Tomoaki Kunugi

Bio: Tomoaki Kunugi is an academic researcher from Kyoto University. The author has contributed to research in topics: Turbulence & Heat transfer. The author has an hindex of 27, co-authored 309 publications receiving 2886 citations. Previous affiliations of Tomoaki Kunugi include Chiba University & Japan Atomic Energy Research Institute.

Measurements of 3D flow in a micro-pipe via micro digital holographic particle tracking velocimetry

Abstract: This paper details high time-resolution flow field measurements in a micro-pipe made by a micro digital holographic particle tracking velocimetry (micro-DHPTV) method. The system consists of an objective lens, a high-speed camera and a single high-frequency double pulsed laser. The volume of the system is 409.6 µm × 92 µm × 92 µm. It is illuminated by a laser beam with a pulse length of 58 ns, a resolution time of 100 µs and a repetition rate of 1 kHz. 104 velocity vectors could be obtained instantaneously in the micro-pipe. Particle positions in the three-dimensional field are reconstructed by a computer-generated hologram. The time evolution of a three-dimensional water flow in a micro-pipe of 92 µm inner diameter is obtained successfully using the micro-DHPTV system. The error of reconstruction in the z-direction is evaluated by analysing the traverse of particles on a glass plate and obtaining the velocity error in the z-direction by uncertainty analysis.

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Abstract: Home PURPOSE OF THE CENTER: To develop the center to address state-of-the-art research, create innovating educational programs, and support technology transfers using commercially viable results to assist the Army Research Laboratory to develop the next generation Future Combat System in the telecommunications sector that assures prevention of perceived threats, and Non Line of Sight/Beyond Line of Sight lethal support.

Plasma{material interactions in current tokamaks and their implications for next step fusion reactors

Abstract: The major increase in discharge duration and plasma energy in a next step DT fusion reactor will give rise to important plasma-material effects that will critically influence its operation, safety and performance. Erosion will increase to a scale of several centimetres from being barely measurable at a micron scale in today's tokamaks. Tritium co-deposited with carbon will strongly affect the operation of machines with carbon plasma facing components. Controlling plasma-wall interactions is critical to achieving high performance in present day tokamaks, and this is likely to continue to be the case in the approach to practical fusion reactors. Recognition of the important consequences of these phenomena stimulated an internationally co-ordinated effort in the field of plasma-surface interactions supporting the Engineering Design Activities of the International Thermonuclear Experimental Reactor project (ITER), and significant progress has been made in better understanding these issues. The paper reviews the underlying physical processes and the existing experimental database of plasma-material interactions both in tokamaks and laboratory simulation facilities for conditions of direct relevance to next step fusion reactors. Two main topical groups of interaction are considered: (i) erosion/redeposition from plasma sputtering and disruptions, including dust and flake generation and (ii) tritium retention and removal. The use of modelling tools to interpret the experimental results and make projections for conditions expected in future devices is explained. Outstanding technical issues and specific recommendations on potential R&D avenues for their resolution are presented.

Theory of cross-correlation analysis of PIV images : Image analysis as measuring technique in flows

Abstract: To improve the performance of particle image velocimetry in measuring instantaneous velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.

The growth of vapor bubbles in superheated liquids. report no. 26-6

Abstract: The growth of a vapor bubble in a superheated liquid is controlled by three factors: the inertia of the liquid, the surface tension, and the vapor pressure. As the bubble grows, evaporation takes place at the bubble boundary, and the temperature and vapor pressure in the bubble are thereby decreased. The heat inflow requirement of evaporation, however, depends on the rate of bubble growth, so that the dynamic problem is linked with a heat diffusion problem. Since the heat diffusion problem has been solved, a quantitative formulation of the dynamic problem can be given. A solution for the radius of the vapor bubble as a function of time is obtained which is valid for sufficiently large radius. This asymptotic solution covers the range of physical interest since the radius at which it becomes valid is near the lower limit of experimental observation. It shows the strong effect of heat diffusion on the rate of bubble growth. Comparison of the predicted radius‐time behavior is made with experimental observations in superheated water, and very good agreement is found.