Energy transfer between grid scale(GS)and subgrid scale(SGS)induced by SGS stress in large eddy simulation is investigated by direct numerical simulation of homogeneous isotropic turbulence and a turbulent mixing layer. From the results of this study, the following conclusions were reached. (1)No correlation between the Leonard term and Cross term exists from the viewpoint of energy transfer. (2)The Smagorinsky model for the Reynolds term predicts very large energy transfer compared with that obtained from the DNS data. (3)The Bardina models for the Reynolds term and Cross term predict large energy transfer from SGS to GS in the high wave number region, which indicates that the Bardina model causes excessive backward scattering in the high wave number region.

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A massively parallel computer, which has a large number of processors, is expected to become the main instrument for scientific numerical analysis including the CFD field. It has been pointed out that efficiency of parallel computing becomes worse when the number of processors increases and granularity comes to fine. Therefore an accelerative technique should be introduced to achieve nearly maximum performance of the massively parallel computer. Some researchers have used the multigrid method, but this technique turned out to be inappropriate for parallel computing of very fine granularity because efficiency rapidly worsens. The purpose of this study is to propose a numerical technique suitable for calculation of incompressible flow on massively parallel computer. In this regard, we choose an extrapolation method as the accelerative technique, which perdicts converged solutions from a suquence of intermediate solutions and is expected to retain its accelerative property for fine granularity. Three existing extrapolation methods ROLE, MPE, ROGE and newly developed LWE are discussed. Furthermore, ROLE and LWE are applied to numerical analysis of Poisson's equation and the results are discussed.

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In this paper, it is mathematically clarified by discussing the behavior of a nonlinear mapping that the extrapolation method described in the previous first report can be applied to numerical procedures for solving nonlinear equations. Guidelines for coping with nonlinear effects in extrapolating solutions of nonlinear equations are also presented. The coupled method is adopted as a numerical algorithm for incompressible flow because it is simple and its procedures can be efficiently parallelized. Parallel codes consisting of the coupled method and the extrapolation method are executed on a Fujitsu AP 1000 to solve 2-D steady flows. It is shown that the parallel efficiency of the coupled method is very high and that the extrapolation method keeps net speed-up high even when granularity becomes fine. It is concluded that these two methods constitute a promising N-S solver suitable for massively parallel computing of very fine granularity.

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An implicit cubic-interpolated propagation(CIP)method for 2D hyperbolic equations is developed. By reconsidering the derivation of a 1D implicit solver, extension to multi-dimensions becomes straightforward. The two-dimensional form is numerically solved by two different approaches, that is, by adopting a directional-splitting technique and by deriving an implicit formulation directly without using directional-splitting. We found that higher order correction terms proportional to Δt² are required in a non-splitting case, while these terms are already included intrinsically in a splitting scheme. Furthermore, we have pointed out that the determination of a profile becomes quite important for implicit calculation, and the interpolation function must be carefully selected to obtain a symmetric profile.

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A study of vortex structure and fluid mixing in pulsatile flow through grroved channels by numerical simulation and experimental flow visualizations is presented. The simulations correspond to experiments for pulsatile flows with / without flow reversal in two grooved channels with different cavity lengths, with Reynolds and Womersley numbers in the ranges of 46.8<Re<117 and 75<α²<367, respectively. The agreement between simulations and experiments in terms of unsteady vortex motion is satisfactory. In most cases a primary vortex grows up during the deceleration phase whthin each cavity in the lower wall and an additional vortex is generated at the upper, flat wall. The primary vortex experiences the cavity filling and emptying process. The primary vortex strength depends on Reynolds and Womersley numbers and reaches its maximum value for a specific Womersley number. The effect of cavity length is negligible at high Womersley numbers. Fluid mixing is observed from a Lagrangian viewpoint as streaklines : fluid is exchanged between cavity and channel flows, depending on the primary vortex. At high Womersley number flows, streaklines indicate the formation of long, thin figers that enter and leave the cavity.

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Presented in this article is an experimental and numerical study aimed at analyzing the wake dynamics downstream of a cylinder in an unsteady flow. The experimental study was carried out by measuring the mean velocity field with a laser Doppler anemometer, visualizing the fluid field by means of laser induced fluorescence, and performing a statistical analysis of the instantaneous velocity signals using Fourier and wavelet transforms. The visualized images were processed to determine the mean-statistical characteristics of large-scale structures in the wake. Experimental results provided the essential information for the numerical investigation of the temporal evolution of large-scale structures. A theoretical model based on the theory of dynamical systems with few degrees of freedom was adopted. The effects induced by the unsteady nature of the incoming flow were simulated. Experimental and numerical results were in excellent agreement, underlining the validity of the methods of analysis and simulation proposed.

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Wavy interface generation is an interesting characteristic of explosive welding. There have been many theoretical and experimental discussions of the mechanism of wavy interface generation, but there is no consensus of opinion as yet. We report on a numerical approach to the analysis of the mechanism of wavy interface generation in explosive welding. The wavy interface generation process is calculated using a two-dimensional finite difference scheme for elastic-plastic materials. In this simulation the equations for a symmetric collision between copper plates are solved. The concept behind this study is that the wavy interface and vortex street are caused by the velocity distribution of shear flow and periodic disturbance at the interface. The calculation results show the deformation process of the wavy interface and we obtain qualitative agreements between numerical and experimental results.

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This experimental atudy examines pressure drop due to pipe friction when a surfactant is added to flowing water / particle slurry, with the goal of using the results in order to reduce power supply requirements when transporting slurry by pump, and improve the heat capacity of the transportation fluid. The following results were obtained : (1)Pressure drop for the water / particle slurry containing the surfactant in which particles accounted for about 12% of the fluid volume, was 25-50% smaller than in case of flowing water. (2)When transporting the water / particle slurry containing the surfactant, it is advisable to reduce the velocity and regulate the Reynolds number Re to approximately 3×10⁴. (3)If the particles in the water / particle slurry are replaced by microcapsules that have thermal energy storage effect due to their latent heat, the heat transported per unit volume of this slurry becomes twice that of plain water, and the required pumping power is reduced to half that of water.

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Flow regime transition and pressure drop in gas-liquid countercurrent two-phase flow was studied in three vertical parallel channels. The conditions for flooding initiation in parallel-channel systems could be predicted well using Imura's correlation for a single channel. After flooding, the flow patterns were different in each channel. Aflow pattern classification diagram for the three-channel 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-channel system that the maximum pressure developed in each channel had a serious effect on the average pressure in the lower plenum, and that the frictional loss coefficient, estimated from the time-averaged pressure in the lower plenum, could be correlated to the relative gas Reynolds number.

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Recently the impetus towards use of aquifer as thermal storage systems has increased. Since the surface of free aquifers fluctuates irregularly due to both inflow and outflow of groundwater, treatment is difficult compared with the case of confined aquifers. In the case of free aquifers, non-equilibrium heat transfer between fluid and particle phases exerts much influence. Even in confined aquifers, the unsteady heat transfer is marked under marble or gravel-component. The inherent properties of soils are dismissed and part of them are reflected poorly in apparent properties such as equivalent heat capacity of conductivity. Therefore, even superficial velocity has been wrongly estimated. In this paper, a two-phase model is introduced for consideration of heat propagation even into the particle phase. Then, the effectiveness of the model is confirmed using a laboratory test apparatus in two dimensions. Finally, significant deviations of temperature propagation by the particle sizes are simulated.

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A multi-dimensional numerical algorithm for detonation gas dynamics is described. The algorithm consists of a dispersion-controlled shock-capturing scheme and a pseudo-kinetic chemical reaction model. One-dimensional results obtained with this algorithm appear to be in good agreement with both the experimental data and self-similar solutions of gaseous detonation. This implies that coefficients of the pseudo-kinetic reaction rate are well tuned. Results of two-dimensional detonation computations in converging chambers reveal some global features which agree with the experimental findings, and can be explained using shock wave dynamic theory. It is shown that the numerical algorithm proposed is capable of predicting the pressure, temperature, and density ratio of detonations in a way suitable for engineering applications. The algorithm can be extended to three-dimensional problems.

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A methanol-fueled direct-injection diesel engine with a glow-assisted ignition system tends to suffer from poor ignitability under low load conditions. Chemical delay phenomena associated with methanol mixture ignition were investigated to improve ignitability. The effects of the vaporization heat of liquid methanol, the surface temperature of the glow-plug, the heat created by the glow-plug and the O₂ excess ratio of methanol-air mixtures on the ignition characteristics were examined. Our numerical model considers these parameters, and a detailed chemical kinetic scheme, including 39 chemical species and 157 elementary reactions, was used to predict the delay in methanol mixture ignition.

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Numerical computations are made of laminar jet diffusion flames taking into account detailed chemical kinetics and multicomponent diffusion and focusing on the effect of pressure and the amounts of hydrocarbon contained in the fuel on the NO_x formation processes and charcteristics. In order to clearly distinguish between thermal NO_x and fuel NO_x originating from N₂ in the air and fuel N, respectively, and to elucidate the effects of interaction between thermal No_x and fuel No_x together with N-containing species, N-containing species originating from N₂ in air and fuel N and their reactions are distinguished in the computations. It was shown that(1)higher pressure results in a decrease in the amount of fuel NO formed and a increase in the amount of thermal NO formed, (2)the tendency of the decrease of the conversion rate of ammonia to fuel NO for high-pressure flames becomes more apparent when the fuel contains greater amounts of methane, (3)the effect of the destruction of thermal NO by N-containing species becomes more apparent for high-pressure flames as thermal NO concentration becomes high.

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We propose a Fredholm-type boundary integral expression of the forced convection heat transfer coefficient from an object. When the Fredholm's kernel function is obtained by a numerical simulation of the forced convection field, it is possible to predict the local heat transfer coefficient from the object with arbitrary surface temperature distributions. Moreover, this expression can be easily applied to the boundary element method(BEM)as a boundary condition of fourth kind, and then the convection-conduction conjugated heat transfer problem can be formulated as a heat conduction problem. Some examples demonstrate the usefulness of the proposed expression.

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To improve the performance of ice thermal storage systems, the problem of freezing on the cooling surface must be addressed. One of the authors has proposed a new ice making method in which a magnetic fluid prevents water from freezing on the cooling surface. Thus, we investigated experimentally the effect of shape control of magnetic fluid using a magnet of freezing of supercooling water. The shape changes and motion of magnetic fluid, which are controlled by controlling the magnetic field, have a slight effect on the supercooling phenomenon. However, the exposure of the cooling surface covered by a film of magnetic fluid reduces the time from controlling the magnetic field until freezing to a few seconds. Therefore, it is possible to use an electric magnet.

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Coal gasification performance of the entrained-flow coal gasifiers tend to be the lower for coal with higher ash fusion temperature because of higher air ratio required to evaluate the combustor gas temperature in order to get the stable slag discharging state. Addition of flux and blending of coals with different characters, known effective to reduce the ash fusion temperature, have been investigated with a gasification test facility(2t / d Process Development Unit)to confirm them in actual gasifiers. This paper reports the proposition of a correlation to predict the ash fluid temperature on the ash acid rate and presents a procedure to decide the suitable rate of flux addition and coal blending. This report also presents the proper selection guidelines of these methods based on the difference in the effects on gasification performance improvements when these methods are applied.

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The purpose of this study is to develop a heating, ventilating and air conditioning(HVAC)system for automobiles which can control the interior environment according to thermal sensations felt by humans and to evaluate the effectiveness of this HVAC system. The facial skin temperature of a passenger was estimated from environmental information, that is air temperature, wind velocity, etc., with a neural network, and the thermal sensation felt by the passenger was calculated from the facial skin temperature. Thus, this HVAC system can estimate the thermal sensation level without the direct measurement of passenger's skin temperature. The passenger's facial skin temperatures calculated by the neural network were stored in a memory IC, and the memory IC was built into the automobile. When the NN was used for retrieving the facial skin temperature of a passenger, the stored result was provided by the memory IC. This HVAC system was capable of controlling the interior environment according to the thermal sensation of the passenger, thus maintaining the passenger's level of comfort.. The passenger was more comfortable with our HVAC system than with the conventional automobile air conditioner, in particular, just after the passenger gets into the automobile. When driving the automobile on the road, this HVAC system also controls the interior environment to maintain the comfort level of the passenger.

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Theoretical analysis of mixed lubrication has been carried out for a piston ring package of an automotive reciprocating engine as a method to elucidate better specifications of rings for reducing friction loss. The starved inlet boundary conditions have been employed for oil film on each ring based upom experimental results obtained through scanning laser-induced-fluorescence oil film thickness measurement. With consideration of oil starvation, the predicted oil film thickness at compression rings was in better agreement with that measured than the former prediction under fully flooded inlet conditions. Film thickness at the 1st compression ring under full load firing conditions was predicted to be smaller than that during motoring, which also agreed with the experimental results, due to the different inlet conditions assumed for the oil film at the 2nd compression and upper rail of the oil ring under different operating conditions. The predicted oil film thickness was much smaller than that measured at both rails of the oil ring, which seems to have been caused mainly by limitations of the spatial analysis of the LIF measurement. Effects of the change of the oil ring surface profile due to tilting during sliding, of vescosity variation and of cylinder bore distortion were not negligible, but were not considered in the analysis.

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A fluorescence image diagnostic method in which a filtered Xe-flash lamp and a video camera are used has been developed to observe the distribution and behavior of oil film on a piston surface in detail. A light source with appropriate spectrum characteristics for measurement of the thickness of thin oil films was employed after theoretical consideration of the absorption spectrum of the fluorescent dye and the oil with the fluorescent dye. A simple correction for measurement results obtained for a curved surface and calibration were carried out. The use of this system ensures that the distribution and behavior of oil film on the piston skirt and piston rings can be quantitatively measured, and the system is shown to have practical applications.

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In order to measure flow velocity in the swirl and radial directions of a cylinder of an engine in practical use by means of a laser Doppler anemometer(LDA)through a small measuring window on the cylinder head, a back scattering fringe mode LDA is used. This LDA, however, can not be used to measure the velocity component in the axial direction of the cylinder. A single incidence-beam reference-mode LDA is developed to measure the velocity component along the optical axis of the LDA and is applied to measure the fluctuating flow velocity in the axial direction of the cylinder. Ensemble-averaged mean velocity and fluctuation intensity of the velocity as measured using the LDA show good agreement with those measured using the conventional fringe-mode LDA. Based on these results, it can be concluded that the reference-mode LDA is applicable to measurements of the flow velocity in the axial direction of the cylinder through the amall window on the cylinder head.

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Axial velocity distribution in an I₂-seeded Ar free jet is investigated by the laser-induced fluorescence(LIF)technique using a ring dye laser with 500 kHz line width. Since the translational temperature in the flow region is low, the hyperfine structure due to the nuclear spin of I₂ molecules is observed in the spectrum of I₂ B-X bands. The spectrum shape is explained by the quantum mechanical theory and the simulated spectra coincide with our measurements. First, the possibility of the translational temperature measurement based on the hyperfine spectrum shape is discussed. Then, axial velocity measurement is performed and the results are found to be in good agreement with those of Ashkenas & Sherman. The applicability and the velocity resolution limit of our measurement technique are also discussed.

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An international comparison of air speed standards has been conducted by Japan and the USA using anemometers. The national standard for low air speed measurement in Japan uses a tow carriage system with a laser-based speed determination system. In the USA, a specially designed low-speed wind tunnel equipped with a laser Doppler anemometer comprises the national standard. Two anemometers, one thermal and one ultrasonic, were selected as the transfer standards, and these were tested in the air speed range of 0.1 to 1m / s. The results showed the two national standards to agree within the calibration uncertainties which were nominated to be between 1% and 9%. The results also indicated that the thermal anemometer used in this program had a transient characteristic and a sensitivity to the atmospheric pressure that required special analysis and data handling procedures. These characteristics and the procedures implemented are discussed and explanations are given that should improve future testing.

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