Spread of Buoyant Jets at the Free Surface

A study is made of the surface spread which occurs when a jet of fluid is discharged at depth into a fluid of greater density. The method of synthesis is used to relate the rate of spread to the conditions obtaining at the point where the jet plus entrained fluid flow reaches the free surface. It is explained how these conditions can be related to the initial conditions at the nozzle by means of dilution diagrams. Experiments are described, which confirm the correlation obtained and also provide the basis of a working diagram for rate of spread. The shape of the curves of this spread diagram are explained and it is shown how the curves can safely be extrapolated, in one direction, into the working prototype range. The spread diagram can be used firstly, as a means of predicting spread, and secondly, as a design diagram for choosing scales for hydraulic models. The method for choosing scales is outlined by an illustrative example and the difficulties of incorporating a nozzle in the model to reproduce a prototype spread are emphasized.