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Showing papers in "Transactions of the Japan Society of Mechanical Engineers. B in 1991"


Journal ArticleDOI
TL;DR: In this paper, an experimental investigation was carried out on the varying properties of void fraction averaged over a tube cross section in an isothermal fully developed air-water two-phase mixture flowing in a horizontal capillary tube of 1.0mm, 2.4mm and 4.9mm inside diameter, using the constant current method.
Abstract: An experimental investigation was carried out on the varying properties of void fraction averaged over a tube cross section in an isothermal fully developed air-water two-phase mixture flowing in a horizontal capillary tube of 1.0mm, 2.4mm and 4.9mm inside diameter, using the constant current method. The flow pattern was observed by video and photograph with streak flashing. Calibration of the void meter was performed using a nonconductive plastic model in bubbly flow, intermittent flow and annular flow. It was found that the scatter of the data of the void fraction was within 20% in each flow region. We obtained correlations between (1) void fraction and gas volume flow rate quality, (2) bubble volocity and total volume flux, (3) lengths of slugs and gas-liquid flow ratio and (4) mean liquid film thickness and pipe diameter

34 citations


Journal ArticleDOI
TL;DR: In this paper, a plug flow of cohesionless granular material in a horizontal pipe was numerically simulated and the movement of each particle in a calculation region, which has periodic boundaries on its inlet and outlet, was solved.
Abstract: Plug flow of cohesionless granular material in a horizontal pipe was numerically simulated. The movement of each particle in a calculation region, which has periodic boundaries on its inlet and outlet, was solved. Contact force was modeled with springs, dashpots, and a slider. Repulsion force of the spring was given based on the contact theory of homogeneous isotropic elastic objects. The damping coefficient of the dashpot was given so as to make the coefficient of rebound constant. As a result, stable plug flow was observed in the present calculation. It is confirmed that the behavior of the plug and each particle is similar to the experimentally observed behavior.

34 citations


Journal ArticleDOI
TL;DR: In this article, a new computational method was developed for the analysis of 3D large-amplitude motion of liquids with free surfaces in moving containers, which is formulated mathematically as a nonlinear initial-boundary value problem under the assumption of irrotational flow of an inviscid fluid.
Abstract: A new computational method has been developed for the analysis of three-dimensional large-amplitude motion of liquids with free surfaces in moving containers. The problem is formulated mathematically as a nonlinear initial-boundary value problem under the assumption of irrotational flow of an inviscid fluid. The free surface is moved during each time step in a Lagrangian manner, and its new position is calculated using a forward-time Taylor series expansion. One of the key features of the present method exists in the algorithm to compute the values of Lagrangian time derivatives in the Taylor series. To evaluate these derivatives, a boundary element method is used. The use of the Taylor series expansion has enabled us to employ a variable time-stepping method. The size of a time increment is determined at each time step so that the remainders of the truncated Taylor series should be equal to or less than a given small error limit. Such a variable time-stepping technique has made a great contribution to numerically stable computations. As a numerical example, a swirl motion of liquid in a cylindrical container subjected to a forced horizontal oscillation has been analyzed.

20 citations


Journal ArticleDOI
TL;DR: In this paper, an electro-hydrodynamical (EHD) condenser utilizing the combination of two kinds of EHD phenomena has been investigated to maximize the augmentation effect, to clarify the details of an EHD pseudo-dropwise condensation.
Abstract: In order to realize the higher performance heat pump, an electro-hydrodynamical (EHD) condenser utilizing the combination of two kinds of EHD phenomena has been researched. In this study, to maximize the augmentation effect, experimental study has been carried out to clarify the details of an EHD pseudo-dropwise condensation. The diameter of the drops has decreased according to the increase of the electric field. The condensation heat transfer coefficients have increased in proportion to the electric field strength to realize the maximum local heat transfer coefficients of over 9000 W/m2K in CFC 113 and over 11000 W/m2K in HCFC 123. Furthermore, the heat transfer coefficients have become of the same order under the condition of the the same quantity of falling condensate.

19 citations



Journal ArticleDOI
Abstract: This paper describes a study on the development of a proper airfoil section for the vertical axis wind turbine (VAWT). We aim to abtain pitching moment in the negative direction without losing the excellent characteristics of a symmetrical-type airfoil section. Thus, we propose an increase of the thickness of the symmetrical-type airfoil by giving a meanline reversal, that is, negative meanline near leading edge and positive one near trailing edge, measured from blade chord line. Thus, the airfoil section can be designed by setting the parameters of a reverse meanline and basic airfoil section, and this airfoil section will be called the TW series airfoil section. From the three component force characteristics measured in wind tunnel experiment, TW series airfoil section is regarded to preferable for VAWT, thus, validity of design concept of TW series airfoil section using reverse meanline was demonstrated.

17 citations


Journal ArticleDOI
TL;DR: In this paper, the dynamic behavior of magnetic fluid surfaces in containers were experimentally examined and it was found that the harmonic wave motion, swirling waves and flow pattern of surface waves were influenced by the magnetic fields.
Abstract: In the present paper, the dynamic behavior of magnetic fluid surfaces in containers were experimentally examined. Experiments were carried out for rectangular, cylindrical and spherical containers. These containers were horizontally oscillated. The vertical nonuniform magnetic field was applied by permanent magnets which were set underneath the containers. The test liquid was a magnetic fluid with fine magnetite particles in a water carrier. It was found that the harmonic wave motion, swirling waves and flow pattern of surface waves were influenced by the magnetic fields. The resonant frequency of the liquid-container system moved toward the high-frequency region with increase of the magnetic field intensity. This behavior was also studied by the linear theory. Theoretical results were qualitatively in good agreement with experimental results.

17 citations


Journal ArticleDOI
TL;DR: An experimental and numerical study was made of converging cylindrical shock waves in this paper, where double exposure holographic interferometry was used to visualize the convergence of the shock wave.
Abstract: An experimental and numerical study was made of converging cylindrical shock waves. The goal of the present study was to clarify the movement and instability of the converging cylindrical shock waves. Experiments were conducted in an annular shock tube of 230 mm o.d. and 210 mm i.d. connected to a cylindrical test section of 210 mm diameter. Double exposure holographic interferometry was used to visualize the converging cylindrical shock waves. Incident shock Mach numbers ranged between 1.1 and 2.0 in air. A numerical simulation was conducted using the TVD finite difference scheme. It was found in the experiments that although the initial shock wave configuration looked cylindrical, it was gradually deformed with propagation towards the center and finally showed mode-four instability. This is attributable to the existence of initial disturbances which were introduced by the struts which supported the inner tube of the annular shock tube. This trend was significant for stronger shock waves indicating that at the last stage of shock wave convergence the initial perturbations of the converging cylindrical shock wave were amplified to form the triple point of Mach reflection. The numerical results correctly predicted the experimental trend.

16 citations


Journal ArticleDOI
TL;DR: In this paper, a method of discretizing a threedimensional closed space into the Voronoi-polyhedron elements was applied to the numerical analysis of heat-conduction problems in heterogeneous solid mixtures.
Abstract: A method of discretizing a three-dimensional closed space into the Voronoi-polyhedron elements was applied to the numerical analysis of heat-conduction problems in heterogeneous solid mixtures. The computation was done for various mixtures of two randomly distributed components. Thermal conductivity of the two-component mixture is more strongly affected by the arrangement of components with respect to the mean heat flow direction than by the shape of components. The statistical mean of thermal conductivity can be roughly approximated by the geometrical average. Empirical formulae were obtained from the results. In order to accurately predict the thermal conductivity of a mixture of three or more components, the numerical calculating method divised in this study can be employed successfully.

15 citations


Journal ArticleDOI
TL;DR: In this article, the performance of the spiral grooves on a rotor of a turbomolecular pump is analyzed by obtaining the solution of the Boltzmann equation by use of the Monte Carlo direct simulation method.
Abstract: The performance of the spiral grooves on a rotor of a turbomolecular pump is analyzed by obtaining the solution of the Boltzmann equation by use of the Monte Carlo direct simulation method. The flow in the grooves is three-dimensional in the transition regime. Also, the mass flux is measured under nearly the same conditions as those used in the theory. The computed mass flux is 23-27% smaller than that of the measured data. The difference may be ascribable to the assumption such as was used in the theory that the gap between the rotor and casing is constant.

14 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used LES to simulate turbulent flows in a duct of square cross section using 160, 000 computational grid points and obtained the Reynolds numbers of 6, 200 and 67, 400.
Abstract: Fully developed turbulent flows in a duct of square cross section are numerically simulated by the LES technique using 160, 000 computational grid points. Reynolds numbers based on the bulk velocity and the duct width are 6, 200 and 67, 400. The representative secondary motion near the corner is reasonably reproduced. The near wall behavior of the Reynolds stress and the corresponding pressure field obtained by LES have elucidated the mechanism of the turbulence-driven secondary flow. The essential factor is the rapid attenuation of the turbulence stress due to the wall effect. The pressure distribution, on the other side, has the gradient along the wall. The imbalance between them causes the secondary motion.

Journal ArticleDOI
TL;DR: In this article, a search was attempted for the noise source of a multiblade fan by measuring the acoustic intensity using a sound transmittable scroll, and by investigating the state of flow in detail by measuring three-dimensional flow and turbulence at the outlet of an impeller with the aid of a small-sized hot wire probe.
Abstract: A search was attempted for the noise source of a multiblade fan by measuring the acoustic intensity using a sound transmittable scroll, and by investigating the state of flow in detail by measuring three-dimensional flow and turbulence at the outlet of an impeller with the aid of a small-sized hot wire probe. As a result, it was clarified that the principal noise sources of a standard multi blade fan are roughly divided into the main flow zone at around 30% from the hub surface of the impeller, and the separation zone near the shroud surface. The former is the noise generated by the turbulence near the blade suction surface in the main flow zone where the blade passage velocity is large. The latter is the noise generated by the turbulence near the blade in the separation zone of the inlet flow.

Journal ArticleDOI
TL;DR: In this paper, the standard k-e two-equation model fails to predict turbulent swirling flow in a pipe rotating around its axis and is modified with the aid of the Reynolds stress model and is applied to the swirling flow.
Abstract: The standard k-e two-equation model fails to predict turbulent swirling flow in a pipe rotating around its axis. In this study, the k-e model is modified with the aid of the Reynolds stress model and is applied to the swirling flow. The laminarization phenomenon and the circumferential velocity profile in the swirling flow are predicted by the model proposed. The Richardson number is introduced to the e-equation to take the curvature effect into account; however, this common method appears to fail in this type of swirling flow.


Journal ArticleDOI
TL;DR: In this paper, the structure of the mixing layer in an axisymmetric round free jet was investigated on the basis of the two-dimensional instantaneous photographs of turbulent eddies, which were taken using a laser-light sheet method with a YAG pulse laser and a 35-mm still camera.
Abstract: The structure of the mixing layer in an axisymmetric round free jet was investigated on the basis of the two-dimensional instantaneous photographs of turbulent eddies, which were taken using a laser-light sheet method with a YAG pulse laser and a 35-mm still camera. Eddies were successfully visualized by titanium dioxide particles seeded in the flow for nitrogen, helium and carbon-dioxide jets having different kinematic viscosities. The observation of the coherent structure of air entrainment eddies shows that the turbulent eddies have unexpectedly coarse spatial distribution and their scale in the horizontal plane is almost identical with that in the vertical one. This suggests that three-dimensional structure is established at the upstream position. It is also shown that in the helium jet having a larger kinematic viscosity and a lower density, eddies of a larger scale are formed and retard mixing with the surrounding air. In addition, we present a detailed discussion of the structure of mixing eddies, based on the formation of the elliptic and hyperbolic points in the shear flow.

Journal ArticleDOI
TL;DR: In this article, a turbulent flow fully developed in a straight parallel-plate channel into a two-dimensional curved channel with a radius ratio of 0.92 was introduced and measurements were made in the entrance section on the time-mean velocity, nonzero components of kinematic turbulent stress and other one-point multiple velocity correlations.
Abstract: Introducing a turbulent flow fully developed in a straight parallel-plate channel into a two-dimensional curved channel with a radius ratio of 0.92, measurements were made in the entrance section on the time-mean velocity, nonzero components of kinematic turbulent stress and other one-point multiple velocity correlations. No significant steady Taylor-Gortler vortices are found and the flow field is completely two-dimensional throughout the entire region of the entrance section. When arranged with wall variables, the time-mean velocity and turbulent stress distributions in the vicinity close to the walls are slightly affected by the wall curvature, while the skewness and flatness of the velocity fluctuation are strongly affected by it. Triple velocity correlations follow a complicated progress to arrive at fully developed states. The results obtained can be used as a data base to verify various types of turbulence models.

Journal ArticleDOI
TL;DR: In this paper, the dynamics of two nonspherical bubbles in a viscous liquid are dealt with, and the governing equations of bubble boundaries are derived by taking account of the translational motion and the deformation of bubbles, and are exact to the first order in perturbation of spherical symmetry for viscous terms.
Abstract: This paper deals with the dynamics of two nonspherical bubbles in a viscous liquid. The governing equations of bubble boundaries are derived by taking account of the translational motion and the deformation of bubbles, and are exact to the first order in perturbation of spherical symmetry for viscous terms. Computations are carried out for both collapsing and growing processes of vapour bubbles. It is shown that the stronger the interaction of bubbles becomes, the more remarkably the effects of viscosity reveal themselves in the early stage of the collapse. Instability on the bubble boundary at the opposite side of another bubble is relieved. It is also shown that the boundary layer around the bubble affects the higher-order distortions from the spherical shape. However, the boundary layer's effects on the translational motion are negligible.

Journal ArticleDOI
TL;DR: In this article, the applicability of the VOF (volume of fluid) method to the analyses of a single rising bubble was examined in order to examine the feasibility of direct simulation of bubbly flows.
Abstract: In order to examine the feasibility of direct simulation of bubbly flows, the applicability of the VOF (volume of fluid) method to the analyses of a single rising bubble was examined in this study. Calculated bubble shapes and terminal velocities under wide ranges of Eotvos number and Morton number were compared with the experimental data summarized by Grace et al. Except for the cases when bubble shapes are spherical-cap and skirted, the VOF method could predict them well by assigning only eight cells to the bubble diameter. Hence, it was confirmed that some modification of this method will enable us to simulate bubbly flows directly under a wide-range of flow conditions. Moreover, the relation between a bubble shape and velocity distribution was examined within the ranges in which the VOF method is valid. It was found that the secondary vortex appearing in wobbling bubbles induces the velocity component normal to the bubble interface, and this velocity is one of the causes of the wobbling shape of the bubble.

Journal ArticleDOI
TL;DR: This paper describes the simulation model for the VM cycle machines, which is based on a technique for the 3rd-order method, and the calculated results are inspected in comparison with the experimental ones.
Abstract: In order to predict and evaluate the performance of the Vuilleumier (VM) cycle machines in research and development, numerical analysis using the computer is significant. It must include a technique for the 3rd-order method, particularly in the case of the detailed analysis of performance and the design optimization. This paper describes our simulation model for the VM cycle machines, which is based on such a method. The working space is divided into thirty-eight control volumes for our prototype VM heat pump, and the fundamental equations are derived rigorously by applying the equations for the conservation of mass, momentum, and energy to each control volume using a staggered mesh. These equations are solved simultaneously by the Adams-Moulton method. Then, our prototype VM heat pump is investigated as to the fluctuations of the working gas pressure and temperature, the energy flow, and the performance. The calculated results are inspected in comparison with the experimental ones.


Journal ArticleDOI
TL;DR: In this article, the effect of applied magnetic field on the characteristics of a vibrating spring-mass system in the magnetic fluid was investigated and it was shown that the application of magnetic field is effective reducing the resonance characteristics of the system.
Abstract: Basic studies of a magnetic fluid viscous damper are carried out theoretically and experimentally to clarify the effect of an applied magnetic field on the characteristics of a vibrating spring-mass system in the magnetic fluid. Experimental study shows that the application of magnetic field is effective reducing the resonance characteristics of the system. Theoretical analysis which is conducted by taking into account the aggregate of magnetic particles shows reasonable agreement with the experimental data.

Journal ArticleDOI
TL;DR: In this article, three different sizes of glass, iron and copper beads were used as the porous media in order to examine the characteristics of transient freezing heat transfer in water-saturated porous media.
Abstract: Analytical and experimental investigations have been performed to examine the characteristics of transient freezing heat transfer in water-saturated porous media. The equation of momentum included Forchheimer's extension as the resistance to flow in the porous media. Three different sizes of glass, iron and copper beads were used as the porous media in this study. The temperature of the cold wall was -10°C. Comparisons of the analytical results with the experimental ones are made, and the effects of superheat and the bead diameter and the physical properties of a porous medium have been discussed for transient freezing heat transfer.

Journal ArticleDOI
TL;DR: In this paper, the authors developed an ultra high-speed servo valve with the spool displacement of 30 micrometers and the bandwidth over 5 kHz, which is used to drive actuators.
Abstract: In a high-speed electrohydraulic servo control system, servo valves are mainly used to drive actuators, and the limit of the response of the system is dependent on the servo valves. The aim of this study is to develop an ultra high-speed servo valve with the spool displacement of 30 micrometers and the bandwidth over 5kHz. Piezoelectric devices have the potential to drive valves in quick response. However, as is well known, the devices have the disadvantage of hysteresis between applied voltage and output force. In this study, commercially available multilayered piezodevices, are used to drive the spool of the valve directly. The hysteresis is removed by introducing an inverse hysteresis element implemented on microcomputers and operated in real time. In this case, we developed an element to operate at the sampling frequency of 50kHz. In addition, we develop a method to drive piezoelectric ceramic devices at high speed, and improve damping characteristics of the spool valve. As a result, a servo valve with the bandwidth over 5kHz is successfully developed.

Journal ArticleDOI
TL;DR: In this article, the effects of the burner dimension, i.e., the outlet diameter of two opposed contraction nozzles and the distance between them, on the velocity profiles and extinction limits of the twin flames were examined.
Abstract: The flow fields of a counterflow nozzle burner and counterflow twin flames for propane-air mixture stabilized with that burner were measured using LDV. The effects of the burner dimension, i.e., the outlet diameter of two opposed contraction nozzles and the distance between them, on the velocity profiles and extinction limits of the twin flames were examined. Results show that the effects of burner dimension on the extinction limit do not appear when the velocity gradient upstream of the front edge of preheating zone is used as a flow parameter and that the ratio of nozzle distance to nozzle outlet diameter is the main factor determining the dimensional effects on the flow characteristics. It is also shown that the flame stretch rate of the twin flames defined at the stagnation plane is about two times as large as that defined at the cold boundary of the flame.

Journal ArticleDOI
TL;DR: In this article, the influence of coal gas fuel properties such as CH4 on NOx formation from NH3 was investigated using experimental study by a laboratory-scale combustor and study of the reaction kinetics.
Abstract: The main combustible gas components of the coal-derived gas fuel are CO and H2. Moreover, a small amount of NH3 and CH4 will be contained. NH3 contained in coal gas fuel will be converted to NOx in the gas turbine combustion process. This paper describes the study of the influence of the coal gas fuel properties such as CH4 on NOx formation from NH3, using experimental study by a laboratory-scale combustor and study of the reaction kinetics. As a result, a small amount of CH4 in coal gas fuel was found to strongly influence NOx formation from NH3 in coal gas fuel.


Journal ArticleDOI
TL;DR: In this article, the effect of radiation heat transfer on the transient combustion of a single fuel droplet with a finite rate of chemical reaction and variable physical properties has been clarified under the assumptions of spherical symmetry.
Abstract: The effect of radiation heat transfer on the transient combustion of a single fuel droplet with a finite rate of chemical reaction and variable physical properties has been clarified under the assumptions of spherical symmetry. Evaporation curves, transient variation of flame location, temperature profiles, and the ratio of flame to droplet radius were compared to the previous results without radiation effect. It was shown that the radiation has at least a 25-percent effect to lower the maximum flame temperature. Further, the present results were compared to the experimental results obtained by several researchers.



Journal ArticleDOI
TL;DR: In this article, the authors used a spectral method with 643 Fourier modes to simulate three-dimensional homogeneous isotropic turbulence with temperature diffusion, and they simulated two cases with Prandlt numbers of 0.71 and 0.20.
Abstract: Direct numerical simulations of three-dimensional homogeneous isotropic turbulence with temperature diffusion were performed by using a spectral method with 643 Fourier modes. Temperature fluctuation was not so large, so we assumed that temperature is a passive scalar. We simulated two cases with Prandlt numbers of 0.71 and 0.20. During the decaying period, the turbulent kinetic energy dissipation rate decayed exponentially with time and the microscale Reynolds number changed from 30 to 17. Spectral distribution of the passive scalar fluctuation spread more widely than that of velocity fluctuation in the case of a Prandtl number of 0.71. In the case of a Prandtl number of 0.20, spectral distribution did not spread as widely, but two-point autocorrelation of the temperature fluctuation showed a negative value at large distance, which shows predominancy of the low wave number components.