A review concerning oscillatory instabilities produced by laser (thermal lens oscillations, optical heartbeats) or hot- wire heating below an interface is given. The dynamical states and bifurcations observed in thermal lensing are described. For the hot-wire experiments, critical quantities for the onset of overstability (Hopf bifurcation) are given and discussed. Three theoretical approaches are developed in order to understand these instability phenomena and recover experimental results : numerical analysis, examination of possible analogies with simpler systems and design of very simple models. The systems under discussion indicate a new candidate for systematic studies in the framework of nonlinear dissipative dynamical systems.

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The velocities and drag forces experienced by two equal-sized spheres freely falling along their center lines are measured using the "falling-spheres" technique at low Reynolds numbers. The width of the test tank, which has a square cross section, is 100 times the diameter of the spheres used. The measurements, with an estimated uncertainty of ±1.2%, show that the lower sphere experiences the Oseen drag and that the upper sphere experiences the Stokes drag, which was predicted by Stimson and Jeffery. Flow visualization using a naturally occurring phenomenon in glycerol illustrates the difference in the hydrodynamic drag force between the lower sphere and the upper sphere. The numerical calculations of Stimson-Jeffery's solution reveal in detail the occurrence of vortex flows within a closed separating region between the two spheres.

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Velocity profiles of the laminar flow in the developing region of an axially rotating pipe are analyzed numerically in this paper and compared with the experimental results obtained when a uniform axial flow is introduced. It is found that the axial velocity in the rotating pipe exceeds the value of the Poiseuille flow at the center, and that a backward flow appears near the pipe wall as the rotation rate becomes large. The greater the rotation rate N becomes, the more remarkable the excess of the axial velocity at the center and the backward flow near the wall tend to become ; experiments show, however, that at about N=3, pipe rotation causes the flow to become unstable and the development of the flow is delayed.

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Mean flow properties and one-point multiple velocity correlations including turbulent stresses have been measured in a two-dimensional turbulent flow through a curved channel with a radius ratio of 0.92. The results for the fully developed region are presented and compared with those of a parallel plate channel .The turbulence energy balance shows that the greatly enhanced turbulent diffusion away from the outer wall extends to about 2/3 of the channel width, and reduces the equilibrium layer thickness considerably. It is found that an existing model for the pressure-strain correlation simulates with good accuracy the experimental values obtained from the turbulent stress balance. The triple correlation balance reveals that the terms relating to the mean flow are of the same order of magnitude as other terms even in the core region where the turbulent diffusion plays an important role.

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A two- or three-dimensional turbulent jet induced by the Coanda effect along a curved wall has been investigated by many researchers. In spite of the many studies of this Coanda-induced jet flow, the flow characteristics have not been completely understood. This paper presents a theoretical analysis using an integral momentum equation and an experimental analysis on velocity and pressure distributions for a two-dimensional jet along a circular cylinder. From the theoretical analysis, the equation of velocity distribution, pressure distribution, decay of jet centerline velocity, changes of jet width and half width, for example, are made clear, and it is shown that they are in good agreement with experimental results.

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The generation and propagation of turbulent slugs in a circular pipe were studied under transient flow conditions. The Reynolds number chosen for the final steady state was above the critical Reynolds number of the experimental apparatus. A turbulent slug was initiated about 10 diameters downstream of the entrance, preceded by unstable waves with a frequency very similar to that of the Tollmien-Schlichting wave. After the passage of the first slug, many slugs appeared in the region of x/D≒14∼40, where x was the axial distance and D was the pipe diameter. The axial propagation velocities of the leading and trailing edges of the first slug were determined and compared with those of slugs in steady pipe flows. Velocity distributions inside and outside the slug were examined.

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When a viscoelastic fluid flows out from a horizontally placed rectangular duct, many cracks and protruding ridges are formed on the upper surface of the jet. This anomalous phenomenon is reported for the first time by the authors. We investigate the critical point of this anomalous phenomenon under various conditions .Fourteen ducts having various heights, widths and lengths are used in this study. They have knife-edge-shaped or semicylinder-shaped duct exits. We also use four kinds of fluids having different flow properties. Moreover, we find an empirical formula for the critical point of the anomalous phenomenon through use of the dimensional analysis method.

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An experimental study is presented outlining the dynamic behavior of a liquid in a cylindrical container subject to horizontal oscillation. The nonlinear effects on dynamic characteristics of the liquid-surface response are investigated. At low excitation acceleration, the liquid surface responds in a concentric standing wave. For excitation acceleration above a critical value, surface instability leads to azimuthal standing waves at half the excitation frequency. The time-dependent amplitudes of the standing waves have been measured using an optoelectronic device equipped with a laser diode as a light source. The frequency spectrum of the local surface deformation has also been computed using fast-Fourier-transform methods. It was found that a subharmonic bifurcation occurred at the critical excitation acceleration. At higher excitation acceleration, the free surface responses became chaotic. In order to visualize the attractor, phase portraits were constructed by embedding the trajectories in a two-dimensional phase space.

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When condensation occurs in a blade passage in a steam turbine, it affects an oblique shock wave originating from the trailing edge of the blade. In the present study, a condensing flow was produced by an expansion of moist air in a supersonic circular nozzle, and following insertion of a wedge-type shock generator into the supersonic parts of the nozzle, the effects of condensation on an oblique shock wave were investigated experimentally. The position of the oblique shock wave relative to the condensation zone and the change of shape of the oblique shock wave due to condensation are discussed. Furthermore, the loads working on the nozzle wall are obtained from the measurement of pressure distribution, and the effect of condensation on the load is discussed.

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This paper describes a theoretical analysis based on potential flow. By use of the vortex lattice method, calculations were performed to obtain unsteady aerodynamic forces acting on oscillating blades with tip clearances. Calculated damping forces in the case of large tip clearance showed good agreement with the experimental data. When the clearance was small, however, a discrepancy was found between the experimental and analytical results .This discrepancy was thought to be ascribable to the viscous effect of the flow near the blade tips. To explain the experimental data it was necessary to apply a model such that each blade should retain finite circulation at the extremity of its tip. From the calculated results for various reduced frequencies it was confirmed that aerodynamic characteristics found in the experimental study could be applied equally to the wide range of reduced frequencies.

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An attempt to control secondary flow was made in order to improve turbine aerodynamic performance. Boundary layer fences were attached to endwalls of a linear turbine rotor cascade. Measurements of total pressure losses and three-dimensional flow velocities were taken for 5 different heights and 7 different pitchwise locations of the fences. It was found that the fences were most effective when they were 1/3 of the inlet boundary layer thickness high and located half a pitch away from the blades. These optimum fences reduced streamwise vorticities, the thickness of the endwall loss region, secondary kinetic energy, and the maximum underturning by half. Moreover they diminished the secondary loss by 22 percent, and the gross loss, including kinetic energy dissipation, by 25 percent. A critical fence height above which the fences trap the pressure side legs of horseshoe vortices was found, and the optimum fences proved to be fences of the minimum critical height.

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The instability of Taylor vortex flows in a gap with a small aspect ratio of concentric rotating cylinders has been investigated. For both the asymmetric and symmetric end conditions, the critical Reynolds number of the transition from the Taylor vortex flow to the wavy Taylor vortex flow has been revealed. In the asymmetric case, the bifurcations between odd numbers of cells and between an odd number and even number of cells are shown in relation to the aspect ratio and Reynolds number. In addition, the bifurcation diagram is drawn in the neighborhood of a certain aspect ratio. The relations, as priority, between primary flow and secondary flow on a bifurcation set are discussed.

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The isolated influence of longitudinal vortices "far enough" from a half-delta wing vortex generator on heat transfer of an otherwise laminar boundary layer was experimentally investigated. The heat transfer measurements were performed using a constant heat-flux surface with 96 embedded thermocouples. The vortex generator's height and angle of attack were varied to account for the influence of the vortex size, position and strength. A large increase in the heat transfer coefficient was found to be associated with the onset of the transition to turbulence rather than to vortical motion. The longitudinal vortices generated inside and outside the boundary layer showed different effects on heat transfer. When the transition did not occur, it was observed that the higher heat transfer coefficients were associated with the downwash region of the vortex, because of the local thinning of the boundary layer. The transition started in the upwash region of the vortex, where the instability was larger.

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This paper investigates how heat transfer and fluid flow are affected by the channel width as it is varied from small to large scale in a wavy sinusoidal channel. The mean Nusselt numbers in periodic fully developed regimes depend on the maximum Nusselt number at the reattachment point of the flow separated from the top of the peak, and reach maximum at P/H=2.0∼1.6 (P:pitch, H:width) ; the friction factor becomes maximal at the same ratio P/H=2.0∼1.6. The performance ratio η_II, at equal pumping power, attains a maximum at P/H=2.29∼2.0. Thus, it can be concluded that the channel is optimal at P/H=2.0 for augmenting heat transfer.

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Experimental and analytical investigations were performed on a direct contact melting process of a phase change material (PCM) which was contained in an inclined rectangular space surrounded by a heat transfer surface and plated fins. The solid phase varied in shape, receiving the latent heat of fusion from the surrounding walls at the contacting spots, and moved within the rectangular space, changing the contacting mode. The numerical method to simulate such a direct contact melting process was proposed. Experiments were also conducted to examine the numerical method, using N-octadecane as the PCM. The experimental and analytical results agreed quite well with each other. It was found from the analytical results that the inclination angle scarcely affected the average melting rate despite the serious effects on the contacting mode and the heat flux distribution over the walls.

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The temperature distribution of a molten carbonate fuel cell was investigated experimentally and analytically during electric power generation. A numerical method to solve the fuel cell temperature distribution was proposed and examined. The method searches for the steady-state temperature whose changes are coupled with the electro-chemical reactions and gas flow. Calculation results were compared with experimental results, and reasonable agreement was obtained. As a consequence, the effect of heat conduction was observed to be closely related to the temperature distribution of the fuel cell.

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Mass transfer coefficients from liquid phase to particles in packed beds have been investigated for gas continuous two phase flow with a stationary gas phase. Liquid holdup existing in packed beds was obtained by using the method of neutron attenuation and a correlation for liquid holdup was presented as a function of the Reynolds number and the Galilei number. Liquid-to-particle mass transfer coefficients were measured by the limiting current technique. Mass transfer coefficients in two phase flow became greater than those in liquid-full single flow, and were arranged by modifying the Reynolds number and the Sherwood number, considering the actual liquid velocity among particles and the ratio of the mass transfer area to the sectional area of liquid film.

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A picture-processing techique is applied to the study of flame motion in a direct-injection diesel engine. From high-speed photographs, two-dimensional cross-correlation coefficients of flame luminosity between two successive frames are obtained. The location and value of the maximum coefficients give us the mean and fluctuating velocities of the flame, respectively. The results show that the fluctuating velocity obtained in a wide region is almost independent of measuring position and size in the middle and later stages of combustion, indicating that the turbulent flow field is almost uniform and isotropic over the space in diesel engines. The effects of the swirl and chamber geometry on flame behavior are discussed in detail.

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The characteristics of roughness of a turbulent flame front in a disc-type combustion chamber were determined through high-speed schlieren photography and image analysis. The correlations between the characteristics of flame-front roughness and the turbulence characteristics or the turbulent burning velocity were discussed. The main results were as follows : (1) The RMS value "α^^-" and the integral scale "L^^-_f" of the flame-front roughness are strongly influenced by the intensity and the integral spatial scale of turbulence. (2) The shape of the power spectrum of flame-front roughness is similar to that of the power spectrum of turbulent flow, and the microscale of the flame-front roughness is nearly equal to the Taylor microscale of turbulence. (3) The ratio of turbulent burning velocity to laminar burning velocity, S_T/S_L, is proportional to the value of √(1+(2α^^-/L^^-_f)²).

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An ammonia converter was constructed using a commercially available platinum catalyst, with the aim of applying it for the measurement of ammonia concentrations. The dependence of the ammonia converter efficiency on the reaction temperature and the ammonia concentration was investigated by measuring the concentration of the converted nitric oxide. The results showed that the catalyst almost completely oxidized ammonia into nitric oxide at temperatures above 600°C in the tested range of ammonia concentrations. In addition, by combining the ammonia converter with a chemiluminescent NO_x analyzer we were able to measure the ammonia concentration in an ammonia-nitric oxide mixture to an accuracy of within 3% by making a correction due to the oxygen concentration.

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A technique for flame diagnostics was developed, in which the luminescence images of OH, CH and C₂ radicals were visualized and processed. Both short-exposure images and time-averaged ones of these radicals were obtained for nonluminous flames. For luminous flames, on the other hand, luminescence images of OH and CH radicals were separated very accurately from the intense background emissions. This was done by processing the monochromatic images of a flame in and around the radical luminescence band obtained using a set of interference optical filters and an image intensifier. The details of the technique were established by spectroscopic observation of a Wolfhard-Parker flame or a turbulent Bunsen flame as well as the computer simulation based on the images. The accuracy of the obtained luminescence images of radicals was evaluated by comparing them with monochrometer data. The present technique is appropriate for the direct visualization of the flame reaction zone and is applicable to industrial flames to which the PLIF technique is difficult to apply.

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In this paper, a practical calculation for the capacity of varying pressure accumulators is developed in detail. To facilitate the calculation of the amount of self-evaporation and the fraction of steam space, two functions of pressure are introduced and are evaluated by using the JSME steam table. Approximated expressions resulting in quick and exact calculations are also given. One of the great merits of the proposed method over existing ones is that the effect of the initial steam space on the accumulator characteristics can be easily and accurately evaluated producing results that are final.

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The objectives of this report are to propose a new method of high performance cool energy storage using ice as a phase change material and to clarify its basic heat transfer characteristics. A working medium vapor layer, a water layer and a working medium liquid layer stratified in this order from the top were kept in an enclosure composed of a condenser, an evaporator and a condensate receiver-and-return tube. Direct contact heat transfers between either water or ice and a working medium in an enclosure was used to achieve high performance cool energy storage and release. In the storage and release processes, water changes phase between liquid and solid, and the working medium circulated naturally with phase changes between vapor and liquid. Experimental apparatus was arranged and R 12 and R 114 were selected as working media. Efficient formation and melting of ice were confirmed by the experiment.

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