The preconditioned flux-splitting method developed by our group is applied to the computation of two-dimensional natural convections. This method is based on the Roe's flux-difference splitting, the LU-SGS scheme, and the preconditioning method. In the present study, the natural convection in a cavity at Ra=10³-10⁶ were calculated by the present method, and the numerical results are compared with the benchmark results already reported by Davis, Okanaga and Chenoweth. Finally, the reliability and the limitation of the present preconditioning method applied to the convection problems are discussed in detail.

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The effects of Reynolds number on turbulent blocking effect by a rigid plane boundary are studied using a boundary-layer theory and a linear theory based on rapid distortion theory (RDT).The three-dimensional energy spectrum for low Reynolds number flows is applied to the linear theory developed for shear-free boundary layer by Hunt & Graham (1978). Fully analytical solutions for the three-component turbulent intensities of velocity fluctuations are obtained. The one-dimensional power spectra are also obtained analytically. The results are compared with the previous analysis at high and moderate Reynolds numbers and laboratory measurement at low Reynolds number. The results show that the blocking effects by the surface become more significant at low Reynolds numbers when the viscous damping is small : the vertical velocity fluctuations decrease and streamwise and spanwise velocity fluctuations increase faster than those at high Reynolds numbers. The spectra are amplified in the higher wavenumber region compared with the high Reynolds case. The solution in the viscous layer explains why the data at low Reynolds numbers show no amplification of turbulence intensities near the surface.

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The Reynolds number influence on turbulent blocking effects by a rigid plane boundary is studied using direct numerical simulation (DNS). A new forcing method using 'simple model eddies' (Townsend 1976) for DNS of stationary homogeneous isotropic turbulence is proposed. A force field is obtained in real space by sprinkling many space-filling 'simple model eddies' whose centers are randomly but uniformly distributed in space and whose axes of rotation are random. The method is applied to a shear-free turbulent boundary layer over a rigid plane boundary and the blocking effects are investigated. The results show that stationary homogeneous isotropic turbulence is generated in real space using the present method. By using different model eddies with different sizes and rotation speeds, we could change the turbulence properties such as the integral and micro scales, the turbulent Reynolds number and the isotropy of turbulence. Turbulence intensities near the wall showed good agreements with the previous measurement and the linear analysis based on a rapid distortion theory (RDT). The splat effect (i.e., turbulence intensities of the components parallel to the boundary are amplified) occurs near the boundary and the viscous effect prohibits the splat effect at the quasi steady state at low Reynolds number.

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The behavior of the vortical structure in a two-dimensional jet was investigated by the feedback excitation method use the fluctuating velocity with the phase-shift, The experiments were carried out at exit velocity of 10m/sec and two-dimensional nozzle of aspect ratio 14 and Reynolds number is 1.42×10⁴ based on the nozzle height. The jet is excited by the disturbance fed into the jet at the nozzle lips, the excitation intensity u'/U_eo was fixed on 0.04. The effect of excitation was investigated by measuring mean velocities, the fluctuating velocities, and the power spectrum densities. The result suggests that the behavior of the vortical structure is manipulated by use the signal with the phase-shift.

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Flowfield and acoustic-field around moving bodies are simulated by the Arbitrary Lagrangian Eulerian formulation in the finite difference lattice Boltzmann method. The effect of the ALE is checked by comparing flow about a square cylinder in ALE formulation and that in the fixed coordinates, and both agree very well. Matching procedure between the moving grid and fixed grid is also considered. The proposed method in which the both grids are connected through buffer region is shown to be superior to moving overlapped grid. Dipole-like emissions of sound wave from harmonically vibrating bodies in two-and three-dimensional cases are simulated. Sound wave emitted from rapidly rotating elliptic cylinder is also successfully simulated.

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Field measurement and numerical simulation were performed on the distortion of the compression wave generated by train entry and propagating through a slab track Shinkansen tunnel, which is the longest mountain tunnel in the world at present. The pressure of the compression wave measured at 12 locations. In the numerical simulation, the distortion of the compression waveform was calculated by one-dimensional compressible flow analysis which takes account of steady and unsteady friction combined with acoustic analysis on the effect of side branches. The results of numerical simulation agree well with those of the field measurement. Furthermore, the results show that the compression wavefront steepens in the early stage and smoothes down in the later stage of propagation.

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In this study, we present a new numerical method to analyze quantitatively the error of numerical solution by using the adjoint sensitivity analysis method and the modified equation approaches. If a reference case of typical parameters is once calculated with the method, no additional calculation is required to estimate the results of the other numerical parameters such as those of more detailed resolution. Furthermore, we can estimate the strict solution from the sensitivity analysis results and can quantitatively evaluate the error of numerical solutions based on only the numerical procedures.

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The local relative velocity model proposed by Tomiyama, et al. was applied to the estimation of solid volume fraction in solid-liquid two-phase pipe flows with a wide range of the diameter ratio of particle diameter to pipe diameter. The diameter ratio ranged from 0.022 6 to 0.818. No estimation methods proponed so far can cover this diameter ratio range. The local relative velocity model takes into account the effects of the distributions of local volume fractions and local velocities in a cross-sectional area of a pipe, being similar to the drift-flux model. An empirical correlation of the terminal velocity of a single solid particle falling in a liquid-filled pipe was applied to the phase-averaged “local relative velocity”, and a simple empirical correlation of another parameter in the local relative velocity model was deduced from measured solid volume fractions and phase-averaged velocities. Substituting these two correlations into the local relative velocity model, we developed a new simple correlation of solid volume fraction. This correlation was confirmed to yield good estimations of solid volume fractions both qualitatively and quantitatively.

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This paper presents numerical simulations of the interface instability in consideration of surface tension effects using a new surface capturing method that has been developed by the present Authors. The surface capturing method is based on the high order WENO scheme. This method couples the incompressible Navier-Stokes equations with the VOF method, and takes account of the surface tension using the continuum surface force method. The present surface capturing method is applied to a Rayleigh-Taylor instability problem. The growth rate of interface obtained by inviscid flow simulations is in good agreement with the theoretical result. In the viscous flow simulations, the interface grows into the shape of a mushroom with time, and the rolling of vortex is observed in the interface tip. The numerical smearing caused by the numerical diffusion occurs around the interface.

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In order to grasp the aerodynamic characteristics of wings in ground effect, theoretical calculations were made for the ground-effect wings of lift enhancement by the two dimensional panel method assuming that the free surface is rigid wall. Trend analysis and parametric studies on the ground effect have been conducted to evaluate the kind of wings and the modulated wings with the slotted slats and flaps. The tendencies of oscillating the aerodynamic performances of wings have happened cyclically through the growth of the swirls on the surface of airfoils even if in the ground effect. These oscillating frequencies have been shown to reduce through the strong ground effect. Through controlling the growth of the swirls by these wings with slotted slats and flaps there were attained the high tendencies of the lift-drag ratios and rather than less movement on the center of pressure.

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Flow on an airfoil was investigated with plasma synthetic jet actuator. Plasma synthetic jet actuator is a flow control device, which is composed of two electrodes with a.c. signal, using electrohydrodynamic (EHD) effect and induces flow around the electrodes. Plasma synthetic jet actuator has some important advantages ; for example, miniaturization is possible, mechanical maintenance is almost free. Therefore it is expected to apply for flow control around an airfoil. In this study, to observe behavior of the plasma synthetic jet actuator, experimental study was conducted. A NACA0012 airfoil, in which plasma synthetic jet actuator is embedded, was chosen, and the wake velocity behind airfoil is measured by hot wire anemometer with or without operating the actuator.

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The suction performance of turbopumps in cryogenic fluids is basically much better than that in cold water because of thermodynamic effect of cavitation. However, it is not still clear how the thermodynamic effect works on cavitation instabilities such as rotating cavitation and cavitation surge. In the present study, the singularity method is combined with an unsteady heat transfer model to examine the thirmodynamic effects on rotating cavitation. The results are qualitatively compared with existing experiments to clarify the research needs for deeper understanding.

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The present work investigates the effects of shaft vibration on the anymmetric cavitation which is one of instability phenomena on cavitating 3-bladed inducers. Inducer tests under various unbalance conditions have been carried out to make clear the effects of shaft vibration. Consequently, the following results have been obtained. (1) The amplitude of shaft vibration has a strong effect on the occurrence of the asymmetric cavitation, then in the inducer with large vibration amplitude, the asymmetric cavitation easily occurs. (2) The phase of small tip clearance caused by shaft vibration coincides with the position of small cavity. This study shows that the decreasing shaft vibration is greatly important for avoiding harmful asymmetric cavitation.

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Effect of surface wettability on evaporation of water drop has been examined experimentaly using surfaces with various contact angles. To change widely the surface wettability, TiO₂ superhydrophilicity, plasma irradiation and super-wate-reppllent surface are adopted as the heating surface. The range in contact angle achieved by these methods was between 0°and 170°. The relationship between the contact angle and the wetting limit temperature were obtained and it was found that the lifetime of water drop dramatically decreases with contact angle in lower temperature region, and that the wetting limit temperature increases with contact angle.

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Measurements of electrophoretic and electroosmotic velocities were performed by using micron-resolution particle image velocimetry (micro-PIV) and submicron fluorescent particles. Electrophoretic velocity of particles was obtained by micro-PIV measurement in a closed cell, while electroosmotic velocity of buffer solution in a microchannel was calculated by subtracting electrophoretic verocity from observed velocity measured by micro-PIV. Both zeta-potential of particles and microchannel wall were obtained by using electrophoretic and electroosmotic velocities, respectively, which are increased with increasing pH of buffer solution, due to deprotonation. Transient process of zeta-potential at the wall surface in a T-shaped microchannel was detected by spatially-averaged electroosmotic velocities.

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Effects of number of fins, fin pitch and wind velocity on the air cooling were investigated using the experimental cylinders for the air cooling engine of the motorcycle. The experimental cylinders that had various number of fins and fin pitch were tested, and the temperature inside of the cylinder, on the surface of the fins and in the space between the fins was measured. Results indicated that the heat release from the cylinder increased when numbers of fins increased. However, the heat release did not improve when the cylinder had more fins and too narrow fin pitch in the lower wind velocity. Bacause it was difficult for the air to flow into the narrower space between the fins and the cylinder had residual heat between the fins. We also obtained the expression of the heat transfer coefficient using the wind velocity and the fin pitch. This expression is useful for the design of the air cooling cylinder.

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A Homgeneous Charge Compression Ignition (HCCI) engine is supposed to achieve high thermal effciency and low NO_x PM emissions at the same time. Though it is expected to come into practical use, it has some serious problems such as ignition timing control, knocking at high load and securing of high combustion effciency. In this study, a four-stroke HCCI engine running on Di-Methyl Ether (DME) is developed to make it practicable as a generator engine. A new HCCI combustion control method, controlling the gas fraction of internal EGR gas at high temperature, external EGR gas at low temperature and premixture at stoichiometric ratio, is proposed. And effects of the gas fraction on HCCI combustion are researched by numerical calculation with elementally reactions and experiment. To conclude, HCCI combustion can be optimized with controlling the fraction of internal EGR gas, external EGR gas and premixture.

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In order to clarify the effects of density ratio and laminar burning velocity on the vortex bursting phenomenon, the premixed flame propagation in swirling flow has been examined by the numerical calculation for various preheating temperatures and equivalence ratios. In this calculation, the flame is fixed in the computational domain by adding an axial flow to the unburnt premixed gas so as to obtain the steady state propagation characteristics. The obtained results are as follows : The present flame propagation velocities relatively agree on “the back-pressure drive flame propagation theory (radial expansion)” proposed by Ishizuka et al. The variation of the pressure along the vortex axis occurs between the inflow part and the flame front, and the pressure in the burnt region is almost uniform. Therefore, the propagation speed must be estimated by the Bernoulli's equation by using the density of unburnt mixture. We have proposed a new formula on the basis of the present calculation results, and have confirmed that flame propagation speed accords qualitatively and quantitatively with this formula. Moreover, we have suggested that, considering the application to the combustor with swirling flow, the preheating of premixed gas enhances its performance due to the large burning velocity.

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Conventional methods for treating waste and ash generated in incineration furnaces are to melt and solidify the ash at high temperature.Though various types of systems have been installed and in operation, they have some critical problems with their high operation cost including fuel cost, technical difficulties in melting mixed materials contained in ash, and practical in capability in melting iron materials and clinkers. The proposed system here is designed to utilize the combustion heat of unburned carbonaceous materials contained in discharged ash from a waste incineration furnace in order to assist melting the incineration ash to reduce fuel consumption. The furnace system has oxygen burners for burning carbon and for melting iron materials and clinkers. The test operation results conducted by 12t-ash/day test plant are reported. The test has revealed that the proposed system is capable of melting the ash containing 20-30wt.% of iron and clinker rumps of the volume size of around 15 cm³ without auxiliary fuel supply other than unburned carbon residue in ash.

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Effects of H₂O, CO₂, CH₄ and C₂H₄ containing in automotive exhaust gas on NO removal by using a DC corona discharge were invistigated experimentally. In this experiment, N₂/O₂/NO mixture was used as a base gas of the simulated gas. To clarify the effect of the individual coexisting gas on NO removal, each coexisting gas was added to the base gas. The results showed that the existence of H₂O or C₂H₄ was effective for NO removal with low energy density. Also, when negative corona discharge was applied to the simulated exhaust gas (N₂/O₂/NO/H₂O/CO₂/C₂H₄ mixture), more than 90% DeNO_x was achieved. However, the by-products such as CO, O₃, HNO₃ and N₂O increased with increasing the energy density. It was found that the optimum energy density of corona discharge was about 250 J/L for DeNO_x of simulated exhaust gas.

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We studied a treatment method on beavy metal separation and sludge decomposition using a superconducting magnetic separation and a hydrothermal decomposition method. The experiment showed that the superconducting magnetic separation method to which a high gradient magnetic filter was applied proved to be practically used to remove 90% of heavy metal particles and that the hydrothermal decomposition method proved effective in dehydrating sludge and in minimizing the volume. The study also showed a well-posed hydrothermal condition on temperature and oxidation that matched the magnetic separation to remove heavy metal in sludge.

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In the present study, in order to make the thermal simulation model for large lithium-ion secondary batteries, overpotential resistance, enthropy change, cell heat capacity, and heat transfer coefficient for the commerial cell have been measured. Using these measured data, the thermal simulation model calculates the cell temperature during rapid charge and discharge cycles, which calculated results have been compared with the measured temperature to confirm the validity of this model. The one-dimensional thermal simulation model gives the cell temperature profile, which shows the maximum temperature difference between center and surface of 1.6°C during 3C discharge. So we assumed that the cell temperature distribution is uniform during rapid charge and discharge cycles. The thermal simulation model with a representative cell temperature was made in using the measured data described before. The calculated temperature by this model agrees well with the cell temperature measured by a thermocouple. Therefore we can confirm the validity of our thermal simulation model to predict the cell temperature during rapid charge and discharge cycles.

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In order to characterize a radiative conveter for high temperature air combustion furnace, fluid flow characteristics through a wire screen at low Reynolds number were investigated by numerical simulation. It was confirmed that flow resistance results agree with existing experimental data. Drag coefficient of three kinds of wire screen at porosity range : 0.3<β< 1 and Reynolds number range : 1 <Re< 300 were obtained. Empirical formula of fluid resistance through a woven mesh was obtained.

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In order to characterize a radiative converter for high temperature air combustion furnace, heat transfer and fluid flow characteristics through a wire screen at low Reynolds number were investigated by numerical simulation. It was confirmed that heat transfer results agree well with existing experimental data. Nusselt number of three kinds of wire screen at porosity range : 0.3<β<1 and Reynolds number range : 1<Re<300 were obtained. The difference in heat transfer characteristic of parallel wire, crossed mesh, and woven mesh were investigated. A generalized approximation formula of heat transfer coefficient through a wire screen was obtained.

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