JSME International Journal Series B Fluids and Thermal Engineering
Online ISSN : 1347-5371
Print ISSN : 1340-8054
ISSN-L : 1340-8054
Volume 39 , Issue 3
Showing 1-27 articles out of 27 articles from the selected issue
  • Toshio KOBAYASHI, Shigenori TOGASHI
    1996 Volume 39 Issue 3 Pages 453-460
    Published: August 15, 1996
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    In our previous work, we have already computed backward-facing step flow using large eddy simulation (LES) and obtained satisfactory results in comparison to experimental data. In this work, the behavior of time-averaged turbulence models and the influence of the diffusion model in the turbulent energy equation are investigated using the LES database. It is found that the algebraic stress model describes this flow more accurately than the eddy viscosity model, and that the gradient-diffusion model for the turbulent diffusion term cannot accurately predict the turbulent energy distribution in the recirculating region. A new diffusion model using TSDIA theory is applied and the relationship between the reattachment length and the turbulent energy distribution in the recirculating region is discussed.
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  • Shinsuke MOCHIZUKI, Akimine IZAWA, Hideo OSAKA
    1996 Volume 39 Issue 3 Pages 461-469
    Published: August 15, 1996
    Released: February 18, 2008
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    Large-scale coherent motions were investigated experimentally in a d-type rough wall boundary layer modified with longitudinal thin ribs. Higher-order moments and conditional averaged statistics were obtained at Rθ=1 300 and 5 000, where the local skin friction coefficients of modified flow are the same as and about 17% larger than those of smooth wall flow. The magnitude of triple velocity correlations is reduced in most of the layer by drag reduction control using longitudinal thin ribs. The higher-order moments and conditional averaged signals obtained by the VITA analysis show that the turbulence production model with a pair of streamwise vortices interacting with outflow from the roughness grooves is reasonable.
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  • Toshio TAGUCHI, Etsuro HIRAI, Mitsuo KATO, Masahide MIYAMOTO, Yasuo KA ...
    1996 Volume 39 Issue 3 Pages 470-474
    Published: August 15, 1996
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    Low-density choked flow through a parallel plate channel with a narrow gap is studied experimentally for a wide range of Reynolds numbers. In the region from continuum flow to slip flow, the choked flow is analyzed by one-dimensional flow approximation based on the integrated boundary layer equations, taking into account the slip at the channel walls. The calculated discharge coefficients and pressure distributions agree well with the experimental results for a wide range of Reynolds numbers, including the slip flow region. A nondimensional correlation equation of the discharge coefficient is proposed as a function of Rehs/l for Rehs/l<2×102. In the region from slip flow to molecular flow, the experimental results agree well with those of previous work. A nondimensional correlation equation of Cdl/hs is proposed as a function of Re for 7<Re<5×101.
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  • Hideo KASHIMURA, Tsuyoshi YASUNOBU, Toshiyuki AOKI, Kazuyasu MATSUO
    1996 Volume 39 Issue 3 Pages 475-481
    Published: August 15, 1996
    Released: February 18, 2008
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    An experimental study is carried out on the emission of a propagating compression wave from an open end of a tube. A shock tube with a fast opening gate valve instead of a diaphragm is employed for producing compression waves of various strength. The magnitude of the impulsive wave emitted from an open end is compared with the results of aeroacoustic analysis presented in the previous reports. The directivity of the impulsive wave and its attenuation with distance are discussed. It has been shown that the magnitude of the emitted impulsive wave agrees well with the results of the aeroacoustic analysis, and the directivity of the impulsive wave is independent of the strength of the compression wave but depends on the length of the compression wave.
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  • Hideo WATANABE, Akio IHARA, Hiroyuki HASHIMOTO
    1996 Volume 39 Issue 3 Pages 482-488
    Published: August 15, 1996
    Released: February 18, 2008
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    Experiments were performed with two circular cylinders whose walls were porous and permeable in order to investigate the effects of flow of water through the wall. Each cylinder was made of bronze sintered compact, available as a sintered metallic filter. It had an outside diameter of 30 mm, a wall thickness of 2 mm and a nominal filter size of 2 μm or 20 μm. Force coefficients and pressure distributions of the test cylinders were measured over the Reynolds number range of 1.1×105∼4.4×105 and were compared with those of the same porous cylinders into which another circular cylinder, an "inner cylinder" with a solid wall, was inserted to obstruct such a through-flow. The measured results showed that the drag coefficients and the root-mean-square values of the fluctuating lift coefficients of the test cylinder equipped with the inner cylinder were smaller than those with the through-flow. This was caused by the increase in the effective surface roughness and the altered pressure distribution because of the permeability of the cylinder wall. The increase in the drag coefficient was accompanied by the decrease in the Strouhal number of the fluctuating lift, and vice versa.
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  • Kenji OKA, Takahito NOZAKI, Hidesato ITO
    1996 Volume 39 Issue 3 Pages 489-498
    Published: August 15, 1996
    Released: February 18, 2008
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    The loss coefficients and the power-loss coefficients for sharp-edged combining tees with the area ratios of 11. 44 and 17. 72 are determined experimentally. Based on the least squares analyses of the experimental results of both the present authors and previous investigators, empirical equations of loss coefficients for combining tees are proposed. The effects of both the area ratio and the radius of curvature of the wall at the joining edge on loss coefficients are taken into account in deriving the equations. The comparison of the proposed equations with the experimental results shows that the proposed equations can be used to reliably estimate the energy losses at combining tees.
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  • Takao KOBAYASHI, Tohru NAKAYAMA, Hiroyuki TAKATA
    1996 Volume 39 Issue 3 Pages 499-507
    Published: August 15, 1996
    Released: February 18, 2008
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    Aerodynamic characteristics of oscillating cascades of blades accompanied by elastic deformation of blade sections in a uniform incompressible flow are predicted numerically. Unsteady formulation is based on a small perturbation approach with the use of potential equations expressed on a moving computational grid. The governing equations are discretized by the finite element method. Modal shapes of blade oscillation are obtained first and a parametric study on unsteady aerodynamic characteristics is conducted for the two-dimensional cascade of the tip section of a test compressor. Furthermore, the oscillation displacement of the blades is divided into four components, i.e., two translational components (normal and tangential to the blade chord), a rotational component, and a section-deformation component, in order to analyze the contribution of each component to unsteady aerodynamic work which causes flutter excitation. It is shown that the effect of the blade section deformation is very significant in determining the unsteady characteristics of oscillating cascades.
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  • Yoshiatsu OKI, Takahiko TANAHASHI
    1996 Volume 39 Issue 3 Pages 508-516
    Published: August 15, 1996
    Released: February 18, 2008
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    In our previous research, primitive variable methods were proposed in the numerical scheme of magnetic field of thermo-electrically conducting fluids. The point to be emphasized in the above-mentioned scheme is to satisfy the conservation law of magnetic flux effciently. In the present paper, we compare two numerical schemes of magnetic field, namely the cross helicity method and the numerical residual method, concentrating on the convergence of Poisson's equations of the velocity and magnetic fields. Moreover, the relationship between the periodicity of low Prandtl number fluids and the inhibitory effect of convection due to Lorentz force must be clarified quantitatively. The frequency characteristics of kinetic energy, enstrophy, palinstrophy and hydromagnetic cross helicity are calculated using the maximum entropy method.
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  • Akio TOMIYAMA, Akira SOU, Tadashi SAKAGUCHI
    1996 Volume 39 Issue 3 Pages 517-524
    Published: August 15, 1996
    Released: February 18, 2008
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    The feasibility of a detailed numerical simulation of a Taylor bubble in a stagnant liquid filling a vertical pipe was examined in the present study. The simulation was carried out using the volume of fluid method. Since there have been few quantitative experiments on Taylor bubble shape, physical experiments under a wide range of Eotvos and Morton numbers were also conducted using sucrose solution and air at room temperature and atmospheric pressure. It was confirmed by experiments that the bluntness of the nose of the bubble, the flatness of the tail and the liquid film thickness around the bubble are strongly affected by the two dimensionless numbers. Calculated terminal rising velocities and bubble shapes agreed fairly well with all the measured ones, which indicates that the effects of drag force, buoyancy and surface tension force on the bubble were well predicted by the simulation.
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  • Takeo KAJISHIMA, Takayuki SAITO
    1996 Volume 39 Issue 3 Pages 525-532
    Published: August 15, 1996
    Released: February 18, 2008
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    A numerical method for simulation of unsteady flow in a large-scale air-lift pump, which is the main element of a deep-sea mining system, has been developed. We have proposed an iterative scheme for implicit time marching of density and pressure, and numerically simulated an air-water two-phase flow using a drift-flux model. In this paper, we describe improvements in the numerical scheme, especially for the convection term. First, convection terms are discretized based on the velocity component of each phase. Second, the finite difference method, which has excellent energy conservation properties, is applied. Then, the upstream-shifted interpolation technique is introduced. Numerical results for both unsteady and steady-state features show reasonable agreement with the experimental data obtained using an air-lift system of a depth of 200 m.
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  • Toshihiko ISHIDA, Tomohide NIIMI, Tetsuo FUJIMOTO, Hiroshi NAKAYAMA
    1996 Volume 39 Issue 3 Pages 533-539
    Published: August 15, 1996
    Released: February 18, 2008
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    As a method for analysis of supersonic flow, visualization of the flow field structure using LIF of tracers seeded in a carrier gas has been employed. In this study, the capability of imaging of supersonic flow using O2-LIPF (laser-induced predissociative fluorescence) is examined. Since oxygen is one of the main constituents of air, O2-LIPF may enable visualization of air flow in a high-speed wind tunnel without tracers. However, because the visualization of the flow field below room temperature using O2-LIPF is very difficult, it has been applied only to high enthalpy and combustion flow, not to high-speed flow at low temperature. In this study, the supersonic oxygen flow is visualized by O2-LIPF using an ArF excimer laser and a high-sensitivity CCD camera. If the CCD camera is set at a long exposure time (1200 sec) and the scattered laser beam is suppressed sufficiently, the supersonic oxygen flow below room temperature can be imaged successfully using O2-LIPF.
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  • Hiromu TSURUSAKI, Hirofumi SHIMIZU, Yoshinobu TSUJIMOTO, Yoshiki YOSHI ...
    1996 Volume 39 Issue 3 Pages 540-545
    Published: August 15, 1996
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    The internal flow of a cross-flow fan (CFF) is affected strongly by an eccentric vortex generated in the CFF. However, the mechanism of growth of the eccentric vortex is not clear. Therefore, a design method for the CFF has not yet been established. In order to study the internal flow of the CFF, the authors measured the velocity distributions by particle-tracking velocimetry (PTV) using an experimental apparatus for water flow visualization. The pathline images photographed with a digital still camera were analyzed by a computer program developed by one of the authors in order to obtain velocity distributions. Before the measurements of the internal flow were carried out, the measurement accuracy of this PTV was examined, and it was confirmed that this PTV was useful to this study. The measured results on the internal flow were discussed from several points of view and useful information on the flow field of the CFF was obtained.
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  • Eiji TOMITA, Yoshisuke HAMAMOTO, Hiroyuki TSUTSUMI, Shiro TAKASAKI
    1996 Volume 39 Issue 3 Pages 546-553
    Published: August 15, 1996
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    For the study of the combustion in a transient gas jet used in gas diesel engines, it is very important to investigate the entrainment process of the surroundings of the jet. In this study, a path line method utilizing a CCD random shutter camera with various shutter times was applied. Large (40 μm), lightweight microballoon particles are used for scattering the path lines of the surroundings and fine particles (0.75 μm) are used for visualizing the approximate shape of the jet. The transient gas velocity was also measured with a two-component laser Doppler velocimeter (LDV). Consequently, (1) the jet configuration and the entrainment process could be visualized simultaneously, and (2) this path line method was found to be very useful for estimating the air mass entrained because of the good agreement with the values obtained using LDV.
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  • Wu-Qiang LONG, Hiroyuki OHTSUKA, Tomio OBOKATA
    1996 Volume 39 Issue 3 Pages 554-561
    Published: August 15, 1996
    Released: February 18, 2008
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    To study the flow characteristics and particle diameters in a wide-angle conical spray proposed for premixed combustion diesel engines, an unsteady conical spray in air has been analyzed using a phase Doppler anemometer (PDA). In these experiments, the injection frequency is 20.8 Hz and the fuel injection quanTITY is 10.3 mg per cycle. Axial and radial bulk particle velocities and mean particle diameter distributions are obtained. As a result, it is found that the mean velocity distribution profile resembles the Goertler distribution, and the Sauter mean droplet diameter in the conical spray is as small as 30 μm. The relationship between particle diameter and velocity over the entire spray is negative and unusual compared with steady pressure spray flows, but is found to be normal if the spray is divided into several parts. We also find that small-diameter particles (20 μm) which are injected at a high speed (60 m/s) in the earliest stage lose velocity rapidly, merge into bigger particles, and are overtaken by bigger but slower particles which are emitted during a later stage. Large-diameter (50 μm) particles gather at the tip of the spray since they travel further from the nozzle exit.
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  • Seiji SHIMIZU, Ze-Long WU
    1996 Volume 39 Issue 3 Pages 562-567
    Published: August 15, 1996
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    It has been shown that the premixed abrasive water jet system has a greater capacity for drilling and cutting than the conventional abrasive water jet system. In the present investigation, the motion of spherical particles in a premixed abrasive water jet nozzle is investigated theoretically. The flow in the nozzle is treated as one-dimensional flow. Convergent nozzles with and without a cylindrical focusing section are studied. The numerical results show that the particle velocity at the outlet of the nozzle has a tendency to increase in proportion to the square root of the injection pressure. The outlet particle velocity decreases with increasing diameter and specific gravity of the particles. The optimum length of the focusing section increases with increasing diameter and specific gravity of the particles.
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  • Yasunori ADACHI, Hitoshi SOYAMA, Yoshiaki YAMAUCHI, Kazunori SATO, Tos ...
    1996 Volume 39 Issue 3 Pages 568-574
    Published: August 15, 1996
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    In order to establish a useful monitoring method for material erosion caused by high-speed submerged water jets, we clarify the main source of cavitation noises around free jets by using two hydrophones, and also analyze the AE characteristics of the impulsive pressures induced by cavitation on the specimen for the impinging jets. Clearly, the energies of high-frequency components in the jets change markedly with injection pressure and standoff distance.
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  • Akinori FURUKAWA, Shin-ichirou SHIRASU, Sinzi SATO
    1996 Volume 39 Issue 3 Pages 575-582
    Published: August 15, 1996
    Released: February 18, 2008
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    Gas accumulation and its extension in a centrifugal impeller of a two-phase flow pump cause head degradation. In order to decrease the head degradation, a special type of impeller has been designed based on the following concepts. The open impeller consists of two stages of rotating and stationary circular cascades with an appropriate number of thin blades for creating a dispersive effect of each cascade inlet for gas-phase flow. The outer rotating cascade has a large blade outlet angle to keep the pump head high even at high void fraction. Holes on the rotating disk, through which recirculating liquid flows may blow off the gas accumulation region, are equipped in each flow passage. The newly conceptualized impeller was examined experimentally. Results are discussed in the present paper with help of visual observation of gas behavior in the impeller flow passage.
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  • Kiyoshi TAKANO, Ichiro TANASAWA, Shigefumi NISHIO
    1996 Volume 39 Issue 3 Pages 583-589
    Published: August 15, 1996
    Released: February 18, 2008
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    A further experiment was carried out to confirm EHD (electro-hydrodynamic) effect on enhancement of evaporation of a liquid droplet. A steady-state heat flux during evaporation of a single droplet was measured by controlling the flow rates of liquid and heat supplied to the droplet. The liquids used in this experiment were refrigerant R113 and ethanol. A DC electric voltage was applied between the heat transfer surface and a needle nozzle which was used to supply the test liquid. The result indicated that in the case of R113 droplet, a higher electric voltage was needed to enhance evaporation. On the other hand, in the case of ethanol droplet, evaporation enhancement was observed at a lower voltage, in particular at the region of low surface superheat. This tendency agreed with the result of a preceding report of this study in which the evaporation time of an ethanol droplet was measured. In the present experiment, the enhancement ratios of evaporation of R113 and ethanol droplets were 1∼2.8 and 1∼7.6, respectively.
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  • Shigeru AKAIKE, Koji KIKUYAMA, Motohiro KITADA, Kazutoshi KUWAYAMA
    1996 Volume 39 Issue 3 Pages 590-596
    Published: August 15, 1996
    Released: February 18, 2008
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    Rotational noise is one of the main sources of noise emitted by a fan. This type of noise has discrete frequency components, and is so severe that many methods have been developed for its reduction. There have been few studies on rotational noise, however, to clarify the generation mechanism and determine concrete methods for noise reduction. In the present study the spacings of the blades were changed and comparisons were made with a fan having equally spaced blades. The discrete frequency components were found to be suppressed in the fan with unequally spaced blades and the noise tended to become white noise if the blade spacing and blade setting angles were properly chosen. The instantaneous pressure change on the shroud due to blade passing was examined since it is closely related to the discrete frequency components of noise. By decomposing the measured pressure change in terms of a Fourier series the characteristics of rotational noise were analyzed and compared with simulation results obtained using a pressure wave model. The prediction of the rotational noise emitted by axial fans with unequally spaced blades is presented and found to agree well with the experimental results.
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  • Hiroshi NAGAI, Ichiro FUJIMOTO, Hideo TANAKA, Susumu ISHII
    1996 Volume 39 Issue 3 Pages 597-607
    Published: August 15, 1996
    Released: February 18, 2008
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    A comparison of mistuning effects on the torsional flutter suppression between fully stalled and unstalled cascades is made focusing on variation of the natural frequency and blade arrangement. Numerical results are obtained for fundamental characteristics of flutter suppression effects. In both stalled and unstalled cascades, the larger the variation of natural frequency the more stable the cascades. Furthermore, the difference in flutter modes caused by mistuning between both cascades is clarified.
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  • Kenichiro NAGAI, Kazuhiko TOSHIMITSU, Masanobu NAMBA
    1996 Volume 39 Issue 3 Pages 608-614
    Published: August 15, 1996
    Released: February 18, 2008
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    A theoretical analysis of the cascade flutter suppression using active acoustic excitations is presented. A model considered herein is a three-dimensional linear cascade of flat plates oscillating in a subsonic flow between parallel walls. One of the walls is partially made of actuator surface like a loudspeaker which generates sound waves with the same frequency as that of the blade oscillation. The unsteady aerodynamic work on blades due to oscillation and interaction with the acoustic disturbances generated from the actuator surface is calculated. Dependence of the aerodynamic work on the location, width, vibration modes of the actuator surface and the phase difference between the cascade and actuator surface oscillations are investigated. Numerical results show the optimum conditions of the actuator surface oscillation for effective flutter suppression.
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  • Akira NISHI
    1996 Volume 39 Issue 3 Pages 615-620
    Published: August 15, 1996
    Released: February 18, 2008
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    If the compression process of a regenerative gas turbine cycle is replaced by an isothermal compression process, higher thermal efficiency can be expected. This new cycle is a combination of parts of the Brayton and Ericsson cycles, and it is expected to achieve high efficiency. Isothermal compression in this cycle can be achieved by using a hydraulic air compressor, which converts hydraulic energy to energy of compressed air. The performance of such a system was analyzed by assuming conventional operating conditions and component characteristics. As a result the higher thermal efficiency of the system was proved. The application of this system to a conventional hydraulic power plant was discussed.
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  • Hiroshi ISHII, Yasushige KASHIWABARA
    1996 Volume 39 Issue 3 Pages 621-631
    Published: August 15, 1996
    Released: February 18, 2008
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    This study investigates the effects of various parameters on the inception and post-stall characteristics of surge and rotating stall in multistage axial compressors, using a numerical model for multiblade-row compressors. The parameters described in this study are the shape of the total pressure loss and deviation angle characteristics, IGV (inlet guide vane) outlet flow angle, inlet flow distortion, and bleeding. It is found that there are two types of rotating stall differing in magnitude, that inlet distortion and the deterioration in compressor performance reduce the inception margin of unstable behavior, and that there is an optimal bleeding that can optimize the inception margin of unstable behavior. The usefulness of the present model is examined through numerical investigations, and the validity of the model is confirmed by comparing predicted results obtained using the model with test results obtained using a single-stage compressor and a 3-stage compressor.
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  • Masahiro ISHIDA, Hironobu UEKI, Noboru MATSUMURA, Zhi-Li CHEN
    1996 Volume 39 Issue 3 Pages 632-639
    Published: August 15, 1996
    Released: February 18, 2008
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    The burned zone excess air ratio λd in the diffusion combustion process was analyzed using the two-zone model, and it was compared with the excess air ratio λf estimated using a steady diffusion flame model of the fuel spray. It is found that λd is dependent on the fuel spray penetration and ignition delay. If the premixed combustion fraction is less than 50%, the NO formation is minimally influenced by the excess air ratio during premixed combustion and is dependent on the excess air ratio λd which determines the maximum temperature during diffusion combustion. It is clarified by analysis of the two-zone model that the large reduction in NOx due to timing retard is mainly caused by decreases in both combustion temperature and combustion pressure, and the small reduction in NOx occurring when the nozzle-hole diameter is decreased, is due to a small decrease in combustion pressure resulting from a decrease in the heat release rate during premixed combustion.
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  • Shin-ichi INAGE, Masaya OHTSUKA
    1996 Volume 39 Issue 3 Pages 640-646
    Published: August 15, 1996
    Released: February 18, 2008
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    The authors propose a new turbulent premixed combustion model based on a hyperbolic tangent approximation of the reaction progress variable distribution in a one-dimensional laminar flame. Several different conventional models including FL (flamelet), EBU (eddy break up), ED (eddy dissipation) and FS (flame sheet) models are compared with the proposed model. Main features of the proposed model are as follows : (1) The model in constructed from a laminar flamelet part and a distributed flame part. (2) The model is applicable to laminar and turbulent flame analyses, and it does not depend upon the types of turbulent models. (3) Its distributed flame part includes EBU, ED and FS models as approximations.
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  • Yasuo YOSHIKAWA, Hitoshi KUNIMI, Shizuo ISHIZAWA
    1996 Volume 39 Issue 3 Pages 647-652
    Published: August 15, 1996
    Released: February 18, 2008
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    The effect of the introduction of low-emission vehicles on air quality improvement in the South Coast Air Basin (SCAB) around the Greater Los Angeles area in California is studied using a three-dimensional numerical simulation model which solves the urban-scale atmospheric diffusion equations and photochemical reactions. The results indicate that replacing all the light duty vehicles (LDVs) with ZEV, which satisfy the strictest regulations, will reduce the total mass emission from automobiles (CO by 83%, NOx by 66%, and ROG by 85%). Ozone concentration over the SCAB is also shown. Replacement of LDVs with 1994 regulation level vehicles, TLEV, LEV and ZEV, will reduce the maximum ozone concentration by 14%, 17%, 18% and 20%, respectively.
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  • Yoshifumi MORIYA, Noriaki ISHII
    1996 Volume 39 Issue 3 Pages 653-659
    Published: August 15, 1996
    Released: February 18, 2008
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    The present study introduces a humidity control apparatus which can hygienically and automatically maintain an appropriate humidity level of indoor air without either a water supply or a drainage system. In humidification using this apparatus, the desiccant takes up water vapor from the outdoor air in the adsorption process, and releases it indoors by desorption. Therefore, no water supply is required. An apparatus having no water supply is hygienic, because it does not propagate bacteria and does not scatter the calcium and magnesium salts found in water. In dehumidification using this apparatus, water vapor is removed from the indoor air by the desiccant and is released outdoors by desorption, eliminating the need for a drainage system. The absence of a drainage system also eliminates such problems as water leakage and installation.
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