The Velocity - Distribution in a Liquid - into - Liquid Jet

The distribution of velocity in a liquid-into-liquid jet, issuing from a cylindrical tube with a tapering approach, has been measured by photographing the traces made by suspended particles, with strong illumination and a determined exposure. The results have been compared with the theory for a jet issuing from a point in an infinite plane, and it is shown that, supposing the equivalent point source to be within the orifice, good agreement is found except in the immediate neighbourhood of the orifice. An expression has been derived connecting the distance of the equivalent point source from the orifice with the Reynolds's number. This enables the loss of kinetic energy of the jet to be worked out. O R some time experiments have been in progress in the physics laboratory at University College, London, on the instability of a liquid-into-liquid jet. F I n particular, attention has been devoted to the nature of the motion produced by a periodic disturbance, acting on a fine jet of water flowing through a circular orifice into a shallow tank of water. In this connexion it is of interest to determine the distribution of velocity in the undisturbed jet, especially as comparatively little has been done experimentally on streaming without rigid walls. T h e behaviour of a laminar jet of viscous liquid has been recently worked out by Schlichting (I) on certain simplifying assumptions, of which the most serious is that the jet issues from a point aperture, giving, as it does, an infinite velocity. One of the objects of this work was, therefore, to see how far Schlichting's theory could be applied to an actual jet, issuing from a circular aperture of finite size. T h e theory has proved to be very successful in interpreting the results, and it is shown here how, with slight modification, it can be made to give the velocity everywhere except in the immediate neighbourhood of the orifice. One consequence of this work is that the loss of kinetic energy due to viscosity can be worked out.