Terutoshi Murakami

Acoustic emission from interaction of a vortex ring with a sphere

Acoustic waves emitted by a vortex ring interacting with a fixed solid sphere are studied experimentally and theoretically. The experiments are carried out for two kindsof vortex-sphere arrangement: (A) a vortex ring passes over the sphere, and (B) a vortex ring passes by the sphere. The vortex motion is examined optically by means of a photosensor system, and the pressure signals of the emitted wave are detected by ½-inch microphones in the far field. In case A, the measured diameter of the vortex ring after passing the sphere increases from its initial diameter. The observed acoustic wave is dominated mainly by a dipole emission, and some contribution from a quadrupole radiation is present. In case B, the emitted wave is characterized by a rotating dipole emission in which the dipole axis rotates as the vortex position changes relative to the sphere.

Method for the time-resolved measurement of the size and position of a moving particle using an image sensor

A new method for the continuous measurement of both the size and position of a moving particle using a two-dimensional metal-oxide-semiconductor-type image sensor is described. With this method the particle position is determined precisely by the number of the scanning line and the pixel number within one frame image in place of the frame number used in ordinary video camera methods. This simple and novel sizing method, associated with the image storage property of the image sensor over one field interval, was first described and applied by König et al. [J. Aerosol. Sci. 17, 157 (1986)]. The numerical analysis and the experiment to verify the sizing method are performed. Details of the system and its application for a freely falling small glass sphere are presented.

Acoustic waves emitted by a vortex ring passing near a wedge-like plate

Acoustic waves emitted by a vortex ring moving near a thin wedge-like plate of finite width have been studied. The experiments are performed for three configurations: the plate (A) is held edgeways to the direction of the vortex motion, (B) is held sideways to the direction, and (C) is held edgeways at an angle of 45° against the vortex motion. The observed sound wave is of dipole radiation type, and the magnitude of the pressure is large in the direction of the normal to the plate plane and small in parallel. The observed pressure is proportional to the third power of the vortex speed. The instantaneous force exerted on the plate by the vortex motion has also been examined. The force vector is mainly normal to the plate plane. The observed profiles agree within a reasonable degree of accuracy with the theoretical ones calculated for the vortex ring interacting with the flat plate of thickness zero.

Approximate Theory of a Converging Shock Wave in Condensed Media

An approximate formula is derived to describe the growth of a converging shock wave and is shown to be valid for a weak shock. The shock pressure or density in condensed media can be evaluated very easily by using this formula.

Liquid Atomization by Supersonic Jet Observed with Laser Holography

Gas atomization has become one of the most efficient means of producing metal powders. In this method, the molten metal is atomized by supersonic freejets, and the powder with the diameter less than 30 μm is now being obtained. However, the detailed structure of the jet as well as the breakup process of the melted metal droplet is not known. In the present research, the diagnostic system based on the laser holography is constructed to clarify the process of gas atomization, and the breakup process of water droplet by supersonic jet is obtained.

Visualization of submicron particles

A new laser holographic technique has been developed to visualize sub-micron particles. If the size of the particle is comparable with or less than wavelength, it is very difficult to obtain the image of small particles by the conventional optical method.We have obtained the holographic interference fringes by means of superposition of the reference light and the scattered light of comparable intensity by a particle irradiated at the beam waist of focused coherent light. The two-dimensional particle location is measured in terms of the center of holographic fringes, and the three dimensional depth of particle position from the recording plane is obtained by the reconstruction of the hologram.

Shock wave structures in weakly ionized gases using the Krook kinetic model

The structures of the normal shock waves in weakly ionized nonequilibrium flows have been analyzed by the Krook kinetic models using the Maxwellian or the ellipsoidal distribution functions, and the calculated results were compared with those obtained from the bimodal approximations.