bluuebunny/crossref_metadata_2025 huggingface dataset:
The Dietary Inflammatory Index and asthma burden in children: A latent class analysis
Authors: Cilluffo Giovanna , Han Yueh‐Ying , Ferrante Giuliana , Dello Russo Marika , Lauria Fabio , Fasola Salvatore , Montalbano Laura , Malizia Velia , Forno Erick , La Grutta Stefania
Published: September 2021

Introduction

Unbalanced dietary intake has been increasingly recognized as an important modifiable risk factor for asthma. In this study, we assessed whether a pro‐inflammatory diet is associated with higher asthma burden in three steps: (1) identification of asthma latent classes (LC) based on symptoms, indoor exposures, and pulmonary function; (2) identification of risk factors associated with LC membership; and (3) estimation of the probabilities of LC membership with variation in DII.

Methods

A cross‐sectional study on 415 children aged 5–14 years (266 with persistent asthma and 149 controls). LC analysis was performed in asthmatic children. The DII was calculated based on a semiquantitative food frequency questionnaire. Elastic net logistic regression was used to investigate whether increasing DII was associated with worse asthma burden.

Results

Two LCs were identified. Children in Class 1, “high burden,” had higher symptom burden and worse lung function. Children in Class 2, “low burden,” had lower symptom burden and less impaired lung function but were more subject to indoor exposures. DII was the only risk factor significantly associated with Class 1 membership. As the DII increased (from −4.0 to +4.0), the probability of Class 1 membership increased from 32% to 65% when compared with control group, whereas it increased from 41% to 72% when compared with Class 2.

Conclusions

We identified two phenotypes of persistent asthma associated with different disease burden linked to indoor exposures. An increasing DII was associated with high‐burden asthma, providing further evidence about the role of a pro‐inflammatory diet in asthma morbidity.
Good Guesses
Authors: Dorst Kevin , Mandelkern Matthew
Published: September 2021

This paper is aboutguessing: how people respond to a question when they aren't certain of the answer. Guesses show surprising and systematic patterns that the most obvious theories don't explain. We argue that these patterns reveal that people aim to optimize a tradeoff between accuracy and informativity when forming their guess. After spelling out our theory, we use it to argue that guessing plays a central role in our cognitive lives. In particular, our account of guessing yields new theories of belief, assertion, and theconjunction fallacy—the psychological finding that people sometimes rank a conjunction as more probable than one of its conjuncts. More generally, we suggest that guessing helps explain how boundedly rational agents like us navigate a complex, uncertain world.
Upscaling ecological restoration: toward a new legal principle and protocol on ecological restoration in international law
Authors: Cliquet An , Telesetsky Anastasia , Akhtar‐Khavari Afshin , Decleer Kris
Published: September 2021

The United Nations Decade of Ecosystem Restoration is an opportunity for States to advance the development of substantive and qualitative international law obligations for conducting restoration activities. This will help countries move beyond the more quantitative target‐driven approach that currently focuses international commitments on the percentage of degraded areas that have to be restored. In this paper, we argue for two pathways for States to accelerate and pursue international obligations to undertake ecological restoration. Firstly, we advocate for the development of a new international legal principle on ecological restoration, adding to existing international environmental law principles such as the prevention principle, and aiming at achieving the highest level of recovery possible. Secondly, we advocate to utilize available mechanisms through the 1992 Convention on Biological Diversity and create a new protocol that will spell out a high ambition level for ecological restoration and a legal basis for adopting generally accepted rules and standards for restoration. The voluntary SER Principles and Standards can play an important role in the development of the legal principle on ecological restoration and standards of best practice.
An empirical investigation of determinants of life insurers’ performance: Evidence from selected countries in Central, Eastern, and Southeastern Europe (CESEE)
Authors: Srbinoski Bojan , Poposki Klime , Čibej Gorazd
Published: September 2021

Central, Eastern, and Southeastern Europe's life insurance market has received limited attention in the literature due to a lack of available data and lower level of maturity. However, part of the region is characterized by extraordinary growth rates, moderate to high concentration, a heavy presence of foreign affiliates, recent regulatory compliance, and low insurance culture. This study analyzes the firm‐specific, industry and macroeconomic determinants of life insurers’ performance in selected CESEE countries. We employ a dynamic panel GMM two‐step system estimator and uncover the most important drivers of life insurers’ profitability in the region. We find that size, leverage, liquidity, reinsurance, market share, and business growth matter for total profitability, while expense management drive underwriting profitability. The study expands the current literature on insurers’ performance by examining a neglected region and discusses location‐specific characteristics for foreign presence in the region.
From the Main Determinants of Self‐Declared Minimum Income to the Measure of Sub‐National Purchasing Power Parity
Authors: Carbonnier Clément
Published: September 2021

Exploiting a French living condition survey from 2008 to 2015, this paper documents the main determinants of self‐declared minimum income necessary to achieve decent living. Declared minimum income is strongly related to actual income. Isolating this relationship, it is possible to highlight the other determinants: family composition, housing tenure, socioprofessional status, region, and degree of urbanization. A sub‐national measure of purchasing power parity is then developed. From a macroeconomic point of view, it leads to lower Gini index and higher rate of poverty in PPP terms than in nominal terms. However, these changes are heterogeneous, with increased poverty concentration around Paris, Mediterranean coast, and in the North. It is worth noting that the North, the poorest region in nominal terms, presents relatively low price of housing but a relatively high cost of living.
Inference of Heterogeneous Treatment Effects using Observational Data with High-Dimensional Covariates
Authors: Qiu Yumou , Tao Jing , Zhou Xiao-Hua
Published: September 2021

This study proposes novel estimation and inference approaches for heterogeneous local treatment effects using high-dimensional covariates and observational data without a strong ignorability assumption. To achieve this, with a binary instrumental variable, the parameters of interest are identified on an unobservable subgroup of the population (compliers). Lasso estimation under a non-convex objective function is developed for a two-stage generalized linear model, and a debiased estimator is proposed to construct confidence intervals for treatment effects conditioned on covariates. Notably, this approach simultaneously corrects the biases due to high-dimensional estimation at both stages. The finite sample performance is evaluated via simulation studies, and real data analysis is performed on the Oregon Health Insurance Experiment to illustrate the feasibility of the proposed procedure.
Assessing the origin of pisoids within a travertine system in the border of Puna Plateau, Argentina
Authors: Mors R. Agustin , Gomez Fernando J. , Astini Ricardo A. , Celestian Aaron J. , Corsetti Frank A.
Published: September 2021

The origin of pisoids in a diversity of environments has been recently discussed. While traditionally considered physico‐chemical sedimentary products developed in turbulent environments, or even grown in situ, new results show that microbes may influence their development. In the Terma Los Hornos travertine system, two types of actively forming pisoids were recognized: (i) laminated pisoids with a concentrically laminated crust surrounding a nucleus; and (ii) dendriform radial pisoids with no distinct nucleus. Laminated pisoids form in turbulent pools at the base of waterfalls, while dendritic pisoids develop within small depressions between terracettes, and they can occur superposed as a result of episodic transport and recycling within the travertine system (for example, dendritic textures as nucleus of laminated pisoids). The laminated pisoids are characterized by laterally constant laminae thickness with high inheritance and low amounts of randomly distributed organic matter and microbial remains, suggesting a predominantly abiogenic origin. In contrast, the dendritic pisoids exhibit an intimate relationship with diatoms and filamentous bacteria suggesting a stronger biotic influence in their formation. Thus, both abiogenic and biogenic carbonate structures can coexist in the same hydrothermal system. Pisoids found in the stratigraphic record of Terma Los Hornos allowed to test the preservation potential of the primary signals and reconstructing early diagenetic overprints.
The Complexity of the Concept of Literary Autonomy
Authors: Tevdoradze Nino
Published: September 2021

This paper is an attempt to analyse the concept of literary autonomy, to explore its various manifestations in previous and current theories of literary studies and literary aesthetics, and to fit it into a broad outlook of literature's specificity and uniqueness. It defends the idea of literature's separate identity, however, not at the expense of breaking free of the concept of meaning in the strict sense, seeking special literary value in the independence of aesthetic value from other values, or in the claim that literature has no purpose outside of itself, and then argues that such position need not be confounded with reductionism.
Collagen Fibril Orientation in Tissue Specimens From Atherosclerotic Plaque Explored Using Small Angle X-Ray Scattering
Authors: Silva Herbert , Tassone Christopher , Ross Elsie Gyang , Lee Jason T. , Zhou Wei , Nelson Drew
Published: September 2021

Atherosclerotic plaques can gradually develop in certain arteries. Disruption of fibrous tissue in plaques can result in plaque rupture and thromboembolism, leading to heart attacks and strokes. Collagen fibrils are important tissue building blocks and tissue strength depends on how fibrils are oriented. Fibril orientation in plaque tissue may potentially influence vulnerability to disruption. While X-ray scattering has previously been used to characterize fibril orientations in soft tissues and bones, it has never been used for characterization of human atherosclerotic plaque tissue. This study served to explore fibril orientation in specimens from human plaques using small angle X-ray scattering (SAXS). Plaque tissue was extracted from human femoral and carotid arteries, and each tissue specimen contained a region of calcified material. Three-dimensional (3D) collagen fibril orientation was determined along scan lines that started away from and then extended toward a given calcification. Fibrils were found to be oriented mainly in the circumferential direction of the plaque tissue at the majority of locations away from calcifications. However, in a number of cases, the dominant fibril direction differed near a calcification, changing from circumferential to longitudinal or thickness (radial) directions. Further study is needed to elucidate how these fibril orientations may influence plaque tissue stress–strain behavior and vulnerability to rupture.
Reversed-Torsion-Type Crush Energy Absorption Structure and Its Inexpensive Partial-Heating Torsion Manufacturing Method Based on Origami Engineering
Authors: Xilu Zhao , Kong Chenghai , Yang Yang , Hagiwara Ichiro
Published: September 2021

Current vehicle energy absorbers face two problems during a collision in that there is only a 70% collapse in length and there is a high initial peak load. These problems arise because the presently used energy-absorbing column has no deployment shrinkage function. It has been shown that a column called the Reversed Spiral Origami Structure (RSO) developed by Nojima solves the above two problems. However, in the case of the existing technology of the RSO, the forming cost of hydroforming is too expensive for application to a real vehicle structure. Therefore, a new structure imitating RSO, named the Reversed Torsion Origami Structure (RTO), has been developed, which has excellent energy absorption in simulation. Here, a manufacturing system is developed for the RTO cheaply. Excellent results are obtained also in a physical experiment. The RTO can replace conventional energy absorbers and is expected to be widely used in not only automobile structures but also building structures.
Sorting of Poly-Disperse Particle by Entrapment Using Liquid Carrier System
Authors: Khalil Ibrahim , Khoda Bashir
Published: September 2021

A thin viscous layer is found over a substrate when it is immersed in a polymer solution. The layer thickness depends on the polymer and the solvent type, their volume fraction, and the substrate. If the liquid solution contains particles, they are entrapped on the viscous polymer layer, acting as the binder. The trade-off between the viscous force and the centrifugal force on the particle determines the entrapment. Furthermore, the size of entrained particles is dictated by the binder concentration of the solution. A particle filtration technique is presented using the entrapment phenomenon from a polydisperse mixture. A dimensionless number called the entrapment factor is introduced to correlate the particle entrapment with various parameters. By changing the entrapment factor, three distinct entrapment regimes are achieved and explained from a polydisperse mixture. The experimental result shows that entrapped particles become larger as the factor increases, which can be controlled with multiple parameters of the dipping process. The proposed technique can lead to a filtration process of the wide-range polydisperse particle mixture over the capillary filtration processes.
Design and Performance Evaluation of a Hybrid Hand Exoskeleton for Hand Opening/Closing
Authors: Gull Muhammad Ahsan , Bai Shaoping , Blicher Jakob Udby , Staermose Tobias Glaston
Published: September 2021

Finger extensor muscle weakness and flexor hypertonia are the most commonly reported issues among patients suffering from amyotrophic lateral sclerosis (ALS). Moreover, the relative hyperflexion of the wrist and fingers has limited their ability to voluntarily open the hand and interact with the external environment. In this work, a hybrid hand exoskeleton is developed to prevent the relative hyperflexion of the fingers and wrist and facilitate the users in their functional hand opening by compensating the flexor hypertonia. This exoskeleton, combining a passive device with the soft extra muscle (SEM) glove, assists users in normal hand opening/closing required for some basic activities of daily living. The paper presents kinematic and static models of passive hand exoskeleton design. Moreover, the proposed design is tested and evaluated by comparing the volunteer hand opening with the exoskeleton assistance using the flex sensors attached on the dorsal side of the middle finger, ring finger, and thumb with both healthy subjects and patients. The results show the effectiveness of using the hybrid exoskeleton in improving anatomical hand opening/closing capabilities.
The Influence of Deterministic Surface Roughness and Freestream Turbulence on Transitional Boundary Layers: Heat Transfer Distributions and a New Transition Onset Correlation
Authors: Gramespacher Christoph , Stripf Matthias , Bauer Hans-Jörg
Published: September 2021

Heat transfer measurements in transitional flat plate boundary layers subjected to surface roughness, strong pressure gradients, and freestream turbulence are presented. The surfaces considered consist of a smooth reference and 26 deterministic surface topographies that vary in roughness element aspect ratio, height, and density. They are designed to cover the full range of roughness regimes from smooth over transitionally rough to fully rough. For each surface, two pressure distributions, characteristic for a suction and a pressure side turbine vane, are investigated. Inlet Reynolds numbers range from 3.0 × 105 to 6.0 × 105 and inlet turbulence intensity is varied between 1% and 8%. Furthermore, different turbulence Reynolds numbers, i.e., turbulence length scales, are realized while the incident turbulence intensity is kept constant. Additionally, the turbulence intensity and Reynolds stress distributions in the freestream along the flat plate are measured using x-wire probes. Results show a strong influence of roughness and turbulence intensity on the onset of transition. The new data set is used to develop an improved correlation considering the roughness height, density, and shape as well as the turbulence intensity and turbulent length scales.
Scale-Resolving Simulations of Steady and Pulsatile Flow Through Healthy and Stenotic Heart Valves
Authors: Hoeijmakers M. J. M. M. , Morgenthaler V. , Rutten M. C. M. , van de Vosse F. N.
Published: September 2021

Blood-flow downstream of stenotic and healthy aortic valves exhibits intermittent random fluctuations in the velocity field which are associated with turbulence. Such flows warrant the use of computationally demanding scale-resolving models. The aim of this work was to compute and quantify this turbulent flow in healthy and stenotic heart valves for steady and pulsatile flow conditions. Large eddy simulations (LESs) and Reynolds-averaged Navier–Stokes (RANS) simulations were used to compute the flow field at inlet Reynolds numbers of 2700 and 5400 for valves with an opening area of 70 mm2 and 175 mm2 and their projected orifice-plate type counterparts. Power spectra and turbulent kinetic energy were quantified on the centerline. Projected geometries exhibited an increased pressure-drop (>90%) and elevated turbulent kinetic energy levels (>147%). Turbulence production was an order of magnitude higher in stenotic heart valves compared to healthy valves. Pulsatile flow stabilizes flow in the acceleration phase, whereas onset of deceleration triggered (healthy valve) or amplified (stenotic valve) turbulence. Simplification of the aortic valve by projecting the orifice area should be avoided in computational fluid dynamics (CFD). RANS simulations may be used to predict the transvalvular pressure-drop, but scale-resolving models are recommended when detailed information of the flow field is required.
Models of Shear-Induced Platelet Activation and Numerical Implementation With Computational Fluid Dynamics Approaches
Authors: Han Dong , Zhang Jiafeng , Griffith Bartley P. , Wu Zhongjun J.
Published: September 2021

Shear-induced platelet activation is one of the critical outcomes when blood is exposed to elevated shear stress. Excessively activated platelets in the circulation can lead to thrombus formation and platelet consumption, resulting in serious adverse events such as thromboembolism and bleeding. While experimental observations reveal that it is related to the shear stress level and exposure time, the underlying mechanism of shear-induced platelet activation is not fully understood. Various models have been proposed to relate shear stress levels to platelet activation, yet most are modified from the empirically calibrated power-law model. Newly developed multiscale platelet models are tested as a promising approach to capture a single platelet's dynamic shape during activation, but it would be computationally expensive to employ it for a large-scale analysis. This paper summarizes the current numerical models used to study the shear-induced platelet activation and their computational applications in the risk assessment of a particular flow pattern and clot formation prediction.
Alarms, Shutdowns and Trip Rationalization
Authors: Mohamed Rasidi , Sukeri Syafeq Moazari , Mendoza Robert , Kurz Rainer
Published: September 2021

A key function for a control system in a gas turbine train is to keep the operation of all components within a range of parameters that keep the unit safe. If the operating parameters of components fall outside the desired range for safe operation, the control system will detect these and create an alarm. For critical parameters, the control system may initiate an alarm and a shutdown of the unit. In many instances, an alarm may precede the shutdown command.

Frequent discussions evolve around situations that lead to a shutdown of the train, as shutdowns impact the availability of the turbomachinery equipment, but in a wider sense also the availability of the compressor station. Therefore, shutdowns impact the profitability of a system. On the other hand, shutdowns may prevent significant, costly damage to the equipment, with significant downtime, and financial implications.

In this lecture, we will discuss different methodologies for shutdown requirements, in the effort to maximize availability of units. Particular emphasis will be given to aging machines as well as machines where the instrumentation, and the control algorithms may no longer be state of the art, or where unnecessary or spurious shutdowns plague an installation.
Experimental and Numerical Investigations of the Effects of Real Shape Modeling and Non-Equilibrium Condensation Modeling on the Flow Pattern in Steam Turbine
Authors: Tabata Soichiro , Sasao Yasuhiro , Segawa Kiyoshi
Published: September 2021

This study presents the results of measurements in a scaled model turbine test rig operated at Mitsubishi Hitachi Power Systems, Ltd. In this paper, the flow pattern obtained by traverse measurements is compared with the results of CFD.

In order to investigate the flow field in the low pressure steam turbine, the tests are carried out using a test turbine (4 stages) of × 0.33 scale. The velocity and pressure fields are evaluated by traverse measurements.

The corresponding CFD are performed by ANSYS CFX. Generally, shroud and stub are used in last stage rotating blades of industrial steam turbine to provide high structural stability by increasing stiffness and damping. In this study, the shroud and stub are modeled in CFD to evaluate the effect on flow pattern. Besides, in order to evaluate the effects of super cooling in blade rows, non-equilibrium condensation is modeled in CFD by ANSYS CFX. The computation model is constructed as accurate reproduction of the scaled model test steam turbine including some steam pipes, supporting sheet metal and the measurement equipment such as traverse pipes and instruments. However, the simple computation model which consists of blade rows with cavities (multi stages) and short diffuser is applied for non-equilibrium condensation calculation due to convergence problems.

Comparative evaluation of the test results with the corresponding CFD results showed that the flow patterns predicted by CFD are good. In order to capture the flow pattern characteristics by CFD, it is necessary to consider both real shape modeling and non-equilibrium condensation modeling.
Assessment of Rotor Stability for Steam Turbine Considering Labyrinth Seal Characteristics of Fluid Destabilization Force and Vibrational Frequency Effect of Bearing Coefficients
Authors: Hombo Ryokichi , Murata Kenichi , Waki Yuichiro , Nagata Nobuhiro , Iwasaki Makoto , Matsumoto Kazuyuki
Published: September 2021

Accurate evaluation of the rotor stability is important for increasing the performance of the Steam Turbines. This paper discusses the important factors (such as destabilization force, bearing coefficient) for the evaluation of rotor stability.

The destabilization force which varies with the type of seal suggests that seal shape plays an important role. In the past, several researchers have studied the fluid destabilization force both numerically and experimentally and prediction of the same can be done fairly accurately by applying CFD techniques. The characteristics of the fluid destabilization force can be accurately evaluated by investigating the sensitivity of parameters such as clearance and swirl velocity for each seal type using CFD.

In the case of partial admission operation in which the bearing load changes (such as control stage of steam turbines), the frequency ratio effect on bearing coefficients is higher in the case of light-load (Sommerfeld number is large) than in the case of high-load (Sommerfeld number is small).

In order to estimate the frequency ratio effects due to varying load accurately, an experimental study and analytical study were carried out. As a result of comparison of the test results to analytical results, the test results are in good agreement with thermo-elastic-hydrodynamic-lubrication (TEHL) analysis which considers deformation of pad obtained by 3D-FEM.

The evaluation of rotor stability at each bearing load by partial admission (example: Governing Valve test) is in agreement with the field data of steam turbine.

For new designs and modification designs, this assessment considering the characteristics of each parameter is effective for improving the quality of rotor design.
Rotating Brush Seal Design and Performance Testing
Authors: Sarawate Neelesh , Trivedi Deepak
Published: September 2021

Brush seals are widely used in various turbomachinery applications because they provide reduced leakage than labyrinth seals in a compact space. Brush seals are generally mounted on static components and their flexible bristle tips engage the rotor to form a dynamic seal. In this paper, development of a brush seal mounted on a rotor is discussed. Benefits of this enhancement to brush seal include avoiding localized rubs on the rotor, which reduces heating of a local spot and resulting rotor bow and instabilities. The bristles are angled circumferentially instead of axially and are supported by a conical backplate. Under rotation, the bristles are pushed towards the backplate by the centrifugal force. Seal configurations are designed to fit into interstage and inter-shaft locations. A modeling approach for predicting stiffness and operating stresses in these seals also is outlined. A test setup is developed to characterize the performance of rotating brush seals under engine-representative centrifugal force and pressure differentials. Presented results demonstrate that brush seal can achieve tight effective gaps and desired performance after undergoing initial wear.
Loop Transient Performance With a Closed Loop sCO2 Brayton Cycle
Authors: Cich Stefan D. , Moore J. Jeffrey , Towler Meera Day , Mortzheim Jason
Published: September 2021

Recent testing has been completed on a 1 MWe supercritical carbon dioxide (sCO2) closed loop recuperated cycle under funding from the US Department of Energy (DOE) Sunshot initiative and industry partners. Some of the goals of this funding included the development of a 1 MWe loop, a 10 MWe turbine, and performance and mechanical testing. One of the key challenges that presented itself was the filling, start-up, and shut down of the entire system. Understanding the loop transient performance is important when having to bring a turbine online, transitioning from peak to partial loading, and also managing routine and emergency shut downs. Due to large changes in density near the critical point for CO2 and its tendency to form dry ice when expanded to atmospheric pressure, managing loop filling and venting is critical in ensuring that components are not damaged. With successful testing up to 715°C and 234 bar, this paper will provide updated data to, “Loop Filling and Start Up with a Closed Loop sCO2 Brayton Cycle [1].” While the previous paper focused on early trips and start up challenges, this paper will focus on the specific challenges at maximum operating conditions, and how the loop was managed when getting up to these high temperatures and pressures and how the loop behaved during a high temperature trip when compared to a controlled shut down from maximum operating conditions.
Radial Inlet and Exit Off-Design Performance Prediction for a 10 MWe Supercritical CO2 Axial Turbine
Authors: Marshall Michael , Vandeputte Thomas , Cich Stefan , Herrara Megan
Published: September 2021

During the development of a sCO2 turbine for the STEP program under DOE funding, radial inlet and exit designs were completed under mechanical and thermal constraints while seeking to maximize aerodynamic performance [1]. The flow path geometries of the designs were optimized at a single steady-state, design condition to minimize the total pressure loss. In order to efficiently characterize changes in performance across a range of operating points of the closed-loop cycle, off-design loss models for the inlet and exit diffuser have been created from CFD simulation results. To generate boundary conditions for the exit diffuser, numerous 1D exit profiles were selected from a regression analysis of turbine map points as a function of pressure ratio and corrected speed; radial inlet conditions emanated from planned cycle operating points. From base equation forms that include dynamic pressure and swirl components, equation constants were optimized to provide a best fit to CFD results. The equations generated were able to be integrated into existing STEP cycle modeling tools to enhance the prediction of turbine response as the operating point deviates significantly from design values. The methods outlined in this paper can provide a guide for evaluating the off-design performance of turbine inlet and exit designs dissimilar from conventional designs for which correlations are available.
Dynamic Model of Multistage Centrifugal Compressor With a Stage-by-Stage Anti-Surge Recirculating System
Authors: Casari Nicola , Pinelli Michele , Suman Alessio , Manganelli Matteo , Morini Mirko , Brun Klaus , Larosiliere Louis , Jariwala Vishal
Published: September 2021

The operability region of a centrifugal compressor is bounded by the low-flow (or high-pressure ratio) limit, commonly referred to as surge. The exact location of the surge line on the map can vary depending on the operating condition and, as a result, a typical Surge Avoidance Line is established at 10% to 15% above the stated flow for the theoretical surge line. The current state of the art of centrifugal compressor surge control is to utilize a global recycle valve to return flow from the discharge side of a centrifugal compressor to the suction side to increase the flow through the compressor and, thus, avoid entering the surge region. This is conventionally handled by defining a compressor surge control line that conservatively assumes that all stages must be kept out of surge at all the time. In compressors with multiple stages, the amount of energy loss is disproportion-ally large since the energy that was added in each stage is lost during system level (or global) recycling.

This work proposes an internal stage-wise recycling that provides a much more controlled flow recycling to affect only those stages that may be on the verge of surge. The amount of flow needed for such a scheme will be much smaller than highly conservative global recycling approach. Also, the flow does not leave the compressor casing and therefore does not cross the pressure boundary. Compared to global recycling this inherently has less loss depending upon application and specific of control design.
Technological Choices for Vibratory Robustness of Turbine Bladed Disk
Authors: Herran Mathieu , Dijoud Marc , Colette Christophe
Published: September 2021

Robustness of gas turbine, turbojet or turboprop components with respect to vibratory stress is a guarantee of the success of developments made on time and in service reliability objectives achievement.

Currently, it is proposed to achieve the required robustness by components geometry optimization to reduce their mechanical stress levels. It may also be possible to improve the endurance limits of the materials. These optimizations and choices, consumers in time and complexity of manufacture, may be necessary when the required robustness is not found to be achieved during the engine verification. By taking the effects of potential uncertainties and dispersions into account earlier in the development process, technological choices may be more likely to achieve the desired robustness requirement.

This paper investigates several simple technological choices to control and reduce the vibratory levels present on the rotors of helicopter turboshaft engines. These technological choices are major choices in the engine architecture with or without additional parts to increase mechanical resistance margins.

Gas turbine architecture has a direct impact on the level of excitations and vibratory appropriations, particularly the choice of rotor-stator blade numbers or technologies and shapes of links between rotors. Additional parts allow to increase the vibratory margins on the scale of the component. In this category, the benefit of dampers and intentional mistuning will be recalled. Particular attention will be paid to the relative weight between these technological choices in comparison with the mistuning effect on dynamic levels.

Technological choices will be quantified and illustrated by mechanical and statistical analysis and experimental industrial examples.
Effect of Droplet Starting Conditions on the Spray Dispersion Resulting From a Swirl Cup Injector
Authors: Bürkle Niklas , Holz Simon , Bärow Enrico , Koch Rainer , Bauer Hans-Jörg
Published: September 2021

In this work a numerical investigation of the sensitivities of the spray dispersion to different droplet starting parameters in a realistic three-dimensional fuel injector geometry is presented. The simulations are carried out using an Euler-Lagrange method. An extended version of the primary atomization model PAMELA [1,2] is used to predict the droplet diameter and to set the droplet starting conditions. Spray characteristics are compared to experimental data [3].

Thereby, a strong influence of the initial droplet velocities, the recirculation zone, the precessing vortex core as well as the turbulence modelling approach on the spray dispersion was identified. Droplet starting conditions which provide good agreement to the experimental data are determined.

The study demonstrates that the presented approach is a viable option to predict the spray dispersion in combustors. Moreover, valuable insights on necessary improvements for modeling primary atomization are given.
Constraint Handling in Bayesian Optimization -- A Comparative Study of Support Vector Machine, Augmented Lagrangian and Expected Feasible Improvement
Authors: Jin Yuan , Yang Zheyi , Dai Shiran , Lebret Yann , Jung Olivier
Published: September 2021

Many engineering problems involve complex constraints which can be computationally costly. To reduce the overall numerical cost, such constrained optimization problems are solved via surrogate models constructed on a Design of Experiment (DoE). Meanwhile, complex constraints may lead to infeasible initial DoE, which can be problematic for subsequent sequential optimization. In this study, we address constrained optimization problem in a Bayesian optimization framework. A comparative study is conducted to evaluate the performance of three approaches namely Expected Feasible Improvement (EFI) and slack Augmented Lagrangian method (AL) and Expected Improvement with Probabilistic Support Vector Machine in constraint handling with feasible or infeasible initial DoE. AL is capable to start sequential optimization with infeasible initial DoE, while EFI requires extra a priori enrichment to find at least one feasible sample. Empirical experiments are performed on both analytical functions and a low pressure turbine disc design problem. Through these benchmark problems, EFI and AL are shown to have overall similar performance in problems with inequality constraints. However, the performance of EIPSVM is affected strongly by the corresponding hyperparameter values. In addition, we show evidences that with an appropriate handling of infeasible initial DoE, EFI does not necessarily underperform compared with AL solving optimization problems with mixed inequality and equality constraints.
Considerations for the Extension of Gas Path Analysis To Electrified Aircraft Propulsion Systems
Authors: Simon Donald L. , Thomas Randy , Dunlap Kyle M.
Published: September 2021

Aircraft operators rely on gas path analysis techniques for monitoring the performance and health of their gas turbine engine assets. This is accomplished by analyzing discernable shifts in measurement parameters acquired from the engine. This paper reviews the founding mathematical principles of gas path analysis, including conventional approaches applied for estimating engine performance deterioration. Considerations for extending the application of gas path analysis techniques to Electrified Aircraft Propulsion (EAP) systems is also discussed, and simulated results from their application to an EAP concept comprised of turbomachinery and electrical system hardware is provided. Results are provided comparing the parameter estimation accuracy offered by taking a whole-system approach towards the problem setup versus that offered by analyzing each subsystem individually. For the latter, the importance of having accurate direct or inferred measurements of external mechanical torque loads placed upon turbomachinery shafts is emphasized.
Importance of Non-Equilibrium Modelling for Compressors
Authors: Spencer Robert , Przytarski Pawel , Adami Paolo , Grothe Patrick , Wheeler Andrew
Published: September 2021

This paper investigates the importance of non-equilibrium boundary layer modelling for three compressor blade geometries, using RANS and high fidelity simulations. We find that capturing non-equilibrium effects in RANS is crucial to capturing the correct boundary-layer loss. This is because the production of turbulence within the non-equilibrium region affects both the loss generation in the non-equilibrium region, but also the final equilibrium state. We show that capturing the correct non-equilibrium behaviour is possible by adapting industry standard models (in this case the k-omega SST model). We show that for the range of cases studied here, non-equilibrium effects can modify the trailing-edge momentum thickness by up to 40 percent, and can change the trailing-edge shape factor from 1.8 to 2.1.
Hydrogen Blending Into Ansaldo Energia AE94.3A Gas Turbine: High Pressure Tests, Field Experience and Modelling Considerations
Authors: Ciani A. , Tay-Wo-Chong L. , Amato A. , Bertolotto E. , Spataro G.
Published: September 2021

Fuel flexibility in gas turbine development has become increasingly important and modern engines need to cope with a broad variety of fuels. The target to operate power plants with hydrogen-based fuels and low emissions will be of paramount importance in a future focusing on electric power decarbonization.

Ansaldo Energia AE94.3A engine acquired broad experience with operation of various natural gas and hydrogen fuel blends, starting in 2006 in the Brindisi (Italy) power plant. Based on the exhaustive experience acquired in the field, this paper describes the latest advancements characterizing the operation of the AE94.3A burner with high pressure combustion tests adding hydrogen blends ranging from 0 to 40% in volume. The interpretation of the test results is supported by reactive and non-reactive simulations describing the effects of varying fuel reactivity on the flame structure as well as the impact of fuel / air momentum flux ratio on the fuel / air interaction and fuel distribution in the combustion chamber.

As expected, increasing amounts of hydrogen in the fuel are also associated with higher amounts of NOx production, however this effect could be countered by optimization of the fuel staging strategy, based on the mentioned CFD considerations and feedback from high pressure tests.
Analysis of LES and 1D Hot-Wire Data to Determine Actively Generated Main Flow Turbulence in a Film Cooling Test Rig
Authors: Fischer Lukas , Straußwald Michael , Pfitzner Michael
Published: September 2021

A vortex generator was incorporated into a wind tunnel to investigate more realistic inflow conditions for film cooling test rigs. The flow field signals are sampled numerically by probes in LES simulations and experimentally by using 1D hot-wire measurements to determine turbulence quantities. The LES shows that the turbulence is anisotropic which cannot be detected by the 1D hot-wire. Furthermore, the integral length scale which shall provide insight into the sizes of the turbulent eddies is determined using two approaches. The first uses the one probe at two times correlation method and could be evaluated from the numerical and experimental probes. The second correlation method exploits the spatial resolution in the LES domain by using the two probes at one time approach. Both methods show combustor-like turbulence length scales downstream of the vortex generator if the triple decomposition is applied onto the velocity signal.
Effects of Surface Waviness on Fan Blade Boundary Layer Transition and Profile Loss — Part I: Methodology and Computational Results
Authors: Lee Jinwook , Spakovszky Zoltán S. , Greitzer Edward M. , Drela Mark , Talbotec Jérôme
Published: September 2021

This two-part paper describes a new approach to determine the effect of surface waviness, arising from manufacture of composite fan blades, on transition onset location movement and hence fan profile losses. The approach includes analysis and computations of unsteady disturbances in boundary layers over a wavy surface, assessed and supported by wind tunnel measurements of these disturbances and the transition location. An integrated framework is developed for analysis of surface waviness effects on natural transition. The framework, referred to as the extended eN method, traces the evolution of disturbance energy transfer in flow over a wavy surface, from external acoustic noise through exponential growth of Tollmien-Schlichting (TS) waves, to the start and end of the transition process. The computational results show that surface waviness affects the transition onset location due to the interaction between the surface waviness and the TS boundary layer instability, and that the interaction is strongest when the geometric and TS wavelengths match. The condition at which this occurs, and the initial amplitude of the boundary layer disturbances that grow to create the transition onset is maximized, is called receptivity amplification. The results provide first-of-a-kind descriptions of the mechanism for the changes in transition onset location as well as quantitative calculations for the effects of surface waviness on fan performance due to changes in surface wavelength, surface wave amplitude, and the location at which the waviness is initiated on the fan blade.
Detection of Machinery Failure Signs From Big Time-Series Data Obtained by Flow Simulation of Intermediate-Pressure Steam Turbines
Authors: Komatsu Kazuhiko , Miyazawa Hironori , Yiran Cheng , Sato Masayuki , Furusawa Takashi , Yamamoto Satoru , Kobayashi Hiroaki
Published: September 2021

The periodic maintenance, repair, and overhaul (MRO) of turbine blades in thermal power plants are essential to maintain a stable power supply. During MRO, older and less-efficient power plants are put into operation, which results in wastage of additional fuels. Such a situation forces thermal power plants to work under off-design conditions. Moreover, such an operation accelerates blade deterioration, which may lead to sudden failure. Therefore, a method for avoiding unexpected failures needs to be developed. To detect the signs of machinery failures, the analysis of time-series data is required. However, data for various blade conditions must be collected from actual operating steam turbines. Further, obtaining abnormal or failure data is difficult. Thus, this paper proposes a classification approach to analyze big time-series data alternatively collected from numerical results. The time-series data from various normal and abnormal cases of actual intermediate-pressure steam-turbine operation were obtained through numerical simulation. Thereafter, useful features were extracted and classified using K-means clustering to judge whether the turbine is operating normally or abnormally. The experimental results indicate that the status of the blade can be appropriately classified. By checking data from real turbine blades using our classification results, the status of these blades can be estimated. Thus, this approach can help decide on the appropriate timing for MRO.
Spark Ignition of SPP Injector Under Sub-Atmospheric Conditions
Authors: Zhao Qianpeng , Mu Yong , Yang Jinhu , Wang Yulan , Xu Gang
Published: September 2021

The sub-atmospheric ignition performance of an SPP (Stratified Partially Premixed) injector and combustor is investigated experimentally on the high-altitude test facility. In order to explore the influence of sub-atmospheric pressure on reignition performance and flame propagation mode, experiments are conducted under different pressures ranging from 19 kPa to 101 kPa. The inlet temperature and pressure drop of the injector (ΔPsw/P3t) are kept constant at 303 K and 3% respectively. The transparent quartz window mounted on the sidewall of the model combustor provides optical access of flame signals. Ignition fuel-air ratio (FAR) under different inlet pressures are experimentally acquired. The spark ignition processes, including the formation of flame kernel, the flame development and stabilization are recorded by a high-speed camera at a rate of 5kHz. Experimental results indicate that the minimum ignition FAR grows rapidly as the inlet air pressure decreases. An algorithm is developed to track the trajectory of flame kernels within 25ms following the spark during its breakup and motion processes. Results show that the calculated trajectory provides a clear description of the flame evolution process. Under different inlet air pressures, the propagation trajectories of flame kernels share similarities in initial phase. It is pivotal for a successful ignition that the initial flame kernel keeps enough intensity and moves into CTRZ (Center-Toroidal Recirculation Zone) along radial direction. Finally, the time-averaged non-reacting flow field under inlet pressure of 54kPa and fuel mass flow of 8kg/h is simulated. The effects of flow structure and fuel spatial distribution on kernel propagation and flame evolution are analyzed.