bluuebunny/crossref_metadata_2025_split huggingface dataset:
3-D Computational Study of a Diffuser Augmented Micro Wind Turbine
Authors: M. S. Kiran , Rajawat Aakash , Ranjan Pritanshu 
Published: October 2021

Abstract
The present study focuses on the design optimization of a 3D DAMWT (Diffuser Augmented Micro Wind Turbine geometry). DAMWTS are compact devices with a swept area of only few square meters and energy production capacity of a few kilowatts. Their small size makes it convenient for domestic power generation. The box-shaped shroud makes it possible to stack multiple DAMWTS in an array configuration, thereby multiplying power output. 3-D CFD simulations were carried out using the k-ω SST turbulence model to compare the performance characteristics of different turbine geometries with a square inlet. With a constant shroud diffuser angle of 12 degrees as obtained in a previous study, the shroud nozzle angle and curvature were varied to obtain the maximum velocity factor and minimize flow stagnation at the inlet. Best performance was obtained with a nozzle angle of approximately 27 degrees and semi-concave curvature, with a velocity factor of 1.2. Further increase in nozzle angle resulted in a decline in performance and an increased flow stagnation. To analyze the influence of stacking on flow characteristics, a computational study of two DAMWTS placed horizontally next to each other was carried out. An investigation of the effectiveness of Vortex Generators in inhibiting flow stagnation at the inlet was also conducted.
Influence of Rectangular Strips’ Size on Aerodynamic Performance of a High-Speed Train Subjected to Crosswind
Authors: Wang Mengying , Sun Zhenxu , Ju Shengjun , Yang Guowei 
Published: October 2021

Abstract
Conventional studies usually assume that the train surface is smooth, so as to simplify the numerical calculation. In fact, the surface of the train is irregular, which will change the flow characteristics in the boundary layer and further affect the aerodynamic performance of a train. In this work, roughness is applied to the roof of a 1:25 scaled train model in the form of longitudinal strips. Firstly, the improved delayed detached eddy simulation (IDDES) method is adopted to simulate the aerodynamic performance of the train model with both smooth and rough surface, which are subjected to crosswind. Results show that the side force coefficient and the roll moment coefficient subjected to rough model decreased by 3.71% and 10.56% compared with the smooth model. Then, the width, height and length of the strips are selected as variables to design different numerical simulation schemes based on the orthogonal experimental design method. Through variance analysis, it can be found that four design parameters have no significant effect on the side force coefficient. Meanwhile, for the roll moment coefficient, the length of the strips in the straight region of the train has a significant effect and the width of the strips has a highly significant effect on it. These conclusions can provide a theoretical basis to improve the aerodynamic performance of the high-speed train subjected to crosswind.
Computational Study of Viscoelastic Flows in Microchannels
Authors: Xue Guanyang , Cheng Xuanhong , Oztekin Alparslan 
Published: October 2021

Abstract
Computational Fluid Dynamics (CFD) simulations have been performed in a 2D cross-section of the microchannel to characterize the viscoelastic flow field using OpenFOAM with customized stabilizing methods. The continuity and momentum equations coupled with the Giesekus constitutive model are solved. The computational domain consists of a straight main channel that is 100 μm in width and a 1:4 square-shaped cavity in the middle of the channel. The mesh convergence study is performed with both structured and unstructured cells. Flow and stress fields are compared with different cell densities. The numerical study is carried out on various Deborah numbers (De). The first normal stress difference is computed to examine the elastic lift force for future studies for nanoparticle separations. The vortex on the expansion side shrinks while the contraction side expands as De is increased. A banded zone of stronger N1 in the bulk region of the cavity, observed at higher De, could be favorable in particle separation applications. As the simulation process being validated, this study can help with future improvements to achieve higher flow rates.
Numerical Investigation of Cloud Cavitation and Its Induced Shock Waves
Authors: Ushioku Takahiro , Yoshimura Hiroaki 
Published: October 2021

Abstract
This paper numerically investigates unsteady behavior of cloud cavitation, in particular, to elucidate the induced shock wave emission. To do this, we consider a submerged water-jet injection into still water through a nozzle and make some numerical analysis of two-dimensional multiphase flows by Navier-Stokes equations. In our previous study [7], we have shown that twin vortices symmetrically appear in the injected water, which plays an essential role in performing the unsteady behavior of a cloud of bubbles. In this paper, we further illustrate the elementary process of the emission of the shock waves. First, we set up the mixture model of liquid and gas in Lagrangian description by the SPH method, together with the details on the treatment of boundary conditions. Second, we show the velocity fields of the multiphase flow to illustrate the inception, growth as well as the collapse of the cloud. In particular, we explain the mechanism of the collapse of the cloud in view of the motion of the twin vortices. Further, we investigate the pressure fields of the multiphase flow in order to demonstrate how the shock wave is emitted associated with the collapse of the cloud. Finally, we show that a small shock wave may be released prior to the main shock wave emission.
Three-Dimensional Two-Phase Flow Simulations of Water Braking Phenomena for High-Speed Test Track Sled
Authors: Terrazas Jose , Rodriguez Arturo , Kumar Vinod , Adansi Richard , Kotteda V. M. Krushnarao 
Published: October 2021

Abstract
Specializing in high-speed testing, Holloman High-Speed Test Track (HHSTT) uses a process called ‘water braking’ as a method to bring vehicles at the test track to a stop. This method takes advantage of the higher density of water, compared to air, to increase braking capability through momentum exchange. By studying water braking using Computational Fluid Dynamics (CFD), forces acting on track vehicles can be approximated and prepared for prior to actual test. In this study, focus will be made on the brake component of the track sled that is responsible for interacting with the water for braking. By discretizing a volume space around our brake, we accelerate water and air to relatively simulate the brake engaging. The model is a multi-phase flow that uses the governing equations of gas and liquid phases with the finite volume method, to perform 3D simulations. By adjusting the inflow velocity of air and water, it is possible to simulate HHSTT sled tests at various operational speeds. In the development of the 3D predictive model, convergence issues associated with the numerical mesh, initial/boundary conditions, and compressibility of the fluids were encountered. Once resolved, the effect of inflow velocities of water and air on the braking of the sled are studied.
Assessment of Predictive Capability of Hybrid RANS/LES Turbulence Models for Thermofluid Applications
Authors: Zope Anup , Schemmel Avery , Wang Xiao , Bhushan Shanti , Singh Prashant , Luke Edward 
Published: October 2021

Abstract
In this study, we have assessed performance of URANS model, various hybrid RANS/LES turbulence models such as detached eddy simulation, Nichols-Nelson HRLES model, dynamic HRLES (DHRL) model, as well as LES for two classes of problems: (a) heat transfer due to subsonic swirling flow subjected to a sudden expansion leading to cylindrical chamber, and (b) flow separation due to oblique shock wave-turbulent boundary layer interaction (STBLI). The results are assessed using the heat transfer characteristics, separation and reattachment characteristics, and capability to predict flow unsteadiness. The study indicates that URANS can predict large scale flow features reasonably well. However, it fails to resolve turbulence. PANS improves TKE prediction, hence, improves heat transfer prediction. Among the hybrid RANS/LES models, DHRL coupled with ILES is capable of providing accurate prediction of flow separation/reattachment characteristics for boundary layer flows. For free-shear dominated flows, implicit LES performs better compared to the explicit LES models.
A Gas-Particle Analogue to the Richtmyer-Meshkov Instability: Comparing Multiphase Simulations to Shock Tube Experiments
Authors: Ouellet Frederick , Rollin Bertrand , Durant Bradford , Koneru Rahul Babu , Balachandar S. 
Published: October 2021

Abstract
A research area emerging in the multiphase flow community is the study of Shock-Driven Multi-phase Instability (SDMI), a gas-particle analog of the traditional fluid-fluid Richtmyer-Meshkov instability (RMI). In this work, we study the interaction of planar air shocks with corrugated glass particle curtains through the use of numerical simulations with an Eulerian-Lagrangian approach. This approach has simulations track computational particle trajectories in a Lagrangian framework while evolving the surrounding fluid flow on a fixed Eulerian mesh. In addition to observing the evolution of the perturbed particle curtain in the simulations, we also observe the evolution of the curtain of gas which is initially trapped inside of the particle curtain as the simulation progresses. The objective of this study is to compare the evolving simulation curtains (both particle and gas) to a comparable set of shock tube experiments performed to analyze traditional fluid RMI evolution. The simulations are set to match the experimental shock Mach numbers and perturbation wavelengths (3.6 and 7.2 mm) while matching the Atwood number of the experiments to the multiphase Atwood number of the simulations. However, multiple particle diameters are tested in the simulations to get a view into the impact of the particle diameter on the evolution of the particle curtain. This simulation setup allows for a one-to-one comparison between RMI and SDMI under comparable conditions while also allowing for a separate study into the validity of the use of both the multiphase Atwood number and the fluid-only Atwood number to compare the single-phase and multiphase instabilities. In particular, we show that this validity is at least partly dependent on the diameters of the particles in the curtain (thus, dependent on the Stokes number of the flow). We also analyze the effect of the multiphase terms of the vorticity evolution equation on the vorticity deposition in SDMI. Also discussed is the effect of the particle diameter on the multiphase generation terms as well as in the baroclinic vorticity generation term in SDMI as the shock passes over the curtain.
Application of Scale-Resolving Simulations and Hybrid Models for Contraction-Expansion Pipe Flows
Authors: Darihaki Farzin , Zhang Jun , Shirazi Siamack A. 
Published: October 2021

Abstract
Contractions and expansions are commonly found in various piping systems including flow control in the oil and gas industry. They impose complex flow characteristics such as flow recirculation, boundary layer separation and unsteady re-attachment. Computational Fluid Dynamics (CFD) using RANS simulations can offer general information about the time-averaged flow properties in expansion and contraction geometries including the pressure drop across the fitting. However, they generally fail to provide details of turbulent flow such as shedding of vortices and high turbulent intensities which are observed in experimental data at the expansion and contraction regions. Large Eddy Simulations (LES) can resolve a turbulence spectrum by filtering Navir-Stokes equations over the computational cells. In this study, LES is utilized to examine a sudden-contraction and expansion pipe flow. Furthermore, Stress-Blended Eddy Simulations (SBES) as a hybrid LES-RANS model is employed for comparison. All of these Scale-Resolving Simulations (SRS) are examined against the experimental data and compared to commonly used RANS simulations. Various flow parameters are examined at different locations for a 50.8 mm pipe which is suddenly reduced to a 25.4 mm pipe and then suddenly expands to the original size, and highlights of each model are presented. The details of the turbulent flow in these geometries are critical to many applications such as particle-laden flows and this investigation would provide insight into the appropriate flow modeling in the expansion and contraction geometries.
Computational Analysis of Non-Premixed Combustion in a Scramjet Combustor With a Wedge Shaped Strut Injector
Authors: Katare Sajal , Yadav Nagendra P. 
Published: October 2021

Abstract
This paper focuses the computational study of non-premixed combustion in a scramjet combustor. The wedge shaped strut injector was used in the combustion process. In order to investigate the flame holding mechanism of the wedge shaped strut in supersonic flow, the two-dimensional coupled implicit RANS equations, the standard k-ε turbulence model and the finite-rate/eddy-dissipation reaction model are introduced to simulate the flow field of the hydrogen fueled scramjet combustor with a strut flame holder under different conditions. The static pressure of the case under the engine ignition condition is much higher than that of the case under the cold flow condition. The reflection of shock waves improves the mixing of hydrogen with the stream of inlet air and thus increases combustion efficiency. The mass flow rate of air is optimized for the best performance of engine.
Liutex Core Line for Vortex Structure in Turbulence
Authors: Alvarez Oscar , Yu Yifei , Liu Chaoqun 
Published: October 2021

Abstract
Liutex is a vortex identification method that provides a vector interpretation of local fluid rotation. Liutex produces a vector quantity which can be used to determine the absolute and relative strength of a vortex, the local rotation axis of a vortex, the vortex core center, the size of the vortex core, and the vortex boundary. Vortex identification and visualization is essential in computational fluid turbulence analysis and fluid mechanics in general. Until Liutex, there has not been a way to identify the core of a vortex structure or even the center of rotation of a vortex structure. Since Liutex, tools have been created to assist in the identification and analysis of vortical structures. The Liutex Core Line has been developed to better understand turbulent fluid structures. A Liutex core is defined as a concentration of Liutex vectors and defined to be unique and the Liutex core line is the center of rotation of that Liutex core. Currently, iso-surfaces are the most popular way to visualize the structure of turbulent flow but there is no reason to believe that it is the best way to represent a vortex’s structure. Previous methods that use iso-surface are strongly threshold dependent and since the Liutex core line is unique, it is independent of threshold and can show the real vortex structure. In this paper we show the benefits and promises of the Liutex Core Line as a better way of representing vortex structures.
Investigation of the Effect of Cross Section on the Convective Heat Transfer Performance of Nanoemulsion in Microchannel Heat Exchanger
Authors: Gameda Takele , Kabir M. Mehdi , Xu Jiajun 
Published: October 2021

Abstract
The present study aims to numerically investigate the effect of cross section on the heat transfer performance of single-phase flow of Ethanol/Polyalphaolefin nanoemulsion fluid with ethanol concentrations of 8 wt.% in a microchannel heat exchanger. While the exterior geometry of the microchannels’ solid structure remains the same, four different cross sections of channels including: circular, upward semi-circular, rectangular, and trapezoidal, are designed with keeping the channels’ wetted perimeters, mass flow rate, and Reynolds number constant for comparison purposes. In the present study, the hydrodynamic and heat transfer characteristics, including local Nusselt number, heat transfer coefficient, and velocity profile, were investigated under a uniform wall heat flux boundary conditions within the laminar flow regime. The channel models of different cross sections were developed by the COMSOL-Multiphysics for numerical analysis. The heat transfer characteristics were then compared for different cross sections under the same operating conditions, and the effect of aspect ratio for rectangular and trapezoidal cross sections were also studied.
Experimental and Computational Studies on Flow Characteristics of Single Expansion Nozzle
Authors: Inturi Dakshina Murthy , Pinnam Lovaraju , Vegesna Ramachandra Raju 
Published: October 2021

Abstract
The present investigation aims to study the flow field characteristics of a single expansion nozzle (SEN). The flow field characteristics of conventional convergent-divergent (C-D) nozzle are also investigated for comparison. The experimental and computational studies were carried out for nozzle pressure ratios of 1.45, 1.55, 1.75, 2, 3, 4 and 5. The studies reveal that, for the single expansion nozzle the oblique shock moves towards the solid boundary with the increase of nozzle pressure ratio, which makes the flow to accelerate continuously in the majority of the divergent portion. The single expansion nozzle delivers the flow with higher Mach number than the C-D nozzle at the exit of the nozzle.
Normative data on cardiovascular autonomic function in Greenlandic Inuit
Authors: Christensen Marie Mathilde Bjerg , Hansen Christian Stevns , Fleischer Jesper , Vistisen Dorte , Byberg Stine , Larsen Trine , Laursen Jens Christian , Jørgensen Marit Eika 
Published: October 2021

IntroductionDiabetes is increasing among Greenlandic Inuit; however, the prevalence of cardiovascular autonomic neuropathy (CAN) is yet unknown. The assessment of CAN requires an ability to differentiate between normal and abnormal. The aim was to establish normative reference data of cardiovascular autonomic function in Greenlandic Inuit.Research design and methodsIn this cross-sectional study, cardiovascular autonomic function was evaluated in participants without diabetes during theGreenlandic Population Study 2018and in the town Qasigiannguit in 2020. Assessment included cardiovascular autonomic reflex tests (CARTs) and power spectral analysis of heart rate variability (HRV). Normative reference limits were estimated by applying quantile regression models at the lowest fifth percentile, with age as the exposure variable and adjusted for sex. HRV models were additionally adjusted for resting heart rate.ResultsBased on examinations of 383 participants (60.6% females), normative reference data was established for all outcomes. Mean age was 52 years (SD 12.9). Higher age was inversely associated with all outcomes of CARTs and HRV. A linear fall in cardiovascular autonomic function tended to level off beyond age of 60 years for supine-to-upright position ratio. However, the number of observations in subjects older than 60 years was limited, which may have caused a flattening of the curve around that age. No other associations were found.ConclusionsThe general level of the CARTs and HRV for all age groups is notably lower than in previous studies from other nationalities. We speculate that sociodemographic and cultural aspects of the Greenlandic Inuit population including body mass index, smoking, physical activity and alcohol consumption may have affected the cardiovascular autonomic function.
Overview of attacks against civilian infrastructure during the Syrian civil war, 2012–2018
Authors: Muzzall Evan , Perlman Brian , Rubenstein Leonard S , Haar Rohini J 
Published: October 2021

BackgroundHundreds of thousands of people have been killed during the Syrian civil war and millions more displaced along with an unconscionable amount of destroyed civilian infrastructure.MethodsWe aggregate attack data from Airwars, Physicians for Human Rights and the Safeguarding Health in Conflict Coalition/Insecurity Insight to provide a summary of attacks against civilian infrastructure during the years 2012–2018. Specifically, we explore relationships between date of attack, governorate, perpetrator and weapon for 2689 attacks against five civilian infrastructure classes: healthcare, private, public, school and unknown. Multiple correspondence analysis (MCA) via squared cosine distance, k-means clustering of the MCA row coordinates, binomial lasso classification and Cramer’s V coefficients are used to produce and investigate these correlations.ResultsFrequencies and proportions of attacks against the civilian infrastructure classes by year, governorate, perpetrator and weapon are presented. MCA results identify variation along the first two dimensions for the variables year, governorate, perpetrator and healthcare infrastructure in four topics of interest: (1) Syrian government attacks against healthcare infrastructure, (2) US-led Coalition offensives in Raqqa in 2017, (3) Russian violence in Aleppo in 2016 and (4) airstrikes on non-healthcare infrastructure. These topics of interest are supported by results of the k-means clustering, binomial lasso classification and Cramer’s V coefficients.DiscussionFindings suggest that violence against healthcare infrastructure correlates strongly with specific perpetrators. We hope that the results of this study provide researchers with valuable data and insights that can be used in future analyses to better understand the Syrian conflict.
Impact of stimulation among non-crying neonates with intact cord versus clamped cord on birth outcomes: observation study
Authors: KC Ashish , Budhathoki Shyam Sundar , Thapa Jeevan , Niermeyer Susan , Gurung Rejina , Singhal Nalini 
Published: October 2021

BackgroundStimulation of non-crying neonates after birth can help transition to spontaneous breathing. In this study, we aim to assess the impact of intact versus clamped umbilical cord on spontaneous breathing after stimulation of non-crying neonates.MethodsThis is an observational study among non-crying neonates (n=3073) born in hospitals of Nepal. Non-crying neonates born vaginally at gestational age ≥34 weeks were observed for their response to stimulation with the cord intact or clamped. Obstetric characteristics of the neonates were analysed. Association of spontaneous breathing with cord management was assessed using logistic regression.ResultsAmong non-crying neonates, 2563 received stimulation. Of these, a higher proportion of the neonates were breathing in the group with cord intact as compared with the group cord clamped (81.1% vs 68.9%, p<0.0001). The use of bag-and-mask ventilation was lower among those who were stimulated with the cord intact than those who were stimulated with cord clamped (18.0% vs 32.4%, p<0.0001). The proportion of neonates with Apgar Score ≤3 at 1 min was lower with the cord intact than with cord clamped (7.6% vs 11.5%, p=0.001). In multivariate analysis, neonates with intact cord had 84% increased odds of spontaneous breathing (adjusted OR, 1.84; 95% CI: 1.48 to 2.29) compared with those with cord clamped.ConclusionsStimulation of non-crying neonates with intact cord was associated with more spontaneous breathing than among infants who were stimulated with cord clamped. Intact cord stimulation may help establish spontaneous breathing in apnoeic neonates, but residual confounding variables may be contributing to the findings. This study provides evidence for further controlled research to evaluate the effect of initial steps of resuscitation with cord intact.