A new approach to deduce the effective viscosity of bubbly liquid with considering non-equilibrium bubble deformations in transient shear flows was proposed. Simultaneous measurement of the bubble shape and the spatio-temporal velocity distribution clarified that bubble deformation has delay from a variation of the local Capillary number under a transient process of flows from a stationary state to a rigid body rotation (spin-up) in a rotating cylinder. Relative viscosity of the bubbly liquid against the single phase condition estimated by the proposed method shows 60 % increase as the maximum. Such large increase of the effective viscosity cannot be introduced by mixture of spherical bubbles and bubbles with equilibrium deformations, and thus the non-equilibrium bubble deformations take a primary role on the modification of the effective viscosity in unsteady shear flows.

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The vertical axis wind turbine can correspond to the wind direction change in principle and is possible to increase the output by stack it up vertically. However, it is pointed out that the control is difficult, because the self-start is weak and the rotational speed rises rapidly. In this study, we report on the method by which the generating operation can be continued at ease when the wind of the mean speed from 12m/s to 15m/s blows to the small giro-mill type vertical axis wind turbine and under the situation with large wind speed fluctuation in the vicinity of ground. In this method, firstly, the slide shaft is installed squarely to the rotation axis of the vertical axis wind turbine. The flat plate wing in the tip of this slide shaft is parallel to the plane of rotation under a usual rotational speed, and the axial resistance torque is small. However, the flat plate wing begins to tilt when the rotational speed exceeds a certain value, and it becomes finally right-angled to the plane of rotation, and large axial resistance torque is generated. By this method, the runaway of the vertical axis wind turbine is prevented. In the paper, various problems on this are clarified and are verified through the wind tunnel experiment, and the practicable method has been clarified.

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The laminar-turbulent transition of a boundary layer induced by an injection of jet in the inlet region of a circular pipe was experimentally investigated. The jet was periodically injected radially from a small hole in the inlet region into the pipe flow. Axial velocity was measured by a hot-wire anemometer. The turbulence induced by the jet within the boundary layer developed into turbulent patches which then grew in the axial, circumferential and radial directions downstream. The shape of the patches shown by the intermittency factor in the diametrical plane was similar to the turbulent spot in the flat plate boundary layer. Their property became similar to the turbulent slug in the pipe flow developed downstream. The turbulent patches protruded from the boundary layer after they grew and reached the circumferential opposite side, although they stayed within the boundary layer as long as the shape was turbulent spot-like in the diametrical plane. The propagation velocity at the leading edge became faster than the bulk velocity, though it turned slower at the trailing edge. Therefore, the growth rate of its streamwise length varied downstream. The growth rate of the patches' circumferential length was smaller than that in the turbulent spot under zero pressure gradient and was almost the same as the spot under favorable pressure gradient.

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We have investigated aggregation phenomena in a suspension composed of rod-like hematite particles, which have a magnetic moment normal to the particle axis direction, by means of Brownian dynamics simulations. The present Brownian dynamics method takes into account the spin rotational Brownian motion around the particle axis in addition to the ordinary translational and rotational Brownian motion. First, the validity of the present simulation method has been clarified by comparing with results obtained by the fully-established Monte Carlo method. Then, from performing the simulations, we have investigated the influences of magnetic particle-field and particle-particle interactions, shear rate and volumetric fraction of particles on particle aggregation phenomena. Snapshots of aggregate structures are used for qualitative discussion and cluster size distribution, radial distribution function and orientational correlation functions of the direction of particle axis and magnetic moment are focused on for quantitative discussion. The main results obtained here are summarized as follows. The raft-like clusters are significantly formed at a magnetic particle-particle interaction much larger than that for a magnetic spherical particle suspension. This is because the rotational Brownian motion has a significant influence on the formation of clusters for a suspension composed of rod-like particles with large aspect ratio. An applied magnetic field enhances the formation of raft-like clusters. A shear flow does not have a significant influence on the internal structures of clusters, but influences the cluster size distribution of raft-like clusters. The volumetric fraction of particles has a significant effect on the growth of raft-like clusters and clear cluster formation appears from a volumetric fraction between 0.01 and 0.05 in the present simulation circumstances.

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The purpose of this study is to understand the relationship between the vortex structure and the drag characteristic of a circular cylinder during accelerated motion from a rest. Wake flow of the accelerated circular cylinder was visualized by fluorescent dye technique. Drag act on the accelerated cylinder was determined by the measurement device using an expansion coil. The development of a twin vortex separated from the cylinder was observed during the accelerated motion. At the beginning of the accelerated motion, drag showed sudden change at the same time that the twin vortex collapsed temporarily. Then the twin vortex was gradually grown by supplying vorticity of shear layer vortices. We confirmed that drag coefficient of accelerated circular cylinder was influenced depending on the accelerations.

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A ventilated sheathed nozzle for producing abrasive suspension jets (ASJs) has been developed as a means of extending the effective standoff distance and improving the cutting capabilities under submerged conditions. In the present investigation, submerged cutting tests were conducted with aluminum specimens at a jetting pressure of 30 MPa to clarify the effects of sheath length and air flow rate on the cutting capability of ASJs. The nozzle used in the tests was a conical convergent nozzle with a focusing section. For the range of experimental conditions used, improved cutting was achieved with a shorter nozzle sheath. High-speed observations and measurements of the flow rate distribution of water jets were also carried out at a jetting pressure of 10 MPa in order to investigate the flow structure of air coated ASJs under submerged conditions. The cutting capability was found to drastically improve for small standoff distances since air coated ASJs are formed downstream of the sheath exit.

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Gas transport through the gas diffusion layer (GDL) is important in Polymer Electrolyte Fuel Cell (PEFC). GDL consists of random fiber structure, so GDL may have anisotropy for the transport properties. We have developed the measuring method of the effective diffusivity through GDLs and measured those through-plane and in-plane values. In this work, the effective diffusivity through GDL on each directions and the convection mass transfer at GDL-Channel interface were investigated. The coefficient has been measured in various gas flow rate and diffusion area of GDL of especially through-plane direction. It was found that the in-plane diffusivity is higher than the through-plane value. In addition, convective mass transfer was evaluated by using Sherwood number and compared with asymptotic results for laminar convective mass transfer. The resulting Sherwood number closed to asymptotic results almost.

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This study aims to reveal the factors which restrict operating output range in a natural-gas-fuelled PCCI engine. For this purpose, experiments were performed using a single-cylinder test engine. Effects of compression ratio and intake charge pressure on the performance and combustion characteristics were investigated. To analyze the relation between operating output range and combustion characteristics, numerical study was conducted using chemical kinetics calculation and cycle simulation with a simple ignition model. The results showed that regardless of compression ratio and intake charge pressure the pressure rise rate reaches the limit when the ignition timing moves close to TDC as the fuel quantity is increased. And also, the combustion efficiency and combustion duration vary the temperature and quantity of residual gas, which remarkably advances the ignition timing for the low intake charge temperature case.

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The heat transfer and fluid flow characteristics of a viscoelastic fluid flow in a serpentine channel are described in this paper. The average heat transfer coefficient, pressure loss, and flow visualization were measured under the Reynolds number conditions of Re = 0.5 ～ 2.0. Water solutions of polyacrylamide with sucrose and plain sucrose were employed as viscoelastic fluids and Newtonian fluids, respectively. An increase in the Nusselt number with increasing Reynolds number in the case of the viscoelastic fluid flow was observed in the serpentine channel, while in the case of the Newtonian fluid flow, the Nusselt number remained approximately constant. The visualization results revealed that unsteady flows with a large fluctuation and longitudinal vortex-like secondary flows were generated in the case of the viscoelastic fluid flow, particularly downstream of the inflection point of the serpentine channel. This was believed to be attributed to the increase in the flow instability and the normal stresses produced by the elastic property of the fluids. Further, the Nusselt number increased even in the case of the viscoelastic fluid flow in the straight channel, relative to that in the case of the Newtonian fluid flow. However, this increase moderate in comparison to that in case of the serpentine channel, which indicates that the heat transfer enhancement can be obtained effectively by a combination of the viscoelastic fluid flow and channel geometry. A considerable increase in the pressure loss penalty was observed in the case of the viscoelastic fluid flow. However, the viscoelastic fluid case showed a higher overall performance in terms of the pumping power.

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