiently high accuracy. Recently, a comprehensive set of experimental data, collected through laser-based diagnostics in atmospheric, jet-wall, stagnation, premixed flames, was published for all isomers of C1-C4 alkane and alcohol fuels [1–3]. The rapid formation of NO through the flame front via the prompt (Fenimore) route was shown to be strongly coupled to the maximum concentration of the methylidyne radical, [CH]peak, and the flow residence time within the CH layer. A proper description of CH formation is then a prerequisite for accurate predictions of NO concentrations in hydrocarbon-air flames. However, a comparison against the Laser-Induced Fluorescence (LIF) experimental data of [3] revealed that 1) modern thermochemical mechanisms are unable to accurately capture the stoichiometric dependence of [CH]peak, and 2) for a given equivalence ratio, the predictions of different mechanisms span over more than an order of magnitude. This paper presents an optimization of the specific rate of a selection of nine elementary reactions included in the San Diego combustion mechanism [4]. A quasi-Newton algorithm is used to minimize an objective function defined as the sum of squares of the relative difference between the numerical and experimental CH-LIF data of [3], while constraining the specific rates to physically reasonable values. A mechanism properly describing CH formation for lean to rich, C1-C3 alkane-air flames is obtained. This optimized mechanism will enable accurate predictions of prompt-NO formation over a wide range of equivalence ratios and alkane fuels. Suggestions regarding which reactions require further investigations, either through experimental or theoretical assessments of the individual specific rates, are also provided.
Mixing and Combustion Characterization of a Staged Combustor With Multiple, High Mass-Ratio Jets in Crossflow
Authors: Jain Nishant , Seitzman Jerry M.
Published: August 2017

This study focuses on elucidating the flow and combustion features in the jet/pilot interaction zone of RQL-type air-staged combustors. Multiple air jets enter normally into a vitiated crossflow consisting of the combustion products of natural gas and air (up to an equivalence ratio of ϕ∼1.3). These jets in crossflow (JICF) interact in a test-section with a rectangular cross section whose dimensions are only 3–4 times the size of the jet diameters. In the test section, a total of five jets (three on the bottom and two on the top) can be used to attain parallel and staggered-opposed jet configurations. The combustion and mixing properties are examined using chemiluminescence imaging and planar Mie scattering from seed particles, with the latter also used for PIV velocity measurements. Results are acquired for mass ratios (total jet mass flow to pilot mass flow) as high as two. At these high mass ratios, the jet velocities range from 50–250 m/s while the pilot (crossflow) velocity ranges from 5–35 m/s. At high mass ratios, and therefore high jet momentum ratios, the jets impinge on the opposite walls well before they can transition into a typical far-field regime for unconfined JICF configurations. In these cases, the jet-wall interaction plays a significant role in redirecting the jet momentum and mixing the jet and crossflow fluids. In the case of the staggered-opposed jet configurations, the jet-wall interaction of a jet can greatly influence the near-field region of its neighboring opposed jet. With the high temperature crossflow, chemical times are sufficiently fast that combustion seem to be mixing limited rather than chemistry limited under the conditions considered.
Performance Analysis of a Combined Cycle Power Plant Through Exergetic and Environmental Indices
Authors: Torres González Edgar Vicente , Lugo Leyte Raúl , Salazar Pereyra Martín , Lugo Méndez Helen Denise , Toledo Velázquez Miguel , Ambriz García Juan José
Published: August 2017

In this paper is carried out a comparison between a gas turbine power plant and a combined cycle power plant through exergetic and environmental indices in order to determine performance and sustainability aspects of a gas turbine and combined cycle plant. First of all, an exergetic analysis of the gas turbine and the combined is carried out then the exergetic and environmental indices are calculated for the gas turbine (case A) and the combined cycle (case B). The exergetic indices are exergetic efficiency, waste exergy ratio, exergy destruction factor, recoverable exergy ratio, environmental effect factor and exergetic sustainability. Besides, the environmental indices are global warming, smog formation and acid rain indices. In the case A, the two gas turbines generate 278.4 MW; whereas 415.19 MW of electricity power is generated by the combined cycle (case B). The results show that exergetic sustainability index for cases A and B are 0.02888 and 0.1058 respectively. The steam turbine cycle improves the overall efficiency, as well as, the reviewed exergetic indexes. Besides, the environmental indices of the gas turbines (case A) are lower than the combined cycle environmental indices (case B), since the combustion gases are only generated in the combustion chamber.
Numerical Investigation of Optimized Arrangements for Effusion Cooling in Gas Turbine Combustor Applications
Authors: Mazzei L. , Puggelli S. , Andreini A. , Facchini B.
Published: August 2017

The high cooling performance and the capability of providing thermo-acoustic damping are increasing the application of effusion cooling in lean burn aero-engine combustors. The numerical characterization through Computational Fluid Dynamics (CFD) has gained strong interest, however standard Reynolds Average Navier-Stokes (RANS) techniques are not capable of providing high fidelity predictions in the presence of swirling flows interacting with the cooling system. The exploitation of Large Eddy Simulation (LES) would represent the ideal solution, but the high spatial resolution required in the near-wall region, together with the well-known issues related to an accurate specification of turbulent boundary conditions at the inlets, still represent a critical challenge for its extensive use with realistic conditions in terms of Reynolds number and geometrical complexity. Therefore different scale-resolving models such as Scale Adaptive Simulation (SAS) and Detached Eddy Simulation (DES) are gaining popularity due to the promising results highlighted.

At this purpose, a SAS approach was employed in this work to quantify the film coverage offered by different effusion cooling schemes in the presence of a swirler, highly unsteady flow field. The main goal is determine if well-known design practices derived from investigations carried out on flat plates with uniform mainstream conditions may be confirmed also under realistic flow conditions. In particular, the geometrical parameters evaluated in the work are the inclination angle, the compound angle and the pattern of the perforation. The results clearly highlight how a reduction of the inclination angle is able to keep coolant more attached to the wall, whereas the application of a compound angle increases the turbulent diffusion in the lateral direction, ultimately increasing coolant protection.
Small Aircraft Turbine Noise From Combustion of Synthetic Kerosene Fuels
Authors: Soloiu Valentin , Knowles Aliyah , Moncada Jose , Simons Emerald , Muinos Martin , Ngo Huong Kim
Published: August 2017

In this paper the use of alternative fuels — synthetic kerosene based — were investigated in a small aircraft gas turbine engine to determine their sound and vibrations signature at Georgia Southern University’s Aerospace Engine Laboratory. Three types of fuels were used: a natural gas, a coal derived synthetic kerosene and Jet-A as a reference fuel. The alternative fuels are Fischer-Tropsch process fuels. Synthetic fuels are attractive in the aviation industry because of their potential for reducing energy dependence and the growing need for higher efficiencies, while reducing emissions.

The research SR-30 gas turbine was used to evaluate combustion noise from the selected fuels. The turbine can operate at a maximum speed of 80,000 rpm, produce a maximum thrust of 40 lbf, has a pressure ratio of 3.4 to 1, and a specific fuel consumption of 1.22 lbfuel/thrust per hour. The measurement transducers were state of the art Brüel & Kjaer ¼ inch microphone and a triaxial accelerometer which were interfaced with the analysis software, Brüel & Kjaer Pulse 21. Data was taken at 70,000 rpm for a time span of five minutes at stabilized conditions. One-third octave analysis indicated highest sound difference between the fuels at 400 Hz, and a more pure sound level was obtained. The difference for Jet A was as much as 6 dBA higher for exhaust measurement at 400 Hz, and for FT-NG the exhaust had a higher decibel reading from the exhaust side by as much as 4.4 dBA at the 400 Hz frequency, and FT-CG had as much as 7.3 dBA difference at 315 Hz. The sound from the combustion of these fuels produced the differences of sound when the positions of the microphones changed. However, with this new introduction of sound measurement locations and angles, the combustion differences are still distinct and show a more in depth view of the sound quality that is being received by the microphone.
Investigation on Intelligent Rotor Vibration Control Based on Electromagnetic Damping Seal
Authors: Shao Xing , Wang Weimin , Jie Fengli , Jiang Xingan
Published: August 2017

Higher energy level and more compact structure are the trend of centrifugal compressor, which may lead to the rotordynamics instability problems and high vibration. These problems restrict the improvement of the the rotating machinery operation efficiency and bring about potential safety problems, especially, such as the subsynchronous vibration and unbalance vibration. Aiming at the potential instability caused by the excitation of the seal, a seal combined with electromagnetic damping function was designed in “Investigation on the seal structure design and rotor vibration controller for back-to-back centrifugal compressor (GT2016-56900)”. Here, the capability of the Active Magnetic Bearing (AMB)-Hole Pattern Seal (HPS) is investigated in the aspect of function and load characteristic. Furthermore, the electromagnetic damping seal actuator also has the potential to implement the unbalance control. In the aspect of control theory, we combined the damping control algorithm, which is used to control the rotor instability vibration, with the self-optimizing control algorithm for fundamental vibration control of rotor bearing system. The independently optimized control strategy was chosen according to the different frequency vibration waveform. Moreover, we built a comprehensive vibration control experiment platform that is mainly combined with the rotor, tilting pad bearings and electromagnetic damping seal actuator. We did experiment on simulating the instability condition, the control of the instable low frequency vibration, and the control of fundamental frequency vibration. The experimental results show that with the control hardware of high speed FPGA module and the self-optimizing control algorithm, the electromagnetic damping sealing can not only solve the instability caused by the original seal of centrifugal compressor to improve the system stability, but also be used as the active actuator to effectively control the vibration of the rotor system. At the same time, it is also found in the experiment that how to effectively restrain the influence of irrelevant noise and the reasonable selection of initial control parameters have a very important influence on the overall control effect, which is the urgent problem to be solved in the following work. This paper also provides a new design idea and a set of feasible active vibration control strategies for the high speed centrifugal compressor and has guiding significance for solving the problem of multi-frequency vibration and rotor stability of high speed centrifugal compressor.
Novel Centrifugal Compressor Architecture for Wide-Range Operation: A Feasibility Assessment
Authors: Krivitzky Eric M. , Larosiliere Louis M.
Published: August 2017

Turbocharger compressor performance plays a critical role in the ability of advanced Internal Combustion Engines (ICE) to meet the required fuel economy and drivability targets. Increased use of exhaust gas recirculation (EGR) combined with engine downsizing has pushed compressor operation towards — and often beyond — the stability boundary. However, certain applications and market trends require that no compromise be made to the rated power conditions. This has led to a highly disparate set of requirements for a single turbocharger system resulting in much of the compressor map, including the highest-efficiency area, unused or underutilized. A large percentage of the drive cycle is spent operating the compressor at low flow rates and low pressure ratios, near the compressor surge line, in an area of low efficiency. Compromises in efficiency in critical regions of engine operation result from balancing the disparate requirements.

A current approach to meeting these disparate flow targets is the use of two turbochargers in series that are sized such that the operating compressor efficiency is markedly improved. This paper introduces a novel, hybrid single-stage compressor architecture which aerodynamically matches the functions of a series sequential dual turbocharger compression system. The use of a variable flow rate inducer bypass can provide a throttleable work-adding alternate flowpath for high-flow conditions, essentially emulating an efficient large compressor when the bypass is open and a small compressor when the bypass is closed. Using the variable bypass, the low-flow performance improves through an aerodynamically regulated inducer that is tailored to this flow regime. An engineering feasibility assessment supported by CFD, vector diagram analysis, and structural FEA suggest a substantial potential for improved performance across a wide flow range with this novel architecture.
LES-Based Scattering Matrix Method for Low-Order Acoustic Network Models
Authors: Yoon Changjin , Graham Owen , Han Fei , Kim Kwanwoo , Maxted Katsuo , Caley Thomas , Lee Jong Guen
Published: August 2017

The identification of scattering matrix method is conducted using high fidelity Large Eddy Simulations. From a series of LES results, the scattering matrices of a plain orifice and a lean premixed nozzle are evaluated and compared with the corresponding experimental data. It is confirmed that LES simulations are capable of predicting the acoustic scattering matrix, with some limitations. The magnitude of the scattering matrices imply that the acoustic energy transfer across the orifice and mixer agree fairly well with that of the scattering matrices from the experimental data. Moreover, the phase angle of transmission/reflection elements for the traveling wave in the upstream region consistently follows the experimental trends. The phase angle of transmission/reflection elements for traveling waves in the downstream region, however, shows a significant discrepancy with the experimental measurements. For the direct use of the LES-based scattering matrix method, the accuracy of determination of the phase angle of reflection/transmission of the traveling wave in the downstream region needs further study.
Testing of a Novel Post Combustion Acid Removal Process for the Direct-Fired, Oxy-Combustion Allam Cycle Power Generation System
Authors: Lu Xijia , Martin Scott , McGroddy Mike , Swanson Mike , Stanislowski Josh , Laumb Jason D.
Published: August 2017

The Allam Cycle is a high performance oxy-fuel, supercritical CO2 power cycle that offers significant benefits over traditional fossil and hydrocarbon fuel-based power generation systems. A major benefit arises in the elimination of costly pre-combustion acid gas removal (AGR) for sulfur-(SOx) and nitrogen-based (NOx) impurities by utilizing a novel downstream cleanup process that utilizes NOx first as a gas phase catalyst to effect SOx oxidation, followed by NOx removal. The basic reactions required for this process, which have been well-demonstrated in several facilities for the cleanup of exhaust gasses, ultimately convert SOx and NOx species to sulfuric, nitric and nitrous acids for removal from the supercritical CO2 stream. The process results in simplified and significantly lower cost removal of these species and utilizes conditions inherent to the Allam Cycle that are ideally suited to facilitate this process.

8 Rivers Capital and the Energy & Environmental Research Center (EERC), supported by the state of North Dakota, the US Department of Energy (DOE) and an Industrial consortium from the State of North Dakota, are currently working together to test and optimize this novel impurity removal process for pressurized, semi-closed supercritical CO2 cycles, such as the Allam Cycle. Both reaction kinetic modeling and on-site testing have been completed. Initial results show that both SOx and NOx can be substantially removed from CO2-rich exhaust gas containing excess oxygen under 20 bar operating pressure utilizing a simple packed spray column. Sensitivity of the removal rate to the concentration of oxygen and NOx was investigated. Follow-on work will focus on system optimization to improve removal efficiency and removal control, to minimize metallurgy and corrosion risks from handling concentrated acids, and to reduce overall CAPX/OPEX of the system.
Centrifugal Compressor Polytropic Performance: Consistently Accurate Results From Improved Real Gas Calculations
Authors: Evans B. Fred , Huble Spencer R.
Published: August 2017

This paper compares various methods employed to determine centrifugal compressor performance. Results show that classic Schultz style end point analyses prescribed by ASME PTC 10 [1], [2] can be augmented by numerical stepwise techniques that provide consistently accurate results without limiting assumptions. A small stage method very closely approaching the classical definition of polytropic analysis is implemented in which the accuracy of the results only depends upon the quality of the applied fluid equation of state. It is no longer necessary to distinguish between ideal and real gas methods since real gas methods are easy to implement using today’s computational tools.
Testing Advanced SiC Fiber Tows at Elevated Temperature in Silicic Acid-Saturated Steam
Authors: Robertson S. J. , Sprinkle K. B. , Ruggles-Wrenn M. B.
Published: August 2017

Investigating stressed oxidation and scale crystallization kinetics of advanced SiC fibers at elevated temperature in steam is a challenging yet essential undertaking for the assessment of the effects of oxidation on mechanical properties of SiC-SiC ceramic matrix composites (CMCs). Moisture in the oxidizing environment is known to change oxidation rates, reduce scale viscosity and lower temperatures for scale crystallization. In order to study these phenomena, a facility for testing SiC fiber tows in creep at elevated temperatures in air, in steam and in steam saturated with silicic acid was developed. The newly constructed test facility was validated through creep testing of Hi-Nicalon™-S fibers at 800°C in steam saturated with silicic acid. Testing in saturated steam resulted in formation of a uniform oxide scale. Details of the test facility design, development and experimental validation are presented.
Large-Eddy and Unsteady Reynolds-Averaged Navier-Stokes Simulations of an Axial Flow Pump for Cardiac Support
Authors: Torner Benjamin , Hallier Sebastian , Witte Matthias , Wurm Frank-Hendrik
Published: August 2017

The use of implantable pumps for cardiac support (Ventricular Assist Devices) has proven to be a promising option for the treatment of advanced heart failure. Avoiding blood damage and achieving high efficiencies represent two main challenges in the optimization process. To improve VADs, it is important to understand the turbulent flow field in depth in order to minimize losses and blood damage. The application of the Large-eddy simulation (LES) is an appropriate approach to simulate the flow field because turbulent structures and flow patterns, which are connected to losses and blood damage, are directly resolved. The focus of this paper is the comparison between an LES and an Unsteady Reynolds-Averaged Navier-Stokes simulation (URANS) because the latter one is the most frequently used approach for simulating the flow in VADs. Integral quantities like pressure head and efficiency are in a good agreement between both methods. Additionally, the mean velocity fields show similar tendencies. However, LES and URANS show different results for the turbulent kinetic energy. Deviations of several tens of percent can be also observed for a blood damage parameter, which depend on velocity gradients. Possible reasons for the deviations will be investigated in future works.
Ultrasonic harmonic generation from materials with up to cubic nonlinearity
Authors: Kube Christopher M. , Arguelles Andrea P.
Published: August 2017

This letter considers the combined effects of quadratic and cubic nonlinearity on plane wave propagation in generally anisotropic elastic solids. Displacement solutions are derived that represent the fundamental, second-, and third-harmonic waves. In arriving at the solutions, the quadratic and cubic nonlinearity parameters for generally anisotropic materials are defined. The effects of quadratic and cubic nonlinearity are shown to influence the amplitude and phase of the fundamental wave. In addition, the phase of the third-harmonic depends on a simple combination of the quadratic and cubic nonlinearity parameters. Nonlinearity parameters are given explicitly for materials having isotropic and cubic symmetry. Lastly, acoustic nonlinearity surfaces are introduced, which illustrate the nonlinearity parameters as a function of various propagation directions in anisotropic materials.
The evolutionary basis of premature migration in Pacific salmon highlights the utility of genomics for informing conservation
Authors: Prince Daniel J. , O’Rourke Sean M. , Thompson Tasha Q. , Ali Omar A. , Lyman Hannah S. , Saglam Ismail K. , Hotaling Thomas J. , Spidle Adrian P. , Miller Michael R.
Published: August 2017

Accounting for specific alleles can be necessary to prevent the loss of significant biodiversity and ecosystem services.
Webinar | Humanized mouse models in checkpoint inhibitor development
Authors: Joyce-Shaikh Barbara , Keck James
Published: August 2017

Humanized tumor xenograft mouse models are powerful experimental systems for studying in vivo interactions between human immune cells and human tumors. These models are generated by engrafting both human hematopoietic stem cells and human tumor tissue into immunodeficient mice, such as the NOD/SCID gamma (NSG) strain. In recent years, humanized tumor xenograft mouse models have been integrated into checkpoint inhibitor development programs at many pharmaceutical and biotechnology companies as an indispensable part of the drug development process. As these models have improved, they have been shown to support higher levels of human myeloid-derived cells and regulatory T cells, and have been used successfully in recent studies of anti-PD1 drugs in lung, breast, bladder, and melanoma. Join our experts to hear about the latest research developments utilizing these cutting-edge models.
A central neural circuit for itch sensation
Authors: Mu Di , Deng Juan , Liu Ke-Fei , Wu Zhen-Yu , Shi Yu-Feng , Guo Wei-Min , Mao Qun-Quan , Liu Xing-Jun , Li Hui , Sun Yan-Gang
Published: August 2017

The circuits of itching and scratching

Itch is a major clinical problem with poor treatment options. In the past few years, much progress has been made in identifying itch-selective molecules and neurons. However, we know very little about the brain circuits underlying itch processing. Mu
et al.
found that a subpopulation of itch-processing neurons in the spinal cord directly excite other neurons that project to a brain stem structure called the parabrachial nucleus. Inhibition of this spino-parabrachial pathway reduced itching and scratching in mice.

Science
, this issue p.
695
How microbes survive in the open ocean
Authors: Zehr Jonathan P. , Weitz Joshua S. , Joint Ian
Published: August 2017

Ubiquitous nonmotile marine microorganisms access dilute nutrients via diffusion
Addressing spin states with infrared light
Authors: Falk Abram L.
Published: August 2017

Divacancy defects in silicon carbide could be nodes in long-distance quantum networks
A twin tale to keep you up at night
The Less You Know the Sounder You Sleep
Juliet Butler
4th Estate, 2017. 448 pp.
Authors: Craig Jeffrey M.
Published: August 2017

A fictionalized story of two real sisters sheds light on the darker side of human research
Loss of dual leucine zipper kinase signaling is protective in animal models of neurodegenerative disease
Authors: Le Pichon Claire E. , Meilandt William J. , Dominguez Sara , Solanoy Hilda , Lin Han , Ngu Hai , Gogineni Alvin , Sengupta Ghosh Arundhati , Jiang Zhiyu , Lee Seung-Hye , Maloney Janice , Gandham Vineela D. , Pozniak Christine D. , Wang Bei , Lee Sebum , Siu Michael , Patel Snahel , Modrusan Zora , Liu Xingrong , Rudhard York , Baca Miriam , Gustafson Amy , Kaminker Josh , Carano Richard A. D. , Huang Eric J. , Foreman Oded , Weimer Robby , Scearce-Levie Kimberly , Lewcock Joseph W.
Published: August 2017

Blocking dual leucine zipper kinase slows disease progression in animal models of ALS and Alzheimer’s disease.
Characterization of
cis
-Acting RNA Elements of Zika Virus by Using a Self-Splicing Ribozyme-Dependent Infectious Clone
Authors: Liu Zhong-Yu , Yu Jiu-Yang , Huang Xing-Yao , Fan Hang , Li Xiao-Feng , Deng Yong-Qiang , Ji Xue , Cheng Meng-Li , Ye Qing , Zhao Hui , Han Jian-Feng , An Xiao-Ping , Jiang Tao , Zhang Bo , Tong Yi-Gang , Qin Cheng-Feng
Published: August 2017

Zika virus (ZIKV) has caused significant outbreaks and epidemics in the Americas recently, raising global concern due to its ability to cause microcephaly and other neurological complications. A stable and efficient infectious clone of ZIKV is urgently needed. However, the instability and toxicity of flavivirus cDNA clones in
Escherichia coli
hosts has hindered the development of ZIKV infectious clones. Here, using a novel self-splicing ribozyme-based strategy, we generated a stable infectious cDNA clone of a contemporary ZIKV strain imported from Venezuela to China in 2016. The constructed clone contained a modified version of the group II self-splicing intron
P.li.LSUI2
near the junction between the E and NS1 genes, which were removed from the RNA transcripts by an easy-to-establish
in vitro
splicing reaction. Transfection of the spliced RNAs into BHK-21 cells led to the production of infectious progeny virus that resembled the parental virus. Finally, potential
cis
-acting RNA elements in ZIKV genomic RNA were identified based on this novel reverse genetics system, and the critical role of 5′-SLA promoter and 5′-3′ cyclization sequences were characterized by a combination of different assays. Our results provide another stable and reliable reverse genetics system for ZIKV that will help study ZIKV infection and pathogenesis, and the novel self-splicing intron-based strategy could be further expanded for the construction of infectious clones from other emerging and reemerging flaviviruses.

IMPORTANCE
The ongoing Zika virus (ZIKV) outbreaks have drawn global concern due to the unexpected causal link to fetus microcephaly and other severe neurological complications. The infectious cDNA clones of ZIKV are critical for the research community to study the virus, understand the disease, and inform vaccine design and antiviral screening. A panel of existing technologies have been utilized to develop ZIKV infectious clones. Here, we successfully generated a stable infectious clone of a 2016 ZIKV strain using a novel self-splicing ribozyme-based technology that abolished the potential toxicity of ZIKV cDNA clones to the
E. coli
host. Moreover, two crucial
cis
-acting replication elements (5′-SLA and 5′-CS) of ZIKV were first identified using this novel reverse genetics system. This novel self-splicing ribozyme-based reverse genetics platform will be widely utilized in future ZIKV studies and provide insight for the development of infectious clones of other emerging viruses.