An experimental study was performed on the choking due to the friction in supersonic Fanno flows in long constant-area ducts. The results show that the choking condition of the flow is much different from the calculated value by the previous one-dimensional theory. For a given inlet Mach number and a friction coefficient of a duct, for example, the maximum possible length of the duct is shorter than that predicted by the theory. The reason has been well explained by replacing a normal shock wave assumed in the theory by a pseudo-shock wave in real flow.

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In order to obtain fundamental knowledge of liquid breakup phenomena, the three dimensional flow field of oscillatory liquid jet in pinch off was numerically studied by the developed method, CIP-LSM. In the present paper, not only the liquid jet shape but also its inner structure was investigated. The numerical results of liquid shapes and velocity distributions were compared with the corresponding experimental ones. From the results, CIP-LSM was confirmed to have potential to simulate liquid breakup phenomena in which surface tension was predominant. It was revealed that inner structures of the liquid jet were constructed due to the surface tension at the nozzle exit. The jet breakup was demonstrated to occur at the fluid element injected with the minimum acceleration.

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Granulation is generally performed in a stirred vessel, by spraying binders onto row materials stirring the particles. However, the conventional granulation system has some problems. First, there are double peaks in the particle diameter distribution that degrade the quality of final products. Second, it takes too long time to determine the operating and producing conditions for a desired particle diameter distribution. Therefore, it is required for us to sophisticatedly control a granulation process in a stirred vessel with aid of computer simulations. In the present study, we carry out numerical experiments of granulation processes in a simplified stirred vessel to clarify the reason why double peaks in the particle diameter distribution appear. Through the study, it is confirmed that the particle diameter distribution approaches to an asymptotic state at the final stage of granulation, and the double peaks are generated by the statistical destruction of large particles.

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In the present study, motions of two small solid particles, which are lifted by the shock-induced flow behind a propagating shock wave, are numerically simulated to investigate the dynamic characteristics from the viewpoint of direct and indirect interactions between the two particles. The particle Reynolds number is 6 000, and the time period considered ranges from the time when the shock passes the particles to the time when the boundary layer thickness grows to the same order as the particle size. Three cases are considered for their initial arrangement on the wall. In the first case, they are placed tandem, aligned with the direction of shock propagation. Results show that they are lifted up, keeping contact each other. In the second case, they are seperated by three times as large as the particle size. As a result, the rear particle is lifted higher because the flow before the rear particle has been changed by the front particle. In the third case, they are placed in the spanwise direction. They are also lifted by the shock-induced flow, increasing the separation distance between them due to repulsive fluid force. In these three cases, the average height of two particles becomes larger than that in the case of one particle alone, which was studied in the previous work.

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Instability of a thin liquid sheet, which is related to industrial applications such as atomization, has been studied experimentally. Flow visualization shows that a plane liquid sheet starts fluttering downstream with a certain streamwise wave length and breaks up into droplets. For a detail investigation of the fluttering disturbance, an initial disturbance was generated by loudspeakers that are connected to spanwise slots opened on the nozzle walls. In order to quantify frequency and growth rate of the disturbance, the gradient of the liquid surface was dynamically measured by a novel laser angle detector. The measurements indicate that the amplitude of the fluttering exponentially increases in the streamwise direction and the growth rate depends on its wave number. The frequency at the maximum growth rate corresponds to the fluttering frequency observed in the unexcited flow. These results led to the conclusion that the fluttering is caused by linear instability of the flow.

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A radial flow between two parallel disk shape plates, which simulates a flow in the disk shape planar-type solid oxide fuel cell (SOFC), was experimentally investigated. A temperature distribution in the planar-type SOFC is strongly affected by the gas flow behavior, and hence we tried to clarify flow pattern at various flowrates by using particle image velocimetry (PIV). It was found that optimum flow condition in the fuel channel was attained in the case of the Reynolds number of about 5. For this operating condition, a flow field near the anode surface shows uniform velocity distribution. On the other hand, in the upper air channel, non-uniform flow distribution was enlarged and large-scale vortex appears with increase of flow rate. In the lower air channel, local high velocity region exists at a high flow rate. For the present disk channel the optimum flow field in the air channel was obtained around the Reynolds number of 30. These results suggest the necessity of improvement of the channel shape and injection method of air.

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This paper describes the prediction of index of thrombus formation in shear blood flow by computational fluid dynamics (CFD) with Lattice Boltzmann Method (LBM), applying to backward facing flow, which is simple model of shear flow in the rotary blood pumps and complicated geometry of medical fluid devices. Assuming that the blood flow is multiphase flow composed of blood plasma and solid protein, the effects of surface tension and adhesion force to the wall are added to LBM computation. It is found that the thrombus formation occurs just after the reattachment point and behind the step. These results correspond to our previous observation results. To predict thrombus formation in every case of blood flow, effects of threshold level of physical parameters such as shear rate, adhesion force (effective distance from the wall) are estimated.

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The swimming behavior of small aquatic insects was analyzed by a digital high speed camera system. The test aquatic insects were some kinds of water beetles. It was found that the average thrust force of water beetles arises from the drag difference between the power stroke and the recovery stroke in beating movement of their hindlegs. A swimming mechanism based on the kinematic analysis of water beetle swimming was designed and produced. A swimming mechanism was composed of polystyrene foam resin body, permanent magnet, and polyethyleneterephthalate film fin. A swimming mechanism was driven by the magnetic torque acting on the permanent magnet in the alternating magnetic field. Locomotion characteristics of a swimming mechanism were studied. It was found that the swimming velocity of the mechanism depends on the frequency of alternating magnetic field. The flow field around a swimming mechanism was visualized by slow shutter speed photograph. Experimental data are useful to design of micro swimming robot.

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An experimental study of the aerodynamic characteristics of 3-dimensional flapping wing in hovering flight is conducted in the wide range of parameters, which are Reynolds number, reduced frequency and wing planforms. Lift and power are measured on scaled flapping wings, which mimic bumblebee and cicada wings, and which are delta wings with different locations of maximum chord.The results show that lift and power (1) are almost unchanged in Re=800-5000, (2) increase as the reduced frequency increases, although the effeciency is constant, and (3) increase as the location of maximum chord moves from wing base to tip, although the effeciency decreases.

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The effects of the screw inclination on the sealing performance of a viscoseal, which is a type of noncontact seal, are described. The experimental sealing performance, determined by the seal coefficient, which is based on the Euler number, the clearance Reynolds number and ratio of the radial clearance to the screw length, is generally inferior to the theoretical results when the viscoseals are horizontal. The sealing pressure in the working fluid is closely related to the resultant force, which is based on not only the pressurized force but also gravity and the centrifugal force. The resultant force is simulated under the assumption that these three types of forces are employed and is compared with the experimental results. The simulated circumferential pressure distribution is found to be eccentric and qualitatively similar to the experimental results. Also, the inferiority of the sealing performance seems to be based on the decrease in the pressurized force which is caused by the eccentricity of the pressure distribution. The corrected sealing performance, which is simulated by taking into account the resultant force based on these forces are in good agreement with the experimental results.

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In the previous research, the authors have been proposed a unique flowmeter, which utilizes a lateral flow force generated on the plate with minute slope in a rectangular flow line. In the previous works, the test flowmeter was investigated experimentally to confirm the torque versus flow characteristics. Although the results showed expected performance in terms of linearity and repeatability, the deviation between the experimental and analytical results occurred on the high flow rate condition. Then the theoretical analysis using the CFD approach was conducted to obtain the detailed information of the flow behavior inside the flowmeter. It was found that one of the reasons for this deviation was caused by the remarkable pressure drop and flow disturbance at the inlet region of the flowmeter. In this paper, in order to improve the performance of the present flowmeter, the revised configuration of the flowmeter is proposed. Basic static characteristics are studied experimentally including the measurement of pressure distribution inside the flowmeter to verify the performance of the revised configuration. In addition, the dynamic characteristics are also investigated and compared with commercial flowmeters.

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Presented in this paper are measured data of aerodynamics of a NACA 0012 airfoil and resulting far-field sound at a Reynolds number of 2×10⁵ to 5×10⁵ and angle of attack of lifting case around maximum lifting to deep stall case Overall level of the generated sound gradually grows with increase of the angle of attack until maximum lift angle, and suddenly increases when the airfoil is stalled. Then, the overall level of the sound decreases when the angle of attack is further increased. In the maximum lifting condition, the measured surface pressure showed short bubble formed on suction surface of the airfoil and most contributions to the far-field sound come from a Strouhal number range of 1 to 20. In the light stall condition, long bubble is formed on suction surface, and the measured sound spectra monotonously decay. In the deep stall condition, the long bubble is disappeared and aerodynamic sound decreases in the frequency range between low frequency and middle frequency except for a weak peak at a Strouhal number of near the 0.6.

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In this paper, we discuss an identification of aerodynamic sound sources in a flow around a two-dimensional NACA0012 airfoil at a Reynolds number of 2×10⁵ to 5×10⁵ under stalled conditions. This study is carried out mainly by experimental method based on the results by the measurement of surface pressure, unsteady flow, resulting far-field sound with high accuracy. Also, the computation was performed by Large-Eddy Simulation (LES) for an incompressible flow. Then, we investigated under the light stall condition (LS) when long bubble formed and under the deep stall condition (DS) when completely stalled. As a result, peaks were observed at a Strouhal number of 0.5 to 0.6 not only in aerodynamic sound spectra but also in surface pressure spectra, the coherence spectra between surface pressure and aerodynamic sound, and the coherence spectra between flow velocity and aerodynamic sound. The flow measurements indicate that the vortices based on Strouhal number of 0.5 to 0.6 formed outside of the separated shear layer. Also, some results showed that strong sound sources existed near the airfoil surface in LS but the sound sources disappeared in DS. This is due to the difference in whether the separated flow passes near the suction surface or not.

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The objective of the present paper is to investigate the periodic flow behavior of the separation and reattachment process over a backward facing step in low Reynolds number range. The flow near a reattachment point on a step side wall was measured by Micro Flow Sensor. The characteristic frequency of the flow fluctuation near the wall was estimated to be about 36 Hz from FFT (fast Fourier transform) and Wavelet analyses, and the vortex structure around the spanwise axis was visualized with a high-speed video camera. Near wall flow shows the periodic vortices with one or two dominant frequencies as Reynolds number increases. The change of the vortex structure influences the periodic flow behavior downstream of the reattachment point.

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Since the propulsion mechanism in fluid using elastic fin like a caudal fin and a pectoral fin of fish is effective, many studies of elastic fin for propulsion in water and development of fish robot using elastic fin were carried out. However, the optimum elasticity of fin is not constant and changed by the movement task and environment, such as swimming speed and oscillating frequency. It is very difficult to exchange fins of the different stiffness while swimming. Thus, we aimed to develop the variable-stiffness fin, and made a fin with variable-effective-length spring. This fin enables its apparent stiffness dynamically. This paper describes the structure of the propulsion mechanism in fluid using fin with variable-effective-length spring and characteristics of thrust and lateral forces, and thrust efficiency. Furthermore, the relationship between the thrust force and the flow-field around the fin is discussed.

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The purpose of this experimental research is to clarify both the aspect-ratio effect and the Reynolds-number effect, especially for the flow of cross-flow impellers with shorter axes. Particle-image-velocimetry (PIV) technique and a hot-wire anemometer are used for measurements of flow velocity. The impeller rotates without any casings. The authors study two kinds of the impellers, that is, one with forward-cambered blades and the other with radial-flat blades. As a result, observing eccentric-vortex revolution by using hot-wire measurements and flow visualisations, the flow can be classified into three modes. According to this classification, the authors show flow-regime maps for both impellers. Using PIV results, the authors define outflow rate Q from the impeller. Outflow-rate coefficient C_Q is independent of the Reynolds number for both impellers. For the radial-flat-blade impeller, C_Q is not affected by aspect ratio L/D₂. But, for the forward-cambered-blade impeller, C_Q increases with L/D₂.

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The flow in a rotating Pelton bucket is simulated by a Moving-Particle Semi-Implicit Method (MPS) under operating conditions of design and off-design points. The computed flow pattern is varied with the operating condition, especially, in the high unit speed operating condition, the spilt flow from the cutout can be simulated. The corresponding output power of a runner is estimated under the assumption that each bucket has the same torque variation with its rotation as the computed bucket. The output power of the runner has a tendency similar to that of the model test.

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The spontaneous movement of condensate drops by applying bulk temperature gradient on the heat transfer surface in Marangoni condensation was investigated, considering the application to the heat transfer devices. In Marangoni condensation process, the removal of condensate on the heat transfer surface is important to keep good heat transfer. It may be useful for the heat transfer device in which the liquid movement occurs without external forces such as gravity, vapor shear force. As a result of experiment using water-ethanol vapor mixture, the movement of droplets from low temperature-side to high temperature-side could be observed on the heat transfer surface arranged horizontally. The relation between the velocity of drop movement and the gradient of surface tension was studied for different concentrations. Furthermore, the effect of inclination of condensing surface was examined.

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The present study performed three-dimensional numerical simulation of vortex structures and the heat transfer behind a hill mounted in a laminar boundary layer. A vortex pair is symmetrically formed in the separation bubble behind the hill, and a hairpin vortex is periodically shed in the wake. The hairpin vortex moves downstream with time, and the gradient of the head of the hairpin vortex increases. Further downstream, the hairpin vortex is deformed to the Ω shape. In the growing process of the hairpin vortex, secondary vortices of the horn shape grow near the wall. The dissipation rate of temperature fluctuation around the hairpin vortex increases because the heated fluid near the wall is removed to the free stream by Q2 ejection. Heat transfer increases due to the legs of hairpin vortex and secondary vortices. These vortices generate high turbulences in the flow field and also contributes to increases of the Reynolds shear stress and turbulent heat flux.

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To improve absorption chiller performance, aqueous solution of LiBr and LiI mixture at 1 : 0.7 ratio was proposed for absorbing medium since it has higher solution limit than conventional LiBr solution. But the component LiI solution has higher equilibrium pressure than LiBr solution. To investigate the absorption performance of the new liquid, experiments were carried out using horizontal pipe column. Experimental range of mass concentration was 62-66% for the mixture and 62-63% for LiBr solution. Absorption rate of LiBr solution at 62 and 63% is almost equal to mixture solution at 63% and 64% respectively. Mixture is inferior to LiBr at the same concentration. But at the maximum concentration, mixture solution has about 20 to 50% higher values than Libr solution. Surface temperature of the falling films was measured by thermal video camera and it was used to determine heat transfer coefficient and mass transfer coefficient. They are larger values for mixture solution. This is due to the smaller viscosity of the mixture solution.

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A hot-water supply system was constructed to utilize wasted heat of an air-conditioning system with HFC134a refrigerant. A desuperheater was equipped ahead of the condenser of an air-conditioning machine to extract thermal energy of compressed high-temperature refrigerant. HFC134a was selected as refrigerant because its pressure was relatively lower at higher temperature. The required refrigerant charge was investigated and performance of the air conditioning system with/ without a desuperheater was compared to assess the effect of installing a desuperheater. It was concluded that the required refrigerant charge increased by installing a desuperheater, and that the ability of cooling heat exchange was similar for both with/without a desuperheater with required refrigerant charges. It was also shown that cooling COP decreased 15% by installing a desuperheater, because the work done by the compressor increased, but the overall energy efficiency including cooling and hot-water supply increased 34%.

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A novel modeling scheme of SOFC anodes based on the stochastic reconstruction technique and the Lattice Boltzmann method (LBM) is proposed and evaluated for the performance assessment and optimization of anode microstructures. Cross-sectional microscopy images are processed to obtain two-dimensional phase maps (i.e., Ni, YSZ and pore), of which two-point correlation functions are used to reconstruct a three-dimensional model microstructure. Then, the diffusivity, electrical conductivity and polarization resistance of the reconstructed anode are obtained through the LBM simulation. The predicted tortuosity factors of Ni phase are slightly larger than the experimental result. However, the predicted anodic polarization resistance is in good agreement with the literature data. Thus, the proposed method predicts the anode performance for a given microstructure, and is considered as a promising tool for designing SOFC anodes.

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In this study, we have numerically investigated flame spread over solid fuel in partially premixed atmospheres, which may occur under poorly ventilated conditions, forming the combustible mixtures of oxygen and fuel vapors. The compressible model is adopted. For simplicity, the pyrolysis region is moved based on the heat transfer to the unburned solid surface. That is, the flame spread is determined by the motion of fuel injection area on the solid surface. To confirm the validity of our numerical model, experimentally measured temperature profiles of thin filter paper sheets are compared. To consider partially premixed atmospheres, methane is added in the ambient air by keeping the fuel concentration under lean flammable limit. For discussing the flame structure, the flame index is obtained to observe premixed and non-premixed flames. Results show that, the good agreement is obtained between simulated and measured temperature profiles. In partially premixed atmospheres, the flame spread rate is increased, with the expanded high temperature region. This is because the premixed region exists along the original diffusion flame, resulting in the increase of flame temperature to support the larger flame spread rate.

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Deflagration-to-detonation transition (DDT) using flame jets was experimentally studied to improve performance of pulse detonation engines. The detonation tube has a total length of 7350 mm and an inner diameter of 50 mm. Three types of configuration of sub-chambers supplying flame jets were arranged : two flame jets colliding at the tube center (counter type), two flame jets forming a swirl inside the detonation tube (offset type), and one flame jet supplied in the axis direction of the detonation tube (conventional type). Test gas was a stoichiometric acetylene-air mixture. The experimental results show that early emanation of the flame jet is more effective to achieve the shortest DDT time rather than formation of a strong shock wave owing to higher jet velocity. For reduction of time from the jet emanation to detonation initiation, the flame jet supplied into wider space, which is given by the offset type and the conventional type, is superior to the counter type causing local enhancement of turbulence by mutual jet collision. With reference to the offset type, formation of swirling flame generated by jet emanation in the oblique direction to the tube axis has good performance for promotion of DDT process.

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The influence of the addition of hydrogen to methane mixtures on its local burning velocity has been investigated directly. Hydrogen added lean and rich methane mixtures having nearly the same laminar burning velocity with different rates of addition of hydrogen δ_H were prepared.A two-dimensional sequential laser tomography technique was used to obtain the temporal statistical relationship between the flame shape and the flame displacement. The local flame displacement velocity S_F and curvature of turbulent flames were quantitatively measured as the key parameters on turbulent combustion. Additionally, the Markstein number Ma was obtained from outwardly propagating spherical laminar flames, in order to examine the effect of positive stretch on burning velocity. It was found that the trends of the mean values of measured S_F with respect to δ_H and the equivalence ratio φ corresponded well the turbulent burning velocity. The trends of Ma with respect to δ_H and φ could possibly explain qualitatively the local burning velocity and turbulent burning velocity.

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An experimental study has been conducted to reveal combustion and emission characteristics of biodiesel-fuel engine equipped with EGR. The effect of ambient temperature and oxygen concentration on ignition delay time at self-ignition combustion of biodiesel was measured by using a constant volume combustion chamber. Engine bench test results show that low smoke emission achieved by using biodiesel and high pressure injection enables high EGR ratio, which results in lower NO_x emission compared to gas oil. Also, it is indicated that a large amount of EGR combined with high-pressure injection is effective to reduce SOF content in PM emission from biodiesel.

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In order to clarify the effect of heterogeneity of distribution of oxygen concentration in a combustion chamber induced by EGR on the soot and NO emissions from the diesel engine, the combustion characteristics of diesel spray flame achieved in a rapid compression and expansion machine (RCEM) at various patterns of oxygen distribution in the chamber are investigated. The distribution of oxygen in a chamber is controlled by changing the location, phase, and duration of EGR gas injection with multi-port intake system. The multi-port intake system can make the circler distributions of oxygen with different gradient of oxygen concentration between-260 and 260 mol/m⁴. NO and soot emissions are measured at different oxygen concentration distributions. Results indicate that the amount of oxygen entrained into the spray upstream the luminous flame region affects the NO and soot emissions from diesel flame strongly.

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