Slugging of a stagnant liquid at a V-shaped elbow in a hilly-terrain pipeline is experimentally investigated to obtain information on flow regime and critical conditions of the slugging. According to flow observation using a high-speed camera, the flow is classified into seven flow regimes, i.e. static puddle, wavy puddle, periodic slug flow, periodic semi-slug flow, aperiodic semi-slug flow, film flow and pebble flow. The onset of the slugging is well predicted not by the Mishima-Ishii's model, but by the Wallis parameter used for flooding in a pipe. This means that the slugging at the V-shaped elbow is similar to the flooding caused by interfacial shear stress. An empirical correlation based on a modified Wallis parameter is proposed to represent the effects of inclination angle, pipe diameter and fluid properties on the onset of slugging.

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The ghost fluid method is improved so as to consider the nonequilibrium phase transition at the vapor-liquid interface during the collapse of bubbles in a compressible liquid. In the present method, the ghost fluids are defined so that the conservation laws at the vapor-liquid interfaces are satisfied; the nonequilibrium condensation and evaporation for the collapse of nonspherical bubbles are taken into account. Also, the idea of adaptive zonal grids is implemented in the ghost fluid method to dissolve the fine structure of the interface of the violent collapsing bubble. The present method is applied to the collapse of a spherical vapor bubble, and the numerical results are compared with the experimental results by Akhatov et al. It is shown that the present method can predict successfully the violent collapse of a spherical bubble even though the Eulerian grid is employed. Also, the present method is applied to simulate the collapse of an axi-symmetric nonspherical vapor bubble induced by the interaction of an incident shock wave with the bubble. The liquid-jet formation and the generation of shock waves from the collapsing nonspherical bubble are also simulated successfully by taking the nonequilibrium condensation and evaporation of vapor into account. When the liquid jet develops on the upstream surface of the bubble, the vapor temperature close to the upstream surface increases due to the latent heat by condensation. After the bubble rebounds, the low temperature region caused by the evaporation is found inside the bubble.

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The oscillatory behaviors in a supersonic cavity flow are visualized by LIF (Laser-Induced Fluorescence) and schlieren methods. In the LIF method, an argon-ion laser is used as a light source to excite the iodine molecules seeded into the working gas. The iodine fluorescence, whose intensity is known to be a function of temperature, is detected by the photomultiplier. The pressure oscillation on the bottom wall of the cavity is also measured simultaneously with the fluorescence detection. The phase of fluorescence-intensity oscillation is corrected on the basis of the cavity-bottom pressure oscillation and the correction is performed at every fluorescence detection point. As a result, the temperature oscillations inside and outside the cavity are qualitatively visualized in two-dimensional sense. In the schlieren method, the light source is controlled so as to flash responding to a specific phase of the periodic pressure signal and the oscillatory motion of the shear layer developing along the cavity span is captured. By carefully observing both of the visualization results, the relation between the temperature oscillation and shear-layer motion is clarified.

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A novel combined Pressure-/Temperature-Sensitive Paint (PSP/TSP) sensor, which consists of dot arrays of PSP and TSP, has been developed for simultaneous measurements of pressure and temperature on a solid surface. Conventional combined PSP/TSP sensors suffer from the photodegradation caused by interaction between PSP and TSP luminophores. In the proposed sensor, dot arrays of PSP and TSP were separately arranged for avoiding the interaction. The PSP and TSP dots were made of PtTFPP and CdSe/ZnS, respectively, so that the luminescences from each dot array could be separately detected by optical filters. We investigated fundamental properties of the dot array sensor: photostability, pressure sensitivity and temperature sensitivity. As a result, the photodegradation was not observed in the dot array sensor. It was also shown that PtTFPP dot array had the pressure sensitivity of 0.53%/kPa, and CdSe/ZnS dot array had the temperature sensitivity of -0.61%/K, which were almost the same sensitivities as conventional PSPs and TSPs. Therefore, the proposed sensor will be a preferable sensor for the simultaneous measurement of pressure and temperature.

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An attempt has been made to examine the effects of flamelet on the local flow in turbulent premixed flames in a reaction-sheet regime. Vectors of the flamelet motion and gas velocity have been measured simultaneously by use of a four-element electrostatic probe and a three-color, six-beam LDV system on the centerline of the turbulent flame brush. It has been clearly shown that change in the gas velocity across the flamelet differs whether the flamelet passes in the unburnt-to-burnt or burnt-to-unburnt direction. When the flamelet passes in the unburnt-to-burnt direction, the unburnt mixture exists above the flamelet and the burnt gas below the flamelet. The acceleration due to thermal expansion occurs perpendicularly downward to the flamelet, consequently, the gas velocity component normal to the flamelet decreases in the burnt gas. When the flamelet passes in the burnt-to-unburnt direction, the burnt gas exists below the flamelet and the unburnt mixture above the flamelet. The acceleration due to thermal expansion occurs perpendicularly upward to the flamelet, consequently, the gas velocity component normal to the flamelet decreases in the unburnt mixture.

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The HCCI engine has attracted for high efficiency and low exhaust emissions. However, the HCCI combustion process has two issues to be resolved : ignition timing control, slower combustion. In order to overcome these issues, it is necessary to investigate in detail the low-temperature oxidation reactions that distinctly characterize HCCI combustion and the state of combustion. In this study, spectroscopic measurements were made at a high compression ratio of approximately 15:1, which is sufficiently high for practical operation. Simultaneously, the combustion condition in the cylinder was visualized via a sapphire observation window that was provided in the top of the cylinder head by taking advantage of the simple structure of the two-stroke test engine. The results revealed that the ignition delay period and the manner in which autoignition occurred tended to differ at different compression ratios when EGR was applied, which is believed to be effective in moderating HCCI combustion.

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