Unsteady control effect of non-thermal plasma on leading edge separation flow was investigated experimentally. Wind tunnel experiment was done using a NACA0015 airfoil of 9 cm chord length of c under Reynolds number condition of Re=U_∞c/ν=1.2×10⁵, where U_∞ : flow velocity, ν : kinematic viscosity. A pulse modulated mode with a fundamental frequency of 5 kHz was adapted to apply voltage to dielectric-barrier discharge electrodes which were mounted on the leading edge of the airfoil. First, effect of pulse modulation frequency on separation control was investigated. Second, effect of duty cycle was studied. Finally, FFT characteristic of wake flow under the separation control flow was discussed. An optimum frequency of f corresponds to fc/U_∞=0.47 and 10% duty (discharge power of 0.18 W) was found to exist for unsteady excitation of the leading edge separation. FFT analysis result indicates that this optimum unsteady control of the dielectric-barrier discharge has a role to organize coherent structure of the separation flow.

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The three-dimensional numerical simulation was conducted for design and development of the fuel reformer for on-site fuel cell. The simulation model made by thermal fluid analysis software STAR-CD was applied to analysis of the gas flow, the heat transfer, and the catalytic reaction in the fuel reformer. Distributions of the gas flow, the heat flux and the chemical reactions in the fuel reformer were able to calculate. Residual reactant CH₄ fraction error calculated was c. a. 10% compared with the theoretical equilibrium value. The calculation results showed that a short inflow manifold in the catalyst layer enhanced the uniformity of circumferential gas flow distribution, and that a buffer surface at the high temperature area had an effect to reduce the circumferential distribution of reactions. These suggest that this analysis has reasonable potential for disigning of the fuel reformer.

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A bubble motion in aqueous surfactant solutions is investigated with the numerical simulation. It is known that the reduction of the terminal velocity of rising bubbles is explained by the so-called Marangoni effect, which is caused by the surfactant adsorption to the air/water interface. But few studies have been done for the shear-induced lift force acting on a bubble under the presence of the Marangoni effect. Here, we conduct the simulation on the force acting on the contaminated bubble in a linear shear flow. To consider the Marangoni effect on the bubble motion, the balance equation for the concentration in liquid phase and the interfacial concentration at bubble surface are solved on the three-dimensional boundary-fitted grid system. The surfactant adsorption and desorption processes to the air/water interface are considered by the Langmuir's kinetics laws. The present simulation showed that the reduction of the lift force occurs when the surface concentration becomes sufficiently large. They also showed that the azimuthal distribution of surface concentration of surfactant gives a large influence to the lift force, although it doesn't to the drag force.

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We have developed the modified periodic-shell boundary condition (BC) for dissipative particle dynamics (DPD) simulations, which enables us to simulate an outer flow problem around an obstacle using a small simulation region. In order to clarify the validity of this BC, we have treated a uniform flow around a circular cylinder. The present BC was compared with the ordinary BC such as a uniform flow condition. Also, the present results were compared with those of the numerical results of the Navier-Stokes equations. The ordinary uniform BC is seen to give rise to significantly distorted flow fields and also to significant disappearance of dissipative particles out of the simulation region. In contrast, for the present modified periodic-shell BC, the number density of dissipative particles are kept almost constant during a simulation run, and the flow field is in reasonable agreement with that, which was obtained by the numerical simulations of the Navier-Stokes equations.

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The direct simulation Monte Carlo (DSMC) method is widely used for simulating rarefied gas flows, and in most cases, the phenomenological model with a local equilibrium assumption is chosen as a collision model. Since most collisions in the rarefied gas regime are binary ones, to make the vibrational transitional collision model for the DSMC method without the local equilibrium assumption, binary collision processes of diatomic molecules were analyzed. The semiclassical approach, in which the vibrational motion is treated quantum mechanically and other degrees of freedom are investigated with the classical mechanics, was introduced. The scheme was verified using the vibrational transition rate coefficient comparing with the empirical relation and the existent numerical results. The transition probability was obtained as a function of the initial translational and rotational energy. From collinear collisions, the transition probability can be described with a simple function of the relative translational energy. The total rotational energy of collisional pairs is appeared to be important for general collisions with rotational energies.

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We propose a new micromixing process utilizing gas-liquid free interface. This new process enhances mixing by narrowing and winding flow due to the existence of bubbles. Moreover, because shear stress does not work on gas-liquid free interface, this process will reduce pressure drop. Through flow experiment and CFD analysis, we compared the mixing performance of the new micromixer with that of conventional Y flow micromixer. The experimental result proved that the new micromixer can promote more mixing than Y flow micromixer. Furthermore, the CFD analysis revealed that the new micromixer can reduce pressure drop.

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For high-accurate prediction of fan tone noise, unsteady flow-field around single stage fan used in an experiment was numerically analyzed with a CFD code based on Unsteady Reynolds-Averaged Navier-Stoke equations. The pressure fluctuations with Blade Passing Frequency (BPF) and their higher order components were extracted by Fast Fourier Transform (FFT). These pressure fluctuations were decomposed into circumferential acoustic modes and radial modes by FFT and Bessel functions. It was confirmed that the circumferential mode of the pressure waves generated by the interaction between the rotor wakes and the stator vanes agreed with theoretical one. By the radial mode analyses, it was found that the waves propagating upstream of the stator vanes decayed and scattered into higher order BPF waves while when those waves interacted with the rotor blades. From these results, the behavior and structure of three-dimensional waves are revealed.

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Our experimental results [T. Sanada, et. al., ASME-FEDSM 2007-37129] showed that spraying relatively low pressure stream (0.1MPa-0.2MPa), mixed with super-purified water in the nozzle, on a solid surface, caused harsh erosion. We turned our attention to the occurrence of a strong focused rarefaction wave in the middle of the droplet, possibly cavitation. Experimental results that the degrees of the erosion are heavily dependent on temperature also may support the existence of cavitation. We numerically studied the dynamics of high speed liquid droplet impacts on a solid surface by solving the Euler equation of gas-liquid two phase compressible flow. We discuss the possibility of cavitation as the primary cause of the experimentally observed harsh erosion on the solid surface.

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The wake oscillation of a circular cylinder, which is placed near a rigid plane boundary, with tangential blowing from a surface slot is investigated experimentally under the condition of Re=2.7 ×10⁴. The time-mean surface pressure measurements on the circular cylinder, flow visualizations and velocity fluctuation measurements were carried out for various momentum coefficient C_μ and clearances between the circular cylinder and the rigid plane boundary changed. Based on these experiments it is found that periodic velocity fluctuation, which is associated with vortex shedding (Karman vortices), is suppressed by the tangential blowing. However, in the case of the cylinder placed near the rigid plane boundary, the reverse flow occurs in the clearance between the cylinder and the boundary, in particular C_μ increases. The level of flow unsteadiness naturally increases. Moreover, velocity fluctuation measurements revealed that the velocity fluctuation classified into two cases, one being the velocity fluctuation occurring Periodically (H/D>0.1) and the other occurring non-periodically (H/D=0.1).

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The purpose of this study is to make clear the effect of the spin-up acceleration on the boundary layer over the rotating wafer surface. In this paper, onset and breakdown of transient vortices are investigated because transient vortices interfere with the formation of uniform thin film. The air flow fields on the wafer surface are measured by a hot-wire anemometer. The onset of transient vortices over the rotating wafer is detected by the spectra of the tangential fluctuating velocity. It is found that transient vortices appear at higher Reynolds number in the case of higher spin-up acceleration of the wafer. On the other hand, transient vortices break down at a certain Reynolds number and the transition of the boundary layer to the turbulent state is independent of the spin-up acceleration.

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Rubber products, e.g. oil seal, are produced by vulcanization molding and the vulcanization molding of rubber product is performed by past experience, trial and error. In order to reduce surplus rubber and defective product, numerical analysis of flow phenomena of unvulcanized rubber was performed using FIDAP. The analysis was conducted taken the characteristic of unvulcanized rubber obtained by experiment, without considering the effect of the heat. The results showed that the filling state of numerical results represented good agreement with the experimental results. And it was clarified from the numerical results that high shear stress acted during unvulcanized rubber fill up to a narrow channel such as side surface of metal insert. In this paper, the flow phenomena under the condition of vulcanization molding are shown and the optimum flow condition would be discussed with experimental and numerical results.

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By the application of our developed magnetic intelligent fluid, MCF (magnetic compound fluid) to the silicon oil rubber, we could make the MCF rubber highly sensitive to temperature and electric conduction. It is useful for the element material in haptic robot sensor and et al. By mixing Cu and Ni particles in the silicon oil rubber and by applying a strong magnetic field to that, it can have high density of magnetic clusters. We clarified the electric resistance under tensile strain. The experimental results could be explained by using the relation of electric resistance among apparent cross sectional area and length of the particles, guessed from the results by SEM of the formation of the clusters.

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The flow characteristics of functional fluid, which suspended micro scale diamond particles in insulated silicon oil, were investigated by microscopic observation and micro particle image velocimetry. This functional fluid has two specific flow structures induced under the high voltage alternating electric field. One pattern of the flow structure consists of a reciprocating parallel flow generated along an electric flux line in one direction between the electrodes under low-electric-intensity and high-frequency conditions. The other pattern of the flow structure consists of a rotational flow formed under high-electric-intensity and low-frequency conditions. These specific flow structures will contribute actively to a polishing process and to the development of micro fluidic devices in the future. In this study, the electric field conditions to generate the rotational flow structure were discussed. And also the detail structure of the rotational flow was investigated with velocity vector distributions and vorticity distributions.

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The turbulent channel flow over a backward-facing step was investigated experimentally by using suction through a slit at the bottom corner of the step. Suction was continuously applied, and the direction of the suction was perpendicular and horizontal to the main flow. The suction flow rate ratio was varied from 0.00 to 0.15. The wall static pressure and local heat transfer coefficient were measured behind the backward-facing step. The velocity profiles and turbulent quantities were measured by PIV. It was found that the pressure drop at the step was reduced and the heat transfer coefficient in the recirculating region was improved by the suction. The suction direction did not affect to the heat transfer or fluid flow characteristics. Enhancement of the heat transfer coefficient was related to the increase in turbulent energy, Reynolds shear stress and turbulent diffusions. However, the region where these quantities increase was limited to the area immediately behind the step. When the suction flow rate were larger, the periodic fluctuating motion was found.

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Particle motion and flow structure were experimentally investigated in grid-generated turbulence with spherical or columnar particle dispersions. Particle motions were taken by a high-speed video camera and instantaneous streamwise and horizontal velocities were measured using a PIV. The results show that columnar particles fall without clustering in the free-falling particle experiment, whereas spherical particles form clusters during the falling process. Turbulence intensity in the grid-generated turbulence with columnar particle dispersion is larger than that in the turbulence with spherical particle dispersion. It is found by flow visualization that these differences in particle motion and fluid structure are attributed to the irregular horizontal movements and rotation of columnar particles.

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We have developed a nonlinear inversion scheme for retrieving collision kernels of droplets from the time evolution of droplet size distributions in turbulent air flows. In order to obtain reference data to validate the scheme, we have performed three-dimensional direct numerical simulations (DNS) of colliding droplets in isotropic steady turbulent flows. In the DNS, air turbulence is calculated using a quasi-spectral method, and droplet motions are tracked by a Lagrange method. The collision kernels retrieved by the nonlinear inversion scheme are compared with those obtained by the DNS for flows with various Reynolds numbers. The collision kernels retrieved from our previous linear scheme are also compared to the reference data. The results show that both the linear and nonlinear schemes can retrieve the collision kernels with fair accuracy in low Reynolds number flows. In higher Reynolds number flows, however, retrieval errors of the linear scheme become larger but those of the nonlinear scheme stay small. Thus, the present nonlinear scheme is more robust than our earlier linear scheme.

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Authors have been proposing a new type of sewage pump impeller designed to further improve pump efficiency and performance in passing foreign bodies. And pump performance, internal flow and behavior of the radial thrust have been clarified by LDV measurement and CFD analysis. However, hydraulic design of pumps is integral calculus operation whereas flow analysis is differential calculus operation. Therefore, even if complicated internal flow was clarified by CFD analysis, it is difficult to improve pump performance if the cause and outbreak mechanism of each hydraulic loss were not clarified. This paper proposes loss analytical method of this pump equipped with a single blade impeller. As a result of having compared experimental values and CFD analysis values with loss analysis values about the head curve, they almost matched in a wide range of flow rates. When the flow flows backward to the impeller from the volute casing, the hydraulic loss becomes small in an appearance, but the power loss becomes excessive and the pump efficiency decreases.

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The conventional boundary element method (BEM) needs a domain integral in heat conduction analysis with heat generation or initial temperature distribution. This paper shows that the three-dimensional heat conduction problem can be solved effectively by using the triple-reciprocity boundary element method without internal cells. In this method, the distribution of heat generation and initial temperature are interpolated by using integral equations. In this method, time-dependant fundamental solutions are used. A new computer program was developed and applied to solving several problems.

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Heat transfer coefficients were measured on tube bundles of fundamental layouts including in-line layouts embedded horizontally in a liquid-fluidized bed. Tested tube layouts were single tubes, transversal single tube rows, longitudinal single tube rows and in-line arranged tube bundles. A total of 7 kinds of particles were used. Comparisons of the experimental data showed a good agreement with the heat transfer correlation developed for staggered layouts, when the average liquid velocity through each tube bundle was used as the reference velocity for the particle Reynolds number. Distribution of local heat transfer coefficient was also investigated around tubes.

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In the present study, new experimental results will be reported on the enhancement of heat transport by a pulsating heat pipe (PHP) using a self-rewetting fluid as a working fluid. Self-rewetting fluids have a property that the surface tension increases with temperature unlike other common liquids. The increasing surface tension at a higher temperature means that the liquid will be drawn towards a heated surface if a dry spot appears. Thus, in boiling, a dryout phenomenon may be prevented at a higher heat flux. In the present experiment, butanol was added to water at a concentration of less than 1wt% to make the self-rewetting fluid. A pulsating heat pipe made from extruded multiport tubing was partially filled with the butanol-water mixture and tested for its heat transport capability at different input power levels. One end of the PHP was heated using a copper block equipped with two cartridge heaters. A fin was attached to the opposite end to be cooled by a fan. The experiments showed that the maximum heat transport capability was enhanced by a factor of four when the maximum heater temperature was limited to 110 degrees C. Thus, the use of a self-rewetting fluid in a PHP has been shown to be highly effective in improving the heat transport capability of pulsating heat pipes.

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In order to develop a technology which can efficiently convert sewage sludge into solid fuel, the effect of the hydrothermal treatment on the dehydration performance and the carbon balance in this treatment were investigated. The raw sewage sludge cake with water content of about 80% could not be dehydrated by increasing the pressure of the mechanical press. On the other hand, after the hydrothermal treatment, the sewage sludge became easy to be dehydrated by the mechanical press. Carbon content in the residual solid after the mechanical press decreased with the rise of the reaction temperature of the hydrothermal treatment due to solubilization of part of volatile and fixed carbons in the sludge. By employing the hydrothermal treatment combined with the mechanical dehydration and solid material yielded from the dehydrated water, we can reduce the required energy for drying sewage sludge down to about two-thirds of that of conventional drying processes.

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In this study, characteristics of performance degradation caused by starved operation in one cell of a DMFC stack were investigated by comprehensive study based on the measurement of electrochemical behavior of cell and gas analysis of CO₂, and O₂ emissions in anode off gas. As a result, it was made clear that the degradation appears as decay of catalyzer activity only in anode, which is attributed to corrosion of carbon used as anodic catalyst support. This carbon corrosion reaction is predicted to be triggered by O₂ which is generated in the anodic reaction of water electrolysis caused in potential reversal. Since the degradation was suppressed by the use of carbon free catalyst such as Pt-Ru-black, it is estimated that use of much more tough anti-corrosive material than Ketjenblack which is used in this study is effective to mitigate performance decay caused by methanol starved operation.

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Two-dimensional direct numerical simulations (DNS) with and without a radiation model are applied to a spray jet flame, and the effect of the radiation on the spray flame behavior is studied in detail. N-decane (C₁₀H₂₂) is used as a liquid spray fuel, and the droplet motion is calculated by the Lagrangian method. As the combustion reaction model, Arrhenius formulation (ARRS) and enthalpy-based flamelet/progress-variable approach (FPVA-E) for a one-step global reaction are employed. Radiation is taken into account using the discrete ordinate method. The validity of the FPVA-E coupled with the radiation model is assessed by comparing with the reference solution obtained by the ARRS with the radiation model. The results by the ARRS with the radiation model show that the radiation acts to enhance the thermal diffusion and greatly affects the spray flame structure. The effect of the radiation on the spray jet flame can be well captured by the FPVA-E coupled with the radiation model.

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3-D movement of flame fronts in lean and rich hydrocarbon-air turbulent premixed Bunsen flames, having the identical laminar burning velocities, were examined by a four-element electrostatic probe. Measurements were conducted at an off-axis position in turbulent flame brush. The probability distributions of the magnitude and of the direction cosines of the velocity vector of the flamelet were examined. The results showed differences between the lean and rich propane flames but not between the lean and rich methane-flame pairs. The lean propane flame has the same probability distribution of direction cosines as the methane flames. The probability distributions of the direction cosines for the rich propane flame are, however, quite different, that there is a much greater tendency for outward flamelet motion. Although these results for rich propane flame exhibit a larger most probable outward-motion direction cosine for burnt - to- unburnt passage than for unburnt - to - burnt passage, as has been found in all Bunsen-flame data and explained previously, this is the first example in Bunsen-flame data in which the most probable value of the direction cosine in the radial direction for unburnt - to - burnt passage is positive, that is, contrary to the other Bunsen-flame results, the average flamelet velocity direction is outward at this off-axis position even for unburnt - to - burnt passage. The exceptional characteristics of rich propane were explained by nonlinear enhancement of the average flamelet burning velocity through preferential oxygen diffusion to turbulence-induced flamelet bulges convex to wards the fresh mixture.

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The lean premixed flame stabilized by a bluff-body downstream of a coaxial nozzle is actively controlled by using micro magnetic flap actuators attached to the outer jet noz+zle. CH radical luminescence, CO and NO_x, emissions are measured to assess the controlled flame, while PLIF is employed to elucidate the control mechanism. At both of full and partial load conditions, which are represented by the equivalent ratio of φ = 0.72 and 0.48, respectively, the flame stability and also the CO emission are drastically improved without an increase of NO_x emission. At φ = 0.72, stable lean premixed combustion is achieved through the fuel / air mixing enhanced by the large-scale vortices, which are formed when the flaps are driven at the Strouhal number of unity. On the other hand, at φ = 0.48, the premixed combustion, which is otherwise hard to achieve, is stabilized by the stratified mixing due to the induced small-scale vortices produced at the Strouhal number much larger than unity.

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An evaporation process plays an important role on the combustion and emission formation processes in a direct injection (D. I.) gasoline engines. An experimental study was conducted on the evaporation process of the non-axisymmetric wall-impinging spray injected by the hole type injector for a D. I. gasoline engine. For the quantitative measurement of the vapor of the non-axisymmetric spray, the image processing technique using the Laser Absorption Scattering (LAS) principle was newly developed. The total amount of fuel vapor in the whole spray was obtained from the optical thickness image of the vapor and the Lambert Beer's law. The amount of fuel vapor in the wall-impinging spray is decreased compared with the free spray. In addition, the amount of fuel vapor is decreased as the distance between nozzle tip and the impingement wall is decreased.

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Effects of fuel atomization on cold starting of a 4 stroke cycle spark ignition engine were investigated experimentally. Two kinds of ultrasonic fuel injectors using a micro nozzle array (MNA injectors) were applied, whose nozzle diameter d=4 and 6 μm, respectively. A conventional port fuel injector (PFI injector) was also used for comparison. The Sauter mean diameters (SMDs) of the sprays were 15 μm (MNA, d = 4 μm), 23μm (MNA, d = 6 μm), and 59 μm (PFI), respectively, An air cooled, single cylinder, 4 stroke cycle, spark ignition engine was used. The first ignition cycles and the cumulative fuel amount were investigated at a wide range of the air fuel ratio. For the MNA injector (d = 4μm), the first ignition cycle became much earlier when compared with the PFI injector. The cumulative fuel amount during cold starting reduced by about 30%. It is shown that, by use of the MNA injector, the unburned hydrocarbon emissions during cold starting could be reduced.

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The purpose of this study is to develop the nozzle, which is able to obtain the spray with high-dispersion and high-penetration and to apply the atomization enhancement nozzle developed in this study to an actual Diesel injector. In this paper, the effects of geometric shape and dimension of the atomization enhancement nozzle on atomization of intermittent spray were investigated. Moreover, spread of the spray of the atomization enhancement nozzle, which was invented in this study, was compared with a single hole nozzle used in the actual Diesel nozzle. As the results, although the spray tip penetration of the atomization enhancement nozzle was short, spread of the spray became large significantly compared with the single hole nozzle at the intermittent injection.

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