bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Simulation of Airflow and Ellipsoidal Particle Deposition in Human Upper and Central Respiratory Tract
Authors: Kiasadegh Morteza , Dehghani Zahra , Naseri Arash , Abouali Omid , Ahmadi Goodarz 
Published: November 2019

Abstract
Steady airflow pattern during a full breathing cycle in human upper and central respiratory tract was simulated by solving the Navier-Stokes and continuity equations. For ellipsoidal fiber trajectory analysis under cyclic breathing condition, several user defined functions (UDFs) were developed and coupled to the ANSYS-Fluent discrete phase model (DPM). The developed model accounted for solving the coupled translational and rotational equations of motion of ellipsoidal fibers. The airway passage model was extended from the vestibule to the fifth generation of the bronchial bifurcations obtained mostly from computed tomography (CT) scan. A constant flow rate of 15 L/min was used to simulate the normal breathing condition. The velocity and pressure fields for different regions of the respiratory track were evaluated and used for Lagrangian particle trajectory analysis. Total and regional depositions of each region for a range of ellipsoidal particle diameter and aspect ratios were evaluated and the results compared with the experimental data.
Experimental Study of Mixing of Two-Layer Density-Stratified Fluid by a Vortex Ring
Authors: Cao Lile , Ito Ryo , Degawa Tomohiro , Matsuda Yu , Takamure Kotaro , Uchiyama Tomomi 
Published: November 2019

Abstract
This study experimentally investigates the mixing of a two-layer density-stratified fluid of water (upper layer) and aqueous sodium chloride (NaCl) solution (lower layer) induced by the interaction between a vortex ring and the density interface. The vortex ring, which consists of water, is launched from an orifice in the upper layer toward the density interface, after which its motion, along with the behavior of the lower fluid, is visualized through a planar laser-induced fluorescence method. The Atwood number that expresses the nondimensional density jump across the density interface is set at 0.0055, and the Reynolds number Re of the vortex ring is varied from 2050 to 3070. The visualization experiment clarifies that the vortex ring penetrating the density interface is bounced while collapsing in the lower fluid. Furthermore, it elucidates that the bounced upper fluid entrains the lower fluid into the upper layer by inducing a second vortex ring consisting of the lower fluid. Thus, this study reveals the effect of Re on the mixing of the upper and lower fluid induced by the launched vortex ring.
Aerodynamic Design and Assessment of a Compact, Single Stage Axial Fan for Low Noise Emission
Authors: Kessler Daniel , Giesecke Daniel , Friedrichs Jens , Leuschner Jörg 
Published: November 2019

Abstract
Axial fans used in automotive and especially in locomotive cooling systems have to follow several, partially contrary specifications. In addition to geometrical and aerodynamic specifications, acoustic limits must be taken into account for new fan stage designs. Legislation will tweak axial fan requirements in the future further and further to lower their noise emission and maximize their efficiency.
The main focus of this paper is to design and test a single stage axial fan for locomotive cooling systems with high aerodynamic efficiency and low noise emissions. The fan stage is designed to be installed in a so-called tower construction. The available construction space is limited. Therefore, special attention is paid to reduce the axial length. Extensive blade sweep and dihedral are implemented in the design process. The fan stage design is validated by experimental tests including aerodynamic and acoustic studies.
During the aerodynamic studies, it was found that an often used approximation about the static pressure downstream the fan cannot be applied. Downstream the fan stage no further components are installed. Therefore, the static pressure at this position must be approximated. An alternative approach is developed using the results of additional studies including a downstream pipe and scaling factors. The results of the approach are plausible.
The acoustic tests were carried out at a fan test facility at TU Braunschweig. To evaluate the impact of the halls acoustic repercussion on the test results, different tests were done. Additionally, another axial fan was tested which has been investigated a few years ago in an acoustic test chamber.
The studies show the positive effect of the design methodology on aerodynamic and acoustic of the fan stage. All requirements were achieved as well as a reduction of the axial length of the fan stage.
Mechanism of Wall Turbulence Modulation With Premixed Hydrogen Combustion
Authors: Ohta Takashi , Onishi Yuta , Sakai Yasuyuki 
Published: November 2019

Abstract
In order to clarify the mechanism of modulation of turbulence structures such as quasi-streamwise vortices affected by a flame propagating toward a wall, we perform a direct numerical simulation of wall turbulence with premixed hydrogen-air combustion using a detailed chemical reaction mechanism. As a result, existing quasi-streamwise vortices in turbulence near the wall are found to be suppressed, disappearing as the flame approaches. Hence, the turbulent flow tends to become laminar. Moreover, according to the analysis of the vorticity transport equation, it is found that the suppression is due to thermal expansion of the flame rather than an increase in viscosity. From the viewpoint of chemical reactions, it is revealed that thermal expansion inside turbulence vortices is mainly caused by reactions involving H2 and H2O2.
Visualization of Bubble Dissolution As a Means to Measure Dissolved Nitrogen Concentration
Authors: Sato Taisuke , Yamashita Tatsuya , Ando Keita 
Published: November 2019

Abstract
In ultrasonic cleaning, violent cavitation bubble dynamics causes material damage to cleaning surfaces, which is called cavitation erosion. The control of the dissolved gas concentration in cleaning liquid is effective to avoid cavitation erosion. The dissolved oxygen (DO) concentration is easily measured by a commercial DO meter, but the dissolved nitrogen (DN) concentration in water where multiple gas species are dissolved cannot be accurately measured with a commercially available DN meter. Therefore, it is important to construct a new method of measurement of DN concentration. In this study, we visualize the diffusion driven dissolution of bubble in air-saturated water and degassed water. The Epstein-Plesset theory considering multiple gas species is derived and compared with the experimental result where the DN concentration is treated as a fitting parameter in order to estimate the unknown DN concentration. Results indicates that the DN concentration can be measured by comparison between the theory and the relatively slow dissolution of bubble.
Uncertainty Quantification of Molten Hafnium Infusion Into a B4C Packed-Bed
Authors: Schiaffino Arturo , Kotteda V. M. Krushnarao , Kumar Vinod , Bronson Arturo , Shantha-Kumar Sanjay 
Published: November 2019

Abstract
In the manufacturing of metal matrix composites (MMC), liquid-metal reactive infusion with a solid mesh or particles composed of ceramic or metal may be used. The objective of this study is to determine the uncertainty quantification of the modeling of liquid hafnium infusion to expedite the processing and improve properties of MMCs ultimately. Uncertainty quantification (UQ) characterized the uncertainty scientifically especially for high-performance computing with observed physics and/or chemistry of the phenomena and predicted from estimated parameters. In this work, molten hafnium infusing through a boron carbide packed bed is modeled to optimize the manufacturing of components used for a hypersonic vehicle. The creation of molten matrix composites by the infiltration of molten metal represents a formidable challenge to be accurately modeled. First, the structural randomness associated with porous mediums complicates the prediction of the flow passing through it. Secondly, the properties of the molten metal could vary inside our control volume, since the temperature inside the control volume is not constant. Also, there are several chemical reactions and solidification rates occurring in during the impregnation. Given the recent advances in high-performance computing, an in-house pore network simulator are implemented along with Dakota, an open-source, exascale software, to determine the optimal parameters (e.g., porosity and temperature) and uncertainty quantification for the modeling.
Suppression of Secondary Flows in a Transonic Centrifugal Compressor Impeller Using an Inverse Design Method Based on Meridional Viscous Flow Analysis
Authors: Ito Sasuga , Okada Shin , Kawakami Yuki , Manabe Kaito , Furukawa Masato , Yamada Kazutoyo 
Published: November 2019

Abstract
Secondary flows in transonic centrifugal compressor impellers affect their aerodynamic performance. In open-type impellers, low energy fluids can accumulate on the suction surfaces near the trailing edge tip side since the secondary flows and tip leakage flows interfere each other and complex flow phenomena can be generated around the impellers. Therefore, designers must consider the effect of secondary flows to avoid the aerodynamic performance degradation while designing compressor impellers. In this paper, a novel design concept about suppression of secondary flows in centrifugal compressor impellers to improve their aerodynamic performance. A transonic centrifugal compressor impeller was redesigned with the present design concept by a two-dimensional inverse method based on a meridional viscous flow calculation in this study.
A design concept was introduced in above calculation process. As the design concept, by bending vortex filaments with controlling peak positions of the blade loading distributions, induced velocity due to bound vortices at the blades was generated in radial opposite direction of the secondary flows on the suction surface.
Due to investigate the effect of the design concept in this paper, three-dimensional Reynolds Averaged Navier-Stokes simulations were carried out, and the vortex cores were visualized by a critical point theory and colored by non-dimensional helicity. In the conventional transonic centrifugal compressor impeller, the secondary flow vortices were confirmed and one of the vortices was broken down. In the redesigned impeller, the breakdown of the secondary flow vortices was not observed and the accumulation of the low energy fluids was suppressed compared with the conventional impeller. The total pressure ratio and adiabatic efficiency of the redesign impeller were higher than that of the conventional impeller, and the secondary flows were successfully suppressed in this research.
Experimental Study of Free-Surface Deformation and Cavitation Bubble Dynamics in a Megasonic Cleaning Bath
Authors: Katano Yu , Ando Keita 
Published: November 2019

Abstract
Underwater ultrasound causes various physical phenomena in megasonic cleaning baths, e.g. cavitation inception, bubble translation and free-surface deformation (FSD) due to acoustic radiation pressure. Because FSD is especially noticeable in the case of high frequency ultrasound due to its high directivity, it is essential to investigate the interaction between FSD and bubble translation in megasonic cleaning bath. In our present experiments, we construct a typical setup for megasonic cleaning and irradiate water with 1 MHz ultrasound vertically upwards. We visualize FSD and bubbles and analyze the height of FSD and the translational velocity in frequency space. The bubbles translate in both short and long time scales caused by bubble-bubble interaction and periodic FSD, respectively, and the latter has periodicity. The most dominant frequency component in FSD shows good agreement with that in the translational velocity of the bubbles and does not depend on whether cavitation occurs or not. Therefore, it is suggested that FSD causes periodicity of bubble translation.
Relationship Between Macroscopic Rheological Properties and Microstructure of a Dilute Suspension by a Two-Way Coupling Numerical Scheme
Authors: Fukui Tomohiro , Kawaguchi Misa , Morinishi Koji 
Published: November 2019

Abstract
The rheological properties of a suspension depend on particle shape, spatial arrangement of the particles and hydrodynamic interactions as well as the concentration of the particles. So far, we proposed a two-way coupling numerical scheme to evaluate the effects of particle rotation on the rheological properties. This particle rotation decreases the fluid resistance. However, these studies were conducted on the condition that suspended particles were homogeneously distributed. Therefore, the particles in this study are randomly scattered in a suspension for better practical applications. Pressure-driven suspension flow simulations were conducted to consider the effects of inertia on the relationship between spatial arrangement of the particles and the rheological properties of a suspension. The channel width and axial length were set 400 μm and 1620 μm, respectively, and periodic boundary conditions were applied in the flow direction. The rigid spherical particles whose diameter was 20 μm were randomly scattered in the channel as an initial condition. The concentration of the suspension was set 1.02% for dilute assumption, and the suspension flows with the Reynolds number from 2 to 128 were reproduced in order to investigate the inertial effects of the suspended particles on the rheological properties. The rheological properties of the suspension were evaluated in terms of power-law index (non-Newtonian index). The velocity profile of a suspension for low Reynolds number conditions exhibited almost parabolic. This indicates the suspension behaves as a Newtonian fluid. For higher Reynolds number conditions, on the other hand, the lift force on the particles increased and they migrated toward the equilibrium y-axis position, where the lift force is zero. These changes in the y-axis position of the particles caused a change in microstructure of the suspension, which were followed by a change in macroscopic rheological properties. Owing to these microstructure changes, the non-Newtonian (thixotropic) properties were enhanced as the Reynolds number increased.
The Spike Dynamics Source Model for Ejecta in the FLAG Code
Authors: Harrison Alan K. 
Published: November 2019

Abstract
The Lagrangian hydrocode FLAG employs a subgrid model to represent the ejection of particulate mass (“ejecta”) from a shocked metal surface. With a conforming mesh used in typical simulations, the calculations of ejecta production, properties and launch are carried out independently on each mesh face lying on the surface of the metal. Based on experimental evidence [1] that ejecta production is greatest when the shock releases to the liquid state, the ejection process is modeled as a Richtmyer-Meshkov instability (RMI) of the liquid metal surface, in which the metal spikes that form break up to become ejecta. The model applies to the case in which surface perturbations such as machining grooves can be well approximated as a single-mode sinusoidal perturbation; in this case the RMI spikes are actually sheets.
The FLAG model includes (1) a description of RMI spike and bubble growth rates [2] and (2) the Self-Similar Velocity Distribution (SSVD) model of the velocity field within a spike as varying linearly from zero (in the fluid frame) at the base to a maximum value at the tip [3]. We report here on the improvement of this model by incorporating (3) a spike breakup treatment based on the Taylor Analogy Breakup (TAB) model [5], as extended to apply to sheet breakup [6,7], and (4) a new model for the inflow of metal into the base of the spikes. Combining all these elements allows us to self-consistently reconcile the evolving shape of the spikes (elongation and thinning) with the inflow, and with the corresponding properties of the bubbles, under the assumption of incompressibility. Since the model describes the motion of each fluid element into and along the spike, and subsequent fragmentation of the spike into ejecta, it predicts not only mass ejection rate but also the sizes and velocities of the particles launched in this process. We describe the new self-consistent model and its implementation in FLAG.
Experimental Evaluation of Wind Tunnel Test Apparatus for Active Flow Control
Authors: Pesch Alexander H. , Hess Diana V. 
Published: November 2019

Abstract
Active control of flow dynamics is an ever-increasing field of study. This paper presents details on a new experimental apparatus for the testing of dynamic fluid-structure interaction and the control thereof. Specifically, the experimental apparatus involves an open return wind tunnel with an actuated rigid airfoil. The airfoil is replaceable, but this initial evaluation uses a flat plate as a basic geometry airfoil. The pitch of the airfoil is actively controlled in real-time via an angle sensor, microcontroller, and brushed DC electric motor. For a given PID controller, sine sweeps are performed to identify the closed-loop frequency response at varying wind speeds. The wind creates a destabilizing feedback torque on the airfoil which increases with wind speed and results in a change in the closed-loop frequency response. A model of the system is augmented with a mathematical model for the wind dynamics. The assumed form wind model is manually tuned to match the closed-loop frequency response for all wind speeds. Finally, steady-state tests are conducted in which the setpoint for angle of attack is incrementally changed and the frequency spectrum is found for the angle sensor, in the control loop, and a hotwire behind the airfoil which is not in the control loop. The results from the angle sensor show the system holds steady, with slight variation at low frequencies for high angles of attack. The results from the hotwire show a distinct sheading frequency at low angles of attack, which is replaced by chaotic low frequency flow at high angles of attack characteristic of flow separation.
The Dynamic Measurement of Impinging Sheet Thickness via Partial Coherent Interferometry
Authors: Shang Weixiao , Chen Jun 
Published: November 2019

Abstract
In this work, the thicknesses of a series of impinging sheets formed by two ethanol jets under different jet velocities are measured and compared with the theoretical model via a non-intrusive technique, the partial coherent interferometry. An interferometer with the calibrated partial coherence property is used to record the interference pattern by passing one optical path through the impinging sheet. The thickness is measured by analyzing the change of degree of coherence before and after the sheet insertion. The Reynolds numbers and Weber numbers of this experiment range from 269 to 370 and 35 to 67, respectively. The experimental results show that the jet velocity controls the size of the sheet but not affects the thickness distribution. The measured thicknesses are different from the theoretical predictions and indicate that the velocity inside the sheet may not be a constant along the radial direction.
Wingtip Vortex Stability and Control Using Mean Flow Perturbation
Authors: Bodling Andrew L. , Garmann Daniel J. 
Published: November 2019

Abstract
Wingtip vortices generated by aircraft are the source of induced drag. Therefore, flow control devices such as winglets have been created to reduce the impact of tip vortices and consequently improve the wings performance. To use other flow control devices such as periodic heat-flux sources, the receptivity to the actuator must be fully optimized to be effective. The optimization process includes actuator placement, frequency selection and spatial modulation. The Mean Flow Perturbation (MFP) technique is a linear stability analysis that can be used to understand the receptivity of base flows to small perturbations. Its advantage over other linear stability analyses is that it can be applied fairly easily to complex 3-D flows in a relatively efficient manner, embedded within traditional flow-solver frameworks. This technique can help in gaining a better understanding of the receptivity of a flow control actuator that is used to control a complex 3-D flow. The current study seeks to apply the MFP technique to the author’s previous work on unsteady tip vortices. The aspect-ratio-four, rounded-tip wing has a NACA0012 section and operates at a Reynolds number of Re = 2 × 105 and incidence of α = 12°. The objective is to uncover the least stable mode shapes and frequencies of the structure using MFP in hopes of informing future flow control design techniques. At these conditions, the MFP shows a dominant least stable frequency and mode shape that occurs near the trailing edge of the wingtip. A region near the incipient separation of the vortex also showed with a definitive spatial wavelength that may be susceptible to tailored control.
Numerical Simulations of Turbulent Flow Through a 90° Elbow
Authors: Venters Ravon , Helenbrook Brian , Ahmadi Goodarz 
Published: November 2019

Abstract
Turbulent flow in an elbow has been numerically investigated. The flow was modeled using two approaches; Reynolds Averaged Navier-Stokes (RANS) and Direct Numerical Simulation (DNS) methods. The DNS allows for all the scales of turbulence to be evaluated, providing a detailed depiction of the flow. The RANS simulation, which is typically used in industry, evaluates time-averaged components of the flow. The numerical results are accompanied by experimental data, which was used to validate the two methods. Profiles of the mean and root-mean-square (RMS) fluctuating components were compared at various points along the midplane of the elbow. Upstream of the elbow, the predicted mean and RMS velocities from the RANS and DNS simulations compared well with the experiment, differing slightly near the walls. However, downstream of the elbow, the RANS deviated from the experiment and DNS, showing a longer region of flow re-circulation. This caused the mean and RMS velocities to significantly differ. Examining the cross-section flow field, secondary motion was clearly present. Upstream secondary motion of the first kind was observed which is caused by anisotropy of the reynolds stresses in the turbulent flow. Downstream of the bend, the flow transitions to secondary motion of the second kind which is caused by streamline curvature. Qualitatively, the RANS and DNS showed similar results upstream of the bend, however downstream, the magnitude of the secondary motion differed significantly.