The purpose of our study is to analyze the engineeringly turbulent flows. In these case, LES (Large Eddy Simulation) is expected to be the most effective method. Since three dimensional unsteady calculation is carried out in LES, it is possible to understand the flow visually using computer graphic system and to offer useful information. In order to achieve the purpose, it is necessary to analyze the benchmark problem and to show the effectiveness in the first step. In this paper, a turbulent channel flow at Re_τ = 360 based on the friction velocity u_τ and channel width δ is analyzed using the Dynamic Smagorinsky model with GSMAC (Generalized Simplified Marker and Cell) FEM. In order to confirm its effectiveness, numerical results are compared with the DNS data and other results and the present scheme is verified.

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The transport equation of subgrid scale (SGS) kinetic energy, K_SGS, is used for the large-eddy simulation (LES), considering its possible consistency with dynamic procedure. The smallest scale portion in computationally resolved turbulence, which can be estimated in the dynamic model, has closer relationship with largest scale in SGS. Therefore the dynamically determined parameter is more suitable for describing the energy transfer between resolved and SGS turbulence, rather than the energy dissipation through the SGS eddy-viscosity in the filtered equation of motion. Such an energy transfer is represented by the production term in the transport equation of K_SGS in our model. Computational examination has been conducted for fully developed turbulent flow in a plane channel. Agreement with DNS database was fine and it was improved by refining the grid.

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Shapes and rising velocities of single bubbles rising through vertical pipes were measured under stagnant, laminar flow and turbulent flow conditions to examine the wall effects on the drag force and bubble shape. Experiments were conducted using air and water, and three pipes of inside diameter D = 13.3, 15.9 and 24.8mm. The ratio λ of equivalent bubble diameter d to D was varied from 0.2 to 2.0 in each experiment. The drag coefficient was correlated in the form of C_D0φ>(λ) where C_D0 is the drag coefficient of a bubble in an infinite stagnant liquid and the multiplier φ(λ) is given as the arithmetic mean of Clift's and Wallis's multipliers. Bubble shapes were expressed as a function of the liquid Reynolds number. It was also confirmed through interface tracking simulation that the proposed correlations are applicable not only to the air-water system but also to a low viscosity system, the Morton number of which is less than 10^-8.

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To clarify the mechanism of noise generation from a low pressure axial flow fan, time fluctuating velocity was measured around the rotor blades, especially near the rotor tip, by using a hot-wire sensor from a relative flame of reference fixed to the rotor blades. Two sensors were used to obtain the cross-correlation between velocity fluctuations at the reference point and other locations. The results are summarized as follows. If the flow rate was lower than the design condition and the tip leakage flow became to attach to the following blade, the sound pressure level was increased. From the cross-correlation of velocity fluctuations the leakage flow flew downstream spirally, in which a discrete frequency velocity component with low frequency was predominant. It is possibly considered to be the cause of the noise generation of low frequency band.

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The new PIV image processing method is proposed to apply to the cavitation flow field. Two CCD cameras take each image shots of good quality utilizing the difference of the scatter light intensity between the seeding particles and the bubbles. From the image of the seeding particles, the cavitation aspect information such as the equivalent void fraction and the cavity boundary is obtained by using the binary process of the light intensity. From both images of the seeding particles and the bubbles, two velocity informations are obtained individually inside or outside area of the cavity by using the cross correlation method and finally composed into one. For the evaluation of this PIV measurement and processing, the experiment was carried out about the wake vortex cavitation flow behind a wedge. And also, cavity boundary, equivalent void fraction, velocity vector and vorticity map were discussed in detail.

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The objective of this study is to promote disintegration of liquid jet by cavitation inside the nozzle. Using 2 D nozzle, the effects of the nozzle dimensions on the liquid breakup are investigated. When L/W of the 2 D nozzle is low, disturbance of the liquid flow due to cavitation inside nozzle is maintained from the inlet to the outlet of the nozzle, significantly promoting breakup of the issuing jet. The similarity between the cylindrical nozzle and the 2 D nozzle are found for the disturbance inside the nozzle and the breakup of issuing liquid jet.

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A control of periodic vortex shedding behind a cylindrical bluff body has been made experimentally by vibrating side-plates with piezoelectric actuators. Entrainment of the vortex shedding frequency occurs by the vibration with amplitude of 20∼65 μm. The entrainment effect is evaluated quantitatively by introducing an integral scale of the frequency in the power spectral density distribution. When the side-plates are vibrated with an opposite phase in a half span of the body, the vortex shedding follows up the vibration. In the mid span, a switching phenomenon of the vortex shedding is observed.

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In our previous researches, we estimated the reduced quantity of aerodynamic drag of trains by smoothing under-floor construction. However, we did not compare the results of wind tunnel tests with those of on-track tests, or verify the accuracy of wind tunnel tests for the aerodynamic drag of trains. In this research, we estimated the aerodynamic drag of a train-set by wind tunnel tests. Regarding the reduced quantity of the aerodynamic drag of trains, we compared the results of wind tunnel tests with those of on-track tests. These test results show that the reduced quantity of the aerodynamic drag of trains by wind tunnel tests approximately agrees with that by on-track tests.

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Tunnels in the New Toumei-Meishin expressway have large cross sectional areas in order to accommodate three lanes of traffic. However, the amount of heat released and smoke generated when fires occur in tunnels with such large cross sectional areas has not been studied. In this study, results of three-dimensional large eddy simulations (LES) are compared to full-scale experimental results in order to determine heat release rates from fires in tunnels having large cross sectional areas. It is shown that the maximum heat release rate increases proportionally with the fire source size, i. e. the gasoline pool area, while ventilation velocity has little effect on heat release rate. It is also found that heat release rates in tunnels with large cross sectional areas are much larger than in conventional two-lane tunnels.

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In order to introduce wind turbine generator system (WTGS), an assessment of the wind energy resources is inevitable. While the use of WTGS expands over the world, complex terrain has become important as the site proposed for a WTGS. In those region contribution of local effects on the wind energy resources is quite large and intensity of wind turbulence, which brings about complicated aerodynamics loads on the wind turbine, is much larger than that over the flat terrain. The purpose of the present work is to clarify the influence of the complex terrain on the atmospheric boundary layer flow, especially focusing on the turbulence characteristics of the wind flow. The wind measurements were carried out at Tappi Wind-Park during the period from August 22nd to November 6th in 2001. We evaluated the influence of the slope on the vertical profile of mean wind speed and the integral scale of the turbulence, and examined the power spectrum of the wind fluctuation. The influence of the wake from the neighboring wind turbine has been also extracted from the wind measurement.

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The low-pressure axial flow fans with an outer ring, used for cooling automobile radiators, have a significantly large tip clearance between the ring tip and the fan shroud. It has been found that the turbulent reverse flow, which occurs at the tip clearance, greatly affects the fan performance and noise level. Therefore, in order to improve the fan performance and noise level it is important to decrease the effect of leakage at the tip clearance. The authors investigated the performance of the straight-through type of labyrinth seal which operates in an extremely low static pressure difference with a large clearance. It was hoped that by sealing this clearance with the labyrinth seal the performance would be improved. It was verified that the labyrinth seal satisfied almost the same performance as that predicted by the previous theory. This theory was established by experimental studies in the condition of quite high static pressure difference when the labyrinth is stationary. However, it was later discovered that the leakage rate decreased significantly even though there was far lower ring speed in comparison to past research results where the ring rotated. This phenomenon is conspicuous in a lower differential pressure. However, the cause of this phenomenon has not been determined.

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This paper discusses the straight-through type labyrinth seal. This labyrinth seal is used for axial flow fans, which have an outer ring at the blade tip to seal the clearance between the ring tip and the fan shroud, in order to prevent the reverse flow or leakage. These fans are used for the cooling of automobile radiators. In these cases, the labyrinth seal is used in an extremely low static pressure difference and a large clearance. A significant decrease of the leakage rate was reported even when the labyrinth seal rotated in comparatively low speed in this unique condition according to the authors' former report. However, this phenomenon is different from past research. Furthermore the cause of this phenomenon has not been determined. Therefore, the internal flow was depicted with Computational Fluid Dynamics (CFD) in order to clarify the cause of this phenomenon. The results of CFD show that the leakage rate decreases significantly because the carry-over flow is intercepted in the expansion groove. This is the newly discovered phenomenon which occurs under the unique condition of an extremely low differential pressure. It has not been pointed out before as the reason why the rotation decreases the leakage rate.

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We proposed a new type of viscous fluid damper of non-sedimentation type having complex fluids : MF (magnetic fluid), MR (magneto-rheological fluid), MCF (magnetic compound fluid). The damper never has the sedimentation of particles by using permanent magnet settled in a cylinder. We also used an electro-magnet by applying steady or fluctuating magnetic fields and then the damper is suitable as semi-active damper. To investigate the effect of damping, we measured displacement ratio under low frequency of the vibration. By comparing among the differences of the damping effects by three kinds of the fluids, MCF has the largest damping effect. In case of using fluctuating magnetic field, it is also larger than in that of steady magnetic field. The cause is due to the cluster of particles aggregated like a chain or necklace in the MCF.

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A Vibrating Elastic Plate Flow Generators (VEPFG) induces a strong fluid jet by a thin plate excited at the leading edge. The fluid-dynamic performances and working conditions of a VEPFG with mass ratios sufficiently high were analyzed by use of a method based on small perturbation and potential flow concept, including forces of elasticity, inertia, and fluid-dynamics. The optimum performances were found to be obtained close to resonant conditions ; the thrust coefficients are of the order of 1×10⁶, quite high compared with those for low mass ratios, which are unity at most. The efficiency levels, however, are of the order of 50 percent, relatively low compared with those for the low mass ratio region, which are above 95 percent. The feature might make the high-mass-ratio VEPFG a very compact and powerful flow generator, particularly in air.

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Using the time-space averaged momentum and energy equations obtained in the preceding report, a theoretical relation was derived to estimate the drag increase and the heat-transfer enhancement in the channel with a turbulence promoter. The investigation of the relation and the results of DNS for the channel with a wing-type vortex generator (VG) show that the heat-transfer efficiency η (i. e., the ratio of the heat transfer enhancement to the drag increase from the smooth channel) is larger when VG is installed in the laminar flow than in the turbulent flow from the following reasons. (I) The large pressure drag on VG in the turbulent flow decreases η. (II) The change of velocity distribution from the laminar parabolic one increases the convective heat transfer near the wall. This effect raises η without the penalty of drag increase.

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An experimental study is performed on free convection heat transfer in a stably straified fluid between coaxial cylinders. The stratified layer is formed using a sucrose aqueous solution, and is heated from the outer cylinder at constant heat flux and cooled from the inner cylinder at constant temperature. The experimental results shows that the heat transfer in a stratified fluid is quite different from that in a non-stratified fluid. The effects of the stratification appears conspicuously in the lower part of the fluid : the formation of small cellular convection layers leads to marked deterioration of the local heat transfer coefficient in the lower part, whereas the local heat transfer coefficient increases in the downward for a non-stratified fluid. When the convection layers in the lower part grow thick and contact with the cooling surface of the inner cylinder, the local heat transfer coefficient rapidly increases and approaches that of non-stratified fluid. Mean heat transfer coefficient is governed by such characteristics of the heat transfer in the lower part.

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For condensation from a steam-gas mixture flowing normal to horizontal rows of tubes, an approximate equation was obtained with an analogy relation between heat and mass transfer taking account of the mass absorption effect on the wall in the previous study. These correlations gave good predictions when the non-condensing gas fraction was more than 75%. At the fraction less than 75%, some modification is necessary on the mass transfer correlation because it was obtained from the heat transfer correlation without the condensation. Condensation heat transfer on horizontal stainless steel tubes was investigated experimentally for the modification of mass transfer correlation. The experiment was conducted in a wide range of non-condensing gas fraction and the modification was proposed.

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A gas engine heat pump (GHP) is the type of compression heat pump that is driven by the motive power from the gas engine. To improve the performance of this GHP greatly, it is necessary to add the heat pump driven by the waste heat from the gas engine to the GHP. This paper suggests the new hybrid heat pump in which the waste heat driven heat pump is combined with the compression heat pump. This system can be driven by the motive power and the waste heat from the gas engine simultaneously. In this paper, the hybrid heat pump whose waste heat driven heat pump is the absorption heat pump is adopted. The working-fluids are ammonia and water. The performance of this hybrid heat pump is analyzed with the simulation. As a result, it was found that gas engine hybrid air conditioning system with the new hybrid heat pump can realize the very high efficiency-primary energy ratio is about 2.4.

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This paper has dealt with the natural convection heat transfer of the microcapsule slurry composed of phase change material (PCM) as a latent heat storage substance. A rectangular cavity with two opposing heating and cooling vertical walls was selected as the present research model. The temperature difference between heating and cooling walls, the width of the cavity and the PCM concentration were set as parameters of natural convection heat transfer. The heat transfer coefficient of heating and cooling wall, the flow velocity profile and the temperature distribution of the microcapsule slurry were calculated by numerical computation. It was clarified that the transportation of latent heat evolved by melting and solidifying of the PCM in the slurry exerted on a strong influence on the natural convection heat transfer. Moreover, it was found that the heat transfer coefficient reached at the local maximal value with an increase in temperature difference between heating and cooling walls. In addition, Nusselt number was influenced by the transportation effect of latent heat that was caused by melting and solidifying of the PCM. The numerical results revealed quantitatively that the natural convection heat transfer depended on the PCM concentration, temperature difference between heating and cooling walls, and width of the rectangular cavity.

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In order to clarify the effects of mixing on the temperature dependence of ignition delay in fuel sprays, experiments were conducted for n-heptane spray in a constant volume vessel. The results show that negative temperature coefficient (NTC) is observed at low ambient pressures accompanying two stage ignition. High-speed shadowgraph images of spray indicate that at a temperature in the NTC region, ignition initiates in wellmixed mixture along the combustion chamber wall. The reason of NTC phenomena in the fuel spray is theoretically elucidated considering the change of ignition delay according to the evolution of equivalence ratio and temperature in the spray.

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An experimental study was made on the flame propagating through a lean methane/air mixture flow with periodic concentration fluctuation by using an original stagnation flow type burner. The burner was devised so as to fluctuate the mixture concentration (equivalence ratio) only in the direction of flow of constant velocity. For the fluctuation with the mean equivalence ratio of 0.85, the amplitude of 0.06 and the frequency ranging from 3 Hz to 50 Hz, the following results were obtained : (1) Phase difference exists between the fluctuations of burning velocity and flame position in the stream and the former fluctuation precedes the latter one, meaning that the fluctuating flame has the maximum burning velocity (the minimum burning velocity) before it gets to the uppermost stream (the lowermost stream). (2) For a certain range of the fluctuation frequency, the maximum and minimum burning velocities of the flame are higher and lower, respectively, than those estimated for the mixture equivalence ratio fluctuation at the burner exit. Similar tendencies are found for both the temperature and the CO concentration of the burnt gas. This can be caused by the periodic change of the direction of flame movement ; when the flame moves against (along) the fuel flow, the mass flux at the flame front increases (decreases) as compared with the stationary flame.

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In this study, we applied luminous spectroscopic analysis and Planar Laser Induced Fluorescence (PLIF) method on lean Homogeneous Charge Compression Ignition (HCCI) combustion to obtain some ideas of ignition timing control and combustion rate control methods in HCCI engines. In the tests, we used an optical access engine and n-C₁₂H₂₆ as a fuel. Inlet air temperatures and inlet oxygen concentrations were changed as the test parameters, and the following conclusions were obtained : (1) After low temperature reaction, LIF signal from hydrocarbon was disappeared. This was because that hydrocarbon was changed to another molecules or per oxides. (2) In high temperature reaction region, OH radical was appeared across a wide area in the combustion chamber.

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Homogeneous Charge Compression Ignition (HCCI) engines with lean fuel/air mixtures have a number of advantages over conventional spark ignition engines and compression ignition engines. As the onset of HCCI combustion depends on the autoignition of the fuel, it is quite difficult to control the start of combustion directly. The experimental results showed that Pulsed Flame Jet (PFJ) behaved as a trigger for the autoignition of the fuel in the combustion chamber. Therefore it was revealed that PFJ has a potential for controlling the start of HCCI combustion directly.

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An impinging distribution spray combustion system, named OSKA, was applied to a small direct injection diesel engine in order to reduce the wall quenching originated emittants, e. g. SOF and THC. Experimentation was carried out using a single cylinder engine of bore × stroke of 93×92 mm, with varying the piston cavity geometry and, the injection and impinging conditions. The combustion chamber geometry has great effects on emission characteristics and performances. KIVA 3 numerical analysis on the flow characterization has helped to interpret these effects. It also clarified the effect of dimple.

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A series of experiments were carried out to evaluate the simultaneous NO_x and SO_x removal using the plasma-chemical hybrid process and to quantify all the reaction byproducts such as N₂O and CO. The oxidation from NO to NO₂ without decreasing NO_x concentration and with least power consumption is the key for obtaining the optimum reactor operating condition. The produced NO₂ was totally converted to N₂ and Na₂SO₄ with Na₂SO₃ or Na₂S by the chemical reactor, while NaOH was used to neutralize H₂SO₃ and H₂SO₄ in the solution. The final products is water soluble and nontoxic Na₂SO₄. The NO₂ reduction was more effective for Na₂S than Na₂SO₃ but 2 ppm of H₂S was produced. The hybrid process showed nearly 100% NO_x and SO_x simultaneous removal with less than 11 ppm of N₂O and CO, and the power consumption using the pulse plasma reactor was less than 1/4 using the packed-bed plasma reactor.

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