Hirotake Imamoto

Flow visualization in a transverse cross section of an open-channel flow

Abstract Secondary flow is of prime importance in investigations of the three-dimensional structure of turbulent flow in an open channel. Since Nikuradse showed the influence of secondary flow on the velocity distribution in a cross section and Prandtl discovered that there are two kinds of secondary flows, many researchers have investigated these flows experimentally or theoretically. Because mean values were obtained by velocity measurements, secondary flow was elusive because of its intermittent production and instability. Flow visualization is an effective technique for observing the three-dimensional motion of flow. In this paper, a direct way of visualizing the instantaneous motion of secondary flow in an open channel is shown and the characteristics of the flows are investigated.

Visualization of longitudinal eddies near the edge of a flood plain in an open channel flow

Tracer method was used to visualize longitudinal eddies near the edge of a flood plain in an open channel flow. Neutral particle tracers were illuminated by a laser light sheet which was obtained from a 5mW He-Ne gas laser. Set the laser light sheet on a cross section, a vertical section or a horizontal section, pass lines of neutral tracers were observed by a 35 mm still camera or a video camera. Many attractive pictures were taken by a moving camera or a fixed one. Based on these pictures, the three dimensional model of longitudinal eddies near the edge is illustrated.