Entrainment by a plume or jet at a density interface

Abstract

The rate of entrainment through the end of a plume or jet which impinges on a density interface has been determined in the laboratory, where the interface was produced by layers of fresh and salt water and the plume by a salt-water source. Observations of the impingement area indicated that entrainment was confined to a region about the size of the plume cross-section. It was thus concluded that the entrainment flux into the plume must be a function of the local width, velocity and buoyancy difference, and these can be combined into a single para- meter, the Froude number. Measurements of the volume flux showed it to be proportional to the cube of the Froude number. The flux of buoyancy from the salt-to fresh-water volumes is consequently proportional to the Froude number. In the second part of the study the density distribution in the initially fresh layer was derived and is verified by the experiments. This distribution has direct applications in the analysis of convective motions in the atmosphere and the ocean.