Sadatoshi Taneda

Experimental Investigation of the Wake behind a Sphere at Low Reynolds Numbers

Wakes produced by a sphere moving in a tank of water were photo-graphically investigated at Reynolds numbers from 5 to 300. Main results obtained are as follows.

Experimental Investigation of the Wakes behind Cylinders and Plates at Low Reynolds Numbers

Wakes behind cylinders and plates were photographically investigated at Reynolds numbers from 0.1 to 2,000. Main results are as follows. In the case of a circular cylinder, the rear twin-vortices begin to form at R =5 ( R is U d /ν), then become more and more enlarged as R increases, and finally become asymmetrical at about R =45. The laminar wake, on the other hand, begins to oscillate sinusoidally some distance downstream at R =30. In the case of a flat plate parallel to the flow, the wake begins to oscillate sinusoidally some distance downstream at about R =700 ( R is U l /ν, where l is the length of the plate). Lastly, some detailed knowledges about the structure and the nature of the Karman vortex street are obtained by a new method.

Visualization of Separating Stokes Flows

This paper provides photographs of separating Stokes flows. Silicone oil and glycerine were used as the working fluid. The aluminum powder method and the glass beads method were used for flow visualization. The flows studied are flows around bodies placed in a uniform flow, flows past bodies placed near a plane wall, flows past a fence, flows past a step, flows past a wall cavity, and flows near a sharp corner. It is found that there is a remarkable agreement between the experimental results and the theoretical ones.

Experimental Investigation of Vortex Streets

Vortex streets behind circular cylinders and fiat plates were investigated experimentally in a water tank. Photography and hot-wire techniques were used. The important points resulting from the investigation are as follows. (1) Walls increase the stability of the wake. (2) Two parallel walls have a compressing effect on the vortex street. (3) The vortex street of a single row is formed near a single plane wall. (4) Not only laminar wakes but also turbulent wakes show a strong tendency to form the Karman vortex street. (5) When a certain periodic disturbance is given to a wake, a stable symmetrical vortex street are formed. (6) Vortex filaments behind tapered cylinders and whirling cylinders are straight but inclined to the cylinder axis.

Downstream Development of the Wakes behind Cylinders

Wake development behind circular cylinders and flat plates was investigated in the research water tanks. The aluminium dust method was used to observe the flow patterns. At the intermediate Reynolds number range the Karman vortex streets are formed in the wakes behind cylindrical obstacles. But these primary Karman vortex streets are not stable. They are more and more deformed as the distance from the obstacle is increased, and finally break down. Thereafter, however, the wake in most cases begins to rearrange itself again into a configuration of the Karman vortex street. The dimension of the secondary Karman vortex street thus produced is much larger than that of the primary one. For the circular cylinder, when Reynolds number is lower than about 150, the ratio of the wave length of the secondary vortex street to that of the primary one is about 1.8 to 3.6, while it is about 10 when Reynolds number is higher than about 150. Sometimes the secondary Karman vortex street simply decays by viscous diffusion a...

Unsteady Flow past a Flat Plate Normal to the Direction of Motion

The development of the separated flow past a flat plate which was started from rest either impulsively or with uniform acceleration was investigated experimentally by using flow-visualization techniques. The flow is irrotational initially. The onset of separation takes place at the two edges of the plate. The symmetrical twin-vortices are always formed at small times no matter how large the Reynolds number may be. The length of the wake bubble is nearly proportional to ( U t / d ) 2/3 or ( a t 2 / d ) 2/3 at small values of (ν t / d 2 ) (where U is the plate speed, t the time from the start, d the plate length, a the acceleration and ν the kinematic viscosity). The length of the symmetrical wake bubble exceeds 4.1 plate lengths at a d 3 /ν 2 =4.2×10 2 .

Unsteady Flow past a Circular Cylinder

The symmetrical unsteady vortices behind a circular cylinder started from rest either impulsively of with uniform acceleration were investigated experimentally using a flow visualization technique. The variation of the length of the vortices with time was determined from the photographs obtained at Reynolds numbers ranging from 31 to 1700 and dimensionless accelerations from 195 to 2.44×10 5 . The length of the unsteady vortices exceeds 4.3 cylinder diameters at about a Reynolds number of 100, or a dimensionless acceleration of 500. The secondary vortices were formed upstream side of the main vortices at Reynolds numbers higher than 550, or dimensionless accelerations higher than 5×10 5 .

Waving Motions of Flags

The waving motions of flags are investigated experimentally in a wind tunnel. Several cases are examined: when a flag is placed in a uniform flow, when a flag is placed in a one-sided flow, and when a splitter plate is placed in the wake of a flag. The wave mode, the wave form, the wave velocity, the frequency and the drag are determined for many kinds of flags at Reynolds numbers ranging from 10 3 to 3×10 5 .

An Experiment on the Flow around a Waving Plate

The flow around a flexible plate performing a swimming motion was investigated using hot-wire anemometers, pressure transistors and flow visualization techniques. It was found that the swimming motion accelerates the flow near the surface in the wave direction, reduces the boundary layer thickness, and suppresses the turbulent fluctuation.

The Stability of Two-Dimensional Laminar Wakes at Low Reynolds Numbers

This paper is concerned with the stability of a two-dimensional laminer wake. The development of small disturbances excited artificially is investigated both experimentally and theoretically. Experiments are made in an experimental water-tank at Reynolds numbers between 10 and 600 for a flat plate and between 0.8 and 60 for a circular cylinder. The amplification rate, the wave length and the wave velocity of the disturbance are measured from the photographs of the flow. The neutral stability curve is determined both for the fiat plate and for the circular cylinder. The minimum critical Reynolds number below which all disturbances are damped is found to be about 1.0 for the circular cylinder. Theoretical investigations are made by the method of small oscillations. The agreement between the theory and the experiment is fairly good.