[in Japanese]

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The turbulent boundary layer flow has experimetally been studied under a steep favourable pressure gradient, whose maxmum value in non-dimentional form, K=ν/U₁²dU₁/dx, is 8.8×10^-6. The tubulent bulge in the outer layer keeps the similar shape in the statistical sense, suggesting that its turbulent structure maintains nearly the equilibrium condition, from which we can evaluate the change of turbulent characteristics along the line of constant intermittency. The turbulent intensity along the line decreases abruptly from a downstream location, and it coinsides with the starting point of relaminarization evalualed by various criteria proposed so far. Further downstream, both turbulent intensity and Reynolds stress decrease gradually, and especially the decrease of Reynolds stress seems to be due to the decrease of the number of the burst occurence. The turbulent production and dissipation also decrease in this flow region.

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Scattering of sound incident upon an arbitrary vorticity field is investigated, and general formula of the scattered wave is presented. Under the condition of weakly unsteady field, the scattering amplitude is expressed as a function f (n, n₀, ω) dependent on unit vectors n₀ and n in the incident and scattered directions respectively, and also on the vorticity distribution ω through its Fourier component of the wave number k₀ (n-n₀), k₀ being the incident wave number. The amplitude satisfies the reciprocity relation f (n, n₀, ω) =f (-n₀, -n, -ω), which can be deduced from the energy conservation and linearity of the scattering process and the time reversal invariance of the basic equations. Explicit expressions of the amplitude are given for the two vortex systems known as Hill's spherical vortex and a vortex ring of thin vortex core.
General amplitude formula in two dimensional problem is also derived and applied to several cases (a vortex filament, a vortex pair, vortex arrays, etc.), some of which are compared with known formulae. Comments are given about relationship to the associated fields of the scattering problem.

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The present investigation aims at elucidating the condensation phenomena of a vapour including the vapour-condensate (liquid) interaction by using a shock tube. A stagnant gas of high temperature and high pressure is generated in the region between a reflected shock wave and an end wall of the shock tube. The wall itself being kept at an initial room temperature, the vapour adjacent to the wall is cooled and begins to condense forming a thin and uniform liquid film on the end wall.
The thickness of the growing liquid film and the gas temperature at the liquid surface have been measured as a function of time by means of an optical diagnostic technique. A theoretical analysis also has been made corresponding to the experiment. Condensation and thermal accommodation coefficients of a methanol vapour have been determined from the comparison between the theory and the experiment. They were found to be 0.035 and 0. 03-0. 07 respectively. A flow field and an unsteady thermal boundary layer near the phase-changing interface have been theoretically clarified.

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Wind tunnel experiments on the turbulent characteristics of a purely oscillatory flow were performed with the aids of the Laser Doppler anemometer as well as the hot wire anemometers, along with the advanced electronic data processing system.
The following results were obtained.
(i) Turbulence as predicted by the linear stability theory is triggered at the later stage of the acceleration period but it is suppressed at low level. While, with the beginning of the flow deceleration, turbulence is generated explosively near the wall and is propagated towards the central part of the duct.
(ii) Turbulent energy is almost completely dissipated within the decelerating period by strong turbulence, and thus the negative production can scarcely be expected.
(iii) The spectrum follows the steeper power law compared with the Kolmogorov spectrum.
(iv) The statistics of oscillatory flow remarkably differs from the steady turbulent flows.

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Experimental study has been made using a large oscillating water tunnel. Simultaneous measurement of the two components in horizontal and vertical directions, of a velocity at each measuring point has been made, and thereby the velocity profiles, turbulent shear stresses, etc. in boundary layers have been studied. The procedure of periodic ensemble averaging, modified by an application of a finite Fourier series for the estimation of the most probable values of the periodic averages, has permitted the separation of the periodic components and the turbulent fluctuations.
From this measurement the phenomenon of the explosive generation of turbulence during the deceleration period and also the occurrence of negative Reynolds stresses at the beginning of the acceleration period, of the free-stream velocity in purely oscillatory flow, have been clarified.
Also, by the flow visualization technique of thin-layered milk method developed by the writers it has been made clear that the process of generation of turbulence at the later stage of deceleration period is similar to the phenomenon of bursting in steady uni-directional flow, but that the eddies formed at an early stage of acceleration period are of a large scale and peculiar to purely oscillatory flow.
Furthermore, experiment on steady uni-directional flow was conducted using the same water tunnel, and by the same flow-visualization technique the process of generation of turbulence has been observed and compared with that in oscillatory flow.

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