Entrainment by Buoyant Jet between Confined Walls

Quasi-two-dimensional turbulence was investigated experimentally in an apparatus consisting of two closely spaced vertical parallel walls. A jet of salt water was injected downward between the walls. Entrainment of fluid by the turbulence produced an expanding buoyant jet that was many times wider than the wall spacing. Photographs were taken of the turbulent motion in the confined region. The volume flux in the plume was measured using a direct method for a range of source flow from the limit of a jet to that of a plume. The variation of volume flux with distance in the plume followed closely the relationship derived using a linear spreading hypothesis. Despite the anisotropic nature of the turbulent motion and the frictional retardation of the plume by the walls, the spreading rate of the confined plume was remarkably similar to that of a line plume, which is a two-dimensional flow. Flow visualization revealed significant differences in the turbulent structures for cases of jet and plume.