Mathematical modeling of transport processes during solidification of binary systems is reviewed. Special attention is devoted to the solidification rate-determining heat and/or species transfer processes by diffusion and melt convection. The discussion focuses on the prediction of solidification in the presence of complicated interfacial structures. The emphasis in this review is on the macroscopic aspects of solidification and not on the prediction of microstructural features; however, their interconnection is addressed. Various simplifications of the models are examined and future modeling needs are discussed.

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Many physical and chemical processes are included in turbulent premixed combustion and interact with each other in a complex way. These are characterized by the turbulence Reynolds number and the Damkohler number. Various regimes of turbulent premixed combustion are identified depending on these dimensionless parameters. In general, two important regimes are identified, namely the wrinkled laminar flame and the distributed reaction zone. Using newly developed experimental techniques, the characteristic features of the wrinkled laminar flame are being revealed and studies on the distributed reaction zone are under way. In the present review, essential problems relating to the modeling of physical processes in the wrinkled laminar flame are first described; secondly, new experimental findings relating to the distributed reaction zone are presented, and finally the transition mechanism of the turbulent premixed flame structure is discussed.

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Mean flow properties, including turbulent stresses, were fully measured in a turbulent Taylor vortex flow between stationary outer and rotating inner cylinders with a radius ratio of 1/0.92. The static pressure distribution on the outer wall confirmed that many turbulent Taylor vortex pairs about twice as high as the channel width continued to exist over a wide range of Taylor numbers varying by more than one digit. A new technique using a grid was effectively applied to fix a vortex pair to be measured at the required position during the velocity field measurements. In the core region extending over 60% of the channel width, the secondary flow contributed to the angular momentum transfer by about 90%. The turbulent stress distributions were characterized by production and convection due to the secondary flow.

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A theoretical analysis is presented for the unsteady laminar flow of an incompressible fluid between parallel disks with a time-varying gap width and a central fluid source. The gap width h and the flow rate q of the source are independently varied arbitrarily with time. New series solutions to the Navier-Stokes equations are obtained on the basis of an original asymptotic expansion in the radial direction and a new theory of "multifold series expansion" in the time variable. The solutions can precisely describe the complicated nonlinear interaction between the two coexisting flows. Experiments were carried out for the case where h and q were changed sinusoidally with a variety of mean values, amplitudes and phase differences. It has been confirmed that the present solutions agree very well with the experiments over a wide range of the flow conditions and the variations of h(t) and q(t).

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The heat generation in an unsteady flow between an oscillating plane and a fixed plane is studied theoretically. It is assumed that one of the two planes is oscillating in the horizontal and vertical directions. The flow is two-dimensional and the fluid is viscous and incompressible. The equations governing the flow and the heat are analyzed taking the viscous dissipation into account. The coordinate in the direction along the surfaces of the planes is found to be separable in these equation. The governing equations depending on only two independent variables, the coordinate in the direction perpendicular to the plane surfaces and the time, are solved numerically using a finite difference method. It is found that, under the condition of a very large Prandtl number, the oscillation combined in the horizontal and vertical directions strongly enhances the heat generation in the viscous flow. If a small vertical oscillation is superposed on the horizontal one, the temperature depends on the coordinate along the plane surface in the antisymmetrical form through the convection term in the energy equation. This dependency plays an important role in heat generation. The mechanism of heat generation due to the combined oscillation is physically clarified using an order-of-magnitude analysis.

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A simulation program for rarefied gas flow with the pressure conditions given at the upstream and downstream boundaries has been developed. With the pressure conditions given at the upstream and downstream boundaries, flow velocities at these boundaries are revised in every time step according to the number of molecules going in and out. Thus, a steady solution for the continuous flow properties at the upstream and downstream boundaries is obtained by averaging the flow properties after a certain time. The algorithm of molecular movements and collisions is based on the direct simulation Monte Carlo method by Bird. Results of the calculation by this program are compared with and verified by Dong's empirical results for a 2-D Poiseuille flow.

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Constitutive equations for magnetic fluids have been investigated by some researchers, however, these equations cannot describe the phenomena of magnetic fluids perfectly for lack of some elements which the constitutive equations should satisfy, for example, some do not consider viscoelastic effects, some do not satisfy the principle of material frame indifference, some are not formulated by using the thermodynamic method. We introduce a new way of determining constitutive equations for magnetic fluids. It is a method which is a combination of the theory of integrity bases and the principle of maximal dissipation rate based on the thermodynamic discussion. Compared with previous methods, it has such merits as the following: all equations satisfy the principle of material frame indifference and only include the terms which are permitted by thermodynamics; non-Nowtonian effects except magnetic effects can be described because nonlinear terms are considered; we can obtain the constitutive equations not only in the case of the compound processes but in that of the complex processes as well.

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A developing turbulent flow of power law fluids in the entrance region of curved pipes has been investigated by measuring an axial component of the mean and the fluctuating velocity with an optical fiber LDV under the condition of power index n>0.75, two curvature radius ratios R_C=10 and 30, and Reynolds numbers Re=10000∼33000. Turbulent flow develops more mildly than laminar flow, which leads to longer inlet length. A Reynolds stress equation model is applied to predict a fully developed turbulent flow. Numerical results are in moderate agreement with experimental results within the power index n=1∼0.9. In addition, an approximate expression for the turbulent friction coefficient is presented on the basis of the boundary layer theory.

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A method for analyzing the mold-filling dynamics of thermosets in a circular channel has been developed. A constitutive equation model to describe isothermal viscosity changes of commercial molding compounds was derived as a function of time and temperature. This model was used for predicting actual nonisothermal viscosity changes. The simultaneous equations, including the conservation equations of total mass, momentum and energy, and the constitutive equation model were solved numerically to obtain rheological changes of an epoxy compound during mold filling in a circular channel. The calculated profiles of apparent mean viscosity with time of the epoxy compound corresponded well with the experimental data.

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This paper describes the numerical simulation of the steady gas-particle two-phase flow field inside a JPL nozzle. The computations use a time-dependent technique using the TVD-MacCormack algorithm for both gas and particle phases. The nozzle flows considered here are inviscid, and spherical particles of 1μm in diameter are treated. Numerical results show that the nozzle expansion is delayed when the interaction between gas and particle phases becomes strong. In addition, it is seen that a particle-free zone exists near the wall downstream of the throat.

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The velocity fields around a circular cylinder which was started impulsively in a water tank were measured by flow visualization techniques. The pressure on the surface of the cylinder was estimated by the line integral of Temple's equation using the measured velocities on a closed circuit which was selected to avoid the cumber-some estimation of viscous terms. The estimated distributions of the pressure coefficient C_pθ at Re=1200, disagree with those of the numerical analysis for Re=1000 by Bar-Lev and Yang, but agree with those of the numerical analysis for Re=500 by Collins and Dennis. The variation of the local values of the pressure coefficient C_pθ (θ=90°and 180°, θ: azimuthal angle measured from the frontal stagnation point of the cylinder) with elapsed time was found to be similar to that of C_pθ obtained by both the conventional numerical analysis and the experimental study, though their quantitative agreement is insufficient.

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The presence of particles or water droplets in the flow of turbomachinery, especially in the low-pressure stages of steam turbines, leads to erosion of the moving blades and causes additional loss. This report describes a measurement technique for droplet sizing and velocity in atomized droplet flow by using a two-color, four-beam fiber laser doppler velocimeter (LDV) system. The optical probe system forms two coaxial measurement volumes with different diameters in which droplet sizes are evaluated by light scattering intensity. Measurements are performed for atomized droplet flow in the wake of a fixed blade. Test results demonstrate that relatively large droplets concentrate in the wake and are slowly accelerated by the stream. While the droplet velocities are influenced by the wake profile, the droplet sizes tend to be particularly affected by wetness rather than by stream velocity.

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An attempt to increase the turbine blade aerodynamic force was made by installing boundary layer fences on the endwalls of a linear turbine rotor cascade. The height and location of the fences were varied to optimize these parameters. Static pressures measured on the passage surface correlated well with surface secondary flow patterns visualized by the oil flow method. The fences favorably attenuated local unloadings in the tip region of the suction surface associated with the endwall crossflow and the passage vortex three-dimensional separation, but unfavorably inhibited a passage-vortex-induced local loading also on the suction surface. The fences were most effective when their height was one-third of the inlet endwall boundary layer thickness and located half a blade pitch away from the blades. The optimum fences then reduced the tangential force defect to 60 percent of the unfenced blading value.

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Pump performance depends on the outlet flow of the impeller. A method of surface singularities for core flow in the centrifugal impeller, combined with an integral method for a boundary layer, would explain the mechanism of the performance change caused by cutting the outlet edge of the impeller blades down. This method is applied to flows in the impellers with various cut-downs of the blade edge, and then the calculated results are compared with the experimental ones. Both results are shown to be quantitatively in good agreement. On the influence of cutting the blade edge on the outlet flow, it is indicated that the cut of the pressure surface results in the decrease of relative flow angle with the decrease of radial velocity in the core flow, while that of the suction surface results only in a decrease in radial velocity. The change in the flow separation region due to the cut on the suction surface, however, contributes to the deterioration of pump performance.

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Small signal gain coefficients of a supersonic flow CO chemical laser are calculated using a theoretical model which was developed previously and compared with the corresponding experimental results. It is shown that the model predicts the gain characteristics only qualitatively. The measured small signal gain coefficients are rather small compared with the calculated results. In the present investigation, the theoretical model is improved significantly by modifying the relaxation rate constants and by including the effects of the boundary layers which develop in the optical test section. However, further improvement on the theoretical model is necessary by including the effects of the nozzle boundary layers and shock waves.

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This paper aims to clarify the laminarization phenomena of strongly heated gas flows in a circular tube through numerical simulation. For this purpose, a k-ε turbulence model, which was originally proposed by Nagano et al., was modified so as to improve its prediction accuracy, particularly in the turbulent-to-laminar transition region. After that, this modified model was applied to the strongly heated gas flows. According to the numerical results, the streamwise variation of the heat transfer coefficient of the laminarizing flows can be predicted more accurately by the modified version than by either the original model or Jones and Launder's model, and its accuracy level can be favorably compared with that of the k-kL model by Kawamura. Moreover, it was concluded that the streamwise variation of the turbulent energy of the laminarizing flows can be clearly distinguished from those of the flows in which the Nusselt number decreases simply as a result of the local change in gas viscosity. Calculated criteria for the occurrence of the laminarization were in good agreement with the experimental results by Ogawa.

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The possibility of removing the pollutants by arc plasma injection from dirty gas containing higher concentrations of NO_x, SO_x, HCl and dust emitted from a municipal refuse incinerator has been studied in this paper. A low-power arc plasma generator is designed and operated continuously on argon gas with high stability. The air is injected from a capillary into an argon plasma jet, and the formation of NO_x is measured in order to assess the generation of specific radicals in the plasma wake. The optimum injection points for generating radicals and for the stable operation of the plasma are discussed; the formation of NO_x in the presence of oxygen for a practical system is also evaluated.

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This paper describes the numerical analysis of the deformation process of a droplet impinging upon a flat surface. The calculation has been based on the basic equations of the SMAC method in the cylindrical coordinates, under the consideration of the surface tension. When Re, Fr and We numbers were the same, the experimental results were in good agreement with the calculated ones at each nondimensional time. Then the heat transfer model has been constructed for the case of impingement upon the hot wall surface, and basic equations were solved by the energy method, one-dimensional heat conduction method, and two-dimensional heat conduction method. The experimental results of the evaporation lifetime of the droplet agree well with the calculated ones, as shown by the latter two methods. It was quite possible to simulate the temperature profile in the droplet, although the convection flow inside the droplet and the evaporation process were disregarded in the models.

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This experimental study aims at investigating the influence of the buoyancy upon the turbulent diffusion of gas jets. Carbon dioxide, helium and air are separately discharged upward or downward from a perpendicular convergent round nozzle into still air. The velocity and the concentration measurements are carried out in order to investigate the diffusion structure of the buoyant jet. The influence of the exit Froude number on the nondimensional length from the nozzle exit to the end of the fully developed region is examined. The velocity and the concentration fluctuations are analyzed in detail for understanding the local character of the jet diffusion. The probability density functions of the velocity and the concentration fluctuations are determined over the whole region of the jet. The skewness and the flatness factors of these probability density functions are also calculated.

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The effects of radiant heat fluxes on the stability range and burning velocity of a laminar premixed flame were examined by inserting a water-cooled Bunsen burner into a radiant heat recirculation-type furnace. The intensity of the radiant heat flux in the furnace was altered by regulating the surface temperatures of the furnace wall and downstream permeable board. It was found that the flame blowoff and flashback limits were hardly affected by a radiation field as intense as the one surrounded by a refractory whose temperature was between 1250K and 1450K, and that no perceptible changes appeared in either the laminar burning velocity or flame thickness.

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An experimental study was made of the structure of the propane jet diffusion flame discharged normal to a free stream of air with a uniform velocity profile. The velocity profile in the flame was measured by application of the forward scattering LDV system. A gas chromatograph was used to measure the concentration profile of the major species in the flame. The results showed that the flame configuration were correlated well with the ratio of fuel jet to cross-flow velocity. The transition from an elliptic to a kidney shape was observed in the contour of constant velocity in the transverse cross section normal to the jet axis of the flame. A peak in the CO concentration profile was observed below the jet axis where the C₃H₈ concentration showed a maximum, and above the location at a minimum O₂ concentration. The CO₂ concentration profile had dual peaks which bore a resemblance to the temperature profile.

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Confined turbulent premixed flames stabilized by a pilot flame were investigated to elucidate the local fine structure of flames and its influence on mixing processes in the combustor. The fine flame structure was classified on the basis of the measured turbulence characteristics, and the probability density functions (PDF's) of local fluctuating velocity and temperature were examined in detail. A plateaulike distribution in the temperature PDF, which may correspond to a "distributed reaction zone", was observed in a limited portion of the flame in addition to a typical bimodal distribution corresponding to the structure of a "wrinkled laminar flame" or "laminar flamelets". The influence of the fine flame structure on the mixing processes was examined using an inert gas tracer.

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The scavenging process of a 2-stroke cycle engine dominates not only fresh-air charging but also the airflow in a cylinder at the compression end. So, the combustion performance of a 2-stroke cycle diesel engine depends on scavenging efficiency η_s, and the scavenging-air swirl intensity in the cylinder. In this report, first, the scavenging airflow is investigated by operating a 2-stroke cycle engine rig. From the LDV measurement of the air velocity in a cylinder during the compression stroke, it is shown that the scavenging port made by the combination of a large-angle port and a small-angle port has high scavenging ability and sufficient swirl intensity for air-fuel mixing. Secondly, the numerical analysis method of the gas flow in a cylinder during the compression stroke is developed. This method employs an approximation of a 2-D axisymmetrical flow to save computation time, but uses, for the initial condition, the calculated results of a 3-D scavenging flow simulation to ensure the accuracy of the starting swirl-flow pattern which is deeply affected by the port arrangement. Some calculated results are compared with the experimental data, and it is concluded that this method can simulate the flow pattern in a cylinder during the compression stroke with good accuracy.

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This paper gives the experimental results obtained with a two-stroke cycle single-cylinder research engine using an electrically heated combustion chamber to simulate the combustion chamber of a low-heat-rejection(LHR) DI diesel engine with the M-combustion system. In this report, the experiment was performed to investigate the influences of combustion chamber surface temperature and swirl ratio on the combustion of a LHR DI diesel engine with the M-conbustion system. It is found that the combustion of fuel deposited on the surface is greatly affected by the combustion chamber surface temperature, and the diesel combustion is controlled by the swirl and the surface temperature of the combustion chamber.

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Absorption and desorption of fuel by motor oil that coats the cylinder side wall with a thin oil film is thought to be one of the important sources of unburnt hydrocarbon emissions from spark ignition engines. A simplistic model which describes the dynamic process of fuel absorption and desorption in the thin oil film has been developed. Calculated results show that the rate of the absorption and desorption process is comparable to the engine motion, and the amount of unburnt fuel emitted from the oil film depends on the position of the oil film, rotating speed, diffusion coefficient, oil layer thickness, existing cycles of the oil layer and initial fuel concentration in the motor oil. It is also demonstrated that the synthetic model which is the sequential connection of the four models, i.e., the fuel diffusion through the oil layer, the cylinder pressure, the ring gas pressure and the oil layer thickness, is useful in estimating the dynamic process in the engine given its specifications and operating conditions.

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