bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bubble Generation Behavior Around a Rotating Body in Highly Viscous Fluid
Authors: Akatsuka Shigeto , Saito Shimpei , Yuasa Tomohisa , Kaneko Akiko , Abe Yutaka 
Published: November 2019

Abstract
Inside an automobile engine, there are a camshaft, a crankshaft, a chain sprocket, etc. that transmit driving force. There are many rotating parts installed there. For example, there are gears soaking in engine oil, and bubbles are generated by rotating gears which drag air into engine oil. That raises void fraction of the engine oil. The void fraction is the gas phase fraction per unit volume. In general, high void fraction causes decreasing performance of the engine oil, such as lubrication, cooling and pressure transmission. Although it is required to reduce void fraction and establish a defoaming technique, the processes of bubble generation have not been clarified. One of the reasons is difficulty to measure void fraction and other physical parameters in oil flow using a real engine. Therefore, the influence of rotating speed, number of teeth, and kinematic viscosity of test fluid on bubble generation behavior is not grasped in detail.
In this study, the motivation is to understand the mechanism of bubble generation behavior around a rotating body. Detailed visualization was conducted around a rotating body soaking in fluid. The actual phenomena were reproduced by using silicone oil having the same kinematic viscosity of real engine oil. From the visualization using a high speed video camera, there are some characteristic phenomena such as dragging air, subdividing bubbles, and bubbles coalescence. By using observed images, we measured bubble diameter and bubble number density with image processing. Rotating speed, shapes of the rotating bodies, and kinematic viscosity of the test fluids affected on bubble generation behavior. In particular, as the rotating speed increased, the bubble diameter decreased and the bubble number density increased.
A Comprehensive Study of Asymmetric Micro-Droplet Splitting in T-Junction
Authors: Cheng Way Lee , Sadr Reza , Han Arum 
Published: November 2019

Abstract
Splitting a single droplet into two unequal portions using a microfluidic T-junction has been an important functional feature of many modern lab-on-a-chip devices. A recent study introduced a general criterion for asymmetric droplet break-up in the range of intermediate Capillary numbers. The current work attempts to analyze, in more details, the different underlying mechanisms governing the asymmetric break-up process. In particular, this work focuses on the relationship between the break-up mechanism versus the splitting ratio of the daughter droplets. CFD simulation is used to closely monitor the effect of different fluid properties on the evolution of droplet break-up process. The splitting ratio under different flow conditions is characterized. Four mechanisms for primary droplet break-up are defined as follows: break-up with permanent obstruction, unstable break-up, breakup with tunnels and non-breakup. In particular, the main focus of this study is on the unstable break-up mechanisms where is very likely results to a much-deviated splitting ratio. Typically, yet unexpectedly, the resulting splitting ratio is often larger than the pressure gradient ratio in the T-junction. However, the two ratios are approximately equals to each other under a limited set of flow conditions. It has been observed that the splitting ratio could be more than double the pressure gradient ratio of the T-junction. The break-up is observed to be in the permanent obstruction mode if the splitting ratio is about the same magnitude as the pressure gradient ratio. The effects of the T-junction geometry on the break-up will also be examined.
Computational Study of Mach Number Effects on Dynamic Stall
Authors: Kim Taesoon , Kim Seungtae , Lim Jiseop , Kim Junkyu , Jee Solkeun 
Published: November 2019

Abstract
A rotorcraft main-rotor blade experiences a broad range of the Mach number in high-speed forward flights or rapid maneuvering conditions. Near the boundary of the flight envelope, the rotor blade often encounters severe dynamic stall which limits the overall aerodynamic performance. Of interest here is effects of the Mach number on the dynamic stall. A rotor airfoil, VR-12, is computationally investigated for both static and dynamic stall conditions with varying the Mach number from 0.2 to 0.4. For the small enough Mach number 0.2, both static and dynamic stall are significantly influenced by flow separation due to adverse pressure gradient. For the highest Mach number 0.4, compressibility near the leading edge is no longer negligible, forming a shock there. The shock-induced separation occurs near the leading edge, which dominates both the static and dynamic stall at the high Mach number. At the intermediate Mach number 0.3, it is observed that both adverse pressure gradient and the shock affect the stall. Current computations are conducted with the unsteady Reynolds-averaged Navier Stokes approach with the Spalart-Allmaras model. Numerical results are compared to relevant wind-tunnel test data.
3D Numerical Study of the Transport Characteristics of an Evaporating Water Droplet Sessile on Heated Superhydrophobic Substrates
Authors: Peng Yikun , Li Shanshan , Pan Zhenhai 
Published: November 2019

Abstract
Evaporation of sessile droplets on superhydrophobic substrates is an important fundamental problem. Classic diffusion-based model only considers vapor diffusion and assumes an isothermal profile along the droplet interface. The diffusion based model extremely overestimates the evaporation rate for droplets evaporating on heated superhydrophobic substrates, and results in a deviation of evaporation lifetime up to 52.5%. The present 3D numerical model considers various effects including vapor diffusion, buoyancy-driven flow and evaporative cooling, etc., with conjugate heat and mass transfer solved throughout the computational domain. Evaporation of a sessile water droplet with an initial volume of 3 μL is investigated on superhydrophobic substrates (contact angle: 160 deg) with heating temperature ranging from 40 °C to 60 °C. The deviation of evaporation lifetime is less than 2% for 40 °C and 50 °C substrates. A single-roll asymmetric vortex is produced inside the droplet rather than the symmetric recirculation flow predicted by 2D axisymmetric simulation. The evaporative cooling along the droplet interface is observed, but the coolest point appears on the one side of the droplet instead of the droplet top owing to the asymmetrical rolling flow inside the droplet. It is seen that the buoyancy-driven convection significantly speeds up the evaporation as the substrate temperature increases. Influence of relative humidity is also discussed and indicates a stronger impact for low substrate temperature. The present model not only precisely predicts the instantaneous evaporation rate and the total evaporation time, but also reveals the important underlying transport characteristics, which provides new insights into evaporation of water droplets resting on heated superhydrophobic substrates.
Influence of Plasma-Induced Flow Direction on the Instability of the Jet Boundary Layer
Authors: Miyagi Norimasa , Kimura Motoaki 
Published: November 2019

Abstract
In this study, the influence of the direction of the plasma-induced flow generated by a plasma actuator (PA) on the jet flow was investigated. Nozzles equipped with two types of PAs to generate forward (Type A) and backward (Type B) flows were used in this investigation. At a duty ratio was 50%, for both Types A and B, the fluctuation due to the plasma-induced flow yielded the most stable fluctuation near the nozzle exit. In the case of the Type B PA, the centerline velocity was increased by the contraction of the main flow near the nozzle exit due to the influence of the backflow. Additionally, the fluctuation of the jet boundary layer became stronger as the duty ratio was increased. From these factors, it is considered that the backflow by the plasma induced flow effectively works on the diffusion of the jet structure.
Experimental Study of Bubble-Droplet Interactions in Improved Primary Oil Separation
Authors: Karp Joel R. , Mancilla Ernesto , Santos Paulo H. D. , Neto Moisés A. Marcelino , Morales Rigoberto E. M. 
Published: November 2019

Abstract
The interactions between dispersed oil droplets and gas bubbles was experimentally studied in this work. An experimental set-up was built in the Multiphase Flow Research Center (NUEM) in the Federal University of Technology – Paraná (UTFPR) to conduct a fundamental evaluation of the interactions between sessile gas bubbles and oil droplets employing side-view flow visualization. Tap water was used as the continuous phase, whereas pure nitrogen and colored vegetable oil were employed as the dispersed phases. The bubble-droplet attachment consisted in the encapsulation of the bubble by the droplet, presenting phenomenological similarities to droplet-droplet coalescence. The contact between the dispersed phases induces the formation of a connecting bridge, which grows rapidly with time, with the height of the bridge being comparable to the size of the droplet after 57.0 ms. The inherent asymmetry of the phenomenon induced a significant horizontal displacement of the bubble towards the droplet, whose position remained unaltered. The evaluation of the bridge meniscus corroborated to this observation, since the contact angle on the droplet side decayed faster with time in comparison to the contact angle on the bubble side. The hydrodynamics of the rising aggregate is also evaluated, by the obtainment of its size, three-dimensional trajectory and terminal velocity. The stable aggregates formed presented an increase factor of 150 to 180%, based on the terminal velocity of the individual droplet. The radius of the bubble was found to be the major influence on the hydrodynamics of the aggregate, allowing the definition of a critical bubble radius based on trajectory instabilities.
Immobilization of Magnetic Beads for Microfluidic Immunoassays
Authors: Nguyen Thanh-Qua , Kim Jeongyun , Lee Daewoong , Choi Ji-Seob , Park Jaeho , Jeon Hojeong , Park Woo-Tae , Lee Sangyoup 
Published: November 2019

Abstract
Employing magnetic beads (MBs) to microfluidic chips has enabled diverse microscale biomedical applications involving isolation of target molecules, such as, separation, and biosensing. In this report a microfluidic immunoassay chip that can temporarily immobilize MBs for the detection of target biomarkers within a sample solution flown through its channels is introduced. A through-hole structure of the MB capture zone and valves that can control the direction of the flow enabled immobilization of MBs with high reproducibility. Controlling immobilization of MBs shows promise for reproducible immunoassay signal detections for the same concentration of biomarker which is crucial for quantification of the assay. In addition, the structure and position of the captured MBs can potentially be optimal for immunoassay performances where immunoassay reagents including the antigen and the detection antibody are flown through the MB captured through hole maximizing contact for high binding efficiencies.
Experimental Analysis of a Liquid-Gas Two-Phase Flow in a Flow Distributor
Authors: Lino Luiz H. M. , Eidt Henrique K. , Rodrigues Carolina C. , Ofuchi Cesar Y. , Santos Paulo H. D. , Neves Flavio , Silva Marco J. , Morales Rigoberto E. M. 
Published: November 2019

Abstract
The main goal of this work is to analyze the efficiency of a two-phase flow distribution system for different operational conditions, which was designed and built by the Multiphase Flow Research Center (NUEM). The distribution system is composed of a two tangential inlets, a cyclonic chamber, and four outlets. The working principle of this apparatus is based on the combined action of centrifugal and gravitational forces, which causes the development of a liquid film, facilitating the flow distribution. Four outlets are located perpendicularly to the cyclonic chamber in order to distribute the flow equally to some extent. Experimental tests were performed using water and air in a vertical 52-mm ID acrylic pipe. Two flow patterns (bubble and slug) at the input of the inlets were visually identified through the use of a high-speed camera. To verify the flow distribution, wire-mesh sensors were installed at each outlet and graduated beakers and a timer was used in order to estimate the liquid volume flowing at the outlets. The results showed that the flow distribution system has a satisfactory efficiency of distribution.
Design and Modelling of a Cartridge Pressure Amplifier
Authors: Zardin Barbara , Cillo Giovanni , Zavadinka Peter , Hanusovsky Juraj , Borghi Massimo 
Published: November 2019

Abstract
This works describes the modelling and simulation of a compact cartridge pressure amplifier for linear actuators, especially designed to fit within the rod of the piston. Hydraulic pressure amplifiers of the cylinder type are appreciated in hydraulic systems where high pressure work is needed, especially for a small part of the overall duty cycle. The use of these boosters allows the designer not to oversize the system, which will perform confining the high pressure operation only on the side of the hydraulic actuator.
Starting from a previous research work on the same topic, this work proposes new designs for the cartridge amplifier to explore the influence of the control valve, which is the responsible for the delivering of the fluid to the amplifier. The new designs are discussed and then the results coming from the simulation performed with a lumped parameter model in a virtual test rig are shown. The operation of the amplifier is then applied to a more realistic duty cycle to illustrate and validate its operation.
Effects of Cyclist Size and Position Within Formations on Drag and Side Force in the Presence of Cross Winds
Authors: Nedyalkov Ivaylo , Cunningham Alec , Lovell Adam 
Published: November 2019

Abstract
In the absence of cross-winds, a cyclist can expend up to 90% of their energy to overcome drag and can save up to 30% of that energy if riding behind another cyclist. The aerodynamic forces acting on cyclists in the presence of cross wind have not been studied in much detail. The effect of the offset distances between cyclists on the aerodynamic forces has been investigated in the literature for configurations of two cyclists. In the present study, 1:11 scale models of two different cyclists were rapid-prototyped and tested in a wind tunnel. The effect of the size of the cyclist was studied by placing the larger cyclist model behind the smaller one; the smaller behind the larger one; and the larger model behind an identical (larger model) copy. The effect of position within the group was studied by measuring the forces on each of the four cyclists placed in a favorable formation. The results suggest that the size of the cyclist matters, particularly when the leading cyclist is smaller than the drafting cyclist, and the effect is more prominent for the side forces. The results also show that in a formation of four cyclists, the leading cyclist experiences minor drag reduction compared to riding alone. The second and third cyclists experience the largest force reductions within the group, and the fourth cyclist experiences force reduction, which is not as significant. The results appear to be dependent on the Reynolds number, but may still be valuable for racing strategies and recreational cycling.
Study of Enhanced Self Mixing in Ferrofluid Flow in an Elbow Channel Under the Influence of Non-Uniform Magnetic Field
Authors: Anand Nadish , Gould Richard 
Published: November 2019

Abstract
This paper investigates numerically the various parameters dictating the vortical (self)-mixing induced by a non-uniform magnetic field in a ferrofluid flow in an elbow channel. The elbow bend region of the channel has two current carrying conductors placed symmetrically and parametrically from the channel and are used to generate a non-uniform magnetic field. The ferrofluid is assumed to be pre-magnetized, isothermal and electrically non-conductive as it enters the channel and has a prescribed inlet magnetization and temperature. The mixing efficiency is characterized by introducing different mixing scalars based on velocity of the fluid and are compared in order to determine the overall suitability of each scalar to quantify the flow vortical (self)-mixing. Parametric studies were performed by varying parameters influencing the magnetic field and the initial flow field. This resulted in variations in non-dimensional groups which control different aspects of the flow and helped establish their relationship with mixing efficiency. It was found that at higher Reynolds numbers the flow mixing induced by the lateral gradient in the Kelvin Body Force (KBF) dissipates and higher electrical inputs are required to sustain mixing in the flow. The effects of mixing enhancement on the pressure gradient across the channel was also established, along with the introduction of an enhanced viscosity term which is due to the non-collinearity of the magnetization vector and the magnetic field vector.
On the Effect of Trailing Edge Under-Filing on the Apparent Slip Factor of Centrifugal Impellers
Authors: Litfin Oliver , Delgado Antonio 
Published: November 2019

Abstract
The trailing edge flow in a centrifugal impeller is of great importance as it determines the exit flow velocity triangle and therefore the work transferred to the fluid. The present study deals with the impact of trailing edge under-filing on the impeller exit flow and the resulting slip factor. Different under-filed trailing edge shapes are investigated by means of numerical simulations. 2D-RANS simulations are performed for a wide range of blade angles. For the default cut-off trailing edge configuration an attached and a separated flow regime around the blade trailing edge can be distinguished, mainly depending on the blade exit angle. The occurrence of the separated flow regime is associated with a significant change in performance, mainly due to the reduced flow deflection at the impeller exit. Under-filing of the trailing edge leads to less apparent slip for blade angles up to 40 degrees. This can be attributed to the fact that under-filing prevents the attached flow regime occurring in case of the default trailing edge. Additional DES simulations provide deeper insight into the detailed flow structures involved in this phenomena and reveal the turbulent flow structures in the trailing edge and wake flow. The obtained results provide a deep insight into trailing edge flows in centrifugal pump impellers and help to get a better understanding of the phenomena involved. Moreover, the results can provide an explanation to the often observed deviation of the apparent impeller slip from the theoretical slip predicted by slip factor models.
The Minimum Flow Rate of Liquid-Oxygen When Considering a Throttling of a Gas Generator Cycle Engine
Authors: Nakata Daisuke , Minato Ryojiro , Yoshikawa Inaho , Yagihashi Hiromitsu , Arimatsu Koki , Uchiumi Masaharu 
Published: November 2019

Abstract
Currently in development at Muroran Institute of Technology, a small gas-generator-cycle air turbo ramjet engine (GG-ATR) for a supersonic unmanned aerial vehicle requiring deep throttling uses liquid oxygen/ethanol as a propellant. However, it is difficult to maintain a liquid-phase flow at a low mass flow rate or at a low pressure due to flashing in the feedline. In response, we investigated the ability of our ground test facility to feed liquid oxygen at a low mass flow rate. The experimental results of the flow tests validated the proposed one-dimensional model, including heat input and the density change in the feed line. The minimum possible flow rate as a subcooled liquid flow was examined with the model and the throttling level of 75 % was possible when assuming 110 K in tank temperature.
CFD-Based Hydraulic Design and Manufacturing of a Multistage Low Specific-Speed Diffuser Pump
Authors: van der Schoot Martijn , Bruurs Kevin , van der Zijden Eric 
Published: November 2019

Abstract
A multistage low specific-speed diffuser pump was designed to achieve very good hydraulic performance with a newly designed integrated diffuser, crossover and return guide vane. The diffuser was designed using a continuous crossover design. The design space of this diffuser was limited because of the usage of a mechanical pump design from a similar existing pump. This paper presents the simulation-based design of this new pump and the role that simulation can play in the manufacturing process.
A new diffuser has been designed to obtain optimum efficiency and to ensure that the pump will operate most of its time very close its best efficiency point. The new diffuser was designed using an approach where the diffuser vane was stretched to completely cover the area starting just behind the impeller trailing edge towards the eye of the next stage impeller. This means that the diffuser vanes should now convert velocity into pressure, guide the fluid to the next stage impeller eye while reducing the swirl and uniformizing the flow. The shape of the diffuser has been optimized using response surfaces that were created using Computation Fluid Dynamics (CFD). This way, a diffuser with a minimum amount of losses was obtained, due to smooth and gradual area changes of the waterway.
The final design incorporating this diffuser was analyzed using steady-state CFD to create the full performance curve. The design was transferred into a real physical product by manufacturing it. The resulting casting of the diffuser component was scanned using a 3D scanner. The 3D model of the scan was used to make a comparison using CFD between the performance of the designed and the manufactured diffuser. This provided understanding in how deviations due to the manufacturing process influence the performance. Finally, the complete pump underwent a performance test and its results closely matched the performance as calculated using CFD.
Numerical Simulation for Optimizing Tooth Profile Using Bezier Curve
Authors: Qiu Kevin , Samadi Reza 
Published: November 2019

Abstract
The research hereby introduces a novel approach to reduce tooth bending stress using a parametric numeric simulation. This Finite Element Method (FEM) is used to determine optimal design variables for an asymmetric root profile of a helical gear defined by a rational cubic Bezier curve. The gear is first modelled using a machine design software and later implemented into a 3D computer aided design (CAD) package to modify the root spline geometry using a script. A nonlinear relationship exists between the design variables and tooth bending stress. Additionally, certain trends exist between the design variables to exhibit a more optimal root profile. The simulation results show that the proposed method is feasible as the general optimization process results in significant bending stress reduction. The numerical simulation demonstrates that bending stress can be reduced by as much as 10.75% by the proposed approach.