The aim of this works is to review a recent powerful trends in systematic cavitation studies. At first, it is shown that most of the existing studies on the cavitation are not only insufficient in grasping the real situation and/or the cavitation aspects, but are also lacking in the most essential concept regarding the controlling factors, principally due to the rather low-speed observations. To rebuild the cavitation concept completely, a new approach is undertaken. For detailed information, several excellent recent reviews such as those by Drs. Rood, Arndt, Okada and Iwai, should be referred to.

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In order to clarify the necessary conditions for cavitation-erosion tests with a vibratory apparatus, we carefully measure the cavitation-nuclei-size distributions and the relative air content rate of test water with respect to time by means of a Coulter counter and a van Slyke apparatus, respectively. It is found that the exponent of the distribution curve and the volume concentration of nuclei characterizing the nuclei-size distributions do not fluctuate with time during the equilibrium period, and that the relative air content rate first decreases monotonously with time and then reaches a definite equilibrium value after 40min which is longer than the 15min recommended by the ASTM.

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The condensation coefficient (c. c.) of vapour is investigated on the basis of the transition state theory which is treated in the framework of statistical mechanics of gases and liquids. The theoretical c. c. is reconfirmed to be the ratio of the rotational partition function of a liquid molecule to that of a vapour molecule and is given by thermodynamic quantities available in the literature. The applicability of the theory is clarified through a comparison of molecular flux equation at the vapour-liquid interface with rigorous molecular flux equations based on the molecular gas dynamics of the monoatomic moleoules. It is shown that theoretical predictions of c. c. for water, carbontetrachloride, and glycerol vapour are in good agreement with the experimental results and are significantly smaller than unity.

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Long-span gates vibrating in the streamwise direction push and draw water in the reservoir; thus the gate is accompanied by the added mass of water. Moreover, waves propagating in the upstream direction are formed on the free reservoir surface, resulting in a fluid damping effect on the vibrating gates. The added mass and the fluid damping coefficient were derived theoretically in a dimensionless form in a previous study. To verify the theoretical results of the added mass and the fluid damping coefficient, the experimental results of a model test are presented in this study. A planar vertical gate undergoes free damped vibrations in air and still water. The added mass and the fluid damping coefficient are calculated from the measured frequencies and damping ratios of the damped vibrations. Consequently, it is shown that there is good agreement between the theoretical and experimental results.

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In previous simulations, the modified GSMAC method, which is more applicable to in-out flow problems, was proposed. In the present paper, however, this scheme is extended to three-dimensional analysis. As an example, flow in a cubic lid-driven cavity having many verified experimental and numerical results has been calculated at the Reynolds numbers of 1000 and 3200. Consequently, the velocity profiles are in good agreement with those of the pseudospectral method at Re=400 and 1000, and the TGL vortices, which give a three-dimensional effect, have been simulated.

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Clean room facilities have recently become indispensable to various kinds of industries. In order to design a clean room, it is important to consider the improvement of the working environment as well as energy conservation. The air flow in a clean room is very complex. It consists of recirculation flows, and the direction of mean air flow is changed locally. A method of numerical simulation has been developed to delineate guidelines for the ventilation design of a clean room. This paper presents a modified finite element analysis for solving unsteady incompressible Navier-Stokes equations. This scheme is based on the algorithm of the HSMAC (highly simplified marker and cell) method in SOLA and the general idea of orthogonal decomposition. It has actually been applied to the case of the lid-driven square cavity flow at Reynolds number 10000, and to air flow in a conventional clean room. Unsteady flow simulations in terms of stream lines, equipressure lines and equivorticity lines are obtained on a color graphic display.

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A new zonal approach for compressible viscous flow computation using a TVD finite volume method has been developed. The two-dimensional, Reynolds-averaged Navier-Stokes equations are discretized spatially by a cell-centered finite volume formulation. The inviscid fluxes at cell interfaces are evaluated through the MUSCL-type approach of an upwind scheme. The viscous fluxes are determined in a central differencing manner. In the present approach, the computational domain is divided into nonoverlapping zones. The zonal boundaries are constructed from the cell interfaces, since the finite volume formulation with the cell-centered control volumes is used. Consequently, communication from one zone to another is accomplished by numerical fluxes through the zonal boundaries. The use of the finite volume formulation can ensure the uniqueness of the zonal boundaries and the complete conservation of the numerical fluxes across the zonal boundaries, which results in a highly accurate zonal approach. In order to demonstrate the versatility of the present zonal approach, numerical results are presented for viscous flows through a transonic turbine cascade.

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An underexpanded annular impinging jet is studied experimentally and it is shown that the aerodynamic characteristics of the impinging jet depend significantly on the distance H between the nozzle exit plane and the impinged flat plate. The annular impinging jet diverges in the downstream direction provided H is smaller than a critical value H_C. The feature of the jet changes significantly at H=H_c. The stream lines issuing from the inner edge of the annular nozzle join at a point upstream of the impinged plate. However, a vortex ring may appear on the plate even for H>H_c depending on the magnitude of loss in the stagnation pressure at the jet axis.

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The stabilizing structure for the phenomenon where the flow rate of a loop with a cross pipe switches nonperiodically between a high level and a low level under certain flow conditions was investigated analytically and experimentally. With numerical analysis, a pair of vortices appeared downstream from where the axes of the main pipe and the side branches crossed. As the upstream vortex grew larger, it drifted further upstream and resulted in swirls with a high pressure loss. Conversely, when the downstream vortex grew larger, the flow became nonswirling with a low pressure loss. Two methods for stabilizing nonswirling flow were confirmed by experimentation: use of a flow diverter, and removal of the region where vortices appear by narrowing the downstream region at the cross pipe.

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This experimental study is concerned with the instability of several Taylor vortex flows between concentric cylinders for a symmetric end condition. The flow has several characteristic patterns: primary mode, normal secondary mode, and anomalous mode which has outward flow on either the upper or the lower end plate and/or on both end plates of cylinders. It is found that the anomalous mode changes to another anomalous mode or the secondary normal mode or primary mode when the Reynolds number is gradually decreased. Consequently, a bifurcation set of complex flows is presented with the bifurcation diagram in a symmetric system.

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An experimental study has been conducted on fully developed turbulent flows through rectangular ducts with one rough wall. Two ducts, one with a long-side rough wall and the other with a short-side rough wall, have been used. The distributions of the mean velocities and turbulent stresses over a whole cross section in the fully developed region were measured by hot-wire anemometry. The secondary flow distributions in both the rough ducts were remarkably different from those in the smooth-walled duct. In the long-side rough duct, only one large secondary flow vortex appeared near the short-side wall. In the short-side rough duct, a similar large longitudinal vortex also appeared near the corner formed by the rough and the smooth walls. Furthermore, it was revealed that the contribution of turbulent shear stress <u₂u₃>^^^- was as important as that of the turbulent normal stresses (<u²₂>^^^--<u²₃>^^^-) for the generation of the secondary flow of the second kind in both the rough ducts.

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By the finite difference method, flows around cylinders with rectangular cross sections of various width-to-height ratios of 0.4 to 8 have been computed in the range of Reynolds numbers from 100 to 1.2×10³. We have successfully simulated some interesting phenomena whereby a flow around the cylinder with a B/H ratio of 2 is fully separated from the leading edges at the Reynolds number of 800, while for the cylinder with a B/H ratio of 2.8, a fully separated flow changes to an alternate reattachment flow with lapse of time at the Reynolds number of 1.2×10³, and two components with different Strouhal frequencies appear in a flow field around the cylinder with the B/H ratio of 6 at the Reynolds number of 800. Namely, the flow pattern critically changes when the B/H ratio is 2.8 and 6 at Reynolds numbers of 500 to 1.2×10³. It is clarified by the numerical simulation that the component with a high Strouhal frequency is induced by the vortices separated from the trailing edges and that the low Strouhal component is due to the oscillation of flow over the side surfaces accompanied by the movement of separation bubbles. Finally, the computed results of flow patterns, base pressure, drag force and Strouhal number show a good agreement with the experimental results.

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Statistical characteristics of a three-dimensional jet issuing from a cruciform nozzle have been examined experimentally to clarify the features of the present flow field due to the secondary flows. In the extent of x/d≥50 where the mean velocity profile U/U_ox shows the similarity, the ratio of the integral length scales L_u/L_v on the x axis assumes a constant value. In the relatively upstream portion, both the skewness factors S(u) and S(v) show a negative value, while both the flatness factors F(u) and F(v) take a positive value. The turbulent large eddy structure conjectured from the space-time correlation is significantly different at each location throughout the cross section.

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The mean velocity and root-mean-square value of the turbulence component in pulsating round jets of low pulsation frequency were measured in the axial range of z/d≤30 by means of a hot wire anemometer, where z is the distance from the nozzle and d is the nozzle diameter. The measured values were approximated by the finite Fourier series. The time-averaged velocity on the jet axis decayed faster than the steady value. The time-averaged width of the pulsating jet, represented by the half-value radius of the time-averaged velocity, was slightly greater than the steady value. However, the time-averaged flow rate did not differ from that of the steady jet. The profiles of the time-averaged velocity and the amplitude of the fundamental velocity component became similar downstream at about z/d=5 and 10, respectively. A quasi-steady model for predicting the instantaneous velocity and turbulence on the jet axis was proposed.

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To investigate the critical condition of encapsulated drop formation in liquid-liquid-gas systems, the dynamic behavior of a rising gas bubble across the interface between two immiscible liquids was analyzed experimentally and theoretically. The experiment revealed that an encapsulated liquid drop was formed by a gas bubble passing through the liquid-liquid interface or rebounding from the interface without the rupture of the liquid film between the interface and the gas bubble. A theoretical analysis based on an effective and simple model was developed by considering interface tension and liquid viscosity. The numerical results agreed with the experimental results.

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Perturbations of the hydrodynamic force on a three-blade centrifugal pump impeller were analyzed by transforming the static pressure change obtained on an impeller blade into Fourier series. Comparisons of the forces exerted on a blade and an impeller were made between the three- and seven-blade impellers, and the effects of the blade number on the hydrodynamic force were examined. It is found that there are few differences in the hydrodynamic force exerted on one blade between the impellers of different blade numbers. However, the hydrodynamic force on the impeller obtained by the vector summation of each blade force exhibits larger fluctuations for the three-blade impeller than that for the seven-blade one.

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The effects of gap size on heat transfer characteristics were investigated experimentally for a vertical rectangular flow channel with gaps of 2.5mm, 6mm and 18mm. As a result, the following was revealed. The flow shows a nature of forced convective heat transfer when Gr_x/Re^(21)/18_xPr^1/2 is less than 2.5×10^-4, and a free-convective heat transfer when Gr_x/Re^(21)/18_xPr^1/2 is higher than 1.8×10^-3, for all three gap sizes of the flow channel. As for the data for a gap of 2.5mm in the transition region between forced convection and free convection, it was confirmed that the heat transfer coefficient higher than that predicted by the heat transfer correlation for turbulent forced convection along a flat plate was due to the acceleration of the main flow through the development of the boundary layer, not to buoyancy force.

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This study involves to the analysis of fins used in various types of compact heat exchangers for automotive and room air conditioners. Numerical analysis is an effective means of studying fins. However, in the case of louvered fins, it may be inconvenient to handle numerical calculation by means of a finite difference scheme based on ordinary rectangular grids. The numerical analysis method used in this study employs an oblique grid fitting to an inclining fin so that the analysis can be applied to various types of fins. It has been clarified that the visual streamline of flow visualization for louvered fins corresponds to the result of this numerical calculation, and that the pattern of the streamline affects the heat transfer performance of the louvered fins.

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A combination of a cogeneration system and an aquifer thermal energy storage method, known as Co-Gene ATES, has been investigated numerically, based on the performance of fundamental elements of the system as obtained experimentally in previous investigations in a heavy-snowfall zone. The results obtained were as follows: (1) The yearly total coefficient of performance of Co-Gene ATES was estimated at 3.04, and the energy cost was a quarter of that of a conventional system. (2) In a comparison of Co-Gene ATES with conventional equipment, a financial break-even point of 6.3 years was estimated from an economic feasibility study, taking the recovery factor in the charge well as 60% and the increase in fuel cost as 1%, which in turn led to a 3% increase in the cost of electricity. (3) We proposed a method that estimated the optimum condition of system by the life gain. When the lifetime of Co-Gene ATES is 15 years, the optimum condition is that the proportion of snow-melt road area to total road area is 100%, and that of snow-melt roof to total roof area is 0%; financial break-even point of 3.3 years and a life gain of 9 hundred million yen were estimated.

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The effects of correlated scattering on the combined conductive and radiative heat transfer through a packed layer of glass beads are theoretically examined. The energy equation and the spherical harmonic equations of the first order for radiative transfer are numerically solved utilizing the correlated or uncorrelated radiative properties for packed glass spheres. The correlated scattering calculations for temperature profiles and mean total effective thermal conductivities are compared with the uncorrelated scattering calculations and our previous experimental results. The results show that the correlated scattering estimations agree well with the experimental results within the accuracy of experimental uncertainity. Moreover, it was found that the correlated scattering estimations for the mean total effective thermal conductivities are smaller than the uncorrelated Scattering ones, but the relative difference observed between them is always less than 2% for the examined system parameters.

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A new numerical method of evaluating radiative heat transfer was incorporated into the framework of the numerical prediction of diffsion flames. The model of radiative heat transfer was based on tihe idea of the heat ray tracing method originally proposed by Hayasaka et al. The present method enables us to evaluate both the radiative heat loss from a flame and the local formation and oxidation rate of soot, which significantly interact with each other. Some predicted results were compared with those of experiments.

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Experimental work and numerical analysis were carried out to evaluate the performance of the catalytic combustor using the methanol mixture. The catalyst used was a platinum-loaded γ-Al₂O₃ monolith. The temperature profiles and the emission characteristics were determined in the transient stage. From the experimental results, considerable formaldehyde emission was detected in the start-up period. It was also discovered that the transient emission characteristics were improved by the preheating of the catalyst bed and by reducing the space velocity. A modified quasi-steady-state model is used to analyze the transient behavior of the catalytic combustor. The initial temperatures of the catalyst and the space velocity were used as the parameters in the model. The temperature profiles and the emission characteristics from the numerical analysis agreed well with the experimental results.

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A study of over-fire air injection point and air-injection methods and multistage injection methods in pulverized coal combustion was carried out. It was possible to predict NO_x emission for multistaged combustion by treating it as a function of the over-fire air injection point and injection rate for two-stage combustion.

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