In this study, a scheme for introduction of vortex elements over a solid surface was proposed for a vortex method. Vortex elements were introduced and vorticity redistributions were made over the solid surface in this scheme. Thickness of vorticity layer and panel size were figured out with a non-dimensional thickness of vorticity layer defined by using kinematic viscosity coefficient and friction velocity based on the wall shear stress. To invdstigate effectiveness of this scheme, flows around a two-dimensional circular cylinder in a uniform flow were simulated through changing the non-dimensional thickness of vorticity layer and the initial calculation conditions. The simulations show that this scheme is effective : in spite of the initial conditions the calculation parameters could be automatically determined by using the non-dimensional thickness of vorticity layer, and the calculated results of the flow characteristics had good agreements with the other calculated results.

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This paper describes a numerical method for simulating fluid-structure interaction, especially two-dimensional fluid-elastic body interaction problems. A model is formulated for the elastic shell made of thin film. Numerical simulations of the incompressible unsteady flow around the moving and deforming elastic body in response to the fluid dynamic force are carried out by using the model. It is found that the proposed elastic body model could be useful for investigating the mechanism of the deformation of moving elastic shell.

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The effects of coherent vortices on turbulent energy transfer were examined in an acoustically excited two-dimensional parabolic jet. Production terms in the energy transport equation were evaluated based on the results of hotwire conditional measurements. Difference in vortex arrangement gave significant influence on the energy transport process among mean flow, coherent structure and incoherent turbulence. When the symmetrical vortex arrangement was excited, most of the mean flow energy directly dissipated into random incoherent turbulence. For the anti-symmetrical mode, large amounts of positive and negative turbulent energy fluxes were produced around strong large-scale coherent vortices. Fine-scale vortices between the streamwisely adjacent coherent vortices played important roles in the turbulent energy transport process for the anti-symmetrical vortex arrangement.

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The air flow in a clean room model was examined during opening and shutting of a swing type door. The scale ratio of the model was 1/10 and the door was driven at constant angular velocity by a pulse motor. The velocity field such as the velocity map, the vorticity map and the flow behavior of the floating particles were visualized by utilizing PIV measurement. At the start of the door opening, two starting vortices are generated behind the door and near the wall. At the end of the door shutting, a jet flows in the clean room through the gap of the door and the wall. The generation of the vortices and the jet produces the inflow and outflow of the contaminant through between the clean room and the front room.

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Numerical prediction of dipole sound based on Lighthill-Curle's equation gives little information on the structure of sound sources. On the other hand, a hybrid method that combines the large eddy simulation (LES) and the compact Green's function proposed by Howe provides detailed information on the vortices in the flow that most contribute to the generation of sound. However, when the dipole sound is evaluated from the momentum change in fluid inside a finite computational domain, the result does not in general agree with the sound evaluated from the fluctuating pressure on the body surface because contribution from vortices outside the computational domain is not taken into account. In this study, the balance of momentum in a finite computational domain is considered strictly, and the effect of outer vortices is replaced with contribution from inner properties by using an imaginary velocity potential ψi.This method allows quantitative prediction of dipole sound and also gives accurate information about sound sources.

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A model to simulate the drag reductoin by dilute addition of polymer or surfactant (Toms effect) is proposed based on the discrete element model. The dimension of the discrete element, which represents the polymer or the rod-like micelle, is very small compared to that of the velocity fluctuation of the fluid. So it is assumed that the element is in equilibrium state in the fluid and turns to the direction of an eigenvector of the velocity gradient tensor. And the macroscopic effect of the discrete elements is modeled as the stress assuming the elements are independent each other. Direct numerical simulations are carried out with this new model using the rigid dumbbell element as a discrete element model and it is shown that the drag reduction up to 37% drag reduction rate is reproduced. In addition the followings are indicated as concluding remarks. (1) The drag reduction can be reproduced without assuming the macrostructures formed as the network of elongated polymers or rod-like micelles. (2) The drag reduction and the stress deficit can be reproduced without the elasticity.

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The validity of the Simple Counting Algorithm (SCA) for the volume tracking simulations of a single bubble in stagnant liquid is examined. As a result, it is confirmed that (i) the SCA can keep sharp interface, but (ii) the volume of bubble is increased. An improved SCA is proposed in order to reduce the volume error. Numerical simulations of a single air bubble rising in stagnant water are carried out using a course grid, i.e. only 6 cells to the bubble equivalent diameter. The volume of bubble is conserved well and a sharp interface is kept for as long as 12 seconds.

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We developed a method of effective polymer coating and investigated its new drag reduction effect. The ends of polymer chains are anchored on the wall by insoluble binder, and the other ends dissolve in water. The turbulent drag reduction by means of this polymer coating was investigated in a rectangular channel flow and in a boundary layer flow. The influence of molecular weight on the drag reduction was investigated in a channel flow. The polymer of molecule weight 3.6 millions showed highest drag reduction. The turbulent velocity profiles were measured in a channel flow using a LDV system. The drag reduction was caused by the increase in the intercept of the logarithmic velocity profile. For a boundary layer flow, the drag reduction was observed in the transitional region.

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Thermohydraulic analyses for a fundamental water experiment simulating thermal striping phenomena at T-junction piping systems were carried out using a quasi-direct numerical simulation code DINUS-3. Calculated results were compared with the experimental results on the flow patterns in the downstream region of the systems, the arched vortex structures under the deflection jet condition, the generation frequency of the arched vortex in the various conditions ; i.e., diameter ratio α, flow velocity ratio β and Reynolds number. From the comparisons, it was confirmed that (1) the DINUS-3 code is applicable to the flow pattern classifications in the downstream region of the T-junction piping systems, (2) the arched vortex characteristics with lower frequency components can be estimated numerically by the DINUS-3 code, and (3) special attentions should be paid to the arched vortex generations with lower frequency components of fluid temperature fluctuations, which might induced high-cycle thermal fatigue for the design of T-junction systems.

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In the former study, a method called FSI-DM was developed. This FSI-DM is the method of connecting fluid and solid parts using a discontinuous mesh, and the density of the mesh inside the solid and the fluid can be changeable. The temperature results by CFD were within ±7 degrees ascompared with the experimental results. In the present study, in order to predict a vapor condensation, the analogy was assumed between heat transfer and vapor transfer in the boundary layer formed on the surface of the parts inside a headlamp and transport equations of velocity, temperature and vapor concentration was analyzed. As the results, after turn on the bulb, the moisture was once emitted from plastic parts to fluid inside the headlamp, and moisture concentration of fluid became rise. In such stage, by cooling down the surface of the lens, the fog on the surface of the lens arose.

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Growth process and three-dimensional deformation process of the disturbance wave, which appears in the laminar-turbulent transition process of a radial liquid sheet flow, are clarified. The radial liquid sheet is formed by the release of a radial liquid-film flowing on a disk from the edge of the disk to still air. When the Reynolds number is large, a concentric disturbance wave ('D wave') appears and grows downstream on free surfaces of the liquid sheet. 'D wave' is caused by the unstable disturbance, which is attributable to the inflectional velocity distribution of the liquid sheet. After the growth and the three-dimensional deformation of 'D wave', a laminar-turbulent transition occurs. The detail observation and amplitude measurement of 'D wave', which is excited by supersonic wave, reveal growth process and three-dimensional deformation process of the 'D wave'.

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Strong adverse flows tend to occur in the suction surface/wall corner of high-load blade cascades of axial compressors. In a two-dimensional cascade wind tunnel test, effects of tip clearances on the cascade pressure coefficient Cp and flow structures in the corner were surveyed. Addition of a tip clearance was found to alter the flow conditions in the suction corner of axial compressor blade cascade. Tip clearance of 0.4 mm for the test blade of chord length of 100 mm in a typical high-load stator blade cascade increased the pressure coefficient Cp and lessened the corner loss coefficient compared with the cases with no clearance or with wider clearance. The issuing jet through the tip clearance of 0.4 mm was found to have eliminated strong vortices in the corner zone. It suggests a very useful means of improving the axial compressor performances.

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This paper reports the particle tracking algorithm using a self-organizing map (SOM) developed for 3D-PTV measurement and its performance evaluation in numerical simulations. The algorithm using SOM has high applicability to many engineering problems including the particle identification in a time-series of visualization images with tracer particles. This algorithm has been applied to the two models of the uniform flow in 3D space and the cubic cavity flow obtained by numerical simulation. In the performance tests for the two flow models, the normalized displacement defined for 3D flow is introduced to evaluate the high reliability of the present algorithm in 3D particle tracking. The test results show that the present algorithm can be successfully applied to 3D flow measurements even for higher normalized displacement up to about 3 and the correct ratio of particle tracking in the preset method is influenced mainly by the number of isolated particle images.

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In the present study, we propose a method for realizing the thermo-magnetic cycle with a gas-liquid two-phase flow by boiling a binary mixture of temperature sensitive magnetic fluid (TSMF) with an organic liquid of n-hexane, which has a lower boiling point. The boiling point of the fluid was adjusted below the boiling point of TSMF. From results of experiment, it was found that with the two-phase flow, the driving force was highly enhanced by applying magnetic field, showing substantial decrease in spatial averaging magnetization by n-hexane gas bubbles. Owing to sufficient magnetic driving force, it was observed that a self-circulation state of the device is possible, yielding that the proposed binary mixture of TSMF enables to design the self-circulation heat transport system by utilization of two-phase flow, which can operate only with its own magnetic driving force provided from temperature difference.

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The linear Rapid Distortion Theory (RDT) is applied to stable thermally stratified air (Pr=0.7), thermally stratified water (Pr=6) and salt-stratified liquid (Sc-600) flows without mean shear. Effects of diffusivity and viscosity are included in the analysis and turbulence quanitities such as turbulent scalar fluxes and their cospectra are obtained. The results are compared with previous laboratory measurements and direct numerical simulations (DNS). The results show that counter-gradient scalar transfer (CGST), which transports scalar counter to the mean gradient (i.e. negative eddy diffusivity), can be predicted by linear RDT as shown in the previous studies. However, the persistent downgradient scalar transfer (P-DGST) at small scales in air flows and the persistent CGST (P-CGST) at small scales in water flows can not be predicted by RDT. In a linear process, CGST occurs first at small scales and it spreads to all scales regardless ofPr orSc when the initial length scale of turbulence is sufficiently large. The results suggest that the turbulent scalar transfer at small scales in a strongly stably stratified flow is dominated by nonlinear processes and only the large-scale wave-like motions are controlled by linear processes.

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A series of direct numerical simulation in modeled counter-flow heat exchangers with oblique wavy walls is made toward optimal shape design of recuperators. The effects of oblique angles and amplitudes of the wavy walls are systematically examined, and the heat transfer and pressure loss characteristics are investigated. The flow structures are drastically modified due to the counter-rotating streamwise vortices induced by the wavy walls. By using optimal oblique angles and amplitude of the wavy walls, significant heat transfer enhancement is achieved with relatively-small pressure loss penalty. When thermal coupling of hot and cold fluid passages is considered, the averaged Nusselt number can be larger than that for isothermal heated condition. This is due to the dissimilarity between the velocity and thermal fields near the top and bottom walls. It is also found that the secondary flow and the associated thermal fields strongly depend on the Reynolds number.

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Numerical simulations were carried out for heat transfer during oscillatory flow in a circular straight tube with a solid tube in its center. The solid tube was inserted to enhance axial heat transfer by increasing lateral heat transfer effect for high frequency. The results show that the axial heat transfer increases with an increase in the inserted tube diameter. The results also show that the inserted tube materials do not have any substantial effect on the axial heat transfer. The efficiency based on the ratio of heat transfer to the work done becomes larger compared with that in a bundle of circular capillary tubes.

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A polycarbonate cylindrical tube of 32 mm inner diameter and 2000 mm long is mounted horizontally on a lathe, and concentration limits of flame propagation are determined as a function of rotational speed up to 2000 rpm. Mixtures of air and either of methane and propane, and their diluted mixtures with either of nitrogen and carbon dioxide are investigated. To prevent entrainment of ambient air, both ends are closed and the mixture is ignited at one end by an electric spark. Results show that with increasing the rotational speed, rich methane and lean propane limits remain almost constant, whereas lean methane and rich propane limits are varied away from the stoichiometry and the ranges of flame propagation are widened. It is interesting to note that the equivalence ratio at rich propane limit is increases from 2.05 at 0 rpm to 2.710 at 1 210 rpm, which exceeds the standard flammability limit of 2.5 determined with an upward propagation flame in a tube of 5 cm diameter. With increasing the rotational speed, the area of flame propagation in the φ (equivalence ratio) -χ (added inert gas concentration) plane is widened. The equivalence ratios at lean limit are decreased in methane and those at rich limits are increased in propane. The maximum allowable dilution ratio χ is increased, and the equivalence ratio at which the maximum occur is shifted towards to lean side in methane, whereas rich side in propane. There aspects can be explained on the basis of diffusional stratification of species of different molecular weight in the field of centrifugal force of rotation.

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This study estimates that all the human beings will be able to sustain only by the total amount of the natural energies as solar, wind, and/or hydro-power, at the end of this 21st century. At that time, the total population in all over the world should increase up to 13 billion. As the 1st step, this paper estimates the overall potential of the wind power in all over the world. The surface of the earth is divided into around 380 000 square meshes according to the technique called N-code developed by T. Nishioka, and the geographical feature factors are calculated for these meshes. The concept of this feature factor is fundamentally based on the statistical correlation between the wind velocity and the geographical features, and this method was also adopted by the “Green Energy” Project developed by our Ministry of Agriculture, Forestry and Fisheries in 1978-1988. It is shown that the geographical feature factors give well correlation between the wind velocities and the distances from the sea and also the land ratio. At the beginning of coming 22nd century, if we would assume population of all over the world to be 13 billion, we figured out that the wind turbines could provide 7.7% of total energy demand which would by consumed on the earth at the beginning of the 22nd century.

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In this study, numerical simulations for the flame structure and NO_x formation of counterflow diffusion flame with oxygen-enriched air were made by using the GRI chemical reaction mechanism (NO_x included) in order to elucidate the effect of strain rate on reduction of NO_x formation. The following conclusions were reached : (1) As the strain rate increases, the maximum heat release rate increases, and the width of high-temperature zone becomes narrow. (2) In the case where the strain rate is small, the thermal NO mechanism is dominant of NO formation, and NO formation by the prompt NO mechanism is negative. (3) As the strain rate increases, NO formation by the prompt NO mechanism increases, and it becomes positive when strain rate exceeds 400s^-1. At the same time, since the width of high-temperature zone becomes narrow, that by the thermal NO mechanism decreases, and it becomes smaller than that by prompt NO mechanism for the case where the strain rate exceeds 1200 s^-1. The decrease rate of thermal NO is bigger than the increase rate of prompt NO, so that the total NO formation is reduced by the increase in the strain rate.

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In order to predict accurately the NO_x emission of turbulent diffusion flame, we proposed the combination method based on the laminar flamelet model. In this method, the detailed kinetics calculation is separated from the turbulent flow calculation, and then they are recombined in terms of recombination parameters. We examined whether this method could be extended to diluted fuel and preheated oxidizer conditions. With the aim to find out the recombination parameters and to prove the validity of them for these conditions, we carried out the numerical calculation for the unsteady combustion characteristics of counterflow diffusion flame, in which the spout velocities of counterflow varied in a cyclic. The obtained results are as follows : It is necessary for extending this method to change the definition of the mixture fraction Z in consideration of fuel dilution. The production/consumption rates of major stable species are mostly determined by the scalar dissipation rate at flame surface SDR_q, and the production rates of intermediate products and nitric oxides are mostly determined by SDR_q and the maximum flame temperature T_max. Consequently, it is verified that SDR_q and T_max are appropriate as the recombination parameters for diluted fuel and preheated oxidizer conditions.

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Cellularity of the propagating spherical laminar flames induced by the flame instability was studied for methane and propane-air mixtures at the equivalence ratios from 0.8 to 1.3 and the initial pressure from 0.10 to 0.50 MPa. The Markstein number was employed to quantify the effects of the equivalence ratio and the pressure of the mixture on the cellularity due to the flame instability. The critical Peclet number, or the critical flame radius normalized by the flame thickness, at which the cells are created over the entire laminar flame surface, decresed with decreasing the equivalence ratio for the methane mixture and decreased with increasing the equivalence ratio for the propane mixture. It decreased with increasing the initial pressure at all the equivalence ratios. It decreased as the Markstein number decreased. The flame was no longer stabilized by the flame stretch at the large Peclet number though the positive flame stretch will restrain the Darrieus-Landau flame instability. Especially with the negative Markstein number, the flame was unstable even at the small Peclet number.

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This research analyzed characteristics of combustion and emissions in a spark-ignition internal combustion engine fueled with methanol-reformed gas. Experiments were done with a model gas with 67% of hydrogen and 33% of carbon monoxide that corresponds to the thermally decomposed methanol. This research cleared influences of in-cylinder air motion by swirl on thermal efficiency and exhaust emissions. While the enhanced air motion is effective to improve the combustion efficiency, it simultaneously increases the heat transfer from burning gas to the combustion chamber wall. Because of this, the thermal efficiency decreases in some cases. Influence of EGR on NO_x emission and thermal efficiency in the combustion was also analyzed in this research.

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One of the authors has proposed an HCCI combustion engine system that was fueled with dimethyl ether (DME) with a high cetane number and methanol-reformed gas (MRG) with a high anti-knock property in the previous research. In the system, both DME and MRG are to be produced from methanol by onboard-reformers utilizing the exhaust-heat from the engine. High overall thermal-efficiency has been achieved over a wide operable-range by both the lean HCCI combustion and the waste-heat recovery. While the MRG used in the research was the thermally decomposed methanol, methanol can be reformed to various compositions of hydrogen, carbon monoxide and carbon dioxide. This research aims to find the optimum MRG composition for the system in terms of the ignition control and the overall thermal efficiency. Characteristics of the HCCI combustion of DME and four types of MRG model-gases are experimentaly analyzed. The overall thermal-efficiency was also evaluated for ideal reforming conditions for each case.

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The heat release rate patterns of direct injection diesel engine with common rail injection system were investigated and fitted by the method of approximation based on wiebe function. The approximations were divided to pilot combustion part and main combustion part, and fitted by 2 step approximations respectively. From the analytical results about heat release rates of pilot combustion part and main combustion part, ignition delays, heat release durations and total amount of heat release were quantitatively descrived as a function of engine operating conditions of engine revolution, pilot injection timing and amount, main injection timing and amount. The ignition timing was effected by the gas temperature in cylinder at injection timing and descrived as a function of injection timing, and the heat release duration was descrived as a function of ignition delay. The ignition delay and heat release duration were almost independed on the engine revolutions for the 4 valve-engine which was examined. The heat release amounts of pilot combustion were effected by pilot injection timing and that of main combustion were a function of injection amounts. The predicted results such as pressure curve of pilot and main combustion parts and dP/dθ curve by using the above relations had a good agreement to the experiments.

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