[in Japanese]

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Instabilities in two-phase liquid metal MHD channel flow are investigated on the basis of the dispersion relation for the extended models of bubbly liquid and homogeneous mixture including MHD effect. In the bubbly liquid flow in open-circuit MHD channel, it is shown that the unstable wave associated with bubble slip is supressed for moderate void fraction but promoted for high and extremely low void fraction, and that the spatially growing wave associated with volume oscillation of bubbles is extended over all the frequencies. On the other hand, in the homogeneous mixture flow in closedcircuit MHD channel, an unstable wave caused by the stratified structure of the main flow due to the Lorentz force does not appear at least for high void fraction. These results show that the MHD effect makes the two-phase turbulence reduce and they are convenient for two-phase liquid metal MHD generation.

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In order to clarify the overall structure of the vortex shedding from a cruciform circular cylinder, the flows on the surface of and just behind the cylinder were examined in detail through the measurement of the fluctuating velocity and the flow visualization.
The results are summarized as follows : The flow passage across along the corner of a cruciform circular cylinder is already skewed and locally moves the separation line backward, and also originates the streamwise vortices from the positions of the minimum surface pressure on the cruciform circular cylinder. The vortex formation region behind the cruciform circular cylinder has a three-dimensional large scale circulation flow near the wake center. The shedding vortex from the cylinder forms complex structure based on the combination of the L-shape vortices and the U-shape vortices.

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A jet from a nozzle whose exit edge is rounded at the inside radiates by far more sound than from a usual sharp edge nozzle. The cause of such increase in the sound emission has been traced to the unsteadiness of flow separation on the (streamwisely-) convex wall. The unsteady behaviour of separation of the flow on a convex wall is profoundly influenced by disturbances in the flow, especially when the disturbance is slight. For a laminar flow with very little disturbances in the flow, the separation point remains quite fixed, while for a flow with a turbulent boundary layer it exhibits considerable fluctuation.
For a flow condition in which the boundary layer is regarded as laminar (in some aspects) but is affected by fair amount of disturbances, the separation point fluctuates violently, and as a result, very remarkable increase in sound emission takes place. Investigation on the mode of fluctuation of the separation point has also been made, in relation to the disturbance characteristics of the flow.

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