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Yoshisuke HAMAMOTO
1999 Volume 65 Issue 632 Pages
1179-1184
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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Hidetaka OKUI, Myeong-Kwan PARK, Shuzo OSHIMA, Ryuichiro YAMANE
1999 Volume 65 Issue 632 Pages
1185-1191
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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It is well known that the pseudo-shock in the straight duct oscillates severely, and causes vibration and noise of fluid machines. In the previous paper, the performance of the diffuser is shown to be improved by the passive control method without noticeable changes of the pseudo-shock stracture, and a new passive control method of the pseudo-shock useing the bypass system was proposed. In the present paper, the effectiveness of these methods for the oscillation suppression of the pseudo-shock was investigated exprimentally. Both of these methods can suppress the wall pressure fluctuation, reducing the pressure gradient and the shock oscillation amplitude.
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Hidetaka OKUI, Myeong-Kwan PARK, Shuzo OSHIMA, Ryuichiro YAMANE
1999 Volume 65 Issue 632 Pages
1192-1199
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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Oscillation of the pseudo shock in the rectangular duct with the porous wall was investigated numerically. In the simulation, 2nd order accurate, Harten Yee's upwind TVD scheme was used for high resolution and numerical stability, and Chien's κ-ε two equation model was used as the turbulence model. To simulate the effect of the blowing and suction on the porous wall, Darcy's law was used on the porous wall boundary. The boundary layer thickness under the first shock wave oscillates due to the shock oscillation, which changes the strength of the first shock wave changes, so that it suppresses the pressure fluctuation downstream of the first shock wave. The effects of some parameters of the passive control on the pseudo-shock oscillation were investigated.
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Bin CHEN, Fumihiko MIKAMI, Nobuhide NISHIKAWA
1999 Volume 65 Issue 632 Pages
1200-1207
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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The purpose of the paper is to investigate two layer convection driven by settling of particles and temperature difference using a continuum model of suspensions. A two-dimensional numerical simulation method for polydisperse suspensions is proposed. Numerical results of settling velocity of particles using polydisperse settling model are in good agreement with experimental results. The FCT (flux-correctedtransport) procedure overcomes the problem of false oscillations of concentration field. The calculated distributions of the vertical and horizontal velocity were compared with the experimental results. The numerical results of velocity, temperature and interface profiles agreed quantitatively well in early stages and qualitatively well in later stages with our experimental results. The development and vanishing of two-layer convection cells are clarified.
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Nobuhiko YAMASAKI, Masanobu NAMBA
1999 Volume 65 Issue 632 Pages
1208-1215
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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The TVD scheme combined with the finite difference method, which has been developed in the first part of the present papers to solve the linear unsteady flowfield of vibrating cascade blades, has been applied successfully to the vibrating supersonic through-flow fan cascade blades. Numerical example calculations indicate that the present calculation well predicts the general trend of dependences of the unsteady aerodynamic forces on various parameters, with little numerical oscillation in solutions. The steep changes in the flowfield accompanied by the spatial numerical oscillation predicted by the Lax Wendroff and the finite volume method are captured as less steep change in the present calculation.
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Tadaharu KISHIBE, Shojiro KAJI
1999 Volume 65 Issue 632 Pages
1216-1223
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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The swirling flow field including non axisymmetric phenomena in a rotating hollow turbine shaft is solved using computational fluid dynamics. The three dimensional compressible Navier-Stokes equations are adopted and discretized by an implicit TVD scheme. No axisymmetric assumption is applied in order to find non axisymmetric phenomena. The computational domain, therefore, is extended circumferentially to 360°and axisymmetric boundary conditions along the center axis are avoided. The existence of a rotating spiral vortex at the place where the swirling flow turns radially outward is shown. The spiral vortex rotates about the shaft center axis in the same direction as the circumferential velocity of the main flow. Conversely, the vortex has a spiral form opposite to the rotational direction of the fluid. The first non-axisymmetric mode of a single spiral vortex is transformed into the second mode of a double spiral vortex at a specific rotating speed of the shaft.
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Nobuyuki YAMAGUCHI, Kazuhiko YOKOTA, Yoshinobu TSUJIMOTO
1999 Volume 65 Issue 632 Pages
1224-1231
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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A theoretical method has been proposed for prediction of the fluttering of a flexible thin sheet or web of such as paper blown in high speed flow of fluid. It assumes self-excited aeroelastic oscillation of the sheet with infinitesimally small amplitude. The flow and the sheet motion are expressed terms of discretized vortices over the sheet and the wake, and motions of a number of short segments of flexible beams connected each other. The connecting conditions yield a homogeneous linear simultaneous equations concerning the unknowns including the strength of vortices and the sheet motions at each connecting points. The coefficient matrix of the equations determines the oscillation modes, the frequencies, the amplifying/damping rates, and thus the modes and the stability/instability of the system. The method is particularly suited to solve the situation where the oscillation modes are far from those in vacuum and progressive waves are predominant.
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Nobuyuki YAMAGUCHI, Tooru SEKIGUCHI, Kazuhiko YOKOTA, Yoshinobu TSUJIM ...
1999 Volume 65 Issue 632 Pages
1232-1239
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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Flutter behaviors of flexible thin sheets of such as papers and plastic films blown in wind, whose mass ratios are very low, tend to deviate far from those for ordinarily stiff materials. A theoretical prediction method of the flutter occurrence developed by the authors was applied to the low mass ratio region, and the results explained well the tendencies found in the experimental data. The predicted results have shown clearly the effects of both the fluid friction and the added mass effect by surrounding fluids in the region for the low mass ratios, compared with those for higher mass ratios whose behaviors are dominated mainly by elasticity and inertia force, and fluid pressure. The flutter limits and the behaviors in a region for very low mass ratios, which has not yet been observed experimentally, were predicted by the method and given in this report.
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Hironori HORIGUCHI, Fabien WAHL, Satoshi WATANABE, Yoshinobu TSUJIMOTO
1999 Volume 65 Issue 632 Pages
1240-1248
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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With the idea of reducing the region of rotating cavitation by cutting back leading edge alternately and enhancing the stability of alternate blade cavitation, an analysis of steady cavitation on uneven chord cascade and its stability were made. The cavities on longer uncut blades are generally longer but it becomes shorter for a certain range of inlet cavitation number. This peculiar behavior is explained by the choking effect of cavities. It is also shown that the region with stable cavities can be extended and the onset region of rotating cavitation can be diminished by alternately Cutting back the blades.
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Hironori HORIGUCHI, Fabien WAHL, Satoshi WATANABE, Yoshinobu TSUJIMOTO
1999 Volume 65 Issue 632 Pages
1249-1255
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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The present report describes about the effects of the amount of the alternate cutting back of the leading edges on the steady cavitation, its stability and the onset region of rotating cavitation. It was found that, by increasing the amount of cutting back, we can increase the range of cavitation number with stable cavitation and diminish the onset region of rotating cavitation.
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Takashi SHIMAZU, Haruo KATAGIRI, Shigeru SAKAMOTO, Hidetoshi SHIMIZU, ...
1999 Volume 65 Issue 632 Pages
1256-1262
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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Improving a cooling capacity is the most important technique to develop highly efficient automotive brake rotors. We have developed new methods of analyzing flow phenomena in vent holes of brake rotors. Using these analysis methods, we have realized new brake rotors with a higher cooling performance than those of conventional brake rotors, by 18%.
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Muneyuki KAWASE, Junichiro FUKUTOMI, Yoshiyuki NAKASE, Tadaaki KUWAUCH ...
1999 Volume 65 Issue 632 Pages
1263-1270
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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This paper describes the performance in the winnowing fan, which are used for head feeding type combines mainly used in Asia. The effects of blade angle and the bracket configurations at the inlet on the efficiency and internal flow conditions are experimentally investigated. The fan efficiency and the uniformity of flow along an axis are improved by reforming blade angle and bracket shape with holes. In addition, in this experiment we found that both of these two methods uniform the velocity distributions at fan exit and combination of these two methods make it possible to improve the fan efficiency in the limited design condition.
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Masaki FUCHIWAKI, Kazuhiro TANAKA, Akira TANAKA
1999 Volume 65 Issue 632 Pages
1271-1276
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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Most of experimental visualization and numerical results on the flow field separated from a leading edge around a moving airfoil show a continuous streakline from the leading edge and big reverse flow between the streakline and the suction surface. However, they have not exactly clarified yet the dynamic behavior of vortices separated from the leading edge because unsteady separation around a moving airfoil is very complicated phenomenon due to many parameters. In the present study the flow fields around pitching airfoils have been visualized by using a schlieren method with a high speed camera in a wind tunnel at low Reynolds number region. It has been observed that small vortices are shed discretely from the leading and trailing edge and that they stand in line on the integrated streakline of separation shear layer. By counting vortices in the VTR frames it was clarified that the number of vortex shedding from the leading and trailing edge during one pitching cycle strongly depends on the non-dimensional pitching rate. Furthermore, the vortices moving up to the leading edge on the suction surface of the pitching airfoil are visualized. They play an important role to balance the number of vortex shedding from both edges.
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Hajime NAKAMURA, Tamotsu IGARASHI, Takayuki TSUTSUI
1999 Volume 65 Issue 632 Pages
1277-1282
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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Experimental studies have been carried out to clarify the flow around a circular cylinder accompanying asymmetric separated shear layers. To control the flow, one or two tripping wires were attached on the surface of the cylinder. Three flow patterns were employed, that is, the laminar separation, turbulent separation and direct separation types. The flow behind the circular cylinder is dominated by the both separated shear layers. The Strouhal number behind the cylinder, the base pressure and the darg force acting on the cylinder become the intermediate values between those of the upper and the lower side flow patterns. In the case of asymmetric shear layers, the correlation between the Strouhal number and the drag force is the same as that of the symmetric ones. In the case of the turbulent shear layer from one side of the cylinder, the lift force of C
L=0.5∼0.8 is generated. The wake Strouhal number S
*w/U
s(mean), defined by the mean velocity of the two shear layers U
s(mean) and the wake width at the position of vortex formation d
w, becomes almost a constant for various combinations of the flow patterns.
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Hideharu MAKITA, Akira NISHIZAWA
1999 Volume 65 Issue 632 Pages
1283-1290
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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Interaction between turbulent spots was experimentally investigated in a laminar boundary layer by using a rake of 16 I-type hotwires. Instantaneous plane views of a single spot showed that several small scale streaky structures elongated in the streamwise direction were arranged in staggered style inside the arrowhead-shaped area. The oldest streaky structures constructed the arrowhead. Newer structures were produced near the wing tip and in the interface between the turbulent and the calmed regions. When the two spots were simultaneously generated, their wing tips came to overlap each other as they grew downstream. Mutual interaction between the streaky structures at the wing tips gave birth to a strong velocity-defect region on the symmetry plane of the merged portion.
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Yuji SUZUKI, Nobuhide KASAGI
1999 Volume 65 Issue 632 Pages
1291-1298
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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A three-dimensional particle tracking velocimeter (3-D PTV) was successfully applied to turbulent air flow measurement in a strongly curved U-bend of square cross-section. He-filled bubbles, of which specific density was very close to that of air were employed as a flow tracer. Distributions of the mean velocities and Reynolds stresses were obtained at 90°downstream of the inlet to the curved section. The secondary flow as strong as 20% of the bulk mean velocity is observed in the cross-stream plane ; it results in a marked trough in the streamwise velocity at a distance of about 0.3 times the channel height from the inner wall. The present experimental result is mostly in good agreement with the LDV data of Chang et al. (1983). Moreover, turbulent statistics including all Reynolds stress components are obtained. The production mechanism of turbulent kinetic energy as well as the distributions of invariants for stress anisotropy tensor are discussed in detail.
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Osami KITOH, Tadateru TANIOKA, Yukihiro KANEKO
1999 Volume 65 Issue 632 Pages
1299-1306
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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The skewed wall turbulent flow, driven by sudden span wise wall motion superimposed on plane Poiseulle flow, has been simulated by Direct Numerical Simulation (DNS). The time evolution of the mean velocities and the Reynolds stresses have been studied. Just after the spanwise wall motion starts the flow skewness is confined to the narrow wall region (y
+<30) and the flow soon becomes another collateral flow again. During the evolution stage, turbulent kinetic energy first decreases and then increases. The time when q^
-2 takes its minimum depends on the Reynolds number of the flow. The difference between shear driven and pressure driven skewed flow is also shown. The production and pressure strain terms in the Reynolds stress transport equation are shown to play an important role in leading to non parallel vectors of velocity gradient and Reynolds shear stresses.
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Kakuji OGAWARA
1999 Volume 65 Issue 632 Pages
1307-1311
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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Numerical experiments were conducted to examine applicability of Pyragas' Delayed feedback (DFB) control theory for active control of the coupled map lattice (CML). CML is known as a simple model with the essential feature of spatiotemporal chaos. Assuming spatiotemporal chaos reprsents wall turbulence, DFB control theory was applied to examine possibility of active control of turbulence. Notable feature of this study is that DFB control units are distributed to each non-linear element of CML. Since each control unit works independently, the control algorithm is simple and applicability to a real system is promising. Simulation results show that the present method can stabilize the whole CML, even though only 20% of the lattice or the non-linear elements were controlled by DFB method.
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Isao MISU, Nobumi SAIDA, Takashi YATABE
1999 Volume 65 Issue 632 Pages
1312-1317
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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The velocities and the wall shear stresses are respectively measured with a hot-wire and a hot -film gage embedded in a wall. The sensors are operated by the constant temperature anemometer Iso-cross-correlation curves between the velocity and the wall shear stress averaged over a short time period of the bursting process and over a long time period are obtained from experimental data. The shapes of those curves become flatter and more elongated stream wise as pressure gradient is decreased to a negative value. It is concluded that the bursting under the favorable pressure gradients tends to be restricted near the wall in the scale of the wall coordinate.
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Ryuichi NAGAOSA
1999 Volume 65 Issue 632 Pages
1318-1325
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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This paper aims to discuss suitable grid resolution for a direct numerical simulation (DNS) of wall-bounded turbulence using a finite difference method (FDM). All spatial derivatives are approximated by a second-order central difference. The fully-developed turbulence statistics in a turbulent flow near a flat wall is evaluated using the FDM. The accuracy of the DNS based on the finite difference approximation is confirmed by the DNS database evaluated by a spectral method (Kasagi, N. et al. ASME J. Heat Transf. 114, (1992), 598). In order to discuss the effect of the grid resolution in both the streamwise and spanwise directions, the numbers of grid points in these directions are reduced. The effect of the grid resolution on the fully-developed turbulence statistics near the wall is finally discussed.
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Yasuaki KOZATO, Shigeki IMAO, Toshio TANAKA, Hideo KOHNO
1999 Volume 65 Issue 632 Pages
1326-1331
Published: April 25, 1999
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This paper presents an experimental investigation of a radial turbulent jet (main jet) discharged from a cylindrical nozzle in the presence of a lateral control flow from an annular nozzle. The main content of this report concerns with the mean and fluctuating velocity properties of a deflected jet. The effects of the impingement conditions which are the nozzle distances in this report were claified. The measurement of mean velocities, turbulent intensities of each component, and Reynolds shear stresses were carried out. The properties of the deflected jet are affected by the control flow in the region just behind the impingement of two jets, but they agree well with those of the radial free jet in the downstream section when the components are dissolved into the mean stream direction and its perpendicular directions.
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Nobuyoshi SUZUKI, Osamu MOCHIZUKI, Masaru KIYA
1999 Volume 65 Issue 632 Pages
1332-1338
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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Flow separation from a flat plate airfoil is controlleed by impinging vortex rings. The vortex rings were generated at a position apart from the airfoil to act as a carrier of energy to suppress the separation Momentum defects in the wake of the airfoil were obtained as functions of the circulation and the frequency of introduction of the vortex ring to demonstrate that the separation zone is actually reduced. The mechanism of suppression of separation is clarified by the phase-averaged flow visualization and velocity distributions.
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Yuichi MURAI, Xiang-Qun SONG, Takashi TAKAGI, Masa-aki ISHIKAWA, Fujio ...
1999 Volume 65 Issue 632 Pages
1339-1346
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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The inverse energy cascade, which is one of the important phenomen α to enhance the large scale flow instability in bubbly flow, is investigated by measuring a local two phase flow structure driven by buoyant bubbles using Particle Imaging Velocimetry (PIV). In the PIV, flow field of liquid phase is measured by separating an original image to respective two phase images using a statistical thresholding method for image parameters of bubble and particle. The present results obtained in case that bubble Reynolds number and average void fraction are less than 30 and 1.5% respectively, confirm the presence of a large energy-decaying with slope index of sharper than -5/3 in log log diagram of energy spectrum at high wavenumber region. Also an important relationship between the energy spectrum and bubble-bubble interval distance is detected.
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Yuichi MURAI, Atsuhide KITAGAWA, Xiang-Qun SONG, Fujio YAMAMOTO, Junic ...
1999 Volume 65 Issue 632 Pages
1347-1354
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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The inverse energy cascade in bubbly flow is investigated by a numerical simulation using the Eulerian-Lagrangian model in which the governing equations are formulated with emphasis on the translational motion of bubbles in non-uniform flow. This paper is concerned with the validation of the numerical model and various parametric dependency on the inverse cascade. The calculated results reveal that, 1) continuous growth of the spatial fluctuation scale in a bubble-induced flow is well predicted by the present numerical model and the results have a good analogy with the experimental results which are introduced in our first report, 2) the strong relationship between energy-decaying process and bubble-bubble distance interval identified also by the present analysis, 3) the slope of energy-decaying at high wavenumber region depends on the kinetic viscosity of liquid, and that at low wave number region depends on inuniformity of buoyancy distribution which changes due to the bubble motion.
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Katsuhiro KIKUCHI, Nobuaki YAMAUCHI, Masanobu IIDA, Mitsunori YANAGIZA ...
1999 Volume 65 Issue 632 Pages
1355-1361
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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A numerical algorithm to optimize the nose configuration of train is developed to reduce the pressure variation caused when a train runs. A pressure field is generated around a moving train, which is viewed as a pressure variation by an observer on the ground because it moves with the train. Since the pressure variation when a train runs is closely related to the form of train nose configuration, its improvement is one means of reducing the pressure variation. In this algorithm, the train nose configuration is designed to minimize the peak-to-peak value of static pressure around the train by using the Stokes stream function for axisymmetric flow combined with nonlinear programming. An optimized train nose configuration can be obtained in a very short CPU time with a 6% smaller peak-to-peak value of pressure variation. In addition, experiments using models corresponding to the case under consideration have been carried out to confirm the numerical validity. The results indicate that this algorithm is efficient in designing the train nose configuration with smaller pressure variation during train operation.
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Yoshiyuki WAKI, Takuji ISHIKAWA, Shuzo OSHIMA, Ryuichiro YAMANE, Motoh ...
1999 Volume 65 Issue 632 Pages
1362-1369
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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It is pointed out that mass transport in an artery, such as LDL transport, influences the progression of stenosis severely. Mass transport in pulsatile blood flow, which has intermittent time, through an stenosed aorta is analyzed numerically. Flow is assumed to be periodic and axisymmetric. Non-Newtonian viscosity of blood and movement of arterial wall are considered. The effect of inter-mittency, pulsation and wall movement on mass transport is investigated. Flow pattern, concentration pattern and distribution of concentration on the wall are obtained. It is found that the instantaneous mass flux on the wall is dominated by the apparent St number using angular velocity of unsteady time. However, time-mean mass flux is influenced by the intermittent time. The flow intermittency contributes to smoothing the concentration distribution and decreasing the time mean mass flux on the wall.
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Koji KOYAMADA, Yasuharu YAMADA, Toshihiko NISHIO, Hidetoshi KOTERA
1999 Volume 65 Issue 632 Pages
1370-1376
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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In this paper, we propose a technique that uses thermal measurement results for improved accuracy in thermal simulation of electronic apparatuses. Because the modeling of the electronic components in such apparatuses has hitherto been very poor, the thermal simulation results cannot satisfy the required accuracy. To solve this problem, we first represent a component as a set of cubic blocks with equivalent thermal conductivities and contact thermal resistances, and then identify these by using the thermal measurement results for the component. We regard the identification of parameters as an optimization problem that involves minimizing the difference between the calculated and measured results.n To solve the problem, we combine genetic algorithms and a thermal simulation tool. Our technique was successfully applied to the construction of an accurate thermal model, which we validated by using thermal measurement results.
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Keizou KAWAMURA, Tadakatsu NAKAJIMA, Hitoshi MATSUSHIMA
1999 Volume 65 Issue 632 Pages
1377-1382
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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The Cooling performance of a plate fin-type heat sink equipped with a cooling fan was investigated experimentally. The heat sink was 80 mm long, 43 mm wide, and 24 mm in height, (including the 4-mm-thick base). The cooling fan was 40×40×15 mm and was set to direct the air flow vertically at the downstream half of the heat sink. We focused on the influence of the height that the fan was set at, which we varied from 5 to 20 mm, had on the heat transfer coefficient of the heat sink. The maximum value of the heat transfer coefficient was achieved at a setting height of 5 mm. At this heigth, the volumetric heat transfer coefficient was 1.8 times as high as with a parallel flow under the same fan power. This indicates that the cooling performance of heat sinks with cooling fan can be improved by using this kind of compact structure.
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Satoshi KUMAGAI, Kazunori KAWABATA, Hiroyuki YOSHIKAWA, Ryohachi SHIMA ...
1999 Volume 65 Issue 632 Pages
1383-1388
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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High heat flux far exceeding CHF in microbubble emission boiling (MEB) should be considered a result of violent growing and collapsing behavior of coalescent bubbles in that regime, which introduces subcooled liquid to the surface to make steady solid-liquid contact even in the high surface temperature region. This bubble behavior generates a moment of high pressure in the vicinity of the surface. In this study, a measurement of the pressure fluctuation in the liquid near the surface was performed synchronously with a recording of the bubble motion by a high speed video camera. The experimental results reveal that the peak value of the pressure fluctuation corresponds to the bubble collapse. The image processing method was also applied to the video pictures to analyze the bubble motion and some information was obtained.
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Takao YOKOYAMA, Atsushi SATOH, Chuichi ITOH, Takushi YOSHIDA
1999 Volume 65 Issue 632 Pages
1389-1394
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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The SPEAR-SYSTEM, one of the Hot-Runner molding, is rational and economical thermal valve-gate system. A resin around the SPEAR which is heating object like a spear, sorts into the solidification-layer and flow-layer. The former takes important role of insulator, then prevents a resin leak at molding. Though location of the interface of solidification varies due to flow and thermal condition, quantitative treatment is not applied yet. Engineers have just depended on their experiences for thermal design as to Hot-Runner System. In this paper we have measured temperature field inside the Runner-bush and location of the interface, on the other hand established a numerical code and compared both values. As a result, we have confirmed agreements between the experiment and the numerical. Therefore we could forecast what happens in flow and temperature field around Spear under a variety of conditions.
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Ken-ichi ABE, Kazuhiko SUGA
1999 Volume 65 Issue 632 Pages
1395-1402
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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In order to reveal unknown characteristics of complex turbulent passive scalar fields, large eddy simulations in forced convection regimes were performed under several strain conditions, including a flow impingement and a flow separation. By using the simulation results, relations between the dynamic and scalar fields were carefully examined. It was then confirmed that the scalar was transported by a large vortex structure near the examined regions wherever the mean shear vanished, though in the high shear regions, the scalar transport was governed by a coherent structure due to the high shear strain. In addition, a priori explorations were attempted by processing the data, focusing on the derivation of a possible direction for modeling the passive scalar transport in complex strain fields algebraically. The a priori tests suggested that an expanded form of the GGDH model introducing quadratic products of the Reynolds stresses was promising for general flow cases.
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Hironori SAITOH, Sadanari MOCHIZUKI, Akira MURATA, Hiroshi SAITOH
1999 Volume 65 Issue 632 Pages
1403-1408
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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In modern gas turbines, turbine section operates under severe thermal conditions. Effective cooling of the turbine section is required to keep their safe working. This study deals with flow and heat transfer in the low-pressure turbine section which has cavities formed by an assembly of turbine disks. This paper focuses on the heat transfer characteristics of the most upstream disk surface, and the effects of the forced convection with radial throughflow and the natural convection in a centrifugal acceleration field were investigated through flow visualization and heat transfer experiments. This study employs three dimensionless parameters which govern flow and heat transfer in rotating cavities. These are throughflow Reynolds number, rotational Reynolds number, and Rayleigh number. The results showed that, for the effect of the forced convection, meat Nusselt number did not increase monotonically with increasing throughflow Reynolds number at a constant rotational Reynolds number, and for the effect of bouyancy force Nusselt number decreased with increasing Rayleigh number.
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Masahiro OSAKABE, Kiyoyuki YAGI, Tsugue ITOH, Kunimitsu OHMASA
1999 Volume 65 Issue 632 Pages
1409-1416
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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In order to improve a boiler efficiency, latent heat recovery from the flue gas is very important concept. Condensation heat transfer on horizontal tubes was investigated experimentally by using an actual flue gas from a natural gas boiler. The parametric studies concerning the effects of tubes stages, gas velocities, SO
2 in the flue gas and Teflon lining on tubes were conducted at a wide range of tube surface temperature. The heat transfer was enhanced at the second stage due to the wake turbulence of the first stage. No significant decrease of the condensation on the second stage due to the condensate falling from the first stage could be observed. Even at the high gas velocity condition, the condensation pattern was similar to that observed in the previous low gas velocity experiments. The effect of SO
2 in the flue gas on the condensation behavior could not be observed. The heat and mass transfer behaviors on the stainless steel and Teflon lining surface were well predicted with the analogy correlation. The above results suggested that the heat and mass transfer were dominated with the convection and diffusion process in the gas side.
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Yoshio Utaka, Katsuaki Takahashi, Takao Tsuboi
1999 Volume 65 Issue 632 Pages
1417-1423
Published: April 25, 1999
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The objective of the study is to clarify experimentally the variation of the vapor concentration of binary mixture generated during nucleate boiling in a saturated pool under the various boiling conditions. The generated vapor concentrations in the bulk vapor layer were measured for the binary mixtures of water-ethanol and ethanol-acetone under various liquid concentrations, the heat fluxes and the liquid layer heights from the thin wires at the atmospheric pressure. Two methods of measuring concentration, i.e. the dew point method and the laser absorption method were adopted to confirm the reliability of the results. The measured results by using both methods coincided well with each oher. The measured concentrations of the bulk vapor for various superheats of heating wires, the depth of liquid layer and liquid concentrations were almost independently of those parameters and were almost in equilibrium with bulk liquid conditions even under the higher heat fluxes and lower liquid heights.
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Hiromichi UMEMIYA, Atsushi SUZUKI
1999 Volume 65 Issue 632 Pages
1424-1431
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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An experimental Study has been made on the effect of bio-filter in a packed bed. By using a packed bed of glass beads in stead of aquifer, groundwater recharge was reappeared. Measurements were made on microorganism number density, COD, turbidity, iron concentration, and pH. Emphasis was placed on the removal effect of COD. The conclusions were as follows. 1) Bio filter is formed at the upstream end of the packed bed. It is composed of general microorganism and iron bacteria. The number densities of microorganism and iron bacteria are increased with the passage of time and io-filter is thickly formed. 2) Bio-filter is very useful to COD removal, because organism is consumed by oxidation with iron bacteria and iron. 3) Iron is removed by the physical filter effect of bio-filter and oxidation with iron bacteria. 4) Turbidity is removed by the physical filter effect of bio filter. 5) Light is an effective system for COD removal. 6) Environmental temperature is usefulness to bio-filter formation and water purification.
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Katsunori HANAMURA, Kazuyuki AKAGI, Kimihito KOYANAGI
1999 Volume 65 Issue 632 Pages
1432-1437
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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An experimental study on autothermic reforming in a porous catalyst has been performed. In the system, a mixture of methane, steam and air is introduced into the porous catalyst, where the flow direction reverses reqularly. By the reciprocating flow system, the product gas enthalpy is effectively regenerated into an enthalpy increase in the mixture through the porous medium, which provides heat storage. The flammability limit is extended to the equivalence ratio of 4.7. That is, most of the methane supplied is converted into hydrogen, using the combustion heat released by the residual methane. The most striking feature is that the thermal efficiency, which is defined as the ratii of the reforming-reaction heat to the combustion heat, reaches 70%, and the methane conversion is more than 80∼90%.
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Katsuhide OHIRA, Kenji NAKAMICHI
1999 Volume 65 Issue 632 Pages
1438-1445
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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Slush hydrogen is a mixture of solid hydrogen particles and liquid hydrogen, and is being considered as a spaceplane fuel or as a means of transport for hydrogen used as a source of clean energy. This paper describes the fabrication of three variations of capacitance type densimeters using combinations of a flat plate and two cylinders for the electrodes, as well as presenting subsequent measurement of the density of slush hydrogen made using the freeze-thaw method. The density values measured for slush hydrogen with a solid weight % of up to 30% were generally found to correspond to within +0.5% of the density values estimated from the latent heat of evaporation of liquid hydrogen. Because the flat plate/cylinder electrode type densimeter allowed easy penetration of solid hydrogen particles within the electrodes, highly accurate density measurements were obtained compared to those simultaneously measured using densimeters witn parallel flat plate electrodes. The practical applicability of the new type slush hydrogen densimeter was accordingly confirmed.
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Tri Agung ROHMAT, Xiao WANG, Tetsuro OBARA, Shigeharu OHYAGI
1999 Volume 65 Issue 632 Pages
1446-1451
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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A numerical study on a planar diffusion flame stabilized behind a backward-facing step is performed. Computational model is set to simulate our experimental study where a fuel gas is supplied from a porous plate behind the backward-facing step. A flame sheet model is used because the simulation is focused on the stabilized flame. The computational scheme is the SIMPLE with the QUICK for convection terms. Although the model is restricted to two-dimensional, the results show that the flame deforms due to the Kelvin-Helmholtz instability arising from the density change due to combustion. Comparison with the experiment is succesfully performed by the schlieren photography and the temperature variation.
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Xu Boyan, Mikio FURUYAMA, Makoto HISHIDA
1999 Volume 65 Issue 632 Pages
1452-1458
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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This paper deals with LPG and CNG jets, which will be used for gas fuel supply system of automobile engine. Variation of tip penetration and vortex radius at the front of jets with injection time of the fuel are numerically calculated with a modified transient jet model based on original WITZE's model. Following conclusions were derived : (1) No significant difference was found in the variation of the tip penetration of fuel jet between LPG and CNG jets. (2) Growing speed of the front vortex of the LPG jet is slightly slower than that of the CNG jet. (3) When the same amount of LPG or CNG fuel is injected into a fuel supply tube, the more the number of injection holes is and the less of each injection hole radius is, the penetration of the jet and the radius of front vortex are decreased. The tip penetration is decreased with decrease in injection pressure.
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Jiro SENDA, Takatsugu ASAI, Bungo KAWAGUCHI, Hajime FUJIMOTO
1999 Volume 65 Issue 632 Pages
1459-1466
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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The new injection system by using mixed fuel dissolved with liquefied CO
2 was proposed in this paper. Liquefied CO
2 was mixed into n-tridecane under pressurized state in order to promote the spray atomization and evaporation due to the effect of the flash boiling phenomena in fuel injection, and to control the combustion process due to the effect of internal EGR effect of CO
2 gas. Therefore, the simultaneous reduction of soot and NO
x cas be achieved effectively by use of this injection system. In this paper, the characteristics of diesel fuel spray dissolved with liquefied CO
2 were investigated quantitatively by means of several optical measurements. And the spray characteristics were revealed by the analysis of chemical thermodynamics. As a result, the atomization of this fuel is promoted due to the flash boiling much more than n-tridecane as the reference of the normal fuel and the spray structure is highly diHerent from that of the normal fuel.Moreover, thenumerical analysis for the atomization and the vaporization process wan carried out based on the flash boiling spray models.
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Osamu TSUBOUCHI, Yoshiaki NAKAMURA
1999 Volume 65 Issue 632 Pages
1467-1472
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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A plate burner with a stack of ceramic filaments, which are catalyzed with Pd are investigated by experiment. As the features of this burner a flame is held near the burner surface because its complicated passages of premixed gas cause vortices to be produced, and also the plate is cooled well by the low temperature premixed gas due to the large passage surface area. The flame made by gas phase reaction activates the catalyst, so that catalytic reaction is caused on the plate surface. Therefore, a preheating device to heat up the burner will not be needed. Two key issues have been examined in this study ; one is the relation between gas phase reaction and surface reaction, and the other is combustion characteristics of this burner. As a result, it is confirmed that the flame made by gas phase reaction causes surface phase reaction a few minutes after ignition. Furthermore, surface reaction activities by catalyst are reduced as either combustion load or excess air ratio increases. However, the concentrations of NO
x and CO can be reduced in a high activity region of catalyst.
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Osamu FUJITA, Masao KIKUCHI, Kenichi ITO, Atsuki SATO, Takashi SAKURAY ...
1999 Volume 65 Issue 632 Pages
1473-1478
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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An experimental study of flame spread phenomena over ETFE (Ethylene-Tetrafluoroethylene) insulated wire was performed under microgravity to obtain fundamental data on fire safety in space. The effects of the parameters thought dominant for wire combustion in fires-the ambient oxygen concentration, wire initial temperature, T
i, and wire diameter, d
ω, - were investigated in the microgravity experiments. A series of comparative experiments were also conducted at normal gravity. Flame shape under microgravity changed depending on the state of the molten fuel accumulation. Experimental results showed that there existed a possibility of higher flame spread rates under microgravity than at normal gravity, in spite of lower flame temperature in microgravity. Wire initial temperature, T
i, had a very large influence both on flame spread rates and extinction limit of the wire under microgravity. The degree of flame spread rate decreased with increase in d
ω and, correspondingly, the increase with decrease in d
ω under microgravity was higher than at normal gravity.
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Hideaki MORIKAWA, Yasuo MORIYOSHI, Takeyuki KAMIMOTO
1999 Volume 65 Issue 632 Pages
1479-1484
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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Since the local inhomogeneity of mixture concentration inside a combustion chamber affects the combustion characteristics, a basic research on combustion phenomenon in stratified charge conditions is required. The authors have made experiments with a constant-volume chamber, which can simulate an idealized stratified charge field by using a removable partition, to obtain the combustion characteristics. As a result, it was found that pressure behavior strongly depends on flame propagation process and that the unburnt hydrocarbon amount can be reduced when a charge stratification of two combustible mixtures or that of a combustible mixture and air are made, while it increases due to a bulk quench when a combustible mixture and a too lean incombustible mixture are charge stratified.
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Katsumi KATAOKA, Yoshitaka ATSUMI, Daisuke SEGAWA, Toshikazu KADOTA, Y ...
1999 Volume 65 Issue 632 Pages
1485-1490
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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An experimental study was made on a natural gas fueled spark ignition engine to improve its thermal efficiency and exhaust emissions by the lean burn operation. A multi-cylinder engine was tested for purposes of practical application. Investigated were the effects of the piston design and the gas motion induced by a shrouded inlet valve on the combustion process, the thermal efficiency, exhaust emissions and the lean limit of stable operation. It was found that a bowl-in-piston resulted in higher thermal efficiency and extended lean limit as compared with a flat piston. A shrouded inlet valve generally resulted in shorter duration of combustion, lower NO
x emissions and lower thermal efficiency than a conventional valve. When a shrouded inlet valve was set so as to direct the mixture flow toward the prechamber throat, the lean limit was extended with low exhaust emissions and relatively high thermal efficiency.
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Takashi ARAKI, Takemi CHIKAHISA, Yukio HISHINUMA
1999 Volume 65 Issue 632 Pages
1491-1497
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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The authors previously reported significant reductions of particulate emissions by generating strong turbulence during combustion process. Extending this, it was attempted to reduce NO
x, particulate, and fuel consumption simultaneously by two-stage combustion ; forming a fuel rich mixture at the initial combustion stage to prevent NO
x formation, and inducing strong turbulence in the combustion chamber at the later stage of combustion to oxidize the particulate. The purpose of this study is to examine the further potential and extent of the two-stage combustion for the emission control. The paper shows experimental results for variety trials of piston configurations, EGR-combinations, and fumigation technology together with the two-satge combustion system. The result was not successful for realizing apparent improvement in emission and fuel consumption over wide range of operating conditions, although simultaneous reduction in NO
x and smoke was possible at limited conditions with the two-stage combustion. The paper provides information for discussing points to be investigated in the next stage and options for future combustion control technology.
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Kenichi HASHIZUME, Ryo MORIKAWA, Takahiro MATSUE, Tetsuya KOYAMA
1999 Volume 65 Issue 632 Pages
1498-1501
Published: April 25, 1999
Released on J-STAGE: March 28, 2008
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An analytical solution for the theoretical fin efficiency of serrated fins was derived in the 1st report. This solution was given as a function of the modified Bessel functions, therefore, a compurter having any solver for the modified Based functions is needed to calculate the fin efficiency. In this report, an approximation equation is presented for the theoretical fin efficiency, which enables the calculation with a pocked calculator. The deviation of the calculated result from the analytical solution is within ±1.5% for the industrially practical ranges.
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