As a fundamental consideration in hydraulic valve dynamics, transient flow through a pipe orifice has been studied via a numerical analysis. Steady axisymmetric viscous fluid flow was first investigated to confirm the present SIMPLER-based finite volume methodology. Time-dependent calculation for a suddenly imposed pressure gradient has shown two distinct characteristic time constants for the transient state. The first characteristic time is commonly considered to correspond to the flow rate change, while the second one concerning the variation of flow structure has not been treated in earlier studies. The final settling of flow is completed in the second characteristic time which is almost ten times larger than the first one under the present condition.

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Turbulent pulsating air flows in the entrance region of a square duct are investigated with a hot-wire anemometer system. The velocity waveforms, the mean and turbulence components of the axial velocity, and the entrance length are obtained as major characteristics of the developing turbulent pulsating flows. An inviscid flow theory coupled with the quasi-steady wall shear stress assumption is presented to describe the developing axial mean velocity profiles. A good agreement is seen between the measured and theoretically predicted values. The propagation of turbulence generated near the entrance of the square duct is satisfactorily approximated by an empirical correlation of the propagation of turbulence proposed previously. The local turbulence intensity is found to be slightly weaker in the accelerating phase than in the decelerating phase. The entrance length is about 60 times as large as the hydraulic diameter.

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The characteristics of flow oscillations in density wave instabilities are experimentally investigated by means of a deterministic method based on chaotic dynamics. The results are as follows. (1) The flow oscillation analyzed in this paper is chaotic and obeys a dynamics with a small degree of freedom. (2) Given the mass flux, the dimension of the attractor in the unstable region decreases with the heat flux, which means that the randomness of the dynamics gradually attenuates with departure from the marginal stability boundary, and the structure of the attractor becomes simpler. (3) The dimension of the attractor can be related to the fundamental frequency, which means that the characteristics of the chaotic dynamics generating the density wave instability depend mainly on the fundamental frequency in the flow oscillation independent of the differences in the experimental conditions. (4) The least number of significant figures of the time-series data is two, but it is plausible to take more than three if possible.

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In generating a pulsed high-speed liquid jet by the impact of a high-speed projectile on a container filled with a liquid, complicated shock wave phenomena subsequently appear. The shock waves affect the liquid jet not only at the earlier stage of its formation but also at the later stage of its propagation. This paper reports results of experiments performed in order to understand the entire process of the generation of a liquid jet. The liquid jet was driven either by the impact of a polyethylene projectile directly on a container which was filled with water and connected to a nozzle or by collision of the projectile with a metal piston which transfers the momentum of the projectile to compress the liquid. The resulting shock wave and liquid jet were observed by double-exposure holographic interferometry. Impact pressures were measured with commercial pressure transducers and also with laboratory-fabricated pressure transducers made from polyvinylidenedifluoride (PVDF) piezo film. Shock waves were emitted in front of the water jet through the liquid/gas interface at the nozzle exit whether the speed of the water jet was supersonic or subsonic in terms of the speed of sound in air. This transmission process of the shock wave was demonstrated in an experiment in which an underwater micro explosion was carried out just below the air/water interface. A numerical simulation was conducted to understand the nozzle flow and the pressure history in the nozzle.

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In this study, compression waves produced by trains which enter a hooded tunnel at high speed were numerically investigated. Equations of the one-dimensional, unsteady and compressible flow in which the area of a tube is dependent on the time and the distance were numerically solved by the method of characteristics. The calculations were performed for tunnels with various hoods of different shapes in cases in which the speed of the train was 200 km/h or 300 km/h, and the effects of the shape of the hood on the shape and the strength of compression waves were quantitatively clarified. The results show that the pressure gradient of compression waves is greatly affected by the shape of the hood.

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Computer simulation of refrigerating cycles for automotive air conditioners is effective in predicting performance of the cycle. A proper mathematical model of a compressor is necessary to predict the performance exactly. In this study, the mathematical model of a vane compressor for the automotive air conditioning cycle is developed. The model consists of two control volumes, a cylinder and a rear case, and a compressor body. It takes account of the thermal effect of lubricating oil and heat transfer between refrigerant and the compressor body. Validity of the model is confirmed by comparison between experimental results and calculated ones. The transient behavior in the cycle simulation depends on the compressor modeling noticeably.

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Thermal radiation characteristics of real surfaces of metallic materials are strongly affected by surface roughness and existing surface film. In actual industrial and natural environments, the surface state is not stable, and the radiation characteristics change with time. In this paper, we present an idea for modelling such dynamic change in the surface state in an air-oxidation process at high temperatures. Transient behavior of reflection characteristics of real surfaces is described on the basis of an electromagnetic theory of interference and diffraction of radiation. Numerical simulation is performed to reproduce the notable phenomenon of spectrum transition which was found in a previous experimental investigation.

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The diffusion process of the intake mixture (homogeneous mixture of air and gaseous fuel) in the cylinders of dual-intake valve S. I. engines has been analyzed numerically using the GTT and CIP methods and the k-ε turbulence model. The following has been found : When the fuel is supplied into only one intake port in one engine in which a tumbling vortex is generated, the intake mixture is localized mainly in half of the combustion chamber and the fuel concentration is stratified. In another engine in which a swirl is generated by holding one intake valve closed, a relatively homogeneous mixture or an axially stratified mixture is formed in the combustion chamber, depending on whether fuel supply is early or late.

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Chemiluminescence emission from opposed jet burner flames was measured by a charge coupled device (CCD) camera with an image intensifier. Radial profiles of the emission intensity of OH, CH and C₂ radicals were obtained by the Abel inversion of the side-on observations. The profiles of emission intensity of these radicals are similar, and each maximum is located at the center of the flame zone. The emission of C₂ and CH radicals produced in the early stage of the combustion reaction was observed even on the burned-gas side of the flame zone where the mean temperature is significantly high, suggesting that unburned mixture exists on the burned-gas side of the flame zone. It was found that the profiles of OH emission intensity and NO concentration are similar. This fact suggests that NO originating from the prompt NO mechanism is predominant in the distributed reaction zone.

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Emission from the area of autoignition in an actual S. I. engine is observed under knocking operation using optical fibers. The difference in emission intensity observed between knocking and nonknocking operation is mainly due to the emission intensities of the OH and C₂ radicals. The emission intensity from these two species increases sharply when autoignition occurs. In addition, emission intensity from the C₂ radical shows two peaks in some cycles. Since the first peak is due to the autoignition reaction, the second peak is thought to be caused by soot formation in some cycles under knocking operation. This second peak corresponded to shadowlike matter seen in high-speed shadowgraphs taken during the expansion stroke.

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The Catalytic combustion of a lean premixed propane mixture was investigated below the catalyst temperature of 650°C and without gas-phase reaction, using a platinum-impregnated foam catalyst. The temperature distribution in the catalyst plate and the composition of the exhaust gas were measured at air ratios of about 2.2 to 5.8 and heat loads 43kW/m² to 115 kW/m² under stable combustion conditions. Since the maximum temperature was observed very near the inlet of the catalyst plate, it is thought that the reaction rate of the catalyst is high and the reaction zone is narrow. When the air ratio was decreased while keeping the heat load constant, the maximum temperature in the catalyst plate increased, but the outlet surface temperature of the catalyst plate was almost constant. The temperature distribution of the outlet surface of the catalyst plate was influenced by natural convection and showed higher temperature in the upper region. The combustion efficiency was strongly related with the catalyst temperature and showed almost the same value when the maximum temperatures are the same. The range of stable catalytic combustion was investigated and its relation to the catalyst thickness was determined.

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In this paper, we attempt to clarify the jet structure and the behavior of severely erosive cavitation clouds around a high-speed submerged water jet, using a high-speed movie camera with a framing rate of ten thousand frames. The effects of the injection pressure and the nozzle geometry on cavitation are also investigated. The experiments are performed with both a free jet and an impinging jet. It is clearly found that the cavitation clouds are periodically discharged. The cavitation clouds are also closely related to downstream instability and to the impinging erosion.

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In order to make precise force measurements for supercavitating hydrofoils, behavior of the disc drag as well as the effects of the gap between the test foil and the facing side-wall are carefully investigated for three typical supercavitating hydrofoils whose nose shapes are slightly modified, in a wider range of cavitation number σ, for various incidences α_i and gap distances h. Unexpectedly from Numachi's disc-drag experiments, the disc drag significantly decreases within the transient region from the subcavitating region to the supercavitating region. It is also very sensitive to foil shapes as well as incidences.

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In order to clarify supercavitating hydrofoil performance numerically, especially in the base-vented state at a low incidence, we attempt to perform numerical simulations for three typical thin supercavitating hydrofoils with pseudo-Kirchhoff noses by means of the QUICK method. The precise water-tunnel tests on the supercavitating steady lift- and drag-performance for the foils are examined after the marked effects of leading edge and the peculiar behavior of disc drag have been clarified. The analyses agree well with the experiments, especially in the base-vented flow at low incidences, showing several interesting facts.

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Power generation experiments have been performed for disk MHD generators with different channel shapes. The increase in the enthalpy extraction ratio by enlargement of the area ratio has been shown experimentally, and the highest enthalpy extraction ratio of 18.0% was achieved. The experimental results have shown that for the generator with the large area ratio, the wall static pressure in the MHD channel is kept lower than that for the small-area-ratio generator. These phenomena suggest that a high Hall parameter is obtained by enlargement of the area ratio. Furthermore, the swirl ratio at the channel exit was measured and was characterized by the ratio between Hall current and mass flow rate of the working gas.

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In the present paper, the conservation laws for micropolar electrically conducting fluids with many small fine particles are discussed on the basis of a nonequilibrium thermodynamics relation which leads easily to precise expressions of the energy flux vector and the dissipation function of micropolar fluids. The thermodynamic pressure defined here is based on the local conservation laws of mass, momentum and entropy, which satisfies the mutually complementary relationship with the sum of kinetic energy and internal energy. As a result we obtain Euler's thermodynamic relation as a homogeneous function in the first order of entropy, density and pressure. The above discussion takes into account the three parts of nonpolar fluid, polar fluid and micropolar electrically conducting fluid.

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A new analytical method for two-phase flow is proposed, in which the most easily occurring and, thus, most stable two-phase flow situation is assumed to be realized. Flow structure is considered to be self-controlled so as to realize the most stable two-phase flow situation. In the present study, the flow situation with smaller pressure energy consumption rate for unit mass of penetrating two-phase fluid through each channel cross section is assumed to be more stable. In addition, two-dimensional turbulent flow analysis is applied to the annular flow regime in which partical or total downflow of the liquid film is allowed. Experimental analysis based on the data from an air-water two-phase flow experiment, which was performed at atmospheric pressure and room temperature, indicated the applicability of the proposed analytical method.

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An experimental study is conducted to investigate the onset of instability of a liquid surface under an electric field applied in a stepwise manner. The critical voltages and the response times above which the liquid surface becomes unstable are measured under electric fields applied in two different ways. Instability criteria are derived theoretically using a modified Rayleigh-Taylor instability equation for the cases of a perfectly conducting liquid and a perfectly insulating liquid. According to the results of the experiment and theoretical analysis, consideration is made of the mechanism of the onset of EHD (electro-hydrodynamic) instability of the liquid surface having a long electrical relaxation time.

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The turbulent state of superfluid helium at very low temperatures presents some important and unresolved problems. The turbulent state has a dense tangle of quantized vortex filaments that are characteristic of superfluid. Little is known, however, about their dynamics, particularly, interactive motion. The present paper studies numerically three-dimensional dynamics of two interacting vortex filaments. The equations of motion and the method of numerical calculation follow those of Schwarz. Two identical vortex rings which are initially placed far apart proceed abreast toward the same direction. They gradually become close due to their interaction, then suddenly collide. The critical distance where the collision occurs is determined by the competition between the local self-induced field of one ring and the nonlocal field from the partner. The critical distance is greatly influenced by an applied superflow field.

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This paper presents some waveform analyses of the recorded pressure fluctuation in a water hammer due to collapse of a cooling cavity and the estimated velocity of the liquid column in collision with the blind end of a pipe. Real damping and peak period shortening, whose effects are similar in appearance on a graph of the change with time, are separated from each other by drawing graphs of the change with cycle number. The discussion on the damping is generalized using logarithmic decrements. It is proved that the air in the cavity strengthens the damping, the strengthening is greater earlier in the water hammer cycle, and the peak period shortening takes place rapidly not later than between the 2nd and the 3rd peaks in the case where the initial air concentration is over 30%, and is almost completed within this interval. In addition, considering the minor fluctuation in pressure bottoms, physical mechanisms of the damping and the peak period shortening are discussed.

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The purpose of the present work is to simulate the three-dimensional flow in an air-cushion and suction pad, which acts as repulsive and suction forces to strips, by ejecting a jet to the surface of the strip. A new type of pad, which uses an annular jet, is proposed to generate the strong repulsive force. A simple numerical calculation using the discrete vortex stick method is carried out to study the generation mechanism of the repulsive and suction forces. The numerical results of the development of transient flow in the gap between the pad and the surface of strips is discussed. The results show that the existence of circulatory flow outside the jet plays an important role in generating negative pressure, and circulatory flow is constantly formed in the gap in the case where the length of the pad fringe is large whereas the gap clearance is not so large.

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