Hiroyuki Honji

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 .

Cross-stream survey of the upper 400 m of the Kuroshio by an ADCP on a towed fish

A section across the Kuroshio and the adjacent area on the East China Sea shelf was measured by an Acoustic Doppler Current Profiler (ADCP) mounted on a towed fish. The section covered the upper 400 m with a horizontal interval of 200 m and a depth interval of 8 m. The measured vertical profiles made it possible to construct a detailed contour plot of velocity in this section. The calculated volume transport of the Kuroshio through this section and extrapolated to 700 m depth was 27.2 Sv (1 Sv = 1×106m3s−1), 30–40% higher than estimated by geostrophy with a level of no motion of 700 db.

Experimental observation of internal symmetric solitary waves in a two-layer fluid

Water tank experiments were conducted on the internal symmetric solitary waves generated by gravity flow intrusion at the horizontal interface of a two-layer fluid. Velocity distributions in the waves were first measured using an image processor. Flow visualization studies revealed some new features of the solitary waves, including a marked decrease in the phase velocities of two large-amplitude, oppositely propagating waves after their head-on collision.

A numerical study of steady streamings in oscillatory flow over a wavy wall

Steady streamings induced in a fluid, oscillating at small amplitudes over a wavy wall in a flume, have been analyzed numerically and observed over a wide range of the Stokes layer thickness. It has been found that the computed streamline patterns of steady streamings agree well with the observed flow patterns.

WAVY WAKE FORMATION IN THE ABSENCE OF SUBMERGED BODIES IN ELECTROLYZED SALT WATER

It has been found experimentally that in electrolyzed salt water, a wavy wake forms in the absence of submerged bodies downstream of a localized region influenced by the magnetic field of permanent magnets moving at a constant velocity. The lower and upper critical numbers of a dimensionless current density ( Q ) for the formation region of the wavy wakes decrease with Reynolds number. A straight wake and a meandering wake also form at smaller and larger values of Q , respectively. No wake formation of this type occurs in nonelectrolytic common fluids.

Self-governing profiling system

Abstract A self-governing profiling system with a depth capability of 100 m has been developed for measuring flow velocity, temperature, salinity, and turbidity of water in the near-bottom parts of shelf seas. In the system, a moving profiler unit holding the sensors for measuring the above parameters and depth and containing a data-recording device is made to move up and down, in cycles, along a mooring line. This motion of the profiler unit is governed by a self-contained microprocessor. The system has been field-tested: examples of recorded data are presented.

Steady flow patterns of internal solitary bulges in a stratified fluid

Steady streamline patterns are demonstrated of a solitary bulge forming on an interfacial transition region in fresh and salt water. The bulge is composed of a vortex pair at αa≳1.3, with α the inverse of the characteristic thickness and a the bulge amplitude.

A note on internal wavetrains and the associated undulation of the sea surface observed upstream of seamounts

An internal wavetrain, generated by a tidal current in superposition with the Tsushima Warm Current, has been observed by use of an acoustic echo-sounder upstream of the ‘Shichiri-Ga-Sone’ Seamounts in the East Tsushima Strait of the Japan Sea. The sea surface above the internal wavetrain was simultaneously observed and was found to be undulated at the wavelength of the internal wave.

Vortex Rings in a Stratified Fluid

Unsteady motions of vortex rings in a stably stratified fluid, of which the density profile has a gradual step change, have been observed using an electrolytic flow visualization technique. Some new types of distorted vortex rings wave observed to from in the nonhomogeneous fluid.