MECHANICS AND CORRELATIONS OF FLOW PHENOMENA IN INTERSECTING DUCTS

Three kinds of experiments are conducted to determine flow characteris tics inside two intersecting square ducts: flow Visualization by means of the dye injection, hydrogen bubble and string methods, velocity me asurement using the laser Doppler anemometry, and pressure measurement using a piezometer. Angle of intersection and Reynolds number are var ied. Four distinct flow regimes are disclosed: entrance, initial centr ifugal, intersecting and final centrifugal regions. The geometrical di viding line in the intersection zone of the two ducts forms a flow div ider separating the flow network into two independent, symmetrical flo w units. Each flow unit constitutes a curved passage with a ''radius o f curvature'' whose magnitude varies with the angle of intersection. H ence, the secondary effects prevail in each unit, resulting in complet e flow mixing. The mechanisms disclosed by the flow visualization and LDA methods are supported by the quantitative results from the piezome ter measurements. The string method discloses an important evidence th at the intersecting zone promotes turbulence. A location of the maximu m energy grade and minimum hydraulic grade is disclosed on the flow di vider where the surrounding streamlines congregate and disperse.