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Sayaka YOSHIMURA, Takahiro YASUDA, Yasunari TAKANO
Article type: Article
Session ID: 203
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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When a thin flat plate is released in still air, the plate automatically sets into a rotational motion. This phenomenon is called autorotation. In this state, it is supposed that vortex shedding and unsteady fluid-dynamic forces interact each other. In this study, a discrete vortex method is used to found the effect of the vortex shedding on fluid dynamic forces acting on an auto rotating elliptic cylinder. By the calculation, it was found that the vortex shedding from the cylinder affects the fluid dynamic forces especially at the phases from -45 to -180 degree for drag coefficient and from -15 to -140 degree for lift coefficient.
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Masanori MATSUMURA, Syunsuke WATANABE
Article type: Article
Session ID: 204
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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The purpose of this investigation is to clarify the effects of the splitter plate in the wake of a bluff body. The base pressure of a body that generates the wake and the fluctuating velocity vector in the wake were measured under the many conditions of plate location and width. As the result of this study, it was found that the base pressure and the Reynolds shear stress can be controlled by the splitter plate, and there is an optimum condition to reduce the drag of a body and to increase the Reynolds shear stress in the wake.
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Yoshihiro INOUE, Junichi FUJITA, Yoshimasa YAMADA, Shintaro YAMASHITA
Article type: Article
Session ID: 205
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Wakes behind a circular cylinder have been investigated by velocity profile measurements using the ultrasonic Doppler method. Experiments were performed in a free-surface water channel within the Re_d range of 250 to 800 at a rotational speed ratio of U*_c=0 and 1.25, and fluctuating velocity fields, v(y, t), were measured. Changes in the deflection amount and width of the separated shear layer are indicated from intensity distributions of velocity fluctuation. According to the analysis based on the POD, it is clarified that the present flow fields may be represented by the reduced order model of the vortex structure. Integral of v(y, t) with respect to y is related with the averaged vorticity, and its time history indicates a stability of vortex shedding mode.
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Takamasa KONDO, Michihisa TSUTAHARA, Kazumasa MOCHIZUKI
Article type: Article
Session ID: 206
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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The acoustic waves emitted from various objects have been simulated by the Finite Difference Lattice Boltzmann Method (FDLBM) using a two-dimensional thermal compressible lattice BGK model. We have obtained same accurate results of the acoustic waves by this method. FDLBM, however, requires structured grids, so we have only used this grid style in same cases. But, for the complex flow field, unstructured grids should be used. In this paper, the acoustic waves emitted from a circular cylinder simulated by the Finite Volume Lattice Boltzmann Method (FVLBM) using a two-dimensional thermal compressible lattice BGK model, in unstructured grids. We clarified that the acoustic waves can be calculated directly by this FVLBM model in unstructured grids.
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Michihisa TSUTAHARA, Akinori TAMURA
Article type: Article
Session ID: 207
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Direct simulation of aero-acoustic waves has been successfully simulated by the finite difference lattice Boltzmann method (FDLBM). So far the sound waves emitted from a stationary body, such as the Aeolian tone or edge tone, but more demands are expected for direct simulation of aero-acoustic waves emitted from moving bodies, especially, rotating bodies such as fans and rotors. Then we proposed the FDLBM with the arbitrary Lagrangian Eulerian (ALE) formulation. In this report, we simulated the acoustic waves emitted from three-dimensional rotor by the FDLBM with the ALE formulation, and good result is obtained.
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Yusuke MIZUTANI, Masato YOSHINO
Article type: Article
Session ID: 208
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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The lattice Boltzmann method for two-phase immiscible fluids with large density differences proposed by Inamuro et al. [J. Comput. Phys., 198(2004), 628-644] is applied to the problem of liquid-gas flows through solid bodies in a square duct. Considering wetting dynamics of solid walls by liquid-gas fluids, the boundary condition followed by the Cahn theory is introduced on the walls. We first investigate the characteristics of wettability in terms of a contact angle between the liquid-gas interface and the wall. After confirming the validity of the method, we next carry out the simulations of liquid-gas rising flows through solid bodies in a square duct. It is found from these simulations that the present method can be useful for the problems of multiphase flows through complicated geometries.
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Takeshi SETA, Kenichi OKUI, Eisyun TAKEGOSHI
Article type: Article
Session ID: 209
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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The lattice Boltzmann method (LBM) is adopted to simulate natural convection in porous media at the representative elementary volume (REV) scale. The influence of porous media is considered by including the porosity into the equilibrium distribution function and by adding a force term to the evolution equation. The temperature field is simulated by a simplified thermal energy distribution function which neglects the compression work done by the pressure and the viscous heat dissipation. A comprehensive parametric study of natural convective flows is carried out for various values of Rayleigh number (Ra), of Darcy number (Da), and of porosity (ε). The results of the LBM indicate that the average Nusselt number (Nu) increases with the fluid Rayleigh number, the Darcy number, or the porosity of the medium. The comparison with those of earlier studies shows good quantitative agreement for the whole range of Darcy and Rayleigh numbers. It is reasonably concluded that the lattice Boltzmann method may have applicability to simulate natural convection in porous media.
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Yuichi HIROKAWA, Teruo MATSUZAWA
Article type: Article
Session ID: 210
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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We have proposed the Mixture Multi-component Extension (MME), which is a modification of the Lattice Boltzmann Method (LBM), to expand single-component LBM models to miscible multi-component LBM models. The advantages of this modification include flexible application to various LBM models, and analysis of molecular diffusion and convection of each component simultaneously. In this paper, we show a modification of MME in order to simulate chemical reaction, and an example of thermal reactive miscible multi-component flow by MME.
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Kazutoyo YAMADA, Ken-ichi FUNAZAKI, Jun OGASAWARA
Article type: Article
Session ID: 211
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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The present work is an attempt to apply Lattice Boltzmann Method (LBM) to simulation of the separated flow in turbomachinery. The test model, with a semi-circular leading edge and two flat plates, was used to investigate the details of separation/reattachment of boundary layer seen in turbomachinery. The result of LBM was compared with those of experiment and LES. In both LBM and LES, the separation bubble was overestimated compared with that in experiment. However, the separation bubble in LBM result was smaller than in LES, although both schemes have same-order accuracy in space, and was close to the experimental one.
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Kangbin LEI
Article type: Article
Session ID: 212
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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The Cartesian gird method has been used to simulate the 3D flows around arbitrary geometry. In the Cartesian gird method, the cut cell approach is employed to improve the accuracy in representing the complicated object boundary. However, the detailed discretizations of the Cut Cell method for 3D simulation of incompressible viscous flows were scarcely reported. In this study, a 3D cut cell method for viscous incompressible flows is developed based on the VCAD (Volume-CAD) data system, and the numerical discretizations on the 3D cut cell boundaries and some calculation results are shown.
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Guanghao WU, Binghu PIAO, Shigeaki KURODA
Article type: Article
Session ID: 213
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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This paper describes a Cartesian grid method with cut cells for the calculation of incompressible viscous flows with moving physical boundaries. In this method, no cell merging technique is required in the conventional sense. Only pressure component on small cut cells is calculated directly. The code is developed based on Fractional Step Method on Finite Volume Method. In time integration, the second order explicit Adams-Bashforth method is used for the convective terms and second order implicit Crank-Nicholson method is used for the diffusive terms. Moving boundaries are accommodated by up-dating the local cut cell information on a stationary background mesh as the boundaries move. The code is tested on an oscillating circle cylinder and compared with other previous numerical results.
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Binghu Piao, Shigeaki Kuroda
Article type: Article
Session ID: 214
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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In this paper, a mass conservative overset grid method is developed for simulating unsteady, incompressible flows. The governing equations are solved using a second-order accurate, finite volume method based on fractional step method. A direct interpolation algorithm is used to exchange variables between two grid systems. The algorithm satisfies global and local mass conservation in each grid. The present method is used to solve flow around a circular cylinder, cavity flow, channel flow, and fairly good results are obtained.
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Shinsuke Tajiri, Michihisa Tsutahara, Masahiko Sakamoto, Masakazu Taji ...
Article type: Article
Session ID: 215
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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We have analyzed the flow in the semi-open-type nozzle for ship driven by high-pressure gas experimentally. We proposed a new finite difference lattice Boltzmann model which allows us to consider the immiscible two-phase and the different density of two fluids for numerical analysis of flow in the nozzle. We also demonstrate that this new model works well. The surface tension model was satisfied with Laplace s law. Two-dimensional cavity flows with proposed finite different lattice Boltzmann model for the different density is calculated and compared to the result by the Finite Difference Method.
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Yoshinori MURASE, Hiroyuki TAKAHIRA
Article type: Article
Session ID: 216
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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We simulated the bubble collapse accompanied by the formation of liquid jet using the Boundary Element Method. We apply the smoothing technique to prevent numerical instability of the surface mesh. The curvature effect is taken into account in the smoothing of the grid points. We compare the present three-dimensional numerical results with the axisymmetric results. It is shown that present numerical results have sufficient agreement with the axisymmetric ones. It is also shown that present method is effective for the simulation of three-dimensional asymmetric bubbles.
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Shinya YUASA, Keisuke SHUTO, Hiroyuki TAKAHIRA
Article type: Article
Session ID: 217
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Using the Ghost Fluid Method for compressible two-phase flows in which one fluid is much stiffer than the other, the numerical oscillations occur near the interface. To prevent this problem, we suggested the modification of the value of the grid points near the interface using the one-dimensional Riemann solutions. We applied this method to the problem of water shock-cylindrical air bubble interaction. The results showed that the modification using the Riemann solutions improves the numerical stability of the Ghost Fluid Method. We succeeded in simulating the violent bubble collapse with good mass conservation.
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Noriaki TSUZUKI, Shunichi SATO, Takashi ABE
Article type: Article
Session ID: 218
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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The feasibility and design plans of a miniature rotorcraft for Mars exploration were studied from the standpoint of the aerodynamic characteristics of the rotor at the insect-scale low Reynolds number.
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Seiichi YOSHIDA, Hiromu HASHIMOTO
Article type: Article
Session ID: 219
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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This research work aims to develop the simulator of dragonfly's wing motion used for the observation of flow patterns around the wings under unsteady state conditions. As the first step, the lift and drag coefficient of dragonfly's wing are measured by changing the attack angle step by step, in which the selection of the range of attack angle is based on the high-speed video image of dragonfly's free flight. It is made clean the effect on the lift and drag coefficients experimentally.
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Seiichi YOSHIBA, Yuji YAMASHIRO, Hiromu HASHIMOTO
Article type: Article
Session ID: 220
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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This research work aims to develop the simulator of dragonfly's wing motion used for the observation of flow patterns around the wings under unsteady state conditions. As the second step, the lift and drag coefficient of artificial wing are measured by changing the attack angle step by step, in which the selection of the range of attack angle is based on the high-speed video image of dragonfly's free flight. The experimental resuts of artificial wings are compared with those of natural wings.
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Jun ISHIKAWA, Hiromu HASHIMOTO
Article type: Article
Session ID: 221
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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This research work aims to develop the simulator of dragonfly's sing motion used for the observation of flow patterns around the wings under unsteady state conditions. At the third step, the simulation mechanism modeling the natural wing motion is designed based on the measured and observed results. The flapping and feathering motions of the simulator are recorded by the high-speed video camera, and it is compared with the natural wing motion mentioned in the first report.
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Haruyoshi YAMASHITA, Takenori MATSUBARA, Muneshige OKUDE
Article type: Article
Session ID: 222
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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In order to improve the lift capability of the wing-in-ground effect craft, the experimental aerodynamic performances were conducted for the ground effect wings through setting the vortex generators. Its performances have been evaluated the higher lift enhancement by controlling the stall at the higher angles of attack even if falling behind at the lower them.
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Hiroto TANAKA, Kazunori HOSHINO, Kiyoshi MATSUMOTO, Isao SHIMOYAMA
Article type: Article
Session ID: 223
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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A butterfly-type ornithopter (BTO) was developed to investigate flapping flight of butterflies. The BTO has the same values of wing length, flapping frequency and wing loading as butterflies. It flew forward when its center of gravity was appropriate. Its longitudinal motion was measured with a high-speed video camera. We found that the angle of attack of the body axis, α_<body>, varied coincidentally with flapping motion. Periodical change of α_<body> in the flight of a real butterfly was also observed. To reveal the effect of the change of abody on the aerodynamics, we visualized the flow around the BTO both in tethered flight and in free flight. In tethered flights, leading edge vortex was attached to the wing during downstroke when α_<body> was 20°, but it separated from the wing when α_<body> was 40°. However, in a free flight, leading edge vortex was attached to the wing in spite of the large value of α_<body>, 50°, in the beginning of downstroke.
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Hiroshi Isshiki
Article type: Article
Session ID: 224
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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There are three kinds of MAVs (Micro Air Vehicles), namely, fixed, rotary and flapping wing planes. Each of them has the unique characteristics and may be used according to the mission. The development of the flapping wing planes is far behind the fixed and rotary wing planes. On the other hand, flying creatures such as birds and insects inspired the flapping foil planes to mimic the superior ability of flying creatures. Some kinds of birds and insects can migrate several thousands kilometers. And insects represented by a dragonfly show the outstanding motion performance. It's very valuable to develop MAV having very high motion performance such as flying insects. This may be the advantage of developing flapping foil planes to fixed and rotary wing planes.
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Keisuke OHIRA, Koji ISOGAI, Yuichi KAMISAWA, Takaaki YAMAMOTO
Article type: Article
Session ID: 225
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Possibility of human-powered ornithopter has been studied. As the first step, the optimum flapping motion, which attains the highest propulsive efficiency, has been determined using an unsteady lifting-surface theory. The performance of the flapping motion thus determined has also been examined using a Navier-Stokes code and a scale model, elucidating the problems to be solved for realizing the human-powered ornithoper.
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Yoshikata Muguruma
Article type: Article
Session ID: 226
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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This paper describes a new ornithoputer wing from beetle flying. Beetle has rigid wing and flexible wing. So, Our ornithoputer have rigid wing and two flexible wings that propelled by human power. This ornithoputer fly by the rigid wing and propel by the two flexible wings. Pilot ride and lie down on it then he begins to swim in the sky.
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Yoshinobu INADA, Hao WANG, Hao LIU
Article type: Article
Session ID: 227
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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The aerodynamic force acting on the flapping wing of insect like three-axis flapping robot "MOTH-1" was measured while it was moving in a hovering mode. Two flapping modes were used; one is the 1^<st> Fourier approximation of actual hovering motion and the other is its 3^<rd> Fourier approximation. Measured aerodynamic force of 3^<rd> Fourier approximation was larger than that of 1^<st> one, indicating the higher order oscillation in the 3^<rd> Fourier approximation exerted additional force on the wing. Thus, the higher order oscillation in the motion, especially in the feathering motion, may act as the enhancer of aerodynamic force by manipulating the angle of attack of flapping wing.
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Hitoshi MIYAKE, Hiroyuki SUNADA, Jun SHIRAHATA
Article type: Article
Session ID: 228
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Indirect flight mechanism of the insects is not cleared enough to recognize the multiplying mechanism of the wing fluttering frequency from the external skeleton's moving. This describes our approaches toward the mechanism by the structural and functional models
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Daisuke KONDO, Kenkichi OHBA
Article type: Article
Session ID: 230
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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The purpose of this study is to investigate flow pattern around mosquito's wing while it is beating. We constructed an experimental apparatus to simulate the beating motion of mosquito. An enlarged scale model experiment was carried out using a very low speed wind tunnel under the condition that Reynolds number and Strouhal number were made equal to those of real mosquito. The flow field around rectangular and realistic wing models moving up and down was visualized using smoke and laser light sheet and it was analyzed by a PIV system. It was observed that unsteady vortices were generated on the upper surface of the model wing in the period of downstroke. Further more, we made some experiments using a realistic wing model to simulate the real flapping motion.
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Hikaru AONO, Hao LIU
Article type: Article
Session ID: 231
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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The unsteady aerodynamics phenomena of insect flight is induced by a lot of factors including the flight speed, wingbeat frequency, wing and body shapes as well as the motion of flapping. The present study is focused on the influence of the reduced frequency parameter k on the production of lift force in flapping flight. To this end, we develop a biology-inspired dynamic flight simulator based on an in-house CFD code and a realistic insect morphology. With the simulator, we carry out computations in hovering flight for several cases of the reduced frequency parameter as that 0.125, 0.193 and 0.305. The simulated results indicate that the smaller the reduced frequency parameter, the lower the lift force is produced during a beating cycle.
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Shigeru Kumagai, Hiroaki Hasegawa, Takeru Sugawara
Article type: Article
Session ID: 232
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Separation is mostly an undesirable phenomenon and boundary layer control is an important technique for flow separation problems on airfoils and in diffusers. Longitudinal (streamwise) vortices are produced by the interaction between jets and a freestream. This technique for separation or stall control is known as the vortex generator jet method. The vortex generator jet method is an active control technique which provides a time-varying control action to optimize performance under a wide range of flow conditions. In this study, an active separation control system using vortex generator jets with rectangular orifices has been developed. The active separation control system can be practically applied to the flow separation control of a two-dimensional diffuser. It was confirmed that our active separation control system could adaptively suppress flow separation for the flow fields caused by some changes in freestream velocity and the divergence angle of the diffuser.
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Takashi NAITOH, Seishi Suzuki
Article type: Article
Session ID: 233
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Flow fields of zero-net-mass-flux (synthetic) jets are categorized by four patterns named as 'a laminar jet', 'laminar rings', 'a transient jet', and 'a turbulent jet'. These flow patterns change the characteristics of the jets. It seemed that Reynolds number and Strouhal number are inadequate to determine the flow patterns of this type of jets. Then, we carried out additional experiments in another condition, and examine formation parameters and those combinations governed this flow fields. As a result, it turns out that these flow patterns are arranged with the non-dimensional parameter of Reynolds number and Womersley number multiplied by the square root of the contraction ratio of the area of a piston to that of an orifice.
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Takeru SUGAWARA, Hiroaki HASEGAWA, Shigeru KUMAGAI
Article type: Article
Session ID: 234
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Jets issuing through small holes in a wall into a freestream have proven effective in the control of flow separation. This technique is known as the vortex generator jet method (VGJ). If a precursor signal of separation is found, the separation control system using VGJ can be operated just before the onset of separation. Therefore, flow field with no separation is always attained. In this study, to generate managed separation, the divergence angle of the diffuser was controlled by a stepping motor. Flow separation occurs when the divergence angle reaches at 20 degrees in our experimental condition. The distributions of the velocity and turbulence intensity of the air flow were measured by using an X-type hot wire probe. The vertical turbulent intensity at the upstream location of the divergent portion is enhanced before the onset of separation.
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Takehiro NOMURA, Hiroyuki ABE, Masahide MURAKAMI
Article type: Article
Session ID: 235
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Solid type vortex generators that are known to be effective on suppressing flow separation have been widely used in various fluid mechanical elements such as intakes and airfoils of airplanes, but it is not adaptable to flow field variation, that is it become just an obstacle to augment the drag in the situations when it does not work. In this study, wind tunnel tests have been carried out for a vertical blowing jet type vortex generator installed on an airfoil model to investigate the separation control capability. This study was investigated on the effects of configuration, location and blowing speed of the vortex generator to the lift and drag. As a result vortex generator was found to have a high capability in separation control.
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Kazuyuki SHISHINO, Toru SAWAI, Masuo KAJI
Article type: Article
Session ID: 236
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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This paper presents the effect of surfactant additives on frictional pressure gradient and gas-liquid interfacial structure for the air-water two-phase flow in a 13.5mm diameter horizontal pipe. The surfactant (CTAC) used in the experiments was n-hexadecyltrimethylammonium chloride mixed with a counter-ion sodium salicylate. In the slug flow, the addition of CTAC produces the pressure drop reduction up to 40% at a liquid Reynolds number of 6000. At high Reynolds number above 20000, the effectiveness of CTAC addition is not observed. In the annular and stratified flow, the liquid holdup is affected by the addition of CTAC, which increase in the frictional pressure gradient.
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Hideki HIBARA, Yukiharu IWAMOTO, Junji OCHI
Article type: Article
Session ID: 237
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Developing pipe flow of surfactant solutions is investigated experimentally at surfactant concentrations below 100ppm. The rheological behavior of the surfactant solution is clarified based on measurements of the relationship between shear stress and shear rate, and the velocity distribution is investigated based on laser Doppler velocimetry measurements. The results indicate that a maximum drag reduction effect of 70% can be achieved by the addition of surfactant to water, and close to laminar flow can be achieved under drag-suppressed conditions. The velocity distribution under drag-suppressed flow is shown to approach that given by Virk's equation.
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Masashi YAMAKAWA, Kenichi MATSUNO
Article type: Article
Session ID: 238
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Unstructured Moving-Grid Finite-Volume Method is suitable for moving boundary problems. In this paper, simulation of flows around bodies with large deformation using this method is presented. The simulation is flow around bodies which are united into a single body or separated into another multiple bodies. It is necessary appearing cells and cells during solving the flow. A control volume for discretization is considered in the space-time unified space, which assures both physical and geometrical conservation laws even if the grid system is moved as well as deformed with eliminating or merging cells. The unstructured moving-grid finite-volume method is described for two dimensional space in detail and validated using simple test problems. Applications to a two-bodies docking and separation in a supersonic flow show a promising feature of the method.
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Atsushi SHIBATA, Yoshinori SAITO, Ichiro NAKAMORI, Toshiaki IKOHAGI
Article type: Article
Session ID: 239
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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A coupled numerical simulation of gas-liquid two-phase fluid and structure was carried out in order to clarify the erosion mechanism caused by the impact of high-speed droplet Trie present method, which combines a gas-liquid two-phase flow analysis method using local homogeneous model and an elastic wave analysis method based on elastodynamics, was developed. Since the present method for elastodynamics is based on a compressible fluid analysis technique, it is seemed to be appropriate the fluid structure interaction (FSI) problems. In this study, the numerical simulation about a high-speed droplet impacts on the mild-steel surface was carried out. As a result the maximum von Mises equivalent stress is obtained about 380MPa in solid material after droplet impact, and it is indicated that the present method can behavior the yielding behavior.
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Kensaku NUNOURA, Shigeaki KURODA, Binghu PIAO, Makoto TSUBOKURA
Article type: Article
Session ID: 240
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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In this research, flow fields around Gyro-Mill type wind turbine were simulated at Re=4×10^3 by numerical method. Numerical results has shown that the rotation of the wind turbine is more difficult to be generated as Reynolds number decreases, because of a low lift/drag ratio at the low Reynolds number and an interference between blade and vortices. The torque coefficient could be varied from negative quadrant to positive quadrant utilizing a pitch control method based on a knowledge found by an analysis of drag type wind turbine.
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Takuya OSADA, Shigeaki KURODA, Makoto TSUBOKURA, Binghu PIAO, Naomi SE ...
Article type: Article
Session ID: 241
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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It is known that flow structures similar to the famous Taylor vortex can be observed between an outer stationary cylinder and an inner rotating square cylinder, and one of their characteristic features is recognized to be the generation of waves at the boundary of each vortex cell and their propagation toward the outer cylinder wall. The main objective of this study is to investigate the generation process of the waves by using experimental and numerical visualization techniques. It was identified that, in addition to the characteristic vortex and wave structures, remarkable flow appears at the corner of the top (or equivalently the bottom) wall and the edge of the inner cylinder.
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Tomohiro IRIE, Qin Yin Fan
Article type: Article
Session ID: 242
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Karman vortex sheets from a two dimensional circular cylinder at low Reynolds number are calculated using node-centered Finite Volume Method and unstructured mesh. In order to prepare for a coupling analysis between flow and structure oscillation, dependence of mesh density for frequency of vortex shedding are investigated in this paper. The results show that it is possible to capture a periodic vortex shedding using a sufficient quantity of unstructured hybrid mesh (mixture of prism and hexagon mesh).
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Hajime KIHARA
Article type: Article
Session ID: 243
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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This paper describes the numerical analysis of the free surface flow near the transom-stern of a ship. The 2D+T method that is a kind of slender body theory was introduced to the ship-wave problem, which was mathematically formulated based on the potential theory. Nonlinear free surface conditions were satisfied at the exact location on the body surface. Such numerical solutions can be obtained using the boundary element method (BEM). The free surface of the hollow cavity region behind the dry transom can be rationally assessed by the computational modeling. Numerical studies were carried out for nine types of transom shape in a wide range of Froude number. The present procedure was found to be effective for the analysis of the wave-making phenomena due to the transom-stern.
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Tadashi WATANABE, Masaya KONDO
Article type: Article
Session ID: 244
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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The flow-induced vibration of a circular cylinder is simulated numerically. The finite element method is used to solve the three-dimensional incompressible Navier-Stokes equations, and the flow field is coupled with the cylinder motion. The vortex field around the cylinder is visualized under the alternative vortex condition. The vortex field is shown to have three-dimensional structures in the wake of the cylinder. It is found that the frequency of vortex variation increases both in space and time by the flow-induced vibration.
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Yoshifumi YOKOI, Kounosuke OOUCHI, Tomoki MASHIBA, Junpei YAMASHTTA
Article type: Article
Session ID: 245
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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In this study, the flow features of vortex shedding from a circular cylinder oscillating along the direction of the flow were observed by visualizing water flow experiment at the ranges of the frequency ratio f/f_k=0〜6.2, amplitude ratio 2a/d=0.0625〜1.0, and Reynolds number Re=570. The variations of mean vortex shedding frequency were investigated. It is shown that although the cylinder oscillation frequency is lower man the natural Karman vortex's frequency, the lock-in phenomenon arises. Most of the flow patterns showed a complicated aspect, so the classification of flow pattern in the lock-in region was difficult The flow patterns in die lock-in region were classified with the aspect of separated shear layer, the timing of vortex shedding from cylinder and the arrangement of vortices in the wake. Seven kinds of basic form of vortex shedding were obtained and 18 flow patterns obtained by the arrangement of vortices in the wake.
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Wataru KATOH, Shigeaki KURODA, Makoto TSUBOKURA, Binghu PIAO
Article type: Article
Session ID: 246
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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The drag and lift coefficients of a flat-plate elastic wing subjected to a pitching motion were experimentally measured, and the effect of deformation due to fluid force on such an aerodynamic coefficients were investigated by comparing the results with those of a rigid wing. In the case without pitching motion, it was found that both the coefficients of an elastic wing considerably decrease as the Reynolds number increase, which is enhanced as flexibility increases, whereas those of a rigid wing is almost constant within the Reynolds-number range tested here. In the case with pitching motion, in addition to the similar reduction of the drag coefficient in the elastic wing, phase lag of the drag and lift coefficients was observed between the rigid and the elastic wing.
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Jun WATANABE, Kazuo MATSUUCHI, Hiroaki HASEGAWA, Takashi NAKAJIMA
Article type: Article
Session ID: 247
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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The unsteady forces act on the pitching and heaving airfoil. In this study, we measured unsteady forces on a moving 3-dimensional disc type airfoil using load cell and related to the vortices in the wake using PTV. We examined the relation among fluid forces, angle of attack, reduced frequency and vorticity. As a result, it was found that pitehing motion makes the angle of stall larger and lift coefficient depends on reduced frequency. These are same characteristics of 2-dimensional airfoil. We observed the shedding of vortices at the transition instant of pitching motion from up-stroke to down-stroke.
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Nobuyuki YAMAGUCHI, Daisuke SAITOH, Masayuki OGATA
Article type: Article
Session ID: 248
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Flow characteristics of a Vibrating Elastic Plate Flow Generator(VEPFG) was investigated experimentally. The device was a plate made vibrated perpendicularly to itself at the leading edge. The flow was found to be induced for a narrow range of frequency around the plate resonance frequency, with its maximum at the resonance. The optimum conditions were experimentally determined with respect to a group of non-dimensional parameters including flow coefficients, reduced frequency and relative frequency against the relative stiffness. The characteristics were compared with the analytically predicted ones; the prediction showed relatively similar feature and tendency of the flow behavior to the actual conditions.
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Daisuke SAITOH, Nobuyuki YAMAGUCHI, Masayuki OGATA
Article type: Article
Session ID: 249
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Flow structures around a Vibrating Elastic Plate Flow Generator (VEPFG) were investigated by flow visualization. Alternate trailing vortices and side-edge vortices were observed to occur. Tuft grid images obtained were compared with contour lines of time-averaged total pressure distributions downstream of the plate, which has made clear the vortical structure of the induced flow. Flow above the plate surfaces was found to be dominated by reduced frequencies.
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Yasuji TSUBAKISHITA, Akira SADAMOTO
Article type: Article
Session ID: 250
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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The sound characteristics of the transmitted higher-mode waves through the three dimensional curved duct with a splitter have been studied for various lengths and locations of the splitter. A finite difference method for a linearized Euler equation is performed to obtain the sound pressure level (SPL) and time-averaged intensity splitter placed near outer wall of duct can reduce the transmitted power remarkably at a particular length of nearly constant ratio to the wave-length. On the other hand, the splitter placed at the center of the duct yields little reduction of the transmitted power. This is distinct from the case of fundamental plane wave, in which the variation of the splitter location has little effect on the tramsmitted power.
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Yo SASADA, Yutaka OHTA, Eisuke OUTA
Article type: Article
Session ID: 251
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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Active cancellation of the BPF noise radiated from a centrifugal blower is conducted using vibrating flat plates driven by piezo-electric actuators. The fundamental BPF noise can be reduced effectively by controlling the effective noise source extent which is obtained by correlation analysis between the data of pressure fluctuation on the scroll surface and radiated blower noise. Research attention is focused on the effect of blower rotational speed, distribution pattern of the effective noise source is determined precisely. The extent of the 1st BPF noise source can be restricted in the vicinity of the cut off apex, while that of the 2nd BPF moves irregularly together with the blower operating conditions.
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Masahiro SUZUKI
Article type: Article
Session ID: 252
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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As the maximum speed of Shinkansen trains increases, aerodynamic characteristics of pantograph have become an important subject of discussions. To maintain steady current-collecting performance, it is crucial to reduce the fluctuation of the aerodynamic lift force that works on pantographs. We have been investigating to optimize the panhead configuration by combining computational fluid dynamics and numerical optimization techniques. The panhead wears out and changes its shape with time. With consideration given to this situation, we tried to optimize the panhead configuration in this study.
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Hiromu MITANI, Yasuji TSUBAKISHITA, Koichi HAYASHI, Koichi TANAKA
Article type: Article
Session ID: 253
Published: September 18, 2005
Released on J-STAGE: August 01, 2017
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An impulsive pressure wave which is called a micro-pressure wave or a tunnel sonic boom radiating from a tunnel exit is one of the important environmental problems in high-speed railways. In this study, the radiation characteristics of pulse have been studied numerically to show the effect of high temperature zone in tunnel near the exit on the radiated pulse. Especially, the peak values of the radiated pulse are calculated for various thickness and distances from the tunnel end to high temperature zone. The result shows that the local high-temperature region reduces the peak values of radiated pulse by about 30 percents, and changes the direction of the radiated acoustic energy from open end.
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