A vortex anemometer measures the free stream velocity U utilizing the fact that vortex shedding frequency f_v is nearly proportional to the velocity U. In this work, In order to enable to apply it to the low velocity range in wind tunnel experiments, a vortex anemometer was devised using a ring as the vortex generating bluff body. A wind tunnel and a water tunnel were used to obtain the relationship between the Strouhal number St and Reynolds number Re. Results of water tunnel and wind tunnel experiments correlated well and gave a function St(Re) in an extensive Re range. Experiments using three rings with geometrically similar configurations to the prototype ring mentioned above, but with different dimensions, showed universality of the function St(Re). A function for the relationship between f_v and U is proposed from the function St(Re), so that the ring-type anemometer has a higher reliability in a low velocity range where the Pitot-static tube and a manometer system can not be applied. Since it has a very simple configuration, the size can be made small enough to be an alternative of a standard Pitot-static tube.

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The effect of system rotation on energy spectrum, energy transfer function and triadic energy transfer function is investigated using the DNS data of homogeneous decaying turbulence subjected to system rotation. The DNS is performed with 128 Fourier modes at various rotation rate up to 50[rad/s]. The initial Taylor micro-scale Reynolds number is 53.6. The results of this study are summarized as follows : (1) The profile of the energy spectrum approaches the linealized solution with an increase in the rotation. That is, the decay of the energy spectrum is inhibited and promoted in low and high wave number regions, respectively, by the rotation. The absolute value of the energy transfer function decreases with an increase in the rotation. This phenomena is explained by scrambling effect. (2) The rotation gives the directional anisotropy on the energy spectrum and energy transfer function. However the effect of the directional anisotropy on the energy spectrum becomes negligible when the rotation rate is too high. (3) The triadic energy transfer is also prevented by the rotation. The local energy transfer is dominant in the non-local triad for both rotating and non-rotating systems. The rotation also gives the directional anisotropy on the triadic energy transfer function.

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Flow in the vicinity of free surface induced by a bubble plume is utilized as one of effective ways to control the surface floating substances on lakes, oceans, as well as in various kinds of reactors handling a free surface. In this work, a two-dimensional flow analysis based on Eulerian-Lagrangian model and particle tracking velocimetry measurement have been carried out in order to elucidate the surface flow generation process in detail. The present results explore the following points : 1) Surface velocity profile can be predicted by the Eulerian-Lagrangian model with a good agreement with experimental results, 2) maximum velocity of the surface flow increases as large void fraction with small bubble size is supplied, 3) The surface flow is effectively generated in case of bubble plume compared to liquid jet flow because distortion point appears in the vicinity of surface.

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Due to the translational motion of a bubble, droplet or particle, the pressure averaged over its surface is less than the bulk one. In the present study, the depressurization behavior of a spherical body is studied for various Reynolds numbers by the theoretical and the numerical approaches. A dimensionless number C_TDP, which is the depressurization scaled by the fluid density and the translational velocity, is defined. For a small but non-zero Reynolds number, the C_TDP is asymptotically obtained by the Stokes expansion method. The result shows that the C_TDP is finite and it is given by the function of the viscous ratio (μ_p/μ_f). The direct numerical simulation (DNS) is also conducted to obtain the C_TDP in the moderate Reynolds number. At the smallest Reynolds number (Re=0.1), the present DNS results of a clean bubble, a droplet and a rigid particle agree well with the present theoretical results. The C_TDP of a clean bubble monotonously increases with the Reynolds number and it approaches the solution of the potential flow (1/4) at the high Reynolds number. On the other hand, the C_TDP of a rigid particle does not monotonously increase with the Reynolds number and it has maximum value at Re∼O(100) due to the flow separation.

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The prediction of the behavior of a rising bubble near a wall is very important to control a bubbly flow in chemical reactor, or to develop the drag reduction devices using micro bubbles etc. In the present study, theoretical analysis of a deformed bubble rising near the wall is conducted. In the former experimental studies, there is a qualitative discrepancy between the theory for a spherical bubble and experimental results in the low Reynolds number cases. It is well-known that there is no lift force acting on spherical bubble under the creeping now approximation due to the kinematic reversibility. Therefore, in case of the theory of a spherical bubble, weak inertia effect must be taken into account to obtain a lift force. However, there is another possibility to have a lift force, that is, a deformation of bubble. In the present study, to estimate the effect of deformation, we conduct the donlaln perturbation analysis using Lamb's general solution for Stokes flow. The expression for the lift force due to the deformation is shown with the higher order extension. It is also shown that the slight deformation effect becomes more important as a bubble rises closer to the wall and the effect will become larger than that of small inertia below a certain distance from the wall.

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In the twin-rotor type turbine meter measuring system of multiphase flow rate requires homogenized flow of gas and liquid. Therefore, we developed the static mixer to mix them. The mixer pressure loss must reduce due to the line of energy consumption. This paper discussed the homogenization and minimization of two-phase flow, liquid and gas, by the mixer which are compounded of a twist-plates and two-stages WA type static mixer. It is clear that the compound mixer is excellent compared of the four-stage WA type mixer for the pressure loss and mixing effect. Finally, it can be said that the compound mixer is satisfactory for requirement of engineering.

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The swirling jet which impinged on the solid surface was investigated experimentally. The flow visualization was done using smoke-wire method, and the flow near the impingement region was clarified. The measurement of three components of mean velocity and fluctuation velocity was made by rotating probe technique by inclined hot-wire. Each distribution of mean velocity, Reynolds stress ; and wall pressure was illustrated, and the jet characteristics was examined. The experimental result was compared with existing result of the swirling jet which gushes in still air out or existing result of the jet without swirl which impinges on solid surface, and effect of impinging surface on the jet and effect of the intensity of swirl were examined.

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Experimental studies on the lift act on a small disk levitated by a circular impinging jet with confining wall were carried out. The diameters of upper and lower disks were 100 mm and 20∼30 mm, respectively. The mass of the lower disks ranged 1.5∼52 g. The behavior of levitation of the disk and the pressure distributions on the disk were measured in the range of the space between the two disks from 0.5 to 6 mm in the range of the flow rate 10∼50 l/min, and the surface oil-flow patterns on the both disks were visualized. The levitating and falling critical flow rate were obtained by the dimensionless quantities. And the dimensionless lift act on the small disk was also obtained. The lift is almost equal to the weight of the disk. The levitation of the disk depends on a large pressure drop which caused by the vena contracta due to the separation bubble attached on the upper disk.

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Weak pressure waves similar to blast waves are generated in an exhaust pipe of engines of a car during running at high speed. When the waves emitted from the end of the exhaust pipe, a jarring noise is generated. To diminish such the noise effectively, a sub-silencer is installed in front of a main-silencer in the exhaust pipe. In the present study, four types of expansion region were investigated by measuring the pressure decay in the test section. A two-stage expansion model was the most effective to decrease the peak over pressure of the blast waves.

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A double volute casing is widely used to balance the radial thrust of centrifugal pumps, but the optimum volute configuration has not yet been determined. The purpose of this study is to search for the optimum design of a double volute, and several configurations have been investigated. Experiment using the double volute of two-dimensional shape has been performed to investigate the internal flow characteristics, and the changes of both pump overall performances and radial thrust due to the difference of volute configuration have been measured and discussed. The results showed that the best efficiency point of the double volute pump shifts to 90% design flow rate and the main reason of the performance drop by the double volute is attributed to the mixing loss at the volute outlet. The outer channel flow is not effective as the diffuser and the pump performance can be improved by changing the inner volute wall configuration. And the optimum design of a double volute is proposed.

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Demands for higher performance of axial flow pumps have led pump designers to consider the creative strategies for the new type. As a solution, contra-rotating rotors might be applied to a pump. Comparative experiments were conducted for two types, consisting of contra-rotating rotors and a rotor and a stator respectively, which were designed under the same specifications of pump head, flow rate and rotor specific speed. The measured pump performances and flow distributions are shown and the advantages of using contra-rotating type are clarlfied as follows. Contra-rotating type is superior in pump efficiency and cavitation performance in range of partial flow rates to conventional one though the specified pump head and maximum efficiency were not satisfied at design point in the case of contra-rotating test rotors. Results demonstrate that the rear rotor design is important to improve the pump efficiency.

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An experimental study is presented on free convection laminar film condensation of steam-air mixture on a vertical tube. The test tube used is of about 220 mm height and about 6 mm outer diameter. The range of concentration of air is 0.1∼0.9. The average heat flux values or average heat transfer coefficients obtained have been about 2.5 times larger than the corresponding values from the two-phase boundary layer theory for a vertical flat surface. The enhanced values are quantitatively explained by the curvature effect upon the vapor boundary layer, which is analogically derived from single phase free convection heat transfer.

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Pressure drop and heat transfer characteristics of flow in channels with periodically grooved parts are investigated for various configurations of the channel, the Reynolds numbers up to 500 and the Prandtl number 7. The flow and temperature fields are assumed to be two-dimensional and fully developed and the wall temperature is kept to be constant. Heat transfer increases significantly after the bifurcation from steady state flow to oscillatory one with the increase of pressure drop penalty. The efficiency defined as the ratio of the heat transfer enhancement to the drag increase is obtained against the Peclet numbers. It is found that the channels with expanded parts show the efficient performance, while the channels with contracted parts are inefficient.

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A numerical analysis based on adjoint formulation of unsteady forced convection heat transfer is proposed to generally evaluate the heat transfer characteristics under arbitrary thermal boundary conditions. A numerical solution of the adjoint problem enables us to predict the heat transfer characteristics, such as the total transfer rate or the temperature at a specific location, for arbitrary time changes of the thermal boundary conditions. Moreover, using the numerical solution of the adjoint problem, we can obtain the optimal thermal boundary conditions in both time and space to maximize the heat transfer at arbitrary time. Numerical solutions of the adjoint problem in a lid-driven cavity are presented to illustrate the capability of the present method.

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The characteristics of ice melting heat transfer in a horizontal elliptical tube in water were studied experimentally and numerically. This phenomenon is caused by a combination of the natural convection heat transfer of water around a tube and the ice melting heat transfer inside a tube. Large number of studies on melting heat transfer in a simple shape capsule has been done ; however, study of melting heat transfer in a horizontal elliptical tube is less. Results are presented as ice melting characteristics, temperature distributions, flow patterns and melting rate.

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Karman vortex structure behind a highly heated cylinder in a turbulent crossflow has been studied experimentally. The surface temperature of the cylinder is set up to 800°C. The Reynolds number based on the cylinder diameter is 750. For the heated cylinder set in the turbulent crossflow, the Karman vortex street can be clearly observed as the cylinder temperature is increased. Since the local temperature of the generated vortex is remarkably high compared with the main flow, the Karman vortex dissipating energy due to the main flow turbulence decreases with an increasing the cylinder temperature. Then, the local temperature of the vortex also decreases due to the turbulence motion. As the results, the vortex frequency-decreasing rate due to the cylinder heating in the turbulent crossflow becomes 1/2 compared with the laminar case.

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Phase-change velocity and its related physical constants of super-heated water at the liquid surface can be determined by hydrogen bonding and by utilizing the Maxwell-Boltzmann principle. In this paper, we introduced a physical constant and attempted to demonstrate the existence and value for this physical constant. To achieve this, we first measured temperature fluctuation under the bubbles within a pool of boiling water. To further determine the physical constant, a sample analysis model was introduced, and comparisons were made between the experiment data and these calcula-tions.

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The optimal operation of an exhaust heat recovery system in a gas engine cogeneration is investigated in consideration of the influence of chilled and cooling water temperatures on the performance characteristics of exhaust heat and gas fired absorption refrigerators. First, a simulation calculation is carried out to evaluate the performance characteristics of absorption refrigerators. Second, an optimization calculation based on the mixed-integer linear programming is carried out to determine the on/off status of operation and energy flow rates of equipment. In a case study, it is clarified how the strategies for controlling the load of the gas fired absorption refrigerator affect the optimal operation and running cost of the system, and how the optimal operation is advantageous as compared with a conventional one.

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Unstable behavior of detonation waves and re-initiation process are studied in terms of the decoupling of the detonation front. The arrival of the shock front and the reaction front is detected individually by a combination probe which consists of a pressure and an ion probe. The experimental results show that acceleration of the reaction front after the decoupling accounts for detonation re-initiation. The calculated re-initlation point and pressure profiles which are derived from the motion of waves generated by the accelerating flame agree well with the experimental observations.

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Methanol has many advantages as a fuel for automobile use fuel cells compared with hydrogen. There are two types of fuel cell systems using methanol. One is methanol reform type, and the other is direct methanol type. The direct methanol fuel cell system consists of simple and compact equipments, and suited for automobile use. This research analyzed characteristics of power output and thermal efficiency in a direct methanol fuel cell using a newly developed methanol concentration measuring system. Influences of membrane thickness, cell temperature, and methanol solution concentration on power output and thermal efficiency were analyzed.

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A molecular dynamics simulation model has been developed and used to investigate microscopic transport mechanism and various physical properties In the electrolyte membrane for polymer electrolyte fuel cells. It has been succeeded to quantitatively predict the experimental facts that the diffusion coefficients of positive ions and water molecules in the polymer electrolyte are one-order smaller than those in the aqueous solution and that the O-H vibration spectrum has higher frequencies than that in the liquid water. The very low diffusivity in the polymer electrolyte is due to the fact that polar particles form the disordered heterogeneous structure of hydrophilic region constituting transport paths for ions and water molecules. About 80% of positive lons are bonded with sulfate anions at the end of side chains in the polymer and move sequentially from one sulfate anion to the other in the vicinity within 5Å about two or three times per nanosecond. This transport mechanism of ions implies that the main constraining factors for the ion transport in the polymer electrolyte are the coulomb interaction with sulfate anions and the tortuosity of hydrophilic region. Based on the results, guiding princlples to enhance the ion diffusivity in the polymer electrolyte have been proposed.

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A Bunsen type propane-air premixed laminar flame was formed within a vertical tube, of 51 mm inner diameter and 500 mm length, placed at the center of a super-conductive magnet generating a nearly uniform upward magnetic field of 5 T. It was observed how the magnetic field affected the flame contour and burning velocity as well as the distribution patterns of gas temperature and nitrogen oxides (NO and NO₂) concentrations in and around the flame. The influences of secondary factors, such as flame fluctuation, natural convection and the slight nonuniformity in the magnetic field, originating from the structure of the super conductive magnet, are overlaid on the direct effects of the magnetic field. Moreover, the former are more prominent than the latter. Careful investigation was, therefore, necessary to extract or separate the direct effects of the magnetic field from the indirect ones caused by the secondary factors. It appeared that the phenomena such as flame propagation, which were dominated by high-speed chemical reactions, were hardly affected by a magnetic field as intense as 5 T. It is probable that phenomena such as nitrogen oxide formation, which are dominated by low-speed chemical reactions, are slightly affected by the field.

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In this study, the numerical calculation of the Homogeneous Charge Compression Ignition (hereafter HCCI) process is carried out by using Curran et al.'s DME elementary reaction model for DME fueled HCCI engjne. On condition simulating shock tube, the validity of the DME elementary reaction model is investigated. And main elementary reactions releasing heat are investigated in case of multi-stage ignition. As a result, numerical calculation using Curran et al.'s elementary reaction model can qualitatively predict the influence of equivalence ratio, temperature and pressure on the appearance timings of low temperature reaction and high temperature reaction under the pressure and the temperature in HCCI engine.

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Homogeneous Charge Compression Ignition (hereafter HCCI) engine can realize low emission and high thermal efficiency. However, its ignition and combustion processes are difficult to control and thus the reaction mechanisms of auto-ignition and combustion are needed to be clarified. In this study, the numerical calculation of auto-ignition and combustion processes in HCCI engine is carried out. Curran et al.'s DME (Dimethyl Ether) elementary reaction model is used. The results of the calculations are compared with the experimental results and the validity of the elementary reaction model is investigated. And followings are investigated : the influence of equivalence ratio, intake temperature, EGR ratio and engine speed on rate of heat release, ignition timing, ignition temperature and histories of species' mole fractions. As a result, Curran et al.'s model can qualitatively predict the influence of equivalence ratio, intake temperature on the ignition timings and the peeks of the rate of heat release.

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Recently, pre-mixed lean combustion has gained the attention of many researchers, who are investigating compression ignition characteristics of this type of mixture. Previous research in our laboratory has shown that low NO_x combustion can be obtained by PREDIC (PREmixed lean DIesel Combustion) . While NO_x emissions were very good, the PREDIC operating load limit was about half that associated with conventional diesel combustion. Supercharging was found to be effective in expanding the operating region. However, fuel consumption worsened with increasing boost pressure. This arose from increased cooling losses and a decrease in the amount of constant volume combustion(due to early ignition) . So in order to delay ignition, EGR and a lower compression ratio piston were utilized. Results showed that the lower compression ratio piston was more effective in improving the fuel consumption than EGR was. In addition, the smoke density increased with increasing boost pressure because of more fuel coming into contact with the piston surface.

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In gasoline direct injection engines, predictions of the spray formation process and mixing process are required to improve both the fuel consumption rate and exhaust gas emissions. Numerical analysis of these processes using a swirl-type injector has been performed. The effects of injection speed profile and initial injection quantity, which has no tangential momentum, on the above processes are investigated by employing different breakup models for the liquid sheet region and its downstream region. As a result, the decrease in the injection speed at the end of injection duration enables the reproduction of droplets along the spray center-axis while the initially injected spray affects the spray profile.

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