Vortex methods have been used for many fluid engineering problems to simulate flow fields, in particular high Reynolds number flow fields. These methods have some advantages ; (1)are free of grid generation, (2)use a simple algorithm, (3)are inherently free of numerical viscosity, and (4)exhibit self-adaptation for strong shear flow. In three-dimensional flows, a few numerical schemes have been used in actual calculations, but their theoretical foundation is not sufficient in a sense that numerical schemes are not explicitly derived from the Navier-Stokes equations. The present paper aims to give the theoretical foundation of the vortex methods used for three-dimensional flows. In this paper, a basic integral equation concerning the vorticity is derived from the three-dimensional Navier-Stokes equations and typical algorithms of vortex methods, the vorton method, vortex element method and vortex stick method, are then derived from this integral equation. Furthermore, the vorticity field given by the integral equation is shown to be solenoidal, provided the initial one is solenoidal. Finally, the velocity field is analytically obtained for Gaussian distribution of vorticity, which is the typical vorticity distribution in vortex methods, and a new type of Gaussian vorton, which is solenoidal, is proposed and the velocity field induced by this vorton is obtained.

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In this report an experimental and computiational study of the flow behind a two-dimensional square roughness element placed in a laminar boundary layer on a flat plate is described Numerical solutioins of the two-dimensional N-S equations were obtained by the MAC(Marker-and-Cell)method. The experiment was carried out in a low-turbulence wind tunnel. The flow behind the roughness element consisted of a separated region and an external layer. There was no mass transfer between these regions. The computational and the experimental results for these regions were compared. The extent of the separated region depends on κ / δ^*_κ, where κ is the height of the roughness element and δ^*_κ is the displacement thickness at the roughness element. When κ / δ^*_κ is less than a critical value, the computational results agree with the experimental results. The boundary-layer flow separates at the roughness element and returns at 70-κ to the laminar boundary layer. In this case the length of the separated region increases with κ / δ^*_κ. When κ / δ^*_κ is larger than the critical value, the length of the separated region decreases with increasing κ / δ^*_κ, but the computational results do not agree with the experimental ones.

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The flow field of a suipersonic flow chemical oxygen-iodine laser is simulated by solving three-dimensional Navier-Stokes equations and the effects of the mixing / reacting zone structure on the resulting gain region are studied. It is assumed that the flow is laminar and the water vapor condensation due to the supersonic cooling is ignored. A chemical kinetic model encompassing 21 chemical reactions and 10 chemical species is used to determine the chemical composition of the gas mixture. The present results demonstrate that a pair of contrarotating vortices generated behind the I₂ jet greatly enhances the mixing and the simultaneous chemical reaction to produce the excited iodine atom with the singlet oxygen. In the present calculation, the small signal gain coefficient is overestimated to some extent as compared with the experimental one. It is thought that the overestimation is caused by the imperfect chemical kinetic model as well as by ignoring the water vapor condensation and the boundary layers on the upper and lower wall in the present calculation.

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In this study, the characteristics of pressure wave propagation in a vacuum tube have been investigated experimentally from the viewpoint of vacuum protection in the beamlines of a synchrotron radiation facility. Baffle plates having a single orifice of 5, 10 or 15 mm in diameter were installed in shock tubes 5 m in length and 36.6 or 68.8 mm in diameter, in order to slow the pressure wave or shock wave propagation, as a model for the beamline. To evaluate the decay of pressure waves, pressure changes, with time at several locations along the side wall as well as at the end wall of the tube were measured. The results showed that the effect of the orifices on pressure wave propagation and its decay was significant. The present investigation may contribute to the design and construction of high-energy synchrotron radiation facilities with long beamlines.

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When an unsteady compression wave propagating in a tube arrives at its exit, an impulsive wave is emitted toward the surrounding, which causes an impulsive noise. The objective of this work is to investigate the appropriate silencer configuration for reducing this impulsive noise. Five kinds of silencers were installed at a shock tube exit, and their effects on the impulsive noise were investigated numerically and experimentally. Two-dimensional unsteady conservation equations were solved by means of a PLM. Experiments were carried out using a shock tube with an open end. As a result, the effect of silencer configuration on noise reduction was clarified, and it was found that a suitable choice of the silencer could reduce the strength of the impulsive wave by about 25%.

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The governing equations of a cluster of bubbles are derived by taking account of the thermal effects of the internal gas and the three-dimensional translational motion and deformation of each bubble. The equations are applied to the nonlinear oscillations of multiple interacting bubbles. The frequency response curves are obtained for two typical arrangements of bubbles with the same radii. The present results are compared with the results of polytropic analysis in which the thermal effects are evaluated using the effective polytropic index and the effective viscosity. It is shown that the heat transfer inside the bubble is important in investigating the nonlinear bubble oscillations. The polytropic relation for the internal gas does not hold when the nonlinearity of the radial oscillation becomes strong. Both radial and surface oscillations are affected by the translational motion of each bubble. It is also shown that the subharmonic oscillation of interacting bubbles occurs more easily than that of an isolated bubble due to the bubble-bubble interaction.

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In this paper, we discuss the dynamics of a cluster of bubbles in a potential flow. The governing equations for a bubble cluster are derived by using a series expansion of spherical harmonics. The three-dimensional translational motion and deformation of each bubble, which are induced by bubble-bubble interactions and the pressure gradient due to a set of simple sources, are taken into consideration. The accuracy of the present theory is confirmed by comparison of the results with those obtained using the boundary element method. The theory is applied to the dynamics of bubbles traveling around two kinds of axisymmetric body. It is shown that the bubble deformation is greatly affected by the pressure gradient around a body. It is also shown that the degree of bubble growth is reduced by bubble-bubble / bubble-wall interactions. The growth rate of interacting bubbles depends on both the initial radius and the initial location of the bubbles. When a particular bubble grows much faster than the other bubbles, the growth rate of the other bubbles is much lower than that predicted using single-bubble theory.

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The effect of ambient pressure on the dynamics of bubble formation in liquid heated rapidly to the limit of superheat is investigated by heating a fine film heater immersed in ethyl alcohol at a high rate of temperature rise up to 20×10⁶K / s. The heater surface temperature at boiling incipience increases with the increase of the rate of temperature rise and saturates at the rate higher than about 5×10⁶K / s. The saturated temperature agrees well with that of homogeneous nucleation in an ambient pressure range from 0.1 to 2.0 MPa. The nucleated bubbles become smaller to coalesce with the increase of ambient pressure and the measured number density of them reaches 7.0×10¹⁰l / m² for the maximum. The increase of the number density versus the surface temperature agrees qualitatively with that predicted by the fluctuation nucleation theory. As the result, the bubble formation observed at a higher rate of temperature rise is concluded to be due to fluctuation nucleation.

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Regeneration of quasi-streamwise vortices is investigated using a data base obtained by high-resolution LES(Large Eddy Simulation)for channel flow. It has been revealed that quasi-streamwise vortices are regenerated both at the upstream of the upstream end of a parent vortex and at the downstream end of a parent vortex. In both cases, the new vortex has a vorticity of opposite sign to that of the parent vortex and comprises a chain line of vortices in the flow direction with the parent vortex, which is one of the basic organized structures in the near-wall region. It has also been revealed that the main contribution to the generation of new vortices at their infant stage is the tilting of wall-normal vortices, and that to their sustenance at grown-up stage is stretching effect.

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The motivation for this research was to obtain information on the separation characteristics associated with the phenomenon of stall. This separation data will ultimately be utilized as part of an optimum control system to reduce the negative effects associated with stall. Surface shear stress measurements were carried out using MEMS-based sensors on a two-dimensional wing with a Wortmann FX 63-137 airfoil section(chord Reynolds numbers ranged from 1×10⁵ to 6×10⁵). Computational airfoil performance from an airfoil analysis code was compared with the results of measurements. The wall shear stress distribution was measured by five micro hot-film sensors, which were flush mounted on the 2-D wing over the frontal 50% of the chord at various spanwise locations. Hysteresis characteristics were determined from time-averaged and rms shear stress values as well as from airfoil performance curves.

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Buoyancy-induced secondary flows in a heated pipe rotating about a parallel axis are similar to those in a stationary horizontal heated pipe. The effect of buoyancy on fully developed laminar flows and heat transfer in rotating pipes and in horizontal pipes is studied by similarity analysis and computations. The similarity analysis reveals that the flows are characterized by a new fundamental parameter, K_LB, and the Prandtl number, Pr;K_LBplays a role of Peclet number in the cross-section and Pr determines the sensitivity of the axial primary flow to secondary flow. Heat transfer is basically independent of Pr. Based on the dimensionless governing equations, limiting behaviours of velocity and temperature fields are discussed. Similarity conclusions are supported by computational results of contours of velocity and temperature, the friction factor and heat transfer rate. Semi-empirical formulae for the friction factor and the Nusselt number are presented.

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This paper describes in detail experimental results on flow resistance and heat transfer of regenerator wire meshes of a Stirling engine in oscillatory flow. The results show that for Re>300, the friction factor of wire mesh became lower than that in previous studies. It has been clarified that the friction factor in a decelerating period becomes higher than that in an accelerating period under the condition that both Valensi number and maximum Reynolds number exceed certain values. A new experimental method for estimating Nusselt number of wire mesh in oscillatory flow is proposed. This method employs a cylindrical probe having two thermocouples attached on opposite sides of the cylinder facing the direction of oscillatory flow. It has been clarified that Nusselt number of wire mesh becomes a function of Reynolds number and open area ratio. Also, experiments on spring mesh were carried out.

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Mixed convection from a horizontal cylinder imbedded in saturated electrically conducting fluid is investigated using nonsimilarity boundary layer transformation. Variable wall temperature is assumed at the cylinder surface as the thermal boundary condition. The problem is solved numerically using the finite difference technique and double-checked using a local nonsimilarity solution. The effects of the magnetic field on the velocity and temperature profiles, wall shear stress, and Nusselt number are presented. The non-Darican flow model is adopted. The effects of the inertial and boundary parameters on the solution in the presence of a magnetic field are also presented. The problem is solved covering the entire regime of mixed convection.

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The dynamic behavior of a directly combined binary turbine system is investigated experimentally and theoretically in this work. In the theoretical investigation, the dynamic behavior of the system is discussed from the viewpoint of the network theory. In this case, the components of the system are represented as two-or three-port elements of the network and the vapor flow rate and shaft torque are appropriated for the through variable, and the vapor pressure and rotational speed for the across variable. As a result, a very simple network model is derived. The validity of the model is proven by comparison with the experimental results, which are the frequency responses examined with respect to the generator load changes. In addition, it is shown that the present model is very effective in predicting the dynamic behavior and the mechanism of power generation in the directly combined binary turbine systems.

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The interaction between reaction and turbulent mixing strongly affects the structures of a turbulent diffusion flame, the characteristics of which are greatly affected by the combination of working conditions such as burner exit configurations, burner size, fuel and oxidant. This study discusses in detail the turbulent diffusion flame structure and its similarity using a laboratory-scale turbulent diffusion flame measured by laser Rayleigh scattering. It also discusses the factors affecting the similarity in flame structure and the turbulent diffusion flame length determined using its turbulent power spectral density. The -5 / 3 power law holds in the fuel jet and combustion regions but in the air entrainment regions, the -5 / 3 and -1 power laws coexist, and which shows that both turbulent and molecular thermal diffusions become important. The constancy of the turbulent diffusion flame length at a high Reynolds number is discussed with respects to the characteristics of flame structure.

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To study cycle-to-cycle variations in diesel spray direction, images of the spray shape, needle valve motion and sac inner flow of multi-hole-type nozzles were recorded using a high-speed drum camera and two CCD cameras. It was observed that needle valve offset and one-sided sac inner flow during fuel injection induced fluctuation in spray direction and deformation of spray shape.Experiments on the effect of cycle-to-cycle spray variations on emissions under no load conditions and lower engine speeds revealed that when these variations are suppressed, it results in reduced hydrocarbon emission and less white smoke.

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Quartz prechamber models have been installed in a constant volume test rig(CVR)for the investigation of prechamber mixing processes. Planar laser induced fluorescence of acetone has been used for a 2-dimensional visualization of flow structure and quantitative analysis of mixture formation. The prechamber was initially filled with acetone seeded in nitrogen. A jet of lean mixture in an actual lean-burn gas engine was simulated using a flow of pure nitrogen from the CVR. Two different shapes of prechambers were investigated and the dominant influence on the mixing process is presented. Special emphasis was laid on the analysis of mixture homogeneity at ignition timing. The investigations provided an insight into the flow structures inside prechambers. The dominant influence of prechamber shape, especially around its mouth, on flow structures as well as on mixture homogeneity at ignition timing was proved.

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The purpose of our study is to develop a method for estimating the facial skin temperature of an automobile passenger. The facial skin temperature is a good index for evaluating the environment. For the estimation of skin temperature, the rate of change in facial skin temperature was predicted from environmental data using a neural network. Then the facial skin temperature was estimated from the rate of change in facial skin temperature and the initial facial skin temperature calculated from the environmental data. Furthermore, the level of thermal sensation was estimated from the predicted facial skin temperature. By use of a neural network, the rate of change in facial skin temperature could be predicted from the environmental data easily and accurately, and the facial skin temperature could be predicted within ±0.6°C error. This is better than the method in which heat balance equations for the body are used. The thermal sensation could be estimated within ±0.8 error on the scale used.

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