-
田辺 怜, 安藤 正晴, 元祐 昌廣, 本阿弥 眞冶
原稿種別: 本文
セッションID: S0502-5-1
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
A horseshoe vortex is generated at a wing-body junction, and causes various engineering problems. Recent trend for the requirement of energy saving and high efficiency in the design of fluid machinery clearly shows an importance of the control of the horseshoe vortex. In this study, the effects of interaction of the horseshoe vortex with co-rotating longitudinal vortices introduced by the vortex generators on the vortex behavior, the total pressure and the drag force are investigated. The experiments are conducted under the different conditions about strength and spacing of longitudinal vortex pair. NACA 0024 airfoil is set at zero angle of attack. The momentum thickness Reynolds number of the turbulent boundary layer is 1700. Although the total pressure loss is increased by setting the vortex generators, the horseshoe vortex can be moved away from the blade in the narrow spacing of vortex pair and be decayed in the wide spacing by the vortex interaction. The drag force is decreased by selecting appropriate vortex configuration.
抄録全体を表示
-
赤木 富士雄, 川畑 慶佑, 安東 洋一, 古川 雅人, 山口 佳夫
原稿種別: 本文
セッションID: S0502-5-2
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The behavior of a vortex ring generated by a pulsating jet flow, cyclic vortex ring, is investigated experimentally with PIV measurement. The waveform of jet flow is conducted by sine curves under the conditions of amplitude Reynolds' numbers Re_0 of 1200〜5040 and Womersley numbers a of 12.5〜24.4. The results indicate that the separation vortex ring which is formed from separated wall boundary layer in the nozzle during the suction period is transported toward the nozzle exit during discharge period. This separation vortex ring interferes with the formation process and behavior of the cyclic vortex ring. Some characteristic scales and propagation velocity of cyclic vortex ring are expressed as empirical functions with pulsating jet conditions.
抄録全体を表示
-
栗波 智樹, 渕脇 正樹, 田中 和博
原稿種別: 本文
セッションID: S0502-5-3
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
A number of studies on wake structures and the characteristics of dynamic thrusts of an unsteady airfoil have been reported over the years. However, behaviors of vortices that form wake structures and processes from generation to development have not been clarified. The authors measured a flow field in the vicinity of a wall including boundary layers by PIV measurements and clarified the growth and development of vortices generated in the vicinity of the wall quantitatively. We clarified that vortex flow in the vicinity of the wall is different between the rigid NACA0010 and elastic NACA0010. Vortices generated in the vicinity of the wall of elastic NACA0010 develop sufficiency on the wall of and they are separated from the trailing edge far from the center point of heaving amplitude.
抄録全体を表示
-
永田 哲志, 渕脇 正樹, 田中 和博
原稿種別: 本文
セッションID: S0502-5-4
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
Recently, flow field around a moving elastic body with deformation, which are treated as Fluid-Structure Interaction (FSI), are attracted attention. Flow fields with elastic deformation have been reported by numerical methods. However, their flow field and characteristics of dynamic force have not been clarified sufficiently. In this study, we simulate the fluid structure interaction simulation of flow field around an elastic heaving thin film and achieve the bi-directional coupling analysis. The purpose of the present study is to clarify the effect of elastic deformation on dynamic forces and flow field around the elastic thin film.
抄録全体を表示
-
川添 博光, 西村 祐樹, 松野 隆, 山田 剛治
原稿種別: 本文
セッションID: S0502-5-5
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
A delta wing with a saw-tooth leading edge has an ability to improve its aerodynamic performance, which was suggested and confirmed by the authors' previous study. It should not be practical, economical and easily controllable, because the saw-tooth configuration part extends from the apex of the delta wing to the trailing edge. In this research a few petit delta parts beside the whole saw-tooth leading edge was suggested on the basis of CFD results for its optimization by changing their location on the leading edge, the number of petit deltas, and the petit delta configuration. The aerodynamic characteristics of the suggested wing were investigated by experimental as well as numerical studies with the comparison to both the base delta wing without a saw-tooth leading edge and the whole saw-tooth delta wing. It was found that a series of three petit deltas with the modified rear configuration, which are located at the middle of the leading edge, gives the best performances at the attack angle for its taking off and landing. The reason for the best lift and such the complicated flow field as the primary leading edge separation vortex interacted with the flow from the petit deltas was examined in detail.
抄録全体を表示
-
内藤 隆, 堀口 瑞樹, 伊藤 雄大, 大蔵 信之
原稿種別: 本文
セッションID: S0502-5-6
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
Vortex rings with swirl are formed by the nozzle which is equipped with inclined small blades at its outlet. The movement distance and the state of the rings are examined in comparison with the ring without swirl for the Reynolds number range between 2100 and 17000. Depending on the formation condition and the angle of the blades, the movement distance from the nozzle is extended due to the effect of swirling flow suppressing the growth of circumferential instability in the same manner as the vortex ring with swirl generated from a rotating nozzle. In general, as the Reynolds number increases, the movement distance of the ring tends to be decreased because of the reduced circulation.
抄録全体を表示
-
中川 順達, 古林 徹, 高橋 実, 有富 正憲
原稿種別: 本文
セッションID: S0502-6-1
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
We tackle the stability problems on the flow upstream both sheet jets / film flows of liquid lithium planned for the target and coolant of BNCT (Boron Neutron Capture Therapy) using accelerators which makes tumors curable with cell-level selections. The object of our research is the thin and high-speed sheet jets / film flows of liquid lithium in a vacuum because of the ambiance using accelerators, and it serves both as a target of accelerators and as a coolant for the target itself. In this paper, we discuss the framework and stabilizing strategies of the above severe stability problems on the flows upper the outlet of the slit-nozzle.
抄録全体を表示
-
宮城 徳誠, 木村 元昭
原稿種別: 本文
セッションID: S0502-6-2
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
Active control of jet is applied at control of burner flame or air-conditioning. In this study, secondary film flow is built on the outside of axisymmetric jet. And it is driven by the acoustic excitation for active jet control. Furthermore, the velocity ratios of mainstream and film flow and acoustic strouhal number were changed. The freestream velocities were measured by the LDV and jets were visualized by LLS for research of change in jet structure.
抄録全体を表示
-
高曽 徹, 吉田 慎吾, 嘉村 勇毅
原稿種別: 本文
セッションID: S0502-6-3
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The wind induced by an automobile is studied experimentally by using a hot-wire anemometer. Simplified automobile models which are similar to the Ahmed body with 25° and 35° slanted back are ran on the traveling slope. The ensemble averaged velocities were obtained at roadside area. The measured velocity profiles showed that the displaced flows around the vehicle nose are identical for both models, however the wake flows behind the models depend strongly on the slant angle. The trailing vortices behind the 25° slanted model travel outward on the road and induce higher velocity than 35° slanted model in the downstream roadside. The mirror-image of the longitudinal vortex is attributed to the lateral traveling of the trailing vortex.
抄録全体を表示
-
王 智〓, 内山 知実
原稿種別: 本文
セッションID: S0502-6-4
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The behavior of an air bubble cluster rising in water is simulated. A vortex method proposed by one of the authors is used for the simulation. The bubbles, which are initially arranged within a spherical region, rise by the buoyant force, and accordingly induce the water flow around them. A vortex ring is generated behind the bubble cluster. It accelerates the bubble rising velocity and affects the bubble distribution within the cluster. The effect of the vortex ring on the bubble behavior becomes weaker with the increment of the distance between the vortex ring and the bubble cluster.
抄録全体を表示
-
Aung Thuyein WIN, 望月 信介, 亀田 孝嗣
原稿種別: 本文
セッションID: S0502-7-1
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
Hot wire measurement was carried out to find the response of the turbulent structure in fully developed pipe flow to two types of roughness, d-type and k-type. The measurements were emphasized on the response processes relating to types of roughness. The root mean square of fluctuating velocities components and Reynolds shear stress were investigated according to effectiveness of roughness. Comparison has been made on the turbulence data between smooth wall flow and two types of rough wall flow. The turbulence intensities of both types of roughness propagate from the vicinity of wall to the pipe center. Comparison on production term, both Reynolds shear stress and velocity gradient of k-type change largely from smooth wall condition but only changes of Reynolds shear stress is found in d-type.
抄録全体を表示
-
亀田 孝嗣, 望月 信介, 河野 裕之, 大坂 英雄
原稿種別: 本文
セッションID: S0502-7-2
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
Flow visualization by a dye injection method has been made for upstream region of a pyramid obstacle placed in a laminar boundary layer. The Reynolds numbers based on a height of the obstacle and the relative boundary layer thickness were 610 and 0.71 respectively. As the apex angle 2α increases, the vortex center position of a primary necklace vortex moves upstream and upward, and have a peak value. Furthermore, as 2α→180°, the position tends to converge to the upstream edge of the obstacle. The position for attack angle γ=0 is far away from the upstream edge of the obstacle compared with that of γ=45°.Also, the curvature radius of a streak line for the upper part of the obstacle increases with 2α.
抄録全体を表示
-
鵜飼 涼太, 鈴木 博貴, 長田 孝二, 酒井 康彦
原稿種別: 本文
セッションID: S0502-7-3
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
High-Schmidt-number scalar mixing layers in the grid turbulence are experimentally investigated in a water channel by means of the planar laser induced fluorescence (PLIF) technique and the time-resolved particle image velocimetry (PIV). A biplane square grid and a fractal square grid are used to generate turbulence. The Reynolds number based on the effective mesh size and mean velocity is 2,500 in both flows. Fluorescent dye (Rhodamine B; Schmidt number is about 2,100) is homogeneously premixed only in the upper stream, and therefore, the scalar mixing layer with an initial step profile develops downstream of the grid. Various turbulence quantities are evaluated and comparisons are made between turbulence and scalar fields generated by the regular and fractal grids.
抄録全体を表示
-
佃 紗織, 鈴木 博貴, 北山 智之, 長田 孝二, 酒井 康彦
原稿種別: 本文
セッションID: S0502-7-4
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The effects of free-steam turbulence on a turbulent boundary layer are experimentally investigated by using a wind tunnel. For the case with free stream turbulence, turbulence-generating grid is placed upstream of the leading end of a flat plate, on which turbulent boundary layer is developed. The Reynolds number based on the momentum thickness is Re_θ=2990 for the case with and without grid turbulence. Instantaneous streamwise velocity is measured using a hot-wire anemometry with an inhouse I-type probe. The effects of free-stream turbulence on statistical properties of the turbulent boundary layer are discussed.
抄録全体を表示
-
末富 正典, 高見 敏弘, 和田 謙一, 柳瀬 眞一郎, 上田 和哉
原稿種別: 本文
セッションID: S0505-1-1
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
Unsteady flows through a straight pipe is important in engineering and physiology, such as in the piping system of engine and heart-lung machine. The turbulence in a straight pipe has advantages turbulent mixing, diffusion, heat transfer, and promotion of combustion.. Therefore, it is necessary to investigate unsteady motion in detail. However, there is almost no study that measured wall shear stress directly and researched unsteady response of flow resistance in a straight pipe. In the past study, we studied suddenly-accelerated air. In the result, it was confirmed that turbulent transition happened in order from inlet to downstream. In this study, a rib is set at an inlet to cause disturbances. In the case of steady flow, longitudinal vortices are created from behind a rib. It is our purpose to examine the flow condition including the longitudinal vortex. In the result, it became clear that turbulent transition with rib is faster than without rib and that turbulence from rib cause turbulent transition.
抄録全体を表示
-
関下 信正, 渋江 佑介
原稿種別: 本文
セッションID: S0505-1-2
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
Coherent structures were experimentally investigated in a heated air jet vertically ejected from a round nozzle of 30mm in diameter. Some experiments of the present jet, mean velocity at the exit U_a=1.5〜5.0m/s and temperature difference ΔT=0〜100K, were conducted by smoke wire method and smoke method. Coherent structures, vortex pairing and side jet were observed. The side jet occurred in the jet with ΔT=75, 100K and ρ/ρ_∞=0.74〜0.8.
抄録全体を表示
-
浅井 雅人, 鈴木 広幸, 稲澤 歩
原稿種別: 本文
セッションID: S0505-1-3
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
Effects of distributed rectangular roughness on the traveling wave instability are examined experimentally in plane channel flow. Rectangular roughness elements with the height of 4% of the channel half height are distributed in an equal interval on one of the channel walls. Oblique roughness elements as well as two-dimensional roughness elements are considered. A particular attention is focused on dependency of the streamwise growth of Tollmien-Schlichting (T-S) waves on the oblique angle of roughness elements. The two-dimensional roughness destabilizes the flow as predicted by the linear stability theory. When the roughness elements are slightly oblique to the T-S waves, the destabilizing effect is markedly weakened compared with the two-dimensional roughness.
抄録全体を表示
-
近藤 重徳, 茂田 正哉, 伊澤 精一郎, 福西 祐
原稿種別: 本文
セッションID: S0505-1-4
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The characteristics of the velocity fluctuation waves excited by a piezo actuator are investigated. The actuator is driven by two kinds of signals: a sinusoidal and a rectangular signal. In order to investigate the characteristics, two methods are chosen. They are the power spectrum method and the correlation coefficient method. The comparison of the power spectrum peaks of the two cases shows that the fluctuation waves grow along the flow direction at different growth ratios. It is also found that the waveform changes for the rectangular signal case.
抄録全体を表示
-
渡辺 大輔, 前川 博
原稿種別: 本文
セッションID: S0505-1-5
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
Spatial direct numerical simulations are used to study the formation and development of three-dimensional structures in a compressible flat plate boundary layer, where the freestream Mach number is 0.5 and the Reynolds number at the inlet based on the displacement thickness 1000. A pair of stable oblique modes and a two-dimensional unstable T-S wave are superimposed on the laminar profile at the inlet plane of the boundary layer computational box. The magnitudes of the disturbances are chosen to be 1% of the freestream value. Oblique modes with the TS wave produces peak-valley splitting downstream and later hairpin vortices (hairpin packet) on the low speed streak are observed. So-called subharmonic transition appears downstream in the boundary layer. DNS results show that the forming hairpin vortex is responsible for sound waves emission.
抄録全体を表示
-
谷合 哲弥, 石川 仁, 山田 俊輔, 徳川 直子
原稿種別: 本文
セッションID: S0505-2-1
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The purpose of this study is to detect flow transition and separation on aerofoil by surface temperature measurement using an infrared camera. NACA631-012 laminar aerofoil used as test pieces, was pre-heated by a hair-drier. Then a infrared camera took thermal images of surface temperature distribution on the aerofoil. The surface temperature distribution shows the separation and the reattachment point on aerofoil. Transition from laminar to turbulent flow was visualized by infrared thermal image. These results show that the surface temperature measurement by infrared camera was effective in detection of flow transition and separation.
抄録全体を表示
-
関谷 直樹, 松本 彰
原稿種別: 本文
セッションID: S0505-2-2
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
A spot had a highly reproducibility in its velocity perturbations during the initial stage of its downstream development. Thus, we called it a "laminar spot". The purpose of this study was to investigate the generation and the development of an irregularity observed in the velocity waves during the laminar-turbulent transition of the spot. The results obtained show that the lateral distortion of velocity profile due to the vortex-interaction caused the irregularity of the velocity-wave amplitude in the boundary between the low- and high-speed regions in the spot. In addition, the crossover of legs of the longitudinal vortices occurred incidentally in the spot and generated a local ejection of low-momentum fluid. Afterwards, some crossovers of legs were produced in a chain reaction. Consequently, the reproducibility in the velocity waves disappeared almost in the downstream and turbulent regions increased rapidly everywhere in the spot.
抄録全体を表示
-
戸倉 裕介, 前川 博
原稿種別: 本文
セッションID: S0505-2-3
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
Spatial direct numerical simulations (DNS) are performed to study the formation and development of three-dimensional structures in supersonic flat plate boundary layer, where the free stream Mach number is 2.0. Spatially evolving transitional flows subjected to the freestream turbulence are analyzed to study the transition process. Numerical results show that the disturbances introduced in the outer region of the boundary layer induce the breakdown of low-speed streaks at more upstream locations than the case of disturbances introduced only inside the boundary layer. The role of the disturbances outside the boundary layer is similar to the several previous studies of incompressible boundary layer flow.
抄録全体を表示
-
一宮 昌司, 大野 英希
原稿種別: 本文
セッションID: S0505-2-4
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
In order to examine the property of the turbulent transition by the forced disturbance within the inlet region of a circular pipe, turbulent patches were generated by a jet from the wall. Mean and fluctuating velocities were measured by hot-wire anemometers. First, the threshold value of jet flow rate for the generation of turbulent patch was obtained. Next, ensemble-averaged mean and fluctuating velocities and intermittency function were obtained and the variation with jet flow rate was examined. Finally, those variations with jet frequency were examined.
抄録全体を表示
-
矢口 久雄, 矢野 猛, 渡部 正夫, 藤川 重雄
原稿種別: 本文
セッションID: S0507-1-1
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
Nonequilibrium molecular dynamics simulation is carried out to study weak condensation of argon vapor into its nanodroplet. Temperature of the nanodroplet is kept at 90 K by using the velocity scaling method. The nanodroplet grows steadily ranging from about 3.3 to 3.4 nm in the radius R_m which is defined as the radius of the center of transition layer in density profile. The mass fluxes at the vapor-nanodroplet interface are investigated and condensation coefficient of the nanodroplet is successfully determined. As a result, the condensation coefficient is almost equal to the evaporation coefficient obtained by our previous study. The rate of change of R_m can be predicted by the mass fluxes and evaporation/condensation coefficients within about 16 percent error.
抄録全体を表示
-
毛利 信吾, 小笠原 俊樹, 矢口 久雄, 渡部 正夫, 藤川 重雄
原稿種別: 本文
セッションID: S0507-1-2
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The condensation coefficients of water and methanol, i.e., the ratios of condensation mass flux of vapor molecules to their mass flux colliding on the interface, are evaluated by combining the experiment conducted by a shock tube and the numerical simulation of Gaussian-BGK Boltzmann equation applicable to polyatomic gases. Film condensation occurs on the endwall of vapor filled shock-tube, when a shock wave is reflected at the endwall and the vapor eventually becomes supersaturated there. The formed liquid film grows with the lapse of time. The time evolution in thickness of the liquid film is measured by an optical interferometer, and thereby the growth rate of the film is obtained. The rate is incorporated into the kinetic boundary condition at the interface for the Gaussian-BGK Boltzmann equation, the solution of which is in consequence obtained uniquely. The condensation coefficients in nearequilibrium states for water and methanol are found to be close to those evaluated by molecular dynamics simulations at equilibrium states.
抄録全体を表示
-
藤村 洋一, 矢野 猛
原稿種別: 本文
セッションID: S0507-1-3
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The dynamics of spherical symmetric oscillation of a vapor bubble is reconsidered on the basis of the kinetic theory of gases to investigate the existence and stability of nano-bubbles. The bubble radius is assumed to be sufficiently small compared with the mean free path of vapor molecules in a reference state, and thus the vapor is approximated by a free molecular gas. The nonequilibrium behavior of free molecular gas in an oscillating bubble is numerically evaluated, and the resulting velocity distribution function of vapor molecules are subsituted into the Rayleigh equation of bubble dynamics extendend to take acount of the nonequilibrium behaviors of vapor and the evaporation/condensation at the vapor-liquid interface.
抄録全体を表示
-
井田 真人
原稿種別: 本文
セッションID: S0507-1-4
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The dynamics of multiple bubbles under negative pressure is studied numerically and theoretically to show that cavitation inception in multibubble cases can have several patterns different from that in single-bubble cases. Using a multibubble model based on the Rayleigh-Plesset equation, we first show that the suppression of explosive expansion of a bubble due to the interaction of non-identical bubbles, which we reported recently, can take place not only in liquid mercury but also in water. We then found that a relatively large bubble can significantly decrease the cavitation threshold pressure of a neighboring small bubble. By examining the transition region where the dynamics of the suppressed bubble changes dramatically as the inter-bubble distance changes, we determined that the explosive expansion of a bubble can be interrupted and turn into collapse even though the far-field liquid pressure exceeds the bubble's cavitation threshold pressure. Numerical results suggest that the interruption of expansion occurs when the bubble radius is exceeded by the instantaneous unstable equilibrium radius of the bubble. The present findings would be helpful in understanding the complex behavior of cavitation bubbles in practical applications where many cavitation nuclei interact with each other.
抄録全体を表示
-
森本 充洋, 神保 佳典, 小林 一道, 高比良 裕之
原稿種別: 本文
セッションID: S0507-2-1
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The present study is concerned with the interaction of an incident shock wave with in-line two bubbles by using the multi-grid ghost fluid method. The influence of the bubble-bubble distance on the formation of the liquid jets and the shock waves from the collapsing bubbles is investigated. It is shown that the collapse of the upstream bubble is decelerated by the rarefaction wave caused by the reflection of the incident shock wave at the surface of the downstream bubble. The shock waves generated by the collapse of the upstream bubble accelerate the collapse of the downstream bubble, which leads to the generation of higher internal gas pressure and faster liquid-jet velocity from the downstream bubble. It is also shown that there exists an initial bubble-bubble distance where the collapse of the downstream bubble is most accelerated.
抄録全体を表示
-
宮崎 諒司, 榎本 和将, 小笠原 紀行, 一柳 満久, 竹内 伸太郎, 高木 周, 松本 洋一郎
原稿種別: 本文
セッションID: S0507-2-2
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The bubble generation process in a microfluidic T-junction is investigated by high-speed observation to develop a novel technique for monodispersed microbubble generation. The μ-PTV (micron-resolution Particle Tracking Velocimetry) is operated to measure the flow field on the bubble generation by seeding 1.0 urn particles wtih bright-field microscopy. The bubble generation process is highly periodic; therefore, μ-PTV is iteratively con- ducted in the same phase. Time-series velocity-vectors at the order of 1 m/s are measured by this high-speed μ-PTV method. The experimental results show that the proposed technique enables generation of 20〜70 μm diameterbubbles at frequency of 1〜10^2 kHz. Furthermore, the high-speed observation indicates that the bubble generation consists of two stages; intruding stage and squeezing stage. According to the obtained flow field, the liquid gradu- ally flows into the side channel with the growth of the gas tip in the main channel.
抄録全体を表示
-
西 亘, 野上 雅教, 小林 一道, 高比良 裕之
原稿種別: 本文
セッションID: S0507-2-3
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The bubble deformation in a gas-liquid contraction tube flow is observed with a high-speed camera to understand the mechanism of the bubble fission in the tube. It is shown that the surface instability occurs on the tip of a large bubble above the throat, which leads to the continuous detachment of small bubbles into the throat. Two kinds of liquid jets, ie, the forward jet and the counter jet, occur on the surface of small bubble in the throat. The result shows that the forward jet becomes faster as the bubble is pinched off more upstream. The forward jet can be caused by the pressure gradient behind the bubble. The result also shows that the counter jet occurs only when the L/R is small when L is the distance between the upstream and downstream bubbles and R is the bubble radius. The counter jet is caused by the deformation due to the bubble-bubble interaction.
抄録全体を表示
-
熊沢 勇貴, 柴崎 良太, 川島 久宜, 石間 径章
原稿種別: 本文
セッションID: S0507-2-4
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
A contracting motion on the cavitation causes the damage to the fluid machineries. It is important to analyze the radial motion of an expansion and a collapse of a bubble. A minute refrigerant droplet is paid attention to the decrease in the collapse pressure in cavitaion. The purpose of this study is to clarify the mechanism of the suppression of the cavitation with refrigerant droplet injection. The present study is performed in decompression experiment to observe a bubble radial motion in varying pressure fields by using a shock tube. As a result, the collapse radius velocity of the refrigerant vapor bubble is slower than that of the vapor/gas bubble in water. Therefore, the collapse pressure on the cavitation with a refrigerant droplet including a small air bubble becomes smaller than that of the case with air bubble motion in water.
抄録全体を表示
-
野澤 怜, 紀平 光彦, 舟木 治郎, 平田 勝哉
原稿種別: 本文
セッションID: G0500-1-1
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
Aerodynamic characteristics of airfoils have been researched in higher Reynolds number ranges more than 10^6, in a historic context closely related with airplanes' developments in the last century. So, in the present study, we investigate two kinds of basic airfoils such as a NACA0015 and flat plate, at a low Reynolds number Re = 4.0 x 10^3, using two- and three-dimensional computations. As a result, we reveal that the three-dimensionality of flow is not negligible at α ≳ 1Odeg., and that the flat plate is superior to the NACA0015 in the effect of attack angle a upon various aerodynamic characteristics such as the lift coefficient C_L, the drag coefficient C_D and the lift-to-drag ratio C_L/C_D.
抄録全体を表示
-
冨松 佳史, 岡本 正芳
原稿種別: 本文
セッションID: G0500-1-2
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The motion of the small bubbles in the homogeneous isotropic turbulence under gravitation is investigated by means of the one-way coupling methods, in which the effect of the bubblemotion on the fluid field is negligible. The rising velocity is suppressed with increasing the bubble radius. The frequency spectra of the bubble velocity are in proportion to f^<-2> like the Lagrangian inertial spectrum.
抄録全体を表示
-
中島 賢治, 城野 祐生, 山内 貴洋, 金澤 真吾
原稿種別: 本文
セッションID: G0500-1-3
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
When powder with the inhomogeneous void ratio moves in a gas-solid flow, the cluster which has particle-particle influence is formed by fluid dynamic effect and collision effect If the void ratio of the cluster becomes high and particle-particle influence disappears, particles behave as a single particle sedimentation. Then, it is not sure whether there is the critical void ratio that the clustering effect disappears. In this study, we assumed the spherical particle cluster which stood still in the air, and performed simulation to give this a current of air. The gravity is not considered. The sedimentation velocity of a single particle in still air calculated by one-dimensional theory was given in all boundary condition. Direct Numerical Simulation and Hard Sphere Model was used for the flow calculation and particle-particle collision computation respectively. The particle and the fluid assumed glass beads of 60 μm and air of 20℃ respectively. The cluster diameter is 5mm, and Re based on the cluster diameter and the maximum value of the boundary velocity is 81.6. It was found that the particle volume density and the kinetic energy of the whole cluster were in inverse proportion
抄録全体を表示
-
出川 智啓, 前川 博
原稿種別: 本文
セッションID: G0500-1-4
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
This paper presents a new formulation to define boundary conditions for compressible Navier-Stokes equations using a skew-symmetric form of the convection terms. The formulation is based on characteristic wave relations and generalized to the Navier-Stokes equations (hereafter referred to as NSCBC). The average of the divergence form and the advection form leads to the skew-symmetric form for NSCBC. Test examples include a vortex in a supersonic flow leaving the computational domain through a non-reflecting outlet and spurious wave reflections in the computational domain using various finite difference methods. The numerical results reveal that the three NSCBC forms are highly compatible. Especially, when the finite difference schemes higher than 6th order are applied, the numerical differences between them are fairly small. This provides a significant step of the skew-symmetric formulation for compressible flow simulations.
抄録全体を表示
-
壁瀬 航平, 福井 智宏, 森西 晃嗣
原稿種別: 本文
セッションID: G0500-1-5
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
This paper describes a numerical method for simulating fluid-structure interaction problem on fixed Cartesian grid by using virtual flux method in two dimensional flow. Virtual flux method enables us to simulate flow around body on Cartesian grid. Govering equations are based on the incompressible Navier-Stokes equations using artificial compressibility method. The Navier-Stokes equations are discretized on Cartesian grid using third-order weighted ENO scheme. It is found that the virtual flux method is successfully applied for flow simulation around moving body, and the proposed elastic body model is useful for fluid-structure interaction problems.
抄録全体を表示
-
濱田 廣貴, 内山 知実
原稿種別: 本文
セッションID: G0500-1-6
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
This study is concerned with the improvement of the Vortex in Cell (VIC) method for incompressible flow simulation. Staggered grid is used for the discretization of the governing equations to ensure the consistency. The grid is also successfully employed for the re-computation of the vorticity to satisfy the solenoidal condition for the vorticity field. The VIC method is applied to perform the DNS of a turbulent channel flow. The Reynolds number based on the friction velocity and the channel half width is 180. The simulated results, such as the velocity fields and the vortical structures near the wall, are favorably compared with the existing DNS, indicating the validity of the present VIC method.
抄録全体を表示
-
渋沢 遼, 佐々木 誠, 石井 達哉, 生沼 秀司
原稿種別: 本文
セッションID: G0500-2-1
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
Mixing noise of exhaust jets is reduced by decreasing the average velocity with the devices which promote flow mixing between high speed jet and surrounding air. In order to develop mixing devices, it is effective to investigate the flow field caused by the devices. In this study, total pressure distributions downstream of the mixing devices for plug nozzles (V-shaped devices on the plug surface and micro-jet injection from outside) were measured using a Pitot rake, and then the relationship between the flow field and noise reduction was discussed.
抄録全体を表示
-
土井 克則, 真能 翔也, 田中 潤治, 中村 佳朗, 村井 和彦, 甲村 圭司
原稿種別: 本文
セッションID: G0500-2-2
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
A subsonic air jet flow from a slit between a flat plate which is parallel to the flow and a wedge which is normal to the flow emits a discrete-frequency aerodynamic noise. In this study, the mechanism of the noise generation is clarified by numerical simulations, and a way to reduce the noise was suggested by results of the simulation. In the simulation, Navier-Stokes equations are directly solved with relatively low order of accuracy, which can be applied to practical designs and improvements of industrial products. The computational results show that the jet flow from the slit emits a discrete-frequency noise and the frequency is close to that of the experimental measurement. The mechanism of the noise generation is clarified by filtering the computational flow field at the frequency, which is the periodical interaction between a vortex generated by the shear layer from the edge of the wedge and that from the edge of the plate. Furthermore, it is shown in the experimental measurement that the discrete-frequency noise is reduced by making the edge of the plate rounded. These results suggest the validity of the computational results and the noise generation mechanism clarified by consideration based on the results.
抄録全体を表示
-
水野 明哲, 蔦木 貴哉
原稿種別: 本文
セッションID: G0500-2-3
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
In the canal structured road with narrow openings, it turned out in the former work that the breathing effect for ventilation is suppressed. In the current study, numerical analysis was carried out with reduced air velocity in the closed duct. The result showed that the reduction of inlet flow caused mass flow into/from the canal part, which resulted in increase of breathing quantity.
抄録全体を表示
-
佐久間 豊, 鈴木 昌弘
原稿種別: 本文
セッションID: G0500-2-5
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
Pressure and velocity fluctuations around a Shinkansen train running in a tunnel are measured simultaneously to investigate the flow structure that generates aerodynamic force on the train. In particular, a two-component hot-film probe is placed on each right and left side of the 3rd car from the head end of the 16-car outbound train (and the 14th of the inbound) to measure two-dimensional velocities in the directions parallel to the rail and perpendicular to the sides. Twenty pressure gauges are pasted not only on the right and left sides but also on the top and bottom sides of the car. It is shown that large-scale coherent structures exist on the left side of the car as well as on the top and bottom sides. Correlations between velocity and pressure fluctuations indicate that the large-scale structures are composed of rotating flows.
抄録全体を表示
-
中嶋 惇, 大江 祥晃, 田地川 勉, 大場 謙吉
原稿種別: 本文
セッションID: G0500-3-1
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
To design the nets that have resistance to breaking and blowing, the data of aerodynamic characteristics behind of nets is necessary.However, a lot of elements of the unclarification exist in this mechanism and the characteristic though it is confirmed the vortical structure is generated when the wind passes to the net. Then the lattice array made of aluminum that imitated the net was set up in the generated same air flow with a wind tunnel, and the appearance of each flow was examined, and it made to visible, it took a picture, it observed by using the laser seat, and the influence was examined with smoke that generated it by the smoke generator by the difference of the size, the velocity of the wind of the hole of the lattice array board, and the Reynolds number.
抄録全体を表示
-
吉田 英司, 神吉 利彰, 池田 寛, 小園 茂平
原稿種別: 本文
セッションID: G0500-3-2
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The purpose of the present study is to make the Reynolds number of homogeneous turbulence as high as possible using a multi-fan wind tunnel. The wind tunnel has great potentialities to provide fluctuations and various velocity profiles due to the independence of an array of small fans. We applied a number of driving modes with different conditions, such as fractal arrangement of driving fan, random input signal, and suction fans. The measurements revealed characteristics of the turbulence those modes generated.
抄録全体を表示
-
早苗 駿一, 大庭 勝久
原稿種別: 本文
セッションID: G0500-3-3
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
In this study, the compensation algorithm of the thermo-anemometer was improved for the high-precision simultaneous measurement of temperature and velocity fields by digitisation employing FPGA (Field Programmable Gate Array). The first-order lag due to the thermal time constant on the cold-wire sensor was compensated with the digital filter comprised the first-order lead characteristic designed by the bilinear transformation. The temperature compensation was indispensable for the velocity measurement, owing to the response of the hot-wire anemometer depended on both the velocity and the temperature variations in the stratified flow fields. The algorithm incorporated the correct term relative to the physical properties was implemented on FPGA. In the temperature difference range of 0℃ to 60℃, the high-accuracy velocity measurements were realized with an uncertainty of less than 0.92% from the simultaneous and mutual compensation system.
抄録全体を表示
-
小薮 栄太郎, 今田 諭, 藤本 進, 築地 徹浩
原稿種別: 本文
セッションID: G0500-3-4
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
This study investigates wake-induced bypass transition of boundary layers on a fiat-plate which is subjected to favorable and adverse pressure gradients. Detailed boundary layer measurements are executed by use of two single hot-wire probes. A spoked-wheel type wake generator creates periodic wakes in front of the flat plate. This main focus of this study is on how and to what extent the wake-induced bypass transition of a flat-plate boundary layer can be affected by favorable -adverse pressure gradient.
抄録全体を表示
-
浅野 裕, 中尾 晨一, 八鍬 武史
原稿種別: 本文
セッションID: G0500-3-5
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
For toroidal throat Venturi nozzles with various diffuser lengths and half angles, their critical back pressure ratio were experimentally investigated on the theoretical Reynolds number less than 2×10^4. The results showed that the diffuser shapes provided in JIS Z 8767(2006) are not always adequate for flow measurement under the above Reynolds number range. Finally, when the toroidal throat Venturi nozzle is used on flow measurements, its diffuser length is desirable to be longer than lOd and its diffuser half angle should be around 3.5 degrees.
抄録全体を表示
-
山岸 陽一, 木村 茂雄, 森川 浩司, 小島 徹也, 沖 真, 鹿村 千隼
原稿種別: 本文
セッションID: G0500-3-6
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
It is known that occurs at a lower Reynolds number in the case where there exist grooves or roughness on the circular cylinder surface. In this paper, in order to make clear the flow characteristics around a cylinder with 17 and 32 triangular grooves at intervals of 11.25° along the cylinder with a centrally-located stagnation point, the drag coefficient, velocity distribution and turbulence intensity distribution were measured. Moreover, the flow around the cylinder was analyzed by applying the RNG k-ε turbulent model, and surface flow pattern was investigated using the oil-film technique. From these results, a sudden decrease in the mean drag coefficient of a cylinder with 17 and 32 triangular grooves occurs at a lower Reynolds number. For a wide range of 17 grooves compared with 32 triangular grooves. Moreover, the results of the numerical analysis tend to agree well with the experimental values.
抄録全体を表示
-
瀬川 武彦, 武川 信也, Kwing-So Choi
原稿種別: 本文
セッションID: G0500-4-1
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The jet velocities induced by a dielectric barrier discharge (DBD) plasma actuator and their dependences of voltage surge gradient have been investigated by means of PIV system. A DBD plasma actuator with doughnut-shaped electrode generates axisymmetric jets by applying high voltage (V) and high frequency (f_p) square wave signals with various voltage surge velocities (dV/dt). Variations of velocity distributions of axisymmetric jets produced by DBD plasma actuator are measured for amplitude of input voltage, V_m = ±3.3 kV, and 2.5 ≤ f_p ≤ 10 kHz, and 50 ≤ dV/dt ≤ 1,000 volts/μsec. It is found that the speed of tangential jet reaches its maximum when the voltage surge velocity is in the range of 150 ≤ dV/dt ≤ 250 volts/μsec, and the intermittent peak currents occur in certain time scales (δt_s) and δt_s shortens, but also its pace of decrease gets smaller as dV/dt increases. Net power consumptions to generate DBD plasma have been also evaluated by real-time measurements of voltage and current.
抄録全体を表示
-
松野 隆, 太田 健太郎, 金谷 高志, 川口 幹祐, 川添 博光
原稿種別: 本文
セッションID: G0500-4-2
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The driving parameter of SDBD plasma actuator for the effective flow control was explored. Current exploration focused on the modulation frequency and several relevant parameters for unsteady PWM drive of the actuator for drag reduction of the circular cylinder at 8〜12m/s of the freestream velocity. Parametric experiment showed that the principal variable to determine the performance of the actuator was the modulation frequency of the PWM actuation. Higher (Strouhal number is greater than 0.7) PWM modulation frequency has better actuation performance that can reduce the drag of the cylinder model up to 45%. Contrarily negative drag reduction was observed when the PWM modulation frequency was set close to the natural frequency of the wake vortex of the cylinder model.
抄録全体を表示
-
渡辺 正
原稿種別: 本文
セッションID: G0500-4-3
発行日: 2010/09/04
公開日: 2017/08/01
会議録・要旨集
認証あり
The motion of a free droplet and the flow field around the droplet in an oscillating pressure field are simulated numerically using the Arbitrary Lagrangian-Eulerian and level set coupled method. It is shown that the droplet moves toward and stays at the pressure node. The induced flow field is found to be similar to the flow field around an oscillating droplet in a static fluid.
抄録全体を表示