bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sorting of Poly-Disperse Particle by Entrapment Using Liquid Carrier System
Authors: Khalil Ibrahim , Khoda Bashir 
Published: September 2021

AbstractA 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

Abstract
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

AbstractHeat 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

AbstractBlood-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 (&gt;90%) and elevated turbulent kinetic energy levels (&gt;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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.