A supersonic free jet through a multi-aperture circular orifice that induces plume-plume interaction or through a rectangular orifice is investigated by the DSMC method with an improved new collision scheme. When the DSMC method is applied to a continuum or a near continuum fluid, the most serious problem is that it is necessary to divide the flow-field into a network of cells the dimension of which is smaller than the local mean free path. At the meeting of the RGD23 and RGD24, Usami et al. has proposed a new intermolecular collision scheme (U-system) in which velocity components of a molecule are modified according to positions of a collision pair and it enables a large cell dimension. The collision scheme (U-system 3) proposed in the present paper conserves the total energy of each collision pair precisely during an intermolecular collision and improves the stability of the scheme.

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Aerodynamic performance test was carried out using a 1/3 scale, 4-stage model of the helium gas compressor to investigate an effect of end-wall over-camber to prevent decrease of axial velocity in the end-wall boundary layer. The model compressor consists of a rotor, 500mm in diameter, which is driven by an electric motor at a rotational speed of 10800rpm. The rotor blade span of the first stage is 34mm. The test was carried out under the condition that the helium gas pressure of 0.88MPa, temperature of 30℃, and mass flow rate of 12.47kg/s at the inlet. A 3-dimensional aerodynamic code, which was verified using the test data, showed that axial velocity was lowered by using a blade which increased the inlet blade angle around the end-wall region of the casing side in comparison with that using the original design blade, because the inlet flow angle mismatched with the inlet blade angle of the rotor blade, as opposed to the prediction by a conventional air compressor design method. The overall adiabatic efficiency of the full scale 20-stage helium gas compressor was predicted 89.7% from the Reynolds number dependency of the test data by using the original design blade.

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Backward-facing step flows with horizontal or vertical synthetic jets fed from the vicinity of the step edge have been investigated to clarify effects of the synthetic jets on separated-reattachment flows as well as to obtain new knowledge for the active control of the flows. Relations between reattachment length and flow control parameters, such as frequencies and velocities of the jet, have been studied. Then details of the flow fields have been obtained with time-mean as well as phase-locked average procedures. Changes in the reattachment length for constant non-dimensional jet velocity are mostly determined from a ratio of the jet frequency to natural frequency of velocity fluctuation without a jet. The reattachment length becomes a minimum when the jet frequency ratio is around unity and decreases in proportion to the non-dimensional jet velocity to the power of -0.11〜-0.13. The feed of the synthetic jet makes shear layers in the downstream of the step edge be periodical organized vortices which induce organized periodic velocity fluctuation and causes non-organized random fluctuations with lower frequencies. These velocity fluctuations stimulate mixing of the fluids in the main stream and in the reverse flow region to promote the flow reattachment.

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In this study, we deal with the tumbling, which is rotating motion with the axis perpendicular to the falling direction. Our purpose is to reveal the fundamental aerodynamic characteristics of the tumbling, experimentally. Regarding a test plate, we consider a prism with a rectangular cross section with a depth-to-width ratio λ of 0.3. The results are as follows. The reduced terminal rotating rate Ω^*, the lift coefficient C_L, the drag coefficient C_D and the lift-to-drag ratio C_L/C_D are independent of the aspect ratio AR, when AR is greater than 10. As the inertia momen ratio I^* increases from zero to 50, Ω^*, C_L and C_D increase. However, Ω^*, C_L and C_D become almost constant, at I^* greater than 50. We propose the empirical formulae to predict them. At low I^*, the tumbling shows a dominant periodicity of 360deg.

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The secondary flow of the Prandtl's second kind near a right-angled streamwise corner induced by the wall blocking effect is investigated by means of the laboratory experiments using a wind tunnel. A turbulence-generating grid is installed at the entrance to the test section to generate nearly isotropic, grid turbulence. The corner plate having a sharp edge is installed at the downstream of the grid. The turbulent Reynolds number based on the integral length scale in the grid turbulence, Re_L, is 1,400 at the leading edge of the plate. The three components of instantaneous velocities are measured using a hot wire anemometry. The results show that the secondary flow occurs near the corner when the corner is placed in the grid turbulence, whereas no secondary flow is observed in the absence of the grid turbulence. The results agree well with the previous analysis based on the rapid distortion theory. The results confirm the generation of the secondary flow of the Prandtl's second kind along the corner by the wall blocking effect.

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A diffusion field with a one-step reaction (R+B→S) in a liquid grid-turbulence has been experimentally investigated. The instantaneous concentrations of two species R and S are measured simultaneously by the light absorption spectrometric method, while the concentration of species B is determined by the conservation law. The statistics of reactive scalar fields are compared with the nonreactive scalar ones. It is ascertained that the mean concentrations of reactants R and B decrease while that of product S increases in the downstream direction because of the chemical reaction. With regard to the scalar fluctuations, it is also observed that the r.m.s. values for species R become smaller than those in the nonreactive case under the present experimental conditions, whereas the r.m.s. values for species B become larger. Furthermore, the correlation coefficient between species R and B is negative and varies from -0.9 to -0.95 in the present measurement region. The present data give very important information for the modeling of the concentration correlation and chemical source term in a turbulent reactive flow.

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A diffusion field with a competitive-consecutive reaction (A+B→R, R+B→S) in a liquid grid-turbulence has been experimentally investigated. The instantaneous concentrations of two reactive species (R and S) and a nonreactive dye (C) are measured simultaneously by the light absorption spectrometric method. The concentration of species A and B are determined by the conservation law. The statistics of reactive scalar fields are compared with the nonreactive scalar ones. It is found that the mean concentrations of reactants A and B decrease while those of product R and S increase in the downstream direction by a chemical reaction. With regard to the scalar fluctuations, it is also observed that the r.m.s. values for species A become larger than those in the nonreactive case under the present experimental conditions, whereas the r.m.s. values for species B become smaller. Furthermore, the correlation coefficients between species A and B are negative and those between B and R are positive in the present measurement region. The present data give very important information for the modeling of the concentration correlation and chemical source term in a turbulent reactive flow.

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A descending rate of falling particles through a quiescent or a turbulent airflow, in which the turbulent level is kept constant by rotating grids as a turbulent generator, has been investigated considering particle volume fraction and Stokes number as experimental conditions. In the experiment, turbulent flow properties and downward flow induced by particles are measured by means of LDV. Particles velocity is measured by means of 2 D-PTV with laser sheet and CMOS camera. As a consequence, in the quiescent flow a descending rate is reduced for the particles with diameter 0.5mm and volume fraction of 10^<-4>, and further reduction is expected by increasing volume fraction. While, the effect of volume fraction range is expected to be different depending on the diameter. On the other hand, in the turbulent flow (St〜10^3), the descending rate is increased but its mechanism is not explained by existing studies. In the case of solid-air two phase flow, the motion of particles are governed by drag and gravity so that a discrepancy of descending rate between present experiment and prediction by existing equation indicates a change of drag under present experimental conditions.

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Numerous pipes branch off from main pipe in power plant facilities. Main flow initiates a cavity flow in the downward branch pipe with a closed end and thermally stratified layer may form in the branch pipe if there is significant temperature difference in main and branch fluid. Fluctuation of thermally stratified layer may initiate thermal fatigue crack in the branch pipe. Flow visualization experiment was conducted to understand detailed behavior of the layer, for vertical branch pipe with a closed end. The penetration length of main flow in the branch pipe was measured for various main flow velocities. The velocity distributions in the penetrating flow region were obtained by a LDV method. The temperature fluctuation near the thermally stratified layer was measured. Through these experiments it was found that; (1) the driving force of the fluctuations in the branch pipe was not due to thermal phenomena but fluctuation of the spiral flow; (2) the flow regime in the second region was simple structured forced vortex with constant angular velocity, (3) steady thermally stratified layer did not fluctuate periodically in the vertical pipe.

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The purpose of this study is to clarify the mechanism of the large temperature fluctuations in a downward bent pipe with a closed end by experiments and numerical simulations. Flow patterns and vortex structures were visualized by a tracer method in experiments and also visualized by numerical simulations. Liquid temperature was measured by thermocouples and visualized by liquid crystal for the non-uniform temperature conditions to compare with numerical simulations. The vortex structures and the flow patterns obtained by the numerical simulations are similar to those of the experiments. The temperature fluctuation and velocity variation occurs synchronously near thermal stratification layer in the results of numerical simulation. This variation of velocity fluctuates, therefore, the temperature near the thermal stratification layer.

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A modeling of gas-liquid interface is one of key issues of the numerical research on multiphase flows. Especially, a mechanism of bubble coalescence/repulsion is unresolved and there are no valid numerical models. The phenomenon may be related to thermodynamics, electromagnetics, hydrodynamics, and heat and mass transfer. In the experimental studies, it is revealed that a concentration of electrolyte solved in water and ion-pair specificity affect the bubble coalescence. Therefore, it is necessary to take such effects on bubble coalescence into consideration in a gas-liquid interfacial model. In the previous our study, having assumed that the interface has a finite thickness, we have developed a new gas-liquid interfacial model based on thermodynamic and mathematical approach. In that study, we have derived a new governing equation with free energy including the effect of the electric double layer caused by a contamination at the interface. In this paper, we applied the new interfacial model to 2-dimensional numerical simulation. Finally, we evaluated the new governing equation qualitatively by simulating a behavior of a single square microbubble and an interaction between two microbubbles including the electrical force.

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We developed a method for a wind tunnel experiment to predict a visible plume region from a mechanical-draft cooling tower. The diffusions of water vapor and temperature emitted from the cooling tower in the wind tunnel experiment are tracked using tracer gas. It is assumed that the plume-induced fog is generated whenever the instantaneous specific humidity predicted from the concentration of the tracer gas at measuring points is larger than the inferred saturation specific humidity. To estimate the accuracy of the present method, the measurements are compared with the observations. The results show that the visible plume length and height are in good agreement with the observations. Furthermore, it is found that the visible length and height is strongly affected by wind direction to the cooling tower, temperature difference between atmosphere and exit of the cooling tower and atmospheric humidity, and hence the present wind tunnel method considered these conditions is valid to predict the visible plume.

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The existence of tower in horizontal axis wind turbine system has sometimes a large effect on its surrounding fluid flow. In case of upwind turbines, the unsteady aerodynamic loads occur when the blades of a wind turbine are passing in front of the tower. The fluctuation of load causes a variation of power output and affects a fatigue life of the wind turbine, directly concerning the cost problems. The present paper describes a numerical method for calculation of the tower effects on aerodynamic loads, and shows the calculation results. For the calculation of aerodynamic loads on the rotor blades, an inviscid aerodynamic model based on the asymptotic acceleration potential method is adopted, which is capable of calculating the unsteady aerodynamic loads. In the model, the rotor blades are represented by spanwise and chordwise pressure distributions. The tower is represented by pressure distribution, in order to adapt the numerical model to that for calculation of aerodynamic loads on the blades. The calculation results show that the tower effects on aerodynamic loads depend on the distance between rotor plane and tower axis, and the tower radius, along with the operating wind condition.

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In this paper, we describe the stability of a centrifugal blood pump with hydraulic levitating bearings in pulsatile flow, since the ventricular assist device (VAD) set downstream of heart is affected by the pulsation. The test pump was developed for VAD using conical spiral groove bearings. The flow through the pump was excited from 0.25 to 3.0Hz by oscillator driver in the circulatory system. The rotational speed, flow rate, total pressure rise and displacement of rotor from casing center were measured to study stability of test pump. The stability test was done for the whirling motion of impeller and the conditions for stability of the blood pump were determined by the dynamic characteristics test. The results showed increasing whirling motion with increasing fluctuating frequency.

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This paper presents an influence of air flow unbalance on performance of an evaporator and an effect of refrigerant flow path pattern. To estimate the influence, we applied thermal network method that can take refrigerant quality distribution in the heat exchanger into account. The prediction shows that performance of the evaporator falls by 6% with 40% of unbalance of air flow rate for a simple 2 rows and 2 paths heat exchanger. Also, the prediction shows that the performance will be recovered to the level when air flow distribution is uniform by optimizing refrigerant flow path pattern.

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Three-dimensional flow and thermal fields have been solved numerically for the stepped duct laminar flow for different inlet flow conditions, uniform flow and fully developed flow. Attention has been paid to the particle trajectories over the step and their relation to the spatial distributions of the heat transfer coefficient on the bottom wall behind the step. Fluid particles entering the flow recirculation behind the step was found to be started from the small limited area in the vicinity of the side wall for both inlet flow conditions. Such particles, in the uniform flow case, move toward the center of the duct forming spiral motions and they flow downstream one by one before they reach to the center of the duct. However, in developed inlet flow case, such particles proceed together until they reach the center of the duct showing large unique spiral motion and then they flow downstream from the center of the duct. Owing to this, low heat transfer coefficient is obtained at the center of the duct and low heat transfer area becomes larger compared to that in the uniform inlet flow case.

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Development of fast and accurate algorithm of radiative heat transfer simulation is important in terms of efficient thermal design and simulation on diverse engineering area. This paper describes the performance of Hemisphere algorithm which has originally developed as a fast form factor calculation in the field of photorealistic three-dimensional computer graphics. We compared performance of the Hemisphere algorithm with two conventional methods which are frequently used in the field of radiative heat transfer simulation. As a result, the Hemisphere algorithm is significant faster than the conventional methods if one can accept an absolute error of 1.0×10^<-5>. In addition, the result indicates that the Hemisphere algorithm possibly suit for try and error process of large-scale model simulation due to its tolerable form factor distribution.

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By the development of micro-fabrication technology, further smaller-size electronic devices will be available. In such a smaller device, non-equilibrium state might be appeared for careers in metal and/or semiconductor that constitute the device. In such a situation the device performance estimation by the macroscopic transport equations that assume quasi-equilibrium distribution is difficult. Against the background of this difficulty, we are developing a numerical simulation based on Boltzmann transport equation (BTE), which can analyze thermal and electric phenomena even when the state is far from equilibrium. In this paper, we numerically analyzed heat flux and thermoelectric voltage for simple one-dimensional system by solving BTE with discretization of all wave-number spaces. The calculation result of heat flux agreed with the value estimated from Fourier's law.

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In this paper, we perform molecular dynamics (MD) simulations of the interfaces composed of the self-assembled monolayer (SAM) and organic solvent in order to investigate the interfacial heat transfer characteristics of SAMs from the microscopic viewpoint. Archetypal SAMs, i.e., alkanethiol molecules chemically adsorbed on Au (111) substrate, and toluene solvent are adopted for the computational system. Two alkanethiols with different chain lengths, that is, 1-propanethiol (C_3H_7SH) and 1-dodecanethiol (C_<12>H_<25>SH), are used for SAM interface systems. In addition to the SAM interfaces, bare solid substrate without SAM are examined for comparison of the heat transfer characteristics. Nonequilibrium MD (NEMD) simulations in which a temperature gradient is imposed across the interface are performed and the interfacial thermal resistance in each system is discussed. As a result, it is shown that the SAM-solvent interfaces have the smaller thermal resistance as compared with that at the bare Au interface. In order to investigate the mechanisms of the small resistance at SAM-solvent interface, a vibrational character of molecules in the interface region and an adsorbed structure of solvent molecules are discussed.

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The cooled wake in mercury, air, or water at the Reynolds number 44 is analyzed numerically. Effects of fluid kinds on the time-dependence and the cylinder surface values in the cooled wake and the cooled vortex street are elucidated as follows: (1) The streamfunction oscillates with the constant amplitude in both the Karman vortex street in any fluid and the cooled vortex street in mercury and air, but oscillates with the amplitude pluraling in both the transitional process to the cooled vortex street in any fluid and the cooled vortex street in water. (2) The oscillation type in the cooled vortex street depends on the Prandtl number Pr. The oscillation has the constant amplitude at the low and moderate Pr as mercury and air, but, has the amplitude pluraling at the high Pr as water. (3) The distribution and the time-dependence of the local and mean coefficients of wall shear stress c_f, C_f and the local and mean Nusselt numbers Nu, Nu_m are elucidated in the cooled wake in mercury, air and water. (4) In the cooled wake in any fluid, the negative buoyancy makes the Strouhal number St, mean coefficient of wall shear stress C_f, mean Nusselt number Nu_m, and vortex speed U_v small, and the amplitude of wake oscillation large. The cooled vortex street in any fluid oscillates with the frequency less than the Karman vortex street. (5) The St number in any kind of fluid and the C_f and Nu_m numbers in air are decreased suddenly in the transitional process. The decrease behavior of St is different among fluid kinds. (6) The sudden change is an unstable-like phenomenon, and the transitional region with the sudden change is the unstable-like state. The streamfunction oscillation has the amplitude pluraling in the unstable-like state, and has the constant amplitude in the stable-like state.

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We have analyzed current ratios under the rib and channel of a cathode separator having 2mm width rib and channel in a polymer electrolyte fuel cell (PEFC). Three types of membrane electrode assembly (MEA) including the one with a partial electrode (catalyst layer) only under the rib and that only under the channel in addition to the conventional MEA with the electrode on the whole area are prepared for the analysis. As a result, the ratios under the rib are found to be 60% and 40% in low and high current density regions, respectively. These results are in good agreement with that from the method of removing the gas diffusion layer (GDL) under the channel in our previous paper where IR resistance and mass transfer resistance have been assumed to be inversely proportional to the area of GDL with the assumption of constant charge transfer resistance. Both methods provide concrete guidelines for the improvement of PEFC performance. Although the partial electrode method addressed in the present paper is direct and strict way, it is complicated since the three types of MEA are necessary. The GDL removing method is, however, simple and practical.

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In a polymer electrolyte fuel cell (PEFC), we have analyzed the effects of hot press of a gas diffusion layer (GDL) and a membrane electrode assembly (MEA) on each electric generation ratio under 2mm width rib and flow channel in the cases of paper and cloth type GDLs. MEAs having partial electrode (catalyst layer) only under the rib and that only under the channel are prepared and assembled with GDLs by hot press. In the case of paper type GDL, the hot press is found to improve the cell performance by decreasing the contact resistance under the channel in spite of decrease in current under the rib due to decrease in oxygen transport in supplied air. On the other hand, in the case of cloth type GDL, the hot press does not decrease large contact resistance under the channel. This is likely to be due to the unsticking of the GDL from the MEA under the channel by the pressure of the product water transported from electrode under the rib. Such unsticking possibly comes from the low stiffness of the cloth type GDL.

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In the present study, a sooting flame was formed in a reduced-pressure combustion chamber with a premixed flame of methane and oxygen for the surrounding flame and premixed flame of toluene and oxygen for the center flame. We inserted the sampling probe and collected the soot like substances from the toluene-oxygen flame to analyze contents of fullerenes and PAHs at the early stage of the fullerene or PAH formation reactions. The experimental results showed the contents of Acenaphthene, Phenanthrene, Fluoranthene and Phyrene were relatively high in the soot like substances collected through the sampling probe. We considered that at the early stage of the formation mechanism of fullerenes or soot the chemical species of these Acenaphthene, Phenanthrene, Fluoranthene and Phyrene were dominant in the present experiments. The contents of C_<60> in the total fullerenes at the early stage of the combustion reaction were larger than those collected at the main filter and the contents of C_<70> at the early stage of the combustion reaction were smaller than those collected at the main filter.

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Nano meter size particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) have harmful effects for human health. Investigations of the fundamental characteristic of PAHs behavior in combustion process were required for the establishment of the reduction technologies for nano-PM emission. In this paper, PAHs characteristics in diffusion flames of propane gas were investigated using laser diagnostic and gas sampling methods. A laser induced fluorescence (LIF) method was used to obtain the spatial distributions of PAHs. Spatial distributions of soot were also measured by a laser induced incandescence (LII) method. A transition region from PAHs to soot was defined from the results of LIF and LII. Further, PAH concentrations in the test flames were measured using a gas chromatography (GC), and the profiles of PAHs concentrations in the test flames were investigated. As the results, heavier molecules PAHs such as fluorene and pyrene were confirmed as precursors of soot.

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