In the present experiment, a single cavitation bubble is produced in a V-shaped slot by an underwater electric discharge. The motion of the bubble is observed by high-speed photographs and by means of a CCD camera. From the experimental results, the following facts are revealed : The microjet is not necessarily axisymmetric. The cavitation bubble produced near the bottom of the V-slot is divided into two small bubbles by the microjet and the separated bubbles rebound at almost the same time. The area impinged by the microjet spreads over 3-4mm wide in the V-slot and the distances between the separated bubbles are 7-8mm.

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The present experiment investigates streamwise change of the vorticity field around a largescale coherent vortex artificially induced in a fully developed turbulent boundary layer. The vortical structure of the large-scale vortex evolved downstream through the growth, the self-preserving and the decay stages. In the growth stage, its spanwise and normal circulations increased downstream, and the large-scale vortex grew to have vortical structure similar to the natural horseshoe vortex. The vortex still grew upward but the spanwise circulation was kept nearly constant in the self-preserving stage. The convection velocity of its head and leg was 0.56 U_∝ in the growth and self-preserving stages. In the decay stage, each part of the vortex drifted at the local mean velocity, and the vortex became more inclined downstream. There, its vorticity gradually decreased as it flowed downstream. The decay rate of the normal vorticity was smaller than that of the spanwise one throughout the stages.

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This report describes the flow behavior of a water jet impinging on a rotating disk and flowing radially in the form of a thin liquid film on the disk. The flow is governed by the wall friction of the rotating disk, and at the same time, by the impining force. Hence, there is no similarity transformation to reduce the partial differential equations to the ordinary ones. Nevertheless, a similarity-type transformation making use of a stream function is applied to appropriate nonsimilar boundary-layer equations. The final equations are solved numerically by the finite difference method. The results show more realistic velocity profiles than those obtained by Miyasaka.

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Turbulent energy spectra in stably stratified shear flow were studied theoretically based on the turbulent spectral equation and the experimental results. A theoretical expression of the turbulent energy spectra was derived for the inertial subrange. According to this expression, the energy spectra of the stably stratified shear flow approached those of isothermal shear flow as the wave number increased, and the difference in energy spectra between stratified and isothermal flows was directly proportional to the -3rd power of the wave number. The one-dimensional energy spectrum obtained experimentally conformed to the expression.

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An experimental study has been carried out for the turbulnt flow through a circular-sectioned 90°bend of a curvature radius ratio of 4.0 with inlet and outlet straight pipes attached. Three components of mean and fluctuating velocities were measured by the technique of rotating a probe with an inclined hot wire under a Reynolds number of 60000. The flow patterns of main and secondary streams, and Reynolds stress distributions in pipe sections are illustrated with figures, and explanations are added on the process of phenomena in the streamwise direction.

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A numerical method for calculating free molecular flows is developed. An integral equation for the mass flux of incident molecules on walls is used. The integral equation is solved by using the boundary element method. The advantage of the present method over Monte Carol calculation is that results are noise free and there are no sampling errors. As examples of practical engineering applications, the flows in a vacuum vapor deposition chamber and a cryopump are studied. The desired results can be obtained with limited computation time.

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The drift flux model proposed by Zuber and Findlay is based on the difference between the local velocity of each phase and the local velocity of the center of volume. On the other hand, modelling of multiphase flow was carried out in this study based on the velocity difference between the local velocity of each phase and the local velocity of the center of the other conservative quantities: mass, momentum and energy. The derivation of basic equations of the present models were carried out referring to that of the drift flux model. As a result, new relations were deduced among the areaaveraged mass, momentum and energy fluxes of the mixture, the local volume fraction weighted mean velocity of each phase, and the macroscopic velocities of the center of conservative quantities. The usefulness of the proposed relations was confirmed using the experimental data for gas-liquid-solid three-phase flows in vertical pipes.

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The fluid flow resistance and the behavior of liquid film of an annular countercurrent two-phase flow are investigated experimentally in a wide range of flow pattern. Air and water are used for the two-phase flow. Water flows down along the inner surface of a vertical tube and air flows up, counter to the water flow in the tube. The fluctuation of the surface waves of the liquid film is amplified with increasing gas velocity and the waves develop into liquid bridges. Once the bridges are formed, the water is carried upward and flooding starts. The fluid flow resistance of the two-phase flow is approximately 2 times higher than that of the typical single-phase flow, and increases suddenly at 3 times the resistance of the two-phase flow at the beginning of flooding.

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The flow characteristics of an immiscible equal-density liquid-liquid two-phase mixture were investigated to clarify the behavior of a gas-liquid two-phase flow under microgravity. The experiments were carried out in a horizontal transparent acrylic resin tube of 4.5m in length and 25mm I.D., using silicone oil (viscosity μ₀=55.0 mPa·s, density ρ=980 kg/m³) and water mixture as the working fluid in the range of superficial oil velocities of 0.03 to 0.40m/s and superficial water velocities of 0.0017 to 0.7m/s. Seven kinds of flow patterns were observed. In particular, the inverted annular flow and the inverted slug flow occurred. In these flow patterns the water touched the tube wall and the oil flowed in a core region. The mean void fraction was clarified using the drift flux model. Furthermore, the experimental results of the frictional loss were compared with the Lockhart-Martinelli correlation. As a result, it was found that both agreed well in bubbly, slug, and annular flow regimes when the oil touched the tube wall, but neither agreed in the inverted flow patterns when the water touched the wall.

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Characteristic properties of the disturbance were investigated by means of the measurement of wall pressure fluctuation, compared with the linear stability theory. For the measurement of the phase velocity of the disturbance, the pressure was detected through two pressure taps 0.59mm apart, each with an inner diameter of 0.15mm. The pressure chambers were filled with 5000 cSt silicon oil. The detected signals were analyzed by FFT. The measured values of the phase velocity, the frequency and the amplification factor of disturbance were in good agreement with the linear stability theory.

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Drag reduction on the pressure loss of a circular pipe and the drag of a free-falling sphere in water/fine solid particle suspensions has been shown experimentally. The tested suspensions were carbon black, kaolin and SiO₂ suspensions. The pressure loss data of the pipe flows in the laminar and turbulent flow ranges were obtained, and the rheological equation of these suspensions was decided by the flow curve. The experiment for the drag of a sphere was performed on the free-falling sphere in the suspensions. Twenty spheres between 6.35mm and 14.96mm in diameter were tested. Four ultrasonic transducers, which were set facing and in contact with the side wall of the vessel filled with the test suspensions in pairs of ultrasonic transmitter and ultrasonic receiver, were used for the falling velocity measurement. It has been shown from this study that the drag reduction of a sphere occurs in carbon black suspensions, and the range of Reynolds numbers obtained for the reduction is Re≥8×10³.

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Squeeze film flow between a flat plate and a spherical surface subjected to sinusoidal oscillations is investigated. Transmitting force generated in the squeeze films is measured and calculated with a constitutive equation yielding the stress overshoot and the following results have been obtained: The force measured for Separan solutions oscillates with smaller amplitude than for purely viscous liquids and shows a phase lag in comparison of the force of the viscous liquids. Numerical calculation using the constitutive equation gives guantitative or qualitative agreement with the experimental data for the phase lag or for the amplitude, respectively. The energy dissipated in the Separan solutions in one cycle is less than that evaluated for the purely viscous liquids. An apparent Deborah number respectively correlates to each of the decrease in amplitude, the phase lag and the dissipation of energy taken for various experimental conditions. In the analytical results, an impulse evaluated by integrating the force in one cycle gives a positive value and this means that two surfaces are forced to separate by sinusoidal oscillations.

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Incompressible flows around a yawed circular cylinder at Reynolds number 2000 have been calculated by the finite difference method based on the third-order upwind scheme for approximating the nonlinear terms of Navier-Stokes equations. No turbulence model is employed in this study. Computations are carried out in cases with and without end plates in order to investigete the effect of them on the flow. The calcurated pressure distributions around the cylinder are compared with experimental data and the agreement is satisfactory. The results of this computation show the details of the flow especially in the wake region and it is found that the existence of the end plate greatly affect the location of the separation point.

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The objective of the present study was to investigate the suppression of the fluid forces acting on a circular cylinder by controlling the flow around it. The flow control was established by introducing a fine flat plate in the neighbourhood of the main cylinder. Measurements were carried out to change systematically the position of the flat plate, and then the steady and unsteady fluid forces were examined to estimate the magnitude of the reduction themselves and to identify the optimum position of the control flat plate in order to reduce the fluid forces. Furthermore, such matters as the mechanism of the flow control, the structure of the controlled wake and the behaviour of the controlled boundary layer and the separated shear layer were discussed. Then the availability of the present method to reduce the fluid forces and suppress the vortex shedding was synthetically evaluated.

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The modification of the GSMAC finite-element method has been used to simulate the fluid flow created by a pair of rotating rolls. To verify the validity of the results thereby obtained, a flow visualization test was performed by a hydrogen bubble test. The fluid velocity distribution as well as the boundary layer thickness values thus obtained by calculation and test showed a high degree of agreement. The present technique was then applied in analyzing the fluid flow and diffusion of moisture in the dryer section of a paper machine. The numerical analysis clearly defined how the velocity distrubution would vary with or without the air nozzle, and clarified the diffusion effect of the air nozzle.

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This paper presents experimental results for the coupled vibrations of two discs. The upper disc is fixed along the outer boundary while the bottom one is fixed at the inner periphery. The two discs face each other in a fluid-filled cylindrical vessel. The simple theoretical formulae which were presented in the 1st report are examined. The experimental results are in good agreement with the theoretical results, which showed that two coupled frequencies appear for each number of nodal diameters. The difference between the natural frequencies from the theoretical and experimental results is studied, and some modified formulae are presented that predict the natural frequencies of the runner of a centrifugal hydraulic machinery more accurately.

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The distribution of the wall shear stress in the developing flow of a strongly curved tube with the curvature ratio, defined as the ratio of the tube radius to the radius of curvature, of 1/2, 1/3, and 1/7, was measured by means of the electrochemical limited current method for the Dean number range of 139 to 372. The working fluid is the aqueous solution of potassium ferro- and ferricyanide. In the upstream region, the wall shear stress at the inner wall shows the maximum, and this maximum shear stress shifts towards the outer wall for both parabolic and uniform entrance velocity profiles. It should be noted that the maximum shear stress achieved in the middle portion of the curved tube increases with the increase in the curvature ratio. This nonuniformity of wall shear stress profile is associated with the localization of atherogenesis found in the curved arterial vessels.

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In this paper, two kinds of choking processes of flows were numerically investigated. One is the choking process of the flow generated by the shock wave passing over the wedge in a shock tube, and the other is the choking process of the uniform flow produced by sudden reduction of cross-sectional area in a duct. The computations were carried out by solving the two-dimensional Euler-type equations by means of the TVD method. The numerical results agree well with experimental results of the choking process in a shock tube, and clarify the developing process of the sonic line and the effects of choking on the shape and the behavior of the adjusting shock wave produced in the choking process. This shows that the reflected shock wave from the wedge in a shock tube and the shock wave generated at the thoat in the uniform flow develop into adjusting shock wave in the choking process.

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The Reynolds stress transport model (below RSTM) is one of the time-averaged turbulence models. RSTM is superior to eddy viscosity models (typically k-ε model) in universality because it takes account of the Reynolds-stress-transport phenomena. A lot of RSTMs have been proposed and investigated. RSTMs were constructed on the basis of many assumptions which are not clear. This report investigates whether or not each term is modeled reasonably, and deals with the problem of return to isotropy in order to check slow term models in the pressure-strain correlation. It was shown that the four existing models cannot reproduce the phenomenon correctly. I proposed a new nonlinear model and inspected the performance.

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We have calculated fully developed and unsteady flows in a curved duct having an aspect ratio of 2 and a curvature ratio of 8. The present report shows flows obtained by the pressure gradients C=6.93×10⁴ and 7.20×10⁴, at the range of which periodic flow patterns existed. As for the flow at C=6.93×10⁴, it was considered by topological graphs of three velocity components whether an equilibrium state was obtainable in the flow. There existed the only pair of fixed points which correspond to a main secondary flow. The pair of fixed points may, however, be unstable, because any one of the fixed points was a saddle point. On the other hand, as for the flow at C=7.20×10⁴, we obtained the Poincare map formed from an orbit in a phase space of velocity, and showed a torus surface to be stretched and folded. Accordingly, chaos may be considered to be a strange attractor in the higher Dean number.

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When a swirling flow is added to a parallel pipe flow, a shear flow is formed between parallel and swirling flows and flow fluctuations are induced by the instability of the flows. This was indentified on an experimental apparatus of the flows by using an anemometer, and it was found that the experimental results on these flow fluctuation characteristics almost agreed with the theoretical results predicted by the previously published theory about the stability of a single swirling vortex layer in a rigid pipe. Comparing this fluctuation with the fluctuation in a simple swirling flow, the author clarified also the differences between the two.

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Measured data such as static pressure, velocity profiles, distributions of turbulence shear stress and turbulence intensities of the turbulent flow through an abruptly expanding circular duct are reported. The flow induced to the abruptly expanding circular duct was a fully developed one. The flow in the abruptly expanding circular duct reattached at about one diameter downstream and fully developed at about 70 diameters downstream from the abruptly expanding step.

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In the previous paper, we showed that a circular plate with many small holes attached just downstream of the outlet of the feed water pipe is a better device for controlling the distribution of the flow rate into the branch tubes from a header in a multitube heat exchanger. It was also reported that the flow rate distribution in the case with a particular hole diameter is remarkably different from that with the other diameter. In the present experiment, to clarify the mechanism to cause the difference, the flow pattern in the header was visualized by using aluminum powder as a tracer, and the pressure distribution on the bottom wall of the header was measured. The results show that the flow rate distribution is closely related to the flow pattern in the header.

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The purpose of the present study, which is composed of two parts, is to predict analytically the steady performance of a supersonic through-flow fan in terms of design parameters. It is assumed that the fan cascade operates at supersnic axial velocity with a small angle of attack, camber and thickness. In 1st Report, the linearized lifting surface theory for a rotating annular cascade on the basis of the finite radial eigenfunction series approximation developed by the first author is extended to the supersonic through-flow fan model. Expressions of the disturbance flow field are derived, and the integral equation for the steady loading is numerically solved. The fundamental features of the blade surface pressure distribution dependent on the blade profile are demonstrated. The extensive parametric study of steady performance is presented in 2nd Report.

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Numerical solutions for steady loadings are presented for various combinations of prescribed design parameters. At low axial Mach numbers, high solidity and high camber with maximum camber position nearer to the trailing edge are desirable to attain higher total enthalpy increase. The contribution of the camber decreases with increasing axial Mach number. At high axial Mach numbers, the contribution of the angle of attack is predominant.

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We carried out 2-D cascade tests of multiple-circular-arc (MCA) blades with a relatively high camber angle of 56 deg. in the region of inlet Mach number (M₁) 0.4≤M₁≤1.2, and with systematic variations of cascade geometry and incidence angle. Systematic data with respect to inlet Mach number characteristics of the cascade of MCA blades were obtained. We discsussed the effect of space/chord ratio on the performance of cascade of MCA blades, i. e. inlet Mach number characteristics, the relationship between incidence angle and parameters of cascade performance (incidence angle characteristics), in the constant stagger angle of 10°in the 4th report. In the present report, the following items are discussed on the basis of experimental results in the constant stagger angle of 5deg : 1. the effect of space/chord ratio on inlet Mach number characteristics ; 2. the effect of space/chord ratio on the relationship between incidence angle and parameters of cascade performance (incidence angle characteristics) at M₁=0.9, 1.0, 1.1 ; 3. the effect of space/chord ratio on stall incidence angle, and reference incidence angle ; 4. the relationship between incidence angle and critical inlet Mach number in the set of space/chomd ratio of 0.4, 0.6, 0.8 ; 5. the optimal incidence angle and the effective working range of incidence angle which was deduced from the above mentioned relationship of (4) ; 6. relationship between space/chord ratio and deviation angle at optimal incidence angle.

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Channels by skirts are considered in order to style the underside of vehicles in such a way as to facilitate the air flow in relation to stability problems. The ground effect of these channels attached to the middle or/and rear of the vehicle underside is investigated in a wind tunnel with a moving belt and a suction box. Flow visualization of the underside is carried out using the methods of oil and tufts. As a result, these channels can control the flow underneath the underside of the vehicle, which has an important effect on the aerodynamic lift. The diffuser-type channel is effective in reduction of the lift. But effect to the drag are small. From flow patterns, the flow inside the channel on the middle is referred to the flow in a sudden enlargement or a contraction, and that on the rear to that in a diffuser.

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The effect of electric field on frosting phenomenon is investigated. It is known that the frost formation on a heat exchanger seriously affects the performance of the system, and that the application of electric field is one of the promising procedures because dielectric water molecules play a role of solidification nuclei. In order to understand the fundamental characteristics of the frosting phenomenon under the electric field, experiments have been carried out. The electric field is applied between the frosting surface and the mesh electrode which is placed in parallel with the surface. The results of experiments reveal that the apparent mass transfer rate is decreased and the heat transfer rate is increased by applying the electric field because the dendritic frost crystal is removed by the strongly imposed electric field.

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Experimental considerations for the control of oscillating noise were made regarding the results of various steam-injecting visualizations as shown in the previous report. These injecting patterns were analyzed through the photographs selected from the picture film. The present investigation clarified that the condensing oscillation noise has some relationship to the quantity of thermal layers. Temperature distribution and S. P. L. predicted for certain visualized results had correlated well. These experiments were performed for atmospheric pressure, and for temperature differences between the saturated steam and water used for subcooling, 20-70°C.

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In order to investigate the characteristics of step response and heat transfer of an optical fiber thermometer (OFT) having a tip of a 1.27mm diameter sapphire rod sputtered with platinum, OFT heated up to 1000°C was rapidly inserted into a potential core region of a free room-temperature air jet using pendulum motion. The time constant, the heat transfer coefficient of OFT, and the correlation of Nu=(3.07+0.529Re^0.5) Pr^0.38 for Re=380-1800 were obtained. Uncertainty analysis was also carried out to support the conclusions. OFT output shows a very slow response at the quasi-steady period but a considerably quick response at the transient period. It is also made clear that the OFT response at the quasi-steady period is close to a first-order response. Very good agreement is obtained between experiment and numerical simulations, assuming one-dimensional unsteady-state heat conduction inside the sapphire rod.

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Frequency response of an optical fiber thermometer with a blackbody cavity sensor (OFT) was investigated by Fourier analysis, following the first report on its step response. By using typical data of mass-average gas temperature inside the cylinder of an I.C. engine, analytical simulation was carried out to obtain the gas temperature from the temperature variation indicated by OFT. Such high resolution of OFT with a commercially available size as 0.1°C is found to be necessary for the measurement of gas temperature in an engine. The output signal of OFT should be cut off at the 30th harmonic by a filter, since the larger error in obtaining the gas temperature is caused by the higher frequency noise. A reduction error constant is proposed as a reduction error index.

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This paper presents a burst detection method, called a correlation trigger, which can extract Doppler signals from noisy and visually indistinguishable signals. The correlation trigger uses a burst digital correlator in which the strength of correlation is expressed by the height between the peaks and troughs of the correlation function, and depends on the SNR. The results of numerical simulation show that the correlation trigger can detect the Doppler signals down to SNR=-10dB. It was found that the amplitude triggering can not detect low SNR data of less than 0dB, and the reasonable correlation threshold level was one-sixth of the sample number to be correlated. The BDC correlation trigger is effective for low SNR, wide bandwidth, wide dynamic range, small fringe number, and high deta-rate.

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This paper presents experimental results about a mean temperature field obtained in forced convection heat transfer for a turbulent flow through a square duct with a rough wall. The local Nusselt number on the smooth walls of the rough duct was 1.71∼1.97 times that of the smooth-walled duct. Distributions of the local wall heat flux clearly reflected the secondary flow pattern in the duct. In a half cross section including the smooth wall opposite the rough wall, the distribution of the mean temperature was similar to that of the primary flow velocity. The existence of a temperature inner-law was confirmed there. However, the inner-law did not exist in the half section including the rough wall. In this region, dissimilarity appeared between the distributions of the mean temperature and the primary flow velocity. Based on the transport equations of Reynolds stress and turbulent heat flux, the mechanism of the heat transfer enhancement by the rough wall was examined.

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Two-dimensional imaging of OH and CH intermediates in a premixed flame using natural gas bunsen burner by means of laser induced fluorescence techinique are described. A tunable laser beam with a single laser pulse energy of 1.5mJ is focused by a cylindrical concave lens, which forms laser sheet 5mm high and 0.5mm thick. We have chosen a band near 308nm : OH [X²Π(υ=0)→A²Σ(υ=0)] excitation and a band near 431nm : CH [X²Π(υ=0)→A²Δ(υ=0)] excitation. Fluoresence at a right angle is amplified by gated image intensifier and detected by CCD camera. A complete picture of qualitative distribution of OH and CH is obtained by combining several piuctures taken at a series of diffrent distances between the bumer head and laser sheet.

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In the first report, a model for the premixed turbulent flame structure was proposed on the basis of recent experimental results and validated by the good agreement of predictions with measurements of the turbulent burning velocities of 16 mixtures. In this report, the turbulent burning velocity derived and all structural parameters were reduced into dimensionless quantities. As a result, all reduced parameters were expressed with only four dimensionless variables : the Reynolds number Re, a Damkohler number Da_η, the Prandtl number and the ratio of the thickness of the reaction zone to that of the preheat zone of an unstrained laminar flamelet. A generalized correlation between the flame structure and burning velocity was thus obtained and shown in Re-Da_η planes as well as S_T/S_LO-u'/S_LO planes.

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The combustion behavior of coal-water mixture (CWM) droplets was observed in the electric furnace, where the measurement of droplet temperature, video recording and high-speed photography were carried out at sequential steps of the combustion process. The effects of furnace temperature, slurry concentration and oxygen concentration were examined in order to elucidate the combustion mechanism of CWM droplets. The results indicate that they are influenced considerably at each step of the combustion process such as vaporization, ignition, visible envelope flame combustion and char combustion. The effects of the addition of C-heavy oil, A-heavy oil, methanol and kerosene were examined in order to elucidate the feasibility and the mechanism of microexplosion of CWM droplets. The results show that the explosion makes fairly short both ignition delay time and total combustion time in the fuel of C-heavy oil in addition to the CWM.

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In order to establish the operation technologies of the molten carbonate fuel cell (MCFC) power plant, it is necessary to understand the dynamic performance of the stack itself, which is the most important machine in the plant. The authors developed the dynamic performance model of the largescale MCFC, which has the distributions of temperature, current density, and so on. The simulation results agree well with experimental results of a 10-kW-class stack qualitatively. Using this model, the response to the load current was analyzed for three types of MCFC adopting its own gas flow system such as cross-flow, co-flow and counter-flow. The simulation results showed similar voltage response in three types of MCFC. The response of temperature and current density, however, varied extensively

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Experiments were conducted to investigate the effect of heating surface configuration on the heat transport characteristics of closed two-phase thermosyphons by using four kinds of heating surface : smoth, artificially roughened and two grooved surfaces. The working fluids tested were water, methanol and refrigerant R113. The results show that making the heating surface rough is effective in improving both the heat transport efficiency and the performance limit compared with the smooth heating surface. Cutting longitudinal grooves on the heating surface is also effective in improving the heat transport efficiency since the area of the heating surface is increased. However, the heat transfer rate is not always increased at the performance limit by cutting the grooves. The rewetting of the heating surface with a falling liquid film was also examined.

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The alkali metal thermoelectric converter (AMTEC) is an efficient device for the direct conversion of heat to electricity. A new method to supply thermal energy to beta"-alumina solid electrolyte (BASE) tubes is proposed in this paper. Porous metal inserted between a high-temperature thermal source and the BASE tubes not only collects current generated from electrodes but also enhances the heat transfer. An experimental study has been conducted on the disturbance of vapor flow through the porous metal. Its effect on the AMTEC performance has been examined. The calculated results indicate that the sodium vapor flow resistance converted into temperatre difference is in the range from 20K to 50K and the expected increase of power density with porous metal current collection structure is ∼50%. The influence of potential drop along the electrode is also discussed.

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Copper ion-exchanged ZSM-5 zeolite catalyst, which deoxidizes nitrogen oxides (NO_x) in the presence of oxygen and hydrocarbons, was applied to actual diesel engine exhaust. Copper ionexchanged ZSM-5 zeolite effectively reduced NO_x by 25% in normal engine operation, and by 80% when hydrocarbons in the exhaust were increased. Water in the exhaust gas decreased the NO_x reduction rate, but oxygen and sulfur appeared to have only a small effect. Maximum NO_x reduction was observed at 400°C irrespective of hydrocarbon species, and did not decrease with space velocity up to values of 200001/h.

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Diesel fuel spray from a single-hole-type injection nozzle is investigated under steady and atmospheric conditions in order to understand the unsteady Diesel spray. Axial and radial velocity components of the spray at two constant injection pressures of 9.8MPa and 4.9MPa are measured by laser Doppler anemometer (LDA), and turbulence characteristics of the spray flow velocities are analyzed. Distributions of mean velocity and turbulence characteristics in the spray flow are compared with gas jets and other spray flows. It is found that the injected spray is accelerated in the region close to the nozzle exit, and this phenomenon may be estimated as a kind of cavitation caused by expansion of dissolved gas in the fuel. The decrease in centerline velocity along the nozzle axis is very small and the air entrainment factor is also shown to take a smaller value than in previous experiments.

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Knock in internal combustion engines causes various problems, such as increases in thermal loads, abnormal wear and the deterioration of performance. Even the mechanism of thermal loads alone has not been clarified yet. Under this study, therefore, instantaneous temperatures on piston top surfaces of a four-stroke gasoline engine on occurrence of knock, caused by changing the spark timing and octane number, have been measured using highly accurate thin-film thermocouples. Conditions of heat losses according to the intensity of knock have been clarified from the instantaneous heat fluxes and coefficients of heat transfer determined by the measurements.

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The present work investigates the dynamics of a cluster of bubbles in a liquid by means of a series expansion of spherical harmonics. The governing equations of three-dimensional motions for arbitrary configurations of N bubbles are derived by taking account of translational motions and deformations induced by mutual interactions among the bubbles. These equations are exact to the order (R_IC/L_IJO)⁵ for inviscid terms, where R_IC is the characteristic radius of a specified bubble I and L_IJO the initial distance between the centers of the bubbles I and J. Viscous effect of the liquid is considered up to the first order in perturbation of spherical symmetry on the basis of the potential solution. The equations involve previous results for a single and two bubbles as special cases. Characteristic equations for oscillations of N spherical bubbles are also obtained and natural frequencies are calculated for specified configurations of the bubbles. It is shown that the lowest frequency of the bubbles is much lower than that of an isolated bubble.

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This paper deals with the dynamics of a cluster of bubbles. Governing equations derived in the first report are solved to predict collapse motions of the cluster of bubbles under sudden and stepwise increases in pressure of the liquid. A test computation is first performed on the collapse of two vapor bubbles in the neighborhood of a plane rigid wall and is found to be in good agreement with a result obtained by the boundary element method. The collapse motions of one through nine bubbles placed in different configurations are analyzed. It is shown that three-dimensional deformations of the bubbles are greatly affected by traslational motions of individual bubbles. The results show that the pressure at the boundaries of the interacting bubbles can be higher than that of an isolated bubble. Effects of liquid viscosity are also discussed.

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For the first step to find low-drag thin hydrofoils in cascade applicable to Kaplan-turbines, the subcavitating performance and the corresponding cavitation aspects for two different hydrofoils whose shapes are quite the same except the neighborhood of the leading edge within one percent chord. The leading edges are somewhat modified, for two cascade arrangements of a pitch-chordratio t/l=1.14 and of two cascade angles θ₁=23°and 35°, for various cavitation numbers and various incidences. Clearly, a marked change in drag is resulted from such a very small modification around the edge, which is closely related to the boundary layer separation around the leading edge. It is also suggested to the suitable modifications without separation bubble.

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Detailed mean flow measurements have been made in a planar turbulent boundary layer interacting with artificially generated trailing vortex arrays in a free stream. Two parameters, namely, spanwise periodicity of the longitudinal vortex arrays (L/S ; here L denotes the spanwise distance between neighboring airfoils, S airfoil span) and ratio of the longitudinal vortex scale b to boundary layer scale δ₀, were independently varied for five cases. Within the boundary layer, there exists a spanwise transport of streamwise momentum due to pairs of counterrotating secondary flows. As a result, spanwise periodic variation corresponding to the spanwise spacing of airfoil elements arises in the mean flow properties, and is persistently maintained in the far downstream region. The value of L/S plays a dominant role under the distortion process in this flow field. In the case of L/S&gsim;1, the spanwise periodic variations of mean flow profiles are significantly large, and these spanwise periodicities are persistently maintained in the streamwise direction. In the case of L/S<1, although the spanwise variations are small in magnitude, the spanwise periodicities of mean flow profiles change in the streamwise direction, while the effect of b/δ₀ is caused as a local Reynolds number effect.

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An experimental and theoretical study of pulsating flow of magnetic fluid in a pipe applied with a fluctuating magnetic field is made. The flow characteristics which are dependent on frequency, fluctuating flow rate, and radius of the pipe, are measured and compared with theoretical values acoording to aggregated magnetic particles. Through the investigation, it is clarified that the fluctuating pressure difference and phase difference between pressure and flow rate are varied by the magnitude of applyed magnetic field and the phase difference between flow rate and magnetic field.

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In the boundary element method, accuracy in integration of singular integrands ∂/∂n(1/r) and 1/r is very important, especially in the case of a very thin, close boundary with complex curvatures, such as a marine propeller. This paper proposes a method for accurate integration of singular integrals in case of the complex boundary mentioned above. The effects induced by the location of wake, length and mesh division of wake for the analysis of lifting body are also presented.

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An air circulating path for air cleaning and cooling in a closed magnetic hard-disk drive is improved in view of reduction of reverse flow through an opening on a partition between a disk room and an actuator room. Amount of reverse flow is estimated, including effects of velocity fluctuation. The reverse flow is reduced by employing flow balancers and an air guide. The flow blancers form an air curtain that prevents reverse flow from the actuator room to the disk room. An air guide along the upstream-side edge of the opening stabilizes the air curtain.

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