The Proceedings of the Fluids engineering conference
Online ISSN : 2424-2896
2014
Displaying 51-100 of 258 articles from this issue
  • Masatoshi ITO, Takafumi MIZUKAMI, Yumiko YOSHITAKE, Tsutomu TAKAHASHI
    Article type: Article
    Session ID: 0104
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    The shear-banding formation process of wormlike micellar solutions is investigated. The distributions of the flow-induced birefringence and the orientation angle in a concentric cylinder flow cell are evaluated by using a cross-polarizers technique. The birefringence and the angle are almost constant along the radial direction at low shear rate. The high orientation band (H-band) and the SIS state band (SIS-band) are formed when the shear rate exceeds 1s^<-1>. The fluctuations of the birefringence and the angle in the bands are synchronized with stress oscillation at high shear rate. But as for the stress optical coefficient C, only the value of the SIS-band fluctuates significantly.
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  • Hikaru HORIUCHI, Shuichi IWATA, Hideki MORI, Ryo NAGUMO, Tsutomu TAKAH ...
    Article type: Article
    Session ID: 0105
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    We have proposed a new and effective method POD (Pressure Oscillating Defoaming) for increasing the bubble rising velocity. When strong pressure-oscillation are applied to the two vertically aligned air bubbles in viscoelastic fluids, the lower-bubble are approaching the upper-bubble. In the fluid between air bubbles, hydrodynamic interaction may have complex flow structures. To clarify the flow structures, we tried measuring the retardation profile near the bubble by the high speed polarization camera, and flow visualization experiments using tracer particles. It turned out that there is a uniaxial extension behind each bubble, and strong retardation can be seen in the region. When two bubble are close, a uniaxial extension at the tail of the upper-bubble enhances rising velocity of the lower-bubble.
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  • Ryusuke II, Shumpei HARA, Takahiro TSUKAHARA, Yasuo KAWAGUCHI
    Article type: Article
    Session ID: 0106
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    This paper presents experimental investigations of flow instability due to the viscoelasticity in backward-facing step turbulent flow of surfactant fluid. We measured spatial distribution of statistical quantities including Reynolds stress and examined those variations by adding surfactant additives with using PIV. We found the condition (parameter range) in terms of shear rate and the surfactant concentration of viscoelastic fluid for the flow instability.
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  • Mitsuhiro OHTA, Guanghua ZHANG, Yosuke MATSUKUMA
    Article type: Article
    Session ID: 0107
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Numerical simulations of viscoplastic fluid flows across a circular obstacle are performed using a lattice Boltzmann method. In this study, the Papanastasiou (modified Bingham) model is employed and we focus on physical conditions for the onset of nonlinear flows. It is shown that viscosity profiles are greatly depended on Reynolds (Re) and Bingham (Bi) numbers. For low Re and Bi conditions, low viscosity regions close to the plastic viscosity are widely formed around a circular obstacle. Meanwhile, low viscosity regions are limited to a small area around the obstacle for high Re and Bi conditions. Effective (representative) Reynolds and Bingham numbers defined using effective shear rate and viscosity are proposed in order to organize and understand viscoplastic fluid flows across a circular obstacle. The usefulness of effective dimensionless numbers is demonstrated.
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  • Takehiro YAMAMOTO, Hayato NISHIGUCHI
    Article type: Article
    Session ID: 0108
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Pressure-driven flows of a phototactic microalgae suspension in a circular channel illuminated from its outer side were numerically analyzed. Microalgae were modeled by active phototactic particles and the volume-fraction dependence of the suspension viscosity was expressed by the Krieger-Dougherty model. The number density distribution of microalgae in the tube was calculated. It changed with the illumination intensity according to their phototactic behavior and remarkably affected the velocity profile.
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  • Akira SATOH
    Article type: Article
    Session ID: 0109
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    We have investigated the orientational distribution and magneto-rheological characteristics of a disk-like hematite particle dispersion by means of Brownian dynamics simulations. In the situation of a strong applied magnetic field, the particles can freely rotate about the magnetic moment direction together with their magnetic moment aligning along the magnetic field direction, which leads to a linear peak-type orientational distribution, not a single peak-type distribution that is usual for a ferromagnetic particle dispersion. Since the magnetic moment is more strongly restricted to the magnetic field direction with increasing field strength, the viscosity due to the magnetic properties of the particles increases more significantly. An increase in the magnetic particle-particle interaction strength leads to a decrease in the viscosity, and in the range of a magnetic interaction strength where column-like clusters are formed, the viscosity does not show a significant change with increasing magnetic interaction strength.
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  • Ryosuke ITO, Tomohiro TSUJI, Shigeomi CHONO
    Article type: Article
    Session ID: 0110
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    We have performed the experimental investigation on macroscopic electric polarization of a liquid crystal under shear flow between concentric cylinders. The liquid crystal is filled between the concentric cylinders, and sheared by rotating the inner cylinder. We successfully measured the voltage between the cylinders induced by the liquid crystal during the shear flow. From the result, it is found that the voltage profile is pulse-like and irregular, and its maximum value is about 70 mV for 0.202 rpm of inner cylinder revolution. In addition, the maximum value of the voltage increases with increasing the inner cylinder revolution.
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  • Hiroshi SUZUKI, Ruri HIDEMA, Hideki SATO, Yoshiyuki KOMODA
    Article type: Article
    Session ID: 0113
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    In order to study a three-dimensional bulge structure observed in a cavity swept by a viscoelastic fluid, flow visualization experiments have been performed. The cavity depth, the cavity length, the width of wide flow path, the spanwise width of the flow path and the water Reynolds number based on the narrow flow path were fixed at 20 mm, 100 mm, 40 mm, 75 mm and 1,700. The steak lines and path lines were obtained by ink injection method. From the results, it was found that one of path lines shows the reverse flow near the cavity bottom due to the bulge structure formation. The path lines around the bulge structure were also found to be quite different from each other even in the cases when the lines flow at the almost same point. This indicates the bulge structure has non-uniformity on time and on space.
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  • Michio SADATOMI, Akimaro KAWAHARA, Aruta SUZUKI
    Article type: Article
    Session ID: 0201
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Effects of surface tension on vertical upward annular air-liquid flows in a 5.0 mm I.D. circular pipe has been studied experimentally using water and a low surface tension water added by a little Polyoxyethylene Lauryl Ether as the test liquid. Experimental data on frictional pressure drop, mean liquid film thickness, liquid droplet fraction, interfacial shear stress, and interfacial wave velocity were obtained. In this paper, from these, the mean liquid film thickness and the liquid droplet fraction data together with some flow pictures are presented to clarify the effects of surface tension. In addition, test results of several correlations in literatures and the present new correlation against the present data are also shown.
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  • Norio YONEZAWA, Yoshihiko OISHI, Yuji TASAKA, Yuichi MURAI
    Article type: Article
    Session ID: 0202
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    In order to measure three-dimensional flows in large atmospheric space, we have developed a new PIV system based on Multi-layer Color PIV. This new system allows us to determine the six-layer three-dimensional velocity vector fields at a given frame rate just using a single camera view by color coded volumetric projection of light. In this paper, we developed the prototype system, and verified it by simulation of artificial 3D smoke. This system estimates the six-layer two components velocity field in three-dimensional vector field. As the result of verification, reconstructed layers and determined vectors have high correlation value with theoretic image and vector field, around the center of measurement volume. On the other hand, two problems were found. One is a fragility of pattern matching system for strong velocity gradient field. The other is increase of layer reconstruction error against low luminance pixels.
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  • Yoshiki SUGAWARA, Takahiro TUKAHARA, Yasuo KAWAGUCHI
    Article type: Article
    Session ID: 0203
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    In the present study, I photographed two-phase flow containing scattering particle in boundary layer turbulence by a horizontal model wind tunnel. And I divided into a particle aspect and a gas phase by image processing and established the speed of both aspects using the particle imaging velocimetry (PIV) method. Based on the result, I evaluated the main clause of the turbulent stress income and expenditure including the scattering particle. Therefore, I made clear that there are contradicting two effect of scattering particle. In short, existence of scattering particle increases and decreases Reynolds stress of gas phase.
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  • Kota MIKAMI, Hideki MURAKAWA, Katsumi SUGIMOTO, Nobuyuki TAKENAKA
    Article type: Article
    Session ID: 0204
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Measurements of void-fraction distributions around a tube across horizontal tube bundle in liquid-gas two-phase flow were carried out using a void probe technique. Horizontal tube bundle was set in a vertical rectangular channel with 90 × 90 mm^2, and the tube layout was in-line. Outer diameter of the tube was 15 mm, and the pitch to the diameter ratio was 1.5. Void-fraction distributions were compared between 1^<st>, 4^<th> and 7^<th> rows in the 2^<nd> column, and between 1^<st> and 2^<nd> column in 4^<th> row. Furthermore, void-fraction distributions at 4^<th> row in the 2^<nd> column were measured by the void-probes with different length. Void-fraction distributions at 4^<th> and 7^<th> rows were almost the same with each other, and it was confirmed that the inlet effect could be neglected at 4^<th> row. Void-fraction distributions at the 1^<st> column facing on the wall surface was different from at the 2^<nd> column, and it were strongly influenced by the wall surface.
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  • Yuichi MURAI, Hidekazu KITAURA, Yuji TASAKA, Seiji KINO
    Article type: Article
    Session ID: 0205
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Based on experimental findings in laboratory scale about the density destratification process by a bubble plume, a set of numerical simulations have been carried out. Eulerian-Lagrangian bubbly flow model equations are applied for the bubble plume to numerically replay the process in 2D and 3D geometries. Enhancement of the destratification by repetitive bubble injection (RBI) has been confirmed in 2D simulation, which is realized by wavy transport of density currents along horizontal density interfaces. The same effect in a real 3D geometry of a dam lake has been partly observed. However, complexity of the flow domain makes it obscure, implying farther study required to intensity the function of the RBI-based destratification.
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  • Masafumi Saito, Yoshiyuki Tagawa, Masaharu Kameda
    Article type: Article
    Session ID: 0206
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    The purpose of this study is to understand the levitation mechanism of a drop over a moving surface. In our experiment we softly deposit a silicon-oil drop onto the inner wall of a rotating hollow cylinder. With sufficiently large velocity of the wall, the drop steadily levitates. The drop reaches a stable angular position in the cylinder, where the drag and lift balance the weight of the drop. The lift force, which is vital for the levitation, is generated inside a thin air film existing between the drop and the wall. Here three-dimensional shape of the air film plays a crucial role for the magnitude of the lift force. Note that, although the shapes of some levitating drops had been reported, the lift estimated from the shape had not been validated. Using interferometric technique, we measure the three-dimensional shape of the air film under the drop. We then calculate the lift by applying the lubrication theory. This lift is compared with that estimated from the angular position. Both lifts show a fair agreement. Ln addition, we discuss effects of the drop size on the shape and the lift.
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  • Akihito KIYAMA, Yoshiyuki TAGAWA
    Article type: Article
    Session ID: 0207
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    We examine the simple method for generating a liquid jet. We drop a liquid filled test tube on the rigid floor, leading to the emergence of a jet. Within certain experimental conditions, the jet velocity in our experiment agrees well with the semiempirical relation proposed in previous researches. In other conditions, we find that the jet velocity remarkably increases. In order to understand the jet velocity increment, we categorize jets into three types based on their shape and the existence of cavitation bubbles. We find that a jet with cavitation is much faster than that without cavitation bubbles. For elucidating the mechanism of jet velocity increment, we discuss the effect of pressure wave, which propagates in a liquid bath. We propose a model for describing these phenomena and verify it experimentally.
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  • Yuki KATO, Tetsuya KANAGAWA, Akiko KANEKO, Hideaki MONJI, Yutaka ABE, ...
    Article type: Article
    Session ID: 0208
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    We experimentally studied the behavior of a bubbly flow under an earthquake vibration. We focus on the effects of vibration on the bubbly flow in the components by performing visualization experiments of the vertical bubbly flow in a rectangular water tank on which a sinusoidal vibration was applied. As a result, bubble behaviors were affected by oscillation; the cycle of the bubble lean angle was almost the same as that of oscillating table velocity in the low frequency, and response characteristics of bubbles change by acceleration and table's frequency.
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  • Hiroki Karasawa, Shigeo Hosokawa, Akio Tomiyama
    Article type: Article
    Session ID: 0209
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    A measurement method of local instantaneous velocity gradients in turbulent flows are required to evaluate turbulence kinetic energy (TKE) budget. Spatiotemporal Filter Velocimetry (SFV) is therefore applied to evaluation of TKE budget by coupling with a molecular tagging method using photobleaching reaction. Measurements are carried out not only for single-phase turbulent flow but also for bubbly flows with two different bubble diameters to examine effects of bubble diameter on the velocity distribution and TKE budget. As a result, the following conclusions are obtained: (1) Effect of bubble diameter on the distribution of axial mean velocity is weak under the fixed void distribution and the fixed interaction forces between the phases. (2) Effect of bubble diameter on TKE budget is not so large in the bubbly flows whereas the presence of bubbles tend to reduce the magnitudes of the production and diffusion rates.
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  • Shota SHIRAI, Toshiyuki OGASAWARA, Hiroyuki TAKAHIRA
    Article type: Article
    Session ID: 0210
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    The motion of mono-dispersed spherical bubbles rising along an inclined flat plate has been observed experimentally and the effects of the inclination angle and the air flow rate have been instigated. When number density of bubbles becomes higher and the rising velocity along an inclined flat plate becomes slower, the bubbles tend to be horizontally arranged in lines and such arrangements pile up to the bubble cluster. This clustering tendency is similarly confirmed when the no-slip condition, as well as the free-slip condition, is imposed on the bubble surface. On the other hand, the interaction of the no-slip bubbles yields larger displacement in the lateral direction.
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  • Daisuke SHINOHARA, Takayuki SAITO
    Article type: Article
    Session ID: 0211
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    The purpose of this study is to discuss bubble-bubble and bubble wake-wake interactions in a bubble swarm. For this purpose, a bubble-swarm generator that controls the formation and launch of bubbles precisely was employed. Equivalent diameters of the bubbles was about 2.7 mm. The two bubbles were launched side by side and the bubble-bubble distance was 7 mm. The center bubble was launched at the middle of the two leading bubbles 9.75 ms behind the leading bubbles. Using a high speed video camera and PIV, we visualized motion of the bubbles and their surrounding liquid motion. These bubbles linearly ascended during 0.07 sec after launched. An aspect ratio of the center bubble in the time span from 0.02 to 0.07 sec after launched was smaller than those of the leading bubbles. The liquid motion induced by the leading bubbles are considered to enhance dynamic pressure acting on the center bubble.
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  • Kazuaki HATA, Yusuke HIROSE, Hirofumi HIDAI, Masahiro TAKEI
    Article type: Article
    Session ID: 0212
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Temperature control is one of the issues of polymer processing. Electrical Capacitance Tomography (ECT) is a non-intrusive technique which obtains two-dimensional relative permittivity distribution. The relative permittivity distribution means the temperature distribution, because relative permittivity has temperature dependence. In this study, the relative permittivity of polyethylene (PE) and poly methyl methacrylate (PMMA) was measured under a condition which is high temperature polymers melt. A two-electrode sell was used for the measurement and 5000mm^3 polymer was filled between the electrodes. The condition is not ideal for relative permittivity measurement but close to actual polymer processing. Smooth temperature dependence of relative permittivity was observed. It is necessary to select a measuring frequency because the proper frequency depends on temperature range and polymer.
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  • Takahiro TSUKAHARA, Noriko HAMA, Ichiro KUMAGAI, Masayuki OGATA, Yuji ...
    Article type: Article
    Session ID: 0213
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Aimed at reducing power consumption by subsurface aerator, a gyromill type bubble generator was developed based on bubble generating hydrofoils for ship drag reduction. This device utilizes the negative pressure region generated on the surface of the rotating hydrofoil, which enables the subsurface aeration without air compression. Small air bubbles with the diameter from sub-mm to mm order were released from an air outlet of the rotating hydrofoil. In this study, the bubble generation process and the performance of the bubble generator were investigated. In particular, the influence of rotating speed, water depth, and angle of attack on the bubble volume flow rate were reported.
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  • Kentaro MARUI, Daichi TANAKA, Keiya NISHIDA, Yoichi OGATA, Baolu SHI, ...
    Article type: Article
    Session ID: 0214
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Inside the car engine, it is important to control the generation of liquid film and liquid film behavior. The objective of this study is to clarify the mechanism of scattering and apply the CFD model. We have changed flow rate of liquid film and cross-flow velocity, and have taken liquid film behavior in the steady flow using high speed video camera. Wave frequency and liquid film thickness are obtained to find correlation with liquid film behavior. The flow pattern changes into wave, transition, and scattering region in the experimental range. The transition region exists around U_a = 15[m/s]. And in U_a > 15[m/s], transition region exists around t_<avg> = 1[mm] and f = 40[Hz].
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  • Yoshihiko OISHI, Yuji TASAKA, Yuichi MURAI, Yukihiro TOHGE
    Article type: Article
    Session ID: 0215
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Bubble cluster is naturally formed during the bubbles' advection in horizontal turbulent channel flows. The phenomenon cannot be mathematically modeled by the linear sum of bubble-liquid interaction, but it should be assessed with multi-scale modeling in densely dispersed bubbly flow. A series of original geometrical definitions have been proposed to characterize the bubble cluster behavior, such as statistical uniformity of spatial bubble arrangement and bubbles' radial distribution function. From the data analysis, we have found that bubble clustering remains potentially in any flow conditions including the case of large bubble-size deviation
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  • Shinichiro Ito
    Article type: Article
    Session ID: 0301
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    As configurations of soccer balls and volleyball balls evolves in recent years, techniques to produce a non-rotating or low-rotating shot/serve with an unexpected orbit have been established. This so-called knuckle-ball effect of the shot/serve is assumed to be caused by instability of the fluid force of the vortex which occurs behind the moving ball. The This study explains the correlation between the fluctuation of fluid forces and that of a ball wake. Moreover the flow visualization on a ball wake was performed to confirm the affection against the fluid force of the ball.
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  • Gou YAGI, Hiroo OKANAGA, Katsumi AOKI
    Article type: Article
    Session ID: 0302
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Nowadays various type of breaking ball is used in sports. These breaking balls impact the outcome of the game. There are many researches on aerodynamics characteristics of various breaking ball. However, the effect of surface structure to the flow characteristics of a moving ball with rotation is still unknown. In this paper, the effect of the surface structure of ball to the aerodynamics characteristics of the ball is investigated by using wind tunnel experiment. Furthermore, the flow characteristics of four kinds different soccer balls and three kind of different model balls are investigated. These balls were made by 3D printer. It is claritied that the JABULANI's lift coefficient was lower than other soccer balls. Furthermore, the drag coefficient of the model balls become bigger in super critical region as the grooves become deeper, the lift coefficient of model balls were not change.
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  • Jing LI, Makoto TSUBOKURA, Masaya TSUNODA
    Article type: Article
    Session ID: 0303
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    The present study has conducted large-eddy simulation (LES) of smooth and golf ball around the critical Reynolds number. Drag coefficients and the flow field around the sphere and the golf ball have been analyzed. The result shows that the surface roughness on the golf ball surface doesn't strongly affect the flow behavior in the subcritical regime. However, the surface roughness could result in the drag crisis of golf ball occurring at a lower Reynolds number in the supercritical regime compared with the smooth sphere. This is because the flow becomes instable when it passes the dimples at the supercritical Reynolds number and could consequently travel further downstream.
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  • Naoyuki ONODERA, Takayuki AOKI, Keita IZUMIDA
    Article type: Article
    Session ID: 0304
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Motion of a spinning ping-pong ball is strongly affected by the Magnus effect. Since airflows around a ping-pong ball, such as Smash, are turbulent with a high Reynolds number, it is necessary to carry out large scale CFD simulations. We have developed a large-eddy simulation code based on lattice Boltzmann method for GPU supercomputers. Coherent-structure Smagorinsky model is applied to turbulent phenomena, and is suitable for large-scale calculation. Our code achieved fairly good performance by using the TSUBAME supercomputer. In this research, we examine a large-eddy simulation for a motion of the ping-pong ball in table tennis. By executing this large-scale computation, details of airflows around the ping-pong ball were revealed.
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  • Toshihiro HANIU, Hiroaki HASEGAWA, Hideki TAKAGI, Hirofumi SHIMOJO
    Article type: Article
    Session ID: 0305
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    It is known that the finswimming is fast swimming style. The actual motion of a monofin is obviously unsteady. That is, the unsteady forces must also be considered to estimate the propulsive force of a monofin. The aim of this study was to elucidate the relationship between propulsive forces and unsteady flow structure of monofin with different kicking speed in the kick-up (upstroke) and kick-down (downstroke). Experiments were performed in a circulating water channel, the kick-up and kick-down motions of the monofin were operated by a drive unit using a stepping motor. The oscillating (pitching) center in the motion was set at -20° (0° being the horizontal plane) and the pitching angle was ±20°. The peak value of propulsive force during one kick stroke becomes larger with increasing down-kick speed, and the propulsive force is strongly associated with kicking speed during downstroke. Because, the strong vortex ring is generated near the monofin with increasing down-kick speed.
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  • Haoran Cui, Junnichi KUROIWA, Ryozo ISHIWATA
    Article type: Article
    Session ID: 0401
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    When we take account of the environment surrounding, the development of vehicle with low energy consumption is required. Under these conditions the solar car races which develop the better performance energy are held. In these races, the factors which decide the winner are how the air resistance can be reduced. In addition, since vehicles for a solar car race are a lightweight vehicle, crosswind stability of the vehicle is important.
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  • Nariya TANAKA, Toshinosuke AKUTSU
    Article type: Article
    Session ID: 0402
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Form of closed truck has evolved considering maximum consideration on transportation efficiency. As a result, all modem truck shares basic square form design. This experimental study aims to reduce drag force on such a square formed truck using several active flow control methods which influence on separation region. Model used for this study is a 1/14 scale tuck model with ducted fan mounted inside the cargo area to supply necessary air flow. Active flow control using coanda effect effectively reduced drug force by about 20%.
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  • Yosuke Anzai, Koji Fukagata
    Article type: Article
    Session ID: 0403
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    In order to reduce the aerodynamic noises induced from a pantograph contact shoe, flow control over the contact shoe is needed. There are various kind of flow control method, passive and active control method. In this study, flow around a square cylinder controlled by plasma actuators is numerically investigated by means of direct numerical simulation(DNS). The square cylinder is assumed to have plasma actuators on the rear surface and Reynolds number is set at 100. Three different different actuation input are investigated. Reduction of the drag coefficient C_D and the lift coefficient fluctuations C'_L is observed. The suppression of vortex shedding is also observed due to a weakened interaction between two shear layers behind the cylinder. The flows induced by two actuators interact at the mid-section of the rear surface and generate the streamwise jet, which weakens the interaction between two shear layers.
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  • Tengku FIKRI, Hiroo OKANAGA
    Article type: Article
    Session ID: 0404
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    In this study the flow characteristics around square cylinder with various grooves shapes is investigated in detailed by drag coefficient measurement. The cross section configuration of the grooves are rectangular, arc and triangular. The drag is measured by a wind tunnel experiment. As a result, it is understood that square cylinder with grooves has lower drag coefficient compares with square cylinder without grooves. Rectangular shaped grooves has the lowest drag coefficient compared with arc and triangle grooves shape. The square cylinder with the rectangular shape grooves has biggest reduction rate compared to arc and triangular shape grooves.
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  • Kazuma NISHIO, Yousuke KITAGAWA, Shinji TAMANO, Yohei MORINISHI
    Article type: Article
    Session ID: 0405
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    An obstacle in fluid is subjected to hydrodynamic drag force. It is important to reduce the drag force to save energy and to prevent fluid machinery from breaking. We investigated drag-reducing effects of surfactant additives in flows around circular and square cylinders. We performed PIV measurements in the wake region of circular and square cylinders and visualized the free surface around circular and square cylinders. Surfactant addition in flows resulted in making vortices weak and reducing oscillation of free surface in the wake region.
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  • Ryosuke KIDOGAWA, Yukinori KAMETANI, Koji FUKAGATA
    Article type: Article
    Session ID: 0406
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Two-dimensional unsteady Reynolds Averaged Navier-Stokes (2D-URANS) simulation of spatially developing turbulent boundary layer at high Reynolds numbers with a uniform blowing (UB) was carried out aiming at skin friction drag reduction. The friction Reynolds number was set to be 160, 2000, 6000. The mean velocity profiles are shifted from the wall. As a result, the skin friction drag was reduced by UB. It is found that the drag reduction rate is roughly scaled by the blowing velocity expressed in the wall unit.
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  • Monami SASAMORI, Hiroya MAMORI, Kaoru IWAMOTO, Akira MURATA
    Article type: Article
    Session ID: 0407
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Experimental study of a 3-D riblet has been carried out. The lateral spacing of the 3-D riblet surface is sinusoidally varied in the streamwise direction. The obtained maximum drag-reduction rate is about 12% at the bulk Reynolds number of 3400. The flow structure over the 3-D riblet is analyzed in the velocity field obtained by using 2-D Particle Image Velocimetry and is compared with the corresponding flow over the flat surface. Although the lateral spacing of the riblet is larger than the diameter of stramwise vortices, vortices are inhibited approaching to the wall due to characteristic flows in the region near the sinusoidal riblet surface.
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  • Kohei MATSUMOTO, Yuko NAKANO, Masatoshi SANO, Shinji HONAMI
    Article type: Article
    Session ID: 0408
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    An experimental study is performed for multi-passage channel flow with the dielectric barrier discharge plasma actuator (PA). The multi-passage is a reverse flow type, and consists of the five branch channels. PA is installed on the outside wall of the inlet manifold. The Reynolds number based on the bulk velocity and channel width at the main channel is varied from 6.0×10^2 to 2.0×10^3. The wave form with voltage of 5 kV and frequency of 2.5 kHz is applied to the electrode of actuator. The wall static pressure is measured, and the pressure loss and flow rate are evaluated. The velocity profiles are measured by a PIV system to clarify change of the velocity field by on and off of PA. The pressure loss decreases and flow rate in each branch passage improves by the effect of induced flow with PA. The flow uniformity and low pressure loss are related to the reduction of the recirculation region at the manifold.
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  • Mitsuru SATO, Hiroya MAMORI, Kaoru IWAMOTO, Akira MURATA
    Article type: Article
    Session ID: 0409
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Experimental investigation for a periodically converging-diverging turbulent pipe flow is performed to examine a spatial development of a drag reduction effect. A shape of the pipe is designed according to a result of a direct numerical simulation. Three periods of the converging-diverging are provided. At the bulk Reynolds numbers in the range of 3000 to 5000, the maximum drag reduction rates are 29% at the first period, 39% at the second period, and 46% at the third period respectively. Therefore, the drag reduction rate is found to develop in the downstream direction. On the other hand, the drag reduction effect is deteriorate over the bulk Reynolds number of 5000.
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  • Ken YAMAMOTO, Satoshi OGATA
    Article type: Article
    Session ID: 0410
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Since the micro-two-phase flows are sensitive to the pressure fluctuations, which are induced by, e.g., syringe pumps or bubbles in the channels, effects of the external factors on the pressure drop in microchannels were investigated experimentally. The experiment was conducted by measuring the pressure difference between a channel inlet and atmospheric pressure by a pressure transducer in every one millisecond. With a circular glass channel (d = 1.0 mm) and water as the test channel and the test fluid, respectively, it was found that the measured frequencies and amplitudes of the pressure fluctuations induced by syringe pumps with the flow rate of 0.1-2.0 ml/min were 0.063-53 s and 4-183 Pa, respectively for the single-phase flow case. For two-phase flow case, in which only a single bubble was inserted in the channel, it was found that a bubble exiting the channel outlet induced larger (〜 Laplace pressure) temporal pressure fluctuations and it can be reduced to half by modifying the outlet condition.
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  • Yuho ISHIWATA, Hiroya MAMORI, Kaoru IWAMOTO, Akira MURATA
    Article type: Article
    Session ID: 0411
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Experimental investigation on a turbulent channel flow over a traveling wave-like streamwise wall deformation is conducted. The wave propagates on a thin elastic rubber sheet. Parameters of the wave are comparable to the ranges for relaminarization performed by recent similar numerical studies for wall deformation or blowing and suction. The drag reduction rate is 40% at a bulk Reynolds number of 3300 and a skin friction approaches to the value of the uncontrolled turbulent flow as increasing the bulk Reynolds number. A two-dimensional PIV measurement clarifies a characteristic flow produced by the wave. A three-component decomposition for the velocities also shows the suppression of the near-wall turbulence.
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  • Keisuke UCHINO, Koji FUKAGATA
    Article type: Article
    Session ID: 0412
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Dissimilar control in turbulent flow in a channel with streamwise wave-like wall deformation is investigated by means of direct numerical simulation (DNS). We investigated three modes: sinuous mode, varicose mode, and one-side mode (the upper plate is a flat plate, and the lower plate is traveling wave wall) with upstream or downstream wave-like wall deformation. In all cases, analogy factor j/f is found to be less than unity and approaches unity with time. Dissimilarity is observed most strongly in the sinuous and varicose modes in the downstream wave case.
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  • Hiroya MAMORI, Koji FUKAGATA
    Article type: Article
    Session ID: 0413
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Direct numerical simulation of a fully-developed turbulent channel flow under control of a wave-like wall-normal body force is performed. An exponential decay of the wall-normal body force is assumed so that the body force acts in the regions near the walls only. Skin-friction drag reduction effect is confirmed while the net saving rate is negative and, if positive, subtle. The spanwise roller-like vortices are found to produce a negative Reynolds shear stress, which contributes to the drag reduction.
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  • Hideyuki Takezawa, Ken Yamamoto, Satoshi Ogata
    Article type: Article
    Session ID: 0414
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    We studied formation process of gas-liquid interface in a microchannel having hydrophobic cavity-shaped microstructures. The microstructures were fabricated on a test wall by wire electric discharge machining, and the test wall was coated with triazine thiol to induce hydrophobicity. Width and height of the microstructures are 1 mm and 100 μm, respectively, and the microcavities (100 × 100 × 100 μm^3) are aligned on side walls with 100 μm spacings. We experimented with 6 different concentrations of aqueous ethanol solutions in order to investigate the effect of the surface tension. As a result, it was found that formation process of gas-liquid interface can be categorized into 3 types of processes by the difference of the surface tension.
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  • Takuya MINEGISHI, Takahiro TSUKAHARA, Yasuo KAWAGUCHI
    Article type: Article
    Session ID: 0415
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    It is important from an engineering aspect to understand drag-reducing viscoelastic flow, since comprehension of the drag-reduction mechanism may facilitate designs with better additive types and/or channel configurations. In this study, we investigated the attenuation of vortices in fully-developed turbulence of viscoelastic fluid between parallel planes by DNS (Direct Numerical Simulation). We discussed how the viscoelastic stress plays a role in the reduction of the turbulent motions around eddies and how it influences the entire flow field. For determining the major effect of viscoelastic stress, we examined also 3 stage statistical data, with emphasis on the eddy evolution. We found that inhibition of turbulent eddies would be caused by the following aspects: the longitudinal eddy less occurs, the damping of eddies by viscoelastic stress occurs particularly in the ejection area, and the development of eddy is relaxed by the viscoelastic stress during the eddy growing stage.
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  • Ryota Toyoda, Hiroshi Mizunuma
    Article type: Article
    Session ID: 0416
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Drag reduction effect of surfactant solution is caused by SIS(Shear-induced structure). SIS is aggregation of the micelles in surfactant solution. In this study, we experimentally investigated drag-reducing flow using cationic surfactant. The SISs were visualized in turbulent flow to elucidate the induced mechanism and role of a micelle structure in drag reduction. The streamwise changes in the SISs and drag reduction were measured and their relationship was discussed. In our experiment we measured velocity properties and visualized inner flow in upstream and downstream, and there related the results.
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  • Yasufumi HORIMOTO, Susumu GOTO, Genta KAWAHARA
    Article type: Article
    Session ID: 0417
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Turbulence can be suppressed by a small amount of surfactant additives. To understand the physical mechanism of the turbulence suppression, we experimentally investigated the effect of the addition of surfactant on the transition from steady flow to turbulence in a precessing sphere. The most unstable mode of the steady flow for surfactant solution is the same as in the case of water, although turbulence is drastically suppressed by surfactant additives at higher Reynolds numbers.
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  • Akiomi USHIDA, Akira ICHIJO, Tomiichi HASEGAWA, Takatsune NARUMI
    Article type: Article
    Session ID: 0418
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Pressure drop were measured because flow properties of water and surfactant solutions were investigated in capillary flows. Good agreement between water results and predictions of laminar flows and Blasius expressions was obtained. As corresponding to molar concentration ratio, experimental results of surfactant solutions maintained laminar flows in transition regions. Thus, laminarization of surfactant solutions was shown, and relationship between the phenomenon and non-Newtonian properties was discussed. Moreover, viscosity curve was supported to the experimental results.
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  • Jun ITO, Hiroki UCHIKAWA, Shinji TAMANO, Yohei MORINISHI
    Article type: Article
    Session ID: 0419
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    It is known that surfactant additives in wall-bounded turbulent flows yielded the significant drag reduction. In this study, we performed flow visualization and LDV measurement of turbulent boundary layer using new experimental apparatus, in which the size is enlarged compared to old one, in order to clarify the drag-reducing effect at the higher Reynolds number. The nonionic surfactant which mainly consists of ODMAO is injected into the turbulent boundary layer. We could obtain the high drag redution up to 70%.
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  • Michihiro TAKAHASHI, Takahiro TSUKAHARA, Yasuo KAWAGUCHI
    Article type: Article
    Session ID: 0420
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Non-linear k-ε model is applied to viscoelastic turbulent flow. In formulation of a RANS for viscoelastic fluid flow, two main improvements are needed: a modified eddy viscosity closure, and a new closure for a cross-correlation term between the fluctuating components of the viscoelastic conformation and rate of strain tensors (Λ_<ij>) appearing when constitutive equation is averaged. Λ_<ij> was often modeled by the Reynolds stress in the literature. Since many previous studies have constructed a set of RANS equations based on the linear k-ε model, Λ_<ij> was modeled assuming the isotropic Reynolds stress. In this study, anisotropy of Reynolds normal stress was expressed by employing non-linear k-ε model. Thus, from the standpoint that it may be possible to obtain more exactly the normal components of the Reynolds stress, we proposed a new model of Λ_<ij>. Moreover, we found that C_μ, of non-linear k-ε model predicted well the eddy viscosity without modification.
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  • Kazuki USHIKUBO, Koichi NISHIBE, Tamio FUJIWARA, Hiroshi OHUE, Kotaro ...
    Article type: Article
    Session ID: 0501
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    Although there have recently been various studies on synthetic jets, many issues remain to be clarified, including details of the jet structure and the fluid force. In this paper, a jet pump (fan) which utilizes the synthetic jet is proposed. The numerical results of the velocity change with time downstream of the slot are compared with the experimental results. The typical flow patterns inside the pump and the performance curves are demonstrated. Furthermore, the mechanism of pressure restoration for various non-dimensional stroke length L_0 is discussed.
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  • Toma ONODERA, Koichi TSUJIMOTO, Toshihiko SHAKOUCHI, Toshitake ANDO
    Article type: Article
    Session ID: 0502
    Published: October 25, 2014
    Released on J-STAGE: June 19, 2017
    CONFERENCE PROCEEDINGS FREE ACCESS
    In order to develop a new mixing procedure, we conduct DNS (direct numerical simulation) of dynamic control for free jet. The inflow velocity of jet is rotated around a given rotating axis streamwise direction. From view of instantaneous vortex structures, it is found that the structures are markedly modulated, compared with the case of the free jet. In addition, in order to estimate the mixing performance, the statistical entropy is calculated. It is found that the mixing efficiency are markedly improved with the rotational motion than that of the normal jet case.
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