Entraining hydraulic jumps in two-layer flows.

This paper examines the region of rapidly varying flow in a two-layered density-stratified system. It is an extension of a previous analysis (Wilkinson & Wood, 1971) in which the theory for the case of stationary ambient fluid was developed. The analogous phenomenon in open channel hydraulics was the hydraulic jump. In density stratified flows this phenomenon is referred to as an entraining hydraulic jump, or density jump, because ambient fluid is entrained into the faster flowing layer thereby changing its density. Unlike the open channel hydraulic jump, conditions either side of the entraining hydraulic (or density), jump are not uniquely related. A density jump with given flow conditions upstream has a range of possible states which may be attained downstream. The rate of entrainment of ambient fluid into the density jump, and the conditions downstream of the jump, are determined by the downstream control and the upstream conditions. This project is an extension of this work to the case where the ambient fluid is in motion. The analytical and experimental work have demonstrated conclusively that there is a large increase in entrainment as the velocity of the ambient fluid is increased. This work should not only be of fundamental importance, but will also be of considerable interest in a number of geophysical situations and could be of great importance in the mixing of wastes in rivers and estuaries