In order to clarify the effects of cathodic protection on cavitation erosion, cavitation erosion tests are carried out using a vibratory erosion apparatus, and the cavitation aspects are photographed with a xenon flash lamp of 1μs exposure time. With increasing cathodic current, cavitation noises and mass losses (ML) of cavitation erosion markedly decrease when the number of tiny hydrogen bubbles on the specimen surface as well as in the test water increases, and the mass loss rate (MLR) is related to the square of sound pressure level (SPL²) of cavitation ultrasonic noise. The decreases in SPL and ML are due to marked absorption of cavitation energy by hydrogen bubbles produced on the specimen surface.

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Numerical analysis is performed to study the dynamical behavior of vortices generated in a sinusoidal wavy channel for pulsatile flow. This system is employed in order to enhance heat and mass transfer under laminar flow conditions. A pair of counter-rotating vortices periodically moves between the upper and lower walls with one wavelength. The vortex strength has a maximum value at a certain Womersley number, which increases with the net flow Reynolds number. A particle advection procedure also indicates that the vortex dynamics lead to efficient fluid mixing with increasing Womersley number.

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Flow regime transition and pressure drop in gas-liquid countercurrent two-phase flow was studied in three vertical parallel pipes. The conditions for flooding initiation in parallel pipe systems could be well predicted using Imura's correlation which for a single pipe. After flooding, the flow patterns were different in each pipe. A flow pattern classification diagram for the three-pipe system was developed, based on the flow patterns observed under various conditions of gas and liquid flow rates. It was seen from the results of pressure measurement in the three-pipe system that maximum pressure developed in each pipe had a serious effect on the average pressure in lower plenum, and that the frictional loss coefficient, which estimated from the time averaged pressure in lower plenum, could be corresponded to the relative gas Reynolds number.

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The purpose of the present study is to investigate the effects of liquid viscosity on the mean liquid film thicknesses, wave heights, and gas-liquid interfacial shear stresses in vertical-upward cocurrent annular flow in a 26.0mm-inner-diameter-tube. Water and glycerol solution were used as working fluids in order to change the kinematic viscosity of liquid from 0.85×10^-6 to 8.6×10^-6m²/s. The mean liquid film thicknesses and wave heights were determined using the signals of time-varying cross-sectionally averaged holdup which were detected by a constant current method at a distance of about 3.5m from an air-liquid mixer. The pressure gradients were also measured by a U-tube manometer. As a result we proposed correlations for the mean liquid film thicknesses and for the interfacial friction factors. In addition a method for estimating pressure drop was proposed, which verified that the calculated values were in good agreement with the measured values.

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The flow of ER fluid has been analyzed theoretically using the constitutive equation of Bingham fluid. However it is necessary to take account of internal rotation in ER fluid, because it is suspension containing particles. The equation of motion of ER fluid is derived using not only the constitutive equation of stress for Bingham fluid but also the micropolar electrically conducting fluids theory, assuming the equilibrium equation of angular momentum. For yield stress which is the characteristics of ER fluid, the interaction of particles which polarized by applied electric field leads us to the conclusion based on a two-body problem at the cutting surface of cluster. A theoretical equation is derived by dipole-dipole interaction. Yield stress in this study is not dynamic yield stress but static yield stress.

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An annular separation bubble that appears around the inlet corner of a radial diffuser flow between two parallel disks is investigated using flow visualization technique and numerical simulation of Navier-Stokes equations. The parameters of the flow are the radius of the inlet corner r_c, the clearance between parallel disks H, and the Reynolds number Re≡v₀d_p/ν, where v₀, d_p and ν are mean velocity at the inlet pipe, the diameter of the pipe and kinematic viscosity, respectively. The effects of the parameters on the separation bubble are considered. (1) The radius of the reattchment point r_R, and the height of the bubble h_s increase with Re in the laminar regime, but do not change in the turbulent regime. (2) r_R and h_s decrease with increasing r_c. The critical Reynolds number of the separation Re_cs increases with r_c. (3) Both r_R and h_s increase with H, to r_R has a larger increase than h_s.

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A method for simulating flow of extremely low Reynolds number in a vortex-in-cell (VIC) was studied. The viscous diffusion was represented by the random walk method. The validity of this method was proven by applying it to the flows passing over a fence placed vertically at an extremely low Reynolds number. The effects of parameters of the VIC method on the random walk method, such as the number of point vortices, the mesh density and the time increment, were investigated by numerical analysis using a one-dimensional diffusion equation. Changes in the relative error of vorticity depending on those parameters were clarified.

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Experiments for a cluster of equally sized spheres falling freely in quiescent glycerol at low Reynolds numbers are carried out using a large test tank. The numbers of equally sized spheres are 3∼12 on a horizontal line and 4×4∼10×10 on a vertical plane. Each spacing between two neighbouring spheres is equal to the sphere diameter. The numerical results obtained using the superposition method of Oseen's flow field produced by the translation of each sphere during free-fall motion of the cluster of spheres agree well with the experimental results. It is concluded that the dispersive motions of equally sized spheres on a horizontal line or on a vertical plane are classified into "V type" or "W type" depending on whether the number of spheres is odd or even, respectively.

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A new donor-acceptor method and a calculation technique for estimating the surface tension force term have been developed in order to improve VOF (volume of fluid) method. The improved VOF consists of (1) calculation of liquid quantity transferred from donor to acceptor cell by grouped into 11 interface patterns, (2) correction of liquid transfer rate by considering movement in oblique direction, (3) correction of inner cells with defects under conservation of total liquid quantity, (4) highly accurate calculation technique for estimating the surface tension force term by approximating the liquid-vapor interface to a circle. We applied the improved VOF method to a simulation of oscillating liquid drop in which the surface tension force is dominant and the obtained frequency agrees well with the theoretical one.

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A new, efficient and accurate numerical method which consists of perturbed residual equation and residual L2 norm minimization is proposed for boundary value problems of elliptic partial differential equations. For example, Neumann, Dirichlet and mixed boundary value problems in a three dimensional Poisson's equation for the pressure in curved duct flow and cascade flow, are solved. Numerical results demonstrate the effectiveness, robustness and a high convergence rate of this method. Residual Cutting Method is expected to be the numerical solution method applicable to a wide range of partial differential equations with various kinds of boundary conditions.

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A particle method is developed for solving the motion equation of one-dimensional viscous compressible fluids. The particles, representing fluid density, are moved with the acceleration derived from the motion equation. The piston problem is treated and creation of shock waves is simulated considering the effects of nonsolenoidal velocity field and of the kinematic viscosity on the density distribution and the velocity distribution. Our study shows that the nonsolenoidal condition, as well as the kinematic viscosity, must be incorporated into the code to obtain smooth solutions, and that with properly chosen parameters, one can create as strong a shock wave as required.

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The purpose of this research is to construct accurate finite difference schemes for incompressible unsteady flow simulations such as large eddy simulation (LES) or direct numerical simulation (DNS). In the first report, conservative properties of the continuity, momentum and kinetic energy equations for incompressible flow are specified as analytical requirements for a proper set of discretized equations. Convective schemes in a proper set are commutable if the corresponding discretized continuity is satisfied. The proper combination of discretized continuity and pressure terms is required for kinetic energy conservation. The skew-symmetric form is the only proper second-order accurate convective scheme in intuitive convective schemes in a regular grid system. Proper second-order accurate divergence and advective forms are indicated. We need not consider proper rotational form if proper advective form is indicated, since the requirement for the rotational form is that it equals the advective form. Proper fourth-order accurate convective schemes in a regular grid system are obtained from a relatively simple extension of the proper second-order schemes.

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In this report, finite difference schemes in staggered and collocated grid systems are considered in light of the analytical requirements that were discussed in the first report. The standard second-order accurate finite difference scheme with divergence form in a staggered grid system is proper. Proper second-order accurate advective and skew-symmetric forms have been proposed in the staggered grid system. Existing fourth-order accurate convective schemes in a staggered grid system are not proper. Proper higher-order accurate finite difference schemes in a staggered grid system are proposed. This is novel because higher-order staggered grid schemes that conserve momentum and kinetic energy simultaneously do not previously appear in the literature. The pressure term is not conservative in the kinetic energy equation in the collocated grid system, although we can construct proper-second and fourth-order accurate convective schemes in this system.

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In this report, numerical tests of the conservation properties of finite difference schemes are performed. Inviscid flow simulations in a two-dimensional periodic domain are performed using several finite difference schemes that are discussed in the first and second reports. The momentum and kinetic energy are conserved when the proper schemes in regular and staggered grid systems are used. The defect of the finite difference schemes in a collocated grid system is emphasized in the simulation. In addition, plane channel flows at Re=180 and 2000 are simulated using the proper fourth-order accurate finite difference scheme in a staggered grid system and the results are better than those of the second-order accurate algorithm and an existing fourth-order accurate scheme.

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For performance improvement of a disk-shaped MHD generator, it is desirable to give the working inert gas not only radial velocity but also azimuthal velocity at the exit of a supersonic nozzle. Swirl vanes have been installed in the nozzle section, which can induce nonuniform azimuthal velocity distribution. In order to reduce the nonuniform velocity, a new swirl vane using asymmetric nozzles is designed, and its effect is confirmed by wind-tunnel experiment and two-dimensional numerical simulation. Then, the optimized design of the swirl vane is proposed based on a combination of those results.

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A theoretical analysis of cascade flutter suppression using an active acoustic excitation technique is conducted for supersonic cascades. A three-dimensional linear cascade of flat plates oscillating in a supersonic uniform flow between parallel walls is considered. One of the walls is partially composed of an actuator surface such as a loudspeaker which generates sound waves with the same frequency as that of the blade oscillation. The aerodynamic work on blades by unsteady fluid forces due to oscillation of blades themselves and interaction with the acoustic disturbances generated from the actuator surface is calculated. Dependences of the aerodynamic work on the location, width and vibration modes of actuator surface, and the phase difference between the cascade and actuator surface oscillations are investigated. It is revealed that the parametric dependences and the condition of the actuator surface motion for effective flutter suppression are very much different from those for subsonic cascades.

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Among aquatic animals, tuna, mackerel and dolphin seem to have achieved a high-speed and high-efficiency swimming method. Their measured speeds are sometimes higher than those of the theoretical estimations. We investigate the propulsion mechanism by modeling their caudal fin movement as a simple mechanism of two hinges, a rigid caudal arm and a rigid wing. The mechanism enables simultaneous wing heaving and pitching motions. In this study we determine the most effective motion of the wing in the case of an NACA 0015 wing section profile. The calculation result showed that the wing profile was much more effective than a flat plate wing profile. Furthermore, we present an analysis of the behavior of characteristic quantities of oscillating wing mechanism at large swimming number.

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The numerical methods for analyzing a fixed terminator type of wave energy conversion device are described under the condition that the linear water wave theory is applicable. Two methods are proposed in order to calculate the device characteristics of an air chamber. One uses the flow rate and the gage pressure in the air chamber directly, because the interaction between the oscillating water column and the turbine is found to be controlled only by the flow rate and the pressure drop through the turbine in this system. The other method uses the equation of the floating body motion in a manner similar to the equivalent floating body approximation. The relations between these two methods are also examined. The hydrodynamic performance with frequency from zero to infinity is required in the simulation of irregular waves. However, resonances occur when the air chamber breadth is equal to an integral multiple of a half wavelength. Therefore the impulse response function is modified in order to eliminate the effects of the resonance frequency. Finally, it is confirmed that these solutions give good agreement with the experimental data.

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Acoustic resonant vibration occurs in a cavity with a tube bundle when flow velocity reaches some value. The vibration mode is usually transverse to the flow direction and its prevention is easy. However, recently, parallel mode vibration sometimes occurs. The mechanism of vibration was discussed in our previous paper and it seems that the vibration is a kind of self-excited vibration induced by unsteady fluid dynamic force. The damping factor of a system plays a very important role in the vibration; thus the method for estimating the damping factor of acoustic vibration was discussed. The boundary element method is usually used for calculating acoustic vibration; however, it is not able to estimate the damping coefficient. The frequency response of pressure can be calculated by the boundary element method and was used for calculating the damping coefficient. In this paper we describe a method of estimation of damping coefficient and results of calculations based on the method.

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In order to investigate the oscillation of an underexpanded impinging jet and the behavior of plate shock wave in the vicinity of a plate, we visualize the flow field mainly using the Mach-Zehnder technique and measure the pressure on the plate. At a nozzle pressure ratio of 3.0, the shape of the plate shock wave changes periodically with nozzle-plate spacings. However, when the spacing exceeds a certain value, the type of oscillation changes markedly. The change of oscillation is confirmed by interferograms and pressure measurements. Comparing the jet structure with the oscillation, the change can be considered to be caused by instability of the jet boundary.

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High-energy lasers such as GDL require effective diffusers which work at high Mach number and low pressure flow. Their operating Reynolds number (Re) is normally over 105, while up to now, diffuser efficiency (η_D) has been investigated in the range of Re_in<10⁵. In this paper, diffuser efficiency for a developed viscous internal flow at M=4.7(M=Mach number) is measured as function of Reynolds number at the diffuser inlet (Re_in) and the shape of diffusers over a range of 7.5×10⁴<Rr_in<6.0×10⁵. In order to discuss the energy dissipation process in the diffuser, its inlet region is observed with a Mach-Zehnder interferometer. Experimental results confirm a strong interaction between thick boundary layers and shock waves especially in the low Reynolds number region, which degrades the diffuser efficiency.

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The mechanism of aerodynamic sound generation from a circular cylinder is investigated experimentally using coherence functions between surface pressure fluctuation and radiated sound at Reynolds numbers from 10⁴ to 1.4×10⁵. The correlation between the surface pressure fluctuation and the radiated sound at the fundamental frequency is good, indicating the strong contribution of ordered structures to aerodynamic sound generation. The characteristic length of ordered structure L_c is estimated using the integral scale of the spanwise coherence function of surface pressure fluctuations. The sound pressure is calculated using a modified Curle's equation, with the characteristic length and measured surface pressure fluctuations. The predicted spectra of radiated sound are in good agreement with those actually measured up to five times the fundamental frequency. This result shows that L_C is useful for estimating the character of radiated sound from a circular cylinder.

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The multistage axial flow compressor is modeled by the lumped cascade model of interconnected subsystems. Dynamics for each stage of the compressor are established with a state vector which has three state variables of flow rate, pressure and temperature. Compressor characteristics are estimated using the stage stacking method. Lyapunov stability analysis is applied to such a model for each decoupled linear subsystem. A degree of stability is derived from the eigenvalues of symmetric matrices as solutions of the Lyapunov matrix equations. Physically the degree of stability corresponds to the damping coefficient of the Lyapunov function defined at each stage. The degree of stability represents quantitatively the margin between the surge line and the steady state operating lines. The results allow specification of the stage from which the surge will occur when the compressor becomes unstable. The degree of stability is classified into three distribution patterns according to the rotational speed of compressor operation.

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In order to obtain high discharge pressure, of a multiblade fan assembled in a burner of a boiler for industrial use, a cut-off sheet has to be designed under a very narrow clearance. The fan is driven at high rotational speeds under the condition of heavy discharge load. Therefore, the levels of the blade passing frequency (BPF) and its harmonics are much higher than the level of the broad-band noise. In this paper, an additional method that utilizes an auxiliary cut-off sheet, that is, setting up a new partition wall at the cut-off point, is proposed to reduce the fan noise. By means of experimental analysis, the noise reduction mechanism and the effects of design conditions on the shape of the partition wall are established. As a result, the BPF noise and the broad-band noise are markedly decreased without degrading the discharge pressure performance.

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The wave behavior during conduction heat transfer in a finite medium with nonuniform radiative absorption in the thickness direction of a laser pulse with Gaussian temporal profile has been investigated. Using Green's function method and the finite integral transform technique, a solution of the hyperbolic heat conduction equation was derived in the form of integration. Calculations were performed in order to exhibit the propagation and reflection of temperature waves and heat flux through the medium and the results were shown graphically.

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In this paper, a new analytical method for unsteady-state problems of heat conduction in anisotropic materials is presented. Under the assumption that the form of the heat conduction equation in anisotropic materials is invariant under a congruence matrix transformation, the equation of heat conduction can be transformed to an equation of the same form as that for the isotropic case. For this matrix transformation, the temperature gradient and heat flux must satisfy the continuity coditions at a boundary between two different media. This method is applicable to the treatment of thermal resistance of composite slabs, the determination of the Green function for the three-dimensional equation of heat conduction in an anisotropic conductor, and the analysis of temperature distribution in the composite regions of infinite anisotropic heat-conducting solids.

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Experiments have been performed for a turbulent channel flow obstructed with a flat body. The wall static pressure, the local heat transfer coefficient, the skin friction coefficient and fluctuations of streamwise velocity as well as the time-averaged velocity profiles were measured, and the similarity between momentum and heat transport proceses was examined for four different flat bodies. The total performance between heat transfer and pressure drop was estimated under conditions of an equal pumping power. The flat body with a semicirclular front edge gave good performance. The pressure drop was strongly affected by the shape of the front edge of the bodies. Enhancement of the heat transfer coefficient was related to acceleration of mean velocity at the front edge of the bodies and the increase of turbulent intensity in the near-wall region.

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Opposing mixed convective flows adjacent to a vertical, heated cylinder have been investigated experimentally. The flow and heat transfer under the influence of strong buoyancy force are of particular interest. Experiments were conducted for the ranges of Reynolds and modified Rayleigh numbers 2×10³<Re_L<2×10⁴ and 7×10⁹<Ra_L^*<2×10¹². The flow fields around the cylinder were visualized. The results indicate that the separation of forced flow occurs at the bottom edge of the cylinder when the nondimensional parameter (Gr_L^*/Re_L^2.5)=0.8, and reaches the upper edge when (Gr_L^*/Re_L^2.5)=5.0. The local heat transfer coefficients of the cylinder were also measured. The results show that the minimum and maximum coefficients appear at the separation and the reattachment points of the forced flow, respectively. The heat transfer data were correlated with the nondimensional parameters to yield a general heat transfer formula.

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Analytical and experimental investigations were done on the heat removal process of a thermal energy storage capsule, using gelled Glauber salt. The process was approximately treated as a heat production phenomenon due to the crystalization from a solution. First, the relation between the amount of the heat produced and the temperature variation was measured precisely for the equilibrium state. Next, transient heat transfer characteristics of the capsule were measured in the various cooling conditions. Finally, for the case of the initial temperature lower than the saturation temperature of the encapsuled solution, the numerical analyses were performed, approximating the process by the relaxation phenomenon where the crystal grew around crystal nuclei. The results of the numerical solution, concerning the heat flux variation at the capsule wall, agreed well with the experimental results.

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Analytical and experimental investigations were performed on the heat removal process of a thermal energy storage capsule, using gelled Glauber salt. In the analysis, the process was approximately treated as a heat production phenomenon due to the crystalization from a solution. The case of the inital temperature higher than the saturation temperature of the encapsuled solution was discussed, and the numerical analyses were performed, approximating the cooling process by two steps. In the first step, the nucleation theory of the crystal in the supersaturated solution was considered, until the amount of the nuclei exceeded the critical value. Then, in the second step, the process was approximated as the relaxation phenomenon where the crystal grew around crystal nuclei. The results of the numerical solution, concerning the heat flux variation at the capsule wall, and the critical value of the amount of the nuclei, agreed well with the experimental results.

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The thermal performance of the heat pump systems which use bare flat-plate collectors was studied experimentally and analytically. The collector used in the experiments was made of copper plate 1mm thick with copper tubes fixed on the back. The total area of the collectors was 3.24m² and the rated capacity of the compressor in the system was 350W. A COP of about 5.3 was obtained at noon in winter when the temperature of the water at the inlet of the condenser was 40°C. Based on the experimental results, the COP and the power consumption of the compressor were given as functions of the temperature of the water and the evaporation temperature of the refrigerant, R-12, in the collectors. Using these relations, an analysis was made which was able to predict the performance of the system for various weather conditions and for an arbitrary water temperature. The analytical results of the evaporation temperatures and the COP were in good agreement with those in the experiments.

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Combustion characteristics of a single CWM (Coal-Water-Mixture) droplet placed on a hot surface in a test furnace were investigated. The collapsing load of an ash grain which is formed by the combustion of the CWM droplet was also measured to clarify the relationship between the burning temperature and burn-out state of the droplet. Two stage combustion which is usually observed in pulverized coal combustion was observed in the burning sequence of the CWM droplet on the hot surface. The first stage of combustion was due to the burning of flammable gas from the volatile matter in the coal. The second stage was the char combustion of the coal. As the temperature on the hot surface increased, the collapsing load of the ash grain decreased. It reached a minimum load and then increased with an increase of the temperature of the hot surface. It was considered that the combination of the unburned coal at low temperatures and melted ash at high temperatures resulted in the hard grain of ash which had a high collapsing load.

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Dual plate Fourier transform interferometry combined with tomographic techniques was investigated to measure three-dimensional temperature profiles in a premixed flame. The dual plate method can overcome several problems and limitations of conventional Fourier transform interferometry. A six-directional two reference beams holographic interferometer is described, with which the conventional contour fringe and the modulated fringe can be obtained simultaneously. The results obtained are as follows. (1) It is not necessary to know the exact value of carrier frequency to extract the phase distribution from a modified interference fringe. (2) The inherent errors caused by the leakage of Fourier spectra and initial phase value are eliminated by its subtraction process. (3) Instantaneous spatial temperature profiles of a laminar premixed flame are presented.

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Thermal performance of a 2000°C class regenerative heat exchanger having a heat storage bed of cored bricks has been experimentally demonstrated. Heating and cooling switching operations of this heat exchanger have been done employing natural gas fired combustion gas as heating gas and air as cooling gas, which shows technical feasibility of continuous operation of the heat exchanger at temperatures above 2000°C. A two-dimensional heat transfer model explains well the experimentally obtained thermal behavior of the heat exchanger.

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This paper describes in detail experimental results on flow resistance and heat transfer of regenerator wire meshes of a Stirling engine in oscillatory flow. The results show that for Re>300, the friction factor of wire mesh became lower than that in previous studies. It has been clarified that the friction factor in a decelerating period becomes higher than that in an accelerating period under the condition that both Valensi number and maximum Reynolds number exceed Certain values. A new experimental method for estimating Nusselt number of wire mesh in oscillatory flow is proposed. This method employs a cylindrical probe having two thermocouples attached on opposite sides of the cylinder facing the direction of oscillatory flow. It has been clarified that the Nusselt number of wire mesh becomes a function of Reynolds number and open area ratio when aperture size of wire mesh is used as the representative length. Also, experiments on so-called "spring mesh" were carried out.

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In order to develop the utilization technology in which unexploited energy is retrieved and transformed into power, we have proposed a heat engine incorporating shape memory alloy wires. In this work, the output power characteristics are investigated experimentally from the viewpoints of maximization of the output power, stabilization of the power during operation and the amount of work to failure. Experiments are conducted at various heating and cooling temperatures, volocities of heating and cooling water and wire diameters. As a result, it is clarified that the output power increases with increases in both the heating temperature and the velocity of heating water. The output power also increases with decreasing cooling temperature. However, the velocity of cooling water at which the output power is maximum varies with the cooling temperature. Furthermore, the amount of work to failure does not always increase with increasing fatigue life and becomes maximum under the operating conditions at which the output power becomes maximum.

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Exhaust odor is one of the demerits in a direct injection diesel engine. Usually, the evaluation of exhaust odor involves sensory assessment by nose panel and it is difficult to evaluate the odor level using a chemical analyzer, because there are many kinds of odor components in the exhaust gas. In this study, pH measurement of an aqueous solution of a condensed component of exhaust gas, formaldehyde measurement with the reduction FID and sensory assessment using an eye irritant are investigated. It was found that the pH method using a gas sampling bag is simpler and more exact than the cold trap method; however, the correlation between the pH value and the sensory assessment varies with operation conditions. On the other hand, the formaldehyde concentration shows a correlation with the degree of eye irritant.

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Oxidation in the exhaust systems of spark ignition engines is one of the important properties characterizing the behavior of unburnt hydrocarbons. A time-resolved measurement system of hydrocarbon species which consists of a high speed solenoid valve and a gas chromatograph is developed. It is confirmed experimentally that this system can be used to measure hydrocarbon species when the engine is rotating in both the cold starting and warmed-up periods. The difference in the oxidation processes in the exhaust system in methane-fueled and propylene-fueled engines is discussed in relation to the data measured using this system.

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