bluuebunny/crossref_metadata_2025 huggingface dataset:
Patients' productivity losses and informal care costs related to ischemic stroke: a French population‐based study
Authors: Barral M. , Rabier H. , Termoz A. , Serrier H. , Colin C. , Haesebaert J. , Derex L. , Nighoghossian N. , Schott A.‐M. , Viprey M. ,   the Stroke69 Study Group
Published: October 2020

Background and purpose

Large societal costs of stroke should not be ignored. We aimed to estimate patients' productivity losses and informal care costs during the first year after ischemic stroke.

Methods

A cross‐sectional survey was performed within the STROKE69 regional population‐based cohort study. At 1 year post‐stroke, each patient and the corresponding main informal caregiver received questionnaires followed by a telephone interview if necessary. Time losses were valued using the human capital approach and proxy good method for patients with and without a professional activity, respectively.

Results

Among the 222 patients with ischemic stroke (58% men; mean age 68 years; and 86% with a modified Rankin Scale (mRS) score of <3 at 3 months), 54%, 32%, and 25% received informal, formal, and both cares, respectively. Among the 108 main informal caregivers, 63% were women, 74% lived with the patient, and 57% were retired or unemployed. The mean cost of productivity losses was estimated at €7589 ± €12 305 per patient in the first post‐stroke year with 5.4%, 71.2%, and 23.4% of these being attributed to presenteeism, absenteeism, and leisure time, respectively. Informal care was given at an average of 25 h/week. The annual mean estimated total cost of informal care was €10 635 per caregiver.

Conclusions

Informal care and productivity losses of patients with ischemic stroke during the first post‐stroke year represent a significant economic burden for society comparable to direct costs. These costs should be included in economic evaluations with the adoption of a societal perspective to avoid underestimating the societal stroke economic burden.
Transnational mobility networks and academic social capital among early‐career academics: beyond common‐sense assumptions
Authors: Schaer Martine , Jacot Cédric , Dahinden Janine
Published: October 2020

Academic mobility is increasingly presented as indispensable for a successful academic career. This imperative is rooted in the assumption that mobility contributes to academic excellence because it allows academics to build transnational academic networks. Based on biographical interviews and an analysis of the mobility networks of early‐career academics at three universities (Zurich, Cambridge, and UCLA), we examine the composition of these academics’ networks at different times and discuss the role of transnational ties within them. We find that increased mobility does indeed result in more transnational networks, but it does not increase academic social capital. The additional transnational ties mainly consist of transnational kinship and friendship relations. Furthermore, the mobility of early‐career academics triggers various forms of mobility among their family members. Finally, early‐career academics can build transnational academic ties without necessarily becoming mobile themselves, thanks to the mobility of higher‐ranked academics.
Plasminogen activator inhibitor‐1: a potential etiological role in livedoid vasculopathy
Authors: Gao Yimeng , Jin Hongzhong
Published: October 2020

Livedoid vasculopathy (LV) is a chronic, recurrent skin disorder with unknown aetiology and pathogenesis that seriously affects the quality of life of people who suffer from it. Plasminogen activator inhibitor (PAI)‐1 is a primary inhibitory component of the endogenous fibrinolytic system in blood coagulation. PAI‐1 also plays a role in many other physiological processes and activities, including thrombosis, fibrosis, wound healing, angiogenesis, inflammation, cell migration, and adhesion. Enhanced expression and genotype polymorphism of PAI‐1 have been observed in LV patients. In this review, we summarise the known functions of PAI‐1 with emphasis on the roles that PAI‐1 probably plays in the pathogenesis of LV, thereby illustrating that PAI‐1 represents a potential LV biomarker and therapeutic target for treating LV.
The impact of emotional development in people with autism spectrum disorder and intellectual developmental disability
Authors: Sappok T. , Heinrich M. , Böhm J.
Published: October 2020

Background

Intellectual developmental disabilities (IDDs) and autism spectrum disorders (ASDs) are developmental conditions, which may also be associated with impairments in emotional development (ED). ED can be assessed using the Scale of Emotional Development – Short (SED‐S), a five‐stage model consisting of eight domains, which allows to study the relationship between ASD and ED in people with IDD.

Methods

In this retrospective study, the level of ED was compared in 327 adults with IDD with [n = 83; mean age 38.3 years; level of IDD: mild (6), moderate (21), severe (45) and profound (11)] and without [n = 244, mean age 36.9 years; level of IDD: mild (67), moderate (73), severe (68) and profound (36)] ASD. The discriminative ability of the SED‐S was determined by a regression in a training and a validation sample.

Results

The level of ED correlated with the severity of IDD (rs = −.654) and the presence of ASD (rs = −.316). People with additional ASD showed lower levels of ED compared with those with IDD only (mean reference ages 7–18 vs 19–36 months). The developmental profiles were equally balanced in ASD and IDD‐only. A regression analysis revealed three domains (‘Relating‐to‐Peers’, ‘Differentiating‐Emotions’, and ‘Regulating‐Affect’) to be useful for ASD assignment (AUC > 0.70, sensitivity 0.76–0.80, specificity 0.62–0.63).

Conclusions

In people with IDD, additional ASD was associated with delays in ED, which may be considered in diagnostics, treatment and care.
Serum level of interleukin‐22 in patients with cutaneous warts: A case‐control study
Authors: Marie Radwa El‐Sayed Mahmoud , Abuzeid Aya Qamar Eldawla Mahmoud , Attia Fadia M. , Anani Maha Mohamed , Gomaa Amal H. A. , Atef Lina M.
Published: October 2020

Background

Warts are viral cutaneous infections caused by human papilloma virus (HPV), presented by verrucous growth over the skin surface. The immune response is considered to play a crucial role in HPV clearance. It depends on intact cellular immunity including natural killer (NK) cell and cytotoxic T cells. It has been clarified that T‐helper (Th) 1 cytokines (interleukin (IL)‐2, interferon‐γ, and tumor necrosis factor‐a) and IL‐17 are involved in HPV clearance. IL‐22 is one of IL‐10 family of cytokines produced by NK cells, Th1, Th17, and Th22 cells. In the skin, IL‐22 reduces keratinocyte cornification and enhances keratinocyte production of antimicrobial peptides. IL‐22 overexpression has been demonstrated in various viral infections and skin inflammatory disorders.

Aim

The aim of this study was to assess serum levels of IL‐22 in patients with warts and its association with their different clinical characteristics.

Methods

The study included 20 patients with warts and 20 control subjects. Serum concentration of IL‐22 was measured by enzyme‐linked immune sorbent assay.

Results

Serum levels of IL‐22 were significantly higher in patients with warts than in control subjects (P < .001). The levels were significantly higher in patients with recurrent warts after prior treatment than in patients with first‐time warts (P = .007). Moreover, a significant positive correlation was detected between serum levels of IL‐22 and the number of warts (P = .017).

Conclusion

Serum level of IL‐22 was elevated in patients with warts. Thus, IL‐22 may have a crucial role in the antiviral immune response against this infection.
Politics by Other Means in South Africa Today
Authors: BRETT PETER
Published: October 2020

Rick Abel's classic Politics by Other Means (1995) used South Africa to argue for law's ‘potential nobility’, but it did so avoiding a heroic mode characteristic of much anti‐apartheid writing. Abel showed how law could, with strenuous exertion, be turned into a defensive shield for the oppressed. As a sword, however, it was ‘two‐edged’. It allowed the powerful to frustrate or overturn hard‐won symbolic victories. Recently, the heroic mode has returned to South Africa. The Constitutional Court, in particular, is lauded for having combated ‘state capture’ under deposed President Jacob Zuma. A closer examination of this period, however, does much to vindicate Abel's earlier scepticism about law's offensive value. The spectacular deployment of law to fight politicians’ crimes has exposed the judiciary to unexpected political threats. Meanwhile, civil society's efforts to entrust judges with administrative duties shirked by the government has inevitably entailed the sacrifice of some rule of law values.
Enhancing phosphorus availability, soil organic carbon, maize productivity and farm profitability through biochar and organic–inorganic fertilizers in an irrigated maize agroecosystem under semi‐arid climate
Authors: Arif Muhammad , Ali Salman , Ilyas Muhammad , Riaz Muhammad , Akhtar Kashif , Ali Kawsar , Adnan Muhammad , Fahad Shah , Khan Imran , Shah Shahen , Wang Haiyan
Published: October 2020

Biochar amendments offer promising potential to improve soil fertility, soil organic carbon (SOC) and crop yields; however, a limited research has explored these benefits of biochar in the arid and semi‐arid regions. This two‐year field study investigated the effects of Acacia tree biomass‐derived biochar, applied at 0 and 10 t ha‒1 rates with farmyard manure (FYM) or poultry manure (PM) and mineral phosphorus (P) fertilizer combinations (100 kg P ha‐1), on maize (Zea mays L.) productivity, P use efficiency (PUE) and farm profitability. The application of biochar with organic–inorganic P fertilizers significantly increased soil P and SOC contents than the sole organic or inorganic P fertilizers. Addition of biochar and PM as 100% P source resulted in the highest soil P (104% increase over control) and SOC contents (203% higher than control). However, maize productivity and PUE were significantly higher under balanced P fertilizer (50% organic + 50% mineral fertilizer) with biochar and the increase was 110%, 94% and 170% than 100%‐FYM, 100%‐PM and 100% mineral fertilizer, respectively. Maize productivity and yield correlated significantly positively with soil P and SOC contents These positive effects were possibly due to the ability of biochar to improve soil properties, P availability from organic–inorganic fertilizers and SOC which resulted in higher PUE and maize productivity. Despite the significant positive relationship of PUE with net economic returns, biochar incorporation with PM and mineral fertilizer combination was economically profitable, whereas FYM along biochar was not profitable due to short duration of the field experiments.
A Robust Design Perspective on Factors Influencing Geometric Quality in Metal Additive Manufacturing
Authors: Ramesh Sagar Vaishak , Lorin Samuel , Wärmefjord Kristina , Söderberg Rikard
Published: October 2020

Additive manufacturing (AM) for metals is a widely researched, continuously enhanced manufacturing process and is implemented across various industries. However, the AM process exhibits variation that affects the geometric quality of the end product. The effect of process variation on geometric quality is rarely considered during the design stages. In this paper, sources that influence the geometric quality in a metal AM process are reviewed from a robust design perspective and further sorted into control factors and noise factors. A framework for geometric robustness analysis of AM products is presented as an outcome. This framework would facilitate development of methods and tools to produce geometry assured AM products. Also, the prospects of variation simulation to support geometric robustness analysis and the challenges associated with it are discussed.
Turbulence Modeling Using Z-F, RSM, LES and WMLES for Flow Analysis in Z-Shape Ducts
Authors: Karbon Mohammed , Sleiti Ahmad K.
Published: October 2020

Turbulent flow in Z-shape duct configuration is investigated and analyzed using Reynolds Stress Model (RSM), Large Eddy Simulation (LES), ζ-f Model, and Wall-Modeled Large Eddy Simulation (WMLES). The results are validated and compared to experimental data. Both RSM and ζ-f models are based on steady-state RANS solutions, while LES and WMLES models account for temporal variations transient behavior of the flow turbulence. The focus was on regions where RSM has over or under predicted the flow and regions where there are flow separations and high turbulence. LES simulation results have shown under-prediction and over-prediction in the flow separation and re-attachment regions. It is found that the turbulent kinetic energy production in ζ equation is much easier to reproduce accurately than other models. Both mean velocity gradient and local turbulent stress terms are also much easier to resolve properly. The current research has found that ζ-f model not only takes less time to complete the simulation but also the mean flow velocity profile results are in better agreement with experimental data than RSM model despite both are coupled steady-state RANS. ζ-f model numerically resolved both the flow separation and re-attachment regions better than RSM model. WMLES model is employed to investigate the SGS model impact on the small eddies dissipated from the large eddies. Such WMLES model produces much better results than the LES model, however the SGS viscosity damps the energy of the flow.
Modeling Non-Spherical Particulate Systems in the DEM Framework
Authors: Srinivasan Vivek , Tafti Danesh
Published: October 2020

Particulate systems in practical applications have mostly been represented using spherical shapes, even though the majority of particles in archetypal fluid-solid systems are non-spherical. Modeling dense fluid-particulate systems using non-spherical particles involves increased complexity, with computational cost manifesting as the biggest bottleneck.

In this research, a novel Discrete Element Method (DEM) model that incorporates geometry definition, collision detection, and post-collision kinematics has been developed to accurately simulate non-spherical particulate systems. Superellipsoids, which account for 80% of particles commonly found in nature, are used to represent non-spherical shapes. Collisions between these particles are processed using a hierarchical detection method. An event-driven model and a time-driven model have been employed in the current framework to resolve collisions. The collision model’s influence on non-spherical particle dynamics is verified by observing the conservation of momentum and total kinetic energy. Furthermore, the non-spherical DEM model is coupled with an in-house fluid flow solver (GenIDLEST). The combined CFDDEM model results are validated by comparing to experimental measurements in a fluidized bed. The parallel scalability of the non-spherical DEM model is evaluated in terms of its efficiency and speedup. Major factors affecting wall clock time of simulations are analyzed and an estimate of the model’s dependency on these factors is given.
Improved DRW Model for Prediction of Deposition and Dispersion of Nano- and Micro-Particles in Turbulent Flows
Authors: Mofakham Amir A. , Ahmadi Goodarz
Published: October 2020

In this study, the accuracy of the discrete random walk (DRW) stochastic model in generating the instantaneous velocity fluctuations as seen by micro- and nano-particles in inhomogeneous turbulent flows were examined. Particular attention was given to the effects of the non-uniform normal RMS velocity fluctuations and turbulence time scale on the DRW model predictions. The trajectories of randomly injected point-particles with diameters ranging from 10 nm to 30 μm in a duct were evaluated using an in-house Matlab particle tracking code. The particle equation of motion included the drag and Brownian forces. The fully developed mean velocity and RMS fluctuation velocity profiles were exported from the RANS (v2f) simulations and were used for the particle dispersion and transport analysis. It was assumed that the particle-laden flow is sufficiently dilute so that the particle-particle collisions and the two-way coupling effects of particles on the flow could be ignored.

To incorporate the instantaneous turbulence velocity fluctuations effects on particle dispersion, the Conventional-DRW model (in the absence of drift corrections), which was originally developed for homogenous turbulent flows, was first used. It was shown that the Conventional-DRW model leads to superfluous migration of fluid-point particles toward the wall and erroneous particle deposition rate. The Modified-DRW model with an appropriate velocity gradient drift correction term was also tested. It was found that the predicted concentration profiles of tracer particles still are not uniform. It was hypothesized that the reason for this erroneous prediction is due to the inhomogeneous turbulence time macroscale in the channel flow. A new drift correction term as a function of gradients of both RMS fluctuation velocity and the turbulence time macroscale was proposed. It was shown that the new Improved-DRW model with the velocity and time scale drift corrections leads to uniform distributions for fluid-point particles and reasonable concentration profiles for finite-size particles. It was shown that the predicted deposition velocities of different size particles by the proposed Improved-DRW model are in good agreement with the available experimental data as well as the predictions of the empirical models and earlier DNS results.
Computational Analysis of Fiber Dynamics in Human Nasal Cavity
Authors: Ma Jiawei , Tu Jiyuan , Tian Lin , Ahmadi Goodarz
Published: October 2020

Elongated particles, such as asbestos and mineral fibers, are considered severe inhalation hazards due to their ability to penetrate into the deep lung. Frequently the dynamic behavior of the fibrous particles is attributed to their unique needle-like geometry. Therefore, understanding the interactions of the inhaled elongated particles with the airflow environment is of great significance. In this study, the transport and deposition of elongated micro-fibers in a realistic human nasal cavity is investigated numerically. The motion of the micro-fiber is resolved by solving the system of equations governing its coupled translational and rotational motions. The governing equations included the drag, the hydrodynamic torques that were evaluated using the Jeffrey model. The influence of the shear lift force was also included in these simulations. The no-slip wall boundary condition for airflow in the airways was used. Since the surface of airways is covered with mucus, when a fiber touches the surface, it was assumed to be deposited with no rebound. The study allows a close look at the non-spherical particle-flow dynamics with respect to the translation, rotation, coupling, and how the rotation affects the particle’s macroscopic transport and deposition properties. A series of simulations for different microfiber diameters and aspect ratios were performed. The simulation results are compared with the existing experimental data, and earlier computational model predictions and good agreements were obtained. The present study also seeks to provide additional insight into the transport processes of microfibers in the upper respiratory tract.
Performance of Francis Turbine Operating at Excess Load Condition
Authors: Altimemy Muhannad , Caspar Justin , Oztekin Alparslan
Published: October 2020

Computational fluid dynamics simulations are conducted to characterize the spatial and temporal characteristics of the flow field inside a Francis turbine operating in the excess load regime. A high-fidelity Large Eddy Simulation (LES) turbulence model is applied to investigate the flow-induced pressure fluctuations in the draft tube of a Francis Turbine. Probes placed alongside the wall and in the center of the draft tube measure the pressure signal in the draft tube, the pressure over the turbine blades, and the power generated to compare against previous studies featuring design point and partial load operating conditions. The excess load is seen during Francis turbines in order to satisfy a spike in the electrical demand. By characterizing the flow field during these conditions, we can find potential problems with running the turbine at excess load and inspire future studies regarding mitigation methods. Our studies found a robust low-pressure region on the edges of turbine blades, which could cause cavitation in the runner region, which would extend through the draft tube, and high magnitude of pressure fluctuations were observed in the center of the draft tube.
Application of FMI in Metal Casting Press-Forming Process
Authors: Xingli Zhong , Linhong Ji , Sheng Li , Yijia Lu
Published: October 2020

Accurate simulation of metal casting press-forming process needs to consider mutual coupling effects in a number of different fields of physics subsystem. Hydraulic systems, control systems and mechanical systems are the most important subsystems among them. It is difficult to create various subsystems in detail in a single modeling tools, so co-simulation technology is used to take advantage of different tools to achieve the entire physical process of system-level simulation. The paper researched the co-simulation in the Abaqus software and the Matlab software based on FMI standard, considered fully the coupling effect between different systems, and simulated the metal casting press-forming process. The simulation results showed that co-simulation based on FMI standard can be well suited for multi-disciplinary co-simulation in complex mechanical model, and played a well-guiding role in the engineering design. The co-simulation would take more computation time than traditional simulation, but it can be achieved to research the integrated features of system and to reduce greatly experiments costs and prototype trial risks by using this technology.
Micro Machined Slit Between Ridge and Groove in Micro Fluid-Channel to Measure Floating Cell Deformability
Authors: Hashimoto Shigehiro
Published: October 2020

A micro-slit has been designed to measure deformation of a biological single cell passing through the slit. At the middle part of the flow channel, the slit (7 μm height, 0.4 mm width, and 0.1 mm length) has been made by photolithography technique: the combination of the micro-ridge on the transparent polydimethylsiloxane plate and the micro-groove on the glass plate. C2C12 (mouse myoblast cells) was used in the test. The flow of suspension of cells was controlled by the pressure head between the inlet and the outlet. Deformation of cells passing through the micro slit was observed with an inverted phase-contrast microscope. The experimental results show that a cell deforms to the flat circular disk and passes through the micro-slit. Although smaller cells tend to pass the micro-slit easily, some bigger cells also passed the micro-slit. Deformation ratio is independent of the size of each cell. The designed slit has capability to detect quantitative deformability of a single biological cell.
Simulation on Flow Pattern Transition With Liquid Nitrogen and its Vapor Using a Droplet Entrainment Model
Authors: Zhou Rui , Xia Tao , Zhang Xiaobin
Published: October 2020

A droplet entrainment model was applied to characterize the flow pattern transition in the countercurrent horizontal flow with liquid nitrogen (LN2) and vapor nitrogen (VN2). A two-fluid three-field model consisting of liquid film, gas, and droplet was implemented based on the Eulerian-Eulerian model in ANSYS Fluent®. In the droplet entrainment model, the condition and position of the droplet generation were realized by calculating the velocity gradient in the normal direction of the interface towards the gas core. The droplet entrainment and deposition rates were also included and validated according to the available data of water/air in the literature. Three flow patterns, including stratified-wavy flow, churn flow, and pseudo-slug flow, were identified in simulation results with LN2/VN2. Furthermore, ligament breakup was found to be the main droplet entrainment mechanism in the churn and pseudo-slug flow, and there can be a high probability of the occurrence of bubble burst as well. Compared with water/air, the droplets are more easily to be entrained in LN2/VN2 due to the smaller viscosity and surface tension according to the results of droplet mass flow rate. Pressure drop signals of the three flow patterns were also obtained and analyzed.
A Comparative Numerical Study on Two-Phase Boiling Fluid Flow and Heat Transfer in the Microchannel Heat Sink With Different Manifold Arrangements
Authors: Luo Yang , Zhang Jingzhi , Li Wei
Published: October 2020

The manifold microchannel (MMC) heat sink system has been widely used in high-heat-flux chip thermal management due to its high surface-to-volume ratio. Two-phase, three-dimensional numerical methods for subcooled flow boiling have been developed using a self-programming solver based on OpenFOAM. Four different types of manifold arrangements (Z-type, C-type, H-type and U-type) have been investigated at a fixed operational condition. The numerical results evaluate the effects of flow maldistribution caused by different manifold configurations. Before simulating the two-phase boiling flow in MIMC metamodels, single-phase liquid flow fields are performed at first to compare the flow maldistribution in microchannels. It can be concluded from the flow patterns that H-type and U-type manifolds provide a more even and a lower microchannel void fraction, which is conducive to improving the temperature uniformity and decreasing the effective thermal resistance. The simulation results also show that the wall temperature difference of H-type (0.471 K) is only about 10% of the Z-type (4.683 K). In addition, the U-type manifold configuration show the lowest average pressure drop at the inlet and outlet of the MIMC metamodel domain. However, H-type manifold also shows an impressive 59.9% decrease in pressure loss. Results indicate that both the H-type and the U-type manifolds for flow boiling in microchannels are recommended due to their better heat transfer performance and lower pressure drop when compared with Z-type and C-type.
Oblique Micro Grooves on Bottom Wall of Flow Channel to Sort Cells
Authors: Hashimoto Shigehiro
Published: October 2020

The movement of a flowing cell near the oblique micro groove on the bottom surface in the micro flow channel has been measured to sort biological cells in vitro. The micro groove of the rectangular shape (4.5 μm depth, and 0.2 mm length) was fabricated on the polydimethylsiloxane (PDMS) disk by the photolithography technique. The angle between the flow direction and the longitudinal axis of the groove is 45 degree. Variation has been made on the width (0.03 mm < w < 0.05 mm) of the groove. A rectangular flow channel (0.05 mm height × 1 mm width × 25 mm length) has been constructed between two transparent PDMS disks. C2C12 (mouse myoblast cell line) was used in the test. A flow velocity (0.1 mm/s < vx < 2.4 mm/s) of the suspension of cells was controlled by the pressure difference between the inlet and the outlet. The shifted distance of each cell along the oblique groove depends on the diameter of the cell. The malnourished cell with the different density can be distinguished by the shifted distance according to the velocity of the cell.
Experimental Analysis of Lagrangian Coherent Structures and Chaotic Mixing in Rayleigh-Benard Convection
Authors: Watanabe Masahito , Kitamura Yusuke , Hatta Naoki , Yoshimura Hiroaki
Published: October 2020

It is known that some fluid particles may be transported chaotically in Lagrangian description although the velocity field seems to be stable in Eulerian description. A typical example can be found in the system of two-dimensional Rayleigh-Benard convection with perturbed velocity fields, which has been investigated as a low dimensional mechanical model of fluid phenomena associated with natural convection in order to clarify the mechanism of fluid transport (see, for instance, [2]). In this study, we make an experimental study on the global structures of chaotic mixing appeared in the two-dimensional perturbed Rayleigh-Benard convection by analyzing Lagrangian coherent structures (LCSs), which correspond to the invariant manifolds of time-dependent mechanical systems. We develop an apparatus to measure the velocity field by Particle Image Velocimetry (PIV) and then show the LCSs which can be numerically detected from the experimental data by computing Finite-time Lyapunov exponent (FTLE) fields. Finally, we show the global structures of chaotic mixing appeared in the perturbed Rayleigh-Benard convection as well as the steady convection by experiments. In particular, we clarify how the LCSs are entangled with each other around the cell boundaries to carry out chaotic Lagrangian transports.
Numerical Study of Unsteady Behavior of Cloud Cavitation by Smoothed Particle Hydrodynamics
Authors: Ushioku Takahiro , Yoshimura Hiroaki
Published: October 2020

Cavitation generates a portion of cavities called a cavitation cloud, which performs a collective unsteady motion of repeating the process of growth and collapse. In particular, it is considered that a high-pressure shock wave propagates associated with the collapse. In order to understand such unsteady behaviors of the cavitation cloud, much effort has been made for the numerical analysis of internal flows of the cavitation cloud. However, it is not clear how such a cavitation cloud can be identified as a physical entity nor how its unsteady collective motion can be elucidated in the context of the multiphase fluid flow. In this study, we make a two-dimensional numerical analysis of the multiphase flow of the submerged bubbly water jet injecting into still water through a nozzle. To model the bubbly water jet, we employ the mixture model of liquids and gases, and we utilize the Smoothed Particle Hydrodynamics method for the numerical analysis of the unsteady flows in Lagrangian description. Finally, in order to clarify the unsteady behaviors of the cloud cavitation, we show how the cavitation cloud can be generated in the context of velocity fields in the multiphase flow and in particular, we clarify how twin vortices induced by the water jet play an essential role in the expansion and shrinkage of the cloud.
Flow Development of a Liquid Sheet Issued Into Low-Speed Airstream
Authors: Jaberi Amin , Tadjfar Mehran
Published: October 2020

In this study, a liquid sheet with an aspect ratio of 90 and a thickness of 0.35 was experimentally investigated when issued into a low-speed subsonic crossflow. High speed photography and shadowgraphy technique were employed to capture the instantaneous physics of the liquid sheet. Flow visualizations were used to investigate the flow development of the liquid sheet. It was found that this flow exhibited a completely different flow structure than circular or other non-circular liquid sheets. It was found that the liquid sheet developed a concave-like shape in the presence of the transverse airstream. This phenomenon, named as inflated sheet, was absent in regular circular liquid jets injected into gaseous crossflow. It was revealed the inflated sheet was the main feature of the liquid sheet that made the jet characteristics unique. The flow feature of the inflated sheet structure and its alteration with flow condition was fully examined. Moreover, the width and trajectory of the liquid sheet were quantitatively studied at different Weber numbers and for the constant momentum ratio of 40. It was found that the fluid width could be a useful parameter to distinguish different regimes of the flow.
Design Optimization of Splitter Blade Impeller in a Centrifugal Pump
Authors: Takao Shunya , Hayashi Kentarou , Miyabe Masahiro
Published: October 2020

In order to improve suction performance, centrifugal pumps with an inducer are used for rocket pumps, liquid gas transport such as LNG, and general-purpose pumps. Since a higher suction performance than conventional pump is required, a splitter blade that consists of a long blade and a short blade is sometimes adopted. However, the design becomes more difficult due to the increased number of parameters. The stable operation over a wide flow rate range are required in the general-purpose pumps. Therefore it is necessary to design them so that unstable flow phenomena such as surges do not occur. However, the design method to avoid them is not well understood yet.

In this study, we focused on the splitter blade impeller in a general-purpose low-speed centrifugal pump with an inducer. Six parameters such as leading edge position and trailing edge position of the short blade for both hub-side and tip-side were set as design ones. A multi-objective optimization method using a commercial software was applied to improve suction performance while maintaining high efficiency. Then obtained optimal shape were analyzed by CFD calculation and extracted the feature. Furthermore, optimized impellers were manufactured and confirmed the performance over a wide flow rate range by experiments. In addition, a optimizing design method that improves pump performance at lower cost was studied.
A Computational Study of a Biomass Cookstove With Forced Secondary Air Injection
Authors: Cassidy Liam , MacCarty Nordica
Published: October 2020

The use of solid biomass as a primary energy source for cooking is common to nearly half of the world’s population. Household air pollution as a byproduct of biomass combustion creates powerful negative health impacts related to air quality and a strong influence on our global radiative balance. Despite efforts to improve biomass-fueled cooking technology, many current designs still fail to meet WHO guidelines for air quality and consume excessive fuel. One promising method to improve in both of these areas is through introduction of forced primary or secondary air to the combustion process to increase turbulence, mixing, and velocity. Incorporating computational fluid dynamics to the design process for this forced draft air flow can provide insights into the complex and interconnected thermophysical relationships which, otherwise, would require extensive experimentation. The objective of this work is to provide a preliminary computational fluid dynamics study of a secondary air forced draft biomass cookstove. Thermal efficiency and emissions concentrations are investigated relative to various combinations of secondary air flow rates and injection angles. The results from the case study suggest that thermal efficiency of the cookstove is a function of secondary air injection angle, with optimal angle being a function of the specific air-fuel ratio. Additionally, a design trade-off is evident when comparing the pollutant concentration data and thermal efficiency data. Lastly, analysis of the computational results suggests that large pressure gradients about secondary air vortices in the combustion chamber lead to improved thermal efficiency and more complete combustion. The continued development of this work into an open-source computational fluid dynamics tool is underway.
Simulation of Ventilation Flow Through a Room Fitted With a Windcatcher Incorporating Phase Change Materials
Authors: Abdo Peter , Reyes-Cubas Angel
Published: October 2020

Natural ventilation is the process of supplying and removing air through an indoor space by natural means. Windcatcher has been used over centuries for providing natural ventilation using wind power, it is an effective passive method to provide healthy and comfortable indoor environment by decreasing moisture content in the air and reducing pollutants concentration effectively. The windcatcher’s function is based on the wind and on the stack effect resulting from temperature differences. Materials that change phase at certain temperature are frequently referred to as Phase Change Materials (PCMs). PCMs change from solid to liquid and vice versa. PCMs could be used in passive cooling systems and they are directly related to building energy efficiency. In this study air flow through a two-dimensional room fitted with a windcatcher and incorporated with phase change materials (PCMs) is simulated. The temperature change in the room implementing PCM is analyzed to monitor the PCMs’ performance. To achieve this, Ansys Fluent is used to simulate the temperature changes inside the room as well as the melting process of PCM. PCM is placed at the right and left walls of the room and at its bottom. Two cases have been considered (with and without PCM) and the average temperatures at three locations have been compared for an inlet velocity of 1 m/s and an inlet temperature of 302 K. The average temperature at 1.2 m high inside the room with PCM dropped by about 1–2 °C compared to that without PCM.
Measurements of Morphology and Locomotion of Caenorhabditis Elegans With Digital Holographic Microscopy
Authors: Wang Yijie , Chen Jun , Zhang Yuan , Kim Kee-Hong
Published: October 2020

Digital holographic microscopy (DHM) enables 3D volumetric measurements of small objects with high magnification. DHM has been applied to measure a variety of experimental studies, including turbulent boundary layer, spray droplets, individual cells, development of zebrafish embryo, etc. In this study, a DHM system is applied to measure the morphology and locomotion of two groups of Caenorhabditis Elegans (C. Elegans) with different development conditions (ATGL-1 group and n2 group) in an 8-day time period from their hatching to the adult stage, whose body lengths range from hundreds of micrometers to one millimeter. The length and volume are determined to describe the morphology of the C. Elegans at different development stages. The locomotion of the C. Elegans is divided into linear motion and curl motion. The kinetic energy derived from the two types of motion describes the extent of how active the C. Elegans is. The statistics of morphology and locomotion of the two groups of C. Elegans are compared at different development stages to illustrate the influence of the applied development conditions.
Vortex-Induced Rotations of a Pair of Laterally Arranged Square Cylinder in a Two-Dimensional Microchannel
Authors: Li Lichun , Li Shanshan , Yan Zhe , Pan Zhenhai
Published: October 2020

This paper investigates the dynamic response of two freely rotatable rigid square cylinders to two-dimensional laminar flow in a microchannel. The square cylinders are laterally pinned side-by-side in the microchannel with a single freedom of rotation. Finite volume method coupled with a dynamic mesh technique is developed and validated to reveal the detailed motion characteristics of the cylinders and nearby flow structures. Under small Reynolds number (Re = 50), both cylinders oscillate periodically. The oscillate curves (rotating angle v.s. time) are symmetrical with each other but with a certain phase difference. At Re = 150, both cylinders oscillate randomly. Under high Reynolds number (Re = 300), the two cylinders both keep rotating in the opposite direction with the velocity magnitude fluctuating drastically around 1.75. Important motion details are presented to understand the Fluid-Structure interaction mechanism under different Reynolds number, including the time history of rotating angles and rotating velocities, lift and drag coefficients on the cylinders, distribution of pressure around the cylinder sides. Both pressure-induced torque and the shear induced one are obtained and their contributions to both cylinders’ rotation characteristics are quantitatively evaluated. Vortex structures and streamlines around the cylinders at specific moments are also revealed in this paper to help understanding the fluid-structure interaction phenomenon.
Recommendations for Long-Term Operation of High-Performance Submersible Motor Pumps in Mine Dewatering
Authors: Beck David , Wulff Sebastian , Thamsen Paul Uwe , Reich Morris , Worringer Jean Pierre
Published: October 2020

Modern submersible pumps are high performance aggregates for long-term operation, which find application in open-pit mining. Dewatering of groundwater to run an open-pit mine with various conditions for submersible pumps often leads to short-term performance based on different circumstances in the well as well as in the general operation. These result in high maintenance and energy costs and decreases the drawdown in open-pit mining.

To ensure a long-time performance, a proper selection of submersible pump and motor is required.

It is also necessary to consider the geometry of different deep wells in order to take into account the initial conditions of the pumps.

This paper shows recommendations for long-term operation of high-performance submersible pumps due to the conditions of the mining industry. Therefore, a holistic consideration of the aggregate takes place to receive recommendations, which minimize the rate of pump failures and increase the efficiency of the dewatering process. These recommendations are based on various failures found during an investigation. Furthermore, this paper recommends different methods to prevent these failures, for instance clogging and erosion through particles in the well. These recommendations are linked to the research of different submersible motor pumps from various manufacturers in different wells in German open-pit mines with short-term operation caused by several circumstances.
Trilinos Solvers Scalability on a MFiX-Trilinos Framework Applied to Fluidized Bed Simulations
Authors: Rodriguez Arturo , Kotteda V. M. Krushnarao , Rodriguez Luis F. , Kumar Vinod , Munoz Jorge A.
Published: October 2020

MFiX is a multiphase open-source suite that is developed at the National Energy Technology Laboratories. It is widely used by fossil fuel reactor communities to simulate flow in a fluidized bed reactor. It does not have advanced linear iterative solvers even though it spends 70% of the run time in solving the linear system. Trilinos contains algorithms and enabling technologies for the solution of large-scale, sophisticated multi-physics engineering and scientific problems. The library developed at Sandia National Laboratories has more than 60 packages. It consists of state-of-the-art preconditioners, nonlinear solvers, direct solvers, and iterative solvers. The packages are performant and portable on various hybrid computing architectures. To improve the capabilities of MFiX, we developed a framework, MFiX-Trilinos, to integrate the advanced linear solvers in Trilinos with the FORTRAN based multiphase flow solver, MFiX. The framework changes the semantics of the array in FORTRAN and C++ and solve the linear system with packages in Trilinos and returns the solution to MFiX. The preconditioned iterative solvers considered for the analysis are BiCGStab and GMRES. The framework is verified on various fluidized bed problems. The performance of the framework is tested on the Stampede supercomputer. The wall time for multiple sizes of fluidized beds is compared.
Analysis of Coupled CFD-DEM Simulations in Dense Particle-Laden Turbulent Jet Flow
Authors: Weaver Dustin , Miskovic Sanja
Published: October 2020

In this paper, coupled CFD-DEM simulations of dense particle-laden jet flow are performed using CFDEM® coupling interface that couples LAMMPS-based LIGGGHTS® DEM engine with OpenFOAM CFD framework. Suspensions of mono-sized spherical glass particles with 80 microns diameter and a mass loading of 0.23 and 0.86 are considered. Three different CFD meshes are used with an average mesh resolution dimension of 3.06, 2.67, and 1.86 particle diameters and it is determined that mesh resolution does not change results for void fraction calculation (using the divided model) of the CFD-DEM equations. Samples of particle flux are taken at 0.1, 10, and 20 nozzle diameters along the axial direction of the jet region. The numerical results for particle flux are compared with a well cited experimental data found in literature. The CFD-DEM simulations in turbulent jet flow are found to be highly sensitive to initial particle velocity inputs but the experimental data provide sufficient information to produce comparable results.
Investigation of the Flow Instabilities of a Low Specific Speed Pump-Turbine: Part 2 — Flow Control With Fluid Injection
Authors: Deniz Sabri , von Burg Martin , Tiefenthaler Manuel
Published: October 2020

This the second part of a two-part paper focusing on the flow instabilities of low-specific pump turbines. In this part, results of the flow control application with fluid injection (using both water and air) in the vaneless space in order to suppress the flow instabilities of a low specific speed model pump-turbine in turbine mode operation at HSLU (Lucerne University of Applied Sciences) Switzerland are presented.

Based on the analysis of the experimental data, flow visualization, and CFD results focusing especially on the flow features in the vaneless space and at the runner inlet, the onset and development of the flow instabilities are explored as presented in the first part of this paper. Based on these analyses, the flow control technology by injecting air and water as well as suction of the fluid in the vaneless space of the model pump-turbine is implemented for suppressing the flow instabilities and thus extending the operating range of the pump-turbine. Both air- and water-injection are applied by using an external energy source (compressor and pump) and discrete nozzles circumferentially distributed in the vaneless space. The S-shaped pump-turbine characteristics in turbine operating mode are modified so that the slope at speed no load conditions is no more positive meaning an improvement in the stability behavior. To the best of our knowledge, this is the first successful application of flow control with fluid injection in the vaneless space of pump-turbines. Fluid injection is applied at two different guide vane openings, i.e. at 6° and 18°. The analysis of the unsteady pressure data indicates the suppression of flow instability such as rotating stall with fluid injection in the vaneless space. The water injection is more effective than the air injection for modifying the slope of the pump-turbine characteristics.
Two-Phase Wakes in Adiabatic Liquid-Gas Flow Around a Cylinder
Authors: Kim Dohwan , Rau Matthew J.
Published: October 2020

Small tubes and fins have long been used as methods to increase surface area for convective heat transfer in single-phase flow applications. As demands for high heat transfer effectiveness has increased, implementing evaporative phase-change heat transfer in conjunction with small fins, tubes, and surface structures in advanced heat exchanger and heat sink designs has become increasingly attractive. The complex two-phase flow that results from these configurations is poorly understood, particularly in how the gas phase interacts with the flow structure of the wake created by these bluff bodies. An experimental study of liquid-gas bubbly flow around a cylinder was performed to understand these complex flow physics. A 9.5 mm diameter cylinder was installed horizontally within a vertical water channel facility. A high-speed camera captured the movement of the liquid-gas mixture around the cylinder for a range of bubble sizes. Liquid Reynolds number, calculated based on the cylinder diameter, was varied approximately from 100 to 3000. Time-averaged probability of bubble presence was calculated to characterize the cylinder wake and its effects on the bubble motion. The influence of the liquid Reynolds number, superficial air velocity, and bubble size is discussed in the context of the observed two-phase flow patterns.