bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Study and Modelling of the Tip-Leakage Flow for an Isolated Fixed Blade
Authors: Deveaux B. , Fournis C. , Brion V. , Marty J. , Dazin A. 
Published: November 2019

Abstract
The tip-leakage flow has detrimental effects on the performance of compressors. In this paper the effects of gap height and incoming casing boundary layer thickness are analyzed. Velocity and total pressure measurements are carried out in a plane behind the trailing edge of an isolated fixed blade. The total pressure loss is decomposed in a vortex loss and a wake loss. It appears that the increase of total pressure losses with the gap height comes essentially from the vortex part. This observation motivated the development of a model based on an analogy with a jet in crossflow to estimate the tip-leakage vortex circulation. The predictions of this model are consistent with the experimental data for gaps smaller than 4% of chord.
Derivation of an Amplitude Equation for Weakly Nonlinear Pressure Waves of a Very High Frequency in a Compressible Liquid Containing Many Microbubbles
Authors: Akutsu Ryosuke , Kanagawa Tetsuya , Uchiyama Yusuke 
Published: November 2019

Abstract
The present paper theoretically treats weakly nonlinear propagation of plane progressive waves in an initially quiescent compressible liquid containing a tremendously large number of spherical gas bubbles, focusing on the derivation of an amplitude evolution equation (i.e., nonlinear wave equation). We emphasize the following points: (i) the compressibility of the liquid phase, which has long been neglected, is considered; (ii) the wave propagates with a large phase velocity exceeding the speed of sound in pure water; (iii) bubbles are not created or annihilated. From the method of multiple scales with an appropriate scaling of three nondimensional parameters, we can derive an attenuated nonlinear Schrödinger (NLS) equation, where the phase velocity is larger than the speed of sound in a pure liquid.
Consideration of CFD Analysis Accuracy of Box Fan
Authors: Tomimatsu Shigeyuki , Kato Chisachi 
Published: November 2019

Abstract
This CFD benchmark activity for a box fan has been conducted through the Industrial Committee for Supercomputing Promotion (ICSCP) and the Fan Noise Prediction Working Group from the “Promotion of Practical Use of HPC in Turbomachinery” Subcommittee established in the Turbomachinery Society of Japan. In this benchmark activity, various CFD software has been used.
In this study, ANSYS CFX 18.2 is used and the difference in results are investigated by changing the turbulence model and the mesh model. The results between the k-epsilon model and the Shear Stress Transport (SST) model show a reverse trend. That is to say, the k-epsilon model overestimates the pressure difference at the high flow range and the SST model underestimates it at the low flow range compared with the experimental result. In order to improve these numerical results, CFD analysis is conducted by changing mesh models. The number of the blade surface mesh, and the initial height, height ratio, and number of prism layers are changed, but there is no improvement through these approaches. In this paper, CFD verification and validation are conducted for the box fan.
Effect of Active Flow Control Mechanisms on the Turbulent Flow Structures
Authors: Tsubokura Satoshi , Kawaguchi Yasuo 
Published: November 2019

Abstract
Blowing or suction on the wall is expected to efficiently control the characteristics of wall-bounded turbulent flow such as wall-frictional coefficient. To understand the mechanism of the change of turbulence statistics caused by this method, we experimentally investigated the effect of uniformly blowing and suction flow on a turbulent structure in a relatively simple flow, fully developed turbulent channel flow. For blowing, the friction coefficient and the thickness of the low-speed region increased. These results imply that the boundary layer becomes unstable because the growth of viscous sublayer is rapid and the time-scale of reaching a critical thickness is small due to the blowing from the wall. On the other hand, for suction, the opposite tendency appeared.
Impact of Differing Water Contents on Electrostatic Charging
Authors: Weishaar Philipp C. , Mielke Tobias , Schmitz Katharina 
Published: November 2019

Abstract
Hydraulic fluids underwent significant changes in their composition in these past years, which led to an increase in poor conductivity. Since well-established standards for specifying a hydraulic fluid, such as ISO 11158, make no mention of the electric conductivity, the awareness for potential complications is low. With some applications electrostatic discharges contribute to a shortened service life of the hydraulic fluid and the filter elements. Recent work on cavitation and its different forms suggest an underestimated impact of the relative humidity on fluid characteristics and the tendency for cavitation. In relation to electrostatic charges, the relative humidity of a fluid is seldom considered. The results presented in this paper offer an initial observation of the effect of relative humidity on electrostatic charging. To this end three hydraulic fluids, satisfying the specifications of an HLP 46, are prepared with three different levels of relative humidity at 20°C. Subsequently the nine samples are tested with a small-scale test bench in order to garner a qualitative comparison of the charging tendency.
X-Ray Flow Visualization of Cyclopentane Hydrate Formation
Authors: Pillers Roy A. , Morgan Timothy B. , Heindel Theodore J. , Estanga Douglas 
Published: November 2019

Abstract
Natural gas hydrates form under high pressure and low-temperature environments common in deepwater off-shore petroleum production operations. Once hydrates form, they can agglomerate and deposit resulting in solid plugs within the piping system, which could require extensive downtime for remediation and recommission of the systems. Hydrate plug formation is difficult to characterize because of the challenging environments in which they form, the lack of instrumentation for such environments, and the fast reaction time compared to other blocking mechanisms. This study explores the use of X-ray flow visualization, including X-ray radiography and X-ray computed tomography, to help characterize hydrate formation in a laboratory setting. A structure II hydrate was formed in a concentric cylinder mixing tank where a mixture of distilled water and cyclopentane was stirred in the inner tank while the outer tank was cooled. As the tank cooled, the distilled water-cyclopentane mixture converted to hydrate, which was captured with X-ray radiographic videos. Once formed, X-ray computed tomography images were acquired to gather 3D reconstructed images of the hydrate with and without liquid present in the mixing tank. It was shown that X-ray imaging could provide a qualitative assessment of hydrate formation. Quantitative measures were challenging because of the limited contrast between the hydrate and liquid region.
Experimental Investigation for the Better Control of Flows Over a Simplified Vehicle Configuration With Dielectric Barrier Discharge Plasma Actuator
Authors: Sekimoto Satoshi , Shimizu Keigo , Nakashima Takuji , Fujii Kozo , Hiraoka Takenori , Nouzawa Takahide 
Published: November 2019

Abstract
Reduction of aerodynamic drag is a big subject for vehicle development from the point of view of the global environment conservation. On the other hand, the optimization of vehicle body for less aerodynamic drag strictly defines the body shape and limits the freedom of design. Therefore, novel flow control technology is desired to enable small aerodynamic drag with excellent design. In the present study, a dielectric barrier discharge plasma actuator is installed on a simplified vehicle model with the round-shaped rear end to control the flow around the rear end for drag reduction. Experiments are conducted with the model (L840mm × H300mm × W300mm) in a Gottingen type wind tunnel with a ground plate. Reynolds number is fixed at 1,200,000, corresponding to a freestream velocity of approximately 20 m/s. Aerodynamic force, surface pressure near the rear edge, and total pressure and velocity field are measured. In the result of aerodynamic force measurement, driving plasma actuator successfully achieves 3% drag reduction at the most. Flow field measurement of total pressure and two-component velocity shows the difference of vortex structure near the rear end between off and on. Plasma actuation in this study can move the vortex structure away from the body surface rather than suppress the vortex or circulation.
Resolvent Analysis of Turbulent Friction Drag Reduction by Manipulation of Mean Velocity Profile
Authors: Uekusa Riko , Kawagoe Aika , Nabae Yusuke , Fukagata Koji 
Published: November 2019

Abstract
In the present study, we numerically manipulate the mean velocity profile of a turbulent channel flow and assess the friction drag reduction performance by using resolvent analysis. Building on the implication obtained from Kühnen et al. (Nat. Phys., Vol. 14, 2017, pp. 386–390) that modifying mean velocity profile flat leads to significant drag reduction, we first introduce two functions for turbulent mean velocity, which can express ‘flattened’ profiles: one is derived based on the turbulent viscosity model proposed by Reynolds & Tiederman (J. Fluid Mech., Vol. 658, 2010, pp. 336–382), and the other is based on the mean velocity profile of laminar flow. These functions are used as the mean velocity profile for the resolvent analysis, and the flatness of the resulting profiles is characterized by two different measures. As a result, we confirm that, friction drag reduction is achieved if the turbulent mean velocity profile is ‘flattened’. However, we also find that the flatness of the mean velocity profile in the center of the channel alone is not enough to evaluate the drag reduction performance.
Numerical Study on Flow-Induced Vibration Characteristics of Three-Dimensional Hydrofoil in Cavitating Flow
Authors: Wang Chang , Liu Yuan-qing , Du Te-zhuan , Wang Yi-wei 
Published: November 2019

Abstract
With the increasing demand of higher performance and efficiencies for marine propulsion and hydropower system, structures became more flexible and were subjected to high flow rates. Cavitation-structure interaction has become one of the major issues for most engineering applications. In order to analyze the characteristics of unsteady cavitating flow induced vibration, the cloud cavitation flow over three dimensional NACA66 hydrofoil is studied by numerical simulation in this paper. The cavitating flow is modeled by large eddy simulation method and Zwart cavitation model, and the structural vibration model of three dimensional hydrofoil is established. The numerical calculation of fluid-solid coupling is realized based on ANSYS Workbench. The main dimensionless parameters of three-dimensional hydrofoil cavitation flow-induced vibration are obtained by means of dimensional analysis, including density ratio, cavitation number, Reynolds number, and the frequency ratio of flow to structure. The changes of cavity morphology during the cloud cavitation development of flexible hydrofoil and the flow-induced vibration characteristics under cloud cavitation flow of flexible hydrofoil are analyzed. The results showed that the periodic development of cavitation can be divided into three stages: the growth of attached cavity, the development of re-entrant jet and the shedding of cavity in cloud cavitaion stage. The centroid displacement of the free end of the flexible hydrofoil varies periodically with time at the stage of cloud cavitation. The hydrofoil vibration is affected by the development of cloud cavitation, and the vibration frequency corresponds to the shedding frequency of cloud cavitation.
Flow Measurement in Stented Left Coronary Artery Models
Authors: Ono Kensuke , Yamamoto Ken , Tsukahara Takahiro , Motosuke Masahiro , Kawamoto Hiroyoshi , Tahara Satoko , Tanaka Kentaro , Nakamura Sunao 
Published: November 2019

Abstract
Ischemic heart disease, a generic term for angina pectoris and myocardial infarction, is caused by blood flow failure due to a lesion generated in the coronary artery of the heart. Because the ischemic heart disease causes fatal problems, a stent placement technique called the percutaneous coronary intervention (PCI) is frequently performed to expand coarctated arteries to recover the function. However, although the PCI technique is a less-invasive technique, there is a risk of complications such as stent thrombosis and restenosis due to the placed stent. In order to understand the cause and the mechanism of the complications, effects of the stent placement and the stent shape on the blood flow is experimentally investigated. Silicone left coronary artery models were prepared to perform particle tracking velocimetry (PTV) and calculated the wall shear stress (WSS). The measurement results show that the flow structure and the WSS are changed depending on the deformation of the stent and the location of the placed stent.
Tracker: An Opensource Particle Tracking Velocimetry (PTV) Application Applied to Multiphase Flow Reactors
Authors: Weber Justin , Bobek Michael , Rowan Steven , Yang Jingsi , Breault Ronald 
Published: November 2019

Abstract
The US Department of Energy’s National Energy Technology Laboratory is pursuing the development of advanced energy conversion technologies, many of which use gas-solid reactors such as fluidized beds and risers. To understand these units and provide high fidelity particle velocities for model development and validation efforts, particle tracking velocimetry (PTV) is typically used and remains one of only a few ways to extract particle velocities from dense multiphase flow experiments. Combined with the rapidly improving cameras (higher frame rates, higher resolutions, and lower cost) and access to high performance computers, new particle tracking tools are needed.
Tracker is an opensource, cross platform particle tracking velocimetry application for tracking objects in videos and image stacks. The goal of this project is to provide a tool that is, open source, continuously developed, does not rely on expensive software, parallel, has a graphical user interface (GUI), one continuous pipeline (from reading the file to post processing), well documented, and continuously tested and verified.
The application has extensive preprocessing tools, two tracking methods including poly-projection and template matching, visualization tools, and post-processing tools. The techniques are tested using both synthetic data and real experimental images. The application is extremely flexible and is easily extended to other tracking techniques, with plans to add correlation-based algorithms and optical flow algorithms.
The high-fidelity data being generated is now being used to validate computational fluid dynamic models that then will be used to predict the performance of these reactors, helping to achieve the US Department of Energy’s goal of developing novel, compact gas-solid reactors.
Reynolds-Averaged Navier-Stokes Modeling of Turbulent Rayleigh-Taylor, Richtmyer-Meshkov, and Kelvin-Helmholtz Mixing Using a Higher-Order Shock-Capturing Method
Authors: Schilling Oleg 
Published: November 2019

Abstract
A numerical implementation of a large number of Reynolds-averaged Navier–Stokes (RANS) models based on two-, three-, four-equation, and Reynolds stress turbulence models (using either the turbulent kinetic energy dissipation rate or the turbulent lengthscale) in an Eulerian, finite-difference shock-capturing code is described. The code uses third-order weighted essentially nonoscillatory (WENO) reconstruction of the advective fluxes, and second- or fourth-order central difference derivatives for the computation of spatial gradients. A third-order TVD Runge–Kutta time-evolution scheme is used to evolve the fields in time. Improved closures for the turbulence production terms, compressibility corrections, mixture transport coefficients, and a consistent initialization methodology for the turbulent fields are briefly summarized. The code framework allows for systematic comparisons of detailed predictions from a variety of turbulence models of increasing complexity. Applications of the code with selected K–ε based models are illustrated for each of the three instabilities. Simulations of Rayleigh–Taylor unstable flows for Atwood numbers 0.1–0.9 are shown to be consistent with previous implicit LES (ILES) results and with the expectation of increased asymmetry in the mixing layer characteristics with increasing stratification. Simulations of reshocked Richtmyer–Meshkov turbulent mixing corresponding to experiments with light-to-heavy transition in air/sulfur hexafluoride and incident shock Mach number Mas = 1.50, and heavy-to-light transition in sulfur hexafluoride/air with Mas = 1.45 are shown to be in generally good agreement with both pre- and post-reshock mixing layer widths. Finally, simulations of the seven Brown–Roshko Kelvin–Helmholtz experiments with various velocity and density ratios using nitrogen, helium, and air are shown to give mixing layer predictions in good agreement with data. The results indicate that the numerical algorithms and turbulence models are suitable for simulating these classes of inhomogeneous turbulent flows.
Numerical Analysis of Steady Blowing Based Active Flow Control for Flow Over Ahmed Body
Authors: Shah Bansal , Basu Debashis 
Published: November 2019

Abstract
A numerical study is conducted to investigate fluidic actuation with steady injection for active flow control and drag reduction in an Ahmed body. Numerical results are obtained for the unsteady three-dimensional Navier Stokes equations for both baseline as well as steady injection cases. This study examines the use of active flow control devices at the rear of the 25-deg Ahmed model to reduce drag by controlling an unsteady wake. The present work demonstrates that URANS model with grid refinement at critical locations can accurately describe the aerodynamics around the bluff body with computational time of several days compared to several weeks with traditional LES simulations. In order to modify the wake and reduce the pressure drag, active flow control technique using steady blowing was applied through a narrow slit along all rear edges of the model. The effect of inlet velocity for the baseline simulations was analyzed. Computed Results showed AFC achieves significant reduction in the drag coefficient (Cd) values over the baseline simulations.
Cavitation in Co-Rotating Tip Vortices
Authors: Koncoski J. J. , Krane M. H. , Welz J. P. , Hanson D. R. , Willits S. M. , Kunz R. F. 
Published: November 2019

Abstract
This work documents flow characterization and cavitation inception of a co-rotating vortex pair shed from a single fin with a rounded tip at zero angle of attack. The fin was outfitted with a removable tip fabricated using a rapid prototype method. The co-rotating vortices result from surface discontinuities on the removable tip, near a hard wax fairing used to cover the tip attachment bolt. The vortices are shed at different locations along the chord. Flow visualization by oil paint and developed cavitation, and SPIV of the near-wake, indicate that a strong vortex is shed at the trailing edge, while a weaker vortex is shed at 82% chord. Horizontal wandering of the vortices is uncorrelated. Vertical wandering of the vortices is characterized by opposing oscillations about their mutual center. Acoustic cavitation inception in the water tunnel environment is discerned at an index 13% greater than visual detection of cavitation, and occurs within one chord of the trailing edge. The influence of the co-rotating vortex system on cavitation inception must be determined from comparison with measurements of a solitary vortex generated by analogous geometry.
Formation Characteristics of Two-Phase Drops From Coaxial Nozzles
Authors: Kamatani Naoya , Ogata Satoshi 
Published: November 2019

Abstract
The purpose of this study is to clarify the formation characteristics and production conditions of two-layer droplets using coaxial nozzle. In this study, we focus on Newtonian fluid only to pay attention to the fundamental formation characteristics of two-layer droplet. Also, the three liquids flowing in the apparatus were assumed to have the same viscosity and density. First, theoretical equations concerning the outer diameters of the single layer droplet and the two-layer droplet were obtained, and a conditional expression for detaching both nozzles simultaneously from the nozzle in dripping was obtained. These theoretical equations were verified using numerical analysis. By analyzing with various parameters changed, the following six formation modes could be confirmed. 2 interface both dripping, 2 interface both jetting, Outer interface is jetting and The inner interface is dripping, 2 interface comes into contact and the encapsulated liquid is discharged to the outside, Two or more droplets are formed in the interior, Liquid droplets containing liquid droplets and liquid droplets not containing liquid droplets are alternately formed. The validity of each theoretical expression and conditional expression was also be confirmed.
A Numerical Study on the Low Limit Auto-Ignition Temperature of Syngas and Modification of Chemical Kinetic Mechanism
Authors: Jang Seung Eon , Park Jin , Han Sang Hyeon , Kim Hong Jip , Jung Ki Sung , Yoo Chun Sang 
Published: November 2019

Abstract
In this study, the auto ignition with low limit temperature of syngas has been numerically investigated using a 2-D numerical analysis. Previous study showed that auto ignition was observed at above 860 K in co-flow jet experiments using syngas and dry air. However, the auto ignition at this low temperature range could not be predicted with existing chemical mechanisms. Inconsistency of the auto ignition temperature between the experimental and numerical results is thought to be due to the inaccuracy of the chemical kinetic mechanism. The prediction of ignition delay time and sensitivity analysis for each chemical kinetic mechanism were performed to verify the reasons of the inconsistency between the experimental and numerical results. The results which were calculated using the various mechanisms showed significantly differences in the ignition delay time. In this study, we intend to analyze the reason of discrepancy to predict the auto ignition with low pressure and low temperature region of syngas and to improve the chemical kinetic mechanism. A sensitive analysis has been done to investigate the reaction steps which affected the ignition delay time significantly, and the reaction rate of the selected reaction step was modified. Through the modified chemical kinetic mechanism, we could identify the auto ignition in the low temperature region from the 2-D numerical results. Then CEMA (Chemical Explosive Mode Analysis) was used to validate the 2-D numerical analysis with modified chemical kinetic mechanism. From the validation, the calculated λexp, EI, and PI showed reasonable results, so we expect that the modified chemical kinetic mechanism can be used in various low temperature region.
Evaluate a New Pump Design Using CFD Simulation
Authors: Ding Hui , Greenfield Benjamin 
Published: November 2019

Abstract
This paper describes how CFD simulations were used to help evaluating a centrifugal pump performance. The simulated pump was designed totally from scratch. Many aspects of pump performance characteristics were predicted based on the geometry generated using a pump design software. Especially the effects of the free spin of the 3rd rotor in a 3 stage pump assembly on overall performance were evaluated. Pump models, simulation techniques, and simulation approaches will be presented in detail. Simulation results will be discussed and compared with available test data.