Turbulent boundary layers with main stream having negative or positive velocity shear were formed along a concave solid wall in a wind tunnel. Effects of the shear on the separation of the turbulent boundary layers were investigated in detail. A new direction-sensitive hot-wire anemometer system was developed and used exclusively in the measurement of the velocity in the region with flow reversal. We could obtain an instantaneous velocity with positive or negative sign. The backflow factor which is defined as the fraction of time of flow reversal is a useful quantity in describing the separation region. The plot of the backflow factor clearly indicated that the negative shear-greater velocity near the wall-delays the separation, whereas the positive shear results in an early separation. One of the reasons for this difference might be the less large-scale components in the velocity fluctuations in the boundary layer with negative shear.

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Motion of point vortices is analysed numerically by use of the potential flow theory in order to investigate some features of vortex merger in the two-dimensional mixing layer. Merging vortices are replaced by two groups of point vortices and the other vortices by an effective background field. Parameters in the calculation are the distance between the two vortices and their size. A quadrupole moment of the point vortex distribution, which is defined in this paper, is calculated at each step of the motion. This quantity is shown to describe process of merger well. Calculation shows that the two vortices rotate around their center along a nearly elliptical path and merge when they come close to each other. The unified vortex continues to deform even after that. Value of the quadrupole moment changes according to these motions. Time scale of merger is estimated by two ways, one from a motion of each vortex and the other from a decrease of the quadrupole moment. The estimated time scale is proportional to the square of the distance, and depends little on the vortex size if it is within a certain range. This result is consistent with the assumption made by Takaki & Kovasznay (1978). An area increase and an oscillatory deformation of the unified vortex are observed and discussed based upon a variation of the quadrupole moment.

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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. Visualization studies by means of the smoke wire technique were also made.
The following results were obtained.
(i) Although the statistics of oscillatory flow remarkably differ from the steady turbulent flows, the elementary process which maintains the turbulence production is almost the same with that in the steady wall turbulent flows ; i. e. the bursting process, especially the ejection phase is prevailing.
(ii) Probability distributions of u' are skewed towards the positive side during the violent bursting phase.
(iii) The Reynolds stress during the ejection phase is not only stronger but also spreads higher from the wall than that of the sweep phase.
(iv) While in the acceleration period, the vertical velocity profile hardly obeys the log-law, it has the wide log-law region in the decelerating period, especially in the ejection phase.

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This paper is concerned with numerical solutions for flows of a viscous incompressible liquid jet emanating from a small nozzle.
The time-dependent Navier-Stokes equation is solved numerically by utilizing the finite-difference method. Our numerical scheme presented here is basically the same as the MAC method but is improved so as to be capable of estimating with high accuracy by comparatively simple procedure the surface tension, which plays essential role for droplet formation. The velocity and pressure fields in the jet are computed and the change in the shape of surface with time is followed until droplets are formed.
The results were compared with experiments for a number of inlet velocity distributions or various values of other parameters under the consideration of nonlinearity, for which analytical treatment of linearized Navier-Stokes equation has never been successful.
The agreement between experimental and computational results is excellent and our method provides sufficient information to describe the process of droplet formation theoretically.

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