Mechanics and correlations of flow phenomena in intersecting ducts

Three kinds of experiments are conducted to determine flow characteristics inside two intersecting square ducts: flow visualization by means of the dye injection, hydrogen bubble and string methods, velocity measurement using the laser Doppler anemometry, and pressure measurement using a piezometer. Angle of intersection and Reynolds number are varied. Four distinct flow regimes are disclosed: entrance, initial centrifugal, intersecting and final centrifugal regions. The geometrical dividing line in the intersection zone of the two ducts forms a flow divider separating the flow network into two independent, symmetrical flow units. Each flow unit constitutes a curved passage with a radius of curvature whose magnitude varies with the angle of intersection. Hence, the secondary effects prevail in each unit, resulting in complete flow mixing. The mechanisms disclosed by the flow visualization and LDA methods are supported by the quantitative results from the piezometer measurements. The string method discloses an important evidence that the intersecting zone promotes turbulence. A location of the maximum energy grade and minimum hydraulic grade is disclosed on the flow divider where the surrounding streamlines congregate and disperse.