The forces acting on and the flow patterns around a rectangular cylinder with a cross-section of width/height ratio of 0.2-3.0 submerged in oscillatory flow were studied by using a U-tube water tank. Measurements of both in-line and transverse forces on a rectangular cylinder were made in a wide range of Keulegan-Carpenter number (KC) from 1 to 160. The force signals were analyzed spectrally to obtain major frequencies. Flow visualization was also employed to confirm the relationship between flow patterns and force coefficients. In this paper we discussed the influence of the width/height ratio of the rectangular cylinder on the flow patterns and the fluid dynamic characteristics of the cylinder in oscillatory flow. It was found that the drag force coefficient C_D of the cylinder with d/h=0.6 ratios becomes the biggest beyond KC〓120, compared to that with other d/h in oscillatory flow. The good correlation between C_D and wake width has been successfully obtained. The variations of C_D values in low KC number region were classified into three groups, flat-plate-type, square-cylinder-type and circular-cylinder-type by the d/h ratio. In the cases of d/h=0.4 and 0.6, a phenomenon was found that the flat-plate-type can be shifted to square-cylinder-type by changing KC number. Based on the analysis of the major frequency components of the fluctuating transverse forces, it revealed that the value of Strouhal number reduced by the maximum velocity is similar with the result in the case of a uniform flow.

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The unsteady flow field of an incompressible viscous fluid around an impulsively started sphere with slow motion is analyzed in detail using the method of matched asymptotic expansions. First, integral expressions are derived from the nonlinear Oseen-type vorticity equation and then they are solved asymptotically by an approach proposed by one of the authors. In the present paper we show that to complete the matching process, five local regions are necessary, unlike earlier theories, and the essential feature of these regions is similar to the flow around a two-dimensional circular cylinder analyzed by the present authors. Furthermore, the present paper demonstrates that the present approach leads to unique asymptotic solutions without matching with respect to the time coordinate.

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Stall flutter of a compressor cascade is studied by the numerical analysis of the unsteady separated flow around the blades oscillating in a torsional mode. A numerical method is developed for the present study, in which used are a discrete vortex modeling to calculate the convection and the diffusion of vorticity in the separated flow and a grid system deforming together with blade oscillation. The present method is applied to a compressor cascade working at an inlet flow angle where the rotating stall is also liable to occur. The numerical result shows that the strong vortices shed from the leading edge of stalled blades have dominant influences both on the flow behavior and on the flutter excitation of blades, and that the occurrence of stall flutter is closely connected with the propagation of rotating stall.

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Stall flutter of a compressor cascade is studied by the numerical analysis of the unsteady separated flow around the blades oscillating in a torsional mode. When a cascade operates at a stall condition, the unsteady flow behavior changes according to the relationship between the propagation velocity of blade oscillation and the propagation velocity of rotating stall. The propagation of rotating stall is synchronized with, or entrained by, the blade motion and becomes very regular when both propagation velocities are close to each other. The oscillating blades are subjected to intense flutter excitation when the synchronization occurs. On the other hand, when both propagation velocities are largely different from each other, the rotating stall propagates with an almost constant velocity regardless of the instantaneous angles of blades. The propagation of rotating stall becomes irregular under the influence of blade oscillation when the difference of the propagation velocities is in between. The flutter excitation of blades does not occur in the latter two conditions.

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In this study, an advanced Lagrangian vortex-boundary element method is applied to simulate the unsteady impeller-diffuser interaction in a diffuser pump. Velocity calculations based on the Biot-Savart law reduce the need to grid large portions of the flow field and the calculation points are concentrated in the regions where vorticity is present. Lagrangian representation of the evolving vorticity field is well suited to moving boundaries. An integral pressure equation shows that pressure distribution can be estimated directly from the instantaneous velocity and vorticity field. The numerical results are compared with the experimental data and the comparisons show that the method used in this study can provide us insight into the complicated unsteady impeller-deffuser interaction phenomena in a diffuser pump.

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Dynamics of a spherical bubble cloud with nuclei size distribution is investigated numerically when the surrounding pressure is decreased from 50kPa to 10kPa and then increased to 50kPa stepwisely. A set of governing equations for the motion of bubble cloud are formulated combining the averaged equation and the equation of bubble motion with emphasis on the internal phenomena of each bubble. The nuclei size distribution has significant effects on the cloud dynamics in comparsion with the results for mono-dispersed cloud. When the cloud contains multi-dispersed bubbles in their size, the maximum pressure in the bubbly mixture becomes lower than in case of mono-dispersed cloud. however, the maximum pressure emitted from each bubble has the same order for both cases. The range where high-emitted pressure is observed is wider than in mono-dispersed cloud.

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Water hammer phenomena caused by a rapid valve closure, that is, shock phenomena in two-phase flows, are an important problem for the safety assessment of a hypothetical LOCA. This paper presents the results of experimental and analytical studies of the water hammer phenomena in a one-component two-phase bubbly flow. In order to clarify the characteristics of water hammer phenomena, experiments for a one-component two-phase flow of Freon R-113 were conducted and a numerical simulation of pressure transients was developed. An overall picture of the water hammer phenomena in a one-component two-phase flow is presented and discussed.

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We have developed a laser trapping method to control the bubble position without contact. In this method, we use an empty laser cone obtained by focusing a laser ring. Scanning a laser beam circularly using a pair of galvano mirrors creates the laser ring. This method is adequate to trap a rising bubble because the potential barrier created by the light momentum change due to the reflection and refraction on the bubble surface exists only at the upper surface of the bubble. Bubbles of the order of 10 μm in diameter have been trapped and manipulated successfully using a dry objective lens as well as an immersion objective lens. The laser trapping using the dry objective lens with a large working distance has the advantage that the influence of the lens on the bubble is negligible, as a sufficiently large distance can be maintained between the lens surface and the trapped bubble. We have also evaluated the optical force acting on a bubble both experimentally and theoretically. Trajectories of rising bubbles are predicted by taking the optical force into account. It is shown that the optical force in the lateral direction is weaker than that in the axial direction.

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Nowadays, a non-intrusive measurement tool of thermodynamic variables with high sensitivity is strongly demanded for analyses of highly rarefied gas flows. REMPI (resonantly enhanced multiphoton ionization) is the most suitable technique for measurement of gas molecules with very low density. In this study, to examine the fundamental properties of the REMPI spectra, 2R+2 N₂-REMPI spectra including the spectral broadening are calculated and compared with the experimental results. From the calculated REMPI spectra, spectral lines adequate to measure temperature are proposed, especially at relatively high temperature where the measurement error becomes larger because of the overlap of the spectral lines.

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Computations of internal viscous flowfields of scramjet models were conducted at inflow Mach numbers of 3.4 and 5.45. A hybrid unstructured grid method was used to compute the scramjet models with and without a short strut. The numerical method to solve the Navier-Stokes equations on the hybrid unstructured grid was developed using a finite volume cell vertex scheme and the lower-upper symmetric Gauss-Seidel (LU-SGS) implicit time integration algorithm. The computational results revealed that a thick subsonic region did not exist in the combustor near the top wall at Mach number 5.45. It was a desirable feature to avoid unstarting the engine. With the use of a strut, the relatively low velocity regions increased and the downward flow toward the cowl behind the step became strong. An overconcentration of fuel toward the top wall during weak combustion was observed in the experiment. The reason for this was that the airflow near the injector was turned to the top wall due to the small influence of combustion in the experiment.

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The present work is an experimental investigation of turbulent mixing of two co-axial jets with low annular to core area ratio in a non-separating confinement. Experiments were conducted in a newly designed set-up having a duct to nozzle diameter ratio of 1.19. Two centrifugal blowers driven by motors of 30 kW power each generated the air flow. Influence of chute geometry on the turbulent mixing of two co-axial streams is studied by using two chute mixer configurations having 10°and 20° angles of penetration of the annular stream towards the core region at a velocity ratio of 1.8. Contours of mean velocity and streamwise and transverse turbulence intensities were obtained by making measurements close to the point of injection with a very fine grid. The results show an improved mixing due to chutes. A stronger transverse turbulence component (w') is observed close to the injection points, which seems to enhance mixing. Profiles at the downstream locations show a faster approach towards uniform mean velocity and homogeneous turbulence intensity. With the chute model having 20° angle of penetration, nearly complete mixing is achieved at a distance of 2.2 duct radii itself, suggesting feasibility of shortening of the duct by about 50%. However, a higher total pressure loss of about 1.7% is the penalty to be paid for enhanced mixing of the jets.

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The authors proposed the method of performance improvement by injecting moist air as the new propulsion system. The authors investigated on the effect by injecting dry air into the nozzle in former papers but there was the limit because the average fluid density decreased in the nozzle by air. In this study, the method of injecting moist air was investigated to obtain more thrust. Steam of the moist air injected into the nozzle condensed and the average density of fluid increased. By the increase of the density, the thrust increased about 20% comparing with the result of using only dry air and the propulsion efficiency was improved. There are some sources of exhausted heat such as engines and boilers in actual ships and obtaining the steam is relatively easy to make use of them. Our propulsion method is applicable for practical use and desirable for the energy efficiency.

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The purpose of this paper is to propose a turbulence model for the three-dimensional vortex blob method. This model uses a modified version of the core-spreading method introduced by Leonard and Chua (1989) in the spirit of the Smagorinsky type of eddy viscosity. The diffusion of vorticity by the molecular viscosity is represented by the core spreading whose rate is approximated by that of a rectilinear viscous vortex tube. The linear combination of the two viscosities yields a Lagrangian turbulence model, which includes the effects of Reynolds number. We apply each model to an impulsively started round jet forced by two helical disturbances rotating in counter directions and compare the vortical structures of the jet among the models to show that the combined model can be a reasonable turbulence model.

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Dynamic behavior of vortices generated behind the leading and trailing edges of pitching airfoils such as two kinds of flat plates, NACA0010, 0020, 65-0910 and an airfoil with a blunt trailing edge has been visualized using a schlieren technique with a high-speed camera in a wind tunnel. It was observed that small vortices were shed discretely from the leading and trailing edges. The frequency of vortex shedding was strongly dependent on the nondimensional pitching rate and was independent of the airfoil configuration as well as the Reynolds number. The frequecy of vortex shedding from the respective edge during one pitching cycle was the same and this result was observed similarly among all the test airfoils. Vortices existed which moved up from the trailing edge toward the leading edge on the suction surface and they played an important role in balancing the frequency of vortex shedding from the respective edge.

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A method of numerical calculation for radiation heat transfer in a three-dimensional closed space including diffuse and specular surfaces was developed. To enable an analysis of the radiation heat exchange on each surface considering multiple specular reflections and obstacles to rediation in the space, an improved heat ray-tracing method was presented to calculate view factors accurately. The method was determined to be applicable to complicated problems in test calculations using models with specular surfaces and obstacles. Continuing efforts are being applied to more realistic problems. The example examined in this paper is an infrared emitter with a parabolic specular reflector, which is a conventional electric heating apparatus. The measured result for radiant power distribution agrees well with the calculated one. The practical validity of our method was verified.

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The effect of the sectional shape of pipes on the enhancement of longitudinal heat transfer by fluid pulsation in pipe bundles has been investigated. Bundles of circular, triangular, square and hexagonal pipes are considered. Heat transfer characteristics of each pipe and the gross performance as a pipe bundle including the heat conduction in pipe walls, are discussed. The local distribution of longitudinal heat transfer in pipe section reveals the existence of a region where heat is transferred toward the higher temperature end when the pulsation frequency is sufficiently high. As a pipe bundle, only a circular one has narrow gaps among each three pipes, which deteriorate the gross performance of heat transfer. But in the case of the present investigation which assumes acrylic pipes of the same wall thickness, the circular pipe bundle is advantageous to other ones as for the global performance of longitudinal heat transfer including the wall thermal conduction, because the area ratio of pipe walls, whose low thermal conductivity lowers the performance, is least when the pipes are circular.

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A theoretical analysis of impact dynamics and heat transfer is performed on single, deformable, saturated drops to determine heat transfer effectiveness, using idealized shapes to model the deformation. Numerical results are obtained for various liquid drops in the nonwetting regime with diameters of 0.22 to 4.0 mm, wall superheat temperatures of 200 to 600 K and Weber numbers of 12.3 to 50. The drop heat transfer effectiveness is expressed in the form of a correlation equation of four dimensionless parameters, including Weber, Bond and Prandtl numbers, and a new parameter which can be interpreted as the ratio of the inertial force induced by the accelerating vapor flow inside the superheated vapor layer to the elastic restitution force of the drop itself due to surface tension forces. The correlation equation agrees well with the existing experimental data in the absence of air entrainment and drop subcooling.

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The ignition and combustion behavior of single droplets of asphalt/water-emulsified fuel (As/W) were observed in an electric furnace in order to obtain fundamental data for practical use. The ignition delay and burnout time of single droplets of asphalt, 'C'-heavy oil and the As/W emulsions were investigated under specified furnace temperatures. Each fuel showed unique ignition and combustion behavior, and the As/W-emulsified fuel-J (As/W-J) in particular, showed very strong microexplosions. The values of ignition delay and burnout time of As/W emulsified fuels were smaller than those of asphalt and 'C'-heavy oil. This can be explained by the occurrence of microexplosion phenomena caused by the rapid vaporization of the water phase in the droplets. Thus, it is possible to use asphalt/water-emulsified fuels as substitute fuels for 'C'-heavy oil, because of their superior combustibility.

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The interactive combustion of two closely-spaced droplets at elevated pressures was investigated experimentally in a 2.2 second drop tower. Heptane, hexadecane and mixtures of the two were the fuel. A nitrogen-Oxygen ambient with a relatively low oxygen concentration faciliated observation of droplets during combustion at elevated pressures. Results show that staged combustion of binary fuel droplets still exists for interacting droplets at elevated pressures. For pure fuels, the interaction effects are principally observed during the initial heating period. For fuel mixtures, interaction effects are estimated by comparing the transition time of a single droplet to that of the droplet pair.

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A surface reaction occurs at a certain surface temperature when the catalyst is heated up in a reactive mixture. If homogeneous ignition does not occur, a steady state is observed because the heat produced by the surface reaction is balanced with the heat loss caused by convection, conduction and radiation. The steady temperature was defined as the temperature at the steady state. This paper treated the pressure effects on the surface reaction. Hydrogen and oxygen were used as reactants and nitrogen as an inert gas. A spherical platinum catalyst of 1.5 mm in diameter was sustained in the chamber with two wires of 0.1 mm in diameter. As results, there was a maximum steady temperature at a certain relative hydrogen concentration (α_max) and α_max increased with the total pressure. At the steady state, it could be approximated that the heat release was estimated by the mass transfer considering the effect of natural convection. The experimental results could be explained qualitatively by the approximation.

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Flying slag particles have a tendency to deposit and sinter on the exit wall of entrained-bed coal gasifiers. A reasonable measurement to calibrate sintering temperatures in slag containing char and measure the relation between sintering temperatures and fusion temperatures of the slag were examined, using eighteen kinds of coal amorphous slag and char. It was found that a dilatometer was very useful in measuring only sintering temperatures of pure slag powder as the shrinkage of slag containing char was not related to sintering, and that the compressive strength method was reasonable in evaluating sintering behavior of the slag containing char. The lowest sintering temperature of slag tested and measured by a dilatometer, was approximately 650°C. It was also found that the sintering temperature of slag was related to the JIS melting point. The sintering temperature increased to approximately 800°C with an increase in the melting point of slag.

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A new injection system using mixed fuel dissolved with liquefied CO₂ is proposed in this paper. Liquefied CO₂ is mixed with n-Tridecane under pressure in order to promote spray atomization and evaporation due to the effect of the flash boiling phenomenon during fuel injection, and to control the combustion process due to the effect of the internal exhaust gas recirculation (EGR) effct of CO₂ gas. Therefore, a simultaneous recduction of soot and NO_x is achieved effectively using this injection system. In this study, the characteristics of diesel fuel spray dissolved with liquefied CO₂ are investigated quantitatively by several optical measurements. The spray characteristics are revealed by analyzing the chemical thermodynamics. As a result, it is determined that atomization of this fuel is promoted by flash boiling much more than in n-Tridecane, which is normal reference fuel, and the spray structure is considerably different from that of the normal fuel. Moreover, the numerical analysis of atomization and vaporization processes are carried out, based on the flash boiling spray model.

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MTBE (Methyl Tertiary Butyl Ether) blended diesel fuel, and DME (Dimethyl Ether) with the homogeneous charge compression ignition (HCCI) system are very attractive for NO_x and PM (particulate matters) reductions in DI diesel engines, while their effects on combustion and odorous emissions are not clear. In this study, a few percent MTBE blended in diesel fuel gives a lower HCHO (formaldehyde) and an improved exhaust odor than with neat diesel fuel, while over 10% blend, a very low boiling point MTBE forms an overlean mixture and diminishes the positive effect of the O₂ content of MTBE. The study of DME achieved a 100% DME combustion, and hybrid combustion of DME and diesel fuel with HCCI system. Two peaks in heat release during combustion appear in DME and hybrid-operation under an ultra-lean engine operation. Although the homogeneous DME mixture allows the ultra-lean engine operation, It also gives a very strong exhaust odor together with higher HCHO and THC (total hydrocarbon).

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A dynamic analysis of a free piston Vuilleumier cycle heat pump was performed by a time-stepping integration method. The nonlinear relationship between displacement and force for pistons was taken into account for the motion of reciprocating components, in addition to the pressure change of working gas, nonlinear viscous dissipative force due to an oscillating flow and discontinuous damping force caused by solid friction. The displacement of pistons and pressure changes in the Vuilleumier cycle heat pump were integrated by an ideal isothermal thermodynamic relationship. It was assumed that the flow friction was proportional to the kinematic pressure of working gas, and that the solid friction at the seals was due to the functions of the working gas pressure and the tension of seal springs. In order to investigate the dependence of the characteristics of a machine on various dynamical parameters, some calculations were performed for a proposed case study machine and discussed. The roles of working gas pressure, the displacer piston rod and dissipative force due to flow and solid friction were clarified, and the proposed method was found to be very effective in predicting dynamic behavior of free piston Vuilleumier cycle heat pumps and in designing the machine components.

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