Pulsating jets are very common and useful in various industrial aspects. However, they have some different basic characteristics from steady jets. In this research, the authors reveal both the frequency and the amplitude effects of pulsations on a jet, including large-amplitude cases. Experiments are conducted at a Reynolds number of 5000, Strouhal numbers of 0.011-0.27 and velocity-amplitude ratios of 0.1-1.0. Using a hot-wire anemometry, the authors show centre velocities, radial profiles, half widths and total flow rates at several positions downward a nozzle exit. From centre velocities and radial profiles, we can see that the streamwise scale of the potential core is less than three times the diameter. From half widths and total flow rates, we can see that the pulsation enhances mixing, and confirm the frequency and the amplitude effects specifically. On the other hand, from centre velocities and radial profiles, we can not see the both effects clearly. As a result, the authors show the combined frequency-amplitude effect on total flow rate, which consists with small-amplitude results by Crow and Champagne (1971), and find the optimum frequencies.

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Electrochemical Machining (ECM) is an advanced machining technology and has been applied to highly specialized fields, such as aerospace, aeronautics, and medical industries. However, some problems remain to be solved. The efficient tool-design, electrolyte processing, and disposal of metal hydroxide sludge are typical problems. To solve such problems, CFD is thought to have potential as a powerful tool. However, a numerical method that can satisfactorily predict the ECM process has not been established because of the complex flow natures. In the present study, we presented a new model to calculate the flow fields in an ECM process. This model is based on a two-way coupling method, taking the interaction between gas and liquid phases into account. In this coupling method, we assumed that electrolyte and generated hydrogen bubbles over a,cathode surface have the same velocity. Therefore, we could simplify the governing equations. Since the flow field had a non-uniform density distribution due to hydrogen bubbles, a low Mach number approximation was applied to solve the pressure Poisson equation. We simulated ECM process for a flat plate channel configuration. And, we verified the present model by comparing the numerical result with the experimental data. The simulation results show good agreements with experimental data in the view of gap height.

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Computing a flow around a pitching airfoil, the unstructured moving-grid finite-volume method is developed in this paper. The method has been proposed for various moving boundary problems. However, it is limited for compressible inviscid flows. In the case of calculating a viscous flow at high Reynolds number as a flow around a pitching airfoil, it is necessary to solve a boundary layer. So, a hybrid gird system of a prismatic mesh for boundary layer region and tetrahedral mesh for other regions is suitable. In this paper, the unstructured hybrid moving-grid finite-volume method is formulated in four dimensional space-time unified domain to satisfy a geometric conservation law on such a moving grid in addition to satisfy a physical conservation law. The method is apply to a flow around a pitching NACA0012 airfoil, then the results show that the method is effective for a high Reynolds number viscous flow around a moving body.

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Three-dimensional grid-free vortex method for particle-laden gas flow is proposed. The flow region is not resolved into computational grids, but the gas vorticity field is discretized by vortex elements. The behavior of vortex element and the particle motion are simultaneously simulated with the Lagrangian approach. Eight cubic cells are allocated around each particle to compute the effect of the particle on the gas flow. In each cell, the change in the vorticity due to the particle motion is calculated, and it is considered through the change in the strength of vortex element. The grid-free method is applied to simulate a free falling of small spherical solid particles. The particles initially arranged within a spherical region are made to fall in air. It is demonstrated that a downward air flow induced by the falling particles accelerates the particles at the commencement of the fall and that a vortex ring produced around the downward air flow heaves up the particles. These are in good agreement with the existing results, indicating the validity of the present grid-free method.

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Direct numerical simulation of a zero-pressure gradient drag-reducing turbulent boundary layer of viscoelastic fluids was systematically performed at the momentum-thickness Reynolds number Re_<θ_0>=500 and Weissenberg number We=25 using constitutive equation models such as the Oldroyd-B, Giesekus (the mobility factor α=0.01, 0.001, 0.0001) and FENE-P models (the extensibility parameter L^2=100, 1000, 10000), where the ratio of zero shear rate solvent viscosity to solution viscosity, β, was 0.9, 0.99, and 0.999. In the case that the elongational viscosity for the steady elongational flow was identical, the relation between the streamwise variation of the drag reduction ratio and the rheological properties for the steady shear flow such as the shear-thinning, first and second normal stress difference coefficients was clarified.

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In this study, the authors adopted micro bubbles generated by the pressurized dissolution method for the UVP measurement as the reflector of the ultra sound. They are economy and environment-friendly compared with fine solid particles which may pollute the environment. In this study, we used micro bubbles and polyethylene particles for UVP measurement in order to compare the influence of reflectors. In addition, we directly inserted the transducer of the UVP with an accurate movable device into the flow parallel to the flow axis. This method is free from the effects of reflection and refraction at the pipe wall unlike the UVP measurement through the pipe wall, although this method has the disadvantage of the arrangement of the transducer that was immersed in the liquid. The measurement accuracy of the velocity profiles and the possibility of the velocity fluctuation measurement concerning with turbulent intensity using this method was investigated. As a result, the RMS value of the velocity fluctuation, as well as velocity profiles, using axial measurement with micro bubbles as reflectors agreed well with the tendencies of existing data.

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It is known that ring-shaped cavitation clouds are formed when a cavitating water jet impinges on solid wall. The ring-shaped cavitation clouds cause ring-shaped erosion distribution. In this study, we use a confined channel in order to observe the two-dimensional view of cavitating jet. We observe the collapsing behaviors and formation process of cavitation clouds spreading on solid wall in order to directly connect the collapsing behavior of cavitation clouds with the erosion distribution. As a result, at least two types of bubble collapse behavior can be observed. The one is a collapse of cavitation clouds around jet center and the other is in the peripheral portion on the impinging wall.

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The authors have proposed a method, which can measure the distributions of electroosmotic flow velocity and electric field intensity in a micro-channel using μPIV measurement technique. In order to subtract the electrophoretic force effects on the velocities of the tracer particles, two kinds of particles with different electric surface properties were used as the tracer particles. A calibration experiment was firstly conducted using a straight micro-channel to obtain the correlation functions between the apparent electric field intensity and the velocities of the two particles. μPIV measurement was, then, carried out for the target micro-channel to measure the electroosmotic flow and electric fields by applying the same two tracer particles and the correlation function. In the present article, discussion is made on the validity of the present method using two types of channels, namely, a straight channel with a material different to that used in the calibration and a U-bend channel. The results were compared with the experiment using fluorescent dye and also with numerical simulation. In both comparisons, a good agreement was achieved indicating the validity of the method.

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A new system to passively control pitch-angle of rotor blades is proposed in order to prevent over-rotation of a small horizontal axis wind turbine in a strong-wind condition. The system consists of a mandrel bar and a fiber-reinforced rubber pipe in which the metal fiber is arranged with oblique angle. This is installed at the root of each blade respectively. When the rubber pipe is subjected to the centrifugal force due to the rotation of the blade, the fibers are forced to be straight in the loading direction. This yields the torsional deformation of the pipe, and achieves the change of the pitch-angle of the blade corresponding to the revolution of the turbine passively. The tensile tests are performed to examine the fundamental elastic behavior of the fiber-reinforced rubber pipe. To investigate the power performance of the wind turbine with the present passive pitch-angle control system, the wind tunnel tests are carried out. It is confirmed that the present system enables to avoid the over-rotation of wind turbine and realizes the stable power generation even in the strong-wind condition.

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A mechanism promoting perforations in a radial liquid sheet through a hot/cold air flow is investigated. The radial liquid sheet is produced by release of a liquid film spreading on a disk into the air. In the radial liquid sheet, a laminar-turbulent transition occurs just outside the disk edge. The liquid sheet is perforated after the transition and atomized by the perforations increasing with Reynolds number. The perforation is promoted by the impingement of a hot/cold air flow on the transition point. The promotion by the cold air flow suggests that the promotion is not due to evaporation of the liquid sheet. Observations of the liquid sheet in various flow conditions demonstrate critical flow conditions required for the promotion of the perforation by the hot air flow. The observations also show that thin liquid membrane, which is formed after the transition at high Reynolds numbers, is necessary for the promotion of the perforation. A perforation mechanism is proposed for the promotion of the perforation by the hot/cold air flow based on a Marangoni stress affecting on the liquid membrane, which is heated/cooled easily because of its ultimate thinness. The beginning point of the perforation in the liquid membrane and the thickness of the liquid membrane are determined by CCD images of the liquid membrane. The difference in the beginning point of the perforation by air flow temperatures and measured thickness (≒5μm) of the liquid membrane support the validity of the proposed perforation mechanism.

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We have carried out Brownian dynamics simulations of sedimentation phenomena of a dispersion composed of two-kinds of spherical particles in water under the gravity field. This study may be the first step to develop a new technology which enables us to improve the visibility of rivers and lakes. In the present study, we have modeled sub-micrometer-dimension particles, or dirty particles in lakes as small spherical particles, and capturing particles as large spherical particles; these two kinds of particles conduct Brownian motion in water, and large particles adsorb small particles to sediment gradually toward the bottom in the gravity field. From the results of Brownian dynamics simulations, the influences of Brownian motion, particle-particle interaction forces, the size of each particle, and the gravity force on the performance of the adsorption of large particles have been discussed. In addition, we have discussed what the most appropriate situation of large particles is to accomplish the most effective adsorption rate or improve the visibility of water most effectively in terms of capturing particles. The most important conclusion derived from the present results is that, in order to improve the capturing performance, the Brownian motion of large particles have to be activated in an appropriate number density without losing the influence of the gravity.

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The objective of this study was to clarify the unsteady characteristics of the fluid force acting on limbs during swimming. For this objective, an underwater robot arm was developed in this paper. The robot arm has five degrees-of-freedom in order to perform the various complicated limb motions during swimming. In addition, by changing the hand model into the foot one, the robot also can perform the lower limb motions. The joint torques and the resultant thrust can be measured by the force sensors attached to the robot. In a circulating water tank, an experiment to measure the fluid force was conducted for four swimming strokes of the upper and lower limbs. From the experiment, it was found that even the slight difference of the fluid forces between slightly different swimming motions can be quantified by the developed experimental system. In addition, it was suggested that 'nipping' the water by both lower limbs during the kick of the breaststroke almost does not affect the thrust generation. The developed experimental system with the robot arm is useful not only for measuring the unsteady fluid force, but also for the flow visualization in the future studies.

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The efficiency of an artificial kidney is largely dependent on its mass-transfer between blood and dialysate. There are many factors that affect mass-transfer performance of an artificial kidney. This paper describes the effect of housing taper on dialysate flow, and an optimization of its taper length. The dialysate flow in module was calculated, and the momentum change at taper domain was discussed. The fluid force was optimized based on taper length. Compared with the taper length of normal housing, this optimized taper length is as short as 20mm. The fluid force of short taper enforces dialysate flow into hollow-fiber bundle core, and thus results in higher urea clearance.

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This study presents a three-dimensional numerical analysis for the effect of boundary layer thickness on vortex structures and heat transfer behind a hill mounted in a laminar boundary layer. When the thickness of the velocity boundary layer is comparable to the hill height, a hairpin vortex is formed symmetrically to the center of the spanwise direction in the wake. A secondary vortex is formed between the legs, and horn-shaped secondary vortices appear under the concave parts of the hairpin vortex. When the boundary layer thickness increases, the legs and secondary vortices move to the center of the spanwise direction, and thus heat transport and heat transfer increase there. At this time, high-turbulence areas generated locally move to the center of the spanwise direction with an increase of the boundary layer thickness. With a further increase in the boundary layer thickness, steady streamwise vortices are formed downstream of the hill, but the heat transfer decreases.

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An experimental study on heat transfer enhancement for a laminar natural convection boundary layer in air along a vertical flat plate has been performed by inserting short flat plates aligned in the spanwise direction with clearances (split heat transfer promoter) into the near-wall region of the boundary layer. Local heat transfer coefficients in the downstream region of the promoter substantially increase in comparison with those obtained for the usual laminar boundary layer without a promoter. Flow visualization shows that such remarkable heat transfer enhancement is attributed to longitudinal vortices generated by flows passing through the clearances of promoter in addition to vortex motions riding out the promoter. Consequently, it is concluded that the heat transfer enhancement can be achieved in the wide area of the laminar natural convection boundary layer by employing multiple-column split heat transfer promoters.

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Chemical reaction processes using microwaves have attracted attention and a lot of effects caused by microwaves in organic synthesis have been reported. However, most chemical reactors using microwaves that have already been developed are batch-type reactors, and controlling the reaction temperature precisely in batch-type reactors is difficult. We have developed a continuous flow microwave-assisted chemical reactor using electromagnetic simulation, and examined its energy absorption efficiency. It was found that the results of energy absorption efficiency obtained by the simulation corresponded with the measurements within ±9% in water-heating tests and the efficiency by water was 90%. Moreover, we analyzed the temperature rise curve by using an electromagnetic simulation and considered the temperature dependence of dielectric properties. It was found that the simulation results corresponded with the measurements within 3℃ in water-heating tests and within 4℃ in DMF (N, N-dimtheylformamide) heating tests.

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An anode support tubular SOFC is fabricated and the dependence of its polarization characteristics on anode microstructure parameters is investigated experimentally. Nickel yttria-stabilized zirconia (Ni-YSZ) anode supported cell with YSZ electrolyte, lanthanum-strontium-manganite (LSM)-YSZ composite cathode, and LSM cathode layers is fabricated by dip coating. High-resolution images of anode microstructure are successfully obtained by low voltage SEM-EDX and quantified by means of stereology. Cell voltage measurements and impedance spectroscopy are performed at temperatures of 650 and 750℃. A quantitative relationship between polarization characteristics and microstructure parameters such as three-phase boundary length and contiguity is investigated.

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In order to collect fundamental design data concerning CO_2 removal, the authors have concentrated on CO_2 bubble behavior, which dominates anode mass transport in a fuel supply subsystem, especially in anode gas diffusion layers (GDLs). Firstly, effects of fuel supply structure with anode GDLs on CO_2 bubble release was investigated by visualizing CO_2 bubble behavior in anode GDLs with visual passive direct methanol fuel cell (DMFC) modules. Secondly, effects of CO_2 bubbles on fuel tank pressure was investigated with pressurized passive DMFC modules by changing anode GDL wettabilities parametrically. Consequently visual passive DMFC modules revealed the followings; (1) CO_2 bubble behavior was mainly dominated by GDL wettability, not fuel supply structure, (2) hydrophobic anode GDLs (contact angles, 128°) caught CO_2 bubbles on their surfaces, but hydrophilic anode GDLs (contact angles, 47°) set free CO_2 bubbles from their surfaces, (3) CO_2 bubble size was decided by contact angles (bubble diameter, 0.4mm-2.6mm). Furthermore, pressurized passive DMFC modules elucidated that the total volume of CO_2 bubbles present in a fuel tank increased fuel tank pressure, and prevented CO_2 and methanol from transferring in anode GDLs. These results made it clear that CO_2 release was promoted by hydrophilic anode GDLs, but not by hydrophobic ones. In other words, selection of GDL wettability determined CO_2 bubble release characteristics regardless of fuel supply structure.

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An experimental study is performed to provide the empirical data on soot concentration profile in a fuel droplet flame and to get the fundamental knowledge on the effect of water content in the droplet and the atmospheric gas on the soot formation in droplet flames. The laser light scattering technique is applied for non-intrusive qualitative measurements of soot concentration in fuel droplet flames. Measurements are conducted along the diametrical line passing through the front stagnation point of a luminous envelope flame formed around a droplet of various kinds of fuels in the steady stream of the mixture of air and water vapor with uniform profiles of velocity and temperature. The results indicate that the highly sooting region is located deep inside the flame edge. The peak signal of soot decreases with an increase in the velocity of the ambient flow. Increase in oxygen concentration in the ambient flow enhances soot formations in the droplet flame, and the peak position of soot moves outwards. Water vapor in the ambient air stream has negative effects on soot production in the droplet flame and increase in the water concentration results in decrease in the peak concentration of soot. Although water content in an emulsified fuel droplet also has the negative effect on soot reduction, the effect is smaller than that of the ambient water vapor in the flow.

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The ignition enhancement effects of hydrogen addition to lean ethanol vapor-air mixtures are experimentally investigated. Hydrogen addition decreases the lean limit of equivalence ratio from 0.80 down to 0.36. The peak overpressure increases and ignition delay time decreases under the conditions of equivalence ratio below 0.80. Hydrogen addition effect is also confirmed using detailed computations of reaction mechanism. Chain reactions including H_2 are primary ignition enhancing mechanism.

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Coaxial jet spray flames of kerosene/oxygen are studied experimentally in the pressure range of 0.1-1.0MPa. The flame shapes are observed directly, and the spray cross-section is visualized using laser sheet imaging. The droplet size distributions and axial velocity components are measured by phase Doppler anemometry. Direct observation of flames indicates that, as the ambient pressure increases, the flame length decreases, the luminous flame region moves upstream, and the blue flame region at the top of the flame expands. Mie scattering images show that under high pressure, the spray region becomes narrower and shorter. The droplet mean velocity decreases as the droplets move downstream for each pressure condition; however, under high pressure, a region in which the droplet mean velocity decreases moderately appears near the burner port. The droplet mean diameter increases as the distance from the burner port increases, due to a decrease in the number of small droplets and an increase in the ratio of small to large droplets caused by evaporation of the small droplets. In addition, at high pressure, a region appears in which the droplet mean diameter does not change significantly. These results show that spray flame shapes and droplet behavior are strongly affected by ambient pressure.

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This research aims at developing the heat engine system using Shape Memory Alloy (SMA) wires, which work by alternating supply of hot/cold water through the newly developed automatic valves. The SMA wire is connected to the chain and sprocket system having the ratchet type bearing and the spindle with the flywheel. The valves for supplying hot/cold water to the SMA wires are driven by the flywheel, so no outside power is necessary. Output power of the developed heat engine with two φ0.3mm SMA wires is 0.1W at 30〜40rpm. The SMA wire used in the developed heat engine was produced by the Furukawa Electric Co., Ltd. The wire shows the fatigue life of more than 10^5 cycles under conditions of 150MPa in loading and heating/cooling cycle rate of 0.5Hz in the cyclic transformation fatigue tests. The heat engine system works without any adjusting process of a length of SMA wire and water supplying timing. The stress of the SMA wire is kept to be rather higher during working because the engine has no crank system. So, the developed heat engine system is hopeful to use in recovering energy from waste hot water.

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Recently, stricter diesel particulate emissions standards have been setting in many countries. A diesel particulate filter (DPF) has been widely used for the after-treatment of exhaust gas. Since DPF filling causes pressure drop, it is necessary to use the filter with low pressure drop. Then, it is important to examine pressure change due to soot deposition inside the real filter. In this study, we conducted numerical simulation on flow with soot deposition by the Lattice Boltzmann method to observe the relation between soot deposition process and pressure drop during DPF filling. The inner structure of the cordierite filter was obtained by an Xray CT technique. Results show that there are several soot deposition processes when the soot is attached to the filter wall. Interestingly, based on the pressure change rate to accumulated soot, soot deposition process can be distinguished.

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The freezing behavior of liposomes such as internal freezing, contraction by dehydration and disruption of membrane after thawing was examined by microscopic observation. Liposome suspensions were prepared by gentle hydration method using phosphatidylcholine (egg) and distilled water. The observed liposomes ranged in diameter from 5 to 150μm. The sample of liposome suspensions was cooled from -1℃ to -50℃ at cooling rates of 1,2 and 5℃/min and heated to 0℃ at heating rate of 10℃/min. As a result, two different patterns for freezing were observed: internal freezing and contraction without internal freezing. When the internal freezing was observed, the membrane was unexceptionally disrupted after thawing. When the internal freezing was not observed, two different cases were observed after thawing: disruptive and contractive conditions. These different freezing patterns were primarily dependent on the liposome size. In addition, the cooling rate became a key factor determining the freezing patterns in small liposomes.

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