A third-order nonlinear K-ε model proposed by the authors is applied to turbulent flow through a two-dimensional asymmetric diffuser including separation and reattachment. The numerical results show that the present model predicts profiles of the mean velocities and Reynolds stresses better than a representative linear eddy-viscosity model but does not reproduce the flow separation. The model is improved by incorporating a strain-convection effect derived from a two-scale direct-interaction approximation analysis into the Reynolds stress to capture separation and reattachment.

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Numerical analysis has been performed for three-dimensional developing turbulent flow in a rectangular cross sectioned duct with periodic arrays of blocks by using an algebraic Reynolds stress model. Upper and bottom wall of straight duct with rectangular cross section are composed of many blocks, which are periodically located along the flow direction. In the numerical calculation, periodic boundary condition has been used for this flow and an algebraic Reynolds stress model is adopted in order to predict precisely Reynolds stresses. Since the presented algebraic stress model is classified into high Reynolds number turbulent model, wall function method has to be used to set boundary condition of turbulent energy and dissipation. As for this wall function method, we have examined the influence of universal constant which appears in log-law velocity profile by means of changing its value. We have adopted two kinds of universal constants, that is, one is the value with 5.5 for smooth wall and the other is -8.0 for roughened wall. Each calculated result of mean velocity and Reynolds stresses is compared with the experimental data. As the result of this research, it has been found that calculated results for universal constant-8.0 have shown the reasonable result compared with the calculated results for universal constant 5.5. Besides, calculated results of Reynolds stresses for -8.0 are in better agreement with the experimental results than that for 5.5. The calculated results of secondary flow have suggested that flow behavior near wall flow depends on universal constant in log-law velocity profile. These calculated results indicate that the universal constant of log-law velocity which is assumed in wall function, has to be changed according to the wall condition.

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The influence of a drag-reducing surfactant on a zero pressure gradient turbulent boundary layer was investigated using a two-component LDV system. LDV measurements were made for four different momentum thickness Reynolds numbers, R_θ (=U_eθ/ν) =357, 444, 535 and 601, where U_e, θ and ν are the free-stream velocity, momentum thickness and kinematic viscosity, respectively. The amount of drag reduction is from 25.6 to 62.6% when compared to a water flow at the same position and free-stream velocity. The shape factor H (=δ*/θ) increases with increasing drag reduction, where δ* is the displacement thickness. The mean velocity distribution in wall-coordinates indicates the existence of the elastic layer in addition to the standard logarithmic region. It is found that the streamwise turbulence intensity distribution has the additional maximum near the center of the boundary layer, where the solution is not locally in SIS (Shear Induced State) due to the effect of mixing of the potential and turbulent flows. The location of additional maximum of streamwise turbulence intensity is corresponding to the location at which the skewness factor of streamwise turbulent fluctuation is zero. The wall-normal turbulence intensity of the surfactant solution is much smaller than that of water and is almost constant across the boundary layer. Reynolds shear stress distribution does not show the definite maximum near the wall, while it reveals the maximum near the center of the boundary layer. It is also found that the skewness and flatness factors of the wall-normal turbulent fluctuation are almost constant near the outer edge of turbulent boundary layer in the surfactant solution.

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The wind force acting on a cylindrical protuberance placed on a turbulent boundary layer has been investigated. The diameters of the cylindrical protuberance were D=40 and 80 mm, the Reynolds numbers based on D were 5.3×10⁴ and 1.1×10⁵. The turbulent boundary layer thickness where the cylindrical protuberance was placed was various from 26 to 130 mm. An aspect ratio (= height/diameter) was varied from 0.125 to 1.0. The flow visualizations by the surface oil-flow pattern method were carried out. The surface pressure distributions on the cylindrical protuberance were measured and the drag and lift coefficients were determined by integration of the surface pressure of the cylindrical protuberance. It was cleared that the correlations among the fluid force, the turbulent boundary layer thickness and the aspect ratio of the cylindrical protuberance.

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The present study was experimentally investigated on suppression and characteristics of flow-induced vibrations of rectangular prisms with various width-to-height ratios. In the previous report, the response characteristics and generation mechanism of flow-induced vibrations of rotary oscillating rectangular prisms were examined. The present report was made on the suppression of flow-induced vibrations of the rectangular prisms with rotary oscillation. As a result of previous paper, it can be seemed that the prevention of rolling up the shear layer separating from the leading edge of the rectangular prism is the most effective for suppressing flow-induced vibrations of it. In this study, we therefore attempted to prevent the rolling up of the shear layer by the following three method : placement of a small normal plate at upstream of the prism, attachment of four perforated normal plates on upper and lower side surface, and attachment of triangle fairings on front and rear surface. Important results from the present study were that (i) the generation of low-speed and high-speed torsion flutter were completely suppressed by a normal plate placed at upstream of the prisms, (ii) the generation of vortex excitation was completely suppressed by four perforated plates attached to upper and lower side surface, (iii) the generation of low-speed and high-speed torsion flutter were completely suppressed by triangle fairing attached to front and rear surface, and (iv) vortex excitation newly generated at the different reduced velocity U_r when a normal plate or fairings was set up was completely suppressed by increasing from the threshold value of the reduced mass-damping factor C_n.

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Decay processes of secondary flow generated in 90-degree bends are visualized by using a PIV measurement system. The main parameters are a Re number and a curvature ratio of the bend, and three kinds of the 90-degree bend are prepared. It is confirmed that symmetrical and apparent secondary flow, which is a twin-vortex, is formed in a cross section of the pipe shortly after the bend outlet for each curvature ratio where the flow field is analyzed in the time average. However, it is clarified that this secondary flow unsteadily and intensely fluctuates in the cross section regardless of the curvature ratio. Especially, where the curvature ratio is the lowest of 1.0, it is confirmed that the flow field is even more complex and its flow pattern rapidly disappears in more downstream area by the interaction between the secondary flow formed by a centrifugal force and newly generated separation vortex.

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A polygon mirror is one of the important optical scanning components for a laser beam printer, a copy machine and so on. It has the serious troubles related to the fluid dynamic flow structures such as high frequency noise, frosted mirror and jittering of the rotating mirror under high rotating speed condition. The flow structures around the rotating polygon mirror were investigated by the flow visualization using a Particle Image Velocimetry and the velocity measurement using a Laser Doppler Velocimetry. As the results, significant flow structures were clarified and associated with these troubles. The first is the periodical fluctuating structure, which induces the high frequency noise, showing as a bow-shaped region and a pair of the vortex tubes. The second is an alternative flow structure shedding from near the polygon mirror, which is considered as one of the causes of the jittering. In addition, this flow accompanies the complicated three-dimensional vortices on the outskirts of the alternative flow structure. The third is the sinking flow structure toward the polygon mirror contributing the frosted mirror trouble.

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In this paper, the aerodynamic characteristics of a symmetrical ground effect wing are measured in a low turbulence wind tunnel. To change the directions of an Aero-Train in practical use, it must shuttle back and forth. Circular-arc aerofoil seems to be suitable for the Aero-train, while it can run back and forth by changing only the attack angle of wings. Lift and drag characteristics of NACA 6412-modified, circular-arc aerofoils with thickness ratio 9% and 12% were clarified by the 6-component balance. Suction and moving-belt system were used to simulate the ground. Characteristics of two-dimensional aerofoils and three-dimensional wings were compared, and lift-to-drag rations of three aerofoils were compared. Separations on the upper surface of the circular-arc aerofoils were visualized by tuft and oil spot method. It was found that increase of drag in ground effect condition was caused by increase of the induced drag and by enlargement of the separation area on upper surface of circular-arc aerofoils. A circular-arc aerofoil with thickness ratio 9% at the angle of attack 2 degrees had enough lift-to-drag ratio for Aero-Train.

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Boiling heat transfer characteristics were verified for a temperature sensitive magnetic fluid, to which the organic fluid was mixed, yielding a binary-carrier-fluids magnetic fluid. Substantial increase of heat transport capability was achieved in comparison with an ordinary magnetic fluid. In the present study, n-hexane, which has lower boiling point than that of kerosene (mother carrier fluid), was mixed. It was found that the heat transport capability is surely improved with applying magnetic field to the binary mixed magnetic fluid flow. And the effect of vortices predicted by predicted by previous numerical studies is confirmed in the present study, thus the heat transfer characteristics from the heated wall is strongly affected by the vortices.

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Behavior of main and branch pipe flow in a T-junction piping system under the isothermal condition was examined experimentally using flow visualization techniques (the dye injection and smoke method). As a result, it was clarified that flows downstream of the T-junction are classified into three types : stratified flow, deflecting jet, and impinging jet. In the case of the deflecting jet, the flow issuing from the branch pipe into the main duct forms an arch vortex street. Next, the waveform of the axial velocity and its spectrum were measured by using hot wire, and the structure of the vortex was investigated. The frequency with which vortices are shed in an arch vortex street becomes higher with increasing Reynolds number under the condition of a constant velocity ratio and decreases with an increase in velocity ratio. Strouhal number is expressed by an approximate equation under the condition of Reynolds number Re=5000-50000, velocity ratio β=0.33-2.00 and diameter ratio α=2.04-5.20.

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Efficient techniques for cleaning scale in a U-tube of a heat exchanger are desired. Blast cleaning test was carried out using a real size U-tube of 13.5 mm in diameter, 8 m of straight tube length, and 0.3 m in radius of curvature. A combination of plastic particles and glass beads was selected for the blasting media. Swirl motion was added to the blasting media flow. The plastic particle-air two-phase flow with swirl motion in the tube was visualized. The loading ranged from 3.7 to 5.3. The estimated Stokes number was 1700 for the plastic-air two-phase flow. It was observed that just downstream of the bend, flow particle clusters repeatedly followed each other alternatingly located on the upper and lower sides of the tube. In the repeated blast cleaning experiments, it was found that the same characteristic large-scale cleaning distribution occured along the tube.

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A new method for mixing liquids in a vessel without actually making contact with the liquid itself has been developed. The developed method uses the phenomenon referred to as radiation pressure : namely, the pressure produced by ultrasound waves as they pass through a liquid and reach its free surface, which, as a result, is pushed out. The wave of energy required to stimulate the movement of the free surface in the vessel, is generated by an ultrasound device located out side the vessel. In the current study, first, the movement of the free surface was simulated and several types of wave were tested to determine which would produce the appropriate fluid flow for proper mixing in the vessel. Next, the numerical simulations were experimentally verified by observing the flow of liquids in a vessel in a laboratory trial. Lastly, a new mixing device was designed and constructed according to the test resulted, and it was demonstrates that it can mix 250μl of liquid in 0.5 s

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The performance of our recently developed non-contact mixing device was evaluated by using a serum and a reagent as a test liquid. The non-contact mixing device can mix the liquid-without, actually making contact with the liquid itself-by ultrasound irradiated from a sound source installed out-side of the vessel containing the liquid. The present study shows that a mixture of the serum and the reagent can be visualized by the Schlieren imaging method, which uses the difference in their refractive indexes. The gray-scale data from the Schlieren images obtained before and after mixing were used to evaluate the performance of the mixing device. Moreover, under the condition that the dilution of the serum is a parameter, the mixing performance was evaluated in laboratory trials. The trial results show that a highly diluted serum (i.e., twice as diluted as a standard serum) can be mixed with the new non-contact mixing device.

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Purpose of the study is to develop a new and reliable method for the power curve measurement of wind turbine generator system in complex terrain. Since the power absorbed from the wind is proportional to the third power of the wind speed, essential problem in complex terrain is how to measure the real wind speed into the rotor plane of wind turbine. To take account of the effect of topography, a site calibration procedure based on the sectorwise two-poit correlation analysis has been performed. In this paper, the influence of wind characteristics and turbulent intensity for the power curve measurement of NEDO-500 kW wind turbine is investigated and discussed. The measurement campaign has been perfor0med in Tappi wind park from 1996 to 1998.

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Purpose of the study is to investigate the effect of terrain on the performance measurement of a wind turbine generator system in complex terrain. Since the wind energy captured by the rotor plane of wind turbine is proportional to the 3rd power of wind speed, the exact estimation of the wind speed at the point of wind turbine is necessary. However, the definitive method for the wind speed estimation in complex terrain has not yet been established. To predict the local flow field in complex terrain, many researchers have proposed numerical methods and applied their models to very complicated situation such as an actual topography where is not easy to clarify their adequacy. Since a few comprehensive studies on the terrain shapes have been performed, detailed and general understandings of the flow over complex terrain are insufficient for the estimation of the wind energy resources and the performance evaluation of a wind turbine in complex terrain. In this study, the experimental approach by wind-tunnel testing was taken and compared with open air field data.

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This paper shows the pressure distribution on a rotor blade of 10 m-diameter wind turbine. The pressure sensors were mounted inside the blade. The local angle of attack was measured with the use of five-hole pitot tubes at 1 chord length upwind of the blade leading edge. Comparison of the results of three-dimensional field rotor and two-dimensional wind tunnel measurements were carried out. The normal force coefficient shows good agreement at the linear range of low local angle of attack in the field and in the wind tunnel measurements. In this linear part, pressure distribution of field measurement also agrees well with those of wind tunnel measurement. The normal force coefficient at high local angle of attack in field measurement seems to show the stall-delay, where is post stall region at wind tunnel measurement. When the local angle of attack takes a value less than 15 degree, the normal force coefficient increases by the effect of the local slip angle.

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The effect of texture, which is defined as periodic microstructure, on contact-angle hysteresis was investigated. Various textures that consist of lattice-aligned pillars of 1 to 64μm in diameter and 0.1 to 8μm in height were produced on silicon substrate with dry etching. It was found that there are two kinds of tendency. In case the air is trapped between the pillars, the narrower pillar-pitch makes the hysteresis smaller. On the other hand, in the case the air is not trapped, the higher and narrower pillar-pitch makes the hysteresis larger. Thus, by choosing appropriate pillar height and pitch, the hysteresis can be controlled. Such design guideline is also proposed.

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Critical heat flux enhancement by the electrohydrodynamic (EHD) effect has been analyzed quantitatively based on the increased frequency of liquid-vapor interface oscillations around the edge of the bubble. The majority of heat transfer occurs when the liquid film thickness becomes less than 50 μm, which only occurs once per period. The main mechanism of heat flux enhancement induced by the EHD effect would be a result of an increase in surface tension due to the effect of electric lines of force. By representing the terms of the forces for a change in curvature and the surface tension resulting from the electric lines of force, the equation of the liquid-vapor instability was obtained and analyzed. Experimentally it has been shown that as the applied voltage increased, the periodic time interval of the thickness change was shortened. This effect reduces the potential for dryout of the liquid film by making the minimum thickness time period shorter. By measuring the pressure oscillation on the boiling surface, the change of the thin liquid film thickness and the dynamic shape of bubbles, the relationship among the pressure, the liquid film thickness and the bubble shape was clarified. Consequently, this model successfully explains the relationship between the applied voltage and the enhancement of the critical heat flux.

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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 for improvement of higher heat transfer and the conventional spiral finned tube banks under the same test conditions, and that the equation to predict heat transfer coefficient which is necessary on design of the heat exchanger was proposed.

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Heat transfer around a cylindrical protuberance placed in a turbulent boundary layer was measured. The diameter of the cylindrical protuberance, D, was either 40 or 80 mm, and the aspect ratio of the protuberance H/D (=height/diameter) ranged from 0.125 to 1.0. Reynolds number based on D ranged from 1.1×10⁴ to 1.1×10⁵. The thickness of the turbulent boundary layer at the position of the protuberance ranged from δ=26 to 120mm. The local heat transfers on the top and side face of the cylindrical protuberance was measured under the condition of constant heat flux. The present paper investigated the effects of the thickness of the boundary layer and the aspect ratio of the protuberance on the heat transfer. It was found that the overall heat transfer of the protuberance had a maximum at H/δ=0.24.

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Energy transfer from fluid to surface was calculated by using the classical molecular dynamics method in order to investigate effects of surface structures from 0.1 nm to 10 nm on surface energy transfer numerically. Surface structures on a constant surface area were composed of several hundred atoms having various potential energy parameters, in other words, thermal properties. Upper region in the calculation domain was controlled at a constant temperature and one solid atomic layer lower region was controlled at a constant temperature so as to make a temperature gradient in the calculation system. Energy transfer to the surface was much dependent on surface structures in nanometer scale that affected static structure and dynamic behaviors of fluid molecules in the vicinity of the surface.

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In the previous paper, numerical model for absorption within vertical pipes was proposed and compared with the experiments. Agreements were good for pipes with OD 28-15 mm but at 10 mm pipe experiments fell bellow the predicted values. For smaller diameters, the difference between the surface area of the falling liquid film and that of the outer surface of the pipe is not negligible and the thickness of the liquid film is neither negligible. In this paper new model is formulated in cylindrical coordinates and experiments using pipes with 9.52 mm and 7 mm OD are done. Smooth pipes and two kinds of internally finned pipes, which are originally developed and used to enhance the heat transfer characteristics of evaporator and condenser of refrigerator using HFC as refrigerant, are tested in the experiments. The absorption performance is enhanced by 30% compared to the smooth pipes, but the difference between the finned pipes are small.

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Gas absorption and pressure drop characteristics of a slug flow in microchannel were experimentally studied with CO₂ and water system in expectation of high absorption performance by large specific interface area, toroidal flow in slug and high heat transfer capability of microchannel. Absorption rate was measured by detecting volume change of gas bubble along the channel with photo-interrupters, and then absorption time constant was formulated as a function of inner diameter, bubble velocity, and liquid slug length. Pressure drop was also formulated by fitting experimental data to an equation modeled as a sum of Poiseuille flow part and toroidal flow part. Based on the formulas, high mass transfer performance and compactness of the proposed system was demonstrated by comparison with typical gas absorption systems such as falling liquid film and dispersion bubbles. The microchannel gas absorber, of which channel length was set to keep outlet liquid concentration a specified value, was estimated to be more compact by reducing a channel diameter with a slight increase of pressure drop.

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Numerical analyses were performed for the effect of inclined angle on the mixing flow in a square duct with uniform temperature walls (T_w=30°C) and inlet temperature (T₀=10°C). Three-dimensional governing equations were solved numerically for Re=100, Pr=0.72 and various inclined angles (from -90°to 90°). Three-dimensional behavior of fluid in a duct was examined for each angle. Thermal performance was evaluated using the relationship between Nusselt number ratio and pressure loss ratio with and without buoyancy induced flow as a parameter of inclined angles. High heat transfer and low pressure loss region was from -15°to -60° in thermal performance using mean Nusselt number ratio.

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The isothermal wake from a circular cylinder at the Reynolds number Re=300 was analyzed by a DNS computation, computed results were discussed, and features of 3 D motion were elucidated as follows : Qualitative features of the vorticities ω_x, ω_y with the upward direction and the horizontal directions and the velocity ω in the cylinder axis direction were revealed by an analogy of the vorticity ω_z in the cylinder axis direction. The vortex dislocation was visualized in the farwake streaklines, had a band spectrum of time trace of the upward velocity, and was found to be resulted from the ω motion. A mechanism of the vortex dislocation was made clear by the ω motion which was different between the nearwake with f_p=f_wake and farwake with f_p=2f_wake, here f_p is the dominant frequency and f_wake is the wake frequency. The wave lengths of ω_x and ω_y were 1, i. e. the B mode oscillation, in the nearwake, and 2, i. e. the C mode oscillation, in the farwake. The 3D oscillation in the isothermal Karman vortex street at Re=300 was therefore composed of the B mode with the wave length 1 in the nearwake and the C* mode with both the length 2 and the vortex dislocation in the farwake.

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The wake with positive buoyancy at the Reynolds number 300 and the Richardson number 0.3 of air was analyzed by the DNS computation, and revealed as follows : Positive buoyancy effects are that one is Effect I, that is, a decrease of the axial direction vorticity|ωz|, and the other is Effect II, that is, a decrease of the 3D motion, i. e. the vorticities |ωx|, |ωy| with the upward and horizontal directions, and the velocity |w| with the axial direction. Effect II is more dominant than Effect I.That is, the 3D motion moving right and left decreases remarkably, but the suppression of vortex street becomes weak. A space effect of Effect II is that the vortex dislocation becomes vague and a dislocation location becomes time-dependent. A time effect of Effect II is that the frequency of the 3D motion increases, the amplitude of the motion decreases, and the formation region length decreases. A space and time effect of Effect II is that the oscillation mode becomes the B mode with 1 of the wave length Λ, and 2f_wake and 5f_wake of the dominant frequency f_p of the 3D motion in the nearwake, and the A^* mode with 3 of Λ, 2f_wake of f_p, and the weak vortex-dislocation in the farwake, here f_wake is the wake frequency.

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A circular cylinder wake of air with negative buoyancy at low Reynolds numbers was analyzed numerically, and a new vortex street, i.e. “a cooled vortex street”, was discovered as follows : A weak asymmetry in the isothermal wake, i.e. the wavy wake, centipede flow, oscillating twin-vortex, at low Reynolds numbers is amplified remarkably by intensive cooling of a cylinder. As a result, a cooled vortex street with intensive asymmetry occurs. The region of the Reynolds number Re and the Richardson number Ri occurring the cooled vortex street is much wider than those of the Karman vortex street. The Karman vortex street occurs by weak cooling of the isothermal wavy wake and centiped flow. However a Karman vortex street never occurs even though a cylinder is cooled at Re <24. A structure of the cooled vortex street differs extremely from that of the Karman vortex street. That is, the asymmetry degree, size of vortex spiral, and vortex pitch of the cooled vortex street are much greater than those of the Karman vortex street. The cooled vortex street is a governing phenomenon in the cooled wake, and can be identified by employing the asymmetry degree of streamlines.

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A circular cylinder wake of air with negative buoyancy at low Reynolds numbers was analyzed numerically, and a vorticity structure in the cooled wake and a generation mechanism of the cooled vortex street were made clear as follows : With increasing the cooling rate, the angle between shear layers increased and the wake width became large. Furthermore the wake vorticity was generated and the vorticity quantity of shear layers increased. As a result, the shear layers were elongated, and the region with the vorticity near the tips of shear layers became large. These tips rolled up and reached the midplane in the wake mutually. Thus the stable wake, i.e. the cooled vortex street, was formed. The stable rolling of shear layer tips was realized in only the Karman and the cooled vortex streets. Thermo-fluid behavior is extremely different among three groups, i.e. (i) the isothermal wake, Karman vortex street, and oscillating twin-vortex, (ii) the transient flow, and cooled vortex street, and (iii) the symmetric flow. When a flow changes to a different group flow, the coefficient of shear stress and mean Nusselt number on cylinder surface decreases abruptly.

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For insert-pipe-type mufflers with flow, the predominance of resonance in the flow-induced noise occured in particular combinations of muffler configuration and flow velocity as well as for simple expansion-cavity-type mufflers. The phenomenon is caused by a self-excited oscillation based on the feedback response from acoustic resonances of the muffler to the shear flow. Transitions from a tail pipe resonance to a cavity resonance and from a cavity resonance to a tail pipe resonance were also observed. This is called “resonance frequency transition”. The coupled effect of the predominance of resonance and the frequency transition was investigated in the present research. For insert-pipe-type mufflers, predominance of resonance occurred not only at tail pipe resonance frequencies but also at cavity resonance frequencies. Firstly, the frequency transition was demonstrated through the wave theory. Then, the predominance phenomena was expressed in a general way based on the wave theory and the feedback response from sound to flow.

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In this paper, characteristics of injection and developing process of high pressure hydrogen jets were investigated using a constant-volume vessel. As an injection rate profile of a hydrogen jet, injected using an electronically-controlled, hydraulically-actuated gas fuel injector, is significantly related to jet penetrating and dispersing processes, the impact force of the jet was measured. And developing processes of high pressure hydrogen jets were visualized by means of shadowgraph photography to measure jet penetration, dispersion angle, volume, and pseudo equivalence ratio, Moreover, jet penetration profiles were approximated by the momentum theory in consideration of underexpanded jet flows. The results from injection rate measurements show that the injection rates during steady state portion of the injection are proportional to injection pressures and cross-sectional areas of the nozzle orifices. Regarding jet developing processes, the results represent the effects of injection pressure, orifice diameter, and ambient gas density on the jet penetration, dispersion angle, and entrainment. And the jet penetration predicted by the modified momentum theory was in reasonable agreement with the experimental results for various conditions of injection pressure, ambient density, and orifice diameter.

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In this study, underexpanded flows of hydrogen injected into high pressure ambient were focused to clarify the effect of the flow structure on jet developing and mixing processes. Flow behaviors of underexpanded jets injected into atmospheric pressure ambient are well known. However there are few works about the flow under high pressure ambient and about the flow injected through relatively small orifice (<1.0 mm). Therefore, in this study, the jet flows near the nozzle exit were observed by shadowgraph photography with changing conditions of injection, ambient, and nozzle configuration. The objectives are to clarify the effects of those experimental conditions on the jet structures and to suppose the effect of the jet structures on mixing and developing processes. The shadowgraph images were used to measure Mach disc diameter, barrel length, jet radial width, and shock spacing which were related to a pressure ratio of injection to ambient and nozzle diameter. The results show that the pressure ratio has significant effects on underexpanded jet structures and as the increase in the pressure ratio, jet structures near the nozzle exit enlarged, and that the injected mass was conserved at where the Mach disc was generated. From the results, it is supposed that the pressure ratio is significantly related to the scale of the eddy generated just near the shock structure and also related to mixing process.

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Present paper deals with experiments of direct-contact freezing of Hexadecane particles injected from multi-nozzle into stagnant pure water, ethylene glycol 30 wt% water solution and ethylene glycol 50 wt% water solution. The experimental parameters were varied in the ranges of n=0.001-0.51, Re=34-257 and Pr=8.8-42. Main results obtained are summarized in the followings; (1) an empirical equation for drag coefficient of solidified Hexadecane particles was proposed, (2) the relationship between particle density and variations of rising velocity was investigated, (3) the relationship between particle density and Nusselt number of particle swarm was clarified, (4) It was found that one dimensional heat conduction model can be applied to predict the solidification mass fraction of single particle and particle swarm including uniform size particles, and (5) It can be applied to predict the solidification mass fraction of particle swarm including various size particles formed by destruction of laminar and turbulent jet as well.

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It has been understood that DME combustion with the low fuel pressure using electronic controlled injector was not stabilized by defective mixture formation, though the excellent thermal efficiency was obtained at appropriate injection timing. In this paper, the improvement of combustion process in DME compression ignition engine with low-pressure fuel injection was investigated with focusing the influence of the fuel pressure and the combustion assistance by homogeneous charge. As a result, it has been understood that the fuel mixture formation and the combustion are promoted due to the active contact between the fuel molecules and the oxygen molecules, because of the reinforcement of the fuel penetration and securing of positive ignition condition.

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Orinoco-tar produced in Orinoco river basin of Venezuela is the oil sand of ultra-heavy oil, which is different from the conventional crude oil resources. Orinoco-tar/water fuel (Ori/W) is oil-in-water emulsion emulsified by water, so the water of medium makes the viscosity much lower than the net Orinoco-tar as same as the case of the asphalt/water emulsified fuel (As/W). This study aims to investigate the behavior of microexplosion of Ori/W, in particular, the mechanism of microexplosion by the thermal analysis (TG/DTA) and to compare the combustibility with the emulsified fuels made from the residue of crude oil such as asphalt and pitch by the combustion experiments of the single droplets in the falling-down electrically heated furnace. The results show the microexplosion occurs under the same mechanism between Ori/W and As/W and the combustibility of Ori/W is better than the other emulsified fuels as well as Cheavy oil.

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The authors have proposed a new HCCI combustion engine system fueled with DME and methanol-reformed gas (MRG) in the previous research. The research has shown high thermal efficiency over a wide range of the operable equivalence ratio in the system. MRG effectively controls the timing of the second stage heat release by the high temperature oxidation reactions of DME to expand the operable range. The MRG consists of H₂ and CO. However, the effects of the two on the ignition of DME have not been separated yet. This research experimentally investigated each influence of H₂ and CO on HCCI of DME. To separate the effects of H₂ and CO on the ignition, HCCI combustion of DME/H₂ and DME/CO are compared. The results of the analysis show that both H₂ and CO have the effect of retarding the ignition. The results also show that H₂ more largely affects the ignition in HCCI of DME than CO does.

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