The vorticity-stream function formulation is extended to simulate the flow in dynamically loaded journal bearing by using the pressure single-valuedness condition. The computational grid moves according to the motion of journal in the bearing. The motion of journal is due to the gravity and fluid force. The decoupling motion between fluid and solid is simulated by applying the finite difference method to the Navier-Stokes equation instead of the Reynolds equation which is used to the numerical analysis of the journal-bearing flow problem so far. The present results show an excellent agreement with results using the method applying the moving spectral element method to the Navier-Stokes equation, so that effectiveness of the present method is verified.

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An efficient implicit finite-difference scheme for solving supersonic magnet-plasma dynamic (MPD) viscous flows is proposed. The compressible Navier-Stokes equations and the equation of induction induced from the Maxwell equations and the Ohm's law are simultaneously solved using the LU-SGS approach coupled with the diagonal point implicit method. This approach enables to get the convergence of solution. As numerical examples, two types of the flow through the MPD thruster are calculated. The reliability of the present method is verified to show the convergence history of solutions and the calculated results.

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Mode formation and bifurcation in Taylor vortices are interesting physical phenomena which are typical of those in nonlinear dynamics. In this study, we investigate the system with aspect ratios (column height/gap width) of order of unity and present the numerical results of flows in various modes and unsteady transitions between modes. The appearance of the normal two-cell mode, anomalous one-cell mode, twin-cell mode and unsteady mode is predicted. When the flow starts from rest, the flow in an anomalous mode or twin-cell mode is established after the sudden breakdown of symmetric two-cell mode. In the flow of unsteady mode, the values of physical properties vary periodically. When the rotation speed of the inner cylinder decelerates, the mode transition between normal two-cell mode and anomalous one-cell mode and the transition from twin-cell mode to anomalous one-cell mode are found.

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The winnowing fan used for head feeding type combines draw in air along the axis from the inlet of both sides, and then radially discharges it into scroll. Therefore, the internal flow of this fan shows a strong three-dimensionality and the efficiency is low. In order to improve the efficiency and make the axial distribution of discharge flow uniform, the experimental and numerical investigations were carried out. Numerical results using CFD agree well with experimental ones for the mean flow. It is found that this numerical simulation method is useful for investigation of the effect of blade and casing configurations. Moreover unsteady flow conditions in the impeller though rotations are shown. For example, in the impeller, a vortex formed around the leading edge of the blade, grows connect with another one, reduce and disappear.

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Because of strong 3-dimensional flow, it is difficult to produce a uniform flow or improve efficiency with winnowing fans. Through experiments with various types of impellers, it was found in an earlier study that a forward-inclined impeller could produce a uniform flow and improve efficiency. It was then reported in a subsequent study aimed at identifying the mechanism behind this, in which the relationship between velocity and static pressure in an impeller of small inclination angle was examined from the perspective of flow, that flow analysis was effective towards estimating inconsistent flow characteristics. Based on these findings, this project was designed to measure and analyze flow characteristics in a forward-inclined impeller. It was found that forward-inclined impellers have many regions of circulating flow and that the mainstream which moves to the outlet is narrow in effective area. As a result, velocity increases and discharge blow rapidly expands within a short distance. Therefore, good static pressure recovery is obtained.

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Peristaltic flow due to the transverse deflections of the walls of the curved channel is investigated when the inertial effect is negligibly small and the wavelength is sufficiently long compared with the channel width. Theoretical results are presented for the stream function, the flow velocity and the pressure. Theoretical criteria of reflux and of trapping are obtained. The pressure-flow characteristic is found to be linear, and its slope slightly increases with an increasing channel curvature. Reflux near the outer wall is stronger than near the inner wall. The trapped bolus of fluid comprises 2 asymmetrical parts ; the outer one grows but the inner one diminishes as the channel curvature is icreased. Reflux, and trapping as well, occurs in the curved channel over wider ranges of time-mean flow and of amplitude ratio than in the straight channel.

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In this paper, we describes a numerical study of dynamics and efficiency of a two-joint bending propulsion mechanism that is composed of a streamlined body and a caudal fin. First, we extended our analysical model to a model in which the second joint was supported by a spring instead of an actuator by use of an iterative calculation method. Second, we discussed the characteristics of the caudal fin motion and the propulsive efficiency with regard to the variation of the spring constant of the second joint in comparison with the forced motion model so far. It was found that the motion of sufficiently high propulsive efficiency can be attained by spring model with wide variety of spring constant. Finally, we investigated the robustness of the thrust with regard to the temporal variation of the propulsive speed both for the forced motion model so far and for the spring model. It was found that, when the temporal propulsive speed becomes large, the thrust keeps being positive in the spring model although the thrust suddenly decreased to a negative value in the forced motion model. This tendency is especially preferable in the case of propulsion in the ocean.

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An experimental apparatus of the two-joint dolphinlike propulsion mechanism, which is composed of a streamlined body and a rectangular caudal fin, was developed. The first joint in the body part is driven by a stepping motor, the second joint at the end of the body is passively driven by springs. The required torque of the first joint is measured by strain gages. The experimental characteristics of the propulsive efficiency in a channel were investigated, and those were compared with the numerical ones obtained from the theory in the previous paper. The propulsive efficiency of the experiment is around 0.25 while that of the theory is 0.35∼0.4. Next, the motion of the caudal fin was measured. The motion of the caudal fin in the experiment shows similar tendency to that in the theory. Finally, flow visualization around the mechanism was done by using the tydrogen bubble method. It was found that the flow around the body is almost not disturbed and that the wake area after the caudal fin becomes wider and wider as the flow goes ahead.

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In this paper, we constructed a self-propelled two-joint dolphin robot as a simplified model of high-speed swimming animals. The total length of the robot is 1.75m, which is similar to the length of actual fast swimming animals. The robot is composed of a streamlined body and a rectangular caudal fin. The first joint is actuated by an air motor connected to a high pressure a air tank. The second joint is moved passively by springs. A measurement system was developed in order to measure the joint torque and joint angle of the first joint. Firstly, The body drag was measured by towing experiment. Next, swimming experiment was done to measure the joint angle and torque. By using this experimental method, we investigated the characteristics of the propulsive speed and the efficiency with respect to the spring stiffiness of the second joint and the amplitude of the first joint. It was found that the meximum propulsive efficiency did not depend much on these parameters and the robot attained a propulsive efficiency of 0.7. On the other hand, the robot attained a propulsive speed of 1.15m/s. Finally, we compared the experimental results with the theoretical ones. The experimental values show similar tendencies to the theoretical ones although they are somewhat smaller than the theoretical ones.

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In the combined system of polymer additives and riblets, the polymer additives expand the range of non-dimensionalized riblet width s⁺ where the riblets reduce the frictional drag. Although in the higher region of s⁺ the riblets increase the frictional drag as the rough surface, the polymer additives thicken the wall layer, which dumps the drag increase due to riblets and then gives the benefical combined effect in this higher region of s⁺. Based on this scinario, the velocity profile and the pipe frictional coefficient for the combined system were derived from the velocity profile of each system. The turbulent velocity profiles were measured for the combined system using a laser Doppler velocimetry. The measured results agreed well with the derived prediction for the combined system.

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The flow pattern by ultrasonic vibration in a square channel was investigated as basic research into fluid control without contact. A turbulence promoter by ultrasonic vibration was proposed in this experiment. An ultrasonic transducer was fixed to the bottom of a square test channel, and a standing wave field was formed in this channel. The ultrasonic oscillators are bolted Langevin PZT-type vibrators with resonance frequencies of 25.4kHz and 44.21kHz and ultrasonic power varies in a range of 10W to 80W. The fluid velocity was measured by a Laser-Doppler velocimeter. By applying the ultrasonic vibrations into the laminar flow, the flow pattern in the channel was developed by the agitation or turbulence of cavitation bubbles, which consequently, changed from a laminar flow into a uniform flow. Since it is possible to control the the fluid flow from outside due to the easy transmission of ultrasonic vibration in liquid, this technique can be applied to fluid flow in various channels as a non-contacting turbulence promoter.

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In this paper, we investigate the two-particle relative diffusion connected closely with the turbulence structure (which is called here the "two-particle structural diffusion") in the stationary homogeneous isotropic turbulence by the Direct Numerical Simulation (DNS). On the basis of the second invariant value of the velocity gradient tensor, we extract the two separate spatial regions, i.e.the eddying region (with the large negative invariant value) and the straining region (with the large positive invariant value). The eddying regions have the tube-like structure, and the straining regions show the strongly elongated/compressed or sheared velocity fields. Both regions are distributed intermittently in the three dimensional space. In case of the small initial separation between two particles, we observe the rapid growth of displacement of two particles at the intermediate diffusion time, and such a rapid growth occurs suddenly and intermittently in the space. The p.d.f.of two-particle relative velocity, the time evolutions of two-particle displacement and the second invariant of velocity gradient tensor are examined. Consequently, it is found that the intermittent rapid growth of two-particle displacement is mainly caused by the effect of the straining regions rather than the eddying (tube-like) regions.

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Vortical structures in the corner region of a fully developed turbulent square-duct flow have been identified at low Reynolds number Re=7000 by using conditionally sampling data obtained from two-point LDV measurements. A single quasi-streamwise vortex is found to be located roughtly on the corner bisector in the vicinity of a duct corner in a statistical sense. Its diameter and circulation scaled in wall units are shown to be similar to those of a streamwise vortex in canonical near-wall turbulence. The generation process of Reynolds stresses in the corner region is interpreted in terms of quasi-streamwise vortical motion. This vortical motion greatly contributes to the transfer of the streamwise momentum in the cross-flow direction between two walls adjacent to the corner, so that the flows on the two walls strongly interact with each other and the interaction involves a significant difference in Reynolds stress generation from near-wall turbulence. The spatial distributions of fluctuation velocity, streamwise vorticity and Reynolds stresses are presented in the corner region to discuss the flow structure induced by the quasi-streamwise vortex.

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Numerical study is conducted on the vortex breakdown flows in a cylindrical container with rotating bottom disk. The flows are driven by the bottom disk rotating at a constant angular velocity. The aspect ratio h of the cylindrical container is fixed at a value of h=2.0. The top disk of the continer is assumed to be a flat undeformable free surface and the flow axisymmetry is also assumed. The Ψ-Ω method is utilized and numerical solutions are obtained for the Reynolds number Re within the range 1000≤Re≤3000 which covers the steady and unsteady flows. Numerical solutions are also obtained for a cannonical problem of top rigid wall vortex breakdown flows. Results are compared with the existing experimental data for both problems. The comparison exhibited gross similarity to the experimental visualization by Spohn et al.for the free surface flows and Escudier, for the top rigid wall flows. However, close investigation disclosed that the critical Reynolds number Re_c for the onset of breakdown bubble and Re_c for the attachment of recirculating bubble to the free surface are different from those reported by Spohn et al. By comparing the present free surface flow solutions with those obtained for the cannonical problem, the effect of free-slip boundary condition on the occurence of vortex breakdown is quantitatively described.

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Numerical study is performed on the steady axsymmetric vortex breakdown within a cylindrical container with a rotating top lid. The cylindrical container is filled with incompressible viscous fluid and the swirling flow is driven in the container by the top lid rotating at a constant anguler velocity. This flow problem is governed by a combination of two non-dimensional physical parameters, i.e., the Reynolds number Re and the container aspect ratio h. In the past experimental studies, the occurrence of vortex breakdown is known to be confined in a narrow range of h and Re and the region diagram of vortex breakdown was constructed. In the present numerical investigation, the region diagram is reconstructed for the first time by the numerical computation. The axisymmetry of the flow is assumed and the resulting system of governing equations are solved by the Ψ-Ω method. The comparison of the present region diagram obtained for the steady solutions and that obtained experimentally by Escudier exhibited good agreement. This cross check of limiting Re values for the occurrence of vortex breakdown confirms the reliability of both computational method and the experimental methodology. Based on the present numerical solutions, the locations of stagnation points for various aspect ratio h are calculated as functions of Re and these values are also compared with available experimental data. The outcome of present comparison confirms the belief that the steady vortex breakdown within a cylindrical container is actually axisymmetric. Further argument will be discussed in the proceeding studies.

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To precisely solve the Navier-Stokes equation for arbitrary and complicated boundary geometries, a CIP (Cubic Interpolated Pseudo-particle) solution method adapted to three-dimensional, generalized curvilinear coordinate systems is presented. The governing equations are implemented in a transformed space only with the contravariant velocity components, and discretized with a staggered variable arrangement. By applying the method for solving the flows in a three-dimensional cavity space, around a circular cylinder started suddenly and in 180° curved pipe, its computational accuracy is confirmed comparing with the numerial results using a pseudo spectral method, measured length of a twin vortex, measured velocity distributions and calculated results using the QUICK scheme, respectively.

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Field temperature measurement technique with encapsulated liquid crystal particles suspended in a liquid has been investigated considering the viewing angle effect on the color to temperature transformation. Two calibration techniques are studied, one is a neural network and the other is a spline fitting technique, where the calibration points are distributed over the image plane in order to consider the viewing angle effect. The calibration study is carried out with uniform temperature field image captured at various temperatures. It is found that the calibration error due to the viewing angle variation is reduced with an increase in the number of calibration points and by the introduction of smoothing technique. It is found that the spline fitting technique is superior to the neural network technique considering the evaluated temperature error and computing time. The spline fitting technique is applied to the temperature measurement of thermal convection over a heated surface and the thermal structures generated near the top and bottom boundaries are discussed.

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This paper reports on the influence of Coriolis force on the heat transfer characteristics in rotating laminar boundary layer. The experiments have been conducted for the mean flow velocity U_∞=4.0m/s and the angular velocity Ω=4.6rad/s, and the heat flux has been applied uniformly over the plate. Liquid crystal method is applied to measuring the surface temperature distribution. The results indicate that heat transfer has been enhanced on the pressure surface. The velcity measurements show that Coriolis instability induces the counter-rotating longitudinal vortices which argument the heat transfer from the pressure surface. On the other hand, the heat transfer from the suction surface remains unchanged as compared to the no-rotating case, which is due to the Coriolis force that stabilizes the boundary layer. As a consequence, the averaged heat transfer coefficient is higher on the pressure surface than that on the suction surface and the stationary wall by approximately 40%.

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An experimental and theoretical study was conducted to investigate the characteristics of liquid film flowing around side wall of a horizontal circular cylinder. The standing wave with a peak line toward the flow direction appears on the film surface. It was observed that the wave length is strongly dependent on the Weber number. The wave length was obtained theoretically by the force balance on the film surface. Centrifugal force, gravitational force, surface tension and viscous force were estimated by assuming the small amplitude of the wave and the proper velocity distribution in the liquid film. The calculated wave lengths agree with those measured experimentally for water and 20% ethanol solution. As the film Reynolds number Re becomes less than 500, the viscous effect gradually gives an influence on the wave length. The experimental results suggests that the laminar velocity distribution in the liquid film changes to the turbulent-like one as Re is greater than 2000.

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The potential of a clathrate-hydrate is, in this paper, discussed from the points of energy storage and environment issues. The hydrates of methane, carbon dioxide and xenon gases were produced in a high pressure vessel with controlled temperature and pressure. The effects of solubility of guest molecules into water, rate of gas pressure increments, handling of repeated production and dissociation and mixing of fine solid particles into water on production characteristics are revealed. The solubility of guest molecules into water has a great effect on the elapsed time of hydrate production. The increasing rate of gas pressure does not affect hydrate production. The mixing of fine solid particles into water is effective on the production pressure of the hydrates. However, the formation rate of the hydrate is not increased by the mixing.

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Flows around circular cylinders under streamwise pressure gradients were studied experimentally. Pressure distributions on the cylinder surface, frequencies of shedding vortices and wake velocity distributions were obtained under the various pressure gradients. The fundamental characteristics of flows around the circular cylinders, such as pressure distributions on the cylinders, angles of separation, pressure drags as well as velocity profiles and turbulence in the wake flows, exhibit remarkable discontinuous changes at a specific value of pressure gradient. The specific pressure gradient, which may be called "critical pressure gradient", is proved to be around χ_cr=(dp/dx)/(ρU²₀/2d)〓0.05, independently of Reynolds numbers. The vortex shedding vanishes under the pressure gradient more than χ_cr.

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We have conducted Stokesian dynamics simulations to investigate the dynamic properties of ferromagnetic colloidal dispersions subjected to a sinusoidal shear flow. Thick chainlike cluster formation is significantly influenced by an oscillatory shear flow even if the amplitude is relatively small, since the internal structures of thick chainlike clusters are highly sensitive to the change in the direction of the shear flow. The motions of thick chainlike clusters are out of phase to a sinusoidal shear rate, and this phase difference is strongly correlated with that of the viscosity and normal stress coefficients. The viscoelastic properties become more apparent with decreasing frequency of the oscillatory shear flow, since such properties have a strong relationship with thick chainlike cluster formation. In other words, since thick chainlike clusters are more stable for the case of a smaller frequency shear flow, such stable clusters induce significant viscoelastic properties of ferromagnetic colloidal dispersions in a strong applied magnetic field.

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Behavior of multiple stall cells with short length-scale in an axial compressor rotor have been investigated experimentally. In a low-speed research compressor rotor tested, the multiple short length-scale stall cells appeared under a mild stall condition. In order to capture the short length-scale cells in the mild stall state, a so-called 'double phase-locked averaging technique' has been developed, by which the flow field can be measured phase locked to both of the rotor and the stall cell rotation. Then, time-dependent ensemble averages of the 3D velocity components upstream and downstream of the rotor have been obtained with a slanted hot-wire, and the pressure distributions on the casing wall with high response pressure transducers. From the experimental results, the flow mechanism of the short length-scale stall cell has been clarified. The distinctive feature of the stall cell structure is a tornado-like separation vortex which spans from the casing wall ahead of the rotor to the blade suction surface and travels with changing the blade in turn on which the vortex leg stands.

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In this paper the time-dependent characteristics of the thermal convection field in rectangular enclosures with large aspect ratio exposed vertical vibration were numerically examined and the results were compared with the ones of square enclosure. In the computation the Prandtl number, the Rayleigh number and the vibration Grashof number were held constant of 0.71, 10⁴ and 10⁶ respectively. The normalized angular frequency of forced vibration was changed in the range between 10 and 7680. As a result, it was ascertained that the five regimes with respect to the angular frequency proposed by Fu and Shieh for the square enclosure captured the change of surface-average Nusselt number when the chaotic characteristics were considered. It was also revealed that the vortices in the enclosure aligned to the vertical direction in the enclosure with large aspect ratio determined the characteristics of the surface-average Nusselt number on hot and cold side walls.

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Natural convection in a bundle of vertical cylinders, arranged in a equilateral triangle, has been studied numerically using a boundary-fitted coordinate system. Numerical calculations for center-to-center distance between cylinders S/D=1.1∼1.9, 3.0, 4.0 and 7.0 were made of natural convection of air at the modified Grashof numbers Gr-* from 10 to 10⁸. The results show that local Nusselt numbers Nu for uniformly heated cylinders have certain constant values in a wide range of cylinder length except the entrance region of bundle, with decreasing Grashof number. Numerical values of local Nusselt number are in relatively good agreement with those obtained from experiments in air.

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The characteristics of discharge and heat transfer of the continuum and slip choked flows through a narrow parallel-plate channel with uniform heat flux wall are studied by means of experiment, numerical simulation and analytical solution. The numerical results of the discharge coefficient C_d and wall surface temperature distributions agree with the experimental data. The decrease of C_d caused by the heating effect can be correlated with the dimensionless heat input. The analytical expressions of the Nusselt numbers for the developed incompressible slip flow including the viscous-heating are obtained. The Nusselt number based on the adiabatic wall temperature cooperated with the increase of local total temperature for heated wall is proposed, which is free of the viscous heating effect and proved to consistent with the common Nusselt number for low speed internal flow.

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In the flow field of temperature difference exists, the exact measurements of mean and fluctuating values of temperature and velocity by an ordinary hot wire or other instruments would make the matter still difficult. The present paper deals with a newly produced sensor and application of it for actual measurements of the temperature and velocity in the mixing flow field of two gases of different temperature. The gases in the present investigation are hot air and air of room temperature. Regarding a newly produced sensor, it may have a high characteristics for quick response to follow the temperature fluctuation, which would depend on the suction nozzle diameter of surrounding gas and inhale velocity.

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The present paper reports the results of numerical simulations on combined close-contact and natural convection melting in a thermal energy storage micro-capsule of spherical shape. The results show distinct flow patterns due to density inversion passing through the maximum density point. Elucidation of such heat transfer mechanism in of very importance from the viewpoint of the high-efficient and high density heat/ice storage systems employing the latent heat thermal energy storage concept. The present results were compared with the ordinary results using relatively large capsule diameters and approximate solutions obtained previously by Bahrami and Wang.

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The development of 1700°C class hydrogen fueled combustion turbine system with output of 500 MW and thermal efficiency of over 60% (HHV) has been conducted in World Energy Network (WE-NET) program. This paper describes the development of the first stage turbine cooled stator and rotor blades applied to the power generation system. The conceptual design of those cooling blades which were served in hot steam flow was carried out. The hybrid cooling method combining recovery cooling with partial ejection cooling was chosen between several cooling system from a viewpoint of plant efficiency, operational reliability and durability of cooled blades. Also the single crystal super alloy (SC) as a blade substrate and thermal barrier coating (TBC) were applied. The experiments of the scale model turbine cooled blades were carried out using hydrogen-oxygen combustion wind tunnel with practical steam conditions of 1700°C and 2.5MPa. The cooling effectiveness and metal temperature at rated condition and the soundness of TBC and blade substrate of the first stage stator and rotor test blades were clarified.

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A unique method, previously proposed by the author, was applied to the heat transfer augmentation in the flow boiling field. In this method a screen sheet was put on the horizontal heated surface where bubble nucleation occurred. Generated vapor bubbles were trapped between the screen and the wall, became flat and moved along the surface. This restricted bubble behavior caused the heat transfer enhancement. Three types of the screen were tested in the present experiment and the effect of the screen was investigated on the heat transfer and two-phase flow characteristics. In two cases of them, the screen was displaced upward by the bubble nucleation. Compared with the ordinary flow boiling case, heat transfer was enhanced by a factor of 1.2 to 6 within the present experimental range. By using a simple flow model, it was made clear that the effect of the height of the displaced screen was important to evaluate the increase in pressure drop.

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A conjugate numerical model has been proposed to investigate the problem of cooling a fluid flowing through a spiral coil immersed in a chilled water container, which is common in most of beverage dispensers such as a beer dispenser. A simple axi-symmetric numerical procedure is described for determining the temperature of the fluid in the spiral coil and that of the coil surface. A one-dimensional heat balance equation for the fluid flow within a coil is utilized to update the fluid and wall surface temperatures, which are needed to calculate the temperature field in the water container with solid ice walls. SIMPLE algorithm has been used along with the standard turbulence model equations. A reasonably good agreement has been achieved between the prediction and experiment.

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This paper describes an experimental and observational study of iron rust removal method and iron lump formation mechanism within a heat exchanger of a small type heat pump. Since a heat exchanger of a heat pump using water is corroded, heat transfer coefficient (in other words, C.O.P.) is decreased. In this study, iron rust removal system was proposed and cleared the effectiveness. Moreover, iron lump formation mechanism was clarified by an experiment with a double pipe heat exchanger. The conclusions were as follows. 1.C.O.P. of a small type heat pump was recovered by the iron rust removal system. 2.C.O.P. decrease of a heat pump is caused by iron lump grown within a heat exchanger. The source of this iron lump is not the iron rust including water, but the iron rust produced from a heat exchanger.

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An experimental study has been carried out to determine the heat transfer characteristics of solid-liquid fluidized bed in the case of small density difference between particle and liquid. By using low density difference particles, it may be able to fluidize at low velocity and reduce the power of fluidization. In the present study, a bundle of horizontal heated tubes was situated in the fluidized bed which was formed by downward forced flow of water and particles. Flow condition, void fraction of particle bed, and local/average heat transfer coefficient around the heated tubes were observed and measured. The effects of flow velocity, thermophysical properties of particles, particle diameter, heated tube diameter, pitch of heated tubes, and temperature of water on the heat transfer characteristics were extensively determined. It was found that both diameter and specific weight of particles exerted considerable effects on the heat transfer performance.

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This paper reports both the heat transfer performance and the flow characteristics of slush ice flow between horizontal heated plates. A mixture of fine ice particles and ethylene-glycol aqueous solution was adopted as a testing slush ice and was heated by the top or the bottom wall of the flow channel. Experiments were carried out to investigate the effects of heat flux, velocity of slush ice flow, and channel height of test section on the melting heat transfer characteristics. Both the velocity distribution and the ice packing factor distribution in the flow channel were measured in detail. The results revealed that the forced-convection heat transfer and flow characteristics of slush ice were markedly affected by both the velocity distribution and the ice packing factor distribution near the heated wall.

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The flashing characteristics in a pipe downstream from a depressurizing tank were experimentally and analytically investigated on the basis of the transient test and two-phase flow analysis. The following three conclusions were obtained. (1) When the pressure margin of the pump inlet side and the distance to obtain an isothermal condition were sufficient, flashing phenomena did not occur in spite of the decreasing pressure. (2) When the ratio of the cold water injection flow rate to the hot water flow rate M_c/M_h increased, the peak distance of the water temperature fluctuation moved from L/D=1 to 0, and the maximum water temperature fluctuation ratio was about 40% of the temperature difference between hot and cold water near the mixing tee junction. But no problem occurred regarding the pipe material thermal fatigue, so reliability of the mixing tee junction was assured. (3) Due to suppression of flashing phenomena of the mixing pipe system, the decision diagram on the flashing occurrence was obtained from test and analytical results, taking into consideration three factors : the depressurizing ratio in the tank ; the cold water injection flow rate due to remaining sub-cooling ; and the delay time of thermal mixing. The simplified analytical equation was used to decrease the cold water injection flow rate by the optimized pipe length between the mixing tee junction and drain pump. The cold water injection flow rate was minimized when pipe length was about 15 to 20 times the pipe inner diameter.

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Time changes of a two-dimensional distribution of velocities in a nitrogen jet and a methane jet flame are measured by cross-correlation particle-image-velocimetry (PIV). From the measured results in a jet and a jetting flame, it is shown that the velocity gradient at shear layer in the reacting zone is increased due to the local acceleration by buoyancy, resulting in higher turbulence intensities compared with those in a non-reacting jet. Also, from the change of the distribution of velocity vectors with time, it is observed that the turbulence eddies are carried downstream along the gas motion with a little transformation. The time scale of turbulence at every location in the flow is obtained from the autocorrelation function of the velocity fluctuations. Furthermore, this can afford to estimate the turbulence length-scale. It is shown that the characteristic length-scales of a flaming jet are about 1.5 times greater than those of a non-flaming jet.

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Nemerical steady-state analysis was performed in order to make clear the flame structure and the formation process of NO_χ in the methane-air lean-rich combustion flame. In lean-rich flames, the lean and the rich slit burners were set side by side in the combustor. A two-dimensional numerical analysis was performed based on 235 elementary rections with 52 chemical species, using the CHEMKIN thermodynamic database. In the numerical analysis, both Zeldovich NO and prompt NO formation mechanism were taken into account for NO formation process. We found the region in the base of the lean flame where the chemical reaction occurred actively. It concludes that the region was formed by the diffusion of fuel and various radicals from the rich flame, and by thermal influence from the rich flame. It was the evidence that the rich flame influenced the lean flame. This result is useful not only for decreasing the level of NO_χ but also for stabilizing the lean-rich flame.

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In order to remove particulate matter (PM) and nitrogen oxides (NO_χ) contained in diesel exhaust gas, the gas is excited by passing through a corona discharge tubes in a high electric voltage field. A corona discharge collector for PM (CCPM) is designed to collect diesel PM electrically on central electrode and accumulated PM will be removed by a controlled burning (regeneration) process every 15-20 minutes. In a corona discharge reactor for NO_χ removal (CRNR), the NO is oxidized to NO₂, and OH radical generated from H₂O in gas reacts with NO₂, and NO_χ concentration decreases as a result of formation of HNO₃. In this paper, the discharge instability of CCPM by the PM accumulation on electrodes is investigated, and PM collection efficiency>90% is obtained under the condition of 23kV, 0.35mA. As for CRNR, the effect of inlet temperature on the NO_χ reduction rate is discussed experimentally. The NO_χ removal rate of about 95% is observed at an input power of 80 watts. The configuration of a prototype reactor coupled with CCPM and CRNR is proposed in our study.

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Split Injection has a potential to reduce simultaneously both NO_χ and soot emissions from a D.I. Diesel engine. But the mechanisms of simultaneous reduction of both NO_χ and soot emissions have not been clarified. To figure out the mechanism of change in emissions characteristics of the D.I. Diesel engine with the Split injection, an experimental study was conducted by using electrically controlled common rail injection system and a high pressure bomb. One of the sprays from a multi hole nozzle was injected into a two-dimensional model combustion chamber. The spray was observed by schliren photography with a high-speed video camera. In this report, effects of the injection interval under the fixed ratio of injected mass at each injection stage are described. The spray for the 2nd injection has larger tip penetration when the injection interval becomes short. And the height of the 2nd spray along the bottom wall of the model combustion chamber is shorter than 1st spray and single injected spray.

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This paper describes the effect of fuel injection rate shaping on spray combustion. Injection rate shaping with different slope of injection rate rise and drop were examined by using the electronically controllable fuel injection system. The effect on combustion characteristics, i.e., the ignition delay and combustion periods, were investigated through the light emission from spray flame. Two-dimensional temperature and soot distributions in flame were measured by the two color method. The steeper slope of injection rate rise develops the flame evolution in the direction of spray axis and width and cause the earlier start of main combustion. This tendency results in a larger area of high temperature region in flame from initial stage of combustion. The steeper slope of injection rate rise increases total and average soot productions in flame at initial stage of combustion in spite of the enhanced spray formation.

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An experimental study was made to investigate the effect of combustion chamber configuration and top clearance on in-cylinder combustion in a spark-ignited natural gas engine. Flame propagation in a single-cylinder visualization engine was measured from the cylinder axis direction by the high speed schlieren method, over the wide range of combustion chamber configuration and top clearance. The results showed that smaller piston cavity diameter led to more rapid flame propagation, resulting in larger heat release rate and larger cylinder pressure. Top clearance had little effect on flame propagation, resulting in little difference in heat release rate and cylinder pressure.

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An experimental study was made to investigate the effect of swirl ratio, spark plug electrode direction and spark plug position on in-cylinder combustion in a spark-ignited natural gas engine. Flame propagation in a single-cylinder visualization engine was observed from bottom of the piston by the high speed schlieren method, over the wide range of nominal swirl ratio, spark plug electrode direction and spark plug position. The results showed that larger swirl ratio led to more rapid flame propagation, resulting in larger heat release rate and larger cylinder pressure. Spark plug electrode direction had little effect on flame propagation, resulting in little difference in heat release rate and cylinder pressure. Farther spark plug position to cylinder axis led to more rapid flame propagation, resulting in larger heat release rate and larger cylinder pressure, excluding extremely far spark plug position.

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