This study has investigated numerically the interaction of cryogenic hydrogen jet with heated hydrogen cross flow under supercritical pressures relevant to a mixer component in liquid rocket engines. The mixer is considered to be a key component for achieving high reliability of LE-X engine, where an expander bleed cycle is adopted. A two-dimensional simulation of hydrogen jet in cross flow under a supercritical pressure is first performed to explore mixing characteristics in a wide range of injection conditions. Effects of injection temperature and therefore momentum flux ratio on the hydrogen jet in cross flow are comprehensively investigated. A high-order numerical method for the Navier-Stokes equations with a real-fluid equation of state is used for resolving highly unsteady flow fields with large density gradients.

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In this study, multiobjective design exploration for a rocket launch site is conducted using evolutionary computation with large eddy simulation to understand the acoustic characteristics associated with various launch sites. The launch site is described by curved surface. The flat plate inclined with 45 degree is considered as the reference configuration. The objective functions of multiobjective aero-acoustic design optimization are, 1) minimization of averaged sound pressure level near the payload fairing, 2) minimization of maximum pressure on the curved surface of the rocket launch site, and 3) minimization of the change of the curved surface from the reference configuration. Three-dimensional compressible Navier-Stokes equations are solved with the modified weighted compact nonlinear scheme. The total number of evaluation is 2500, and the evaluation of one generation necessitates the use of 6500 nodes using "K" supercomputer. As the results of the flow field analysis of some characteristic non-dominated solutions show the characteristics of acoustic wave and the location of the maximum gradient of the curved surface.

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In the present paper in order to investigate the possibility of flow control using elastic body, we conduct a simulation of a finite-length square cylinder placed inside turbulent channel flow. For an elastic cylinder, the rigorous equation of motion for elastic continuum is solved with a finite volume method; the effect of existence of cylinder in the flow computation is taken into account using the immersed boundary method. From time averaged quantities, we demonstrate that the flow pattern around rigid cylinder is in accordance with that of previous reported experimental results and that the elastic cylinder markedly modulates the wake structure. Further to extract coherent structures, the DMD (dynamic mode decomposition) method are applied.

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In order to develop a new mixing procedure, we conduct DNS (direct numerical simulation) of dynamic control for free jet. The inflow velocity of jet is unidirectionally or alternately rotated around streamwise direction. From view of instantaneous vortex structures, it is found that the structures are markedly modulated, compared with the case of the free jet. In addition, in order to estimate the mixing performance, the statistical entropy is calculated. It is found that the mixing efficiency are improved with the alternate rotation than that of the unidirectional rotation case.

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In order to improve the performance of heat transfer with multiple impinging jet(MIJ), we investigate the DNS (direct numerical simulation) of four round impinging jet arranged at an inflow of flow field. From view of instantaneous vertical structures and time-averaged velocity distribution, it reveals that the generation of vortical structures in MIJ are enhanced due to an interaction between each jet and a peculiar upward flow compared to that of a single impinging jet(SIJ). In order to investigate dominant flow structures, DMD(dynamic mode decomposition) method is applied. It reveals that for SIJ large-scale structures which are formed over the impinging wall, are extracted with DMD, while for MIJ both peculiar structures around upward flow and large-scale structures similar to that of SIJ are extracted.

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Fluid flow and heat transfer of natural convection over a horizontal heated two-dimensional plate is investigated by means of DNS. Special attention is focused on development and separation of natural convection boundary layer flow. The Rayleigh and the Prandtl numbers are 108 and 0.71. Stimulating the thermal instability, a spanwise sinusoidal disturbance is added on surface temperature of the plate edge as a boundary condition. A stable pair of counter-rotating longitudinal vortices appears when the spanwise wavelength of the disturbance is in a range of 0.06 ? D ? 0.09. Between the vortices, the flow separates without a definite recirculation bubble downstream. Intensity of circumferential velocity of the vortices takes its maximum just downstream of the separation point and the value is 8% of the natural convection velocity.

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The fluctuating pressure measurement in a wake of a circular cylinder are performed in hydraulic turbulent flow using pressure measurement system which is composed of a miniature static-pressure probe, tubing and a low-range differential pressure transducer. It is demonstrated that the measured fluctuating pressure can successfully corrected based on the calibration of the dynamic response of measuring system.

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In the present study, the distributions of time-averaged and fluctuated wall shear stresses downstream from an orifice were measured using a Flow Vector Sensor of MEMS. The air flow was supplied to a circular pipe from a blow-down wind tunnel. The diameter of the pipe is D = 51 mm. The diameter ratio are β(=d/D;d,diameter of orifice) = 0.41, 0.5 and 0.62. Near the wall in the recirculating region, the minimum mean skin friction coefficient was located at approximately x/h = 5, and the maximum RMS intensity skin friction coefficient was located at approximately x/h = 7.5. The minimum mean skin friction coefficient decreased with increasing in Reynolds number. The maximum RMS intensity skin friction coefficient increased with increasing in the Reynolds number. The similarity of mean and RMS intensity skin friction coefficients with Reynolds number based a height of orifice and a bulk velocity at orifice was found.

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This study has been conducted to investigate the development of large-scale turbulent structures behind a backwardfacing step. The relative step height to boundary layer thickness of an incoming flow are H/δ0 = 0.63, and the momentum thickness Reynolds number is 3000. Mean and fluctuating velocity distributions were measured by the flying hot-wire technique with I-type multiple probe rake and the ordinary technique with X-type multiple probe rake. Proper orthogonal decomposition was employed to analyze the large scale structures in the separated shear layer. POD coefficients of the u- and v-component at the first mode were found to have a negative correlation with each other.

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In recent years, vortex methods have been used for numerical simulations of various flows. Vortex methods can directly simulate the time evolutions of vorticity field through Lagrangian calculation of the behavior of vortex elements discretizing vorticity fields. In order to extend the applicability of vortex methods, we propose a higher-order time integration method known as Hermite integration method in the field of non-colliding many-body systems called the gravitational N-body problem in Astrophysics. The key ideas of this method are based on derivation of the time derivatives of the Biot-Savart law and base on expanding the solution in the Taylor series. The proposed integration method is applied to simulate three and five vortex systems. Simulation results demonstrate that the proposed integration method has substantially forth-order accuracy and is able to capture the motion of an eye of the Hurricane Isabel.

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Preferential concentration of finite-size heavy solid particles in vortical flow is investigated by means of direct numerical simulations using an immersed boundary method. Particle clusters are created by the action of vortex tubes whose diameter is larger than (particle diameter)/1.1.

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A dynamical model of interacting dipoles in two-dimensional incompressible flows is derived. Each dipole is characterized by the centroid position, the dipole moment, and the length scale. Interactions of two dipoles such as a direct scattering, an exchange scattering, and a merging process are studied using the derived model and the numerical simulations.

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A cylinder rotating around horizontal axis was put on a table rotating around vertical axis. The cylinder diameters and aspect ratios were changed, and the shapes of vortex in rotating cylinder were observed when the speeds of rotating table and rotating cylinder were changed. It was found that there were some patterns of vortex shape, which depended on the aspect ratios and Rossby number. The shapes of vortex were also studied with computer simulation of flow pattern, and they almost accorded with the experimental results.

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In this study, we aim to construct a finite difference method, which spatially and temporally conserves the kinetic energy, for the vorticity equation on the two-dimensional flow field. In order to achieve the temporal kinetic energy conservation, a space-time staggered grid is used for the discretization of governing equations and implicit mid-point rule is applied to the time integration. The method is applied to simulate a two-dimensional viscous flow, known as a lid-driven cavity flow, under the non-periodic boundary condition. The stencil to define the vorticity boundary condition (whether boundary condition is defined on time step n+1 or n+1/2) does not affect the simulation results. However, the initial value of vorticity strongly affects the simulation results when the vorticity boundary condition is defined on time step n+1/2 and the initial value of vorticity set to zero over whole computational domain. As the countermeasure, the necessary of the boundary condition imposed to the vorticity at initial time is clarified. In addition, the results of the evaluations for numerical stability of time integration show higher stability of time integration scheme which uses a space-time staggered grid and implicit mid-point rule, demonstrating the stabile calculations at high diffusion numbers.

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Many researches on flow field around the rigid moving airfoils have examined. In particular, the vortex streets behind the rigid moving airfoils have been clarified by experimental and numerical approaches. However, the flow fields and the dynamic forces on the elastic moving airfoils have not been understood sufficiently because of their fluid-structure coupled problem. Especially, the impact of elastic deformation effects on the flow fields and the dynamic forces have not been clarified. In this study, we investigate the velocity gradient in the vicinity of the wall of elastic moving airfoils with bending stiffness and their dynamic fluid forces.

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It is important and interesting to study growing process of vortex structure on the wall surface of a body because the vortex structure affects the wake structure and flow force on the body in a direct fashion. Especially on a heaving body with deforming wall surface such as an elastic airfoil the precise study is needed. In this study, I studied numerical analysis on the momentum thickness of boundary layer on the wall surface of a moving thin film. As a result, in the flow direction, the momentum thickness of a rigid thin film corresponded approximately to an elastic thin film. So, heaving-direction velocity affects the wake structure of an elastic deformation.

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Flying and aquatic animals release a vortex by pitching a wing or a fin. It is well known that vortex motion plays an important role in generation of unsteady fluid force. However, studies on unsteady propulsion system of birds, insects, and fish are few and inconclusive. The purpose of this study investigates the effect of 3-dimensional airfoil shape on three-dimensional vortex structure in the case of the high reduced frequency. In the present study, pitch-oscillating motion was carried out as a basic unsteady motion. The vortex structure and its behaviour for a discoid airfoil and the NACA0015 airfoil are investigated. The vortical flow fields were measured by a stereo PIV technique. Two significant vortices are released during one cycle of pitching oscillating. For the NACA0015, the strong vortex is generated.

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Effect of apex angle 2α and rotated angle γ has been investigated on the behavior of the necklace vortex generated at the bottom front of a pyramid placed in a laminar boundary layer. Reynolds number based on the height of pyramid H is ReH≒610 and relative boundary layer thickness is δ/H=0.71, considering the symmetry, two typical conditions for γ are chosen, namely, γ = 0° and 45°. For the case of γ = 0°, bottom width D of the pyramids are 16.1mm and 60mm for 2α=30° and 90°, respectively. LDV was employed for velocity measurement. Distribution of spanwise vorticity can be understood by considering convection and production terms in vorticity transport equation .

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In order to understand the aspect of the mutual interference flow from two circular cylinders, the visual observation experiment was performed. The cylinder setting conditions were three kinds of distance ratios (L/d=1.5, 2.5 and 5.5), and seven kinds of arrangement angles (α=0, 15, 30, 45, 60, 75 and 90 degrees). The oscillating conditions were four kinds of amplitude ratios (2a/d=0.25, 0.5, 0.75 and 1.0), and the oscillation frequency ratio f/fK in 24 steps. The Reynolds number was about 640. As the result of experiment, even if the distance ratio was the same, the vortex shedding characteristics changed with arrangement angles. The mutual interference will become remarkable if the distance ratio is small. In the arrangement angle, 30 degrees and 45 degrees are carrying out mutual interference most. Even when a forced in-line oscillation was performed under the conditions in which two circular cylinders are carrying out mutual interference, it was found that a lock-in phenomenon occurs. The vortex shedding features were obtained and flow pattern distributions were shown.

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Vortex structure and drag characteristic of a circular cylinder accelerated from a rest were investigated by flow visualization and drag measurement. The circular cylinder submerged in a water tank was moved with a constant acceleration by using a linear-motor actuator system. The vortex structure in the wake of cylinder was visualized by using dye and particles method. The drag was measured by using a load cell. The formation process of the twin vortex was observed during accelerated motion. The twin vortex behind the circular cylinder showed bilaterally symmetric at initial stage, and collapsed afterwards. The secondary vortex formed near the separation point. The vorticity flux of twin vortex was calculated by using the photographs of flow visualization. These results provided the effect of the vortex structure on time evolution of the drag.

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The oscillation behavior of the necklace vortices formed in front of a square flat plate protuberance standing vertical to the laminar boundary layer flow on the ground wall was investigated by using a moving path line method and a time successive PIV method. The necklace vortex system consisting of eight vortices with the extremely small oscillation appears around the square plate with h/δ=2 at Reynolds number Re=1760. The oscillation with a cycle of five seconds is clearly observed for the eight vortices at Re=2040. The center vorticity of main vortex V1 seems to take the maximum value at about Re=1700, and reduces as the Reynolds number increases beyond 1700.

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Mixing of liquid caused by an air bubble with zigzag or spiral motion in a still liquid in a pipe is investigated experimentally using a photochromic dye. A part of the liquid is activated by UV light and subjected to the liquid motion caused by a rising bubble of Re=209. The visualized mixing patterns showed that the dye is mixed by vortex motions in the bubble wake for both motions. The concentration distributions were deduced from the dye images using Lambert-Beer's law and the mass dispersion of liquid was evaluated. The some bubbles with spiral motion caused stronger mixing than the bubbles with zigzag motion.

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The cyclic vortex rings, which are generated cyclically by a pulsating jet, appear to be an effective method for particles and fluids transport. The effect of the formation conditions of cyclic vortex rings, such as the jet pulsation conditions, conditions of an intermittent period and conditions of a nozzle length, on the behavior of vortex rings from the formation to diffusion is investigated experimentally. The results indicate that the behavior of cyclic vortex rings in the formation process are classified into three patterns, the stable type, the transition type and the unstable type, depending on the jet pulsation conditions and conditions of an intermittent period. In order to generate the stable type cyclic vortex rings which are axisymmetric vortex cores and can move to long distance, it is necessary to set an intermittent period in the pulsating waveform of a jet. The formation behavior of cyclic vortex rings without setting an intermittent period changes from the transition type to the unstable type as the Strouhal number of a pulsating jet is small. It is, then, confirmed that these types of cyclic vortex rings diffuse in an early phase. In the case of the stable type cyclic vortex rings, the volume of vortex rings becomes large as the length of a nozzle is extended.

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Vortex structures in a circular synthetic jet were investigated numerically by using Large Eddy Simulation. The instantaneous velocity vector and vorticity were calculated for two non-dimensional strokes of L/d = 1.18 and 4.72. The simulation results indicate that a vortex ring is formed in a cycle and travels to downstream. The vortex rings travel to downstream and collapse in further downstream. In case of a long stroke L/d = 4.72, it was observed the vortex ring accompanies a small trailing vortex ring. The characteristics of these vortex rings were examined by the iso-surfaces of the vorticity magnitude and the circulation of the vortex rings.

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Magnetic functional fluids are produced by adding needle-like magnetic particles whose long axis is about 100 nm and short axis is 25 nm to magnetic compound fluids which are mixture of magnetic fluid and magnetorheological fluid. Damping property can be controlled by changing mixture ratio of both spherical magnetic particles and needle-like magnetic particles. Basic damping property is investigated experimentally by using a prototype damper. When the total volume fraction of magnetic particles is constant, the damping force of the damper is stronger with increase of the volume fraction of needle-like magnetic particles.

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In this paper, frequency response analysis of a tuned liquid column damper using magnetic fluid (MF-TLCD) based on a linearized method was presented. An MF-TLCD alters the natural frequency of the magnetic fluid column that forms the resident liquid inside the MF-TLCD by applying a magnetic field. The interaction equations of motion under a harmonic type of loading for SDOF damped structure and liquid surface motion in a MFTLCD were expressed. The damping term induced by liquid flows and the magnetic force term were linearized to derive analytical solutions. The analytical results were compared with experimental results.

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Influence of magnetic field direction on the forced convective heat transfer in a rectangular duct flow of a magnetic fluid was investigated experimentally. Experiments were performed in both laminar flow and turbulent flow. Magnetic fluid flow was heated by one-side heater plate with a uniform heat flux, and uniform and non-uniform magnetic field were applied. As a results of experiments in laminar flow, in the case of applying uniform magnetic field, heat transfer enhancement by applying magnetic field perpendicular to the heat transfer direction is larger than that by applying magnetic field parallel to heat transfer direction. However, in the case of applying non-uniform magnetic field, the opposite tendency was obtained. 0n the contrary, in the case of turbulent flow, magnetic field direction hardly influence on the heat transfer. Magnetic field has a role of suppression of turbulent diffusion.

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In the present work, heat transfer characteristics in cubic cavity are investigated experimentally in thermoma gnetic natural convection of temperature sensitive magnetic fluid(TSMF) with Copper particles(non-magnetic particles) under magnetic field. Also we studied on cooling capacity of TSMF with non-magnetic particles in cubic cavity under magnetic field. The experimental results show that the heat transfer characteristic is enhanced when the magnetic field is applied to the TSMF and Copper particles are immersed in the TSMF.

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Magnetic fluid is a liquid which becomes strongly magnetized in a magnetic field. It has been used for some heat transfer devises. There are many boiling bubbles on the heated surface in the devises, but few studies of behavior of boiling bubbles in magnetic fluid have been reported. In this study, electromagnetic induction method is applied to measuring the volume of bubble detachment. Electromagnetic induction method is a measuring method for multiphase flow using Faraday's law of induction. Experiment for measuring bubble detachment in the vertical pipe was performed. Applying a non-uniform magnetic field, the volume of bubble detachment in magnetic fluid was reduced. Consequently, the measuring method has demonstrated a promising capability of measuring bubble detachment behavior in magnetic fluid under a magnetic field.

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Magnetorheological (MR) fluids are one of smart fluids which can be changed their rheological properties in reversible manner by applying magnetic field. While a shear thickening (ST) fluid is speed-activated non-Newtonian fluid; it possesses a low viscosity until the transition of the critical shear rate where it increases dramatically. Their combination can offer both MR and ST effects. This study focuses on a shear thickening MR fluid (ST-MRF) of which the shear thickening properties would be controlled by applied magnetic field. We fabricated a shear thickening fluid (STF) consisting of nano-sized fumed silica particles suspended in a solvent, ethylene glycol, at 25wt% concentration. And then, the micro-sized carbonyl iron particles with different weight fractions were added to the STF to fabricate the ST-MR fluids. The rheological properties in constant rpm tests and oscillatory tests under different magnetic fields have been measured using a HAAKE RS150 parallel disk rheometer with magnetic circuit. The ST-MR fluids exhibit an abrupt increase of shear stress beyond a critical shear rate and a magnetic field controllability of the shear thickening property.

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Electro-adhesive gel (EAG) is a functional material which changes its surface adhesive property according to applied electrical field. This unique property is called "Electro-adhesive effect". In this paper, EAG is applied to a semi-active seismic damper to suppress earthquake-excited vibrations of buildings. The EAG damper has a simple structure and provides superior performance compared with a conventional damper such as an oil damper or a MR damper. Furthermore the EAG damper can serve both as friction damper and viscous damper by controlling applied electric field. In this paper, a small EAG damper is produced experimentally, and the effectiveness of the EAG damper installed in base isolated buildings is verified from the simulation.

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A multi-phase AC arc plasma has been applied in the glass melting technology as a promising heat source. In this work, the high-speed video camera system with appropriate band-pass filter was applied to investigate arc phenomena based on electrode temperature measurements synchronized with vapor observation during the arc. The results show that lower argon gas flow rate leads to larger electrode evaporation, resulting in the constriction of the arc. Correlation between arc phenomena and electrode phenomena in multi-phase AC arc was then investigated.

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The technology of non-thermal plasma contacting with liquid has been paid attention for water treatment because of free radical generation. The advanced oxidation processes (AOPs) utilizing free radicals have been developed to decompose persistent organic pollutants (POPs). In this study, the water treatment method spraying solution into the coaxial cylinder type dielectric barrier discharge (DBD) tube is investigated. The reactor is an alumina tube with 2 mm thickness and 6 mm inner diameter. The reactor has inner powered rod electrode on the central axis of tube and outer grounded electrode on the outer wall of tube. The solution is atomized by the ultrasonic atomizer unit and introduced into the reactor. Acetic acid solution is used as POPs in this experiment. Acetic acid is decomposed in high efficiency and formic acid and oxalic acid are formed as by-products for one pass treatment.

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Innovative energy conversion device has been developed for efficient wind energy utilization. This device has co-axial configuration and the rotational speed of the turbine can be kept constant by controlling rotational torque by Lorentz force with electrical power generation. For larger load resistance, rotational torque increases due to increase in azimuthal component of electric current and friction force by Lorenz force acting radially inner direction. On the other hand, rotational torque decreases for smaller load resistance. Therefore, even when torque increases with increasing wind velocity, the turbine can be operated at a constant rotational speed by controlling load resistance with conversion of wind energy into electric power.

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In order to reduce the amount of chemical solvent used in the washing process, the non-chemical washing technology with micro-bubble is required. In the present study, we focus on the micro-bubble generator with a venturi tube. To clarify washing effect by the micro-bubble generator, washing experiment with cutting oil, grease and oil paint are conducted. As a result, the generations of micro-bubbles from bubble collapses were observed in the venturi tube through a high speed video camera. Additionally, the relation between the oil detachment rate and the flow structure and pressure on the washing surface proposed that the pressure wave and micro-bubble caused by the bubble breakup were the advantage of this washing technology.

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In hypersonic flow, the shock interactions cause high surface heat flux. Furthermore, the unsteady vortices are generated over a compression corner. Present study investigates the relation between the distribution of the surface heat flux and the unsteady vortices. The flow field over the compression corner with 30 deg. is calculated by the three-dimensional numerical simulations. The heat flux distributions on the model surface show some unsteady longitudinal streaks, because the longitudinal vortices merge and separate cyclically.

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Development of boundary layer trip for capsule shaped reentry vehicles under high-enthalpy hypersonic condition was developed in the free-piston shock tunnel HIEST. Wind tunnel test campaign with an 6% scaled Apollo CM model was conducted with stagnation pressure of 30MPa to 60Mpa and with stagnation enthalpy from 3.5MJ/kg to 22MJ/kg. Reynolds number based on model diameter was varied from 0.2 to 1.3 million. To measure heat flux around the model, eighty-four miniature co-axial thermocouples were instrumented on the heat shield surface of the model. Angle-of-attack of the model was fixed to 28degree. A pizza-box configuration boundary layer trip was mounted on the heat shield surface of the model, which trip height k were 0.3mm, 0.6mm and 0.8mm. With k=0.6mm height trip, boundary layer became fully turbulent less than H0=10MJ/kg. However, boundary layer was still laminar over H0=15MJ/kg even with k=0.8mm trip.

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The supersonic free-vortex aerodynamic laser window is one of key technologies for extracting a laser beam from the laser cavity. This paper describes an experimental study on gasdynamic performance of aerodynamic window. Schlieren flow visualization captured oblique shock on the nozzle exit edge and shear layer on the free-vortex, between the atmosphere and the cavity. Inner diameter side flow velocity is faster than outer side has been clarified by PIV measurement.

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In order to understand the interaction phenomena between plasma and shock wave, not only shock tube experiment but also three-dimensional numerical simulation were conducted. From the Schrielen visualization result, the shock wave deformation as like bow like structure was observed ahead of the normal shock wave. From the numerical simulation, it was suggested that the shock wave deformation has the three dimensional structure.

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The detonation is a combustion wave that propagates at the supersonic speed in a stationary reactive mixture in the form that consists of a precursor shock wave and a reaction region induced by the shock. In this study, behavior of the detonation that propagates in a channel with a right corner is calculated by two-dimensional analysis and three-dimensional analysis. The results of this study are as follows: Results due to a change of coordinate system occur no large difference. Theory of Skews gives a similar results in the detonation. When the detonation propagates into a channel with a right corner, the detonation configurations collapse by the Prandtl-Meyer expansion. But its configuration re-generates by interference with the reflected wave and collisions with the wall. When two-dimensional behavior of the detonation is calculated, no large difference are shown on results of the two-dimensional analysis and three-dimensional analysis in the case of the aspect ratio 5.

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In this paper behavior of stress wave in a solid body induced by shock wave is discussed. Interaction between shock and solid sometimes causes serious problem such as the destruction of glass and structures by shock generated from supersonic plane, explosion and so on. In recent years, although the mechanism of interaction has been studied by many researchers, the details of process have not been known enough yet. In this study, the interaction phenomenon between shock wave emitted from diaphragmless shock tube and solid block made in acrylic or polycarbonate is visualized using Schlieren method. Motion of shock wave and its effect on block are examined by numerical simulation of the flow field using TVD scheme. As a result, it is found that stress wave is generated in block by the impingement of shock and its propagation speed depends on the material properties of block and the strength of shock.

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Experiments were conducted with a scale model launching apparatus to investigate the micro-pressure wave generated by axisymmetric trains of quadratic nose profiles. The nose shapes were an ellipsoid of revolution, a paraboloid of revolution, and a cone. The peaks of pressure gradient waveforms of the compression waves generated by those train models entering a tunnel were measured with consideration on effects of the ground and offset of a running train, in a double track tunnel. The peak of pressure gradient generated by the cone nose shape is the largest, and that generated by the paraboloid nose shape is the smallest among the three nose shapes. Difference of the peak values tends to be larger when the trains run in offset position.

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This study is intended to solve the issue of pressure wave to propagate in overlong tunnel for high-speed trains. We generated a weak shock wave by using a shock tube and got the pressure waveform of the shock wave propagating in a long tube. In addition, we placed a tube having porous wall in the specific place and revealed the characteristic of the shock wave propagating the inside tube experimentally.

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For the investigation of the interaction phenomena between the discharged plasma and the shock wave, two-dimensional numerical simulation code was developed. By using simple temperature modulated model, the shock wave deformation and vorticity generation were suggested.

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The relation between the piston compression process and piston mass was investigated by the parametric study with CFD. The piston compression process was evaluated by the maximum piston position. By comparing this parameter with the isentropic theory, the minimum piston mass with isentropic compression was evaluated.

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Experiment and numerical simulation of a gas-solid flow of cold spray process were conducted, in order to study the radial distribution of the particle-diameter number-fraction along the substrate surface. Experimental result shows that the number fraction of smaller particles decreases on the substrate center of φ1, compared to the number fraction of feed-stock powder. However, the present numerical simulation failed to reproduce the experimental result. It implies that additional model, such as eddy interaction model, needs to be added to simulate the particle trajectory.

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The separation and extraction of condensate gas is important for natural gas processing. The purpose of this study is to investigate the effects of nozzle geometry on supersonic swirling flow with non-equilibrium condensation by numerical simulation. In this study, the unsteady three-dimensional compressible Navier-Stokes equations coupled with nucleation rate, turbulence kinetic energy, and specific dissipation rate equations were discretized in space using a cell-centered finite volume method based on the third-order MUSCL TVD scheme, Roe's approximate Riemann solver. The second-order central difference scheme was used for the viscous term. The Euler implicit method was used for the time integration. As a result, possibility of miniaturization of equipment was shown by using a swirl flow and divergence of a nozzle numerically.

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In this study, the oscillation phenomena of underexpanded jet were discussed. The jet becomes underexpanded when the pressure ratio exceeds the critical value across the convergent nozzle discharging it. The jet is not uniform because of the presence of the expansion wave, the compression wave and the shock wave formed in it. In the jet boundary, many vortices are generated by the shearing stress between the supersonic flow of jet and still atmosphere The interaction of vortices and jet is closely related to the strong acoustic noise radiating from such flow field. In this experiment, in order to measure the behavior of jet, the flow field was visualized and the photograpbs were analyzed, and furthermore, the acoustic noise was measured.

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An underexpanded jet is well-known as one of supersonic jets and widely utilized in industlies, such as an assist gas for laser machining and a cooling jet in glass-tempering process. In these processes, the underexpanded jet impinges on the work piece and the jet violently oscillates, which leads to a complex flow field with a noise of high sound pressure level. The oscillation of jet and the noise are critical problems concerning manufacturing efficiency. So this paper focuses on the relation between the jet oscillation and the location of the work piece and especially discusses strength of shock formed in jet. The flow field is visualized using shadowgraphy and the pictures are analyzed. The feature of the jet structure is measured, such as locations of plate shock and oblique shock and strengths of shocks.

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Supersonic jet is used as a cooling jet in glass-tempering process and an assist jet in laser cutting. The jet issuing from a nozzle impinges on a work piece and then, it turns outward and radially spreads out. The radial flow is underexpanded if a supply pressure is very high. In this study, the radial jet is split off from the impinging jet in order to analyze it in detail. The jet is exhausted from a slit nozzle which is composed of two tubes being settled face to face. The flow field is visualized and the sound wave emitted from the jet is measured. As a result, the sound wave is found to have a directivity of 45 degrees against the radial jet plane. And a screech tone is measured which is similar to that observed in an axisymmetric underexpanded jet from a round nozzle.

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