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Masa-aki Ishikawa, Yuichi Murai, Fujio Yamamoto
Article type: Article
Session ID: K-1341
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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A lot of PIV algorithm has been dealt with a translation motion. Therefore, error vectors are obtained for strong deformed flows. Nowadays, recursive processes of a cross-correlation PIV and a gradient-based PIV are used as the control of the influence of strong deformed flows. However, these recursive processes do not correspond to strong deformed flows perfectly. In this study, unknown valuables of the gradient-based method including the velocity gradient tensor are employed because of overcoming of strong deformed flows. The performance of a recursive gradient-based method is estimated by a simulation of a Taylor-Green vortex flow.
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Tomohiro SONE, Akira URITA, Shuji TANAKA
Article type: Article
Session ID: K-1342
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Aerodynamic characteristics and flow structures in wakes of delta wings with aspect ratios of 1.28〜4.0 have been investigated at angle of attack 0 ° to 90 °. The Reynolds number based on the maximum chord length is 1.3×10^5. The delta wings with λ=1.2〜2.0 indicate mostly similar C_<Lmax> and α_<C_<Lmax>>, whereas those for delta wings with λ=2.4〜4.0 change gradually with an increase in λ, but in the unstalled and full stalled conditions, the aerodynamic characteristics are quite similar independently of λ. In the unstalled region, clear trailing vortices are formed in the wakes and ring-type vortices which correspond to their aspect ratios are formed.
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Tatsuya HAYASHI, Masaki FUCHIWAKI, Kazuhiro TANAKA
Article type: Article
Session ID: K-1343
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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The technique of flow control has been developed in recent years. It is well known that drag force for an airfoil can be diminished and thrust could be produced by changing the arrangement of vortex street in the wake from Karman vortex street type to thrust producing vortex street type. We considered it possible to produce thrust of an airfoil adding pitching motion. In this study, the flow pattern behind a pitching airfoil has been visualized and thrust force measured. As a result, the relationship between the thrust producing characteristics and flow patterns in the wake has been clarified.
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Michio Kinjo, Fumihiko Mikami, Nobuhide Nishikawa
Article type: Article
Session ID: K-1344
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Two-color dual laser beam scanning PIV is applied to the measurements of the wake vortices behind an axisymmetric paraboloid to investigate the flows with separation over the body at high angles of attack. In order to record the image with the limited scattering efficiency of small tracer particles, laser beam scanning method was employed with a 3-CCD color digital video camera. The obtained single frame/multi-exposure color PIV image was decomposed into double frame/single exposure images according to the hue component of the pixel values. The developed technique is shown to provide sufficient velocity vectors in the plane normal to the symmetric axis of the body, with the exception in vortex cores. The agreement obtained between the PIV and flow visualization results is seen to be quite reasonable.
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Masaki YAMAGISHI, Tomoko TOGANO, Shinichi TASHIRO
Article type: Article
Session ID: K-1345
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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When the periodic velocity fluctuation is introduced in a mean flow, the separation flow changes in various manners. This report concerns with the "flapping" motion of the separation shear layer by means of the phase averaging of instantaneous velocity fields over the separation region. In order to know the principal motion of the velocity field precisely, wavelet transform is used. The shapes of contour are quite different at each phase and with the frequency of the fluctuation. The separation shear layer is depressed and pulled up with the fluctuating of the velocity in the mean flow. And when the suitable frequency was chosen the separation region disappeared at the phase of depression.
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Shuuji TOTTORI, Takashi YOSHIDA, Masaharu MATSUBARA, Toshihiko IKEDA, ...
Article type: Article
Session ID: K-1401
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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One of the chief difficulties encountered in numerical simulation of the Navier-Stokes equations is the boundary conditions. Specitically, we consider the case of two-dimensional jet discharging into a unbounded domain. The semi-implicit splitting method is used with a staggered grid. A third-order upwind scheme is used for convection terms. Outflow boundary condition is Sommerfeld radition(SRC). At side boundaries, we attempt to introduce the entrainment by apply the analytical solution given by Schlichting to boundary condition. Schlichting's solution provides good result than slip condition.
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Koji KIKUYAMA, Yutaka HASEGAWA, Noboru MATSUMOTO, Michio NISHIKAWA
Article type: Article
Session ID: K-1402
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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In the present study the velocity and turbulent intensity are measured near the concave surface in channels whose radii of center line curvature are 1,000mm and 2,000mm, respectively, on the rotating system. When the channel rotates in such direction as the Coriolis force acts toward the wall, the transition of the boundary layer to the turbulent state is promoted because the Gortler instability is enhanced. For the prediction of the boundary layer transition, Gortler number can be an appropriate parameter because the transition occurs at the point where Gortler number exceeds 7, irrespective of the axial Reynolds number, rotation rate, or curvature radius of the wall.
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Koji KIKUYAMA, Yutaka HASEGAWA, Noboru MATSUMOTO, Michio NISHIKAWA
Article type: Article
Session ID: K-1403
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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For the prediction of the boundary layer flow near the convex surface on rotating system, this study investigated into the effects of system rotation, radii of the wall and the axial Reynolds number, on the boundary layer near convex side, making use of the curved channel on the rotating table. From the measurement results of the velocity distribution, it has been found that Reynolds number based on momentum thickness is an appropriate parameter to predict the boundary layer transition.
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Ryuichi AOYAMA, Hideharu MAKITA, Nobumasa SEKISHITA, Naoyuki TUCHIYA
Article type: Article
Session ID: K-1404
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Merged spots were visualized by a smoke-wire method to clarify interaction phenomena between turbulent spots in a zero pressure gradient laminar boundary layer. The turbulent spots were generated by issuing small air jets from the two holes horizontally displaced at 40mm on a flat plate. The merged spots conformed almost the same outline as the superposition of the individual spots. Inside of the single spot was composed of many small vortices and their number increased around its wing-tip as the spot was convected downstream. When the spots generated in parallel began to merge, the hight of the merged part was enhanced than that of each isolated spot through their mutual interaction then, strong transvers vortices became induced at about Y/δ=1.8 above the merged part in the merged spots. In case of the two spots being generated with phase lag, apparent normal growth was not observed.
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Teruko KAWANA, Hideaki KOIKE, Masayuki KAKEI, Shigeru HAYASHI, Mitsuma ...
Article type: Article
Session ID: K-1405
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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We are developing a turbulent combustion analysis code for large scale numerical simulation of combustion phenomena using parallel computing machines. In this study we calculated as follows. Firstly, zero Mach number approximation is applied to the analysis of subsonic compressible flow, and BFC coordinate is taken for considering the real complicated shape of the burner. Secondly, the stabilization of the simulation including various time scales is realized by coupling equation of continuity with equation of energy conservation via equation of state. The result of LES simulation shows that it is qualitatively valid for the real combusition phenomena.
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Daisuke Kohama, Takatsugu Kameda, Shinsuke Mochizuki, Hideo Osaka
Article type: Article
Session ID: K-1406
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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A direct measurement device with a floating element controlled zero-displacement procedure has been constructed and applied to the wall shear stress measurement of turbulent boundary layers without pressure gradient. The floating element having circular friction area of 20mm diameter is supported by parallel links and controlled to be zero-displacement by an electro-magnetic coil. Calibration curb has better linearity in zero-displacement procedure than in displacement procedure. Practical application of the present device to the zero pressure gradient boundary layer needs to be improvement with considerably smaller wall shear stress compared with the standard values.
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Hideo Osaka, Youzi Kobayashi, Takatsugu Kameda, Shinsuke Mochizuki
Article type: Article
Session ID: K-1407
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Effect of spanwise perturbation was experimentally investigated in the interaction process between a turbulent boundary layer and a common-flow down type streamwise vortex pair introduced from the free stream. The perturbation was added by spanwise oscillation of a delta wing at two different frequencies of 0.5Hz and 1.OHz. The mean velocity and Reynolds stress profiles were measured along the symmetrical planes at the center between the two vortices. The spanwise perturbation produces inflectional point in the mean velocity profile and peaks in the turbulent intensity profile. The peak values is slightly increased in the u_<rms>/U_1, profile but is slightly decreased in the v<rms>/U_1 profile over the range of Δx/d_0=10-50.
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Yasuhiko SAKAI, Takehiro KUSHIDA, Koji OHTA, Kazushige YOSHIDA, Hiroka ...
Article type: Article
Session ID: K-1408
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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In the turbulent boundary layer on the smooth flat plate, the simultaneous measurements of the velocity and wall static pressure by using I-type of hot wire probe and micro pressure transducer. The burst events were picked up by using VTTA (variable-interval time average) method. The results show that the phase-averaged velocity and wall static pressure has strong correlation during the bursting period.
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Masayoshi OKAMOTO, Shinya TAKEUCHI, Nobuyuki SHIMA
Article type: Article
Session ID: K-1409
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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The turbulent flows over a wavy wall and periodic hills include separation, recirculation and reattachment and have been studied experimentally and computationally. In this work, in order to test a third-order nonlinear K-ε model proposed by the authors, the model calculation for a turbulent flow over periodic hills is performed. The present model underpredicts the recirculation velocity butreproduces the flow separation.
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Shinya YASUI, Daigo YOSHIMURA, Yasutaka NAGANO
Article type: Article
Session ID: K-1410
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Direct Numerical Simulation (DNS) has been performed for a turbulent flow in a channel with rough and smooth walls. The Navier-Stokes equation and the equation of continuity for Reynolds number Re_m=4560 have been solved numerically with the finite difference method. As a result, it is found that the values of shear stress and pressure fluctuation increase markedly as the flow goes downstream because of the influence of rough wall. Also it is confirmed that longitudinal vortices are enhanced by the influence of rough wall.
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Yasuhiro OTUDA, Toshihiro TAKAMI, Yosinori KITA
Article type: Article
Session ID: K-1411
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Three-components of velocity and a wall shear stress have been measured using a non-orthogonal triple-sensors probe and a micro flow sensor in unsteady turbulent pipe flows with stepwise time variations. Its response behavior of turbulence distributions has been investigated experimentally. It is found that the response of turbulence characteristics near the pipe center is fairly delayed to the stepwise variation of flow rate because the centerward transport of turbulence becomes slow due to the interaction of triple correlations.
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Hiroshi KAWAMURA, Takahiko SAKAKI
Article type: Article
Session ID: K-1412
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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With an aid of the recent development of computers, various direct numerical simulations (DNS) of turbulence were performed. Although the turbulence itself is unsteady in nature, the mean flow is assumed steady in most of the DNS's. This is because the DNS of the turbulence with an unsteady mean flow requires more computational effort to obtain a stable statistical average. In the present study, a pulsating flow driven by temporally periodic pressure gradient is imposed on the turbulent channel flow. The each period is divided into a number of phases and statistical average is obtained for various turbulence quantities.
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Shuangke LIU, Xuchang XU, Guoqiang DENG, Fuji YAMAMOTO
Article type: Article
Session ID: K-1413
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Characteristic of particles at exit zone in Circulating Fluidized Bed Boiler (CFBB) was measured using Particle Tracking Velocimetry (PTV). As a result, it was found that flowing particles at exit zone in CFBB was divided into two parts: one part was entrainment by airflow flowing towards exit; and others separation from the airflow forming cluster and falling flow.
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Ryo ONISHI, Takenobu MICHIOKA, Kouji NAGATA, Satoru KOMORI
Article type: Article
Session ID: K-1414
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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A large-eddy simulation (LES) based on a finite volume method was applied to a liquid turbulent flow with a rapid chemical reaction. The large eddy probability density function model was used as a subgrid-scale (SGS) model for a rapid reaction. The correlation coefficient in the scale similarity model between the variance of SGS concentration and that of test-filtered concentration was determined using the data of the DNS of liquid isotropic turbulence. To investigate the applicability of the LES to reacting liquid flows, both measurement and LES were performed in a liquid mixing layer with a rapid reaction. The prediction of the LES was in good agreement with the measurement. And the result also showed that the present LES can accurately estimate the concentration statistics in reacting liquid flows.
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Ryoichi KUROSE, Hisao MAKINO, Takenobu MICHIOKA, Satoru KOMORI
Article type: Article
Session ID: K-1415
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Effects of the heat release and the fluid shear on the nonpremixed reaction processes are studied by applying a three-dimensional large eddy simulation (LES) to a compressible, spatially developing nonpremixed reacting plane mixing layer. The fluid shear is generated by the streamwise and spanwise inlet velocity differences between the fuel and oxidizer. SGS turbulence and combustion models used are the dynamic Smagorinsky model (DSM) and the scale similarity filtered reaction rate model (SSFRRM), respectively. The results show that the heat release and the spanwise fluid shear promote the mixing between the fuel and oxidizer and increase the production. Although Reynolds stress and fuel flux are usually positive in the isothermal mixing layer except, for the region near the inlet, these values become negative in certain regions away from the inlet due to the heat release and the spanwise fluid shear.
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Atsuhiro NISHINO, Naozo HATTORI
Article type: Article
Session ID: K-1416
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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In this study, a numerical calculation of supersonic-subsonic mixing layers is performed by solving the three dimensional compressible Navie-Storkes equations in the generalized coordinates. Calculations at convective Mach number of 0.52 suggest the existence of streamwise vortex tubes in the startially developing turbulent mixing layer. Also, a close relation between vorticity and pressure is noticed. The vortices reveal fairly stable behavior in a wide range of x direction.
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Hayato NITTA, Nobuyuki YAMAGUCHI, Masayuki OGATA
Article type: Article
Session ID: K-1417
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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In bubbling-type fluidized beds, because of violent motions of the bed particles, in-bed bodies tend to be often violently excited, and/or happen to be seriously eroded, both, in the worst case, resulting in mechanical failures or plant outage. In some cases the beds induce bodies of various sizes and various masses, whose circulation within the bed should be controlled intentionally, if possible. In the situation, information on the forces exerted on in-bed bodies are indispensable. For the purpose, measurements of force and relevant quantities were conducted on spheres as target in a small experimental fluidized bed.
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Satoshi NUKADA, Nobuyuki YAMAGUCHI, Masayuki OGATA
Article type: Article
Session ID: K-1418
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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In fluidized-beds in-bed bodies tend to be subjected to violent particle forces, which tend heavily excite them and, in some situations, erode them. It is important to know about the particle forces. In some applications the motion of large bodies mixed into the particles should be controlled and guided intentionally for some control purposes. From the aspect, in order to obtain information on the particle motions at impacts on an in-bed circular cylinder, PIV analyses of high-speed video-images of bubbling behaviors in a two-dimensional fluidized-bed were conducted. Obtained data on the particle speeds could be used to estimate the particle forces.
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Toshitsugu TANAKA, Tetsuichiro MUKAI, Toshihiro KAAGUCHI, Yutaka TSUJI
Article type: Article
Session ID: K-1419
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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In this study, a discrete particle model for flows of Group-A particles in Geldert's classification is investigated. The corresponding experiments are made for validation of the numerical predictions. The effects of lubrication and adhesion between particles on the fluidization behavior is examined.
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Toshihiro KAWAGUCHI, Mitsuhide OHKUBO, Toshitsugu TANAKA, Yutaka TSUJI
Article type: Article
Session ID: K-1420
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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We have studied numerically and empirically about density waves in standpipe flows. In our past studies, however, the calculated plug velocity was different from the measured velocity. In the present study, we measured the pressure loss property and modified the fluid drag coefficient. By applying the modified drag coefficient to our calculation model, the calculated plug velocity agreed well with the measured velocity.
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Junichi OHTA, Kunio TAKAGI
Article type: Article
Session ID: K-1421
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Masaru SHINOHARA
Article type: Article
Session ID: K-1422
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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The present study investigates the motion of two or three rigid spheres settling in an incompressible viscous fluid bounded by a vertical circular cylinder both theoretically and experimentally. In our experiment the ratio of the particle radius a to the cylinder radius L is 0.0142 and the particle Reynolds number(Re=av_z/v) is in the range of 0.140-0.156. Here, v_z is the axial velocity of the sphere and v is the kinematic viscosity of fluid. The cylinder Reynolds number (R_L=Lv_z/v) is finite. The velocities of the spheres were obtained experimentally and theoretically taking into account of the first-order inertial effects of boundaries. Method of matched asymptotic expansions was used.
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Mikio YAMANOI, Shuichi TANOUE, Yoshiyuki IEMOTO
Article type: Article
Session ID: K-1423
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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The characteristics of ferrofluids depend on magnetic field gradient. An aggregate effect is one of the most interesting subjects. Aggregations are formed in the ferrofluid whether there is a magnetic field or not. Therefore, they have an effect on rheological characteristics such as shear viscosity, normal stress effects and so on. In this research the Stokes Dynamics simulations are made for aggregate structure of ferrofluids under the strong magnetic field. A result obtained is that a metastable area exists in the aggregation of ferrofluids.
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Noriko SAKAMOTO, Katushi FUJITA, Nobuyoshi KAWABATA, Takuji ISHIKAWA
Article type: Article
Session ID: K-1424
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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The flow of viscoelastic fluid by means of a bead-spring macro model shows non-Newtonian viscosity. The shear flow characteristics of polymer solution are investigated experimentally by using by cone-plate type viscometer. The experimental results are compared with the numerical results by using bead-spring macro model, where three types of models (conventional modeling, present modeling, present modeling + random) are employed. The value and the equation of the spring constant are discussed so that the numerical results show good agreement with the experimental results. It is found that the present modeling + random can consistently express the distribution of polymer chains and the rheological property of viscoelastic fluids.
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Seiji SHIMIZU, Takanori NISHIYAMA, Takao SHIMURA, Tatuyuki OMOTE
Article type: Article
Session ID: K-1425
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Abrasive water suspension jet (AWSJ) has a greater capacity for drilling and cutting than abrasive water injection jet (AWIJ). In the present investigation, the drilling capability of the AWSJ under submerged condition is studied experimentally with specimens of stainless steel at the jetting pressure of 12 MPa and the ambient pressure of 0.1 MPa. Two different aluminum oxides #100 and #220 are used. It is found that the drilling capability decreased steeply with the increase of the standoff distance. The nozzle and the nozzle holder affect the drilling capability of the submerged AWSJ. The grain size of the abrasive also affects the drilling capability of the submerged AWSJ.
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Tutomu TAKAADA, Kazuhiko KATO, Hiromichi OBARA, Yasuaki MATUDAIRA
Article type: Article
Session ID: K-1426
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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It is well known that the regular vortex shedding process named Karman vortex streets always occurs in the wake behind bluff bodies under high Reynolds number. The wake flow with cavitation has the same process and the Strouhal number depends on the cavitation number. But, the interference mechanism between the vortex shedding process and cavitation scale has not been clarified. This study investigated the flow visualization about wake vortex cavitation behind a wedge at several cavitation numbers by using PIV and LDV systems. The vortex shedding process had two modes corresponding to the cavitation number. To examine this mechanism, the flow visualization was executed by using the method which lays the vector map on top of the image map.
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Kazuhiko OKABAYASHI, Koichi MASUBUCHI, Takeharu KOBAYASHI, Risaburo OB ...
Article type: Article
Session ID: K-1427
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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In order to clarify the behavior of the singular vortex cavitation of exceptionally highly erosive, we highspeed-photo-graphycally observe such behavior behind a circular cylinder, with respect to several water temperatures tw at a constant cavitation number σ. With increasing t_w, the behavior drastically changes and shifts from rather low erosive cavitation to the highly erosive singular vortex cavitation near 30℃. It is also clarified that the nuclei scarecely change with t_w.
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Hisanori UENO, Akito NAKAMURA, Masashi KUMITA
Article type: Article
Session ID: K-1428
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Cavitation characteristics of a trochoid pump are experimentally investigated. The cavitating pump delivery was characterized by three boundaries: cavitation inception, beginning of flow decrease and cavitation criticality, and discussed compared with measuring pressures of the pumping chambers and its flow visualization. Values of these critical suction pressures at constant pump speed and the cavitation inception site were determined.
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Yasuhiro Moriguchi, Hiroharu Kato, Yuki Ito, Yoko Hashimoto
Article type: Article
Session ID: K-1429
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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The injection of microbubbles is a promising method in reducing the frictional resistance of a vessel. In this research, in order to solve the mechanism of the resistance reduction, which is not yet clear, the effects of microbubble diameter and of the near wall void fraction were investigated using a two-dimensional flow channel. The reduction rate correlated well with the near wall void fraction. Whereas, the bubble diameter didn't affect to the reduction rate.
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Yasuhiro Saito, Keiichi SATO
Article type: Article
Session ID: K-1430
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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In the present study, a wake-flow field behind a circular cylinder was examined as a representative example of bluff bodies which have a fundamental pattern of separated vortex flow. Cavitation impulses were measured by an accelerometer installed on the outside wall of the test section as well as an impulsive-force sensor flush-mounted on the inside wall. Appearances of cavitation bubbles were observed by a high-speed video camera. Especially, bubble-collapsing behavior near the wall was observed in detail from various view-angles. According to the result, Karman-vortex-like cavities shed downstream are divided into some parts. Then the cavity positioning near the wall collapses rapidly with various kinds of motion patterns.
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Naoto Suzuki, Yasuhiro Saito, Keiichi Sato
Article type: Article
Session ID: K-1431
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Recently, the shock, noise, and erosion produced by collapse of cavitation bubbles have been a crucial problem in fluids engineering. It is known that severe cavitation also occurs in the surroundings of oscillating objects inside of still liquid as well as in high-speed liquid. Few studies, from hydrodynamical viewpoints, have been conducted on cavitation bubbles of vibratory apparatus such as the equipment of ASTM irrespective of its importance. Therefore, in this report, some experiments based on the vibratory apparatus in still liquid were photographically conducted in order to study the vibratory cavitation with high impulse. The main results are related to instantaneous pictures of collapsing bubbles and measurements of impulsive force at the collapse of bubbles.
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Kenta NAKANO, Michi HAYAKAWA, Takeru YANO, Shigeo FIJIKAWA
Article type: Article
Session ID: K-1432
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Cavitation bubbles generated in a starting, submerged water jet are investigated using a conventional photography technique. A number of small spherical bubbles are initially formed in a starting vortex and often connected with each other in the form similar to a vortex ring. Some statistically averaged properties of the ring-shaped bubbles are obtained by analyzing photographic data.
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Eiji ISHII, Hirotaka KAMEYA, Atsushi WATANABE, Masayuki Urashin
Article type: Article
Session ID: K-1433
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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An oil separator is used to separate a gas and a liquid from a gas-liquid mixed flow. However, a waterspout occurs on the free surface of the oil gathered under the chamber. The waterspout elevates a large amount of oil and releases it into a discharge pipe. This process significantly lowers the efficiency of the oil separator. To calculate the flow fields of the waterspouts, we used a cubic interpolated propagation (CIP) code. The code calculates two-phase flows in a three-dimensional unstructured grid space. Also, using the code, we calculated the flow fields of the oil separator. The results showed that low-pressure core generated in the discharge pipe was the driving force of the waterspouts. Moreover, the low-pressure core grew under the circulatory motion of the vortex that formed by the swirl flow.
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Toshio SASAKI, Yuichi MURAI, Fujio YAMAMOTO
Article type: Article
Session ID: K-1434
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Bubbles in a particle sedimentation layer has quite irregular and complicated phenomena due to frequent collision between the bubbles and the particles. This paper shows our trial to find out the fundamental characteristics of the bubble behavior using two approaches. One is two dimensional experimental visualization using image analysis to capture the bubble trajectories. Another is numerical simulation considering the bubble-particle collision. These results reveal the particle clustering structure and the bubble's bouncing phenomenon.
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Hideaki YAMAGISKI, Atsushi OKAJIMA, Shigeo KIMURA, Takahiro KIWATA
Article type: Article
Session ID: K-1435
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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The mechanism of the pressure fluctuation generated by the two phase flow through a capillary tube is studied by the numerical simulation method. The numerical simulation of a bubble behavior through expansion region in a pipes has been carried out by the C-CUP method coupled with CSF model and VOF method where a variable is given by the tangent function, as noise is caused by the compressible of gas-phase. This method can deal with incompressible and compressible two-phase flow including surface tension effect. The results show that pressure pulsation is caused by deformation of a bubble.
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Yukio TOMITA, Kotaro SATO
Article type: Article
Session ID: K-1436
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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The motion of two laser-produced cavitation bubbles near a solid boundary was studied experimentally using high-speed photography. Two bubbles were mainly generated side by side near a solid wall. Eventually they collapsed non-axisymmetrically due to the Bjerknes force resulting from the bubble-bubble interaction as well as the bubble-boundary interaction. The direction of the liquid jet formed inside a smaller bubble, θ_j was estimated to examine the effect of the bubble size ratio, ξ, resulting in a remarkable decrease in θ_j as decreasing ξ, especially in the region of ξ<0.6.
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Eiji OKURA, Hiroyuki TAKAHIRA
Article type: Article
Session ID: K-1437
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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The laser trapping method is useful to make experiments of bubble collapse and nonlinear oscillations because we can successfully hold and control the position of microbubbles without contact. A microbubble of the order of 10 μm in diameter has been trapped by using a dry objective lens with large working distance and observed by CCD camera. We investigate the relationship between scattered intensity and bubble size with scattering theory; the bubble size is measured by pictures of CCD camera and the scattered intensity is taken by photo-multiplier. It is shown that the scattered intensity is nearly proportional to the bubble size.
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Ichiro NAKAMORI, Shinji NAKAMURA, Toshiaki IKOHAGI
Article type: Article
Session ID: K-1438
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Numerical analysis regarding collapsing behavior of a single bubble which is closely related to the material damage has been done. In this study, gas-liquid interface was modeled as the gas-liquid two-phase homogeneous medium. Then, energy equation was also taken into account, and the approximate Rieman solver was introduced to solve the discontinuities numerically. To begin with, the collapsing behavior of a single bubble was analyzed for the purpose of the detailed elucidation of the complicated process. Present analysis was compared to the numerical solution of Rayleigh-Plesset equation. The following were also clarified: Not only collapsing behavior of the bubble including the information of temperature but also whole flow field behavior. Also, regarding bubble collapse time, the solution by the present method agreed with the numerical Rayleigh-Plesset solution, and it was confirmed that the present method is applicable to the nonlinear analysis of the bubble behavior.
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Yoshitaka YASUDA, Hiroyuki TAKAHIRA
Article type: Article
Session ID: K-1439
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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One of the open problems in a microgravity field is an effect of g-jitter on physical phenomena. In this paper, we investigate the motion of an air bubble in a shallow cell that contains a mixture of air and water under oscillatory microgravity fields. To simulate the g-jitter effect on the air bubble we use the Level-Set method that is based on an Eulerian formulation and describes the interface by the zero level of a Lipschitz-continuous function. We analyze the influence of the gas volume ratio and the boundary condition of contact point on the bubble motion. The results show that the smaller the gas volume ratio becomes, the larger the amplitude of the bubble translation becomes. When the contact angle is fixed, the motion of a three-dimensional bubble is similar to that of a two-dimensional bubble.
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Yoshitaka YAMASHITA, Shigeo KIMURA, Atsushi OKAJIMA, Takahiro KIWATA
Article type: Article
Session ID: K-1440
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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The variations of void fraction, bubble diameter and bubble velocity are measured using an electrical resistivity probe when two-phase flow goes through the region of sudden area expansion in the vertical pipe (from 0.05m i.d. to 0.1m i.d.). Air bubbles in the size of 4 to 10mm are made by bubble generator and injected at the position of z=-4m. (z axis is along the vertical pipe and z=0m is taken as the position of sudden area expansion.) In this study two different radial void distributions in the pipe are considerd. One is called as sliding flow regime, which occurs when the bubble diameters are less than 5mm. The other is termed as coring flow regime, which takes place when the bubble diameters are greater than 5mm. At z=0.4m the void fraction has a similar distribution to that in the region before the area expansion. But for just after expansion, average bubble diameter increases by 20%. This shows that a part of bubbles just after expansion merge together, and then break up. The observation using CCD camera can also confirm the merging and breakup of bubbles
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Shigeki NAGAYA, Akira KAKUGAWA, Yoshiaki KODAMA, Koichi HISHIDA
Article type: Article
Session ID: K-1441
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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It has been known that microbubbles, which are injected into the turbulent boundary layer, reduce skin friction, and effect of the reduction can be 80%. Therefore utilizing of microbubbles for drag reduction is expected. However, a mechanism for the reduction has never been revealed clearly yet, it is necessary to understand the mechanism for practical applications. In this study, an objective is to obtain properties of the turbulent flow field with the microbubbles to understand the mechanism of reduction, so that flow field measurements for turbulent channel flow with injected microbubbles are carried out by using PIV/LIF combined system. Capability of the measurement system and results of the measurements are discussed.
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Rin NAGAIKE, Kazuhiko YOKOTA, Yoshinobu TSUJIMOTO
Article type: Article
Session ID: K-1442
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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The flow instabilities were investigated for the heated pipe flow in a natural circulation experimentally and numerically. In the experiments, three types of flow instabilities were observed. The first one was a nonperiodic bubbly flow fluctuation at a low inlet temperature. The second was a periodic slag flow oscillation. The last was a sudden boiling at a high inlet temperature and a low inlet flow speed. The one dimensional numerical simulation was also performed under the assumptions of the homogeneous two-phase flow and the thermodynamic equilibrium. The oscillating solutions and the diverging solutions were obtained and it is considered that they correspond to the slag flow oscillation and the sudden boiling in the experiment, respectively. The numerical results agree well with the experimental ones qualitatively and quantitatively except the period of the slag flow oscillation.
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Yoshiaki RYONO, Yuichi MURAI, Fujio YAMAMOTO
Article type: Article
Session ID: K-1443
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Bubble plume will generate a high-speed and thin surface flow with wide area in sea, lake, and dam. The surface flow has a function to damp the wave motion due to the interaction with rotational motion of the waves. This study concerns with the interaction mechanism based on numerical simulation using the Eulerian-Lagrangian model. This paper shows parametric relationship for the wave damping effect between the wave form and the gas injection condition.
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Yury SEMENOV, Yoshinobu TSUJIMOTO
Article type: Article
Session ID: K-1444
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Two-dimensional viscous unsteady cavity flow past a wedge in the channel is considered. The statement of the problem is based on the concept of viscous-inviscid interaction of the turbulent viscous wake behind the cavity and unsteady inviscid external cavity flow in which the cavity is closed on the displacement thickness of the viscous cavity wake. The obtained non-linear solution of the problem is linearized to study interaction between conventional surge instability and Struohal instability in the cavity wake.
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Kazuyuki MAEDA, Hiroshi GOTODA, Toshihisa UEDA
Article type: Article
Session ID: K-1501
Published: August 22, 2001
Released on J-STAGE: August 01, 2017
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Flame tip oscillation of a Bunsen type premixed flame with burner rotation has been experimentally investigated. The velocity of unburnt gas mixture is measured with and without flame by LDV system. The bimodal histogram of fluctuation is measured at just upstream of the flame tip, which means the velocity of unburnt mixture fluctuates there. This suggests that the oscillation of unburnt gas mixture is caused by the flame oscillation.
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