BUOYANT PLUMES FROM MULTIPORT DIFFUSER DISCHARGE IN DEEP COFLOWING WATER

An experimental study of the central portion of a unidirectional multi port diffuser discharging in the direction of a uniform ambient curren t in deep nonturbulent water was conducted by means of a towed model i n a laboratory tank. The trajectories of the two-dimensional plane plu mes that result after merging of the individual jets can be divided in to weakly deflected plumes (F-a < 0.60), with upstream spreading upon surface interaction, and strongly deflected plumes (F-a > 1.0), with a n intermediate range that contains an upstream blocked wedge. The domi nant parameters F-a is an ambient/discharge Froude number, F-a = u(a)/ j(o)(1/3), where u(a) is the ambient current and j(o) is the two-dimen sional buoyancy flux per unit diffuser length. In each plume regime th e plume trajectory is a straight line, but with a distinctly different functional dependence of the trajectory slope on F-a. For the strongl y deflected case, the plume behavior, its rate of rise, its tendency t o attach to the bottom, and the distance for merging of the individual jets, also depend on the detailed three-dimensional diffuser geometri c characteristics, including port spacing and port height. A ''leakine ss parameter'' has been defined that characterizes these three-dimensi onal influences, in particular the ability of the ambient how to pass through the merging diffuser flow field and allow the diffuser plume t o stay aloft downstream. This behavior is different from earlier slot diffuser experiments by Cederwall (1971) and Roberts (1979) with zero leakiness in which a fully mixed, bottom-attached plume was observed.