Masakazu Tatsuno

Circulatory Streaming around an Oscillating Circular Cylinder at Low Reynolds Numbers

The secondary flow generated by an oscillating circular cylinder immersed in a viscous, incompressible fluid is investigated experimentally. When the modified Reynolds number \(r_{0}\sqrt{\omega/\nu}\) is smaller than about 4, the whole flow field is occupied by only one circulatory streaming (the inner circulation), the direction of which is toward the cylinder along the axis of oscillation and away from the cylinder perpendicular to the axis, where r 0 is the radius of circular cylinder, ω the angular frequency and ν the kinematic viscosity. The distance between the core of the inner circulation and the axis of the cylinder is independent of the outer boundary and the oscillation amplitude. At a critical value of the oscillation amplitude the inner circulation shrinks down sharply. The critical amplitude depends on \(r_{0}\sqrt{\omega/\nu}\), but it is independent of the outer boundary.

Effects of interference among three equidistantly arranged cylinders in a uniform flow

The effects of flow interference among three identical circular cylinders, which were arranged in an equidistant triangular cluster with their axes perpendicular to the uniform flow, were studied at various incidence angles to the uniform flow and at different spacing ratios. The static pressures around the circumference of each cylinder were measured individually and the drag and lift coefficients of each cylinder were determined at Reynolds number of 6.2 × 104 based on the diameter of a single cylinder. The effects of flow interference among the three cylinders are severe when the spacing ratios are small. When two cylinders arranged side by side are upstream of or behind the third one, the flow patterns are not symmetrical with respect to the uniform flow direction and the drag or lift coefficients of the two cylinders in the side-by-side arrangement are not always equal to each other at small spacing ratios. The inclination angles to the uniform flow strongly influence the drag and lift coefficients, the direction of force exerted on each cylinder and the flow patterns around the cylinders. The effects of interference among three cylinders become weak as the spacing ratios are increased.

On the stable posture of a triangular or a square cylinder about its central axis in a uniform flow

The statistically stable posture of a triangular or a square cylinder is experimentally studied when it is free to rotate about its central axis fixed perpendicular to a uniform flow. Both cylinders come to rest in a stable posture with a side perpendicular to the uniform flow.

Secondary flow induced by a circular cylinder performing unharmonic oscillations

When a circular cylinder performs the saw-toothed oscillations, the induced steady streaming is the sum of the circulatory streaming due to the sinusoidal oscillations and an additional flow. The additional flow is approximately unidirectional in the direction of oscillation, and its velocity increases with the increase of S , but is independent of D , where S =ω s 2 / v , D =ω d 2 / v , ω is the angular frequency of the cylinder motion, s the oscillation amplitude, v the kinematic viscosity of the working fluid and d the diameter of the cylinder.

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.

Steady flows around two cylinders at low Reynolds numbers

Steady flow patterns around two circular cylinders are experimentally studied at Reynolds numbers lower than unity. The cylinders are towed at a uniform speed in a tank filled with glycerin, and the dependence of the streamline patterns on the ratio of the radii of the two cylinders, their mutual spacing, and the angle between the line joining the centers and the direction of the flow are studied. When the two cylinders are in tandem arrangements, the process of changes of the first twin eddies in the gap is in accordance with the theoretical results of Miyazaki and Hasimoto. When the two cylinders are in staggered arrangement, the flow separation occurs both at small values of gaps and at large ratio of the radii of the two cylinders.

The Behaviour of Tracer Particles in Flow Visualization by Electrolysis of Water

Flow visualization methods based on the electrolytic technique have not only many superior merits but also some drawbacks. One of the drawbacks is that when a tracer-generating wire is located upstream of a test body, tracer particles do not approach the test body. Consequently, the tracer particles can not indicate the true flow pattern. This phenomenon is more conspicuous if the tracer-generating wire is thicker, and nearer to the test body.

On the stable posture of a pair of parallel cylinders in a uniform flow

Abstract The stable posture of a pair of parallel circular cylinders in a uniform flow was experimentally studied when it was free to rotate about an axis at the middle of the two cylinders. The cylinder pair comes to rest facing the oncoming flow side by side, the line connecting the centers of the two cylinders being perpendicular to the flow, when s d = 0.5, where s is the distance between the center of rotation and the central axis of each cylinder and d is the diameter of the cylinder. When s d = 1.0 or 1.5, the cylinder pair is stable both in tandem, with one cylinder behind the other, and in side-by-side arrangements to the oncoming flow. When s d ⩾ 2.0, the cylinder pair is stable only in tandem arrangements.

Circulatory Streaming in the Vicinity of an Oscillating Square Cylinder

The steady flow generated by an oscillating square cylinder immersed in a viscous, incompressible fluid is investigated experimentally. The flow pattern in the vicinity of the cylinder is classified into three types according to non-dimensional parameters \(r_{0}\sqrt{\omega/\nu}\) and s / r 0 where r 0 is half the side length of the model section, ω the angular frequency, ν the kinematic viscosity and s the oscillation amplitude. Especially, when the oscillation amplitude is small, the flow pattern depends on the value of \(r_{0}\sqrt{\omega/\nu}\). If \(r_{0}\sqrt{\omega/\nu}{ }r_{0}\sqrt{\omega/\nu}{>}1\). When \(r_{0}\sqrt{\omega/\nu}{>}5\), two vortex systems are generated in close vicinity to the cylinder.

Visualization of the Unsteady Flow past Cylinders and Plates Decelerated from Steady Speed

Time-dependent flows around circular cylinders and flat plates, which are decelerated from a steady speed, were investigated by means of a flow visualization technique at low Reynolds numbers. For very small values of deceleration, the twin-vortices behind the test body shorten monotonically during deceleration, but elongate rapidly just before the test body is stopped. For intermediate values of deceleration, the twin-vortices elongate slightly at the first, but after a while they begin to shorten, the elongate again just before the test body is completely sopped. For large values of deceleration, the twin-vortices elongate monotonically. When the test body is decelerated rapidly from one steady speed to another lower speed, a large vortex-pair is formed in the wake during deceleration. After the second speed is reached the vortex-pair leaves the test body and moves backward, and the whole field of flow proceeds to grow into a new steady state.