Journal of the Visualization Society of Japan

A doublet flow is the circular free jet added the annular suction flow mounted on the same axis by using a double coaxial pipe. This flow was proposed for the purpose of diffusion control of a circular free jet. The doublet flow was examined experimentally with respect to time mean and unsteady characteristics over the full flow field by using PIV. It was found from the time mean analysis that as the suction velocity increases, the area average value of the fluctuating velocity increases. From the unsteady analysis, it was found that the vortex structures, which have the vorticity that is nearly equal to that of a jet, exist when the suction velocity is high. The vortex structure behaves intermittently, and exists randomly to the radial directions. Thus, the cause of the increase of the fluctuating velocity as described above is clarified by showing the behaviors of these vortex structures.

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In recent years, research and development activities for next generation supersonic transport are being carried out actively by the world aeronautical communities. In a supersonic air-intake, a cavity with bleed plays an important role in the control of normal shock wave under the cavity/shock wave interaction. The supersonic air-intake flow tends to be unstable due to the shock wave/wall boundary layer or the shock wave/shear layer interactions occurring close to the leading edge of the cavity. In the present study, the effects of cavity/ oblique shock wave interaction and bleeding on the pressure oscillation in the cavity were investigated experimentally in the case of the flow Mach number 1.74 at the cavity entrance and the characteristics of oscillation in the cavity were analyzed using the continuous wavelet transforms.

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Two-dimensional display of streamlines is considered to be suitable for the quantitative evaluation of the characteristics of the flow. In this investigation, a new concept of the flow function is proposed in order to obtain streamlines on an arbitrary section of threedimensional flow for visualizing and evaluating the characteristics of the flow. The streamlines separated by an arbitrary unit flow can be fined with the approximated point sources of the unit flow. These point sources are named simple sources.

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Authors are going to produce a new type rain gauge which measures the rainfall intensity by analysing the rainfall sound emitted from a tinplate can. Relations among the rain drop size, the falling velocity and the intensity of rainfall sound are investigated by outdoor and indoor experiments in which a visualization technique is used : Rain drops falling on the can are irradiated from two different directions by stroboscopes and recorded by a CCD camera. Original images are multiplied into one picture, so that a rain drop appears as a series of twin bright points from which the drop diameter and the falling velocity are measured. The resultant empirical formula for estimating the rain drop size from the sound intensity is installed in the rain gauge. A field experiment shows that the rain gauge can successfully measure the rainfall intensity with fine time resolution by integrating the estimated volume of each rain drop.

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