The particulate jet generated by small solid particles falling from a round orifice into an unbounded quiescent air is simulated. The three-dimensional vertex method for gas-particle two-phase free turbulent flow proposed in a prior study is employed for the simulation. It is clarified that the falling particles induce complicated three-dimensional unsteady air jet involving large-scale eddies. The air takes its maximum velocity at the jet centerline, and the velocity profile satisfies the self-similarity around the centerline. The effect of the particle diameter on the velocity distribution for the two phases is investigated. The entrained air flow rate is favorably compared with the value predicted by the analytical models. This indicates the applicability of the present method for the particulate jet.

抄録全体を表示

The present study develops a new surface capturing method using the WENO scheme for numerical simulations of free surface flows. The present numerical method couples the incompressible Navier-Stokes equations with the VOF method. This surface capturing method eliminates need for special free surface tracking method, and can be easily extended to three-dimensional simulations of free surface flows. The present surface capturing method is applied to a solitary wave propagation problem. The moving free surface is accurately tracked. Present numerical results are. in good agreement with the previous theoretical, numerical and experimental results. The free surface is captured on several grid points although numerical diffusions occur around the discontinuity regions.

抄録全体を表示

An experimental study of the structure of the roll and trailing vortices formed around the blades of four flat paddle impeller in a stirred vessel has been carried out Angle resolved measurements of all three velocity components were performed by synchronizing laser Doppler velocimetry with a rotary encoder coupled to the impeller shaft. Almost all data were obtained in the θ=0°plane. located half-way between two baffles. This experimental method make it possible to capture the details of the vortical structure behind the impeller blade. The formation of roll and trailing vortex is more evident in the resultant axial and circumferential mean velocity vectors and contours of mean vorticity. The size, shape and location of trailing vortex are shown and compared with the results of Rushton turbines.

抄録全体を表示

This paper describes fundamental investigation to apply penetration of micro jet to disintegrate microcapsules in Drug Delivery System (DDS). Deformation processes of a bubble near curved elastic wall by shock wave were observed by optical shadowgraph method using a high-speed camera. It is found that a bubble generates micro jet toward a wall and opposite side whose characteristics are affected by gas of bubble, position of an initial bubble, wall elasticity, and wall curvature. Therefore, changing them about microcapsule can control penetration force by micro jet.

抄録全体を表示

The description of blood flow in vivo is complicated due to the viscoelasticity of vessel walls.
However, conventional researches of the effect of the blood vessel viscoelasticity on the blood pressure wave propagation using non-linear one-dimensional models do not take into account the viscoelasticity, despite it being importance in the analysis of pulse wave propagation in arteries.
Already, we propose a new generalized arterial viscoelastic model that is suitable for numerical simulations of blood flow in systemic arteries. Simulated results were in good agreement with measurements of pressure waves in a silicone rubber tube. The analytical results indicate that the change in the viscoelasticity influences the damping of the wave amplitude and the wave propagation velocity characteristically. Our results demonstrate that for models to be suitable for quantitative numerical analysis of systemic arteries, they should take into account both of the normalized dynamic modules and the loss tangent of viscoelasticity as a function of the frequency.

抄録全体を表示

We have evaluated numerically a second order tensor type constitutive equation which includes both a molecular shape factor and a quadratic closure approximation, by means of comparing the results with the solutions obtained from the original Doi equation without closure approximations. The second order tensor type constitutive equation can simulate three types of director behaviors such as tumbling, wagging and aligning, by setting the molecular shape factor to be smaller than its inherent value based on the molecular aspect ratio. The shear stress and the first normal stress difference determined from the tensor type constitutive equation qualitatively agree with stresses obtained from the Doi equation, for low shear rate. When shear rate is high, however, even qualitative agreement is not obtained. Therefore, the constitutive equation is applicable to slow flows or situations where a velocity field is so simple that only an orientation field is a consideration.

抄録全体を表示

The flow inside the two-dimensional semi-open-type nozzle for a ship propulsion equipment directly driven by high-pressure gas is investigated experimentally. The flow is unsteady and the gas and the water phases separated clearly. We found that these waves appear on the interface for continuous gas ejection. It is clarified that these waves play a important role to pressure distribution. Intermittent gas ejection is also tried. The thrust itself decreases compared with continuous gas ejection, but propulsive efficiency considering gas ejection duration is increased. The flow patterns for intermittent gas ejection are also clarified.

抄録全体を表示

In the present paper, parametric numerical analyses of the separated transonic flows in overex-panded rocket nozzles are conducted. Several types of nozzles are examined numerically to clarify the detailed mechanisms of the occurrence of restricted shock separation (RSS) in the compressed truncated perfect (CTP) nozzle. The parameter of the nozzle contour examined is its length and compression factor. In the CTP nozzle with large length and small compression factor, a positive pressure gradient is formed downstream of the Mach disk before the occurrence of RSS. Under the positive pressure gradient, the flow which passed through the Mach disk rolls up and forms a large vortex ring around the central axis of the nozzle. The vortex ring pushes the separated jet to the nozzle wall and results in RSS.

抄録全体を表示

Effects of gas injection from a nozzle wall on screech reduction of a supersonic under expanded jet are investigated experimentally. From a converging round nozzle, air is injected into the atmosphere (Main jet) at a pressure ratio of 2.25 (M =1.14). The exit diameter of the main jet nozzle is 8.0 mm. From small nozzles mounted in the main jet nozzle wall, air is injected in the normal direction to the main jet (Secondary jet). The exit diameter of the secondary nozzles is 1.0 mm. The number of the secondary nozzles is selected to be 2 or 4, and the mass flow rate of each secondary jet is set at 2.0% or 4.0% of the main jet. With the secondary jets, the screech SPL is reduced by 23 dB at the maximum, and the frequency profile of the broadband noise is also influenced. And with the secondary jets, the total pressure of the main jet is slightly decreased with the increase in the total mass flow rate of the secondary jets. Consequently, it is shown that the gas injection method is effective in screech reduction with a small loss in the total pressure.

抄録全体を表示

A micro-air plasma-jet, whose size was 3.0 mm in length and about 0.7 mm in diameter, was measured spectroscopically in the wavelength region of 200 to 900 nm using a spectrometer. The N₂ 2+ and N⁺₂ 1-bands were predominant in the region of 280 to 500 nm and intense atomic lines of N and 0 in the infrared region. Temperatures of the plasma-jet were determined by applying a spectral matching method to those band spectra. There was a very good agreement between the theoretical and experimental spectra in the main part of the measured wavelength region. It was found that the rotational temperature was 7, 000 to 9, 000 K depending on the band, vibrational temperature about 28, 000 K for both the bands, and the jet was remarkably in thermal non-equilibrium state.

抄録全体を表示

The flow-induced in-line oscillation of a centilevered circular cylinder was experimentally studied by free oscillation tests in a water tunnel. Two hot-film probes were set in the wake of a test cylinder to measure the fluctuating velocity in the near-wake. These probes were moved along the span direction at some reduced velocities Vγ. Two types of test cylinders, AR 10 with the aspect ratio of 10 and AR 21 with the aspect ratio of 21, were investigated. AR 21 with an end plate had two excitation regions against Vγ but AR 10 had one excitation region. The vortex structure of the AR 21 cylinder with the end plate was the symmetrical vortex at the first excitation region and was the alternate vortex from the end of the first excitation region to the second excitation region. So, the valley between these excitation regions is caused by the characteristics of the alternate vortex. Because the vortex structure of the AR 10 cylinder was mainly symmetrical vortex at any reduced velocity, the excitatio region of AR 10 is caused by the instability related to the symmetrical vortex. The vibration characteristic that was caused by aspect ratio was explained by the flow around the tip of cylinder, because AR 10 with end plate had two excitation regions. The aspect ratio of the cylinder influeces the vortex structures and the characteristics of vibration.

抄録全体を表示

Efficiency of a centrifugal pump is known to drop rapidly with a decrease of specific speed n_s in the range of n_s?100. However, below n_s=60 [m, m³/min, min^-1], the pump efficiency is not yet clear, and the spiral angle of volute casing becomes too small to manufacture. To solve this problem, a circular casing is considered appropriate in the very low n_s range. The present study is aimed to reveal the relation between pump efficiecy and a specific speed in the range of n_s?60, when a circular casing is used. The results show that a circular casing gives higher efficiency than a spiral casing, and that radial thrust is considerably small in both casings compared with that of ordinary specific speed pump.

抄録全体を表示

The unsteady cavitation such as rotating cavitation and cavitation surge often occur in the turbopump inducers for rocket engine. In the present study, a method for suppressing the unsteady cavitation in an inducer by jet injection is proposed. Through eight nozzles placed at the upstream of the inducer, jet was injected in circumferential direction. The axial position of nozzles, speed of jet flow and direction of jet injection were changed. Through the experiments with jet injection for various conditions, it was found that the occurrence regions of unsteady cavitation are decreased significantly by jet injection in the same direction as shaft rotation with the jet flow rate about 10% of total flow. The flow field was also examined to clarify the mechanism for suppressing the unsteady cavitation by jet injection. It was found that the incidence angle and cavity length was reduced by jet injection which decreases occurrence regions of unsteady cavitation.

抄録全体を表示

One of the important goals in the design of a turbocharger is to reduce the resonance stress of the turbine blades. The resonance stress of a blade is influenced considerbly by fluctuations of the total pressure in the turbine casing. In this study, we have tried to explain the relationship between the total pressure fluctuation and the resonance stress during blade vibration. To evaluate this relation we measured the total and static pressures at various circumferential locations in a mixed-flow type turbine casing and used Fourier analysis to calculate the excitation force component caused by the total pressure fluctuations. Then resonance stress measurements were performed for the turbine blade in the same casing used for the pressure measurements. Experimental data show that resonance stress increases as total pressure fluctuation increases. Theoretical and experimental results show reasonable agreement.

抄録全体を表示

Assessment of profitability from installed wind turbines is normally a key factor in addition to an accurate measurement of frequency distribution of wind speed in a certain period of time and prediction of power generation under the measured conditions. The frequency distribution of wind speed is evaluated, in general, using the Weibull distribution. In order to predict the frequency distribution from the average wind speed, a formula based on the Rayleigh distribution is often used in which the shape parameter equal to 2 is assumed. The shape parameter is also used by the Weibull distribution, however, its effect on calculation of wind conditions and wind power is not sufficiently clarified. This study reports on evaluation of wind conditions and wind power generated as affected by the change of the shape parameter in the Weibull distribution regarding two wind turbine generator systems, which have the same nominal rated power but different control methods. It further discusses the effect of the shape parameter of prototype wind turbines at a site with the measured wind conditions data.

抄録全体を表示

In recent years the requirement for reduction of energy consumption have been increasing to solve the problems of the global warming and the shortage of petroleum resources. For example in the power generation field, as the thermal power generation occupied 60% of the power generation demand, the improvement of the thermal efficiency is required considerably. This paper described that the heat transfer characteristics of the finned tube banks used for the heat exchanger in the thermal power generation were clarified by testing the serrated finned tubes banks with different fin height for improvement of higher heat transfer and the conventional spiral finned tube banks with different fin height, and that the equation to predict heat transfer coefficient which is neccessary on design of the heat exchanger was proposed.

抄録全体を表示

In recent years the requirement for reduction of energy consumption have been increasing to solve the problems of the global warming and the shortage of petroleum resources. For example in the power generation field, as the thermal power generation occupied 60% of the power generation demand, the improvement of the thermal efficiency is required considerably. This paper described that the pressure drop characteristics of the finned tube banks used for the heat exchanger in the thermal power generation were clarified by testing the serrated finned tubes banks with different fin height for improvement of higher heat transfer and the conventional spiral finned tube banks with different fin height, and that the equation to predict pressure drop which is necessary on design of the heat exchanger was proposed.

抄録全体を表示

It is necessary to develop an effective technology used of the waste energy exhausted at the same time as generation of electric power for popularizing the distributed power supply system, for example, Micro Gas Turbine System, or Fuel Cell System. The thermal storage function is more indispensable for a highly effective operating of distributed system because the demand fluctuation of heat is very large than electricity. In this study, two kinds of the plate fin heat exchanger enclosed the phase change material (PCM) were used as the compact thermal storage unit. Two kinds of PCM (Phase Change Material) were used, which are Sodium acetate trihydrate with a melting point of about 58 C and Paraffin wax with a melting point of about 74.8 C. Here, we made comparison with experimental value and calculated value by the developed numerical simulation for dynamic characteristics in heat charging and discharging of small thermal storage unit. As a result, it was shown that an analytical method in which the latent heat of PCM was considered with total specific heat was effecitve as the numerical analysis model.

抄録全体を表示

New cooling system with a natural-circulation loop has been developed to reduce energy consumption of a cooling system for the telecommunication base site. The cooling system consists of two refrigeration units ; vapor compression refrigeration unit and pre-cooling unit with a natural-circulation loop. A simulation which calculates pressure drop, heat transfer and refrigerant charge has been developed and the experiments were carried out to evaluate the cycle performance of the pre-cooling unit using HFC refrigerants. The measured cooling capacity and operating pressure agreed with the simulation results within ± 10% in the various experimental conditions. In addition, the experimental results indicated that the cooling capacity of R 410 A is approximately 30% larger than that of R 407 C at the temperature difference of 20 K. Also the cooling capacity took a maximum value at the range of refrigerant charge of 2.0-3.0 kg. Furthermore, the cooling capacity slightly increased as the height difference between the evaporator and the condenser increased. These experimental results were in good agreement with the simulation results.

抄録全体を表示

Heat pumps using CO₂ as a natural refrigerant have been developed and are expected to contribute to energy saving in hot water supply. In residential applications, CO₂ heat pumps are used in combination with hot water storage tanks. The objective of this series of papers is to analyze the overall performance of a hot water supply system composed of a CO₂ heat pump and a hot water storage tank by numerical simulation. In the 1st report, a simulation model of a CO₂ heat pump is created based on thermodynamic equations and measured data on an exsting CO₂ heat pump. In addition, the performance of a CO₂ heat pump is clarified in relation to the air temperature as well as the inlet and outlet water temperatures.

抄録全体を表示

Bubble nucleation phenomenon in presence of gas impurities is studied by microcanonical molecular dynamics simulation for Lennard-Jones fluid. First, we investigate effect of molecular diameter of dissolved gas on the nucleation rate with pressure change. As a result, we find increase of the nucleation rate with increase of the pressure, which we call “inverse” pressure phenomenon, when interaction of dissolved gas is very weak. In this case, we confirm that a gas with the larger diameter enhances composition fluctuation or phase separation. Next, we estimate effect of the diameter on spinodal point through calculation of equation of state (EOS), and confirm that effect of the diameter on spinodal point at low temperature range becomes larger as the interaction of dissolved gas becomes weaker. Finally, we examine applicability of the superheat ratio expressed by saturation pressure and spinodal pressure, and confirm its validity to explain the inverse change of the nucleation rate.

抄録全体を表示

The distribution of temperature of cells in stacks, the thermal stress in cells and the stack performance of planar solid oxide fuel cells (SOFC) were analyzed numerically. The effects of different gas-flow types, i. e., parallel- or series- and counter- or co- were discussed. The paralled gas-flow type means both of fuel gas and air are supplied equally into all cells in the stack. On the other hand, the series gas-flow type is what the gases are cascaded in the stack. As the results of this analysis, the distribution of temperature of cells in the case of the series- and counter-flow type was most homogeneous among those of the four flow types, resulting in the decrease of the thermal stress in the cells except for the vicinity of gas inlet. Furthermore, the average cell-voltage in the case of the series- and counter-flow type was highest among those of the four flow types, and hardly decreased with increasing the number of cells.

抄録全体を表示

Chemical reaction of cobalt clusters with ethanol (¹CH₃ ²CH₂ OH) has been investigated by using FT-ICR mass spectrometer. Dominant reaction is ethanol chemisorptions but about some size clusters (Co_n⁺ : 12≤n≤19) complex reactions (involving dehydrogenated chemisorptions) have been observed. By doing isotope experiment (ethanol, ethanol-d, ethanol-d3, ethanol-d6), dissociated two H atoms are specified. This reaction mechanism consists of two steps. At the first step, H atoms are dissociated from methyl (¹CH₃) and hydroxyl (OH). At the second step, two H atoms are dissociated from methylene (¹CH₂, ²CH₂). On these size clusters hydrogen-deuterium exchange has been observed. This H/D exchange takes place on hydroxyl in case of simple chemisorptions of ethanol, and on methyl in case of dehydrogenated chemisorptions.

抄録全体を表示

Chemical reaction of transition metal cluster ions (Fe, Co, Ni) with ethanol was investigated by using the FT-ICR mass spectrometer. Metal clusters with 10-20 atoms were generated by a pulsed laser-vaporization supersonic-expansion cluster beam source directly connected to FT-ICR mass spectrometer. Observed reactions are simple chemisorptions of ethanol and dehydrogenated chemisorptions strongly depending on metal species and cluster size. The reaction of iron clusters show simple chemisorptions and the reaction of nickel clusters show dehydrogenated chemisorptions. However cobalt clusters show both reaction patterns. Thus the reaction patterns change according as periodic table. And the cluster sizes which show the maximum reaction rate also shified according as periodic table.

抄録全体を表示

Experimental observations and numerical simulations were conducted on combustion processes of n-decane polydisperse spray entering gaseous flat-flame stabilized in laminar 2D counterflow configuration. The experimental burner restrained the flow from fluctuating to investigate the effects of spray characteristics. Concerning the calculations, for the gaseous phase, we used Eulerian mass, momentum, energy, and species conservation equations. For the disperse phase, all the individual droplets were tracked without using a droplet parcel model. Firstly, we observed blue and luminous flames experimentally and the intensity of these flames changed unsteadily. Secondly, we examined the spray flame structure numerically should the supplied quantity of liquid fuel changed. Both timeaveraged and instantaneous spray flame structures varied depending on the quantities of spray. Furthermore, the instantaneous structures were consistent with the typical flame structures observed by the experiment. Consequently, these results show that the difference of the supplied liquid fuel spray can cause the variation of spray flame structures.

抄録全体を表示

Ethanol jet phenomena were observed with local contact microwave heating. The ethanol jet heights (velocities) and the shapes were measured by the high speed video camera (Redlake Motionmeter, 1000 fps. black & white CCD. 292pix×110pix, 0.2mm special resolution) and the effects of the exit diameter on the velocity were considered. The microwave output power was from 20W to 60 W. The microwave generator was MATSUSHITA TO-465 A with N-type connector. The coaxial cable was FUJIKURA 3.5 D QEFV (5.6 mm of outer diameter). The exit diameter was from 1 mm to 6 mm. The test section was covered by alumimum plates of 2 mm thickness and the microwave shader (Nisshinbo Engineering MP 135 R-20). The fuel chamber was brass. The jet shapes had many variations as fir tree type, umbrella type, mushroom type, and so on. As the results, the jet velocity was increased with the microwave output power and showed a maximum at an exit diameter in this research.

抄録全体を表示

Formation of ethanol jet phenomena was observed with local contact microwave heating. The inverter-controlled magnetron makes the microwave. The jet heights and the jet shapes were measured with a high-speed video camera. A coaxial cable was used for the microwave transportation and for the heating. The microwave intensity (output power) was ranged from 20 W to 60 W. The exit diameter was from 1mm to 6mm. On the photographic observation, the jet shapes formed were classified into seven types. The pen type was observed with smaller exit diameter, and the arrowhead type was with larger microwave intensity. The spoon type, the fir tree type, the mushroom type and the umbrella type were observed with larger exit diameter. The jet ratio was increased with the increase in the exit diameter and in the microwave intensity. In this research, the smallest droplets were formed in the explosion type. The explosion type ratio had the maximum at a certain exit diameter.

抄録全体を表示

Until now, perfluorinated proton exchange membrane (PEM) has been widely used as the electrolyte for PEMFC. As long as the perfluorinated PEM is used for the electrolyte, both the cell performance and durability of PEMFC strongly depends on the water content in its electrolyte, since the high conductivity of electrolyte is presented only at the sufficient hydrated state. Therefore, the water management of cell is a most important issue to achieve both the high performance and durability of PEMFC. However, it is not easy to manage the vapor transfer through porous electrodes and the phase-exchange from liquid water to vapor. Although a cell simulation analysis is thought to be effective for such a water management, there have been a little reports which studied on the vapor transfer in the cell-stacking direction in the membrane electrode assembly (MEA). In this study, in order to manage the vapor transfer in electrodes according to the design, a cell simulator was developed. The cell simulator can analyze both the liquid water and vapor transfer in the cell-stacking direction and the phase-exchange from liquid water to vapor under the correlation with electrode reactions, heat transfer and ges flow. On the other hand, the water permeation rate through PEM was experimentally evaluated in order that it may be installed into the simulator. By using the cell simulator, the evaluations were conducted on the cell with the water management layer between catalyst layer and gas diffusion layer.

抄録全体を表示

Swirl injector spray at high fuel temperature has features of rapid atomization and evaporation, compared to those at normal fuel temperature. These have a possibility to improve fuel consumption and emissions under cold start condition. The purpose of this study was to reveal the feasibility of improving cold start emissions of a DI engine by using high temperature fuel spray, to make a simulation procedure which can reproduce the spray formation process at high gasoline temperature and to incorporate it with a 3-D in-cylinder calculation of the mixture of in-cylinder gas and the spray. Results show that heating fuel was an affect to reduce the mass of wall-film. Thus using high temperature fuel has the possibility to improve fuel consumption and exhaust emissions under cold start condition.

抄録全体を表示

A supercharged natural gas compression ignition engine has been tested to confirm the performance as ell as the exhaust gas characteristics. The supercharging improved the thermal effciency through the improvement of the combustion efficiency, the mechanical efficiecy, and the cooling loss. The indicated thermal efficiency becomes the highest when in-cylinder temperature is about 1700 K, due to the improved combustion efficiency and the decrease of cooling loss. The supercharging also reduces the NO_x emission. This is because the maximum temperature is kept low while the combustion efficiency is kept high compared with the natural aspiration. The pressure at auto-ignition inceased in case the boost pressure is raised. However, the auto-ignition temperature is the same and 1000-1030K.

抄録全体を表示