In fluid power systems, cavitation under nonsteady flow conditions is a major factor limiting the response and reliability. As the most fundamental phenomenon, the time lag of nonsteady cavitation in restrictors is discussed. First, the times required to establish the single phase flow pattern and for bubbles to grow from cavitation nuclei are estimated and found to be much shorter than that required to generate the nuclei. Then, by applying both the hole theory and theory of rate processes, a predication formula for the time lag is derived. The calculated results coincide with the experimental ones.

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A numerical method is developed to simulate the unsteady axisymmetric flow with a free surface. The method is based on a finite-volume solution of the equations on an orthogonal curvilinear oordinate system. A new iteration technique is used for the boundary condition of the free surface to stabilize the solution. The method is applied to simulate an unsteady motion of a single deformed bubble rising through a quiescent liquid. The numerical results show quantitatively good agreement with those of experiments and calculations of others. In the present study, the transitional phenomena of the initially spherical bubble in reaching the steady state are investigated. It is known experimentally that the rising bubble begins to show an unsteady three-dimensional (spiral or zigzag) motion beyond certain critical Reynolds and Weber numbers. Our numerical results of the axisymmetric flow show unsteady shape oscillations in the parameter range of the three-dimensional motions.

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In the lower oscillating frequency region of the lock-in phenomenon of a rectangular prism with large oscillation angle, primary frequencies twice and three times the oscillating frequency are observed in the power spectrum of velocity fluctuation measured downstream of the prism. Such harmonic frequencies cause problems in the control of vortex shedding which makes use of the lock-in phenomenon. In this study, the mechanism causing the biharmonic frequency is clarified from digital signal processing of velocity fluctuation obtained by a hot wire probe, such as digital band-pass filtering technique, and from image processing of dye-injected visualization of the separated shear layer.

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An experimental study was conducted to investigate the effects of acoustic waves on the growth of three-dimensional perturbations in a plane mixing layer using a novel experimental technique in a towing tunnel. The mixing layer in the transitional regime at Re_m ≈ 100 based on the momentum thickness was investigated by means of flow visualization/flying hot-wire technique. We found that vortex pairing in the mixing layer excited with a subharmonic mode prevents (or delays) the rapid growth of three-dimensionality. In contrast, delayed pairing with a fundamental mode can result in significant growth of three-dimensionality prior to the pairing, where the rollers are bent in the spanwise direction due to the secondary instability of the elliptic vortex. These results are in good agreement with the observations of simulated mixing layers at Re_m=112. The mechanisms responsible for the growth of three-dimensionality during pairing are described.

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The geometry of flow patterns in a numerically simulated compressible mixing layer was studied using three-dimensional critical point theory. The solution trajectories for three first-order linear differential equations are used to classify the elementary three-dimensional flow patterns defined by instantaneous streamlines. Fluid motions characterized by high rates of kinetic energy dissipation and/or high enstrophy are of particular interest. It is found that motions corresponding to high rates of dissipation are characterized by a 3-D rate-of-strain topology which is of the saddle-saddle-unstable-node type, similar to the incompressible mixing layer. The topolygy of the unstable focus compressing type is observed for helical pairing motions of the vortical structures. Fluid motions corresponding to high rates of dilatation dissipation are also characterized by the same topology as the solenoidal dissipation motions. Regions of high enstrophy are found to be characterized by the topology of the unstable-focus-stretching, type the topologies stable-focus-stretching, unstable-focus-compressing, and stable-focus-compressing types are also observed for these resions.

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The leading-edge separation bubble of a blunt circular cylinder aligned with the main flow was forced by a single-frequency sinusoidal disturbance at a Reynolds number of 6.9×10⁴. The amplitude of the forcing was varied from 0.5% to 20% of the main-flow velocity. At forcing amplitudes of less than 10%, the reattachment length attained a minimum at a particular forcing frequency. At higher amplitudes, greater than 14%, the separation bubble was almost eliminated over a range of forcing frequencies. The stronger the disturbance, the wider the range of forcing frequencies where the separation bubble was eliminated. The change in vortex structure in the separated shear layer by the forcing was determined from the distribution of the time-mean and rms velocities, the evolution of the power spectrum of the pressure fluctuation at the center of the shear layer, and the smoke-wire flow visualization at a lower Reynolds number of 1.4×10⁴. A model was presented to explain the forcing frequency at which the reattachment length attained the minimum.

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The characteristics of flow oscillation induced by the interaction of weak normal shock wave with turbulent boundary layer in a supersonic nozzle were investigated experimentally. The fluctuations of wall static pressures with time were measured throughout the interaction region, and the data were analyzed to obtain the root-mean square values and the power spectral density functions. From the variation of power spectral density function distribution in the streamwise direction, it is concluded that the flow oscillation induced by the interaction is independent of the pressure fluctuation in the boundary layer upstream of the interaction region, and that the oscillation is due to the fluctuation of effective cross-sectional area of flow behind the shock wave caused by the unsteadiness of boundary layer in the interaction region.

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A numerical analysis has been performed on developing turbulent flow in simulated rod bundles. The ratio of pitch represented by two rod centers to rod diameter is 1.2 and Reynolds number is 20.0×10⁴. The shape of the simulated rod bundle is that two of half-rods set in a rectangular-section duct. In calculation, an algebraic stress model was adopted in order to predict Reynolds stresses precisely, and the boundary-fitted coordinate system was introduced to set boundary conditions easily. Calculated results were compared with the experimental data available. The calculated profiles of secondary flow and Reynolds stresses in rod bundles are shown in this study. As a result of this calculation, it was found that the present method can predict the distributions of primary mean velocity and turbulent energy well. Moreover, the distributions of wall shear stress along the each wall and secondary flow are obtained without great discrepancy. In calculation, secondary flow is observed not only near corner regions but also near the central region of the duct. The calculated intensity of secondary flow appeared near the central region is small compared to that of corner regions. Although there are a few points of discrepancy with the experimental data, the present method is applicable to turbulent flow having a complex cross-sectional shape.

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This paper proposes a three-equation (k-ε-F) model for compressible turbulence. Recent direct simulations of homogeneous turbulence show that compressibility effects depend more on the initial conditions than on the turbulent Mach number. This implies that the level of compressibility in turbulence may not be predicted only by solving the equations of k and ε. In this study therefore the variable F, which is defined by the dilatational components of turbulence, is introduced and the equation of F is also solved. We also focus on modeling the pressure-dilatation correlation. An analysis of shocklike structures reveals that this correlation is strongly related to the dilatation dissipation. The proposed model is validated by previous direct simulations of compressible turbulence.

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The response of a fully developed pipe flow to an attached ring-type manipulator with rectangular cross section was investigated by measuring the mean velocity profiles. The ring-type element has a height of 0.14 times the pipe radius and was positioned rigidly in a 99.8-mm diameter, smooth-walled, circular pipe in which air was flowing at Reynolds number of 6.2×10⁴. The results indicate that the flow in the core is significantly perturbed and the return of the flow to a self-preserving state without disturbance has been achieved at about 960 times the manipulator height. Furthermore, near the reattachment point, the mean velocity profile in the core region of the pipe is much more uniform and the velocity gradient is steeper near the wall than in a smoth pipe, indicating enhanced mixing. The boundary layer characteristics, such as the skin friction coefficient and boundary layer thickness are also altered in the streamwise direction upon a pulsewise disturbance.

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Flow pattern identification using gas-phase fluctuations is studied analytically. The fundamental waveform of periodic gas-phase or void fraction fluctuations for steady two-phase flow is assumed based on the real waveform of gas-phase fluctuations. The structure of the fundamental wave includes some main flow patterns. Thus the statistical parameter characteristics are directly related to flow structure. That is, the parameter characteristics on the parameter space are revealed, because the parameters of the assumed fluctuations can be calculated for given flow patterns. The results show that for slug or plug flow the relationship between the mean and the standard deviation is described by an equation of a half circle, and that the relationship between the coefficients skewness and excess is described by a quadratic equation in those flows. For bubble, annular or separated flow, the coefficient of skewness is larger than zero, because the flow has a flat or direct-current-like part in the fundamental waveform.

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An experimental study has been carried out for the three-dimensional jet discharging from a round nozzle along a concave surface. Mean and fluctuating veloctities are measured by rotating a probe with an inclined hot wire. The experimental results are compared with the existing results on the jet along a flat surface, and the effects of surface curvature on the jet are elucidated.

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It has been found that the boundary integral equations for the field functions such as those of potential and displacement can be regularized by introduction of their relative quantities. This paper intends to extend this regularization technique to the problems of incompressible viscous flow. It is shown that the basic boundary integral equation of the velocity is regularized by superposing a particular solution of the uniform flow upon the conventional integral equation. In the same way, internal equations for the velocity and the pressure are also regularized. These new equations derived here give accurate numerical results in computing not only the velocity but also the pressure. In addition, this approach is shown to be successful for deriving the integral equation for the boundary pressure which has to date not been included among the conventional equations. Through two-dimensional examples, these new equations are verified to be valid, and applicability of the present regularization technique is shown.

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In order to reduce the drag of a circular cylinder in an uniform stream, a small rod was set upstream of the cylinder. The effect of the Rynolds number on drag reduction of the cylinder was investigated. The drag depends on the ratio of the rod to the cylinder diameter d/D, the distance between the axes of the rod and the cylinder L/D and the Reynolds number Re. Generally, the higher the Reynolds number, the greater the reduction of drag. The optimum conditions of drag reduction are clarified : for Re<4.1×10⁴, d/D=0.25 and L/D=2.0, and for Re≥4.1×10⁴, d/D=0.25 and L/D=1.75. Both are cases without vortex shedding from the rod. The drag with the rod compared to that without the rod decreases by 17% at Re=1.5×10⁴ and 63% at Re=6.2×10⁴.

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The hydrodynamic forces generated by interaction between water and an elliptic cylinder have been investigated experimentally. Five elliptic cylinder models of 12, 20, 30, 60 and 120 mm width, 60 mm height and 200 mm span were used. Period parameters ranging from 0.2 to 3.2 were covered in the investigation. The hydrodynamic forces on a circular cylinder, square cylinder and diagonal square cylinder reported by the present authors depended on the period parameter but not on the Reynolds number, and on the elliptic cylinder in the previous experiments was the same, therefore the experiments were made at the constant frequency of 2 Hz. The results are as follows : the correlation between the hydrodynamic force coefficients and the period parameters are explained, the correlations between the phase difference of the forces and the cylinder acceleration, and the force coefficient for all models are the same at the phase difference angles less than 45 deg. and the value of the maximum phase difference angle is approximately 62 deg.

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The behaviors of ullage in a three-dimensional vane-type surface tension tank were investigated under reduced-gravity conditions. It was observed that the ullage was driven due to surface tension toward the gas inlet/outlet and remained on it. However, it was found that ullage separated under certain conditions depending on the shape and the number of vanes. The critical condition was derived by means of an analytical method and was verified by experiment. From the observation of liquid behaviors during the filling process, it was verified that there existed a critical filling rate at which the outlet flow of liquid through the gas inlet/outlet could be prevented. The critical filling rate increased with the number of vanes or when a baffle was set among the vanes.

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This paper proposes a principle of drag reduction on a ship hull which is accomplished by injecting air of atmospheric pressure into water flow. Expansion of the entrained air in water flow generates the high-speed two-phase water jet, and the drag reduction on the ship hull is caused by this reaction force ; therefore, the fluid drag can be reduced without the addition of an external energy. Three types of sailing bodies which have different spoilers were set in a towing tank, and the drag reductions were measured using various parameters such as sailing velocity, opening angle of the rear plate, and the depth of the sailing body in the water. The drag decreases monotonically with an increase of the sailing velocity and an increase of the opening angle of the rear plate. The sailing velocity at which the drag reduction begins converges toward higher speed as the depth of the sailing body increases. In order to examine the mechanism of the drag reduction analytically, a one-dimensional nonlinear lattice model is applied to the flow system. The proposed model is effective to investigate the flow characteristics.

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Turbulence characteristics of a supersonic turbulent boundary layer with multiple shock wave (λ-type pseudo-shock wave) in a square duct were investigated using a two-component LDV. The free-stream Mach number, flow confinement and Reynolds number upstream of the first-shock wave were of M_∞=1.78, δ_∞/h=0.3 and Re=13×10⁶ m^-1, respectively. It was found that the distributions of the turbulence intesity and Reynolds stress in the boundary-layer with multiple shock wave were different from those of the shock wave-free case. The turbulence intensity increased with decreasing streamwise velocity due to each shock wave in the pseudo-shock wave. Furthermore, the effects of shock wave/turbulent boundary layer interaction on the turbulence characteristics of compressible turbulent boundary layer were clarified quantitatively.

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Time marching methods coupled with a third order upwind TVD scheme are compared from the viewpoints of accuracy, memory requirement and computational cost. The methods examined are the second and the third order Runge-Kutta presented by Shu and Osher, the explicit Euler, the second order Adams-Bashforth, the implicit Euler and the Crank-Nicolson methods. Benchmark problems on time-dependent linear advective transport are solved using these methods. As a result, the Shu and Osher's Runge-Kutta methods of the second and the third order are recommended. The explicit Euler method suffers from oversteepening of the gradient due to numerical diffusion with a negative coefficient. The Adams-Bashforth method is inferior to the Runge-Kutta method in accuracy and memory requirement. The Crank-Nicolson method produces solutions as accurate as the Runge-Kutta method, but requires much CPU time due to the nonlinear feature of the TVD flux limiter.

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Effects of blade thickness on discrete frequency noise (DFN) have been investigated using symmetrical NACA blades of three different thicknesses. It was clarified that the mechanism of DFN generation was different depending on the thickness of the blade. In the case of a thin blade, NACA 0008, the air flow was separated upstream of the trailing edge on the suction side of the blade, but was attached to the trailing edge of the blade on the pressure side. Therefore the frequency and the sound pressure level of DFN were varied with the variation of the attack angle. On the other hand, in the case of a thick blade, NACA 0015 or NACA 0018, the flow was separated upstream of the trailing edge on the pressure side while it was attached to the trailing edge on the suction side. The frequency and sound pressure level of DFN did not vary with the variation of the attack angle in these cases. The location of the rolling up of Karman vortices was very important in the generation of DFN. When rolling up of the Karman vortex took place far from the trailing edge of the blade, the Karman vortices did not have a strong effect on the flow around the blade. However, when Karman vortices rolled up in the vicinity of the blade, the interaction of the Karman vortices with the blade was strong, causing DFN generation.

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Discrete tone noise generated in a uniform jet flow on a two-dimensional wing was investigated. Discrete tone noise is generated by a self-excited feedback loop formed by the acoustic field and the unstable boundary layer. In this work, the coherent flow velocity fluctuation in the boundary layer was reconstructed for the time sequential intensity distribution. From the time sequential flow fluctuation pattern, the following results were obtained. In the boundary layer on the suction side, the pattern of coherent velocity fluctuation intensity moved to the trailing edge and expanded its area with time. On the pressure side, a pseudo-sound wave was generated at the trailing edge, which shifted in the direction opposite that of main flow.

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As an approach to flutter suppression, mistuning effects on fully stalled cascades and unstalled cascades in the torsional mode are investigated, focusing on the fact that the cascade blades fluctuate at a natural frequency brought about through manufacturing processes. Under both stalled and unstalled conditions within the range of normal blade manufacturing imperfection, the larger the coefficent of variation of the natural frequency of a blade group, the more stable the cascade. The flutter suppression effect due to slighter mistuning is expected for stalled cascades rather than for unstalled ones. An irregularly distributed zigzag arrangement gives a fairly high flutter velocity, while an alternating arrangement, which is concluded to be optimum in an unstalled condition, is inferior in the stalled one. Further more, an evaluation method to estimate the flutter velocity from the blade-mistuned arrangement and which takes into account the flutter modal change is proposed.

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The performance of an unsteady sailwing shows special characteristics due to flexible structure, in particular when stretched at small tension. While the attack angle is increased from 0 to 5 degrees at a constant speed, the profile forms of a sailwing varying with time can be measured by a TV camera, observing a slit line projected on the membrane. The profile forms can be recovered from these images by digital image processing techniques and geometric relations between the slit and camera. The experimental results are compared with the results obtained by numerical analysis, taking account of damping forces on the membrane. The numerical method has already been presented in another paper. It is found that the variation with time and the dimensions of the profile forms are in good agreement, and the numerical method proved to be effective in calculating the performance of an unsteady sailwing.

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In this work, the wavefront of a compression wave generated by a train moving into a tunnel is studied. A new one-dimensional flow model in which the flow around the train is considered to be a stream tube is proposed to determine the key parameters that affect the wavefront of the compression wave. From the result, the wavefront is found to be proportional to the lateral velocity at the height of the tunnel wall in steady flow around the train before the train enters the tunnel. This relationship between the wavefront and the velocity of the steady flow is validated from the experimental data. The result indicates that the wavefront of the compression wave can be predicted by investigating the steady flow field around the train in stead of the unsteady flow when the train moves into a tunnel.

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In a subway station, train winds, which are generated by a train that acts as a piston against the tunnel air, adversely affect passengers or air-conditioning of the station. For reducing the winds, in this study, the air volumes of the blowers at Hikarigaoka Station, which are used for longitudinal ventilation in the tunnels, are dynamically controlled in three ways - increasing, decreasing or increasing-decreasing ventilation tuned to the train transit. The unsteady air velocities are measured in the tunnels and at the staircases, and then the air volumes are estimated. Results show that (i) the time histories of the unsteady air velocities are in good agreement with the existing theory, and (ii) the ratio of the reduced train-wind air volume at the staircases to the air controlled volume by the blowers are about 50% at arrival or 70% at departure.

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Instantaneous pressures were measured on the casing wall of a guide vane passage and volute casing of a diffuser pump in order to investigate the interaction between impeller blades and diffuser vanes. The pressure fluctuations were discussed using statistical analysis as well as the ensemble-averaging technique. Frequency spectra of unsteady pressure data show that the dominant frequencies are the impeller blade passage frequency and its higher harmonics. Moreover, the ensemble-averaged pressure data show the spatial distribution of unsteady pressures, which illustrates the rotation of the circumferential pressure mode due to rotor-stator interaction.

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Unsteady pressure measurements were made on the shroud wall of a vaned diffuser in order to investigate the interaction between impeller and diffuser vanes of a mixed-flow/diffuser pump. The pressure data were processed using the ensemble averaging technique and statistical analysis. Detailed pressure distributions are obtained with the aid of the proposed data processing technique. The results indicate that measured pressure distributions can be utilized for discussing characteristics of pressure fluctuations as well as hydraulic force on the diffuser vane in the guide vane passage.

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Three-dimensional potential flow in a screw-type centrifugal pump was calculated in consideration of leakage flow through a tip clearance of the blade. The drop of the theoretical head due to the leakage is calculated, and this result agrees qualitatively with the experimental result. From the nemerical and experimental study on three impellers of different blade twist angles (360°, 540°, 720°), it is found that the drop of the pump head due to the leakage increases with increase in tip length of the blade. Next, effects of prerotation on pump characteristics were investigated by numerical simulation and experiments. In the case of the commercial impeller, it is found that the prerotation does not affect the amount of angular momentum at the impeller outlet. But the numerical results on the 360°twist impeller whose passage is wider than that of a commercial impeller show that the flow around the impeller outlet is influenced by the prerotation. It is found that the difference between the calculated theoretical head and measured pump head increases when the direction of prerotation is opposite to the rotation of the impeller.

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Experimental investigations on improving the performance of the impulse turbine with self-pitch-controlled guide vanes are reported. A new type of guide vanes which are connected by link motion is presented and tested. The behavior of guide vanes in reciprocating flow is also shown relation to the axial flow velocity. The results show that a high-efficiency impulse turbine can developed by the use of guide vanes connected by link motion. Furthermore, it is found that the running and starting characteristics of this turbine in the reciprocating flow can be evaluated from the performance of the turbine with fixed nozzle and diffuser vanes in a unidirectional steady flow.

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Development of a wind turbine generator (WTG) system in Japan seems to have lagged far behind compared with that in European countries and the United States. However, NEDO (New Energy and Industrial Technology Development Organization) has recently reported that Japan is also abundant in wind energy resources, based on a several-year systematic survey conducted throughout the country and that Japan could expect to obtain electricity to meet about 10-20% of national electricity demand from wind resources alone. One of the difficulties of WTG development is the fluctuation in speed and direction of natural wind, which causes fluctuations in both voltage and frequency in the electric utility system. Therefore, the problem that needs to be solved is how far WTG capacity may penetrate into that of the conventional existing electric power systems, for instance, diesel power systems on remote islands. This paper evaluates the actual performance of two 250 kW WTG pilot plants connected to a diesel power electric line system of about 50 MW located on the Miyako islands, Okinawa, Japan. Wind energy resources and wind characteristics on the islands are reported, and the fluctuation of the WTG output and its influence on the total systems are determined and also numerically analyzed. It is confirmed that the multiple WTGs have a tendency to cancel out each other's fluctuations at a rate inversely proportional to the square root of the number. From the results of the investigation and analysis, it is estimated that on the objective island WTG capacity of as much as 10 MW may be permissible, that is, 20% of the existing diesel system only if the WTG system consists of forty 250 kW machines or a much greater number of smaller-scale wind turbine generators.

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Objectives of the present experimental study are to investigate adiabatic efficiencies of a supersonic Faraday MHD (magnetohydrodynamics) generator with cesium seeded argon and at the same time to achieve high enthalpy extractions. MHD power generation experiments were carried out with a shock tube facility. The MHD channel has 35 pairs of electrodes and the width between its insulator walls is expanded along the flow direction. Total pressures were measured at the exit of the MHD channel and total pressure losses were evaluated. Furthermore, the adiabatic effciency was measured for the first time in the present experiments in which an enthalpy extraction ratio of about 10% was achieved. Comparison of these results with those for a disk generator indicates that a Faraday generator has higher adiabatic efficiencies at the same enthalpy extraction ratio. Influences of voltage drops on loading parameters and electrical efficiencies are also discussed.

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Opto-microengines are proposed in this paper. The engines are composed of a vacuum chamber, microrotor and floodlight beam power supply or laser power supply. In the Knudsen number range from 0.05 to 5, the engines can be rotated by the effects of rarefied gas dynamics such as the force induced by a thermal creep flow and a radiometric force. It is revealed that the maximum torques of the engines occurred at the Knudsen numbers of about 0.2. The maximum rotational rate of the engines is achieved at the Knudsen number of 0.5. The effects are induced by heating of the rotor surface of the engine with a laser beam or floodlight beam. The Knudsen number is defined as the ratio of the mean free path length of a gas in the chamber to the rotor blade length of the engine in this paper.

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Heat and mass transfer mechanism in strong stable stratification was experimentally investigated in unsheared water flows downstream of turbulence-generation grids. Instantaneous velocity, temperature and concentration were simultaneously measured using a two-component laser doppler velocimeter (LDV), a resistance thermometer and a laser induced fluorescence technique. The results show that the difference between turbulent diffusions of active heat and passive mass in strongly stratified water flow appears in the high-frequency region, and that it generates a turbulent mass flux slightly larger than the heat flux. The countergradient heat and mass fluxes occur under strong stable stratification conditions, and the countergradient scalar transfer mechanism can be explained in terms of the balance between potential and turbulent kinetic energies. The countergradient scalar flux becomes larger with increasing Prandtl or Schmidt number of the active scalar.

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An experimental investigation was performed to study the effect of a rotating cylinder near the wall of a rectangular duct on heat transfer coefficient and fluid flow of forced convection. Local heat transfer coefficients were first measured by varing the rotational speed and the distance between cylinder and wall. The results showed that the positions of maximum and minimum in the profiles of the heat transfer at a fixed distance from the wall were almost invariable even when the cylinder was rotating. The wall temperature and fluid flow were also visualized using a liquid crystal sheet and fluorescent paint. It was noted that low-temperature streaks appeared on the wall, and that they strongly affected heat transfer characteristics. It was further determined that the position of the reattachment shifted upstream as rotational speed increased.

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A numerical analysis of Navier-Stokes equations with the finite difference method was conducted on a two-dimensional unsteady separated and reattached flow over a blunt flat plate, and the heat transfer characteristics therein were also analyzed. Reynolds and Prandtl numbers treated in the paper are 1000 and 0.7, respectively. It is clarified from the numerical results that at Re=1000, separated shear layer becomes unstable, as it accompanies the formation of spanwise vortices. These vortices coalesce and grow along the separated shear layer. Subsequently, the large-scale vortices are shed almost periodically from the reattached flow region, and they exhibit great effects upon the heat transfer in the separated and reattached flow regions.

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A simple method for measuring the thermal conductivity of low-conductive sheet materials such as a sheet of paper has been developed. A 7059 glass plate of 0.7 mm thickness made of CORNING is used as a reference material. An aluminum hot-wire of 10 mm length having rectangular crosssection of 0.5μm in thickness and 10μm in width is formed on the plate by sputtering and the photolithography technique. Seven kinds of thermal transfer paper for word processors are used as samples. A piece of the paper sample covered with a piece of impermeable polyimide tape that prevents moisture movement is put on the wire, another 7059 glass is placed on the paper sample, and a constant weight is loaded on the glass. The measured thermal conductivities of paper samples were from 0.3 to 0.41 W/(m·K). The data acquisition times are about 1.0 s. Errors in the present measurements are checked by the reference material.

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Three-dimensional elliptic simulations were carried out to study mixed-convection heat transfer in a horizontal square channel with heated and cooled side walls. Governing equations were solved for Re=100, Pγ=0.72 and Gγ/Re²=0∼50 by the SMIPLE method. Three-dimensional spiral flows were observed along the longitudinal direction of the channel. Secondary flow caused by buoyancy force gave rise to flow reversal at the thermally developing region. The flow reversal regions generated by secondary flow near the upper and lower walls partially prevented the main flow. This flow situation could be considered a fundamental phenomenon for mixed convection at the thermally developing region of the horizontal square channel. The effects of Gγ/Re² on the local heat transfer and the intensity of secondary flow were also discussed.

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Combined radiative-convective heat transfer is analyzed in a two-dimensional coaxial jet of nongray gas. The Monte Carlo method is used for the radiative heat transfer analysis. In addition to the nongray analysis, the analysis based on the conventional gray gas assumption is also carried out. From these studies, the gray analysis is found to give higher jet temperature at the nozzle-outlet region and lower temperature at the down-flow region compared with the nongray analysis. The effects of the temperature, velocity, absorbing gas concentration of efflux gas, and the nozzle diameter are also studied using the profile of the jet temperature and of the radiative heat flux emitted from the jet.

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The method of inverse-problem analysis was used to determine the distribution of heat-transfer coefficients of a silicon heater cooled with submerged jets of fluorocarbon liquid. The silicon heater was made specifically to investigate high-performance cooling systems of electronic devices. The heater is constructed of many cells which can independently generate heat and measure the temperature on one side of the heater, and it is colled from the other side of the heater. Inverse-problem analysis was used to correct for heat conduction in the heater and to determine the distribution of heat transfer coefficients on the cooling surface. The heat-transfer coefficients were also measured by independent techniques to confirm the values determined with the inverse-problem analysis. One of these independent techniques was to control the heater power to produce a uniform temperature. Another technique was to use a SUS film heater. The distribution of heat transfer coefficients determined with these three techniques were in reasonable agreement.

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Permeability of the mushy region formed by solidification of a porous medium Saturated with an aqueous solution was measured by a transient method. A packed bed of glass beads with 2.56 mm mean diameter saturated with NaCl aqueous solution was used as the porous medium. Measurements were carried out with various volume fractions of liquid phase and with various initial concentrations and supercooling degrees of the solution. From the measured results, it was found that the permeability was proportional to the n th power of the volume fraction and decreased with increase of the supercooling degree, decreasing slightly with increase of the initial concentration. An experimental equation of the permeability was obtained as a function of the volume fraction, supercooling degree, and initial concentration.

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This paper is a semi-empirical report on the development of a prediction algorithm of pressure drop for impingement cooling of heat sinks with longitudinal fins. The inlet rectangular orifice (slit) is about the heat sink size in length, less than 1/4 of the heat sink size in width and is placed over the center of the heat sink. A physical model suitable for heat sinks with longitudinal fins is considered based on the flow visualization results of our previous study. According to this model, the flow region is divided into five parts : (i) the region of inlet orifice, (ii) the region between the fins under the inlet orifice, where the flow is perpendicular to the fin base, (iii) the region between the fins where the flow is parallel to the fin base except under the inlet orifice, (iv) the outlet of the heat sink, and (v) the region distant from the heat sink. Values are predicted for pressure drop of the heat sinks with longitudinal fins for a variety of orifice width, gaps, fin heights and number of fins. These values agree with the experimental data within ±30%.

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The present paper deals with the new defrosting method by means of the frost sublimation phenomenon with radiant heat. The frost sublimation phenomenon occurs at the triple point of water (273.16 K, 610.5 Pa). The present experimental study focuses on the mass transfer rate of a horizontal frost layer exposed to a moist air flow and radiant heat. It is understood that the mass flux of the frost layer increases with increase of the water vapor mass concentration difference between the frost and main moist air flow, the main air flow velocity, and the infrared radiant heat intensity. The non-dimensional correlation equations of mass transfer, heat transfer and finishing time of the defrosting process have been derived taking into account various parameters.

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The prevention of marine biofouling by ozonation is investigated experimentally. A plate-type heat exchanger made of titanium is used. The length of the plate is 880 mm, the width 300 mm, and the thickness 0.5 mm. The total number of plates is 6 and the total heat transfer area is 0.8m². The ozonation of the sea water is performed for 5 minutes per day for about one month. The prevention of marine biofouling is evaluated from the measured value of overall heat transfer coefficient. In this experiment, the mean concentration of ozone is 2 mg/l, and the sea water velocity in the heat exchanger is 0.5m/s. It is clearly shown that an effective prevention of marine biofouling is attained by ozonation.

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Lewis number and preferential diffusion effects on the flame temperature of coaxial-flow diffusion flames were examined. Flame analysis based on the flame sheet model shows that the flame is strengthened when Le_f>1 or Le_O<1 and weakened when Le_f<1 or Le_O>1, where Le_f and Le_O are the Lewis numbers of fuel and oxygen, respectively. This is caused by the increase or decrease in the total enthalpy in the flame due to the difference in diffusion rates between heat and reactants, and indicates that flame extinction at the flame tip (tip opening) might occur when the flame is weakened. It further shows that for a mixed fuel with two components having different Lewis numbers, Le_f1 and Le_f2, component stratification by preferential diffusion occurs and mixed Lewis number effects become increasingly separated in the downstream direction. Therefore, in the case where Le_f1>1 and Le_f2<1, preferential diffusion might bring about the minimum value in the flame temperature profile and lead to the local blow-off which was observed experimentally.

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From experimental results on vibrating flames with a wrinkled laminar flame structure, it was clarified that the average surface area of the vibrating flame equals to the surface area of an equivalent laminar flame. And the local burning velocities of the flame element are not affected by the surface stretching which were generated by the flame curvature. So, the wrinkles on the flame surface carried downstrem from the upstream, and steady velocity gradients in the unburnt regime have no influence on the averaged burning velocity. It was concluded that the fluctuations of the wrinkled laminar flame carried downstrem from the upstream, does not affect the turbulent burning velocity, even though the fluctuations becomes large in a steady stream involving smooth velocity gradients. These results were confirmed with a newly developed flame-propagation model.

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The authors propose a new turbulent combustion model based on a hyperbolic tangent approximation of the reaction progress variable distribution in a one-dimensional laminar flame. Several different models including FL (flamelet), EBU (eddy break up), ED (eddy dissipation) and FS (flame sheet) models, are compared with the present model. Main features of the present model are as follows (1) The model is constructed from a laminar flamelet part and a distributed flame part. (2) The model is applicable to laminar and turbulent flame analysis, and it is independent of type of turbulence model. (3) Its distributed flame part includes EBU, ED and FS model as approximations.

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Characteristics of the hollow-cone-type spray formed by a swirl atomizer are discussed. Drop diameter, drop and air velocities and directions are measured with PLDV. Fine drops less than 6μm produced by a humidifier are used as seeds to measure the air flow. In the hollow-cone-type spray, large drops fly concentrating along the sheath and entrain air due to their momentum. Air velocity shows a maximum at the center of the spray, and decreases towards the sheath. The entrained air brings smaller drops to the inside of the spray. The air flow changes direction to parallel to the axis at R/R_sh≒0.8. The fluctuation of drop velocities is small in the center, increases outwards and shows a maximum at R/R_sh≒0.8. The relative turbulent intensity of air velocity is small under R/R_sh≒0.8 and increases rapidly over R/R_sh≒0.8.

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The effects of piston head shape on gas flows in the cylinders of four-valve gasoline engines have been numerically analyzed using the authors' GTT method with higher-order schemes for the convection terms of Navier-Stokes equations without any turbulence models. It has been found that among third-order schemes the Chakravarthy-Osher third-order TVD scheme is stabler than the UTOPIA and Kawamura-Kuwahara schemes. Therefore, the TVD scheme allows a larger time increment and enables us to conduct a practical calculation on an engineering workstation. The flow anaysis using the TVD scheme has revealed the following : The convexity or concavity of the piston head greatly affects the forming and collapsing processes of tumbling vortices in the cylinder. Both the decay of the spactially averaged kinetic energy of gas in the cylinder between intake BDC and compression TDC and the averaged kinetic energy of gas around an ignition plug near ignition timing may be used as measures for correlating the gas flow with the combustion phenomenon.

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For aiding design and improving the performance of various Stirling engines and coolers, a Stirling engine thermodynamic and mechanical analysis, SETMA, has been developed and examined. A simple SETMA, whose working space is divided into five control volumes, was developed to enable easy, accurate prediction of the performance of Stirling machines. In this paper, SETMA and fundamental equations are given in detail. Several examinations of the applicability of SETMA will be discussed, comparing the calculated and experimental results of two types of actual engines. As a result, it was found that the optimization of the heat transfer coefficients and friction-loss factors, and careful scanning of the dimensions of the working space markedly improve the calculation accuracy. Concerning the thermodynamic properties referred by SETMA, it was clarified that the SRK equation of state is more suitable than the ideal-gas equation in the case of analyzing higher-pressure-charged Stirling machines.

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Exhaust-water-selective recirculation is proposed for the purpose of reducing the emission of nitrogen oxides from diesel engines. In this method, water is extracted from the exhaust and fed directly into the intake air charge. This system operates as a closed system without a supplementary water charge. The exhaust-water-selective recirculation effectively works to decrease the combustion temperature due to the large heat capacity and heat of vaporization, thereby greatly reducing the amount of exhaust nitric oxide. Particulate emission and brake-specific fuel consumption are lower compared to ordinary exhaust gas recirculation when the amount of recirculated water is not excessive. It is expected that a diesel engine with exhaust-water-selective recirculation may achieve reduction of NO without sacrificing the thermal efficiency, when the system is combined with retarded fuel injection and engine-load-dependent water injection.

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