The structure of a vortex ring was investigated in detail by using flow visualization technique. The flow pattern in the cross section of a vortex ring shows spiral streak lines around the vortex center. The flow rate in the space between the neighboring two streak lines calculated with the velocities tangential to the streak lines keeps a constant value while the streak lines go around the vortex center. Therefore, the spiral streak lines can be regarded as the stream lines on the coordinate system moving with the vortex ring. The velocity at a point in a cross section of the vortex was calculated from the flow rate and the space between the neighboring spiral streak lines. The equi-vorticity lines are nearly concentric circles and they are different from the configuration of the spiral streak lines. The circulation of a vortex ring obtained from the vorticity distribution is in good agreement with that obtained by integrating the velocity along the vortex ring axis.

View full abstract

In this paper, swirl decay, swirling flow pitch and pressure loss in a straight pipe are described. Two types of experiments are performed. First, swirling angle, velocity and pressure measurements are conducted to estimate swirl decay and swirling flow pitch. Either the traditional swirl number, m, or a proposed swirling angle at r/R=0.95, Θ_sw, is employed as the definition of swirl strength for evaluating swirl decay. As a result, it is ascertained that both the swirl number and a proposed swirling angle at r/R=0.95 are useful for swirl strength definition. Change in swirling flow pitch due to swirl decay is confirmed by analyzing the swirling angle distribution. It is confirmed quantitatively that the pitch is long in the annular region and short in the central region of the pipe. When the swirl decays, swirling flow pitch at radius, r, is elongated far downstream. Second, the other equipment and a straight pipe, longer than 120 pipe diameters, are employed for confirming the relationship between swirl strength and pressure loss. Wall-pressure measurements are performed. An equation for pressure loss of swirling flow in a straight pipe which considers pressure loss influenced by the swirler, swirl and pipe friction is proposed by the author. The ratios of each types of pressure loss to the total loss are ascertained. In a straight pipe with a guide vanes type of swirler, inlet length is about 15 pipe diameters. Pressure loss in the transitional region where swirl effect remains decreases and the ratio of pipe friction loss to the total loss increases according to swirl decay.

View full abstract

Heat-island phenomenon is commonly observed around megalopolises. As most of the megalopolises locat near coastal lines in Japan, the heat-island is closely influenced by the see breeze. Recently some researchers indicate that the characteristics of the see breeze has changes due to the influence of the heat-island in some area. In this study, we examined the AMeDAS temperature data set and carried out the numerical simulation using the three dimensional model (HOTMAC) to discuss the heat transport and the interaction between the heat-island and the see breeze in the Osaka Plain.

View full abstract