The flow past a cylinder coated with magnetic fluid at low Reynolds number is studied by a numerical analysis. Non-coaxial magnetic field distribution causes non-uniform thickness of the coating, a recirculating flow in the coating, and lift force on the cylinder. Furthermore, wake of the cylinder is deformed by the application of magnetic field under certain conditions. This fact suggests that magnetic fluid coating deformed by changing the distribution of magnetic field can control the outer flow around the coated cylinder.

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Among the various methods of turbulent flow computation, Large Eddy Simulation (LES) with Dynamic Mixed Subgrid-Scale (SGS) model proposed by Vreman et al, in 1994 is expected to be the most effective method to evaluate the inverse transfer of turbulent energy from unresolved small size eddies to resolved large ones (the backscatter). In this paper, we discuss mainly on the results of a numerical analysis for the turbulent flow around a rectangular cylinder in order to show instantaneous turbulent properties. By phase-averaging these properties, the principal features of periodic phenomena can be made clear. Especially we focus on the relation between SGS dissipation and Grid-Scale (GS) enstrophy. As a result, it is shown that the Vorticity model that has been said to have less physical meaning has, however, possibility to be one of a useful SGS models by reason of positive correlation between SGS dissipation and GS enstrophy.

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This investigation was conducted to develop a closed loop system which controls separation and reattachment process in a backward facing step flow using a row of the vortex generator jet. The system uses wall static pressure as a control feedback signal and jet velocity ratio as a control parameter. Measurement of forward flow fraction shows that the reattachment line is almost parallel to the span-wise direction In velocity ratio variation. The wall static pressure is measured at a point where the pressure gain is highest and the pressure varies linearly with the jet velocity ratio. Step response tests to verify the closed loop system were conducted and the system validity was proved.

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In order to clarify the behavior of the water jet horizontally discharged from a small circular hole set on a circular pipe surface into air, in this paper, for the first step, we systematically observed the jet aspects, the efflux angle, the discharge coefficient and so on, when the hole diameter d is much smaller than the pipe diameter D. Since the upstream kinetic energy from the hole is somewhat higher than the downstream counterpart, the upstream partial jet with higher efflux angle crashes into the downstream partial jet and drives out the latter into up-and down-side, resulting in a marked pair of vortices, so that resulting in a three-dimensional spiral flow accompanying with marked surface waves.

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The temperature and the pressure distributions on a plate in underexpanded impinging jets are experimentally and numerically studied in this paper. The experiments were performed by measuring the adiabatic wall temperature using infrared imaging camera and the wall static pressures on the impinging plate and by visualizing density fields using schlieren method. Numerical calculations were conducted by solving two dimensional axisymmetric compressible Navier-Stokes equations and three dimensional compressible Euler equations. The comparison between the experiments and the calculations shows that the decrease in the stagnation temperature is caused by a recirculating flow carrying the cold air from the jet boundary to the stagnation point. The temperature and pressure ; contours on the impinging plate illustrate azimuthal structures for the circular nozzle, which are also confirmed by the three dimensional calculations.

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The collapsing behavior of bubble clouds in cavitating counter jets was investigated to expect the extension of collapsing area and increase in impulsive pressure. We carefully observed the aspects of cavitation clouds with the high-speed video and analyzed such characteristics of cavitation noise as acoustic power and spectrum based on the cavitation noise measured around the jet. It was found that the magnitude of bubble clouds around the impingjng area depends on the distance between two nozzles. The clouds expand more widely in a case of the standoff distance x_s/d=70, where x_s is the half distance between two nozzles, under the test condition of injection pressure P_I=30 MPa. And it was also found that string-like bubbles exist within the impinging area, which result in relatively high impulsive pressure in the case of x_s/d=190. The acoustic power calculated based on high frequency components of noise also shows relatively high values when x_s/d=70.

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With the aim to clarify the effects of leading edge sweep on unsteady cavitations, experiments were carried out on 4-bladed inducers with forward/backward leading edge sweep. It was found that, with the leading edge sweep, mean cavity length was shorter than that without sweep at the same flow rate and cavitation number. The ranges of alternate blade cavitation and unsteady cavitations, such as rotating cavitation and cavitation surge, were shifted toward lower cavitation number. In addition, it was found that the onset of unsteady cavitation depends on the steady cavity length. A simple scaling rule for steady cavitation development, first proposed by Ihara et al. (1989) for a single hydrofoil, and developed independently by Acosta et al. (1999) for realistic inducers, has been applied to the present cases. It was found that the rule reasonably explains the effects of sweep on steady cavity development. Since the stability of cavitating flow depends only on the steady cavity length, it was confirmed that the scaling rule can also explain the effects of sweep on various kind of cavitation instabilities.

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In this paper characteristics of backlayering of thermal fumes induced by emergency fires in tunnels is studied. The critical velocity used to prevent the thermal fume and smoke from backlayering upwind is firstly evaluated by this study using 3 dimensional LES turbulence model. Simulation result shows that under low heat release rate of fire, the critical velocity increases linearly when heat release rate increases, but this dependent relation will become weak under high heat release rate. Result also shows a supercritical velocity valued 2.5∼2.7 m/s exists, which agrees to the conventional experimental studies.

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The vortex structure within a separated flow region changes when the fluctuation is introduced in a mean flow. This change was investigated by numerical simulation. The artificial periodic velocity fluctuation was introduced into a mean flow upstream of the separation region. This periodic fluctuation flaps the shear layer of the separation region to make vortices be shed with the frequency of fluctuation. For making the separation region narrow, it is most effective that the introduced frequency is about harmonic of the frequency of the vortex shedding from separation region without fluctuation. So in this frequency range, vortices of the characteristic scale are shed periodically, so that this characteristic vortex scale will be significant.

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Stability of the steady state of a collapsible tube conveying fluid is investigated, using a two-dimensional flexible channel model. The model consists of a pair of elastic membranes supported by distributed nonlinear springs equivalent to the hoop tension of the tube. Perturbation equations are numerically solved using a shooting method. In the present study examined are the effects of (1) perturbations of spatial distributions of separation coefficient and viscous resistance induced by the movement of separation point and (2) a length of downstream rigid channel connected to the collapsible segment on the stability. The results show that, depending on the length of downstream channel and the flow rate, the steady states become unstable to different modes of osicillation, while the perturbations induced by the movement of separation point does not affect the stability very much.

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To investigate development of an air-hydrogen supersonic shear layer and distribution of hydrogen concentration, a hydrogen jet was injected into a cold air supersonic free-stream in a parallel direction. The free stream Mach number was 1.81, Using a catalytic reaction on a platinum wire, heat release due to catalytic reaction, a heat transfer coefficient and hydrogen concentration were measured. It was shown that parallel injection was found to affect on mixing condition. The effect of parallel injection on hydrogen concentration profile was clarified. It seemed that there was the stoichiometric condition at the outer edge of shear layer. It was confirmed that the diffusion of Hydrogen, including turbulent mixing, had an effect of flow configuration.

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This paper presents a scheme on a moving grid for 2D flow where the effect of the grid motion is incorporated into a flux term. In constructing the scheme, metrics and Jacobian are estimated numerically so as to satisfy the GCL (Geometric Conservation Law). These are presented in detail. Adopting these metrics and Jacobian, two time-implicit schemes are presented respectively in order to efficiently calculate the flow fields on both an arbitrarily and a rigidly moving grid. The validity and accuracy of the scheme are examined by calculating some examples of the flow fields on a moving grid, where an example using Navier-Stokes equations Is included for practical use in the flow field analysis. Also the problems in GCL which appear in extending the method into 3D flow are discussed.

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In this paper, dissipated wave energy, that is, output energy of the wave power device of a shallow-water soliton incident upon the air pump room in the wave power devlce is obtained by means of theoretical analysis and calculation. In the air pump room, the mass force term in proportion to vertical component of the surface velocity is supplemented to the original Euler equation. Introducing a concept of edge-layer near vertical walls of the air pump room, the matched asymptotic expansion method is applied to obtain uniformly valid solutions throughout the whole region. The matching condition yields a reduced boundary condition to be imposed on the Boussinesq equation in the shallow-water and the air pump room regjons extending on the outside of the edge-layer. Solving these Boussinesq equations by means of numerical calculation under the reduced boundary conditions thus led, the dissipated energy characteristic curve of a shallow-water soliton is plotted against the two parameters, that is, nonlinearity a and dept L of the air pump room.

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The effect of contamination on rising speed of a spherical air bubble in purified water was investigated experimentally. We developed an experimental system that uses a CCD camera coupled with a microscope. By measuring the bubble size and rising speed, we can precisely estimate the drag coefficients of the bubble below Reynolds Number of 100 in the water, where the concentrations of Total Organic Carbon (TOC and particles were controlled. The results show that the bubble behaves as fluid sphere under the condition where the concentrations of both TOC and particles (>φ0.5μm) are less than, respectively, 7 ppb (=μg Carbon/l) and 11/ml. The drag coefficients of the bubble approach to those of solid particle as the concentrations of TOC and particles in the water increase.

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The linear effect of system rotation and the implicit effect of nonlinear interactions modified by the rotation on anisotropic Reynolds stress tensor b_ij for homogeneous decaying turbulence are studied in this paper. A linear solution of the anisotropic tensor in rotating system is presented. After proposed a method to introduce anisotropy into an isotropic turbulence, direct numerical simulation (DNS) of homogeneous decaying turbulence with or without initially anisotropy is carried out. Theoretical analysis indicates that the anisotropic tensor b_ij can be split into two parts : b_ij^z and b_ij^e. DNS results show that b_ij^z decays rapidly by system rotation at the initial period of evolution and its evolution agress well with the linear solution. On the other hand, b_ij^e reflects the implicit effect of the nonlinear interactions modified by the rotation.

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Speeding up of a high speed train has been trued by means of reducing its weight, streamlining its shape, and decreasing its frontal project area. But the reduction of weight decreases the adhesion force of driving wheels to rails. So, too much reduction in weight causes slipping of the driving wheels, and the maximum speed of the train is limited to some extent. In this research we try to use the aerodynamic down-force, which is utilized widely for a racing car, to compensate the decrease in the frictional force between the driving wheels and the ground surface caused by reducing the car weight. Wind tunnel test with using a head-coach model is performed. The wind tunnel is provided with a moving-belt equipment. The down force is created In the space between the bottom surfaces of bogies and the moving belt, and is controlled by changing the shapes of the bottom surface of bogies. Lift and drag of the model, as well as velocity distributions under the model, are measured.

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A small pump (about 10mm on a side) with a rotating helical wire was developed. Hydrodynamic forces generated by the small pump were measured by varying the rotational speed of the helical wire and by varying the fluid viscosity. The measured hydrodynamic forces agree well with those predicted by using the resitive theory based on the hydrodynamics of flow at a low Reynolds number. The measured hydrodynamic forces generated by the pump were proportional to the rotational speed of the helical wire. This suggests that the small pump can be used to control hydrodynamic forces with high accuracy. Furthermore, the hydrodynamic force generated by the pump was also proportional to the fluid viscosity. This suggests that this pump is also a small viscometer.

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In this paper, computing performance of the Time-Space Method (TSM), which has been proposed as a high-speed solver for general heat transfer and fluid flow problems (Saitoh et al., 1994), was thoroughly improved. In the TSM calculations, the coordinate in the timewise direction was considered as one of coordinates in the spatial direction, thereby transforming an ordinary unsteady 3-D initial-value problem into a steady 4-D boundary-value problem. The TSM can take an arbitrary time step, and the time step is determined solely by the resolution in the timewise direction required for the solution and the degree of accuracy. The computing time will be reduced to 1/100th∼1/1000th of conventional schemes for 2-D or 3-D problems. However, in order to apply to three-dimensional larger scale problems, i.e., global warming, urban warming and general ocean circulation, an iterative method in four dimensions due to the TSM procedure shows slower convergence than that in lower dimensions. Motivated by this situation, we further improved the convergence of the TSM by incorporating some key ideas for a natural convection heat transfer problem in a 3-D cubical cavity. In addition, benchmark solutions were presented for validation of computing performance of other numerical schemes proposed.

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In this study, the direct contact melting of a porous material is investigated concerning the effects of the particle diameter, experimentally and analytically. The PCM is made of fine ice particles kept almost in a uniform diameter, which is changed as a parameter. The time dependency of the height of the PCM and the temperature of the heating surface are measured. In the analysis, two analytical models are proposed. One is calculated as the direct contact melting of the whole sample, and another is treated as the assembly of the direct contact melting of the individual particles. As the result, it was found that the amount of the melting increased with the increase in the particle diameter, due to the effects of the permeability in the case of small diameter. But, In the case of large diameter, amount of the melting decreased, as the particle diameter increased, because the direct contact melting occurred independently for the individual particles.

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In relation to the transportation of supercooled water, physical phenomena at the intial stage of solidification of supercooled water were studied, experimentally. In order to observe the inward growth phenomenon, a duct having a rectangular cross section was used. The cold copper plates with a constant temperature were placed at the top and bottom of the duct. Two side walls of the duct were made of acrylic material in order to observe the ice growth. It was found that ice grew on the inner surface towards the upstream direction at a constant speed. It related to the surface temperature and the type of the material. On the other hand, ice growth towards inside related to the inlet water temperature, surface temperature and flow rate. Type of the ice was dendrite ice. Time lag of inward ice growth and its melting at various locations were also investigated. The mechanism of the phenomenon was suggested that the existence of dendrite ice prevent a smooth laminar flow and the supercooled water near the cooling surface is mixed with the inner flow having relatively high temperature. It causes the ice to melt at downstream faster than that of upstream.

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Many kinds of the air conditioning systems with ice thermal energy storage have been proposed so far, and among them a system with a water-embedded-type ice storage vessel, in which both solidification and melting occur on heat exchanger tubes, is widely used because of its simple structure and compactness. However, the water-embedded-type ice storage vessel has a disadvantage, that is, solidification rate is very small. The use of falling water film seems to be one promising ii way of solving this disadvantage. The sensible heat in water could be quickly extracted due to high heat transfer between the solid/liquid interface and the falling water film, and the solidification rate becomes larger than that in a usual water-embedded-type ice storage vessel. In the present study, we systematically investigated the influence of tube wall temperature, film Reynolds number of the falling water and initial water temperature on the solidification rate, and a correlation between dimensionless solidified area and dimensionless time was proposed. In addition, we compared the solidification rate obtained by using the falling water film with that obtained in the usual water-embedded-type ice storage vessel. It was seen that the use of the falling water film is very effective, especially for high initial water temperatures.

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Experimental study was conducted on heat transfer characteristics in rectangular cross-sectioned two-pass serpentine channels with an inclined partition wall. The cross section of the channel at the entrance was 50 mm×25 mm, and the inclination angle of the partition (inner) wall was changed from -6° (convergent channel) to +6° (divergent channel) for three turn clearances of 30 mm, 50 mm, and 70 mm. Distributions of local heat (mass) transfer rates on the long-side wall were measured by the naphthalene sublimation method under a single Reynolds number of 3.5×10⁴. In this paper, influences of the inclination angle of the partition wall and of the turn clearance on heat transfer characteristics in the channels are discussed in detail. Then, the optimum combination of the inclination angle and the turn clearance is examined from viewpoints of the trade-off between the mean heat transfer rate and pressure loss, and of the improvement of uniformity in the distribution of local heat transfer rates.

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This paper describes the forced air-cooling with two new concepts for CPU modules with high heat dissipation. One is slit jet flow system, the other is impingement duct flow system. This electronic equipment has multiple circuit boards (CPU modules), in which CPUs have high heat dissipation and SRAMs have low heat dissipation, loaded in three dimensions and in parallel. The slit jet flow system is very simple compared with the impingement flow system that has a complicated comb-style impingement jet flow system. Moreover, the slit jet flow system has an air duct with slit orifices and an axial fan upstream from the circuit boards. The impingement duct flow system is made of an air duct and a heat sink with fan. The heat sink with fan is attached on CPU. The impingement duct flow system has slit orifices and an axial fan upstream or downstream from the circuit boards. Using the electronic equipment with the slit jet flow system or the impingement duct flow system, the increase in external thermal resistance in the CPUs and the SRAMs was measured after stopping one of the cooling fans or CPU's micro cooling fan. This result shows that the slit jet system and the impingement duct flow system have good cooling performance and redundancy.

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This study proposes a new thermal imaging system using the principle of two-color thermometry to determine the temperature of objects. The system can provide a thermal image of objects without being assigned their emissivity. Applying two-color thermometry to thermography is performed by dividing the detectable wavelength range of a radiation detector into two different ranges using respective band-pass filters. A thermal image is constructed from the two distributions of radiation energy which are measured after passing through each filter. In this study, in order to evaluate the accuracy of imaged temperature in the present system, an error analysis for imaged temperature are carried out and the accuracy in the present system is compared with those in a conventional thermography. This study also demonstrates the performance of the present system by imaging the temperature of objects with different emissivities and at different temperatures.

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A three-dimensional radiation heat transfer analysis and a convection heat transfer are combined to obtain temperature distribution in a wafer during rapid thermal processing with lamp heaters. Calculated data of the temperature distribution from the radiation analysis are transferred to the convection analysis through data files, and calculated data of the convection heat flux on the wafer from the convection analysis are transferred to the radiation analysis. The obtained temperature distributions show that the average temperature of a wafer decreases about 10°C by the effect of natural convection and that the temperature distribution in the wafer increased about 3°C when inlet gas velocity is 0.1 m/s during 1000°C steady-state heating of the wafer. It was found that the calculation mesh size for each analysis of the combined analysis can be changed.

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Condensation/evaporation coefficients for interphase mass transfer between liquid and vapor are studied based on the transition state theory and the molecular dynamics simulation (MD). The condensation coefficient is obtained to be a ratio of partition functions for activated complexes to those for vapor molecules. In a similar way the evaporation coefficient is correlated with a ratio of partition functions between the activated complexes and liquid molecules. The transition state theory indicates that the translation motion of the activated complex is dominant compared with the rotational motion even for multi-atomic molecules. Since the activation energy is also important, an evaluation of the activated state is presented by applying our MD results on argon and water molecules. We can find that the theory can explain the MD results on the condensation/evaporation coefficients.

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A prototype Stirling cycle refrigerator employing helium as a working fluid has been investigated to see whether a freon free machine be a viable alternative for a current household refrigerator. A displacer type or β type Stirling cycle machine of 100 W capacity was designed and tested varying design parameters such as dead space ratio, working fluids, the ratio of the compression space volume to the expansion and the phase difference between a power piston and displacer. The detrimental effect of the dead space on the refrigeration available was confirmed. The refrigeration produced by nitrogen in a expansion space was smaller by 28% than that produced by helium. The optimum volume ratio and the phase difference for a maximum refrigeration have been determined under a design operation condition. Moreover, The refrigeration correlation formula as a function of these parameters was shown.

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Effects of ultra lean premixed gas (ULG) on extinction of adjoined lean premixed flame have been studied numerically, using a detailed chemical model of 177 reaction steps with 32 species. The extinction phenomena of the methane / air flame formed in the counterflow of lean mixtures can be divided two distinct regimes depending on fuel concentrations of leaner side mixture. With the equivalence ratio of the leaner side mixture above approximately 0.4, twin flames are in existence and strongly interact each other. With the leaner side below 0.4 ; the ULG condition, the interaction is weak and the thicker side mixture mainly influences the extinction. However, the ULG side condition affects the extinction boundary slightly even in the weak interaction region. Though the visible flame and the CH peak in the ULG side cannot be observed, the calculated heat release profiles reveal that the reaction in the ULG side exists even in this region. This heat release which is supported with molecular level heat and mass transfer from the flame prevents the heat loss of the flame and extends extinction limits. These diffusion-controlled phenomena play a key role on the effects of the ULG on the flame extinction in the weak interaction condition.

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HURAMAC, a ram accelerator facility at Hiroshima University, has a unique feature, that the ram acceleration tube has rectangular cross section. This rectangular bore ram tube enables itself to install the optical windows and visualization inside the ram tube can be realized. Burning flow fields around the accelerating projectile are investigated for the thermal-choking mode in methane-oxygen-carbon dioxide gas mixtures by taking pictures using an instantaneous shadowgraph method as well as by getting pressure histories at the upper wall of the window section. Three typical shots with different velocities are compared. It is shown that the position of the leading flame held at the surface of the projectile depends on the velocity. It is also found that two stable flame holding positions exist. The position of the flame so much affects the flow pattern around the projectile.

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Experiments have been carried out to examine the behavior of irregular flame propagation in a closed bomb, which appears in very lean propane-air mixtures, and to examine how the lean limits of flame propagation in a long tube are influenced by its diameter. The microgravity technique achieved in a freely falling chamber is employed because the realizations of symmetrical flame propagation in a closed bomb and in a long tube are possible. Experimental condition for the initial mixtures corresponds to room temperature and 0.1 MPa and the fuel used is propane of 99.9% purity. The experimental results show that (1) the flame propagation behavior of propane-air mixtures in a closed bomb close to lower flammability limit is irregular during the burning process and its irregularity occurs when Lewis number is larger than unity, (2) though the lean limit of the flame propagation in a long tube decreases with increasing its diameter, it holds constant when the tube diameter is more than 40 mm, and (3) under microgravity Its limit shifts to lower value more than that obtained under normal gravity.

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New analysis model for catalytic combustion of natural gas in honeycomb was developed. In the new model heat of reaction, thermal radiation, heat conduction, and heat transfer were taken into consideration and temperature dependent reaction model based on the evaluation of catalytic activity was introduced. With the new model numerical analyses were performed to explain the effect of fuel consumption rate, air excessive ratio, diameter of honeycomb cells, axial length of honeycombs and base materials of honeycombs on the characteristics of catalytic reaction. The results prove the propriety of the new model and clarify the effect as follows. (1) The axial position of maximum catalyst temperature shifts dependent on the fuel consumption rate and air excessive ratio. (2) The axial temperature profile of catalyst and burning rate were controlled by the most suitable selection of the diameter of honeycomb cells, axial length of honeycombs. (3) The conductivity of base material has much influence on the characteristics of thermal radiation and heat conduction.

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When Three Way Catalyst (TWC) was used for exhaust gas purification, A/F should be controlled within the window range to keep high conversion efficiency of exhaust gas. However, it was difficult to keep A/F within the window when an engine of the automobile was accelerated or decelerated, even if FF control was excuted. Then, A/F pulse width and amplitude modulation algorithm was proposed as an other approach to improve the conversion efficiency at transient state. This method was to use the O₂ storage capacity of TWC efficiently. For this purpose, A/F periodic operation was set to be the best for the conversion efficiency at the transient state. The algorithm of this method was investigated and good experimental results were obtained.

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Exhaust gas odor in DI diesel engines is reduced mainly by improvement of in-cylinder combustion and by catalytic converter. In this study, the effect of high-pressure injection and an oxidation catalyst on the exhaust odor was investigated by engine with common rail high pressure injection system. At idling condition an injection pressure of 60∼80 MPa showed minimum exhaust odor, total hydrocarbon (THC) and the least aldehyde. However the odor reduction by high-pressure injection is not sufficient. The preconditioned catalyst aging under the high temperature reduces exhaust components and odor just after starting due to good adsorption. At the catalyst temperature above 200°C, there were remarkable reductions of odor, but bellow 200°C, objectionable exhaust odor appears sharply.

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