Microscopic contact angle at a contact line traveling over each backward-facing step with heights of 0.3-1.2 nm was investigated with molecular dynamics (MD). The simulations were performed for a Couette-flow-like geometry which is composed of an upper flat plate and a lower plate with a step. Two kinds of immiscible liquids between the plates were sheared by the lower plate moving with a velocity of 1 m/s. When the contact line reaches the backward-facing step, it tends to be strongly captured (pinned) at the top edge of the step. The minimum contact angle of the receding fluid, which was observed at the moment of the depinning of the contact line, is decreased with the increment in the step height. In order to elucidate the mechanism relating the minimum contact angle to the step height, a description on the stress balance along the step surface was derived under the assumption of the static condition. It has been found that the static contact angle is decreased by the stress on the vertical surface of the step, the stress which associates with the anisotropic pressure in the liquid-liquid interface region. In addition, such decrement in the contact angle is enhanced by the increase in the step height through the intensification of the total shear stress over the vertical surface of the step.

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The Vortex in Cell (VIC) method for bubbly flow, proposed in the authors' prior study, is improved to promote the numerical accuracy and efficiency. The improvements are concerned with a discretization method using staggered grids, a correction method for vorticity and a single-stage calculation method for the convection of vortex element. To enlarge the applicability of the VIC method, vortex elements without core structure are employed. The improved VIC method is applied to simulate a bubble plume. In a tank containing water, small air bubbles are released from the base of the tank. The bubbles rise due to the buoyant force, inducing the water flow around them. The simulation for the plume at the starting period highlights that the rising bubbles induce vortex rings at their top and that a bubble cluster appears owing to the entrainment of the bubbles into the vortex rings. The rising velocity for the top of the bubbles is proportional to the square-root for the flowrate of the released bubbles, being consistent with existing theoretical and numerical investigations. The simulation also demonstrates that the developed bubble plume having some characteristics of a jet is successfully captured.

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To remove particles in two phase fluid, rotating filters were developed based on the phenomena that the concentration of particles decreased by passing through branch pipes. Two types of rotating filters were examined. One of them was composed of outlets set on rotating disk, and the other was composed of outlets set on tank surface and a vane rotating over the outlets. Both systems used the peripheral speed of rotating disk or rotating vane in place of the flow speed in main pipe. Their filtering effects were examined experimentally by using two phase fluid composed of polystyrene spherical particles and salt water with the same specific gravity as particles, and the experimental results showed good agreements with the theoretical predictions. Furthermore, it was examined whether rotating filters could remove water droplets dispersed in air, and they were found to remove them more efficiently than the theoretical predictions because of inertia effects.

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PIV measurements are performed for turbulent flows in a rib-mounted channel whose bottom wall is made of a porous layer. The effects of the wall and rib permeability are investigated focusing on the separating and reattaching flow region. Three kinds of porous media are employed. They have the same porosity of 0.8 but each has different permeability from the others. Two types of square cylinder ribs are used, one of which is an impermeable smooth solid rib and another is a permeable porous rib which is made of the same porous medium as that for the bottom wall. The obtained mean velocity profiles of the solid rib cases indicate that the reverse flow in the recirculation behind the rib becomes weak as the increase of the wall permeability. The recirculation area thus shrinks. The main factor of those phenomena is found to be the increase of the bypassing flow rate through the bottom porous wall below the solid rib. Indeed, the local streamwise flux across the clear channel is confirmed to decrease above the rib and then increase behind the rib, according to the increase of the permeability. In the porous rib case, although the magnitude of the reverse flow becomes weak, the reattachment point shifts downstream and the recirculation bubble is slightly expanded. As the increase of the permeability, the reverse flow becomes weaker and the recirculation region tends to vanish. These are due to the bypassing flow not only through the bottom wall but also through the rib. The decrease of the local streamwise flow rate in front of the rib becomes less than that for the solid rib case. This indicates the increase of the bypassing flow through the rib. The bleeding flow from the back of the rib becomes a dominant factor on the shift of the recirculation area.

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The characteristics of four roll coating system were numerically investigated compared with experimental data to validate theoretical models used in this research. In the theoretical models, a film splitting model using a power-law type equation, a roll gap model based on elasto-hydrodynamics and a flow model from a rotating cylinder system were applied. The parametric computations to each operation condition revealed the steady and dynamic behaviors of a coating film and liquid films on coating rolls. From the results of the frequency response to the speed disturbances of the coating rolls, it was found that the sensitivity of the lowest coating roll to the disturbance was a half of others, which implies that the requirement for the accuracy of a driving system for the coating roll is not so severe compared with others. The experimental data and the numerical results at steady state agreed in large part. The actual properties of materials used in the coating process will be required to predict the coating thickness precisely.

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Flow management of a plane turbulent wall jet has been studied experimentally by utilizing a streamwise vortex pair with periodic variation in strength and radius. The magnitudes of the streamwise vorticity and secondary current induced by the vortex pair are weakened by the periodic variation. The integrated streamwise momentum flux is increased by the introduction of the streamwise vortex pair which consists of two counter-rotating longitudinal vortices into the shear layer. Despite the weakening of the vorticity and secondary current caused by the periodic variation, the increasing increment rate of the momentum flux is slightly increased due to the periodic variation. In an analysis with triple velocity decomposition and phase averaging, it is evident that the periodic fluctuating velocity component contributes significantly to the production of the Reynolds shear stress.

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An experimental study was conducted in order to clarify the response of the fully developed pipe flow to d- and k-type wall roughness of various streamwise lengths. The measurements were set to emphasize on the response processes, which are deformation and relaxation of the mean velocity profile related to the strength and type of roughness. Under the same effective pressure drop, comparison of the mean velocity profiles and three common characteristics of boundary layer thicknesses (displacement, momentum, and energy) revealed that the initial stage of the response to the flow depends on the type of roughness. The total recovery length until the fully developed state depends only on the effective pressure drop caused by the rough wall.

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The relation between the development of the wall boundary layer in a convergent nozzle and free surface waves on the emanated liquid jet has been investigated experimentally. In the convergent nozzle, which forms a water jet along a flat back wall, the velocity profiles of the wall boundary layer were measured using a laser Doppler velocimeter with jet average velocities of U₀ = 5, 10 and 15 m/s. The property of free-surface waves and the intermittency factor of free surface fluctuations were also determined by photography and an optical measurement technique, using laser beam refraction on the jet surface. For the lowest velocity case U₀ = 5 m/s, the mean velocity profiles of the boundary layer under the pressure gradient in the convergent nozzle indicated an inverse transition from turbulent to laminar boundary layer, so-called relaminarization. On the other hand, for the higher velocity case U₀ ≥ 10 m/s, the relaminarization in the convergent section became incomplete. For these cases, the turbulent intensity near the wall increased significantly and the nozzle-exit boundary layer was restored quickly to a turbulent profile for a short parallel section immediately upstream of the nozzle exit plane. The increase in the velocity fluctuation near the wall promotes wave generation downstream of the nozzle exit plane. Therefore, the intermittence of the wave packet almost disappeared and the jet free surface was covered with continuous capillary waves when the turbulent boundary layer was separated from the nozzle exit.

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Critical Heat Flux (CHF) in a non-uniformly heated tube is a very important designing factor of actual boiling two-phase flow equipments. In this series of studies, the CHF in a non-uniformly heated tube was discussed by using the re-distribution of a liquid film caused by the wave interaction. In the present investigation, in order to estimate the influence of the entrainment of droplet under the high heat flux condition on the re-distribution of liquid film, the CHF experiment was conducted. The experimental apparatus was a similar to the forced convective boiling system described in the previous paper, i.e. the eccentric tube with 20 mm I.D., 24 mm O.D., but heated length was just only 450 mm to keep the high heat flux condition. The experimental result expressed the influence of the magnitude of the heat flux as the increasing in the entrainment. The CHF was occurred at the high quality condition, i.e. liquid film dryout and at the low quality condition, i.e. departure from nucleate boiling (DNB), respectively. This obtained CHF was evaluated by using the film flow model, and the empirical correlation of the spreading coefficient of liquid film re-distribution was proposed.

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The purpose of this study is to clarify the fundamental features of NO_x formation in oxy-coal combustion. The pure effects of various factors related to oxygen concentration, flame temperature and flame shape on NO_x formation are investigated by experimental and theoretical analysis, resulting in the following conclusions: (1) In oxy-coal combustion (i.e., CO₂/O₂ atmosphere), the emission of fuel-NO_x increases with O₂ concentration. (2) The flame shape changes from a detached flame to an attached flame with the increase in flame temperature. (3) During oxy-coal combustion, the gasification reaction between CO₂ and carbon on the surface of char particles occurs more vigorously than during combustion in air. (4) The single particle model for estimating NO_x emission is applicable to the detached flame. This implies that in the case of the detached flame the pulverized coal burns with a structure of premixed flame.

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