Hideki Hibara

Analysis of Submerged Water Jets by Visualization Method: Flow Pattern and Self-Induced Vibration of Jet

This paper is concerned with an experimental investigation on plane submerged water jets discharged into quiescent water in an open channel. Flows are visualized by using hydrogen bubbles, solid particles and dye. The results show that the jets attaching to the water surface by the Coanda effect are classified into six types according to their behavior after issuing from the nozzle, and that the self-induced vibration of the jet, which is one of six flow patterns, occurs under the condition of the reduced Froude numberFr*≒0.7∼1.0. An additional analysis of the photographs reveals that the self-induced vibration of the jet is caused by attachment of the jet to the water surface and the ensuing bifurcation of the jet at an attachment point, and that the frequency of vibration is independent of the water level.

Flows in T-Junction Piping System (2nd Report, Numerical Analysis of Vortex Street Formed by Branch Pipe Flow)

Thermohydraulic analyses for a fundamental water experiment simulating thermal striping phenomena at T-junction piping systems were carried out using a quasi-direct numerical simulation code DINUS-3. Calculated results were compared with the experimental results on the flow patterns in the downstream region of the systems, the arched vortex structures under the deflection jet condition, the generation frequency of the arched vortex in the various conditions ; i.e., diameter ratio α, flow velocity ratio β and Reynolds number. From the comparisons, it was confirmed that (1) the DINUS-3 code is applicable to the flow pattern classifications in the downstream region of the T-junction piping systems, (2) the arched vortex characteristics with lower frequency components can be estimated numerically by the DINUS-3 code, and (3) special attentions should be paid to the arched vortex generations with lower frequency components of fluid temperature fluctuations, which might induced high-cycle thermal fatigue for the design of T-junction systems.

A Study of Oscillatory Flow in the Entrance Region of a Curved Pipe. Secondary Flow Visualization and Its Characteristics.

A visualization study has been made to investigate the secondary flow induced in an oscillatory laminar flow in the entrance region of a curved pipe with a curvature ratio of 9.8. The experiments were performed under the condition of a moderate Womersley number a=10, which is a physiologically interesting nondimensional frequency. and a Dean number D=300. The secondary flow motion was rendered visible by means of a tracer method using nylon particles, and photographs were taken at four phases in one cycle and at axial locations from the upper stream tangent to the downstream in the curved pipe. The instantaneous velocity vectors and profiles of the secondary flow and its intensity were obtained from the photographs. We discuss the secondary flow characteristics in the entrance region of the curved pipe. Development of the secondary velocity field can be quite well explained from the axial flow field. The secondary flow pattern changes with the phase at the inlet region are complicated, especially at Ω=20∼50°around the curved turn. The intensity of the secondary flow is high during the inflow term of one cycle in the curved pipe, and is high during the outflow term in the upper stream tangent. The inlet length according to the information regarding the secondary flow agrees with the length evaluated from the amplitude of the axial flow velocity in our previous work given by the reference (7).

Two-Dimensional Impinging Jet on Concave Surface.

Mean and fluctuating velocities have been measured for a two-dimensional gas jet impinging on a solid concave surface. Measurements are made by the technique of rotating a probe with an inclined hot wire under the Reynolds number of 16500. The figures are shown for distributions of the mean velocity, the turbulence energy and the Reynolds stress. And the influence of the curvature of the wall is found evidently in these jet characteristics. Also, the static pressure in the jet and on the surface is calculated by using the measured results of velocities, and the validity of the calculating method is confirmed by comparison with the experimental results.