Experiments on Flow at a 90° Open-Channel Junction

Although open-channel junctions are common in many hydraulic structures, no comprehensive data set has been compiled that describes the 3D flow field within the junction itself. This physical model study examined a 90°, sharp-edged, open-channel junction for channels of equal width. Depth measurements were made using a point gauge while velocity measurements were taken using an acoustic doppler velocimeter over a grid defined throughout the junction region. The average velocity and turbulence intensity were calculated from a time series of velocities that was recorded at each location. In addition, a 2D mapping of the water surface was performed on a 76.2 mm square grid throughout the channel junction. This paper presents the details of the experimental procedure and the general flow characteristics observed. The full data set generated during this experimental work is available for downloading on the Internet. Using a small portion of the data recorded, an evaluation of several previously proposed theories of combining flow in open-channel junctions is presented. This has revealed that the simplified mathematical model gives reasonable prediction of the experimental results. The complete data set describing combining flows at a 90° open-channel junction is presented as a resource for the validation of 3D computational fluid dynamics codes that utilize a free-surface model.