Masaru Sumida

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.

Flow Characteristics in a Square-Sectioned Duct with a Sharp Turn

This paper presents an experimental study of turbulent flow through a squared-sectioned duct with a 180-deg sharp turn. Fluid flow fields are investigated using a laser-Doppler velocimetry, PIV and a visualization method. The mean velocity features of the primary and secondary flows, and the fluctuating longitudinal-velocity at a Reynolds number of 3×104 are illustrated in the form of a contour map. Moreover, the mean quantities characterizing the turning flow, such as deviation of the primary flow and the intensity of turbulence, are shown in a graphic form against the longitudinal distances. Simultaneously, discussions are given on the transition of phenomena in the longitudinal direction.

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).

One Visualization Mehod for Secondary Flow in Curved Pipes.

A new solid-tracer method for visualizing the secondary flow in curved pipes is developed together with the measuring technique to obtain the velocity vectors of the flow field. In this method, the nylon particles suspended in the water flowing are illuminated by a sheet of a strobo light, and their paths are recorded photographically. This method is applied for steady, oscillating and pulsating flows in the fully-developed region of a circular curved pipe with a curvature ratio of 7.6. The obtained velocity vectors and profiles of the secondary flow are in good agreement with the numerical results. The availability of the present method is confirmed for visualization and velocity measurement of the secondary flow motion in curved pipes.

A Study of Oscillatory Flow in Curved Pipes : 2nd Report, Axial Velocity Profile

An axial velocity of a laminar, fully-developed oscillatory flow in a curved pipe was investigated experimentally and numerically. A laser doppler velocimeter was used to measure the axial velocity. The measured result was in good agreement with the numerical analysis, and the effect of oscillatory Dean number D and Womersley number α on velocity near the inside wall became larger than that near the outside wall under the condition of comparatively large Dean number and moderate Womersley number.