A new computational scheme using Lagrangian model of the velocity and molecular mixing for the fluid particle is developed to calculate the reactive scalar field in grid generated turbulence. The model is composed of three parts. The Lagrangian velocity of fluid particle which carries the reacting species is generated by the Random Fourier Modes method. The molecular mixing model(the modified Curl's model)is used to calculate the mixing and diffusion of reactive concentration field, and the chemical reaction model is a second-order and irreversible reaction in the scalar mixing layer. It is shown that the simulated results of the first and second moments of reactive and productive species show the good agreements with of the experimental data.

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Spatial development of a turbulent field generated by a multiscale, fractal-grid is investigated in a wind tunnel. A square type (i.e., fractal elements with square shapes) fractal grid is placed at the inlet of the test section. The Reynolds numbers based on the length of the biggest grid bar are set to 5900 and 11400. Turbulent characteristics in the downstream region of the grid are measured by using a hot wire anemometer. The results on the centerline statistics are compared with those in the previous experiments at the same Reynolds numbers. The results on the centerline statistics generally agree with the previous measurements despite the difference in the size of the test sections used. The spatial developments of cross-sectional profiles are also measured. It is found that the non-uniformity in the mean velocity field almost disappear in the downstream direction, although the non-uniformities of higher-order statistics are still observed even in the far downstream region. In the entire cross section of the tunnel, the ratio of the integral length scale L_u to the Taylor microscale λ hardly changes in the decay region of the rms velocity. These results will provide useful information in clarifying the non Richardson-Kolmogorov cascade process in the fractal-generated turbulence found in the previous measurement (Mazellier and Vassilicos, Physics of Fluids, Vol. 22, 075101 2010).

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The jet flow from an orifice nozzle shows a particular velocity profile with a large velocity gradient at the edge of the jet. Setting an orifice nozzle, second one, with a resonance room just after the first orifice nozzle the jet causes resonance phenomena and the resonance frequency depends on the jet velocity and the volume of resonance room. In this study, a notched nozzle was used as the second one to enhance the flow disturbance or fluctuation, and the effects of the notched nozzle on the mean and fluctuating velocities and the mixing or diffusion characteristics of the jet itself and with the surroundings were examined experimentally using a hot wire measurements. As a result, it was made clear that under a same operation power the flow rate near the nozzle exit of a notched resonance jet is larger than those of an orifice and resonance jets, for example, at x/d = 0.2 (x: distance from the nozzle exit to the downstream, d: nozzle diameter) it is about 2.5 and 1.3 times of theirs, respectively, and others.

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We developed the molecular beam source with a non-diaphragm type small shock tube in order to generate high energy molecular beam and dissociated atomic beam. The measurement of the shock Mach number shows that the convergent type tube, the diameter of which linearly decreases from 4 to 2 mm, successfully increases shock Mach number compared to the straight tube although viscous dissipation increases in the convergent tube. We evaluated the characteristics of shock-heated beams by the time-of-flight technique. The shock tube with the optimized geometry can generate the molecular beam with the translational energy of more than 1 eV at the repetition rate of 0.5 Hz. The translational energy of the beam is reproducibly controlled by the initial pressure ratio. Furthermore, dissociated atomic beam is obtained for oxygen with the fraction of dissociation determined by the initial pressure ratio. These results demonstrate that the molecular beam source using the small convergent shock tube is a useful method to generate high energy and reactive atomic beams.

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The purpose of this study is to know differences between steady and unsteady drag coefficients of a sphere. Though we often have to estimate unsteady drag-forces acting on a moving obstacle, we are obliged to use the well-known steady drag coefficient for the first estimation because of lack of information about effects of unsteadiness on the drag coefficient. The usual way to take account of unsteadiness is an added mass. However, its application is restricted within the simple shape of an obstacle. We propose a way based on the equation of motion to obtain the unsteady drag coefficient. To confirm validity of the way, we measured and analyzed the motion of the falling sphere in water by using a high-speed camera and a motion capture method. The drag coefficients as a function of time were obtained by substituting measured values of velocity and acceleration into the equation of motion. The drag coefficient was 0.52 when the sphere attains the terminal velocity, being quite large at the beginning of motion. Comparing with the values obtained by the other previous studies, our result is reasonable.

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We have theoretically investigated the particle orientational and rheological properties of a dilute suspension composed of spindle-like hematite particles under a simple shear flow. We have derived the basic equation of the orientational distribution function with spin rotational Brownian motion. The basic equation has been solved numerically in order to investigate the influence of the shear rate, magnetic field strength, and rotational Brownian motion on the orientational distribution and rheological properties. For a very strong magnetic field applied in the shear flow direction, the particle inclines in the direction normal to the flow direction. Also, the particle is restricted in a plane normal to the shearing plane due to the spin rotational Brownian motion. The viscosity becomes large with increasing magnetic field strength. In the case of an external magnetic field applied in the direction of the angular velocity of a simple shear flow, the particle inclines toward a plane normal to the shearing plane, while the magnetic moment is restricted in the direction of the magnetic field. The particle can easily rotate around the magnetic moment under circumstances of a weak shear flow. For a strong shear flow, the particle inclines in the shear flow direction and does not rotate around the magnetic moment. The viscosity due to magnetic properties does not occur under the situation of a magnetic field applied in the direction of the angular velocity vector of a simple shear flow.

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Temperature dependence of thermal and electrical contact resistance of copper has been investigated from 20 °C to 300 °C, experimentally. The real contact area increases as the temperature rises even if under the softening temperature, and the contact surfaces stick to each other due to the process of diffused junction at higher than softening temperature. The ratio of real contact area to apparent contact area and mean plane separation between two flat surfaces can be estimated using simple model of thermal and electrical contact resistance, where the ratio of 3.8×10^-6 and mean plane separation of 0.31 μm at 155 °C are obtained. Moreover, the thermal resistance of point contact's samples excluded the effect of apparent contact area as much as possible is also evaluated. The thermal resistance of point contact's samples is one digit or higher than that of two flat surfaces at the same electrical resistance, and the ratio of real contact area to apparent contact area is almost the same as that of the samples with various shapes.

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In this work, the film thermal conductivity and the film-substrate interfacial thermal contact resistance of vertically-aligned single-walled carbon nanotube (VA-SWNT) films were measured with a proposed method utilizing temperature dependence of Raman spectrum. The proposed method harnesses the excitation laser power of the Raman spectroscopy to heat the VA-SWNT films synthesized on a silicon substrate by alcohol catalytic chemical vapor decomposition (ACCVD) method, and measures film temperature from the Raman spectrum. A relationship between the input laser heat and the measured temperature is modeled with a detailed heat conduction equation, and its numerical solutions were compared with the experimentally measured results to extract the film thermal conductivity and the film-substrate interfacial thermal contact resistance. The method found the thermal conductivity of the VA-SWNT film to be around 2 Wm^-1K^-1 and the film-substrate interfacial thermal contact resistance to be around 2×10^-6 m²KW^-1. The obtained film thermal conductivity corresponds to the thermal conductivity equivalent of an individual SWNT of several tens of Wm^-1K^-1. This value was more than an order of magnitude smaller than the values reported on individual SWNTs.

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Experimental investigations have been carried out on combined forced and natural convective flows induced around upward-facing, horizontal heated wedges placed in a uniform vertical downward flow of air. A keen interest was directed to the thermal instability of the laminar boundary layer flows over the wedge and its effect on the heat transfer from the wedges. For the sake of this, comprehensive flow visualization experiments and measurements of the local heat transfer coefficients have been conducted with the wedges of various angles θ from 180°(horizontal plate) to 0° (vertical plate). The results showed that longitudinal vortices appear over the wedges of 180°<θ<135° with increasing buoyancy force and they enhance the heat transfer from the wedges. While, a separation of the boundary layer occurs over the wedges of 110°<θ<0° and the heat transfer was deteriorated significantly. It is also found that the onsets of these thermal instabilities as well as the heat transfer variations are predicted well with the non-dimensional parameter (Gr_L^*/Re_L^2.5).

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This paper describes a debris-bed cooling model for a Sodium-Cooled Fast Reactor (SFR). The model aims at addressing not only the debris-bed consisted of the particles of the diameter with the hundreds of micrometers typically assumed with SFR but also the debris-bed with larger diameter particles. Then, it can cope with wider range of the scenario in the severe accident of SFR. Pressure losses of a laminar flow and a turbulent flow, gravity force and capillary force are considered in the basic equations. The present study model is validated through the analysis of the Sandia ACRR-D10 in-pile experiments utilizing real materials to simulate the SFR environment. Sensitivity analyses are performed by using the present study model to evaluate the influence of gravity force, turbulent flow pressure loss and the diameter of particles. It is shown from the sensitivity analysis, that gravity force influences the temperature and the liquid saturation in the debris-bed with larger diameter particles, while the turbulent flow pressure loss has small influence with the range of these sensitivity analyses.

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[in Japanese]

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