bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of Periodic Reynolds Stress Oscillations in a Forced Turbulent Premixed Swirling Flame
Authors: Douglas Christopher , Lim Jamie , Smith Travis , Emerson Benjamin , Lieuwen Timothy , Jiang Naibo , Fugger Christopher , Yi Tongxun , Felver Josef , Roy Sukesh , Gord James
Published: July 2018

This work is motivated by the thermoacoustic instability challenges associated with ultra-low emissions gas turbine (GT) combustors. It demonstrates the first use of high-speed dual-plane orthogonally-polarized stereoscopic-particle image velocimetry (PIV) and synchronized OH planar laser-induced fluorescence in a premixed swirling flame. We use this technique to explore the effects of combustion and longitudinal acoustic forcing on the time- and phase-averaged flow field—particularly focusing on the behavior of the Reynolds stress in the presence of harmonic forcing. We observe significant differences between ensemble-averaged and time-averaged Reynolds stress. This implies that the large-scale motions are nonergodic, due to coherent oscillations in Reynolds stress associated with the convection of periodic vortical structures. This result has important implications on hydrodynamic stability models and reduced-order computational fluid dynamics simulations, which do show the importance of turbulent transport on the problem, but do not capture these coherent oscillations in their models.
Experimental and Calculation Study of Diesel-Generator Performance in Transient Conditions
Authors: Kuznetsov Alexandr , Kharitonov Sergei , Ryzhov Valeriy
Published: July 2018

To provide pregiven quality ratings of control processes of maximal speed deviation and transient process duration is an important task for diesel generators. Calculation study of methods intended for improving transient process quality is carried out using mathematical dynamic model of diesel engine and control system. Dynamic operation modes of turbocharged engine differ considerably from static ones. Experimental study of one-cylinder diesel engine was conducted with transient condition simulation to validate approaches to the development of engine dynamic model. Based on the study results, mathematical model and computer program to calculate transient processes were developed. Calculation study of methods intended for improving diesel-generator control processes was performed using the computer program.
Fracture Analyses of Soft Materials With Hard Inclusion
Authors: Pei Pengyu , Shi Yan , Yang Guang , Gao Cunfa
Published: July 2018

This paper presents a detailed study on the fracture behaviors of soft materials with hard inclusion. Stress concentrations on the interfaces of hard and soft materials are considered as the key factor for structure fracture. Based on linear fracture theory, the fracture behaviors of soft materials with elliptical hard inclusion are investigated. Stress concentrations, consisting of tensile, hoop, and compressive stress, are observed with changes of inclusion geometries and the modulus ratio of hard and soft materials. And their influences on the categories of principal stress concentration are shown in a phase diagram in the current paper. Finite element analysis is carried out with consideration of the large deformation of soft material, which demonstrates the effectiveness of the theoretical predictions in a great scope of applied loading. Finally, the predictions based on theoretical and simulation results are validated by experiments. This work points out that the hard line inclusion is the source of danger in soft materials just like the crack in brittle materials.
Variable Geometry Stair Ascent and Descent Controller for a Powered Lower Limb Exoskeleton
Authors: Ekelem Andrew , Bastas Gerasimos , Durrough Christina M. , Goldfarb Michael
Published: July 2018

This paper describes a control approach for a lower limb exoskeleton intended to enable stair ascent and descent of variable geometry staircases for individuals with paraplegia resulting from spinal cord injury (SCI). To assess the efficacy of ascent and descent functionality provided by the control approach, the controller was implemented in a lower limb exoskeleton and tested in experimental trials on three subjects with motor-complete SCI on three staircases of varying geometry. Results from the assessments indicate that subjects were able to capably ascend and descend step heights varying from 7.6 to 16.5 cm without changing control settings; the controller provided for step time consistency highly representative of healthy subjects (9.2% variation in exoskeleton step time, relative to 7.7% variation in healthy subjects); and the exoskeleton provided peak joint torques on average 110% and 74% of the healthy-subject peak joint torques during stair ascent and descent, respectively. Subject perceived exertion during the stair ascent and descent activities was rated between “light” and “very light.”
A New Parallel Manipulator With Multiple Operation Modes
Authors: Gallardo-Alvarado Jaime , Rodriguez-Castro Ramon
Published: July 2018

In this work, a new parallel manipulator with multiple operation modes is introduced. The proposed robot is based on a three-degrees-of-freedom (3DOF) parallel manipulator endowed with a three-dof central kinematic chain, where by blocking some specific kinematic pairs, the robot can modify its mobility. Hence, the robot manipulator is able to assume the role of a limited-dof or a nonredundant parallel manipulator. Without loss of generality, the instantaneous kinematics of one member of the family of parallel manipulators generated by the reconfigurable parallel manipulator, the three-RPRRC + RRPRU nonredundant parallel manipulator with decoupled motions, is approached by means of the theory of screws. For the sake of completeness, the finite kinematics of the robot is also investigated. Numerical examples are included with the purpose to clarify the method of kinematic analysis.
Flow Field and Hot Streak Migration Through a High Pressure Cooled Vanes With Representative Lean Burn Combustor Outflow
Authors: Bacci Tommaso , Lenzi Tommaso , Picchi Alessio , Mazzei Lorenzo , Facchini Bruno
Published: July 2018

Modern lean burn aero-engine combustors make use of relevant swirl degrees for flame stabilization. Moreover, important temperature distortions are generated, in tangential and radial directions, due to discrete fuel injection and liner cooling flows respectively. At the same time, more efficient devices are employed for liner cooling and a less intense mixing with the mainstream occurs. As a result, aggressive swirl fields, high turbulence intensities, and strong hot streaks are achieved at the turbine inlet. In order to understand combustor-turbine flow field interactions, it is mandatory to collect reliable experimental data at representative flow conditions. While the separated effects of temperature, swirl, and turbulence on the first turbine stage have been widely investigated, reduced experimental data is available when it comes to consider all these factors together.In this perspective, an annular three-sector combustor simulator with fully cooled high pressure vanes has been designed and installed at the THT Lab of University of Florence. The test rig is equipped with three axial swirlers, effusion cooled liners, and six film cooled high pressure vanes passages, for a vortex-to-vane count ratio of 1:2. The relative clocking position between swirlers and vanes has been chosen in order to have the leading edge of the central NGV aligned with the central swirler. In order to generate representative conditions, a heated mainstream passes though the axial swirlers of the combustor simulator, while the effusion cooled liners are fed by air at ambient temperature. The resulting flow field exiting from the combustor simulator and approaching the cooled vane can be considered representative of a modern Lean Burn aero engine combustor with swirl angles above ±50 deg, turbulence intensities up to about 28% and maximum-to-minimum temperature ratio of about 1.25. With the final aim of investigating the hot streaks evolution through the cooled high pressure vane, the mean aerothermal field (temperature, pressure, and velocity fields) has been evaluated by means of a five-hole probe equipped with a thermocouple and traversed upstream and downstream of the NGV cascade.
Ultimate Bearing Capacity Assessment of Hull Girder With Asymmetric Cross Section
Authors: Li Chenfeng , Fu Peng , Ren Huilong , Xu Weijun , Guedes Soares C.
Published: July 2018

The objective of this study is to investigate the variation of neutral axis of ship hull girder due to asymmetric geometry or asymmetric load, and its influence on the ultimate strength (ULS) of hull girder. In order to account for asymmetric geometries and loads of hull girders, the force equilibrium and force-vector equilibrium criteria together with a minimum convergence factors (error) method are employed to determine the translation and rotation of neutral axis plane (NAP) of symmetric or asymmetric hull cross section in the application of Smith's method at each step of curvature of the hull girder. The ULSs of Dow's 1/3 frigate model with three predefined structural integrity states, one intact and two damaged, respectively, is investigated by the improved Smith's method (ISM) for a range of variation of heeling angles. The influence of asymmetric geometry and load on the motion of NAP and on the ULS are analyzed and discussed. The results show that the improved iteration strategy together with the minimum convergence factors (error) method is efficient and more accurate in searching the translation and rotation of NAP. Finally, the envelope curves of the bending moments in the three predefined integrity states are obtained, which can be used for assessing ULS of hull girders under combined vertical and horizontal wave bending moments.
A Model and Application of Vibratory Surface Grinding
Authors: Bechcinski Grzegorz , Ewad Heisum , Tsiakoumis Vaios , Pawlowski Witold , Kepczak Norbert , McMillan Alison , Batako Andre D. L.
Published: July 2018

This paper presents a model of surface grinding with superimposed oscillation of the workpiece. The parameters of the model were experimentally derived and the equations of motions of the system were solved using Matlab. The results obtained showed a significant decrease in the amplitude of the relative vibration between the wheel and workpiece when the oscillation was superimposed onto the feed motion of the workpiece. A range of experimental work was undertaken and the results showed that the vibratory process had a superior performance in absolute terms with reference to conventional grinding. Low forces along with longer tool life were recorded with the added vibration. A notion of dynamic relief was introduced to express the efficiency of the vibratory process.
Effects of Process Parameters on Crack Inhibition and Mechanical Interlocking in Friction Self-Piercing Riveting of Aluminum Alloy and Magnesium Alloy
Authors: Ma YunWu , He GuanZhong , Lou Ming , Li YongBing , Lin ZhongQin
Published: July 2018

Friction self-piercing riveting (F-SPR) process has shown advantages over fusion welding, solid state welding, and traditional mechanical joining processes in joining dissimilar materials. Because of the thermo-mechanical nature of F-SPR process, formation of the joint is determined by both riveting force and softening degree of materials to be joined. However, it is still not clear that how exactly the riveting force and generated frictional heat jointly influence mechanical interlocking formation and crack inhibition during F-SPR process. To address these issues, F-SPR process was applied to join 2.2 mm-thick aluminum alloy AA6061-T6 to 2.0 mm-thick magnesium alloy AZ31B. The correlation of riveting force, torque responses, and energy input with joint quality was investigated systematically under a wide range of process parameter combinations. It was found that a relatively greater final peak force and higher energy input were favorable to produce sound joints. Based on that, a two-stage F-SPR method was proposed to better control the energy input and riveting force for improved joint quality. The joints produced by the two-stage method exhibited significantly improved lap-shear strength, i.e., 70% higher than traditional self-piercing riveting (SPR) joints and 30% higher than previous one-stage F-SPR joints. This research provides a valuable reference for further understanding the F-SPR joint formation mechanism and conducting process optimization.
Efficient Generation of Engine Representative Tip Timing Data Based on a Reduced Order Model for Bladed Rotors
Authors: Figaschewsky Felix , Hanschke Benjamin , Kühhorn Arnold
Published: July 2018

In modern compressors, the assessment of blade vibration levels as well as health monitoring of the components are fundamental tasks. Traditionally, this assessment is done by the application of strain gauges (SG) to some blades of the assembly. In contrast to SGs, blade tip timing (BTT) offers a contactless monitoring of all blades of a rotor and there is no need of a telemetry system. A major issue in the interpretation of BTT data is the heavily undersampled nature of the signal. Usually, newly developed BTT algorithms are tested with sample data created by simplified structural models neglecting many of the uncertainties and disturbing influences of real applications. This work focuses on the creation of simulated BTT datasets as close as possible to real case measurements. For this purpose, a subset of nominal system modes (SNM) representation of a compressor rotor is utilized. This model is able to include a large number of features present in real measurements, such as mistuning, static blade deflections due to centrifugal loads, aerodynamic damping, and multiple mode resonances. Additionally, manufacturing deviations of the blade geometry, probe positioning errors (PPEs) in the BTT system, and noise in the time of arrivals (TOAs) are captured by the BTT simulation environment. The main advantage of the created data is the possibility to steadily increase the signal complexity. Starting with a “perfect” signal the simulation environment is able to add different uncertainties one after the other. This allows the assessment of the influence of different features occurring in real measurements on the performance and accuracy of the analysis algorithms. Finally, a comparison of simulated BTT data and real data acquired from a rig test is shown to validate the presented approach of BTT data generation.
Prediction of Anterior Cruciate Ligament Force Produced by Tibiofemoral Compression During Controlled Knee Flexion: A New Robotic Testing Methodology
Authors: Markolf Keith L. , Boguszewski Daniel V. , Yamaguchi Kent T. , Lama Christopher J. , McAllister David R.
Published: July 2018

Application of tibiofemoral compression force (TCF) has been shown to produce anterior cruciate ligament (ACL) injuries in a laboratory setting. A new robotic testing methodology was utilized to predict ACL forces generated by TCF without directly loading the ligament. We hypothesized that ACL force, directly recorded by a miniature load cell during an unconstrained test, could be predicted by measurements of anterior tibial restraining force (ARF) recorded during a constrained test. The knee was first flexed under load control with 25 N TCF (tibial displacements and rotations unconstrained) to record a baseline kinematic pathway. Tests were repeated with increasing levels of TCF, while recording ACL force and knee kinematics. Then tests with increasing TCF were performed under displacement control to reproduce the baseline kinematic pathway (tibia constrained), while recording ARF. This allowed testing to 1500 N TCF since the ACL was not loaded. TCF generated ACL force for all knees (n = 10) at 50 deg flexion, and for eight knees at 30 deg flexion (unconstrained test). ACL force (unconstrained test) and ARF (constrained test) had strong linear correlations with TCF at both flexion angles (R2 from 0.85 to 0.99), and ACL force was strongly correlated with ARF at both flexion angles (R2 from 0.76 to 0.99). Under 500 N TCF, the mean error between ACL force prediction from ARF regression and measured ACL force was 4.8±7.3 N at 30 deg and 8.8±27.5 N at 50 deg flexion. Our hypothesis was confirmed for TCF levels up to 500 N, and ARF had a strong linear correlation with TCF up to 1500 N TCF.
Experimental Investigation of Flow Laminarization in a Graphite Flow Channel at High Pressure and High Temperature
Authors: Valentín Francisco I. , Artoun Narbeh , Kawaji Masahiro
Published: July 2018

Hot wire anemometer (HWA) measurements of turbulent gas flow have been performed in upward forced convection experiments at pressures ranging from 0.6 MPa to 6.3 MPa and fluid temperatures ranging from 293 K to 673 K. The results are relevant to deteriorated turbulent heat transfer (DTHT) and flow laminarization in strongly heated gas flows which could occur in gas-cooled very high temperature reactors (VHTRs).2 The HWA signals were analyzed to directly confirm the occurrence of flow laminarization phenomenon due to strong heating. An X-probe was used to collect radial and axial velocity fluctuation data for pressurized air and pure nitrogen flowing through a circular 16.8 mm diameter flow channel in a 2.7 m long graphite test section for local Reynolds numbers varying from 500 to 22,000. Analyses of the Reynolds stresses and turbulence frequency spectra were carried out and used as indicators of laminar, transition, or fully turbulent flow conditions. Low Reynolds stresses indicated the existence of laminar or transitional flow until the local Reynolds number reached a large value, ∼11,000 to 16,000, much higher than the conventional Re = 4000–5000 for transition to fully turbulent flow encountered in pipe flows. The critical Reynolds number indicating the completion of transition approximately doubled as the pressure was increased from 0.6 MPa to 2.8 MPa.
Nanopore Confinement and Pore Connectivity Considerations in Modeling Unconventional Resources
Authors: Sanaei Alireza , Ma Yixin , Jamili Ahmad
Published: July 2018

Gas and liquid production from nanopore shale resources substantially increased during the past decade due to the advances in horizontal drilling and multistage hydraulic fracturing. Transport properties and mechanisms deviate from their bulk behavior when the pore sizes in unconventional formations are in the order of nanoscale. This is due to the dominant molecule–pore wall interaction effects comparing to molecule–molecule interactions in nanopores. Thus, the physics of multiphase flow in current commercial simulators should be changed to include the effect of pore size on both transport mechanisms and fluid properties. In this study, we analyze the effect of fluid confinement on phase behavior, fluid properties, and condensate banking around the hydraulic fracture where nanopores perform as the dominate storage region and dispersed with pores with bulk behavior. We modified critical properties of the fluid components for different pore sizes in the phase behavior calculations. Using experimental results, we developed a new correlation for estimating mean pore size as a function of permeability and porosity. Moreover, we considered pore size distribution of a shale sample to divide the reservoir into different regions. For each region, a specific permeability is assigned using the new developed correlation. Three different types of connectivity are considered between pores and its impact on production mechanisms is analyzed. Results of this study indicated that neglecting nanopore confinement effect on phase behavior results in an underestimation of the production while neglecting permeability change with pore size results in an overestimation of hydrocarbon production. The connectivity of different pore sizes has a significant impact on reservoir performance and determines the dominant factor.
The Role of Frequency and Phase Difference Between the Flow and the Actuation Signal of a Tangential Synthetic Jet on Dynamic Stall Flow Control
Authors: Tadjfar Mehran , Asgari Ehsan
Published: July 2018

In this paper, we have studied the active flow control (AFC) of a pitching airfoil by means of a tangential synthetic jet actuator (SJA) using computational fluid dynamics. The airfoil was NACA0012 which pitched about its quarter-chord with a sinusoidal motion at Reynolds number of 1 × 106. Several high-frequency actuations (HFAs), in the order of nominal shedding frequency of static condition; Fj+= 1.0, 2.0, and 3.0, one low frequency actuation Fj+= 0.2, and one very low frequency actuation Fj+= 0.047 where the frequency of the SJA matched that of the pitching motion of the airfoil were considered. The resulting lift and drag diagrams were compared with each other, as well as with the uncontrolled case and the continuous jet. It was found that oscillations in drag and lift hysteresis curves with the associated local minima and maxima were connected to the ingestion/expulsion cycles of the SJA. At the very low-frequency actuation (LFA), which synched the frequency of the SJA to the frequency of the pitching motion, several phase differences (Δφ) between SJA and pitching motion were studied. Our numerical results have demonstrated that the synched frequency case with Δφ=180deg was far more superior to all other controlled cases studied here and the continued jet of our previous work. This condition even performed better than high frequency actuation with higher jet velocity ratios.
Gradient-Informed Basis Adaptation for Legendre Chaos Expansions
Authors: Tsilifis Panagiotis A.
Published: July 2018

The recently introduced basis adaptation method for homogeneous (Wiener) chaos expansions is explored in a new context where the rotation/projection matrices are computed by discovering the active subspace (AS) where the random input exhibits most of its variability. In the case where a One-dimensional (1D) AS exists, the methodology can be applicable to generalized polynomial chaos expansions (PCE), thus enabling the projection of a high-dimensional input to a single input variable and the efficient estimation of a univariate chaos expansion. Attractive features of this approach, such as the significant computational savings and the high accuracy in computing statistics of interest are investigated.
Experimental and Numerical Investigations of Novel Natural Gas Low NOx Burners for Heavy Duty Gas Turbine
Authors: Cerutti Matteo , Riccio Giovanni , Andreini Antonio , Becchi Riccardo , Facchini Bruno , Picchi Alessio
Published: July 2018

A novel dry low-NOx gas turbine technology requires well-balanced assessments since the early development phases. The weak knowledge of often conflicting aspects, such as operability and manufacturability, make any roadmap difficult to be drawn. Introduction of innovative manufacturing technologies such as the direct metal laser sintering (DMLS) process allows rapid manufacturing of components and test them in dedicated facilities to support real-time development of new products. The use of such a manufacturing process allows the adoption of designed experiment-based development strategies, which are still uncommon at industrial level, due to the reduced time from drawings to test.The paper describes a reactive test campaign performed by BHGE in cooperation with University of Florence, aimed at the exploration of capabilities of different innovative burners in terms of pollutant emissions containment and blow-out margin. In particular, the test campaign has been conceived to provide a robust estimate of the effects of key geometrical parameters on principal burner performances. The flame stabilization mechanism of the investigated burners is based on the swirling flow generated by different setup of two internal channels: corotating and counter-rotating radial and axial swirlers. The effect of both the shape and the size of the internal air passages, as well as of the swirler characteristics, has been matter of investigation. Burners were tested in a single-cup test rig operated at moderate pressure conditions (up to 6 bar), with two levels of preheated air temperature (300 °C and 400 °C). Each burner was equipped with two natural gas feeding lines representing the diffusion (pilot) and premixed (main) fuel supplies: both lines were regulated during tests to assess the effect of fuel split on emissions and to identify a stable low-NOx operating window, within which a lean blow-out test was performed. Dynamic pressure probes were used to evaluate the onset of combustion instabilities. The burner development was supported by computational fluid dynamics (CFD) investigations with the purpose to have a detailed understating of the flow-field and flame structure and to perform a preliminary screening to select the most promising solutions for the testing phase. The post process of the experimental results has allowed to correlate the main design parameters to burner performance variables discovering possible twofold optimizations in terms of emissions and operability.
Micro Silicon–Graphene–Carbon Nanotube Anode for Full Cell Lithium-ion Battery
Authors: Gao Xianfeng , Wang Fenfen , Gollon Sam , Yuan Chis
Published: July 2018

An electrochemically stable hybrid structure material consisting of porous silicon (Si) nanoparticles, carbon nanotubes (CNTs), and reduced graphene oxide (rGO) is developed as an anode material (Si/rGO/CNT) for full cell lithium-ion batteries (LIBs). In the developed hybrid material, the rGO provides a robust matrix with sufficient void space to accommodate the volume change of Si during lithiation/delithiation and a good electric contact. CNTs act as a mechanically stable and electrically conductive support to enhance the overall mechanical strength and conductivity. The developed Si/rGO/CNT composite anode has been first tested in half cell and then in full cell lithium-ion batteries. In half cell, the composite anode shows a high reversible capacity of 1100 mAh g−1 with good capacity retention over 500 cycles when cycled at 1 A g−1. In a full cell lithium-ion battery paired up with LiNi1/3Mn1/3Co1/3O2 (NMC) cathodes, the composite anode shows a specific charge capacity of 161.4 mAh g−1 and a discharge capacity of 152.8 mAh g−1, respectively, with a Coulombic efficiency of 94.7%.
Influence of Leakage Flows on Hot Gas Ingress
Authors: Patinios Marios , Ong Irvin L. , Scobie James A. , Lock Gary D. , Sangan Carl M.
Published: July 2018

One of the most important problems facing gas turbine designers today is the ingestion of hot mainstream gases into the wheel-space between the turbine disk (rotor) and its adjacent casing (stator). A rim seal is fitted at the periphery and a superposed sealant flow—typically fed through the bore of the stator—is used to prevent ingress. The majority of research studies investigating ingress do so in the absence of any leakage paths that exist throughout the engine's architecture. These inevitable pathways are found between the mating interfaces of adjacent pieces of hardware. In an environment where the turbine is subjected to aggressive thermal and centrifugal loading, these interface gaps can be difficult to predict and the resulting leakage flows which pass through them even harder to account for. This paper describes experimental results from a research facility which experimentally models hot gas ingestion into the wheel-space of an axial turbine stage. The facility was specifically designed to incorporate leakage flows through the stator disk; leakage flows were introduced axially through the stator shroud or directly underneath the vane carrier ring. Measurements of CO2 gas concentration, static pressure, and total pressure were used to examine the wheel-space flow structure with and without ingress from the mainstream gas-path. Data are presented for a simple axial-clearance rim-seal. The results support two distinct flow-structures, which are shown to be dependent on the mass-flow ratio of bore and leakage flows. Once the leakage flow was increased above a certain threshold, the flow structure is shown to transition from a classical Batchelor-type rotor-stator system to a vortex-dominated structure. The existence of a toroidal vortex immediately inboard of the outer rim-seal is shown to encourage ingestion.
Prediction of Aerodynamically Induced Blade Vibrations in a Radial Turbine Rotor Using the Nonlinear Harmonic Approach
Authors: Kovachev Nikola , Waldherr Christian U. , Mayer Jürgen F. , Vogt Damian M.
Published: July 2018

Resonant response of turbomachinery blades can lead to high cycle fatigue (HCF) if the vibration amplitudes are excessive. Accurate and reliable simulations of the forced response phenomenon require detailed CFD and FE models that may consume immense computational costs. In the present study, an alternative approach is applied, which incorporates nonlinear harmonic (NLH) CFD simulations in a one-way fluid–structure interaction (FSI) workflow for the prediction of the forced response phenomenon at reduced computational costs. Five resonance crossings excited by the stator in a radial inflow turbocharger turbine are investigated and the aerodynamic excitation and damping are predicted using this approach. Blade vibration amplitudes are obtained from a subsequent forced response analysis combining the aerodynamic excitation with aerodynamic damping and a detailed structural model of the investigated turbine rotor. A comparison with tip timing measurement data shows that all predicted values lay within the range of the mistuned blade response underlining the high quality of the utilized workflow.
Turbomachine Design for Supercritical Carbon Dioxide Within the sCO2-HeRo.eu Project
Authors: Hacks Alexander , Schuster Sebastian , Dohmen Hans Josef , Benra Friedrich-Karl , Brillert Dieter
Published: July 2018

The paper aims to give an overview over the keystones of design of the turbomachine for a supercritical CO2 (sCO2) Brayton cycle. The described turbomachine is developed as part of a demonstration cycle on a laboratory scale with a low through flow. Therefore, the turbomachine is small and operates at high rotational speed. To give an overview on the development, the paper is divided into two parts regarding the aerodynamic and mechanical design. The aerodynamic design includes a detailed description on the steps from choosing an appropriate rotational speed to the design of the compressor impeller. For setting the rotational speed, the expected high windage losses are evaluated considering the reachable efficiencies of the compressor. The final impeller design includes a description of the blading development together with the final geometry parameters and calculated performance. The mechanical analysis shows the important considerations for building a turbomachine with integrated design of the three major components: turbine, alternator, and compressor (TAC). It includes different manufacturing techniques of the impellers, the bearing strategy, the sealing components, and the cooling of the generator utilizing the compressor leakage. Concluding the final design of the TAC is shown and future work on the machine is introduced.
Guiding Actuator Designs for Active Flow Control of the Precessing Vortex Core by Adjoint Linear Stability Analysis
Authors: Müller Jens S. , Lückoff Finn , Oberleithner Kilian
Published: July 2018

The fundamental impact of the precessing vortex core (PVC) as a dominant coherent flow structure in the flow field of swirl-stabilized gas turbine combustors has still not been investigated in depth. In order to do so, the PVC needs to be actively controlled to be able to set its parameters independently to any other of the combustion system. In this work, open-loop actuation is applied in the mixing section between the swirler and the generic combustion chamber of a nonreacting swirling jet setup to investigate the receptivity of the PVC with regard to its lock-in behavior at different streamwise positions. The mean flow in the mixing section as well as in the combustion chamber is measured by stereoscopic particle image velocimetry (SPIV), and the PVC is extracted from the snapshots using proper orthogonal decomposition (POD). The lock-in experiments reveal the axial position in the mixing section that is most suitable for actuation. Furthermore, a global linear stability analysis (LSA) is conducted to determine the adjoint mode of the PVC which reveals the regions of highest receptivity to periodic actuation based on mean flow input only. This theoretical receptivity model is compared with the experimentally obtained receptivity data, and the applicability of the adjoint-based model for the prediction of optimal actuator designs is discussed.
Experimental Study on Pressure Losses in Porous Materials
Authors: Fantozzi Giacomo , Kinell Mats , Carrera Sara Rabal , Nilsson Jenny , Kuesters Yves
Published: July 2018

Recent technological advances in the field of additive manufacturing have made possible to manufacture turbine engine components characterized by controlled permeability in desired areas. These have shown great potential in cooling application such as convective cooling and transpiration cooling and may in the future contribute to an increase of the turbine inlet temperature. This study investigates the effects of the pressure ratio, the thickness of the porous material, and the hatch distance used during manufacturing on the discharge coefficient. Moreover, two different porous structures were tested, and in total, 70 test objects were investigated. Using a scanning electron microscope, it is shown that the porosity and pore radius distribution, which are a result from the used laser power, laser speed, and hatch distance during manufacturing, will characterize the pressure losses in the porous sample. Furthermore, the discharge coefficient increases with increasing pressure ratio, while it decreases with increasing thickness to diameter ratio. The obtained experimental data were used to develop a correlation for the discharge coefficient as a function of the geometrical properties and the pressure ratio.
Reliability-Based Design Optimization of Microstructures With Analytical Formulation
Authors: Acar Pinar
Published: July 2018

Microstructures are stochastic by their nature. These aleatoric uncertainties can alter the expected material performance substantially and thus they must be considered when designing materials. One safe approach would be assuming the worst case scenario of uncertainties in design. However, design under the worst case conditions can lead to over-conservative solutions that provide less effective material properties. Here, a more powerful design approach can be developed by implementing reliability constraints into the optimization problem to achieve superior material properties while satisfying the prescribed design criteria. This is known as reliability-based design optimization (RBDO), and it has not been studied for microstructure design before. In this work, an analytical formulation that models the propagation of microstructural uncertainties to the material properties is utilized to compute the probability of failure. Next, the analytical uncertainty solution is integrated into the optimization problem to define the reliability constraints. The presented optimization under uncertainty scheme is exercised to maximize the yield stress of α-Titanium and magnetostriction of Galfenol, respectively.
Uncertainty Quantification of NOx Emission Due to Operating Conditions and Chemical Kinetic Parameters in a Premixed Burner
Authors: Yousefian Sajjad , Bourque Gilles , Monaghan Rory F. D.
Published: July 2018

Many sources of uncertainty exist when emissions are modeled for a gas turbine combustion system. They originate from uncertain inputs, boundary conditions, calibration, or lack of sufficient fidelity in a model. In this paper, a nonintrusive polynomial chaos expansion (NIPCE) method is coupled with a chemical reactor network (CRN) model using Python to quantify uncertainties of NOx emission in a premixed burner. The first objective of uncertainty quantification (UQ) in this study is development of a global sensitivity analysis method based on the NIPCE method to capture aleatory uncertainty on NOx emission due to variation of operating conditions. The second objective is uncertainty analysis (UA) of NOx emission due to uncertain Arrhenius parameters in a chemical kinetic mechanism to study epistemic uncertainty in emission modeling. A two-reactor CRN consisting of a perfectly stirred reactor (PSR) and a plug flow reactor (PFR) is constructed in this study using Cantera to model NOx emission in a benchmark premixed burner under gas turbine operating conditions. The results of uncertainty and sensitivity analysis (SA) using NIPCE based on point collocation method (PCM) are then compared with the results of advanced Monte Carlo simulation (MCS). A set of surrogate models is also developed based on the NIPCE approach and compared with the forward model in Cantera to predict NOx emissions. The results show the capability of NIPCE approach for UQ using a limited number of evaluations to develop a UQ-enabled emission prediction tool for gas turbine combustion systems.
Intentional Response Reduction by Harmonic Mistuning of Bladed Disks With Aerodynamic Damping
Authors: Willeke Sebastian , Schwerdt Lukas , Panning-von Scheidt Lars , Wallaschek Jörg
Published: July 2018

A harmonic mistuning concept for bladed disks is analyzed in order to intentionally reduce the forced response of specific modes below their tuned amplitude level. By splitting a mode pair associated with a specific nodal diameter pattern, the lightly damped traveling wave mode of the nominally tuned blisk is superposed with its counter-rotating complement. Consequently, a standing wave is formed in which the former wave train benefits from an increase in aerodynamic damping. Unlike previous analyses of randomly perturbed configurations, the mode-specific stabilization is intentionally promoted through adjusting the harmonic content of the mistuning pattern (MT). Through a reorientation of the localized mode shapes in relation to the discrete blades, the response is additionally attenuated by an amount of up to 7.6%. The achievable level of amplitude reduction is analytically predicted based on the properties of the tuned system. Furthermore, the required degree of mistuning for a sufficient separation of a mode pair is derived.
Intelligent Reasoning for Gas Turbine Fault Isolation and Ambiguity Resolution
Authors: Tang Liang , Volponi Allan J.
Published: July 2018

An engine health management (EHM) system typically consists of automated logic for data acquisition, parameter calculation, anomaly detection and eventually, fault identification (or isolation). Accurate fault isolation is pivotal to timely and cost-effective maintenance but is often challenging due to limited fault symptom observability and the intricacy of reasoning with heterogeneous parameters. Traditional fault isolation methods often utilize a single fault isolator (SFI) that primarily relies on gas path performance parameters. While effective for many performance-related faults, such approaches often suffer from ambiguity when two or more faults have signatures that are very similar when monitored by a rather limited number of gas path sensors. In these cases, the ambiguity often has to be resolved by experienced analysts using additional information that takes many different forms, such as various nongas path symptoms, full authority digital engine control fault codes, comparisons with the companion engine, maintenance records, and quite often, the analyst's gas turbine domain knowledge. This paper introduces an intelligent reasoner that combines the strength of an optimal, physics-based SFI and a fuzzy expert system that mimics the analytical process of human experts for ambiguity resolution. A prototype diagnostic reasoner software has been developed and evaluated using existing flight data. Significant performance improvements were observed as compared with traditional SFI results. As a generic reasoning framework, this approach can be applied not only to traditional snapshot data, but to full flight data analytics as well.
Analysis of Deformation of Mistuned Bladed Disks With Friction and Random Crystal Anisotropy Orientation Using Gradient-Based Polynomial Chaos Expansion
Authors: Rajasekharan Rahul , Petrov E. P.
Published: July 2018

Single crystal blades used in high pressure turbine bladed disks of modern gas-turbine engines exhibit material anisotropy. In this paper, the sensitivity analysis is performed to quantify the effects of blade material anisotropy orientation on deformation of a mistuned bladed disk under static centrifugal load. For a realistic, high fidelity model of a bladed disk both: (i) linear and (ii) nonlinear friction contact conditions at blade roots and shrouds are considered. The following two kinds of analysis are performed: (i) local sensitivity analysis (LSA), based on first-order derivatives of system response with respect to design parameters, and (ii) statistical analysis using polynomial chaos expansion (PCE). The PCE is used to transfer the uncertainty in random input parameters to uncertainty in static deformation of the bladed disk. An effective strategy, using gradient information, is proposed to address the “curse of dimensionality” problem associated with statistical analysis of realistic bladed disk.
Restraint Systems in Tactical Vehicles: Uncertainty Study Involving Airbags, Seatbelts, and Military Gear
Authors: Drignei Dorin , Mourelatos Zissimos P. , Zhamo Ervisa , Hu Jingwen , Chen Cong , Reed Matthew , Gruber Rebekah
Published: July 2018

Adding advanced safety features (e.g., airbags) to restraint systems in tactical vehicles could decrease the injury risk of their occupants. The impact of frontal crashes on the occupants has been assessed recently through experimental data and finite element (FE) models. However, the number of such experiments is relatively small due to high cost. In this paper, we conduct an uncertainty study to infer the advantage of including advanced safety features, if a larger number of experiments were possible. We introduce the concept of group injury risk distribution that allows us to quantify under uncertainty the injury risk associated with advanced safety features, while averaging out the effect of uncontrollable factors such as body size. Statistically, the group injury risk distribution is a mixture of individual injury risk distributions of design conditions in the group. We infer that advanced safety features have the potential to reduce substantially injury risk in frontal crashes.
A Thévenin-Inspired Approach to Multiple Scattering in Acoustics
Authors: Williams Randall P. , Hall Neal A.
Published: July 2018

We have previously shown how Thévenin's theorem may be used to solve problems in linear acoustic scattering from a mobile body, by forming the solution as a superposition of the field scattered from the body when held immobile and the solution for radiation from the body in a quiescent field (Williams, R. P. and Hall, N. A., 2016, “Thévenin Acoustics” J. Acoust. Soc. Am., 140(6), pp. 4449–4455). For problems involving scattering from multiple mobile bodies, the approach can be extended by using multiport network formalism. The use of network formalism allows for the effects of multiple scattering to be treated using analogous circuit models, facilitating the integration of scattering effects into circuit-based models of acoustic transducers. In this paper, we first review Thévenin's theorem for electrical and linear acoustic systems, and discuss the Thévenin-inspired approach to scattering from one rigid, mobile cylinder. Two-port formalism is introduced as a way to address problems involving two scatterers. The method is illustrated using the problem of scattering from a pair of rigid, mobile cylinders in an ideal plane progressive wave. The velocities of the cylinders and the resultant pressure field in response to the incoming wave are found. Unique features of the method compared to more conventional approaches are discussed.
Comparison of maximum length sequence and randomized stimulation and averaging methods on the bottlenose dolphin auditory brainstem response
Authors: Burkard Robert , Finneran James J. , Mulsow Jason
Published: July 2018

The purpose of the present study was to compare auditory brainstem responses (ABRs) using two approaches that allow the use of high stimulation rates, but with different temporal variability in the interstimulus interval: maximum length sequences (MLS) and iterative randomized stimulation and averaging (I-RSA). ABRs were obtained to click stimuli in six bottlenose dolphins (Tursiops truncatus). In experiment 1, click level was held constant and click rate varied from 25 to 1250 Hz. For MLS, interstimulus intervals varied by a factor of 6 at each rate, while for I-RSA the interstimulus intervals varied by ± 0.5 ms regardless of rate. In experiment 2, stimulus rates ranged from 100 to 1000 Hz and click level varied from 105 to 135 dB re: 1 μPa. For experiment 1, MLS and I-RSA showed similar decreases in ABR peak amplitudes and increases in ABR peak latencies and interwave intervals with increasing rate. For experiment 2, there was an increase in peak latency and a decrease in peak amplitude with decreasing click level; however, the effects of click level were reduced at higher rates. The results indicate that the greater jitter for MLS compared to I-RSA does not substantially affect the dolphin ABR.
Impaired recovery of the Great Barrier Reef under cumulative stress
Authors: Ortiz Juan-Carlos , Wolff Nicholas H. , Anthony Kenneth R. N. , Devlin Michelle , Lewis Stephen , Mumby Peter J.
Published: July 2018

The GBR is losing its ability to recover from disturbances, but local management action can help partially restore this ability.
Air pollution and visitation at U.S. national parks
Authors: Keiser David , Lade Gabriel , Rudik Ivan
Published: July 2018

Ozone levels in U.S. national parks are similar to those of U.S. cities, and are negatively associated with visitation.
TCR signal strength controls the differentiation of CD4
+
effector and memory T cells
Authors: Snook Jeremy P. , Kim Chulwoo , Williams Matthew A.
Published: July 2018

Strong TCR signals favor the differentiation of short-lived effector T
H
1 cells over long-lived memory T cells.
Prospective Cohort Study of the Tolerability of Prosthetic Joint Infection Empirical Antimicrobial Therapy
Authors: Triffault-Fillit Claire , Valour Florent , Guillo Ronan , Tod Michel , Goutelle Sylvain , Lustig Sébastien , Fessy Michel-Henry , Chidiac Christian , Ferry Tristan ,   on behalf of the Lyon BJI Study Group Tristan Ferry Florent Valour Thomas Perpoint André Boibieux François Biron Patrick Miailhes Florence Ader Agathe Becker Sandrine Roux Claire Triffault-Fillit Fatiha Daoud Johanna Lippman Evelyne Braun Christian Chidiac Yves Gillet Laure Hees Sébastien Lustig Elvire Servien Yannick Herry Romain Gaillard Antoine Schneider Michel-Henry Fessy Anthony Viste Philippe Chaudier Romain Desmarchelier Tanguy Mouton Cyril Courtin Lucie Louboutin Sébastien Martres Franck Trouillet
Published: July 2018

The empirical use of vancomycin in combination with a broad-spectrum beta-lactam is currently recommended after the initial surgery of prosthetic joint infection (PJI). However, the tolerability of such high-dose intravenous regimens is poorly known.