Immiscible lattice gas model was applied to generate flow in complex geometries simulating porous media. It was approved that the complex flow geometries were successfully generated by the present method. The simulating results of the flow through the porous media by the present method qualitatively agree with the Ergun's equation for the flow through porous media. Quantitatively the present results approach to the Ergun's equation higher Reynolds number than 10, although concentration of the flow in specified flow channels were observed. It can be concluded that this technique is useful to simulate flow through complex geometry like porous media.

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No compressible turbulence model with high universality exists. The reason is mainly attributed to the lack of experimental and/or DNS data for compressible turbulent flows, especially around a shock wave. In order to compensate the experimental data, we have used a linear interaction analysis (LIA) and made the amplification of turbulence clear when it passes through a shock wave. In the present work, we investigate the model performances in terms of the behavior of turbulence passing through a shock wave. A k-ε and a Reynolds stress models widely used in incompressible turbulent flow calculations are applied and the results are compared with LIA data. Furthermore, three modified k-ε models are also considered. Through this study, some important model performances are clarified. Especially, it is shown that, when incompressible standard turbulence models are spplied to the present problem, turbulent kinetic energy is always overestimated behind a shock wave, and no existing modification can reproduce the trend of turbulence amplification. These facts suggest the necessity for turbulence models to be modified with focusing the attention on turbulence behavior around a shock wave.

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A fully three-dimensional numerical procedure based on the incompressible, steady Navier-Stokes equations in a general curvilinear coordinate system is proposed for the prediction of developing turbulent flow in a curved and radially rotating pipe. A turbulence model with the modification for streamline carvature and Coriolis force is employed to model the turbulence. The governing equations are solved using a finite volume technique with a nonstaggered variable arrangement. The modified turbulence model yields better agreement between the predictions and experiment for the streamwise and secondary velocities.

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When mist flow is injected from a pipe between horizontal parallel disks, a thin liquid film and liquid droplets are left on the lower disk. The behavior of residual liquid on the disk is studied experimentally. The measured front side or back side contact angle of the liquid droplet exposed to air flow does not agree with the advancing or receding contact angle measured by the falling method. The front side and the back side contact angles are concerned with the advancing contact angle, the receding contact angle of the droplet on the wet disk, and the receding contact angle of the droplet on the dry disk. The gas velocity at the stop position of the droplet agrees well with equilibrium velocity calculated from force balance with the front side and the back side contact angles. The analytical equation for calculating the frequency of the sway of the liquid droplet is proposed.

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In the present paper, the velocity profile around the anterior communicating artery and the wall shear stress at the apex are described. The anterior communicating artery composing the circle of Willis is one of the predilection sites where cerebral aneurysm occurs frequently. The flow field around the anterior communicating artery is simulated by two confluent tubes joining at the angle of 60 degrees, two parallel bifurcating tubes, and the junctional tube, bypass, connecting four tubes. The velocity profile is clarified around the apex where cerebral aneurysm is apt to initiate. In particular, the variation of wall shear stress around the apex at one confluent tube with a high flow rate is estimated from the velocity profile near tube wall, and the relation between the wall shear stress and the generation of aneurysm is discussed physiologically.

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An experimental and numerical study on nonlinear radial oscillation of a gas bubble in liquids is presented. In the experimental part of this study, an oscillatory pressure field is generated in a cylindrical cell, which consists of two piezoceramic transducers and a glass cylinder. A new bubble generator is developed. The generator is able to generate a bubble filled with an arbitrary kind of gas. The bubble motion is observed by high-speed photography. The time history of bubble radius is measured from the pictures to compare with the numerical results. The pressure field has a frequency of 19.2 kHz and an amplitude of 40 kPa. The gas in the bubble is air. The bubble has an initial radius within the range from 0.1 mm to 0.25 mm. A highly viscous silicone oil, whose kinematic viscosity is 100 mm²/s, is used for the liquid to keep the spherical shape of the bubble. In the numerical part of this study, the radial motion of a bubble is calculated by using the Keller equation, which is an approximate equation for the bubble motion in a compressible liquid. The Euler equations, in which the thermal diffusion is taken into account, are solved numerically for precisely estimation of the motion of gas in the bubble. A quantitatively good agreement between the experimental and numerical results is obtained in terms of not only radial-time curves but also frequency responses.

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Our aim is concerned with clustering or grouping of quasi-streamwise vortices. A fact that quasi-streamwise vortices are not distributed homogeneously but intermittengly populated in space in a wall layer, is shown at first by referring to a DNS data for a channel flow. Then, regeneration property of quasi-streamwise vortices is one of the crucially important possible mechanisms for this clustering is shown by a simplified non-dynamical simulation. Next, a wavelet decomposition of quasi-streamwise vortices in two scale-based groups is shown. The interaction between vortices of two groups indicates that individual quasi-streamwise vortices can not survive long without assistance of surrounding large scale structure which is adapted for them. Thus, it is pointed out that large scale structure around a cluster of vortices is an important coherent structure to be investigated more in detail.

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This paper presents a vortex structure at the inlet of an inducer which appears on the boundary of backflow regions. The vortex structure was visualized using vortex cavitations by operating at cavitation number σ=0.050 and recorded by a high speed video. The vortex structure was also observed by using two laser displacement sensors. An FFT analyzer couldn't be used to determine the passing frequency because the periodicity of vortex passage is very weak, i. e., rather irregular. The passing frequency and the shape of vortex lines were determined by counting the pulse from laser displacement sensors which responds to the passage of vortex cavitation. The results show that the number of vortices, its strength, its travelling velocity are functions of flow coefficient and depend on a steady flow velocity profile.

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A linear stability analysis of rotating cavitation in a flat plate cascade was carried out by a singularity method based on the closed cavity model allowing the cavity length freely to change. This analysis does not need any information about the unsteady cavitation characteristics such as mass flow gain factor and cavitation compliance as inputs. It is fuond that there are many solutions of characteristic equations. One of them corresponds to the forward rotating cavitation, which is often observed in the experiments. The propagation velocity ration of this mode agrees with that in experiments, while the onset range is larger than that in experiments. The second solution corresponds to the backward mode, which was also found in semi-actuator disk analyses and identified in an experiment. Other solutions of characteristic equation are found to be associated with the higher order modes of cavity shape fluctuation, which have not yet been identified in experiments.

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One of the authors has made clear the bubble behaviors around the bubble collapsing period as well as the patterns of bubble collapse near solid wall through instantaneous measurement of an impulsive force and bubble appearance under a really flowing condition using a high speed video system composed of an impulsive force sensor and a high speed video camera. In this report, a simultaneous observation of bubble collapsing behavior and cavitation erosion pits is tried in separated vortex flow behind a circular cylinder to experimentally prove the ability of damage for the bubble collapsing patterns reported in the previous papers. As a result, the simultaneous observation of the bubble collapsing behavior and the erosion pits are successfully conducted with the present measurement system so that the damage ability is confirmed, at least, for a collapsing pattern of the axial collapse type, and the details of its collapsing behavior are also shown at the same time.

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Much attention has been focused on vortex cavitation bubbles because of their highly erosive power. In this study, vortex cavitation flow developing in the wake behind a circular cylinder with a typical separated vortex is experimentally examined to solve the process on collapse and impulse of cavitation bubble in the context of the cavitation erosion. From the comparison with the erosion pit distribution obtained in erosion tests due to vortex cavitation, it is experimentally proved that the collapsing process is classified into four patterns, using high-speed-video observations of vortex cavitation bubbles. As a result it is shown that the collapsing process has two different sequential stages so that a vortex cavity of large spatial scale does not collapse all at once.

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An experimental investigation on flow around and in the wake region of a single bubble and two similarly sized air bubbles confined in a channel with downward flow of water was conducted. Velocity measurements of the flow field in the vicinity of bubble's surface, were made using a one CCD camera based Digital Particle Image Velocimetry (DPIV) system using fluorescent particles as tracer for visualization. A second CCD camera was used to detect the bubble's shape and translational motion via back-lighting from a square array of infrared LEDs. In this way both the two-dimensional flow field and the corresponding instantaneous position and shape of the bubble were measured simultaneously. The results reveal that the difference in wake structure between bubble and solid occurs in the vicinity of the interface defining to the bubble's oscillatory motion. Moreover it was shown that the turbulence generated by wake interaction played a significant role in the wake of two bubbles.

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A new erosion model and rebound coefficient was proposed by a modification of Finnie's theoretical approach. The present erosion model includes the effects of impingement velocity, impingement angle, particle density. Main features of the model are as follows : (1) The erosion rate is proposed to the particle velocity cubed. (2) The relationship of the impingement angle and the erosion rate is in good agreement with author's experimental data.

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We have previously reported our studies on the phenomenon of von Neumann reflection of underwater shock waves by experimental and numerical techniques. In this paper, as a further supplement to the previous report, we mainly made our efforts to investigate the change trend of the Mach stem curvature in von Neumann reflection of underwater shock wave. We presented a theoretical analysis model on describing the change of Mach stem curvature on the basis of Whitham's Ray-shock theory. It has been shown that our analytical results agree quite well both experimental and numerical results. Finally, we also presented the theoretical prediction on the domains and transition boundaries between regular reflection, Mach reflection and von Neumann reflection, of underwater shock wave by the above theory, as well as the comparison with those from the experiment and numerical calculation.

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Dependency of geometries of baffle plates in a shock tube on the decay of shock waves was investigated to find an optimal design for acoustic delay lines (ADLs) in beamlines of a synchrotron radiation facility. Fabricating a thin orifice, a coned baffle plate, a diverging tube and a converging tube as a model of the ADL, we performed pressure measurement with piezo-pressure transducers by using a dedicated shock tube and two-dimensional flow visualization around the model by means of Schlieren photography. According to the results of pressure measurements, a theory of one-dimensional steady flow employed generally is not available for the coned baffle. The decay ratios defined by the strength of incident and transmitted shock waves clearly differ among the four types of the ADL models, although all of the models have the same aperture. These results suggest that non-steady phenomena observed by the Schlieren photography, such as shock wave reflection and diffraction, viscous flow behind shock waves, may be involved in shock wave decay through baffle plates.

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Three dimensional flow field around a circular cylinder was analyzed by using a third-order upwind finite-difference method for Reynolds number-1000. Instantaneous flow fields were visualized and investigated in relation to the analysis of time and space correlation reported previously. It was found that beat frequency of drag force corresponds to the phenomena that the streamwise position of Karman vortex near wake moves back and forth. Streamwise vortex pairs around separation line deform primary vortices in the near wake and made secondary streamwise vortices. The three dimensional vortices around separation line influence the separation angle.

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Numerical study of developing turbulent flow in a distorted elliptical duct was carried out at Reynolds number 0.988×10⁵ by using algebraic Reynolds stress model. In a distorted elliptical duct, the configuration of cross section varies from elliptical to circular and from circular to elliptical along streamwise direction with keeping cross sectional area constant. Calculated results for three components of velocity and the five of the six Reynolds stress components were compared with the measuring data at seven different locations to clarify the validity of the present method and the development of turbulent structure. As a result of this numerical study, it was found that the distributions of streamwise velocity, the secondary flow and the averaged intensity of the secondary flow over cross section were reproduced by the present method. Adding to these points, both results displayed that the secondary flow of the second kind at inlet section transformed that of the first kind induced by the pressure gradient at a little distance from the inlet and that of the first kind again transformed that of the second kind at the outlet section. As for the comparison of Reynolds stresses between both results, the present method was able to realize characteristic features of normal and shear stresses qualitatively except for the spanwise normal stress.

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Gas liquid two-phase flow characteristics in a pipe flow of liquid nitrogen are numerically investigated. Firstly, the government equations on two-phase flow of liquid nitrogen based on the unsteady drift-flux model are presented and several characteristics are numerically calculated taking into consideration the effect of cryogenic flow state. It is found that phase change of liquid nitrogen occurs in quite short time interval compared with that of pressurized water in high temperature. Next, it is clarified that the pressure wave in two-phase flow forms strongly steep shape with the time progress because of the nonlinearity based on a compressibility of cryogenic two-phase mixture. According to these theoretical results, it seems reasonable to predict the fundamental characteristics of cryogenic two-phase flow, and the obtained numerical results would contribute to advanced cryogenic engineering applications.

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The objective of this paper is to study the behavior of the wake shed from an inclined circular cylinder protruded from a flat plate turbulent boundary layer. All experiments were performed at an open circuit wind tunnel having a working section of 230 mm×700 mm×1500 mm. The Reynolds number based on the cylinder diameter is 2.5×10⁴. A wall flow pattern was observed using an oil-film flow visualization technique as well as the wall static pressure measurements. Characteristics of the flow field were investigated using both a smoke-wire technique and a hot-wire anemometer. Effects of the secondary flow in the wake on the characteristics of the flow pattern near the wall were made clear.

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Time-averaged flow fields behind finite circular cylinders with aspect ratios from 1.25 to 10 located on a ground boundary in a uniform flow have been determined at a Reynolds number of 3.7×10⁴ and influences of the aspect ratios on the wake structures have been presented. Three-dimensional velocity distributions from 1 to 20 diameters downstream of the cylinders have been obtained using newly developed rotating yaw-meter system, from which the details of the wake flow fields behind the finite circular cylinders have been discussed. Streamlines and vortex lines have been calculated from the velocity fields and the wake structures, such as the features of vortex systems in the wake and their changes in shape with distance downstream, have been presented. Effects of the configurations of free ends of the cylinders on the wake flows have been studied using modified cylinders with hemispherical fairing, circular pipes as well as flat plates.

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Accurate evaluation method of flow rate using medical ultrasonic diagnostic equipment is presented and the factors of the error are discussed. The method takes B-mode ultrasonotomography with pulsed Doppler method and utilizes the video displayed power spectrum. In the method it is assumed that the velocity profile in the blood vessel is axisymmetric and that the power contribution at any Doppler frequency is proportional to the number of red cells with the velocities. The normalized power spectrum is distributed as the velocity profile on the vessel diameter and the profile is rotated. Then the velocity profile in the sectional area of the vessel is integrated and the flow rate is obtained. Experimental data show that the method is accurate compared with the conventional methods using the mean or maximum Doppler frequency. Furthermore, we construct the simplified simulation model and estimate the flow rate using the power spectrum of reflected ultrasound by fast Fourier trnsforms (FFT). It is found that the spectral broadening by FFT using finite discrete data is the major factor of the error. As the maximum velocity increases, the error decreases. Therefore, the error of the flow rate in the blood vessels at diastole is larger than systole.

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Objective of the present study is to investigate the suppression of the fluid forces acting on rectangular cylinders by passive control of flow around it. The width-to-height ratio B/H of the section is varied from 0.3 to 2.0. Flow control is established by introducing a fine flat plate in the upstream of rectangular cylinder. Measurements are carried out to change systematically the position of the plate, and then the steady and unsteady fluid forces are examined to estimate the magnitude of the reduction themselves. Also, such matters as the mechanism of the flow control, the structure of the controlled wake and the behavior of the separated shear layer are investigated. As a result, it is found that the steady and unsteady fluid forces and vortex shedding of the rectangular cylinders with aspect ratio B/H beyond 0.5 can be substantially suppressed using a flat plate with a width of one tenth of the cylinder height.

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Drag and lift forces acting on a spherical bubble in a homogeneous linear shear flow are numerically studied by means of a three-dimensional direct numerical simulation based on a marker and cell (MAC) method for high Reynolds numbers of 0.5&Re&200. The effects of fluid shear rate and the Reynolds number on drag and lift forces acting on a spherical bubble are compared with those on a spherical solid particle. The results show that the drag on a spherical bubble in a linear shear flow increases with the shear rate. The lift force acts on a spherical bubble from the low-speed side to the high-speed side in a linear shear flow. The direction of the lift force on a spherical bubble is different from that on a spherical solid particle for Re≥100. The difference can be well explained with the distributions of pressure and viscous lift acting on the surfaces of bubble and solid particle.

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In this paper, three dimensional velocity distributions were measured using a hotwire probe in the moving blade passage of a single stage axial-flow blower with stationary blade ahead of fan wheel. Measuring points are 6 positions in the axial direction, 11 positions in the radial direction and 18 positions in the circumferential directions per one pitch of moving blade passage. Rotational speeds were 600 rpm, 1500 rpm and 2400 rpm and operating conditions were three points on the decreasing inclination zone of the pressure-discharge curve. Steady velocity distributions were considered in this paper. Discussions were made on the flow leakage through tip clearance, variations of velocity distributions with radii, and velocity distributions and flow turning angle at the outlet of blade passage.

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The wing muscle of a flying insect is the most active muscle known. Aerobic metabolism in this muscle is sustained by an organ of intricate geometry but of simple structure, a trachea. The gas transport system in a flying insect drastically differs from that in a vertebrate in that an insect has no red blood to carry oxygen to a tissue and no diaphragm to drive inspiration/expiration gas flow. Here, properties of the gas transport system in a flying insect were investigated by directly measuring the oxygen partial pressure P₀₂ in a wing muscle of a hawk moth using a needle electrode. Results showed that at the onset of flight, P₀₂ in the moth decreased due to an increase in the metabolic rate. However, during long, stable flight (i.e., about 1 muinutes after onset), P₀₂ increased and then reached a plateau. Furthermore, the maximum P₀₂ in the center of the second DLM (Dorsal Longitudinal Muscle) during flight was higher than that during rest. Our results strongly suggest that a flying insect effectively uses muscle movement, which increases the frequency and volumetric stroke of ventilation, to augment the gas exchange during flight.

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The time course changes of F-actin distribution and morphology of cultured bovine aortic endothelial cells under shear flow conditions were analyzed. Fully confluent endothelial cells cultured on glass were subjected to fluid shear stress of 2 Pa. Experiments were performed for one-way flow for 20, 40 min, 1, 3 and 6 hours. After the flow exposure F-actin filaments were stained with rhodamine-phalloidin. The morphological parameters of endothelial cells (shape index and angle of cell orientation), the appearance frequency of the stress fibers and the angle of stress fiber orientation were measured. F-actin filaments were mainly localized at periphery of the cells, although some filaments were seen as star-like configurations in the center portion under no-flow conditions. In some cells (16%) exposed to shear stress for 20 min, stress fibers which were aligned with cell axes were partly observed. In this stage, however, cell morphological changes were not observed. In many cells (64%) exposed to shear stress for 1 hour, the star-like structure of filaments disappeared in the center portion, and stress fibers appeared. After 6 hours, stress fibers were observed in the most cells (91%) and began to align with flow direction. The cells in which stress fibers appeared significantly elongated, but the cells without stress fibers had kept their polygonal shape. From these results, it is expected that F-actin filaments may play a major role for sensing the level and direction of shear stress and for changing morphology of endothelial cells.

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Three-dimensional numerical simulations were carried out for mixed convective flows over a backward-facing step in a rectangular duct. Reynolds number, expansion ratio and aspect ratio were kept constant at Re=125, ER=2 and AR=16, respectively. Heat flux at the wall downstream of the step was kept uniform, while other walls were kept at adiabatic condition. Effect of the inclination angles, θ₁, θ₂, was the main objective in this study. It was found that when θ₁ was varied, the effect of buoyancy became prominent at θ₁=0°, 180°, while the effect was relatively small for the two horizontal cases (θ₁=90°, 270°). However, there was still small difference between θ₁=90° and 270° in the region immediately after the step where the flow was relatively slow. When θ₂ was varied, flow and thermal fields could no longer be considered as two dimensional, except when θ₂=-90°, 90°. The maximum Nusselt Number, which appears symmetrically near the side walls in pure forced convection cases, was obtained at only one location close to the lower side wall.

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An experimental study of heat transfer has been conducted in a channel flow with rectangular cylinder having the various width-to-height ratio, b/h, of 0.5, 1, 2 and 3. The measurement of heat flux fluctuation at the channel wall and flow visualization of smoke-wire method with high speed video recordings were synchronized in order to investigate the relation between heat transfer enhancement and shedding vortices from the cylinder. It is clarified that heat transfer is augmented by the wall-ward flow which is induced by the clockwise and counter-clockwise vortices shed alternately from the cylinder.

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Two dimensional vortex structure behind a highly heated cylinder has been studied experimentally. The air velocity is set as 1.0 m/s. The surface temperature of the heated cylinder is set at up to 600°C. A particle image velocimetry (PIV) is used to measure two dimensional instantaneous and average velocity. At just downstream of the heated cylinder, the vortex is intensified by increasing wall temperature of heated cylinder. The vortex frequency decreases when the wall temperature is increased. This indicates that the local kinematic viscosity plays a key role in the vortex structure. As a result, the vortex frequency of the heated cylinder can be expressed as a function of Strouhal number and Reynolds number, when the local kinematic viscosity is reasonably estimated by taking into account the effect of the wall heating.

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The heat transfer coefficients during natural convection of water on a downward-facing horizontal surface and that on a vertical surface were measured under the influence of ultrasonic vibration. The multi-type oscillator used in this experiment was able to irradiate in three different frequencies, 28, 45 and 100 kHz, not only continuously, but also intermittently. When ultrasonic vibrations of 28 and 45 kHz were applied to water, cavitation bubbles were generated and the heat transfer coefficient increased remarkably. When an ultrasonic vibration of 100 kHz was applied, the increase in the heat transfer coefficient was small compared to those at 28 and 45 kHz. At 100 kHz, cavitation was not observed at this low ultrasonic power. The uniformity of heat transfer, which depends on the profile of the standing wave by the ultrasonic vibration, was improved by the method of repeatedly applying multi-vibration.

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prediction of pool boiling critical heat flux is studied in this paper. Statistical variances of macrolayer thickness and hovering period of vapor mass are introduced to the conventional macrolayer dry out model. Assumed thickness is twice as thick as the conventional model which coincides with those measured with electrical resistance probes. The effect of distribution function shape is investigated for different skewness factors, which indicates negligible effect even for superheat higher than the critical. As variance of either of hovering period or macrolayer thickness increases, boiling curve is rounded off at the top and critical heat flux decreases for the same averages. When the standard deviation is assumed to be 15-20% of mean value, predicted critical heat flux and dry duration ratio coincide with experiments. These facts show that the macrolayer dry out model is experimentally supported.

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In the present paper, heat transport rates and fluid flow patterns of the meandering closed-loop heat-transport device (MCL-HTD) were experimentally and analytically investigated by using water as an operating liquid. In this type of HTD, heating and cooling parts are connected with each other by a closed loop of tube meandering between them, and operating liquid of a volume fraction is enclosed in the meandering loop. First, heat transport rates of the HTD were measured and it was shown that the effective thermal conductivity of MCL-HTD is much higher than the thermal conductivity of copper. Next, observation of fluid flow in the MCL-HTD was conducted and it was found that a simple flow pattern appears at a high volume fraction of liquid. In such a condition, only two vapor plugs exsist separately in adjacent turns, and one of them starts to grow when the other starts to shrink. When the latter plug disappears, a new vapor plug appears in the turn adjacent to the turn including the grown-up vapor plug. This vapor-plug propagation phenomena was numerically analyzed by a model, and it was shown that the propagation induces liquid flow from the heating to cooling parts or the cooling to heating parts. Such liquid flow results in large temperature differences between the liquid and tube wall at the heating and cooling parts.

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The mechanism of heat pumps for hot water supply using dual heat sources of the ambient air and water and the operating conditions of selecting either one or both heat sources were discussed. Then, the performance of a heat pump which used water and the ambient air as the heat sources to heat water was examined experimentally. When the temperature of the water heat-source was decreased, the heat from the water as well as the heat from the air was used for the heat pump efficientlly until its temperature became approximately that of the evaporation temperature of the heat pump using the ambient air alone as the heat source. When the temperature of the water dropped further, only the heat from the air was absorbed by the evaporators like an ordinary heat pump which used only the evaporator of air heat-source at the same ambient air temperature. A theoretical analysis was made on the performance of a heat pump with dual heat sources. The results agreed well with the experimental results.

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A new closed two-phase loop thermosyphon with multi-stacked radiator cores and a new flow controller forming refrigerant circulation have been developed. When the temperature of the partition wall which separates the liquid return passage from boiling region of the refrigerant tank becomes extremely high, the refrigerant circulation is inhibited. The inhibition factor of the refrigerant circulation was clarified.

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The membrane permeability of a biological cell was measured. Obtaining a reliable information on physico-chemical properties is essential to make clear the freezing process and especially, the prefreezing process which is required to avoid osmotic stress and overgrowth of the ice crystal formed in the intracellular solution. The membrane permeability can be described with Kedem-Katchalsky model's parameters (L_p, ω, σ). Parameters can be defined by measuring the volume change of a single cell suspended in a a solution. PBS or glycerol solutions was used as a suspension for measuring L_p and (σ, ω), respectively. HUVEC (Human Vessel's Endothelial Cell) was used as a test specimen. At first, L_p was measured, and then σ and ω were measured. The analytical solutions of the volume change were used to define L_p and ω, and the numerical solution was used to define σ. Quasi-osmotic equilibrium was assumed for introducing an analytical solution to define ω. With this membrane permeability and the diffusion coefficient, and optimized pre-freezing process might be designed.

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For clarification of effect of fluid type on the development of the Karman vortex street due to negative buoyancy in a circular cylinder wake with a downward freestream of mercury and water, the two-dimensional, laminar, time-dependent continuity equation, Navier-Stokes equations with the buoyancy term, and energy equation are solved numerically. With a decrease in the Prandtl number of the developed vortex street, the phase of temperature fluctuation in delayed than that of velocity, and flow asymmetry increases and temperature asymmetry decreases. Due to negative buoyancy, with decreasing the Prandtl number, a scale and spiral of a vortex become large and strong, and the wake frequency and vortex velocity decrease. The developed vortex street therefore never occurs in any isothermal wake.

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In order to clarify the behavior of ephemeral waves quantitatively, flow parameters such as number and residence zone lengths per unit length along a tube axis, mean values and standard deviations of velocity, width and maximum holdup for ephemeral waves were determined using a weve-vein analysis in two regimes of up-ward huge wave flow and annular flow, and the characteristics in those parameters were clarified. Mean values of velocity, width and maximum holdup of ephemeral waves were compared with those of liquid lumps corresponding to main wave-veins and the differences in the parameters between those liquid lumps were discussed. Furthermore the parameters of both active ephemeral waves and inactive ephemeral waves were determined and the characteristics in those of two types of ephemeral waves were presented.

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This paper reports on a method for designing a compressor and an expansion valve of packaged air conditioners for year-round cooling. The air conditioners can operate at high efficiency when the outdoor air temperature is low by lowering the condensation pressure. In this case, the expansion valve capacity must be increased and the compression ratio must be decreased. However, since increasing the expansion valve capacity and decreasing the compression ratio cannot be done without limitation, an appropriate expansion valve and compressor must be designed taking into account the following three types of conditions : 1) operating conditions ; 2) installation conditions ; and 3) climatic conditions. The simulation results reveal that performance can be sufficiently improved by setting the minimum allowed compression ratio to 1.4 and the expansion valve capacity to twice the standard size, when operating the air conditioners in Tokyo with a tube length of 30 meters

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The authors evaluated the Fractal dimension on turbulent premixed flame based on HTA (Hyperbolic Tangent Approximation) model for fully developed turbulent field. Main results are as follows : (1) The fractal dimension evaluated without a effect of flame stretch is 2.67. (2) The fractal dimension evaluated with the effect of flame stretch is 2.33, This value is in good agreement with experimental data.

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A numerical model has been developed for predicting exhaust gas emissions including NO_x HCHO, CH₃OH and other chemical species in a direct injection diesel engine fueled with methanol. In this model, 39 species with related 157 elementary reactions are taken into account. The effects of air excess ratios and load conditions on the exhaust gas emission characteristics were investigated based on this kinetic model. The model can predicts the formation and destruction of chemical species in the combustion process and the formation of formaldehyde and NO₂ during the expansion stroke.

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An experimental and numerical study of HCHO (Formaldehyde) and other pollutant species formation in the cylinder of a direct-injection diesel engine fueled with methanol has been conducted. Engine tests were carried out under variety of intake conditions including throttling, heating and EGR for the purpose of changing gas composition, temperature in the post-combustion zone. Moreover, the relative importance and influence of individual reactions on HCHO formation and mechanism were assessed with aid of sensitivity analysis.

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Lean combustion has the advantage of low pollutant emission levels, but its combustion rate is very low and the lean mixtures are difficult to ignite and form stable flames. To improve these disadvantages, we have added hydrogen to a methane/air mixture, because the hydrogen has a very large reaction rate and high burning velocity. In this study, we have focused on a tubular flame which is formed in a stretched, rotating flow field. With this flame, effects of hydrogen addition on lean combustion have been investigated. We have measured the flame diameter, temperature distribution, burning velocity, and extinction limit. Results show that, as the concentration of added hydrogen is increased, (1) the flame diameter monotonically increases, (2) the fuel concentration at the extinction linearly decreases, and effective equivalence ratio decreases, and (3) burning velocity increases. These may be explained by the fact that the heat release rate determined in front of the preheat zone increases with the hydrogen addition. Although the details of the mechanism are unclear, the present results provide the first, basic idea on the practically important lean combustion.

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Laser induced fluorescence method was applied for the measurement of NO concentration in the propane and methane diffusion flames. A tunable, narrow band ArF excimer laser was used to excite the D (υ′=0) ←X (υ″=1) band of NO molecule. Emission spectrum of the induced light by a laser beam was measured by a spectroscope. Spectrum of the induced light from the diffusion flame was compared with that of the premixed flame. Although the spectrum had only NO fluorescence components on premixed flame, a lot of strong spectrum components related to the laser induced incandescence of the soot and laser induced breakdown appeared in the spectrum from the diffusion flame. NO fluorescence component was picked out from the emission spectrum with traversing the irradiate position of laser beam in order to obtain the accurate distribution of NO fluorescence on the flame axis. In this paper this method was named as S-LIF method. A planer laser induced fluorescence (P-LIF) method was tried to measure the distribution of NO fluorescence on the flame axis. In the P-LIF method, an interference filter was used to remove the obstructive light component from the LIF image. NO fluorescence distribution measured by P-LIF method was compared with that of S-LIF method. As the result, the P-LIF image qualitatively agreed with the data of S-LIF. It was confirmed that the interference filter did not remove completely the obstructive light components.

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This paper shows that the visible observations of emulsified aspects by a Liquid-Liquid Injection Technique (L. I. T.) are applicable for the evaluation of engine performance. To contribute information for a square combustion chamber design and the engine performance, we studied the visible observations of emulsified spray aspects by using an optical-transmissivity of positive images. The L. I. T. makes use of momentary photo-images by 35 mm camera without the need for high-speed photography. It captures the forced swirling flow in positive film images which show the fuel-air mixing behavior as an intensity of scattering radiation. A relationship between the visible observation results of air-fuel mixing formation and engine performance was confirmed. This study clarified that the L. I. T. and the optical-transmissivity technique is practical and useful for the visible observation of mixture formation.

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Combusting sprays which impinge upon the wall of a constant volume combustion chamber were achieved in a rapid compression machine to examine the effects of injection pressure and ambient density on the heat rejection to the chamber wall. The real heat release, Q_s, was determined by the exhaust gas analysis and the apparent heat release, Q_a, was calculated using cylinder pressure time histories. The heat rejection or heat loss fraction was defined as (Q_s-Q_a)/Q_s, and its variation with operating parameters was discussed. It was shown that the heat rejection decreases as the ambient density and the injection pressure increase, but tends to increase with the fuel injection amount. These trends were understood as the results of the balance among the effects of the heat transfer coefficient, the cylinder gas temperature, and the combustion duration, which are affected by the experimental conditions.

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To improve engine power and reduce exhaust emissions of 4-valve, high-speed DI diesel engines, the intake swirl ratio must be controlled according to the engine operating conditions. This paper discusses a variable swirl intake port consisting of helical port and tangential port with a swirl control valve. The swirl flow characteristics were analyzed on the basis of steady-state air flow tests and 3-dimensional computations. An automesh generator for numerical analysis of twin intake ports was developed to facilitate these computations. The results indicate that the total performance of twin ports can be estimated from that of a single port and that there were no adverse effects from interaction of the port flows in the cylinder.

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Thermal conductivity and thermal diffusivity of combustion chamber deposits in an s.i. engine have been measured for unleaded gasoline containing lubricating oil. The deposits were built-up on the surface thermocouples under different percentages of lubricating oil. After removing the sooted thermocouples from the engine, the thermal properties were determined by combination of several techniques which were established in a previous study. The results show that as a percentage of lubricating oil added in the fuel increases under a constant engine load, the wall temperature decreases, the deposit becomes thicker producing larger thermal diffusivity and smaller thermal conductivity. The results also show that as the engine load decreases under a constant percentage of lubricating oil in the fuel, the deposit exhibits the same tendencies as described above. The fact contrasts with the results in the case of no-lubricating oil that the engine load did not give any influence on the thickness, thermal conductivity, thermal diffusivity and heat capacity.

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