bluuebunny/crossref_metadata_2025 huggingface dataset:
The Optimization of Stiffness Performance of Upstream Pumping Mechanical Seal Based on the Response Surface Method
Authors: Chen Huilong , Liu Jinfeng , Li Tong , Ren Kunteng , Wang Bin
Published: July 2018

The face shape optimization of spiral groove upstream pumping mechanical seal is of great significance. The liquid film stiffness was calculated by considering the cavitation model and dynamic grid in this paper. The regression model was established according to the results of the end face morphology parameters and the stiffness performance. The equivalent cloud images were drawn by using Matlab software. The response surface method is used to analyze the interaction of the upstream pumping mechanical seal face morphology parameters of the groove depth, spiral angle groove diameter ratio and groove width ratio on the stiffness performance. Finally, the numerical simulation of the mechanical seal micro clearance flow is verified. The results show that spiral groove depth should be between 3 and 10 μm. The liquid film stiffness value is becoming smaller with the increase of the helical angle. The best value is around 16°; The influence of the groove diameter ratio and the groove width ratio to the liquid film stiffness is symmetrical distribution basically. And it is better to take 0.5 and 0.4 respectively.
Flow Profiles and Gas/Liquid Separation in First and Second Generation Designs for Ebullated Reactors
Authors: Lane C. D. , Donaldson A. A.
Published: July 2018

Ebullated bed reactor technology is found in the oil and gas industry as part of the hydrocracking process, within which heavy oils are cracked under elevated temperatures and pressures to produce increased fractions of refinable petroleum products. A unique feature of these types of reactors is the presence of an internal gas/liquid separation and liquid recycle line, through which 60 to 90% of the net liquid flow through the column is recycled to maintain fluidized conditions within the internal catalyst bed. The separation efficiency within these systems has a significant impact on overall unit profitability, whereby high levels of gas recirculation results in lower liquid throughput and increased potential of over-cracking of product gases and production of light ends [1]. These units typically operate at gas holdups above 30%, with even small reductions in gas entrainment potentially leading to significant increases in profitability. Due to the severe conditions present within operating units (several MPa pressures, >300°C), pilot-scale experimental systems exploring fluid flow phenomena have typically employed nitrogen and kerosene as analogous fluids[2]. Even within these systems, the ability to visualize flow patterns and parametrically evaluate the effects of separator modifications on gas recirculation has been limited. In an effort to provide strategic focus for future process improvements, Dalhousie University has been collaborating with Ottawa University and Syncrude Canada Ltd. to develop 3D CFD-based simulations of older generation designs to explore fundamental flow characteristics and sensitivity of gas-liquid separation efficiency to changes in geometry and process conditions. This work explores the sensitivity of gas separation efficiency to operational parameters (bubble size, processing rate, gas holdup), geometric design (two generations of separator designs), and computational model choices (drag correlations and packing limiters). Of particular note is the sensitivity of the predicted performance to drag models, for which there is limited empirical validation under the high gas fraction conditions present in this industrial unit, and the sensitivity to packing limiters, which reflect foam formation (an issue observed within operating units). The trends predicted within this work show significant similarities to current operational trends observed in commercial ebullated bed reactors, and provide a basis for predicting the effects of operational changes on the overall performance of these units.
Modified Unsteady Vortex Lattice Method for Aerodynamics of Flapping Wing Models
Authors: Nguyen Anh Tuan , Han Jae-Hung
Published: July 2018

Motivated by extensive possible applications of flapping-wing micro-air vehicles (MAVs) to various different areas, there has been an increasing amount of research related to this issue. In the stage of preliminary studies, one of the most important tasks is to predict the aerodynamic forces generated by the flapping motion. Studying aerodynamics of insects is an efficient way to approach the preliminary design of flapping-wing MAVs. In this paper, a modified version of an Unsteady Vortex Lattice Method (UVLM) is developed to compute aerodynamic forces appearing in flapping-wing models. A hawkmoth-like wing with kinematics based on the real motion is used for the simulations in this paper.
Effects of Dissolved Gas on Unsteady Cavitating Flow Around a Clark Y-11.7% Hydrofoil
Authors: Daido Haruki , Watanabe Satoshi , Tsuda Shin-ichi
Published: July 2018

In the present study, the effects of dissolved gas content on the unsteady cavitating flow around a Clark Y-11.7% hydrofoil are investigated in a cavitation tunnel. Lift and drag forces in various cavitating conditions are directly measured by strain gauges attached on the cantilever supporting the hydrofoil. In addition, the cavitating flow is filmed from the top and the side simultaneously using two high speed video cameras. The high (roughly 6–8ppm) and low (1–2ppm) DO conditions are examined to obtain the qualitative tendencies of the effects of dissolved gas on unsteady cavitation behavior and lift/drag characteristics. It is found that that the relationship between the cavitation behavior and the lift/drag fluctuations does not qualitatively differ in the two different DO conditions, while the amplitude is slightly larger in the low DO condition. At transitional cavity oscillation, in the both DO conditions, the lift/drag coefficients increase during the growth stage of sheet/bubble cavities on the hydrofoil and they decrease when the developed super-cavity disappears. Moreover, it seems that the amplitude of the lift/drag forces in the low DO condition is larger than in the high DO condition but the frequency of lift force fluctuation is not very different.
Observation of Particle Flocculation by kHz-Band Ultrasonic Waves in Solid-Liquid Mixture (Effects of Frequency and Sound Pressure)
Authors: Sugimoto Yasuhiro , Haruna Tatsuya , Sato Keiichi
Published: July 2018

It is important to separate and collect particles from solid-liquid mixture in order to reduce in environmental load and treatment cost of waste fluid. In this study, we try to separate and collect particles from the mixture by ultrasonic waves with relatively low frequency. In the present report, we use slurry of alumina abrasive as removal particles that use for polish and water jet cutting, etc. The particles are fully stirred in test water and then ultrasonic waves are irradiated with some frequencies. The particles behavior observed by a high-speed video camera is analyzed by a time series image analysis and correlated with sound pressure distribution. Particles flocculate to some layers like white bands that correspond to node of sound pressure after irradiation of ultrasonic wave. It is found that particles begin to move just after ultrasonic wave irradiation and flocculate clearly with the increase in sound pressure.
Large Eddy Simulation of Gravity Current Flow Past a Circular Cylinder Using Immersed Boundary Method
Authors: Wang Jae Hwan , Yoon Hyun Sik
Published: July 2018

We investigated the flow of gravity currents past circular cylinders above the smooth bed. In order to simulate the gravity current interacting with cylinder, large eddy simulation (LES) coupled with a direct forcing/fictitious domain (DF/FD) method was employed. The hydrodynamic forces induced by the gravity current on a circular cylinder and the flow features were investigated according to a gap distance from location below the cylinder to the bed and Reynolds number. When the gravity current encounters the circular cylinder, the maximum drag force occurs regardless of gap distance. In addition, Von Karman vortex shedding emerges behind the circular cylinder for larger gap distance. In this regard, the results can be divided into impact, transient and quasi-steady stages based on the characteristics of the hydrodynamic forces varying with time, which is consistent with previous observations. Consequently, our numerical approach well simulated the flow of gravity currents past circular cylinders in good agreement with those of previous studies.
A Meridian Profile Obtained by No Restriction in Optimum Process
Authors: Tsugawa Takuji
Published: July 2018

In previous study of optimum meridian profile of impeller and guide-vane, almost all design parameters included in the specific speed and blade number are variable design parameters in optimum process. As the result, optimum specific speed and blade number were obtained. In the calculation, loss calculation consists of blade-to-blade diffusion loss and axial-symmetrical annular wall friction loss. The calculation result without annular friction loss head isn’t affected by normal diameter and rotational speed. In consideration of diffusion loss and annular friction loss, the result of calculation is affected by normal diameter and rotational speed. In this case study, normal diameter and rotational speed are also variable design parameters. The normal diameter is mid span impeller outlet diameter. So, normal velocity is peripheral velocity of mid span impeller outlet. The initial normal diameter is 100mm and the initial rotational speed is 1000min−1. And then, design parameters and all specification become variable. As there isn’t constant design parameter in this case study, there is no restriction in optimum process. As there is no restriction in optimum process, the best one optimum meridian profile can be obtained. In one case, the object function contains the efficiency and suction specific speed. In the other case, the object function contains the only efficiency. As the result, the optimum meridian profile of impeller and guide-vane can be obtained in each case.
Corner Separations Around a NACA65 Blade in a Decelerating Flow
Authors: Kinoue Yoichi , Ueno Satoshi , Shiomi Norimasa , Setoguchi Toshiaki
Published: July 2018

In order to examine the fundamental characteristics of a corner separation in a decelerating cascade flow, an experimental apparatus was made and the separations around a NACA65 blade in a decelerating channel flow were examined both experimentally and numerically. The two-dimensional calculations show that the NACA65 cascade flow that has 45 deg. of the turning, 1.24 of the solidity and 17 deg. of the stagger angle is similar to the channel flow that has 14 deg. of the stagger angle in terms of the pitchwise blade force. The experimental investigation by the five-hole probe shows that the accumulations of the low energy fluid can be seen around the corner part and the overturning flow due to the secondary flow exists. And, as the periodicity of the blade wake in the pitchwise direction is comparably good, the wake of this channel flow is similar to the wake of the cascade flow for the two pitch portion. PIV measurement showed that the focus-type separation was seen in the momentary streamline along the suction surface of the blade, whereas no apparent separation was seen in the flow along the endwalls. SD diagram consideration showed that the present case on the study was consistent with the relation between the stall indicator S and the diffusion parameter D proposed by Lei et al.
Numerical Prediction of Noise From the Internal Flow in a Centrifugal Blower
Authors: Guo Yang , Kato Chisachi , Yamade Yoshinobu , Ohta Yutaka , Iwase Taku , Takayama Ryo
Published: July 2018

The noise generated from the internal flow in a centrifugal blower was computed by computational aero-acoustics (CAA). The sound sources were obtained by computational fluid dynamics (CFD), using large-eddy simulation (LES) to compute the turbulent flow in the centrifugal blower. The computed sound pressure level (SPL) with sound source from coarse mesh LES is overpredicted, while the computed SPL with sound source from fine mesh LES agrees fairly well with the experimental data. The peak of SPL at blade passing frequency (BPF) of 600 Hz can be somewhat captured by CAA with sound source from fine mesh CFD. However, due to the short computational time, the frequency resolution is not fine in CAA with sound source from fine mesh CFD, which may be the reason of underprediction of the peak value at BPF. Fluid forces acting on the impeller at the plane perpendicular to the axial direction play important role on the predicted SPL at BPF.
High-Efficiency Design Technique of a Single-Channel Submersible Pump Impeller for Waste Treatment
Authors: Cho Bo-Min , Kim Joon-Hyung , Choi Young-Seok , Lee Kyoung-Yong , Oh Hye-Young , Kim Kwang-Yong , Kim Youn-Sung , Kim Jin-Hyuk
Published: July 2018

This study presents the hydrodynamic analysis and optimization for a single-channel submersible pump impeller. The numerical analysis involved the use of the shear stress transport turbulence model to solve three-dimensional Reynolds-averaged Navier-Stokes equations. The optimization process was based on a radial basis neural network model and was conducted by considering two design variables to control the area from the inlet to the outlet of the impeller. The hydrodynamic performance of the pump impeller was optimized by selecting the efficiency as the objective function. The objective function was numerically assessed via Latin hypercube sampling at design points selected in the design space, and the optimization yielded a maximum increase in efficiency of approximately 1% in terms of the design flow rate, as compared to the initial design. The performance curve for the efficiency was also improved in the high flow rate region. Further details of the internal flow fields between the reference and optimum designs are also analyzed and discussed in this work.
Combustion Test of Oxidizer-Rich Single Triplex Injector Preburner for Staged Combustion Cycle Rocket Engine
Authors: Lee Su-Ji , Moon In-Sang , Moon Il-Yoon , Ha Seong-Up
Published: July 2018

In the Republic of Korea, research on staged-combustion cycle liquid propellant rocket engines (LPRE) is proceeding to improve efficiency of rocket engines. Recently oxidizer-rich preburner using single triplex injector is developed in relation to the main injector development and combustion tests have been performed. This preburner is designed to operate in nominal conditions with the combustion pressure of 10 MPa, OF ratio of 60. For a stable ignition, LOx is fed in two steps. Triethylaluminum-Triethylborane (TEAB) is used as hypergolic fuel for ignition, supplied through a fuel injector.

Despite the small amount of fuel flow rate and high pressure condition, the combustion pressure was stably maintained around 10 MPa as designed. As a result of Fast Fourier Transform (FFT) of the combustion chamber dynamic pressure, 1L mode frequencies related to the acoustic instability and hydraulic resistance exist in the combustion chamber. But their amplitudes are less than 1% of the combustion pressure and it does not affect the combustion. Therefore combustion test is stably completed.

In the near future, coupled tests with uni-element triplex injector preburner and uni-element gas/liquid injector main combustion chamber will be carried out.
Effect of Aspect Ratios on the Performance Characteristics of Air Amplifier
Authors: Lee Jeong-Min , Jo Yi-Seul , Kim Sung-Min , Kim Youn-Jea
Published: July 2018

In this study, the flow characteristics of the Coandă nozzle were studied with various values of the aspect ratio of induced flow inlet to outlet. Furthermore, four different applied pressure conditions of compressed air were also considered. Numerical analysis was performed using the commercial CFD code, ANSYS CFX with a shear stress transport (SST) turbulent model. The results of total pressure and velocity distributions were graphically depicted with various geometrical configurations and operating conditions.
Development of Ultrasonic Flowmeter Using Pulsed Doppler Method With Staggered Trigger Pulse
Authors: Murakawa Hideki , Muramatsu Ei , Sugimoto Katsumi , Takenaka Nobuyuki , Furuichi Noriyuki
Published: July 2018

The ultrasonic pulsed Doppler method can be applied to obtain instantaneous velocity distribution along the ultrasonic beam path. This technique has many advantages, and it has been applied for measuring flow rate. However, the method has limitation about the measurable velocity and length. In order to overcome the limitation, a dealiasing method using staggered trigger pulse was applied for measuring velocity profile in a pipe. Furthermore, a multi-wave ultrasonic transducer was proposed for the measurement for improving the velocity measurement accuracy in the near-wall region. The applicability was examined for measuring velocity profile in a pipe with inner diameter of 200 mm. The velocity distributions were accurately obtained over the pipe by combining the velocity distributions at the basic frequency of 8 MHz for the near-wall region and 2 MHz for the region far from the transducer. As a result, it was confirmed that the flow rate measurement was improved by using the multi-wave method.
Effect of Disturbed Flow Condition on Uncertainty of Flowrate Measurement Using Ultrasonic Doppler Velocity Profile Method
Authors: Wada Sanehiro , Furuichi Noriyuki
Published: July 2018

To obtain an uncertainty of flowrate measurement using ultrasonic Doppler velocity profile method (UVP), experiments are carried out using the national standard calibration facility of water flowrate in Japan. Flowrate measurement is based on a multi-path measurement using three transducers. To generate a disturbed flow, obstacle plates are installed upstream of the test section. The maximum difference from the reference flowrate is over 2% when the measurement is performed at 8D downstream of the obstacle plate. At 25D downstream of the obstacle plate, the deviation is within the fundamental uncertainty level. The uncertainty caused by the upstream condition is negligible small for 25D downstream of the final disturbance, however it is estimated to 2.9% for 8D.
Experimental Study of Turbulent Swirling Flow in a Vertical Tube for Heat Transfer Enhancement Using Ultrasonic Velocity Profiler (UVP)
Authors: Hamdani Ari , Tsuzuki Nobuyoshi , Kikura Hiroshige
Published: July 2018

Two-phase swirling flow through a pipe is a complex turbulent flow and its prediction is still challenging. The present paper describes the experimental investigation of the air-water two phase swirling flow in vertical co-current flow. Swirling flow is induced by a twisted tape in a 20 mm inner diameter pipe. The flow is investigated using Ultrasonic Velocity Profiler (UVP), which allows the measurement of liquid and gas velocities simultaneously. Furthermore, simultaneous measurement of void fraction is performed using Wire Mesh Sensor (WMS). The experimental results reveal that swirling flow has significant impact on bubbles’ distribution. In low liquid flow rate, the average bubble velocity is fairly uniform along the radial position and void fraction increases in the near wall region. However, increasing liquid flow rate at constant gas flow rate leads to increase in void fraction in the core region, this is mainly due to drift velocity which is affected by centrifugal force. Experimental findings and parametric trends based on the effects of swirling flow are summarized and discussed.
A Twin Unidirectional Impulse Turbine for Wave Energy Conversion: Effect of Rotor Blade Profile on the Performance
Authors: Takao Manabu , Sato Hideki , Ashraful Alam Miah Md. , Okuhara Shinya , Masaki Genya , Setoguchi Toshiaki
Published: July 2018

There is a twin unidirectional impulse turbine topology in an oscillating water column for wave energy conversion, which has two unidirectional impulse turbines. In this topology, an oscillating airflow is rectified by these turbines. Previous studies show that the mean efficiency of this topology is predicted to be lower than the efficiency of a unidirectional impulse turbine. Therefore, the rectification of this topology needs more improvement. The objective of this study is to investigate the effect of the rotor blade profile on the performance of twin unidirectional impulse turbine by a wind tunnel test and computational fluid dynamics (CFD). In this study, 2 types of the rotor blade profiles in two cases of setting angles of guide vanes has been examined. As a result, the peak efficiency of Type A with θ = 14° was the highest of all turbines tested in this study. Furthermore, the flow state around the rotor and the guide vane is discussed.
Interference Between a Square and a Circular Cylinder
Authors: Kumar Nithin S. , Kumar R. Ajith , Mohan Jayalakshmi
Published: July 2018

The flow visualization studies around a square cylinder (upstream) and a circular cylinder arranged in tandem configuration is studied experimentally to identify the interference flow patterns. Flow visualization studies are carried out in a re-circulating water channel. The investigations are carried out for tandem arrangement varying the center-to-center distance (L) between the cylinders; L/B ratio is varied from 1 to 5 where B is the characteristic length. Experiments were conduct at a Reynolds number of 2100 (based on B). The results are also obtained for two tandem square cylinder configuration. The flow patterns observed are: Alternate Shear Layer Reattachment with and without gap flow, Simultanous shear layer reattachment and detached shear layer flow pattern. The time of persistence (in percentage) for each flow pattern is estimated over a sufficiently long period of observation time to identify the most influential, predominant flow pattern. Though these patterns are identical for square-square and square-circular tandem configurations, their order of predominance is different for both the configurations.
Numerical Simulation of Supersonic Mixing Enhanced by a Three-Dimensional Cavity Flow
Authors: Oka Takayuki , Akagi Fujio , Handa Taro , Ando Youichi , Yamaguchi Sumio
Published: July 2018

The three-dimensional mixing field induced by a novel wall-mounted cavity having a three-dimensional shape, which has been proposed in the other literature, is investigated in detail by solving the Reynolds-averaged Navier-Stokes (RANS) equations computationally. The results indicate that secondary flows are produced from the cavity and that the secondary flows act on the transverse jet such a way that it penetrates highly into the primary flow; i.e., the computational results demonstrates that the proposed cavity functions effectively as a device for enhancing supersonic mixing.
Large-Eddy Simulation of Turbulent Flow Over a Heavy Vehicle With Drag Reduction Devices
Authors: Lee Sangseung , Kim Myeongkyun , You Donghyun
Published: July 2018

In order to improve the fuel efficiency of heavy vehicles, flow control devices aiming at aerodynamic drag reduction are often utilized. Computational simulation has been widely used in the investigation of fluid dynamics associated with aerodynamic drag over a heavy vehicle and control effects of many drag reduction devices. Most previous studies were, however, conducted using computational techniques based on the Reynolds-averaged Navier-Stokes equations and with rather simplified geometries (i.e., GTS, GCM, and Ahmed body), and therefore, the utility of the understanding of the drag-producing flow physics is often impractical and limited.
Lift and Drag Characteristics of an Airfoil and Feedback Flow Control by Flap Actuators in the Low Reynolds Number Region
Authors: Mori Toshiki , Yamaguchi Masashi , Inaoka Kyoji , Senda Mamoru
Published: July 2018

The present paper describes the applicability of the flow control device, mini actuators attached on the leading edge of an airfoil, for the flow separation control under unsteady flow condition in the low Reynolds number region. Lift and drag have been measured for a wide variety of the wind speeds (Reynolds numbers) and the angles of attack. Then, effects of simple feedback flow control, where the time-dependent signal of the lift-drag ratio has been used as an input to detect the stall and served as a trigger to start the actuation, have been explored under the unsteady flow condition for evading the stall.

For every Reynolds number from 30,000 to 80,000, the actuators worked quite well to delay the stall, increasing both in the lift and the stall angle of attack. Then, threshold value of the lift-drag ratio was determined to detect the stall. Effectiveness of the feedback control of the actuation was demonstrated under the condition of the wind speed decrease which would lead to the stall if no-actuation. Immediately after the velocity decrease, the decrease in the lift-drag ratio below the threshold were detected and the dynamic actuations were started, resulting in evading the stall and keeping high lift. The additional operation of the feedback, stopping the actuation when the lift-drag ratio showed lower than the second threshold, was revealed effective to keep the high lift force under the condition combined with the wind speed increase and decrease.
Drag Reduction of Heavy Vehicles Using Various Side Skirts
Authors: Hwang BaeGeun , Lee Eui Jae , Kim Jeong Jae , Lee Sang Joon
Published: July 2018

There are many attempts to save the cost of transportation. Especially, drag reduction of heavy vehicles such as truck or tractor-trailer have enormous effect on the reduction of fuel consumption and CO2 emission, because road freight transport using heavy vehicles occupies majority in physical distribution cost.
Gravitational Settling of Glass Fibers on an Air Bubble
Authors: Lecrivain Gregory , Petrucci Giacomo , Hampel Uwe , Yamamoto Ryoichi
Published: July 2018

Froth flotation is a separation process in which air bubbles are introduced in a water tank to separate the valuable commodities from the valueless material. Based on their relative affinity to water the valuable particles attach to the bubble surface and are carried to the top of the flotation tank to form the froth layer. The resulting froth layer is eventually collected to produce the concentrate. Froth flotation has been used for more than a century in mining operations to separate valuable materials such as rare earth metals from excavated ores. More recently, froth flotation has been employed for the treatment of contaminated water. In the present study, the effect of the particle elongation on the attachment mechanism is investigated in great detail. Using an in-house optical micro-bubble sensor the attachment of micron glass fibres on the surface of a stationary air bubble immersed in stagnant water is investigated. The attachment mechanism is here defined as three successive events: the approach of the particle near the bubble upstream pole, the collision of the solid particle with the gas-liquid interface and the particle sliding on the gas bubble surface. The translational particle velocities together with the particle orientation during entire attachment process are measured and compared with a theoretical model. For the first time the existence of two types of attachment is shown. Upon collision near the upstream pole of the gas bubble the major axis of the fibre aligns with the local bubble surface. If collision occurs at least 30° further downstream the contact is likely to take a punctual form, i.e. the head of the fibre is in contact with the gas-liquid interface.
Coating Onto a Prewet Substrate With Low Weber Number Liquid Curtain
Authors: Liu Yekun , Itoh Masahiro , Kyotoh Harumichi , Nakano Kouichi
Published: July 2018

In recent years, miniaturization and high precision of the LCD screen used for small display has been developed fast. The thin and high-precision film covering the LCD screen is manufactured by slide coating. In slide coating, however, the distance between the slot and the substrate is too small. On the other hand, curtain coating can avoid the influence of the mechanical disturbance and is also a good method for coating on rugged substrate. Nevertheless, curtain coating has not been applied to the LCD screen because the liquid curtain with small discharge, i.e. small Weber number, causes instabilities of the flow and the free surfaces. In the present study, we performed the experiment of the liquid curtain bridged between the exit of slot die and moving roller under very small Weber number (We ∼0.1). It is found that the surface waves are reduced by using a roller pre-wetted by mists and by changing the viscosity of the liquid. Also, the coating window can be drawn in a plane of surface tension and viscosity. Finally, we tried to explain these phenomena by analyzing the equations of liquid curtain.
Prediction of Pressure Fluctuation on a Vehicle by Large Eddy Simulation
Authors: Yamade Yoshinobu , Kato Chisachi , Iida Akiyoshi , Yoshimura Shinobu , Iida Keiichiro
Published: July 2018

The objective of this study is to predict accurately interior aeroacoustics noise of a car for a wide range of frequency between 100 Hz and 4 kHz. One-way coupled simulations of computational fluid dynamics (CFD), structural analysis and acoustical analysis were performed to predict interior aeroacoustics noise. We predicted pressure fluctuations on the outer surfaces of a test car by computing unsteady flow around the car as the first step. Secondary, the predicted pressure fluctuations were fed to the subsequent structural analysis to predict vibration accelerations on the inner surfaces of the test car. Finally, acoustical analysis was performed to predict sound fields in the test car by giving vibration accelerations computed by the structural analysis as the boundary conditions. In this paper, we focus on the unsteady flow computations, which is the first step of the coupled simulations. Large Eddy Simulation (LES) was performed to predict the pressure fluctuations on the outer surfaces of the test car. We used the computational mesh composed of approximately 5 billion hexahedral grids with a spatial resolution of 1.5 mm in the streamwise and spanwise directions to resolve the dynamics of the small vortices in the turbulence boundary layer. Predicted and measured pressure fluctuation at several sampling points on the surface of the test car were compared and they matched well in a wide range of frequency up to 2 kHz.
Aerodynamic Characteristics of a Road Vehicle in Steady-State Cornering
Authors: Nakashima Takuji , Tsubokura Makoto , Okada Yoshihiro , Nouzawa Takahide , Kono Ryosuke , Doi Yasuaki
Published: July 2018

The objective of this study was to investigate the aerodynamics of a road vehicle during cornering. We focused on steady-state cornering and divided the vehicle motion into two components, a yaw rotation and a sideslip motion. The fluid-dynamic characteristics of the vehicle in steady-state cornering and the effects of the two motion components were investigated both by a towing tank experiment and by numerical simulation. The results indicate that both of the motion components generated fluid-dynamic centripetal force and fluid-dynamic yaw moments in opposite directions. The distributions of pressure change on the vehicle body, generated by the motion components, were numerically visualized. The physical mechanisms that generated these aerodynamic characteristics are discussed.
Ultrasonic Measurement of Gas Bubbles Advecting Under a Ship Bottom for Investigating Drag Reduction Performance
Authors: Park Hyun Jin , Tasaka Yuji , Oishi Yoshihiko , Murai Yuichi
Published: July 2018

Bubbles injected into a turbulent boundary layer have a significant potential to reduce frictional shear stress, but this drag reduction technique has not been optimized yet because of its low and unstable performance. If monitoring and controlling of advective bubbles beneath ships are realized, these provide insight for improving the performance. In this paper, we performed experiments using a model ship with 4 m in length in a towing tank with 80 m in distance. The model ship is fully made of acrylic resin and mounts shear stress sensors and ultrasonic measurement system. The shear stress and bubble information, such as a void fraction and a thickness of liquid film above the bubbles, are obtained at three locations arranged at the front, the middle and the rear of the ship bottom plane. By analyzing these data, it is confirmed that the drag reduction occurs when a thin liquid film exists.
A Twin Unidirectional Impulse Turbine With Fluidic Diode for Wave Energy Conversion
Authors: Sato Hideki , Takao Manabu , Okuhura Shinya , Ahsraful Alam Miah Md. , Setoguchi Toshiaki
Published: July 2018

As an air turbine equipped with oscillating water column (OWC) based wave energy plant, a rectification-valve system has been invented to date. However, this turbine system has problems with the durability of the valves and the complex mechanism. Moreover, it has a major fault in that the valves must be large for high output. Therefore, a twin unidirectional impulse turbine topology has been suggested in previous studies in order to use conventional unidirectional turbines without valves [1, 2]. The topology is composed of two unidirectional impulse turbines. However, the past study indicated that the mean efficiency of the topology was shown to be low, when the performance prediction of the topology in oscillating airflow was carried out by means of quasi-steady analysis [2]. Further, the cause of the low efficiency is because part of the air flow gets through the unidirectional impulse turbine in the direction of low efficiency [2].

In this study, a fluidic diode [3, 4] is adopted in order to suppress the air flow rate into the inefficient turbine in a twin unidirectional impulse turbine topology for wave energy plant, and the effect of the fluidic diodes on the performance of twin unidirectional impulse turbine topology is investigated by a wind tunnel test and computational fluid dynamics (CFD). Further, its usefulness is discussed from a view point of the turbine mean efficiency under unsteady flow condition.
Relationship Between Diffusing-Material Lumps and Organized Structures in Turbulent Flow
Authors: Endo Masaya , Tsukahara Takahiro , Kawaguchi Yasuo
Published: July 2018

When a material spreads in the turbulent flow, its instantaneous concentration distribution becomes not homogenous in space, and areas with high concentration containing sudden change of the concentration are formed by the local intense turbulence. In this study, we extracted such localized high-concentration areas by a conditional sampling technique, and observed the behavior of the areas.

In order to realize the scalar diffusion in quasi homogeneous isotropic turbulent flow, a model experiment was performed in a water channel flow. Fluorescent dye was introduced from a nozzle located at the center of the channel, and the concentration images of the dye were obtained at several downstream positions by PLIF measurement. To extract areas of high concentration containing a sudden change of the concentration, three types of analysis techniques including the conditional sampling technique were applied to PLIF images.

By the conditional sampling technique, we can extract areas of high concentration, which cannot be identified by the other two kind methods, and the effectiveness of this technique was proved. It was found that the areas extracted by the conditional sampling technique appear as lumps. The spanwise numerical probability distribution of the lumps roughly follows the Gaussian distribution, and the peak of the distribution decreases while its standard variation increases as streamwise distance increases. This result implies that performing extraction of areas with high concentration appropriately would enable to realize the material diffusing process as a Lagrange particle and provide a prediction method about the material diffusion source and the damage of the pollutant.
Direct Numerical Simulation of Free Jet Under the Rotational Control
Authors: Arumugam Sanmuga , Tsujimoto Koichi , Shakouchi Toshihiko , Ando Toshitake
Published: July 2018

In recent past, a wide variety of applications have been found for the use jets in fields of study of flow control and many researchers have worked on jet flow control to enhance mixing and/or reduce noise. In order to develop a new mixing procedure, a direct numerical simulation (DNS) of dynamic controlled free jets was conducted. To achieve a high accurate computation, space discretisation method was performed using the hybrid scheme consisting sine or cosine series and 6th order compact scheme. The dynamic control proposed here are single and multiple rotating jets which are rotated unidirectionally around streamwise direction. According to the instantaneous vortex structures and, it is found that the flow pattern changes considerably with the rotating frequency. From the contour of streamwise velocity, in both cases, it is clear that the radial jet expansion of controlled jets are significantly enhanced compared to the uncontrolled one. We also concluded that, using the statistical entropy and the entrainment rate, it is clear that the mixing performance is significantly improved compared to the uncontrolled jet and under the same rotating frequency, the mixing performance of single rotating jet control is superior than multiple one.
Influence of Viscoelasticity on Turbulent Flow Over a Backward-Facing Step
Authors: Ikegami Akito , Tsukahara Takahiro , Kawaguchi Yasuo
Published: July 2018

We studied viscoelastic turbulent flow over a backward-facing step of the expansion ratio ER = 1.5 using DNS (direct numerical simulation) at a friction Reynolds number Reτ0 of 100. We chose the Giesekus model as a viscoelastic constitutive equation, and the Weissenberg number is Wiτ0 = 10 and 20. Visualized instantaneous vortices revealing that a few vortices occur only above the recirculation regions in the viscoelastic fluid flow compared to those in the Newtonian flow. This phenomenon might be caused by the fluid viscoelasticity that would suppress the Kelvin-Helmholz vortex emanating from the step edge. The reattachment length from the step is 6.80h for the Newtonian fluid, 7.82h for Wiτ0 = 10, and 8.82h for Wiτ0 = 20, where h is the step height. In the mean velocity distributions normalized by maximum inlet velocity, we have observed no significant difference among the three fluids, except for region near the upper or bottom wall, i.e., the recirculation and recovery regions at the front and behind the reattachment point. The streamwise turbulent intensity u’rms is weaken in the recirculation region of the viscoelastic flows. In terms of v’rms, its magnitude in the recirculation region becomes largest in the case of Wiτ0 = 10, not for the Newtonian fluid flow or more viscoelastic case of Wiτ0 = 20.
Large Scale Motions and Shear Stress Fluctuations in Turbulent Shear Flow
Authors: Ito Hinori , Tsuneyoshi Tatsuya , Feng Shan , Ito Takahiro , Tsuji Yoshiyuki , Hideki Yuya
Published: July 2018

We simultaneously measured the flow field and wall shear stress in a straight pipe and behind an orifice by means of particle image velocimetry (PIV) and the limiting diffusion current technique (LDCT), respectively[1]. The spatio-temporal correlation coefficients of the local vertical velocity and the shear stress fluctuations are presented, and the canonical correlations between the proper orthogonal decomposition (POD) spatial eigenmodes in the recirculation region and the wall shear stress are also discussed[2]. A response time lag occurs between the wall shear stress and the velocity field. The large canonical correlation between the POD eigenmodes and wall shear stress suggests that large-scale flow structures are important for the shear stress fluctuation. These analyses are applied to the shear flow in channel and large scale motions are studied in relation with the shear stress fluctuations.
Experimental and Computational Investigation on Gyromill Wind Turbines Focusing on Wing Camber
Authors: Ejiri Eiji , Iwadate Tomoya
Published: July 2018

Gyromill wind turbines with three different blade profiles were investigated experimentally and numerically in order to verify the effect of the direction of camber on aerodynamic performance.

Experiments were carried out using a model turbine impeller with an axial length of 200 mm and a diameter of 200 mm. The results showed that the maximum power coefficient was higher for blades with negative camber than for ones with positive camber. On the other hand, the operating range of the tip speed ratio tended to be narrower for the blades with negative camber than for the ones with positive camber.

An unsteady numerical flow analysis around the wind turbines was conducted using a commercial code employing the finite volume method. The results showed that the power coefficient of one blade had a maximum value in the second quadrant and that the blades with negative camber were advantageous for obtaining high rotational force in the position, compared with the blades with positive camber and a symmetrical blade.
Aerodynamics of Clustered Wind Lens Turbines
Authors: Goeltenbott Uli , Ohya Yuji , Karasudani Takashi , Jamieson Peter
Published: July 2018

Wind lens turbines, developed by Kyushu University have increased performance due to the duct surrounding the rotor [1]. A Multi rotor system is a promising concept to upscale wind turbine systems beyond 20MW [2]. Results of experimental research on a seven turbine array have shown no loss in performance with closely spaced rotors [3]. In the presented research we analyze the feasibility of using wind lens turbines in multi rotor systems. In a wind tunnel experiment we placed three wind lens turbines in a triangle array normal to smooth flow. At various spacing maximum output power was measured and compared to the values of a stand-alone setup. Optimum tip speed ratio didn’t change when the turbines are set closely next to each other. In a side-by-side setup of two turbines it was found that the rotation direction of the rotors had no influence on the turbines performance. In the three turbines in triangle arrangement the performance of the turbines is influenced by the width of the gap between the brims. At the closest possible spacing (brims of neighboring turbines are in direct contact) the cumulative power of all three turbines decreases compared to the cumulative power of three stand-alone turbines. The brims of the wind lens turbines shed vortices that establish a low pressure region behind the turbine. When the brims are in direct contact vortex shedding is inhibited and hence power drops. When increasing the gap between the turbines the power output restores to the same value, in some cases the power even exceeds the value of the three stand-alone turbines. Further, it was observed that the individual power output doesn’t follow the trend of the cumulative power output. These phenomena can be explained with flow patterns observed in gap flow analysis of bluff bodies where biased wake flow changes drag coefficients of flat plates [5]. However, smoke wire technique used to visualize the flow field couldn’t give us any indication of these known patterns. Further research is necessary to fully understand which mechanisms in three dimensional gap flow cause the effect on the performance of the turbines.
Performance of a Cross-Flow Wind Turbine Located Above a Windbreak Fence
Authors: Sakai Haruka , Kiwata Takahiro , Nakata Hiroaki , Kono Takaaki , Furumichi Hiroko , Nakaguchi Akito
Published: July 2018

The performance of a cross-flow wind turbine located above a windbreak fence (snowbreak fence) and the associated velocity fields were investigated through wind tunnel tests. The effects of the amount of vertical clearance between the wind turbine and the fence, the percentage of the fence area that is nonporous, and the rotational direction of the turbine were examined. In addition, a two-dimensional numerical flow analysis of the cross-flow wind turbine above the fence was performed using the CFD software ANSYS FLUENT 13.0. The fence and wind turbine models were built to a scale of 1:5; the porous fence model had a height of h = 500 mm, and the diameter of the wind turbine was 80 mm. It was found that the relationship between the inflow velocity into the clearance gap and the rotational direction of the turbine affects the power coefficient of the turbine.
Mixing Technology of Stratified Density Layer by Gas-Liquid Two-Phase Jet
Authors: Shimazaki Kyota , Sato Kyosuke , Horiguchi Naoki , Kanagawa Tetsuya , Kaneko Akiko , Abe Yutaka , Yamaguchi Isho , Hayashi Kanetoshi
Published: July 2018

This paper experimentally treats the mixing of a two-layer density-stratified fluid generated by gas-liquid two-phase jet in a cubic tank. The purpose of this study is to clarify the mixing optimum by gas-liquid two-phase jet for destruction of density stratification. The upper and lower fluids were water and salt water, respectively, with the lower fluid issued vertically upward from a circular nozzle put at the center of the bottom in the tank. We conducted the mixing experiment, the experimental parameters were the total superficial velocity and the volumetric flow ratio of the jet. The total superficial velocity and the volumetric flow ratio of the jet range from 1.5 to 6.0 m/s and from 0 to 1.0, respectively. The mixing behaviors of density stratification were visualized and the density variation during the mixing was measured in situ. Based on the visualized and measured results, an evaluation method for the mixing time was developed. We discussed the relation between the experimental parameters and the mixing time. Then, it was clarified that different behaviors between liquid jet and gas-liquid two-phase jet were observed and the effect of the volumetric flow ratio of the jet on the mixing time was varied in each the total superficial velocity of the jet.
The Effects of Bubble Interface Contamination on Bubble Motion, Bubble-Induced Surrounding Liquid Motion and Mass Transfer
Authors: Iburi Yuki , Huang Jie , Saito Takayuki
Published: July 2018

Mass transfer from a bubble to the surrounding liquid plays an important role in chemical engineering processes. To improve the efficiency and safety of the processes, a deep understanding of the mass transfer mechanism from bubbles to the surrounding liquid is essential. In the present study, we examined a CO2 single bubble of 2∼3 mm in equivalent diameter that ascended zigzag in purified water and contaminated water (500ppm 1-pentanol solution). We used a high speed video camera systems with high spatial and temporal resolution, for visualization of the bubble wake and bubble-induced surrounding liquid motion.

The dissolution process of CO2 from the bubble to the surrounding liquid was visualized via LIF/HPTS (Laser Induced Fluorescence) method. HPTS, which is a fluorescent substance, was excited by Ar ion laser with a wavelength of 458 nm, then emitted with a wavelength of 513 nm. A pH level of CO2 solution decreased with increase in CO2 concentration; hence the emission intensity of HPTS was reduced. As a result, dark regions observed below the bubble rear accorded with the bubble wakes; from visualization of this bubble wakes through the high speed video cameras, dynamic CO2 dissolution process was obtained. In the purified water, the bubble shape was oblate ellipsoid, and horse-shoe-like vortices were formed in the rear of the bubble. On the other hand, in the contaminated water, the bubble was nearly spherical. Furthermore, behavior of the vortices changed. These different results in two conditions were caused by the decrease in the surface tension owing to the bubble surface contamination. While the bubble was rising, the non-uniform distribution of the surfactant on the bubble surface occurred. Hence, a gradient of the surface tension was formed on the bubble surface, furthermore, it caused the Marangoni convection.

Meanwhile, in order to consider the relationship between dissolution process and the surrounding liquid motion, we measured the liquid phase velocities via PIV.