With the urgent demand for higher performance in axial turbines, the unsteadiness induced by the mutual interactions between the nozzle and rotor cascade rows has attracted much attention. As the number of published papers on this topic has recently increased considerably, the present state of research is reviewed here under four categories. This report might be expected to deepen our understanding of the unsteadiness within the turbine stages and also to provide some suggestions for further research in this field.

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Vibratory-erosion tests on a typical erosion-resistant material made of 304 stainless steel were carried out. We carefully observed the erosion patterns and the surface roughness aspects with respect to test time, under a specified condition of uniform nuclei-size distribution, by a scanning electron microscope and a profilometer. The eroded surface is classified into three stages from surface topography and roughness profile. In the first stage, the surface is plastically deformed and its roughness rapidly increases. In the second stage, the surface becomes more hardened, so that cracks initiate and propagate ; after that, local removal of material occurs. In addition, the roughness doubles and then increases slightly. In the third stage, almost all the virgin surface is removed and the roughness doubles again. It is found that skewness has, respectively, a positive and a negative value before and after the material removal, while the kurtosis is always positive.

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The GSMAC-FEM (generalized simplified marker and cell FEM), which is an extension of the SMAC-FDM, is a stable and fast scheme for an incompressible viscous flow. The rotational form of the Navier-Stokes equations in which velocity and the Bernoulli function are variables is used in the GSMAC method. Velocity components and Bernoulli function are interpolated as a linear function and a constant function, respectively. This interpolation is simple and convenient for creating the mesh system. However, the approximation which is mentioned above makes it difficult to analyze inlet-outlet flows including the Neumann boundary conditions. The present paper shows a new modified GSMAC method which is applicable to high Reynolds flows with Neumann boundary condition (especially the pressure boundary). The modified scheme consists of an algorithm which satisfies the continuity equation much better than the previous GSMAC method.

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A developing laminar flow of power-law fluids in the entrance region of curved pipes has been investigated by analyzing the three-dimensional elliptic equation numerically and measuring the velocity distribution with an optical fiber LDV. Flow mechanism from the curved pipe inlet to the fully developed region has been made clear under the condition of power index n>0.6, two curvature radius ratios Rc=10 and 30, and Dean number De=100∼500. As the power index decreases, the primary flow becomes more highly distorted and the axial velocity distribution with double peaks appears on the symmetric plane in the initial development. Also, the secondary flow increases dramatically just after entry and declines rapidly to form another vortex pair in a part of the developing region.

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When a viscoelastic fluid flows out from a horizontal duct, many cracks and protruding ridges are formed on the jet surface. The jet states are affected by the shape of the duct exit. For the knife-edge-shaped duct exit, the jet appears in three states, i. e., the stable state, the breakage state, and the multiplication state. For the semicylindrical-shaped duct exit the jet appears as another state instead of the breakage state. We call this the "stationary state". In this state, stationary ridges occur on the jet, and they become uniformly large as the shear rate increases. Anomalous pressure fluctuation is observed near the duct exit in the breakage state and the multiplication state. In the stationary state the pressure fluctuation is not observed, but the disproportional pressure distribution for the duct width direction is observed. A large vortex occurs on the end of the duct floor wall for the knife-edge-shaped duct exit. In the stable state it is steady and two-dimensional, and in the anomalous state it is unsteady and three-dimensional. But for the semicylindridal-shaped duct exit, the vortex does not appear, regardless of the jet state.

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Friction coefficients in air and water of various sleeve-type submersible bearings for vertical pumps were investigated with respect to a variety of bearing materials including SiC-sintered ceramics, WC-cemented carbides, self-fluxing alloys and conventional bearing materials such as rubber, resins, PTFE # and soft sintered alloys. The test equipment simulated the frictional conditions of actual vertical pump shafts, that is, the shaft of the testing apparatus precessed against the bearing. The results showed that when silicon carbide was used as a stationary bearing, lower friction coefficients could be obtained, regardless of the material used for the rotating sleeve. In slurries, the abrasive particles adversely affected the friction coefficients of conventional bearings, however, owing to superior hardness, ceramic bearings maintained low friction coefficients. In air, a combination of silicon carbide and tungsten carbide displayed a low friction coefficient. Also, the results confirmed that dry starting of vertical pumps is also possible when using this combination of materials.

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The entrance flow patterns for viscoelastic fluids are simulated using the finite difference scheme. The Denn model is used as the constitutive equation. The prediction of the dimensionless size of circulating secondary flow (X) for a Newtonian fluid agrees with the experimental observations of Boger et al. and the prediction of Kim-E et al. For a power law fluid, shear thinning decreases X while shear thickening increases it. For a viscoelastic fluid we could predict the same large circulating flows as in our experimental observations for polymer solutions. Then, X for N_Re<0.1 (N_Re: Reynolds number) is the same as for the creeping flow (N_Re→0). Thus, X for the viscoelastic fluid is dependent on the Weissenberg number (N_we) for N_Re<0.1 and on N_we and N_Re for N_Re≥0.1. This result agrees with our experimental observations for polymer solutions.

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To evaluate the influence of pulsatile amplitude, experiments on pulsatile flow of Bingham plastic fluids are performed under the conditions that the time-averaged Reynolds number of a cycle is greater than the critical Reynolds number in the steady state. On the other hand, calculations based on the quasi-steady approximation are performed. These experimental and calculational results show that the characteristic parameters of the pulsatile flow (Φ_{t, 1} and Φ_{z, 1}) obtained from the experiments become greater than the ones obtained from the quasi-steady approximation in a large-amplitude region. Next, the causes of this difference are investigated, and it is suggested that the acceleration parameter plays an important role in explaining the cause of this difference. Finally, the influence of the Hedstrom number is evaluated, and it is suggested that the change of the turbulent viscosity coefficient due to the acceleration becomes notable with the increase in the Hedstrom number.

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An improved near-wall k-ε turbulence model is proposed considering the two characteristic length scales for the dissipation rate, one very near the wall and the other remote from the wall, which are then related to the length scale for turbulent momentum transfer. Consequently, the function f_μ included in the eddy diffusivity model represents two distinct physical effects of low turbulent Reynolds number and wall proximity. The present k-ε model is evaluated for its application to fully developed turbulent pipe and channel flows and found to resolve two serious weaknesses common to previous k-ε models; i.e., it correctly predicts the wall-limiting behavior of the major turbulence quantities such as Reynolds stress, turbulent kinetic energy and its dissipation rate near the wall, and the distributions of eddy diffusivity of momentum and turbulent kinetic energy even in the region far from the wall.

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Turbulent flow in a two-dimensional channel is numerically simulated by the large eddy simulation (LES) technique. A finite difference scheme with about 3.83 million grid points is applied to the case of the Reynolds number 5840. Turbulence statistics are compared with the experimental data and the results of recent large-scale computations; agreements are quite reasonable. Numerical results are stored as a database for the purpose of studying the turbulence structure and the modeling in the near-wall region. As the first report in a series on this research, this paper presents the balance of the terms in the transport equations of the turbulence kinetic energy, the dissipation rate and the Reynolds stress tensor.

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Turbulence properties and the balance of turbulence energy in a two-dimensional impinging jet on a wedge are investigated. The angles between the wedge surface and the jet axis φ are 30°and 45°. The profiles of u'/U_m, v'/U_m and (<q²>^^^-)/(2Um²) in the fully developed flow region are larger than those of the two-dimensional wall jet, but the profile of w'/U_m is almost the same as that of the two-dimensional wall jet, and all profiles exhibit no similarity. Each term of the production, dissipation and diffusion in the turbulence energy equation is larger than that of the two-dimensional wall jet except for the advection term. The production and the diffusion terms in the case of φ=45°are larger than those in the case of φ=30°. The pattern of the isopleths of (<q²>^^^-)/(2U²_j) in the impinging region differs for each case of φ=30°and 45°.

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The flow past a circular cylinder oscillating transversely in a uniform flow was investigated by flow visualization techniques. The frequency of the oscillating cylinder was set in the synchronized range in which the vortex sheds periodically with the same frequency as the oscillating cylinder. The experimental conditions were Re=1100, and A/D=0.2, where Re is the Reynolds number based on the diameter D, and A is the amplitude of the oscillation of the cylinder. The characteristic values (the displacement thickness, the shape factor, and the velocity at the outer edge of the boundary layer) were measured using the hydrogen bubble techniques. From the values, the local skin friction on the cylinder was estimated with the oscillating phase angle during a cycle. The characteristics of the unsteady boundary layer near the separation points, where the dye filaments separate from the cylinder, are discussed in comparison with those of a steady one.

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To obtain the best performance and the optimum geometries for a wide range of conical diffusers, experiments using air flow have been carried out on many conical diffusers having a uniform inlet flow except for the thin inlet boundary layer and tailpipe discharge. When the cone angle, 2α, is between 4 and 30 degrees, the performance may be expressed with a fair degree of accuracy by the functions of cone angles and area ratios with and without appreciable stall, respectively. Pressure recovery coefficients and effectiveness are shown on one chart, together with the optimum geometry lines of diffusers, when the tailpipe length is longer than its pressure recovery length. The pressure recovery length of the tailpipe is examined experimentally. If the tailpipe length is longer than three times the diameter of the tailpipe, the decrease in performance is less than two percent, as compared with the case having a sufficiently long tailpipe. This is true even in the diffuser with a cone angle as large as 30 degrees.

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In piping systems including centrifugal pumps, a pressure pulsation is generated. In this report, a centrifugal pump is assumed to have two characteristics: the generation of pulsation and the propagation of waves. The latter is described by a transfer matrix. The values of these characteristics are obtained through experimentation, and the above assumption is confirmed. A better understanding of the role of the pump in pressure pulsation is achieved. The pulsation source of a centrifugal pump is the pulsating pump head. The experiments make it clear that the strength of the pulsation souce is independent of piping systems, and that its amplitude and phase are both almost constant at constant revolutions of the impeller. The pressure distributions in a pump-piping system may be explained clearly based on the propagation and generation phenomena of pressure waves in a simple pipe system instead of in a pump.

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The present paper studies failure processes of detonation waves propagating in an expanding channel by conducting numerical simulations. A computational procedure, which combines the random choice method with a chemical kinetics simulation code and a step for the effects of the cross-sectional area of the channel, is applied to simulate gasdynamic and chemical phenomena of one-dimensional detonation waves moving through an expanding channel filled with hydrogen and oxygen diluted in an argon mixture. Also, two-dimensional simulations are carried out and compared with the one-dimensional results. It is shown that the present one-dimensional simulations calculate averaged flowfields of the two-dimensional results over the cross section of the channel.

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Using an overlaid grids method, we performed finite difference analysis on two-dimensional flow and heat transfer characteristics of louvered fins which constitute automotive heat exchangers used in forced convection regimes at low Reynolds numbers. In this method, the physical domain is subdivided into certain regions which can easily be represented by Cartesian grids. The maximum total number of the grid points allocated nonuniformly in the respective regions is about 100000. Communication between the grids is accomplished by bilinear interpolation of the dependent variables at grid boundaries. The iterative computation required 30-60 minutes of CPU time on the NEC SX-2 supercomputer. In the range of Re=64-450, the present numerical scheme was validated through comparison of numerical results and corresponding experimental data which were also obtained in the present study.

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The flow characteristic of pure water partly heated on the surface was experimentally investigated using a holographic interferometer. An extremely low velocity of water surface flow compared with that of any other liquid had been previously observed. In this experiment the water surface was cleaned by sucking out the surface layer before heating. The resultant measured surface velocity was about one order of magnitude higher than that obtained without cleaning the surface and was consistent with the velocity expected by Marangoni convection, which was calculated from the temperature distribution on the water surface. The flow characteristic of pure water is not dependent on the absolute value of surface tension force, as was previously thought, but on the surface condition. If the surface is spoiled by a contaminant such as oil, dust or any other inhibiting elements, Rayleigh convection dominates the flow pattern. The effect of liquid film thickness on the flow pattern and on temperature distribution in the liquid phase is also discussed in relation to film breakdown.

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In order to theoretically approach forced-convective filmwise condensation in a vertical tube, we have numerically solved the governing equations for both water vapour flow and condensate film flow with a finite difference scheme. The effect of waves appearing at the vapour-film interface on momentum and heat transfer has been taken into account using a model previously proposed for the two-component two-phase annular flow heat transfer. The present numerical results are compared with the experimental data given by Blangetti. The computed heat transfer results agree fairly well with Blangetti's data for the condensation of water vapour over a wide range of film Reynolds number, 50<Re_f<2000, and for three different vapour flow Reynolds numbers. The present type of numerical analysis is found to be useful for the prediction of forced-convective condensation heat transfer.

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Heat transfer processes in the combustion chamber of a pebble bed regenerative heat exchanger have been analyzed numerically for heating, evacuation, and argon heating periods successively. The calculated results well explain the measured temperature change at the top of the pebble bed. This computer code, which simulates the heat transfer processes for the combustion chamber, is coupled with that for the heat storage pebble bed to allow investigation of the overall unsteady thermal performance of a heat exchanger under the continuous cyclic operation. The analytical results point out that the geometrical optimization both for the combustion chamber and the heat storage bed is important for the improvement of the thermal performance of a regenerative heat exchanger.

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A combustion process showing a slow temperature rise was realized in an intense radiation field by burning a lean combustible mixture in a refractory-lined cylindrical combustion chamber in which a permeable board was placed at the upstream and downstream ends, respectively. It was found by the measurement of the temperature and composition of gas along with the ion current and by high-speed schlieren photography that a laminar flame was attached to the lower part of the red-hot refractory surface and that it spread toward the top center, even if the mixture strength was below the lean flammable limit. The flame becomes convex toward the unburnt mixture due to some instability resulting in a kind of cellular structure. The flickering of the flame, due partly to the wavy motion of the flame base and partly to the cellular structure, is the cause of the slow temperature rise.

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The effects of the mixing process on the power of a supersonic flow CO chemical laser are studied numerically using a leaky stream tube approach. Downstream of the nozzle exits, the flow field is divided into three stream tubes, two stream tubes for the dissociated products of CS₂ diluted in Ar and for O₂, and a third stream tube between these two, in which mixing occurs. The numerical results clearly show the importance of the mixing enhancement. As the growth of the mixing region is reduced, the laser power is lowered significantly. Therefore, the mixing process is a crucial factor in laser power estimation.

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This paper describes the measurement and analysis of the gas flow characteristics in the combustion chamber, which have an important effect on the combustion process. A laser Doppler velocimeter (LDV) was used to measure gas behavior in the combustion chamber under motor-driven operation. The flow patterns at the center of the combustion chamber are obtained first. In order to investigate the influence of engine variables such as speed and combustion chamber shape on the in-cylinder flows, the two components (U, V) of mean velocity and velocity vectors are determined at given crank angles for various speeds and for two shapes of the combustion chamber. In addition, velocity vectors at several radial locations in the combustion chamber show the in-cylinder flow characteristics of the two-stroke S. I. engine.

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