JSME International Journal Series B Fluids and Thermal Engineering
Online ISSN : 1347-5371
Print ISSN : 1340-8054
ISSN-L : 1340-8054
Volume 43 , Issue 2
Showing 1-25 articles out of 25 articles from the selected issue
2000 Volume 43 Issue 2 Pages 117-126
Published: May 15, 2000
Released: February 18, 2008
JOURNALS FREE ACCESS
The swirling flow field, including unsteady 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 tangential velocity of the main flow. Conversely, the vortex has a spiral form opposite 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.
• Akira OJIMA, Kyoji KAMEMOTO
2000 Volume 43 Issue 2 Pages 127-135
Published: May 15, 2000
Released: February 18, 2008
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Recently, the present authors have developed a vortex method for analyses of various two and three-dimensional unsteady flows, aiming its application to various engineering problems. In this paper, a new scheme is proposed for the vorticity creation at a solid surface of a three-dimensional body, in which a number of nascent vortices are introduced in the flow field according to the diffusion and the convection of the vorticity near the solid surface. As an example, the new scheme is applied to the analyses of starting flows around two kinds of bodies : a sphere and a prolate spheroid. As a result of this calculation, the boundary layer separation from the body surface and the development of vortical wake have been reasonably simulated.
• Habib UMUR
2000 Volume 43 Issue 2 Pages 136-142
Published: May 15, 2000
Released: February 18, 2008
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Static pressures in non-circular ducts and pipe fittings (globe, ball and butterfly valves) have been measured in a closed circuit water channel at the range of Reynolds number from 20000 to 80000, which give rise to fully developed turbulent pipe flow, so as to define the friction coefficient (Cf) and resistance coefficients (K). A new proposed equation for friction factor with two new dimensionless parameters as a function of cross sectional area are successfully adopted to fully developed turbulent flow in all cross sections with a precision of better than ± 4%. Measurements showed that friction factors decreased with increasing eccentricity and were in good agreement with the proposed equation. It was also found out that Reynolds number has no effect on resistance coefficients of butterfly, globe and gate valves, but the closing ratio caused K to increase remarkably, and the K value of bends can easily be obtained by an empirical formula based on Moody chart friction factor. Static pressures on fornt and back sides of the circular disc of butterfly valve decreased with Reytnolds nember, remained almost constant inthe radial direction and increased particularly at closing angles of bigger than 60 degrees, where flow rate starts to decrease sharply.
• Zuu-Chang HONG, Ming-Hua CHEN, Wen-Chien DUH
2000 Volume 43 Issue 2 Pages 143-154
Published: May 15, 2000
Released: February 18, 2008
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This study presents a turbulence probability density function (pdf) equation model to solve a self-similar turbulent plane jet flow. The approximate moment method is also applied to solve this pdf equation. The calculated mean velocity, turbulent energy and Reynolds stress agree well with the available experimental data, indicating that the pdf equation model and the moment method can quantitatively describe the statistics of free turbulence. Additionally, the turbulence energy balance and shearstress balance are calculated. According to these calculations the pdf methods are more highly promising than conventional turbulence models in terms of revealing turbulence structure. The applicability of the simple theories of turbulence is also discussed.
• Koh IKEDA, Koji OKAMOTO, Haruki MADARAME
2000 Volume 43 Issue 2 Pages 155-161
Published: May 15, 2000
Released: February 18, 2008
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In this study, a technique for simultaneous measurement of three-dimensional density and velocity distributions was evaluated. Holographic particle image velocimetry (HPIV) was used to reconstruct three-dimensional velocity distributions from three-dimentional particle images recorded on a hgologram. Optical tomography (OT) was used to reconstruct three-dimensional density distributions from multidirectional two-dimensional interferogram images. When a flow field with density variation was illuminated by coherent plane waves, spherical waves were scattered by the particles (particle images), and the illuminating beam was modulated by the density variation (interferogram images). Using a reference beam, both particle and interferogram images could be recorded on a single hologram. Using the spatial filtering extraction (FX) technique, information on both images could be extracted separately from the hologram. In the experiment, a jet of helium gas introduced into air containing small particles was measured. Both particle position and fringe shift caused by the density variation could be observed, demonstrating the effectiveness of the proposed technique.
• Katsuhide OHIRA, Kenji NAKAMICHI
2000 Volume 43 Issue 2 Pages 162-170
Published: May 15, 2000
Released: February 18, 2008
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Slush hydrogen is a mixture of solid hydrogen particles and liquid hydrogen, is being considered as a spaceplane fuel or as a means of transport with hydrogen used as a source of clean energy. In this paper we describe the fabrication of three varieties of capacitance-type densimeters using combinations of a flat plate and two cylinders for the electrodes, and present the subsequent density measurement of slush hydrogen obtained 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 tha latent heat of evaporation of liquid hydrogen. Since the flat-plate/cylinder electrode-type densimeter allowed easy penetration of solid hydrogen particles within the gap between the electrodes, highly accurate density measurements were obtained compared to those simultaneously measured using densimeters with parallel flat plate electrodes. The practical applicability of the new type of slush hydrogen densimeter was thus confirmed.
• Myung Taeck LIM, Byung-Chul CHOI, Young Hong KWAK
2000 Volume 43 Issue 2 Pages 171-179
Published: May 15, 2000
Released: February 18, 2008
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Aging characteristics of automotive catalysts are experimentally investigated under a few steady-state fast aging conditions using a test system configured around an engine and a dynamometer. Temperature of the engine exhaust gas at the inlet, outlet and 4 points within the catalytic converter are measured under various engine operating conditions. Result of the measurements indicates that the temperature is fairly uniform along the center line of the converter during steady-state engine operations. Conversion efficiency of the catalytic converters are monitored as an indicator for deactivation under steady but harsh aging conditions of high temperature and various air-fuel ratio. The conversion efficiencies measured during the aging operations are then used to calibrate a preliminary model which is proposed herein to predict, in principle, the extent of degradation under arbitrary aging conditions as a function of temperature and oxygen concentration of the feed gas.
• Yuichi MURAI, Yoichiro MATSUMOTO, Xiang-qun SONG, Fujio YAMAMOTO
2000 Volume 43 Issue 2 Pages 180-187
Published: May 15, 2000
Released: February 18, 2008
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The turbulence structure in a rising bubbly flow driven by bubble buoyancy has been analyzed using the Eulerian-Lagrangian model. A new method of calculating the two-way interaction between the dispersed bubbles and the liquid phase was proposed to accurately simulate the local fluctuations of liquid flow induced by bubble migration. The present two-dimensional simulation revealed that, (1) in the case of the larger bubble, the turbulence structure has the longer wavelength in the vertical direction, and, (2) the wave spectrum of kinetic energy of the liquid phase is sensitive to the average void fraction and the lift force of the bubbles.
• Yuichi MURAI, Xiang-qun SONG, Takashi TAKAGI, Masa-aki ISHIKAWA, Fujio ...
2000 Volume 43 Issue 2 Pages 188-196
Published: May 15, 2000
Released: February 18, 2008
JOURNALS FREE ACCESS
The inverse energy cascade, which is one of the important phenomena 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 PIV, the flow field of liquid phase is measured by separating an original image to respective phase images using a statistical thresholding method for separating image parameters of bubbbles and particles. The present results obtained in the case where the bubble Reynolds number and average void fraction are less than 30 and 1.5%, respectively, confirm the large energy decay with a slope index steeper than -5/3 in the log-log diagram of energy spectrum in a high wavenumber region. An important relationship between the energy spectrum and the bubble-bubble interval distance is also detected.
• Yuichi MURAI, Atsuhide KITAGAWA, Xiang-qun SONG, Junichi OHTA, Fujio Y ...
2000 Volume 43 Issue 2 Pages 197-205
Published: May 15, 2000
Released: February 18, 2008
JOURNALS FREE ACCESS
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 nonuniform flow. In this paper we are concerned with the validation of the numerical model and various parametric dependencies 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 were introduced in our first report, 2) the strong relationship between energy-decaying process and bubble-bubble distance interval is also identified by the present analysis, and 3) the slope of energy-decaying in the high wavenumber region depends on the kinematic viscosity of liquid, and that in the low wavenumber region depends on inhomogeneous buoyancy distribution which changes due to the bubble motion.
• Satoshi KUMAGAI, Kazunori KAWABATA, Hiroyuki YOSHIKAWA, Ryohachi SHIMA ...
2000 Volume 43 Issue 2 Pages 206-212
Published: May 15, 2000
Released: February 18, 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.
• Atsushi YAMAGUCHI
2000 Volume 43 Issue 2 Pages 213-218
Published: May 15, 2000
Released: February 18, 2008
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Tribological conditions between the piston and cylinder wall are very important criteria to realize high efficiency and reliability in piston pumps and motors, in particular for swash plate types. In this paper we theoretically analyze the solid contacting forces and power losses under medium- and high-speed operations. Three calculating methods are discussed with regard to cavitation of the fluid film. The effects of piston mass, differences between the male and female pistons, rotating cylinder block types and rotating swash plate types are also considered.
• Ryo MIYHAKE, Hiroshi OHKI, Isao YAMAZAKI, Takeo TAKAGI
2000 Volume 43 Issue 2 Pages 219-224
Published: May 15, 2000
Released: February 18, 2008
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Effect of the flow characteristics in a newly developed micro-machined sheath flow chamber on the accuracy of cytometric analysis was investigated. The chamber was formed by laminating three 100-μm-thick photo-etched metal plates. Sample fluid containing cells, which enters the chamber via an axial specimen nozzle, is enveloped by a buffering sheath-fluid and transported to a capillary channel. Microscopic observation and three-dimensional viscous flow analysis predict that the dispersion of cells in the capillary channel is favorably reduced when the Reynolds number is between 500 and 750, which is value associated with low deviation of the analytical results. The five classifications of human white blood cells were determined. and this verified that change of the deviation depends on the Reynolds number. The results confirm Reynolds number of 500-750 is appropriate for good classification.
• Masaaki TAMAGAWA, Teruaki AKAMATSU, Takashi SANO
2000 Volume 43 Issue 2 Pages 225-232
Published: May 15, 2000
Released: February 18, 2008
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This paper describes the effects of the particle inertia and the contact with the wall on hemolysis properties. The newly proposed methods of examining the inertia of red blood cells (particle) on particle path are discussed using computational fluid dynamics (CFD). In these methods, the particles are moved by Stokes drag including effects of difference of density between plasma and internal liquid in the blood. The results of computational analysis using these methods show that (1) the diameter of the particle (red blood cell), that is inertia of the cells, (2) the configuration of the objective wall boundary are important factors for this prediction. The results also show that if the inertia and the contact with the wall are considered, the precision of the prediction of the hemolysis properties will be improved comparing with that they are not considered.
• Yutaka MIYAKE, Koichi TSUJIMOTO, Yasuaki AGATA
2000 Volume 43 Issue 2 Pages 233-242
Published: May 15, 2000
Released: February 18, 2008
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A Direct Numerical Simulation (DNS) is conducted for a turbulent flow in a channel bounded by one rough and another smooth wall. Rough wall is modeled by roughness elements represented by zero-volume wall-normal lines extending from the wall surface to around 15-30 in wall unit, which generate Stokes drag to the local flow. Global Reynolds number based on the mean friction velocities on two walls and channel half width is 400. It is inteded here to demonstrate the validity of the roughness model, comparing the obtained flow with available experimental results. It was confirmed that the model reproduces the experimentally obtained mean flow satisfactorily and that turbulence modification by roughness in the layer above the top of roughness elements is qualitatively coincident with the experimental results.
• Takeshi MIYAMOTO, Keiichi NAKAGOME, Hisashi AKAGAWA
2000 Volume 43 Issue 2 Pages 243-249
Published: May 15, 2000
Released: February 18, 2008
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Three-dimensional computations were carried out to study the effects of engine operating conditions on NOx emissions from premixed lean diesel combustion in a DI (Direct fuel Injection) engine. A modified version of the KIVA II computer code was used for numerical simulations. Qualitatively good agreement between computational and experimental results of the spatial distribution of impinging fuel sprays, the heat release rate, and the relative NOx mass have been achieved. The computational results demonstrate that NOx emissions are significantly influenced by intake air temperature, fuel injection timing, and fuel ignitability. It was also shown that fuel droplets which enter the squish region can later contribute to unburned fuel emissions.
• Yoshihiro KIKUCHI, Hiroshi SUZUKI, Masonori KITAGAWA, Ken-ichiro IKEYA
2000 Volume 43 Issue 2 Pages 250-257
Published: May 15, 2000
Released: February 18, 2008
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An experimental study was conducted to investigate the effect of pulsating Strouhal number, Srp, on flow and heat transfer around a heated cylinder in a pulsating cross-flow. The averaged Reynolds number was kept at 400 while the oscillatory Reynolds number was changed from 40 to 300. Pulsating Strouhal number, Srp, ranged from 0 to 1.37. Two marked peaks of the mean Nusselt number were observed at approximately Srp =0.2 and 0.6. Flow visualization experiments revealed that twin symmetric vortices were periodically formed behind the cylinder at Srp corresponding to the 'lock-on' of the shedding of vortices. From the velocity field measured by particle image velocimetry (PIV), it was determined that the flow reversal approaching the back surface of the cylinder was intensfied by the twin vortices. This flow reversal caused heat transfer enhancement on the back surface of the cylinder.
• Nilson KUNIOSHI, Yumi YATAE, Shigeru MOURI, Seishiro FUKUTANI
2000 Volume 43 Issue 2 Pages 258-263
Published: May 15, 2000
Released: February 18, 2008
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The dynamics of the oxidation reaction of an acetylene molecule with an oxygen atom was investigated through an ab initio molecular orbital method. The three reactions (1) C2H2+O→HCCO+H, (2) HCCO+CH2+CO and (3)C2H2+O→CH2+CO, reported in reaction schemes, were confirmed as being the main elementary steps related to the acetylene oxidation but were found to be not single elementary steps, with each one forming intermediary spacies before the proposed products. These intermediaries are expected to decompose always and much faster than they form, so that those three reactions can be treated as elementary steps without problem. Under ideal conditions, only reaction (3) can be expected to proceed, but vibrations of the atoms in a structure formed during the process can cause its decomposition into HCCO +H, and later the so formed HCCO can meet another H atom and react to CH2+CO. Reactions (1) and (2) are then found to be, respectively, an early and a late step of reaction (3), but each of the three events can occur, depending on how is the collision between the O atom and the vibrating C2H2 molecule. The present results are compared with experimental data reported in the literature, and a qualitative agreement with the data of Miller and Bowman can be seen for reactions (1) and (3), and with the data of Warnatz for reaction (2).
• Yuso OKI, Jun INUMARU
2000 Volume 43 Issue 2 Pages 264-272
Published: May 15, 2000
Released: February 18, 2008
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It is important to clarify the release characteristics of ash components and condensing behavior of released components in a high pressure reducing atomosphere, because these behaviors affect coal ash properties and change the slagging and fouling characteristics in gasifier. 3 brands of pulverized coal were burnt following JIS (Japanese Industrial Standards) regulation to form ash samples, and prepared ash was exposed to a hydrogen/argon mixture reducing gas (hydrogen 3%) at temperature ranging from 600°C to 1460°C for about 2 hours in electric tube furnaces at an atmospheric pressure and pressure of 900 kPa. By analyzing the composition of each sample by XRF, release characteristics of each component was clarified. To obtain referrring data, CCSEM analysis was performed. In this paper, the changes in ash compositon at the temperature in the reductor of a gasifier were quantified. The effect of coal brand and pressure on ash composition was found to be remarkable.
• kouichi KAMIUTO
2000 Volume 43 Issue 2 Pages 273-278
Published: May 15, 2000
Released: February 18, 2008
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The ability of the cubic lattice model for the thermal and radiative properties of open-cellular porous materials in predicting the combined effect of conduction and radiation in plane-parallel, open-cellular porous plates was investigated in comparison with available experimental data. The validities of the P1 approximation to radiative transfer and the simple adding method for the total heat flux were also addressed. It is concluded that the cubic lattice model can be utilized accurately to evaluate the temperature porfiles and heat transfer characteristics in open-cellular porous plates and that the simple adding method gives the fairly accurate total heat flux across the media. In addition, it is found that there exists only a little discrepancy between the results for the temperature profiles and mean total effective thermal conductivities obtained by the P1 approximation and those obtained by the exact numerical method.
• Takayuki TSUTSUI, Tamotsu IGARASHI, Hajime NAKAMURA
2000 Volume 43 Issue 2 Pages 279-287
Published: May 15, 2000
Released: February 18, 2008
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Fuel oil storage tanks are used in the industrial regions of the world to provide a stable energy supply. In cold regions, the oil must be kept warm. In designing the heating system of an oil storage tank, it is necessary to estimate the heat loss from the shell and roof of the tank. To characterize these heat-loss properties, experimental studies were carried out on the fluid flow and local heat transfer around a cylindrical protuberance with a height/diameter ratio of 0.35 mounted on a flat plate in laminar and turbulent boundary layers. The local drag coefficient and characteristics of the local and average heat transfer around the cylindrical protuberance are clarified. The results obtained were compared with the results of an ordinary finite circular cylinder with the height/diameter ratio of 1.
• Takashi TOKUMASU, Yoichiro MATSUMOTO
2000 Volume 43 Issue 2 Pages 288-295
Published: May 15, 2000
Released: February 18, 2008
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In our 3rd report, we introduced a Lennard-Jones (LJ) potential parameter based on the potential obtained by ab initio calculation and collision cross section from the Wang-Chang, Uhlenbeck and Taxman's theory and molecular dynamics (MD) simulation. In the present study, we have improved the dynamic molecular collision (DMC) model to callculate the property of MD simulation better than the previous model. To confirm its validity we calculated the equilibrium state, the transport coefficient (viscosity coefficient and heat conductivity) at various temperatures and the normal shock wave by the direct simulation Monte Carlo (DSMC) method using the DMC model and compared the results with other theoretical and experimental results. Consequently, we found that the diatomic rarefied gas flows could be simulated very well using our model. These results were compared with those obtained by the Larsen Borgnakke model. It was found that this model was more efficient than the previous model.
• Hidetaka OKUI, Myeong-Kwan PARK, Shuzo OSHIMA, Ryuichiro YAMANE
2000 Volume 43 Issue 2 Pages 296-304
Published: May 15, 2000
Released: February 18, 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 upwing 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, 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.
• Takeshi SETA, Koji KONO, Daniel MARTINEZ, Shiyi CHEN
2000 Volume 43 Issue 2 Pages 305-313
Published: May 15, 2000
Released: February 18, 2008
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A finite difference lattice Boltzmann method (FDLBM) for two-phase flows pertinent to isothermal non-ideal fluids is proposed. This FDLBM introduces pseudo-potential and recovers a full set of hydrodynamic equations for non-ideal fluid throgh the Chapman-Enskog expansion procedure. Numerical measurement of surface tension agrees well with theoretical predictions. Simulations of two-phase phenomena, including phase-transition and droplets collision are carried out, showing applicability of the model for two-phase flows. Finite difference Lattice Boltzmann method ensures numerical stability of the scheme. This LB model retains advantages of conventional LB methods such as a linear advection in the kinetic equation and parallel nature in computing.