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Masafumi MIYATA
Article type: Article
Session ID: 1615
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Characteristics of the flow past a circular cylinder surrounded by concentric screen gauze with a diameter of 5 times the cylinder are investigated by means of LDV. The mesh and open area ratio of the screen gauze, used are 18, 0.74 and 30, 0.50, respectively. It is found that the static pressure distribution shows a similar one to the plain cylinder but the drag coefficient decreases substantially. The recirculation region of the cylinder is elongated to the flow direction and the wake shows significantly different features from those for the plain cylinder. The wake behavior differs considerably even for the screen gauze with the mesh 18 and 30.
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Yutaka WAKAI, Shinichi TAKAYAMA, Katsumi AOKI
Article type: Article
Session ID: 1617
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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This paper describes flow characteristics for circular cylinder with grooves of different type. The purpose of this study is to clarify the surface structure in relation to the effectiveness of drag reduction, and the mechanism of drag reduction. Circular cylinders with 32 grooves in the direction of the span were used in this study. The grooves took one of three shapes (arc, triangle, square). The pressure of the surface was measured with a semiconductor pressure transducer at Re=0.4×10^5〜3.9×10^5. The drag coefficient was calculated from the pressure distribution and the numerical analysis. The vortex shedding frequency at wake flow area was measured with hot-wire anemometer. It was clear that the drag coefficient were dependent on the shapes of the grooves.
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Yoshihiro INOUE, Akira ITO, Shintaro YAMASHITA, Hiroshi NAGATA
Article type: Article
Session ID: 1618
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Separated flow past a rotating circular cylinder has been investigated by the flow visualization. Experiments were conducted to investigate the cases in which the velocity ratio of the cylinder's skin to the uniform stream was varied from 0 to 6 at a Reynolds-number of 200. Wake patterns are divided into three main categories in terms of the velocity ratio; (i) regular vortex street, (ii) sheet-like structure, and (iii) turbulent vortex. Visual observations indicate that there exist transitional patterns between one flow regime and the other.
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Ping WU, Hiroyuki HANIU, Katsumi MIYAKOSHI
Article type: Article
Session ID: 1619
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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It is known that the low frequency fluctuation about 1/20 of the Strouhal frequency exists in the wake behind a two-dimensional circular cylinder. However it's origination is not known yet. Local vortex shedding frequency in spanwise direction is considered to differ from one point to another due to different local Strouhal number caused by flow tree-dimensionality. Therefore, interaction between the different vortex shedding frequencies is considered to be the cause of the long time scale fluctuation. In this study, two different vortex shedding frequencies have been forced to occur at a local spanwise position with the use of a circular cylinder with step and particular phase difference TSC (Trans-Spectral Coherence) analysis was conducted to investigate the presence of nonlinear interaction in the wake. Moreover, by means of flow visualization, it is found that the interaction is caused by the formation of longitudinal vortex associated with vortex dislocation.
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Takatoshi NAKATANI, Hiroyuki HANIU, Katsumi MIYAKOSHI
Article type: Article
Session ID: 1620
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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When two circular cylinders of different diameter are placed side by side in a uniform flow, fluctuating fluid forces acting on them vary with the spacing between them. And at very small spacing, switching phenomena are observed. In this study, transitional characteristics of the switching phenomena are investigated by statistical analysis of localized average and localized standard deviation of fluctuating signal of lift acting on the circular cylinder of larger diameter.
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Shigehira OZONO, [in Japanese], Takejiro ICHIKI
Article type: Article
Session ID: 1621
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The flow around rectangular cylinders (depth, d; height, h) placed in linear shear is investigated experimentally. A wide range of shear is realized using a wind tunnel of multi-fan type, where a column of fans are driven independently. The base pressure for d/h = 0.2〜2.0 increases with a shear parameter. Particularly for d/h < 0.6, the base pressure is sensitive to the shear parameter.
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Masaki FUCHIWAKI, Tomoe ODA, Kazuhiro TANAKA
Article type: Article
Session ID: 1622
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The dynamic thrust acting on a heaving airfoil, NACA0010 has been measured by using a six-axes sensor in a water tunnel at low Reynolds number region under the condition of various heaving frequencies and amplitudes. The dynamic thrust depends on the non-dimensional heaving velocity strongly and does not depend on the non-dimensional heaving amplitude. The averaged dynamic thrust during one heaving cycle increases as the non-dimensional heaving velocity increases. The hysteresis loop of dynamic thrust has convex shape characteristics and the dynamic thrust is maximum at the non-dimensional heaving amplitude h = 0.0. The thrust efficiency of heaving airfoil is about 20 % at the non-dimensional heaving velocity V_h = 0.4.
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Masaki FUCHIWAKI, Kazuhiro TANAKA
Article type: Article
Session ID: 1623
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Many studies on unsteady flow behind an unsteady airfoil have been carried out with experimental and numerical approaches. However, the detailed vortex structure has not been understood sufficiently. In order to clarify the quantitative vortex structure behind pitching and heaving airfoils at low Reynolds number region, we have carried out the particle image velocimetry (PIV) measurement at Re = 4000. The thrust producing vortex street was formed behind pitching airfoil with high non-dimensional trailing edge velocity and heaving airfoil with high non-dimensional heaving velocity. The vorticity in the thrust producing vortex street of heaving airfoil was higher than that of pitching airfoil. As a result, velocity profile in the wake of heaving airfoil was larger than that of pitching airfoil. The maximum velocity in the wake increases as the non-dimensional trailing edge velocity and non-dimensional heaving velocity increases.
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Hiroyuki ABE, Takehiko SEGAWA, Yoshihiro KIKUSHIMA, Hiro YOSHIDA
Article type: Article
Session ID: 1624
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Solid (fin) type vortex generators are known to be effective on suppressing flow separations and widely used at various fluid mechanical elements such as intakes or airfoils of airplanes. But the solid type generators themselves are the cause of extra flow drag. In this study we designed a blowing jet type vortex generator to realize smart control of flow separation. The present vortex generators are consisted of small orifices. The airfoil MEL001 installed the vortex generators was recognized improvement of lift at low Reynolds number.
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Ken-ichi FUNAZAKI, Kazutoyo YAMADA, Nobuaki AKAHIRA, Takahiro OTSUKI
Article type: Article
Session ID: 1625
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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This study deals with the investigation of bypass transition process of a flat-plate boundary layer that is subjected to periodic sphere wake passage as an external disturbance. Air-injection type of disturbance is also applied, whose results are then to be compared with those of the sphere wake case. Wall suction is employed to change boundary layer characteristics, seeking for a possibility for the method to control wake-induced boundary layer transition.
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Seiichiro IZAWA, Takeshi SAKAI, Ao-Kui XIONG, Yu FUKUNISHI
Article type: Article
Session ID: 1626
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Semi-automatic feedback and active control of TS waves and oblique waves of a transitional flat-plate boundary layer is carried out using an array of thin piezo-ceramic actuators. The actuators are designed to generate counter waves that cancel the incoming instability waves. The amplitudes and the phases of the actuators are determined based on the velocity fluctuations measured downstream by hotwire sensors. It shown that the system is capable of weakening the TS waves and the oblique waves of small sweep angles.
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Michio NISHIKAWA, Yutaka HASEGAWA, Koji KIKUYAMA, Hirokazu ITO, Ryoich ...
Article type: Article
Session ID: 1627
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The purpose of the present study is to clarify the effects of T-S type instability on the boundary layer developing along the convex surface experimentally and numerically, focusing on transition process from laminar to turbulent state in the rotating system with streamline curvature. The longitudinal velocity and turbulent intensity have been measured near the convex surface whose radius of curvature is 1000mm. When the Coriolis force acts away from the convex wall, the primary instability of T-S instability is enhanced.
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Kouki Murakami, Takehiko Segawa, Hiroshi Mizunuma
Article type: Article
Session ID: 1628
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Measurements of total skin-friction drag by a fiber Bragg grating system (FBG), local velocity distributions by a particle image velocimeter (PIV) and local shear stress distributions by a shear stress sensor downstream of an actuator array using alterative suction and blowing jets was carried out to confirm the drag reducing effect. Ensemble averages of velocity distributions in the x-y plane using PIV were analyzed at various sensor positions in the spanwise direction for the fixed phase of the piston. Slight changes in the velocity profile in the vicinity of the wall, where skin-friction drag may be reduced, were found at several positions of measurement.
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Akihiro KOJIMA, Motoyuki ITOH, Shinji TAMANO, Kazuhiko YOKOTA
Article type: Article
Session ID: 1629
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The influence of a drag-reducing surfactant on a turbulent boundary layer was investigated using a PIV system. PIV measurements were made for a momentum thickness Reynolds number, Re_0(= U_eθ/ν)= 480, where U_e, θ and ν are the free-stream velocity, momentum thickness and kinematic viscosity, respectively. Results of PIV measurement agreed well with those of LDV. PIV measurements showed that the streamwise and wall-normal turbulence intensities and Reynolds shear stress of the surfactant solution were smaller than those of water, respectively, as well as LDV measurements. Fluctuating velocity vector fields of the surfactant solution indicated that there was few near-wall coherent structures as in the case of the canonical wall-bounded turbulent flow.
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Ryo IGUCHI, Motoyuki ITOH, Shinji TAMANO, Kazuhiko YOKOTA, Norio AKINO
Article type: Article
Session ID: 1630
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The purpose of this research is to develop a new technique for the turbulent drag reduction as the passive control. The pressure loss of three kinds of seal fur (Ribbon, Spotted and Harp seals) and an electret nonwoven fabric surfaces was measured in the channel flow using the water and glycerol-water (40 wt%). The data was compared with those of smooth and riblet surface. The drag reduction could be obtained for all kinds of seal fur surfaces; it was estimated to be 11.5 % on ribbon seal, 9.5 % on spotted seal and 3.5 % on harp seal for glycerol-water, while the drag reduction was not achieved for the electret nonwoven fabric surface.
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Toshihiro TAKAMI, Yoshinori KITA, Hiroshi MIYANAGA, Takuya OHSAKI
Article type: Article
Session ID: 1636
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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An unsteady behavior of wall-drag is experimentally investigated in the unsteady turbulent pipe flow, under several flow conditions with a rapid to slow time-variation and a moderate to large distortion of the flow-rate imposed stepwise.
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Kouichi YAMAGATA, Kouta HIRAKAWA, Takashi NAGUMO, Shinji HONAMI
Article type: Article
Session ID: 1637
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The paper presents the flow mechanism of a reattachment process over a backward facing step, which is controlled by vortex generator jets (VGJs). The injection of VGJ upstream of the step introduces the co-rotating longitudinal vortices in a separating shear layer. VGJ produces a primary and secondary vortex. The detailed structure of the longitudinal vortices is clarified, and the effect of the vortices on the separating shear layer downstream of the step is observed. The influence of the velocity ratio and the injection pitch on the flow mechanism is also discussed.
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Masatoshi SANO, Hiroki ENDO, Kenichiro SAKURABA
Article type: Article
Session ID: 1638
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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A turbulent channel flow over a backward-facing step is investigated experimentally. In earlier paper, the authors reported that enhancement of the heat transfer was attained by suction through a slit at the bottom corner of the step. In this case, suction was made horizontal direction to the main flow. In present study, the direction of suction is changed from horizontal to perpendicular. The suction flow ratio is varied from 0.00 to 0.15. The wall static pressure and local heat transfer coefficient are measured behind the backward-facing step. The wall shear stress is measured using the micro flow sensor. The heat transfer characteristic is improved in the way of perpendicular suction as compared with horizontal suction. When the suction flow ratio is 0.05, the highest performance is obtained.
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Masatoshi SANO, Masayuki KUBOTA, Tomohiro SUZUKI
Article type: Article
Session ID: 1639
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Experiments have been performed for a turbulent channel flow obstructed with a triangular cylinder. The triangular cylinder of four kinds of different angles is used. In this study, the particle image velocimetry (PIV) has been applied to measure the flow field. The data processing is performed by means of the phase-averaging, so that the periodic motion associated with the vortex shedding from the triangular cylinder is extracted. It is found that large-scale vortices have a major role on the enhancement of the heat transfer coefficient.
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Hiroshi KURIHARA, Daisuke SUGIZAKI, Takashi NAGUMO, Shinji HONAMI
Article type: Article
Session ID: 1640
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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In order to establish the dynamic control system of turbulent heat transfer using active vortex generators (AVGs), it is necessary to understand heat transfer and flow behavior of longitudinal vortices generated by AVGs. In this study, we measure surface temperatures on the heated wall by thermochromic liquid crystal sheets. The neural network method is applied to conversion of the colors of the liquid crystal sheet images into the temperatures. The AVG is characterized by the angle of attack and the driving cycle. It is found that longitudinal vortices generated by the AVGs enhance the heat transfer through downwash motion toward the wall.
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Yoshihiro INOUE, Akira YASUDA, Shintaro YAMASHITA
Article type: Article
Session ID: 1641
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Flow-induced cavity noise has been investigated for a wall jet over an axisymmetric cavity. Aspect ratio of the cavity width to its height was varied from 0.5 to 1.5. Also, there exists another geometric parameter, that is, a thickness of the wall jet. In the present study, the thickness can be easily changed by movement of the axisymmetric cavity in the axial direction. Experimental results indicate that in a thinner wall jet the 2nd mode of the self-sustained oscillation is dominant, and that the dominant mode is in transition as its thickness increasing.
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Seizou HASEGAWA, Shinzaburo UMEDA, Wen-Jei YANG
Article type: Article
Session ID: 1642
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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In order to promote applications and development of flip-flop flow, its quantitative explanation of interaction between the intersecting main streams and wake flow in the diverging-flow region of the flow passages is definitely needed. An experimental study was performed to investigate flow characteristics in the diverging-flow region inside a single diamond-shaped cylinder and diamond-shaped cylinder bundles by means of two-dimensional laser Doppler velocimetry (LDV). The oscillation characteristics of the flip-flop are clarified. The difference between the oscillations of von Karman vortex streets and the flip-flop flow is also disclosed.
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Hideki HIBARA, Toshiharu MURAMATSU, Junji OCHI, Yukiharu IWAMOTO
Article type: Article
Session ID: 1643
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Visualization by the dye injection method and velocity measurements are carried out in a T-junction piping system with turbulent promoter under the isothermal condition, and the behavior of main and branch pipe flow is examined experimentally. As a result, it is clarified that secondary streams in pipe sections becomes stronger and diffusion of momentum is promoted in case with turbulent promoter.
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Osamu TERASHIMA, Takashi KANEKO, Seiichiro IZAWA, Ao-kui XIONG, Yu FUK ...
Article type: Article
Session ID: 1644
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Two-liquids mixing in a millimeter-scale channel under periodical forcing was simulated by the Lattice Boltzmann Method (LBM) for the purpose of investigating the optimumshape of the channel. The density patterns obtained by solving the advection-diffusion equation agreed with the experimental data. It is also found that the temporal and spatial average of density deviation at outlet region is useful to evaluate the mixing level.
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Shin OBA, Toshiaki KANEMOTO, Masaaki KATAYAMA
Article type: Article
Session ID: 1645
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Turbopumps have weak points, such as the pumping operation becomes unstable in the rising portion, of the head characteristic and/or the cavitation occurs under the low suction head. To overcome simultaneously the both weak points, the authors have proposed the unique pumping system with counter-rotating mechanism. In this paper, the front impeller speed was not as increase as expected that the actual performance than the theoretical performance predicted the previous paper. The cause was considered from the performance and the flow conditions using the trial model in the ideal and the actual rotation speed
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Yasuhiro SAITO, Yoshiyuki UCHIYAMA, Keiichi SATO
Article type: Article
Session ID: 1646
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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In actual flow fields, the cavitation takes the form of the cavitation cloud. It is known that the cavitation cloud causes high impact. The cavitation becomes a vortex type of cavitation cloud in the wake of an obstacle such as a circular cylinder. In this study, collapsing behaviors of cavitation clouds in the wake of a circular cylinder are investigated using a high-speed video camera or a digital still camera. An impulsive pulse acts as a trigger of those observations. In the case of observations using the still camera, double-exposure photographs of cavity behaviors are taken using blue and red flashes.
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Masashi Fukaya, Yoshiaki Tamura, Yoichiro Matsumoto, Tomoyoshi Okamura ...
Article type: Article
Session ID: 1647
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The prediction of cavitation erosion by using numerical flow simulation is necessary for designing small high-speed pumps. This erosion is closely related to the bubble dynamics near the solid surfaces such as impeller blades and casing walls. We developed a new numerical simulation code for investigating bubble behavior in a centrifugal pump. We simulated distributions of the bubble number density, the bubble size and the bubble pressure, which were close to the impeller blade. The numerical results were consistent and revealed a potential of this code to predict flow and bubble behavior under the cavitation erosion conditions in a pump.
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Naohiro ABIKO, Hirofumi SUGAWARA, Ryu EGASHIRA, Takeru YANO, Shigeo FU ...
Article type: Article
Session ID: 1648
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The two-phase bubbly flow in a Laval nozzle is numerically studied with a two-fluid and three-pressure model of averaged equations for two-phase bubbly flow. The governing equations are extended to quasi-one-dimensional flows, and solved with MacCormack scheme. As a result of numerical simulation of subsonic bubbly flow in a Laval nozzle, the distributions of pressure, flow velocity, density and volume fraction rate in each phase are clarified.
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Kazuyoshi KONDOU, Mitio HAYAKAWA, Takeru YANO, Shigeo FUJIKAWA
Article type: Article
Session ID: 1649
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Cavitation generated by submerged water jet can decompose and oxidize organic compounds in water. In this paper, we report the development of a new submerged water jet system, which is capable of oxidizing and decomposing organic compounds by cavitating water jet discharged through a specially devised nozzle with discharge presuure of at most 0.6 MPa. The nozzle consists of a converging part and a diverging part, and chemical reactions take place within cavitation bubbles in the diverging part, where cavitation is initiated by a number of micro air bubbles injected upstream. We use an aqueous solution of indigo carmine as a test liquid, and concentration is measured using a colorimeter. The aqueous solution is kept at the temparature of about 40℃ during experiments.
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Masato Hamada, Satoshi Shishikura, Takayuki Usui, Hiroharu Kato
Article type: Article
Session ID: 1650
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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When microbubbles are injected into turbulent boundary layer, the frictional resistance is reduced. The effect of bubble size is one of the important parameters. The bubble size is changed by adding surfactant, 3-pentanol, to water. The reduction is greater on the upper wall than on the lower wall. But the bubble size is smaller, the reduction on the upper wall is smaller than that without 3-pentanol and the reduction on the lower wall is larger. In other words, the difference in the reduction between upper and lower walls becomes smaller. This phenomenon is explained by the buoyancy force and turbulence diffusion. Further, the local velocity and turbulence intensity distributions were measured using a laser doppler velocimeter. The turbulence intensity increased when microbubbles existed in the turbulent core, whereas, the turbulence intensity decreased when microbubbles existed in the near-wall region.
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Toshiyuki SANADA, Ayaka SATO, Masao WATANABE, Tohru FUKANO
Article type: Article
Session ID: 1651
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Effects of liquid viscosity on the coalescence of a pair of bubbles were experimentally studied by generating nitrogen gas bubbles in a pool filled with silicon oil. We focused on two types of coalescence/bouncing of bubbles, i.e., those between a rising bubble and a free surface, and between a pair of bubbles rising side by side. The former is considered as the extreme case, which is equivalent to coalescence/bouncing between bubbles with finite and infinite diameters. The later is more practical. That is, bubbles were generated simultaneously from a pair of pin-holes on a pipe horizontally placed. We studied the viscosity effects on coalescence of bubbles by investigating the behavior of bubbles with both liquid viscosity and bubble diameter as the parameters. Previous studies reported that We number based on approach velocity could predict whether two bubbles would bounce or coalesce in superpurified water. Our experimental results show that the threshold in the case of low viscosity liquid indicates the same order as the one in the case of superpurified water. On the other hand, in the case of a large viscosity liquid, the threshold differs significantly from the one in the superpurified water.
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Hiroyuki TAKAHIRA, Tomonori HORIUCHI
Article type: Article
Session ID: 1652
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Two numerical algorithms are introduced for the reinitialization procedure of the distance function in the level set method for gas-liquid two-phase flows. One algorithm is based on the reinitialization procedure with constraints proposed by Takahira et al.; the other is the adaptive version of the former algorithm. Both-algorithms are used to improve the mass conservation of two fluids. Numerical tests are performed for the three-dimensional merger of two rising bubbles to evaluate mass conservation for the present algorithms. It is shown that the present algorithms work very well even for a density ratio of the two fluids of 1:1000. It is also shown that the volume conservation (i.e., mass conservation) of bubbles is very good even after bubble merger.
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Masao WATANABE, Toshiyuki SANADA
Article type: Article
Session ID: 1653
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Behavior and shapes of a pair of bubbles rising in a viscous liquid were numerically analyzed by using DSD/ST (Deforming-Spatial-Domain/Space-Time) Finite Element Method in the cylindrical coordinate system. It has been predicted by the analytical and numerical studies that the trailing bubble approaches the leading bubble and then a pair of bubbles rising in the vertical line keeps the mutual equilibrium distance. However, no experimental results have ever confirmed the existence of the equilibrium distance between a pair of bubbles. In this study, we investigated the effects of bubble deformation on behavior of a pair of bubbles rising in line. We clarified that a pair of deformable bubbles reaches an equilibrium distance and the equilibrium distance is considerably unstable.
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Minori SHIROTA, Tomohiro IMAMURA, Masaharu KAMEDA
Article type: Article
Session ID: 1654
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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A new experimental technique to produce single small gas bubbles from an orifice without a bulk liquid flow is developed. Pulsed acoustic wave is exposed to bubbles growing from an orifice. Bubble formation process is recorded by high-speed photography. Under an acoustic field, bubbles are forced to deform to be elongated upward due to high gas momentum blown from the orifice. The upward elongation contributes to lift up the center of mass of bubble, and the bubble is forced to detach from the orifice. The sizes of the detached bubbles are controllable with varying the triggering point of the acoustic wave excitation. Finally, we obtained single small bubbles ranging from about 0.05 mm to 0.2 mm in radius.
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Yukio TOMITA, Tatsuya SAITO
Article type: Article
Session ID: 1655
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Drop impact on a free surface can be followed by the entrainment of air bubbles, causing underwater sounds. It is known that there are three types of mechanisms associated with bubble sounds for the irregular bubble entrainment region. Although the first bubble sound is well recognized, relevant to the oscillation of an air bubble formed by the impact of a satellite droplet with the rising free surface, we have less knowledge about the mechanism of the second bubble sound which has often been used as the sound source of Suikinkutsu, a Japanese traditional musical instrument. In this paper we focus on exploring the mechanism of the second bubble sound due to the surface closure during the falling process of a water column into the water.
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Yoshinori MURASE, Hiroyuki TAKAHIRA
Article type: Article
Session ID: 1656
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The numerical method developed by Yasuda and Takahira has been improved to consider the real gas effect on the motion of a nonspherical collapsing bubble. The van der Waals equation of state is used for the internal gas in dealing with the real gas effect. The heat transfer of the internal gas and the toroidal bubble dynamics after microjet impact are taken into account in the method. The present method is applied to the collapse of a bubble near a rigid boundary in an oscillatory pressure field. The collapse of a toroidal bubble has been simulated successfully. It is shown that the real gas effect does not appear clearly because of the moderate bubble collapse.
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Shigeki YAMAMOTO, Rumi KONISHI, Mitsuhiro MATSUMOTO
Article type: Article
Session ID: 1657
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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When cavitation bubbles collapse violently, local high-temperature high-pressure spots are generated, which can be used for various chemical reactions, i.e., sonochemistry. It is necessary to control a sound field in order to generate these spots efficiently. We report two experimental studies: (1) Observation of a single bubble dynamics in ultrasonic field using a stroboscope and light scattering technique. (2) Amplitude and frequency dependence of the reaction rate of a model chemical reaction with multi bubble conditions.
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Tomoaki TAKATSUKI, Shigeo FUJIKAWA, Takeru YANO, Michio HAYAKAWA
Article type: Article
Session ID: 1658
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The present study aims at developing another method instead of toothbrush for removing dental plaque on teeth. The method is based on large pressure fluctuations from a cluster of micro air-bubbles, which is excited by ultrasound. The excitation condition concerning size of micro bubbles, number of micro bubbles, size of cluster, etc. is derived by a theoretical analysis. Experiments on pressure fluctuation measurement and artificial dental plaque removal are also made.
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Mitsuo MURAOKA, Mitsuhiro MATSUMOTO
Article type: Article
Session ID: 1659
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Molecular dynamics simulations of CO_2-watef-electrolyte systems were carried out to investigate the mechanism of CO_2 gas absorption by aqueous solutions. The CO_2 model developed by Murthy and Singer was found to have much less solubility than experiments. The mass transfer coefficient of the model was almost independent of the salt concentration. To reproduce solubility, the Lennard-Jones potential parameter between water and CO_2 is being tuned.
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Tatsuya ISHIYAMA, Takeru YANO, Shigeo FUJIKAWA
Article type: Article
Session ID: 1660
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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We consider the functional form of the boundary condition for the Boltzmann equation (kinetic boundary condition) at an interface between a vapor and its condensed phase on the basis the of nonequilibrium molecular dynamics simulation. The molecular dynamics system treated here consists of two parallel condensed phases with different tempreratures and the vapor between them. We examine the velocity distribution function of molecules outgoing from the condensed phase in the above system, and thereby we establish a physically appropriate form of kinetic boundary condition at the interface.
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Hisao YAGUCHI, Tatsuya ISHIYAMA, Takeru YANO, Shigeo FUJIKAWA
Article type: Article
Session ID: 1661
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Molecular dynamics simulations of equilibrium state of argon vapor and its own spherical droplet are executed to investigate molecular processes of evaporation and condensation at the vapor-droplet interface. Equilibrium states at about 90K are computed for droplet radii raging from about 14Å to 42Å. Results show that outgoing and incoming molecular fluxes through a sphere enclosing a droplet increase with the decrease in the droplet radius. The equilibrium vapor pressure and density also become large as the droplet radius becomes small.
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Kazumichi KOBAYASHI, Takeru YANO, Shigeo FUJIKAWA
Article type: Article
Session ID: 1662
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Numerical analysis is performed for a normal shock wave in a polyatomic molecule gas based on molecular gas dynamics, where the polyatomic gas is taken to be nitrogen. We adopt the polyatomic version of Gaussian-BGK Boltzmann equation for nitrogen gas and it is solved numerically with a finite difference method. The results agree well with the experimental results by Robben and Talbot (1966) at the shock Mach number 1.71. Furthermore, we examine the transition of rotational energy in the shock wave in terms of velocity distribution functions.
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Tatsuki OTA, Satoru MIKAMI, Sigeo FUJIKAWA, Takeru YANO, Makoto ICHIJO
Article type: Article
Session ID: 1663
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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This paper is concerned with nonequilibrium condensation of methanol vapor on the plane end wall of a shock tube behind a reflected shock wave. The thickness of a liquid film formed on the endwall is measured by an optical method and it is compared with numerical simulations based on Gaussian-BGK Boltzmann equation. The condensation coefficient is determined in a wide range of thermodynamic nonequilibrium conditions of the vapor at the vapor-liquid interface. It is found that the condensation coefficient is decrease with the increase of the pressure ratio that is defined as the ratio of a vapor pressure to a saturated vapor pressure.
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Shugo YASUDA, Shigeru TAKATA, Kazuo AOKI
Article type: Article
Session ID: 1664
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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Half-space problem of evaporation and condensation of a binary mixture of vapors is investigated on the basis of the linearized Boltzmann equation for hard-sphere molecules with the complete condensation condition. The problem is analyzed numerically by a finite-difference method, in which the complicated collision integrals are computed by the extension of the method proposed by Sone, Ohwada, and Aoki [Phys. Fluids A 1, 363 (1989)] to the case of a gas mixture. As a result, the behavior of the mixture is clarified not only at the level of the macroscopic quantities but also at the level of the velocity distribution function. In addition, accurate formulas of the temperature, pressure, and concentration jumps caused by the evaporation or condensation are constructed for arbitrary values of the concentration of a component gas by the use of the Chebyshev polynomial approximation.
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Takahiro YASUDA, Ryo TSUKUBA, Yasunari TAKANO
Article type: Article
Session ID: 1701
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The flow around and the mechanism of unsteady fluid-dynamic forces acting on an auto-rotating elliptic cylinder were investigated by the experiment using wind tunnel and the two-dimensional numerical simulation. The visualization of flow around the auto-rotating cylinder were carried out by the same rotating frequency and falling velocity as the auto-rotating cylinder. The validity of the computation was confirmed through the comparison with the experimental result. The time variation of the vortex shedding from the cylinder was shown by computational results and it was found that at -110 degree, the three vortices exist in the wake of the cylinder. The drag and lift coefficients acting on the cylinder were estimated by both the numerical result and complex velocity potential theory. It was also found that the phenomenon of the lift coefficient at 0 degree are caused by the effect of the rotation of the cylinder.
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Kimiyoshi TAKADA, Toru KOMORIYA, Takumi HASEGAWA, Kazuhiro KAMINAGA
Article type: Article
Session ID: 1702
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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We are studying an aerodynamic characteristics of a windshield wiper in high-speed traveling. As the 1st step of this study, the numerical flow simulation was carried out using fixed wiper on a windshield. Zooming analysis technique was applied in this simulation. Flow visualization around the wiper was executed .by an oil-flaw method. As a result of comparing experiments and calculations, both flow patterns around the wiper agreed roughly.
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Katsuichi YAMAMOTO, Juetsu KUROSAWA
Article type: Article
Session ID: 1703
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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A simplified numerical simulation model is constructed for the purpose of studying the flow around the reed valve in the automotive air conditioning compressor. The Fluid-Structure Interactive Method is used. The model is investigated whether it is possible to know the difference of the valve performance in case of using the new rigidity or configuration. The constant coefficient is adapted to control the lubricant oil reaction force that acts at the occasion when the valve leaves from the contact surface of the seat. This work shows the benefit of the constant coefficient at the limited pressure conditions and the difference of the available conditions for the suction side and discharge.
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Masamichi NAKAGAWA, Takashi YABE, Ryozo YAMAMOTO, Masaya MISAKI
Article type: Article
Session ID: 1704
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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The effects of dimples on a golf ball surface are known as the results of boundary layer control; (1) drag reduction, (2) lift production in back-spinning, and (3) trajectory stabilization. The present paper describes the effect of (2) lift production mentioned above. We analyzed its aerodynamics theoretically, measured both coefficients of drag and lift simultaneously for model dimpled spheres using the wind tunnel, visualized the flow field around each model sphere by the smoke wire method, and investigated the characteristics of lift production dependent on the back-spin speed. We verified that a smooth sphere produces the negative lift, in low back-spin speed, and that the dimples make the lift positive always. Hence asymmetric separations determine the descent angle of wake. We also found that the coefficient of lift measured is proportional to the descent angle of wake visualized, same as the result of our analysis.
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Shinichi TAKAYAMA, Takuya SHIMADA, Katsumi AOKI
Article type: Article
Session ID: 1705
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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This paper describes flow characteristics around rotating circular cylinder with arc grooves. In this study, thirty-two arc grooves set on die cylinder surface, and the groove depth changes to three types. The pressure of cylinder surface is measured, and the wake of the circular cylinder with grooves is measured by hot-wire anemometer. The drag and lift coefficients are calculation from this pressure distribution. In the case of smooth cylinder, the drag coefficient and the lift coefficient decreases at α=0.3 in Re=1.2×10^5, and the lift coefficient has negative value at α=0.5. In the case of circular cylinder with grooves, the drag coefficient increases as α increases, and the lift coefficient increases monotonously, too. As grooves depth becomes deeper, the drag coefficient does not influence for α increases, and the increasing inclination of the lift coefficient becomes small. These phenomena have a connection with the change of Karman vortex range.
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Kazuo MATSUUCHI
Article type: Article
Session ID: 1706
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
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We numerically investigated the flow force exerted on an object with respect to the generation of high dynamic lift when vortices are in motion. Virtual momentum plays a crucial role on the generation of unsteady forces and the time derivative of the distance between vortices determines the force.
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