A round jet in an ambient co-axial stream

Abstract

Measurements were made of the mean velocity profiles in a jet immersed in a stream whose velocity was in the same direction as that of the jet. They showed a mean velocity on the jet axis falling inversely as the distance downstream of the jet origin, a behaviour demonstrably inconsistent with any theory which assumes that the turbulence at each section of the jet is in local equilibrium. A mixing length, L_M, and a length, L_d, characterizing the rate of dissipation are defined and it is shown that L_M increases with distance downstream more rapidly than the jet width, and L_d less rapidly.