bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental and Modeling Study on Tension Characteristics of a 2.5D Woven Composites
Authors: Teng Xuefeng , Shi Duoqi , Yang Xiaoguang 
Published: November 2019

Abstract
2.5D woven composites have recently attracted much attention in the fields of aerospace and automobile industry due to their excellent properties such as low density, high thermal shock resistance, high specific strength and enhanced mechanical properties. Before the 2.5D woven composites are applied as load-bearing structure, it is necessary to have an in-depth understanding of their mechanical behavior and load transfer mechanism under external loads. In this paper, in-plane tensile tests including longitude direction and transverse direction were conducted for a 2.5D woven SiO2f/SiO2 composites at room temperature. With the full-field displacements and strains retrieved by digital image correlation (DIC) method, the mechanical properties and deformation features of the 2.5D woven composites were obtained and observed. The results show that the composite has a lower elastic modulus and fracture strength in the weft direction, and the warp yarn has weaker mechanical properties than weft yarn in the loading direction due to its crimp feature. Remarkable deformation features of the full-field displacement and strain distributions were observed, indicating that the woven structure has a great influence on the deformation evolution and load-bearing mechanism of the composite. Also, based on the actual geometrical architecture of the composite, a mesoscale finite element (FE) model was established and the deformation characteristics of the material were analyzed. The crimp of the warp yarns causes the local fiber axis to rotate with respect to the global coordinate system, which causes the effective modulus in the global direction to vary. Local coordinate systems were assigned to each node such that the local 1 direction is always parallel to the local fiber axis along the length of the warp yarns, which improves the accuracy of the simulation results. Deformation features of the 2.5D woven SiO2f/SiO2 composites were obtained in FEM simulation and discussed comparing with experimental results.
Impact of Foreign Object Damage to Leading Edge on Fatigue Capability of CMC Turbine Vanes
Authors: Obuchi Kenro , Watanabe Fumiaki , Kuroki Hiroshi , Arai Kazuyoshi 
Published: November 2019

Abstract
Ceramic matrix composites (CMCs) are expected to make turbine components lighter because they have lower density than nickel-based super alloys which have been used for turbine components. Also they are expected to improve the efficiency of gas turbine engines by realizing higher turbine inlet temperature (TIT), because they have higher temperature capability.
One of the technical issues of CMCs is that they have relatively low impact resistance comparing with nickel-based alloy. In the previous work, it was estimated that the foreign object damage (FOD) on CMC turbine vanes under the actual engine condition is less than 0.36-mm-depth. The concern of such damaged CMC turbine vanes is a decrease in a fatigue capability due to the dent particular to the leading edge (L/E). The fatigue strength reduction can be caused by the stress concentration due to the dented shape and the oxidation due to the coating spallation. There are various works about the impact resistance or the fatigue capability of CMCs, but there are little works which assess the fatigue capability of CMCs which was damaged by foreign object.
The objective of this work was to clarify the impact of FOD to L/E on the fatigue capability of SiC/SiC CMC turbine vane.
The tension-tension low cycle fatigue (LCF) tests and high cycle fatigue (HCF) tests were conducted using four types of test pieces at elevated temperature in the steam environment. The first one was smooth test piece with anti-oxidation coating, the second one was the test piece which had notch with coating, the third one was the test piece which had notch without coating at notched area and the fourth one was the test piece which was damaged by dropped weight test simulating FOD.
The result showed that impact of stress concentration due to notch shape on fatigue capability is small. It was also cleared that uncoated condition did not have impact on the LCF capability but had impact on the HCF capability. The HCF strength reduction of TP without coating to the TP with coating was about 35% at 107 cycles. More fiber breakage was observed at the fracture surface of the TP without coating tested in HCF condition, on the other hand more fiber pullout was observed at that of other TPs. The results suggest that the HCF strength reduction was caused by oxidation when the bare CMC was exposed by FOD.
From this work, it was concluded that the loss of coating due to FOD impacted on HCF strength of CMC turbine vane, but it can be accepted because turbine vane is normally designed so that it can endure the stress concentration at L/E due to FOD (typically kt = 3).
Investigation of Turbulence Characteristics in a Tip Leakage Flow Model Using Large-Eddy Simulation
Authors: Gao Yanfei , Liu Yangwei , Lu Lipeng 
Published: November 2019

Abstract
A simple tip leakage flow (TLF) model which consists of a square duct with a longitudinal slit on the top of a side wall is proposed to reproduce the jet flow/main flow shear mechanism of the tip leakage vortex (TLV) rolling-up in turbomachinery. Large-eddy simulation (LES) is employed to investigate the turbulence characteristics of the flow model under low Reynolds number condition. The geometry and boundary conditions of the flow model are simplified from a compressor rotor and modified to apply to low-Re condition for LES. The vortex structures and turbulence characteristics of the LES results are compared with the measurements of the rotor. It is found that the flow model could reproduce similar flow field and turbulence structures compared with the TLF in the real rotor, thus it can be used to investigate the turbulence in practical flows. Reynolds-Averaged Navier-Stokes (RANS) calculations are also carried out. The mean flow and turbulence behaviors of different cases are analyzed. The budgets of turbulent kinetic energy (k) are analyzed to investigate the turbulence transport nature in the TLF model, indicating that the non-equilibrium transport process of k is significant, especially the pressure and turbulent transport, which is not predicted by RANS.
Design of 20 kW Turbomachinery for Closed Loop Supercritical Carbon Dioxide Brayton Test Loop Facility
Authors: Seshadri Lakshminarayanan , Sathish Sharath , Kumar Pramod , Giri Gaurav , Nassar Abdul , Moroz Leonid , Setty Raghavendra , Gopi Pramod Chandra , Namburi Adi Narayana 
Published: November 2019

Abstract
Indian Institute of Science, Bangalore in collaboration with Sandia National Labs has developed a 140kW (thermal) simple recuperated supercritical CO2 (s-CO2) test facility to enable power generation of up to net 20 kWe output using turbomachinery components. The primary intent of the test loop is to understand the design and operational aspects of an s-CO2 Brayton cycle for distributed power generation. This paper describes the development of suitable turbomachinery to be deployed in the test loop. Turbomachinery design study is primarily performed using a commercial design tool AxStream® for both design and off-design operating conditions with a maximum cycle temperature limit of 525°C and a pressure of 145 bar. Present design considers a decoupled turbine and compressor driven independently by an electrical motor and a generator pair. This arrangement provides flexibility to independently assess compressor and turbine prototypes and also helps establish stable operation of the s-CO2 Brayton test loop. A range of single stage compressor and turbine geometries are independently evaluated considering un-coupled shafts and appropriate loss models using the above boundary conditions. Specific geometries are filtered based on total-to-total efficiency for a given shaft speed. The speed of the turbo-machinery is restricted to 40,000 rpm to enable independent testing and characterization using direct drive high-speed Switched Reluctance (SRM) motor-generator pair that is being developed in-house for this purpose. The investigation reveals the absence of a suitable compressor and turbine geometry at desired operating speed, hence, to circumvent the problem of low blade heights in the preliminary impeller design at 40,000 rpm, the turbomachinery is designed for 65,000 rpm and the off-design condition is taken for study.
Application of the Nozzle Analogy to Easily Predict Steam Turbine Performance With Minimal Geometric Input
Authors: Fuls W. F. , Clark J. S. , Marx A. C. 
Published: November 2019

Abstract
A simple method for modelling steam turbines using a nozzle analogy was recently published. The method describes both stator and rotor components of a turbine with an appropriate nozzle definition, and makes use of the traditional velocity triangles to determine work output. What makes the method convenient is that it only requires a reasonable estimate of the effective nozzle throat area per blade row, as well as properly chosen loss coefficients. A complete turbine train with multiple stages can easily be solved using a simple 1-D pressure correction method. The method was demonstrated to match detailed inter-stage turbine data quite accurately.
This paper elaborates on the application of the method. It presents a more thorough procedure for establishing the nozzle throat areas using a turbine lay-out drawing, as well as consideration of possible reaction ratio variation between successive stages. Furthermore, the loss coefficients are determined using the methods described by Traupel and Zehner. The paper presents these in a compressed and digitized format for easy implementation in a software code.
A case study is presented to show how the model can quantify improvements to blade profiles. Another case study models a complete boiler feed pump turbine connected to the feedwater pumps and includes the partial arc governing stage and cold re-heat supply. This specific model demonstrated the method’s ability to accurately model a turbine at low load and high back pressure conditions.
Turbine system modelers can apply the method presented here to their own equipment and obtain trustworthy results without the need for detailed profile geometry or complex CFD analyses. The method is however limited to subsonic flow between blade rows, hence some modern transonic last stage blade designs might not be adequately represented.
Igniter Testing for sCO2 Oxy-Combustion
Authors: Katcher Kelsi M. , Allison Timothy C. , Coogan Shane , Jin Yuin , Lim Chansun , Chang Sungho 
Published: November 2019

Abstract
Utilizing direct-fired sCO2 oxy-combustion is attractive for power generation applications because of the cycle’s inherent carbon capture, high efficiency, and small machinery footprint. However, there is a large amount of uncertainty regarding the combustion process of natural gas in carbon dioxide diluent at supercritical pressures. One such area of uncertainty is in regards to the ignition system. The performance of most common ignition systems is not proven at the elevated pressures and densities typical of these cycles.
This paper presents an evaluation and down-selection of potential ignition systems considered for a sCO2 oxy-combustor igniter. The ignition systems considered include spark ignition, laser ignition, heating element auto-ignition, external preheat auto-ignition, ignition using solid or liquid fuels, and external torch ignition. After a preliminary review, spark ignition and laser ignition were chosen for system reliability and repeatability. To further quantify the practicality of each system, a spark igniter and laser igniter were lab-scale tested to determine breakdown energies associated with these igniters. The spark igniter was tested using gaseous CO2 and SF6 (to attain higher fluid densities). The laser igniter was tested using supercritical CO2 and gaseous CO2. An additional round of testing was conducted using the laser igniter in a constant volume combustion chamber (CVCC). Natural gas was combusted with oxygen in varying levels of CO2 dilution to determine the required laser power for stable, reliable ignition and to quantify the high dilution flammability limit. Based on these test results, a laser igniter was selected as the most practical option for high-pressure sCO2 combustor ignition.
Aspects of Creep Fatigue Lifetime Assessment for High Temperature Components With Accumulative Model
Authors: Linn Stefan , Kontermann Christian , Oechsner Matthias 
Published: November 2019

Abstract
Alternating temperatures induce thermomechanical stresses in thick-walled components such as turbine rotors or housings, which can lead to fatigue and superimposed creep. Subsequently, damage can occur at their heated surfaces. Under the nowadays prevailing operating conditions of power plants with multiple cold, warm and hot starts as reaction to the high volatility of electric demand from fossil fired power plants for ensuring grid stability, methods for lifetime assessment are coming more into the focus of investigations and research. Engineers are trying to estimate the residual lifetimes of in-service components and operators of power plants ask for strategies to minimize the calculative material damage while simultaneously providing a maximum flexibility with shortest response times on altered demands. Among constitutive models, which are not subject of this paper, accumulative models for lifetime assessment were introduced several decades ago and are partially considered in applicable standards. Such models based on a damage accumulation are easy to apply but they are considered to be either very imprecise or very conservative, while the conservatism reflects the necessity of large safety margins.
This paper summarize a few measures, which are suitable to improve the predictive quality of models based on a simple time-fraction rule. The proposed model is based on a synthesis of hysteresis loops for isothermal and non-isothermal conditions, concepts for consideration of cyclic softening or hardening during lifetime, concepts for dealing with internal back stresses, mean strains or stresses, and for accounting of creep-fatigue interaction. The latter is based on a so-called transition time concept, where the creep damage during dwell times partially attributes to the portion of fatigue damage, which in turn is determined from fatigue life curves for dwell time experiments. In addition, the model comprises a concept for the post-processing of transient FEM calculations and dealing with multiaxial loading conditions.
Since the essentials of the proposed method with the transition time concept were published more than 10 years ago, the listed modifications improve the benefit for daily engineering usage. Validation experiments provide evidence of the models predicting capabilities with acceptable uncertainty.
Geometric Mistuning Reduced Order Model Development Utilizing Bayesian Surrogate Models for Component Mode Calculations
Authors: Beck Joseph A. , Brown Jeffrey M. , Kaszynski Alex A. , Carper Emily B. , Gillaugh Daniel L. 
Published: November 2019

Abstract
By design, Integrally Bladed Rotors (IBRs) are meant to be tuned, rotationally periodic structures. However, unique variations in geometries and material properties from sector-to-sector, referred to as mistuning, destroy the structural periodicity. This results in mode localization that can induce forced response levels greater than what is predicted with a tuned-structure analysis. Furthermore, mistuning and mode localization are random processes that require stochastic treatments when analyzing the distribution of fleet responses. Generating this distribution can be computationally intensive when using the full finite element model. To overcome this expense, Reduced Order Models (ROMs) have been developed to accommodate fast calculations of mistuned forced response levels for a fleet of random IBRs. Usually, ROMs can be classified by two main families: frequency-based and geometry-based methods. Frequency-based ROMs assume mode shapes do not change due to mistuning. However, this assumption has been shown to cause errors that propagate to the fleet distribution. To circumvent these errors, geometry-based ROMs have been developed to provide accurate predictions. However, these methods require recalculating modal data during ROM formulations. This increases the computational expense in computing fleet distributions. A new geometry-based ROM is presented to reduce this cost. The developed ROM utilizes a Bayesian surrogate model in place of sector modal calculations required in ROM formulations. This method, referred to as the Surrogate Modal Analysis for Geometry Mistuning Assessments (SMAGMA), will propagate the uncertainties of the surrogate prediction to the forced response. Assessments of the ROM accuracy are made by comparing results to the true forced response levels and results computed by a frequency-based ROM.
Flow in a Scaled Turbine Coolant Channel With Roughness due to Additive Manufacturing
Authors: Hanson David R. , McClain Stephen T. , Snyder Jacob C. , Kunz Robert F. , Thole Karen A. 
Published: November 2019

Abstract
Additive manufacturing (AM) approaches such as Laser Powder Bed Fusion (L-PBF) are being explored to reduce manufacturing costs of gas turbine components. Surfaces of additively manufactured components exhibit distinctive roughness characteristics that significantly affect the pressure losses and heat transfer. For this study, a coupon with a vertical internal flow passage was created using L-PBF and characterized using x-ray tomography. The roughness pattern was extracted using the spanwise-planar extraction approach. Also, two surfaces consisting of distributions of ellipsoids were created to capture the important statistical characteristics of the original rough surface. The resulting roughness geometries were scaled by 102x and applied to the internal wall of the Roughness Internal Flow Tunnel (RIFT). Measurements of friction losses and velocity profiles were obtained. Detailed Reynolds-Averaged Navier Stokes (RANS) simulations using grid-resolved roughness of flow in the RIFT were also performed using an in-house Computational Fluid Dynamics (CFD) code. The present approach combining experimental measurements and CFD simulation of an up-scaled roughness coupon provides a more detailed picture of the flow-field within the roughened channel than was previously available. The measured friction factor of the baseline up-scaled rough channel is within 15% of the original engine-scale channel within the fully turbulent regime. The ellipsoid surfaces are seen to have a friction factor 30% lower than the up-scaled rough channel; the authors hypothesize that this is due to bulk span-wise ridges being present in the up-scaled rough surface but not in the ellipsoid surfaces.
Investigating Instabilities in a Rotating Detonation Combustor Operating With Natural Gas-Hydrogen Fuel Blend: Effect of Air Preheat and Annulus Width
Authors: Roy Arnab , Bedick Clinton , Ferguson Donald , Sidwell Todd , Strakey Peter 
Published: November 2019

Abstract
Propagation characteristics of a detonation wave in an air-breathing Rotating Detonation Combustor (RDC) using natural gas-hydrogen fuel blends is presented in this paper. Short duration (∼up to 6s) experiments were performed on a 152.4mm OD uncooled RDC with two different annulus gap widths (5.08mm and 7.62mm) over a range of equivalence ratios (0.6–1.0) at varying inlet air temperatures (∼65°C-204°C) and natural gas content (up to 15%) with pre-combustion operating pressure slightly above ambient.
It was observed that the RDC, with an annulus gap width of 5.08mm, was inherently unstable when natural gas (NG) was added to the hydrogen fuel while operating at pre-combustion pressures near ambient and at an inlet air temperature of 65°C. Increasing the annulus gap width to 7.62mm improved the stability of the detonation wave at similar temperatures and pressure permitting operation with as much as 5% NG by volume. While observed speeds of the detonation waves were still below theoretical values, an increase in inlet air temperature reduced the variability in wave speed. The frequency analysis thus explored in this study is an effort to quantify detonation instability in an RDC under varying operational envelope. The data presented is relevant towards developing strategies to sustain a stable detonation wave in an RDC using natural gas for land based power generation.
Validation Studies of Linear Oscillating Compressor Cascade and Use of Influence Coefficient Method
Authors: Phan H. M. , He L. 
Published: November 2019

Abstract
Advanced predictions of blade flutter have been continually pursued. It is noted however that validation cases of unsteady CFD methods against experimental cases with detailed 3D unsteady pressures are still rather lacking. The main objectives of the present work are two-folds. Firstly, validate and understand the characteristics of blade tip clearance, as well as a bubble-type flow separation for an unsteady CFD solver against a 3D oscillating cascade experiment. And secondly, examine the applicability of the Influence Coefficient Method (ICM) as widely used in an oscillating linear cascade setup.
In the first part, the capability of a widely used commercial solver (CFX) for unsteady flows induced by a 3D oscillating compressor cascade is examined. The present computations have shown consistently a destabilizing effect of increasing blade tip clearance, in agreement with the experiment. More remarkably, the computational analyses reveal a distinctive interplay between the inlet endwall boundary layer and the tip clearance in relation to the aerodynamic damping. Different inlet endwall boundary layer thicknesses are shown to lead to qualitatively different aeroelastic stability characteristics in relation to tip clearance. The aero-damping variation with the tip-clearance under the influence of the inlet endwall boundary layer seems to correlate closely to a balancing act between the passage vortex and the tip-leakage vortex. The tip clearance aeroelastic behaviour seems also in line with a simple quasi-steady analysis. On the other hand, the mid-chord laminar bubble separation on suction surface, though with a clear signature in the local aero-damping, has negligible effects on the overall stability.
The second part aims to examine computationally the applicability of the influence coefficient method in a linear cascade setup. The comparison between the cascade based ICM data and a baseline ‘tuned cascade’ shows that the differences in the sensitivity to the far-field treatment can be significant, depending on interblade phase angles. On the other hand, non-linearity effects closely relevant to the basic linear assumption of the ICM are shown to only have a small influence. The present results suggest that extra caution should be exercised when comparing a CFD-based tuned cascade model with a finite cascade-based ICM model, at conditions close to acoustic resonance. The resultant discrepancies may well arise from the inherently different far-field sensitivities between the two models, rather than those typical numerical and physical modelling aspects of interest (e.g. meshing, spatial and temporal discretization errors as well as turbulence modelling).