In the mixing of a jet with a cross-stream, it is found that in the near field, defined as the region of the flow from the jet exit to a distance of a few diameters downstream of this exit, a considerable amount of dynamical adjustment takes place. This near-field region characterizes the subsequent behaviour and development of the jet, its wake and the cross-stream in the vicinity of this mixing region. The rapid evolution of the flow gives rise to a pair of bound vortices attached to the lee side of the jet boundary, to fast development of the turbulent and mean vorticity, to a vortex-shedding system, and to the largest rates of entrainment of cross-stream flow into the jet. Furthermore, it is found that the geometrical configuration of the boundaries at the jet exit plays an important role in the mixing and development processes.An intrinsic method is proposed for the delineation of the flow boundaries between the jet and the cross-stream. Calculations of mass, momentum and vorticity fluxes have been made. The vorticity flux gives evidence of the rapid stretching and tilting of the vorticity vector field in the near-field region.

An analytic solution for the velocity field of a vortex street generated in a viscous fluid is developed. A method is presented for the determination of the true transverse spacing of vortices. Experimental geometry and velocity data, obtained by hot-wire techniques, are presented.The experimental results verified the validity of the analytic solution. The vortices of a real viscous vortex street were found to resemble very closely the exponential solution of the Navier-Stokes equations for an isolated axisymmetric rectilinear vortex. Three basic regions of vortex street behaviour were apparent at each Reynolds number investigated-a ‘formation region’ in which the vortex street is developed and large dissipation of vorticity occurs, a ‘stable region’ in which the vortices display a stable periodic laminar regularity, and an ‘unstable region’ in which the street disappears and turbulence develops. Geometry and velocities were determined.

The wall-jet is the flow of fluid emanating from a narrow slot and blowing over a rigid wall. The configuration of the turbulent wall-jet is that of a very narrow, plane, turbulent half-jet investigated by Liepmann & Laufer (1947). The width of the slot is of the order of the boundary layer on the infinite wall and the jet, in this case, mixes with a stream moving with constant velocity. This flow has drawn considerable basic and applied interest in the past few years for it has the characteristics of both a boundary-layer and a free-mixing flow.

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Measurements of local mean aerosol concentration were made with a hot-wire anemometer and a special circuit including an electronic filter and counter. The concentration distribution of the liquid phase in a plane jet of air was measured and an analysis of the diffusion process is given and compared with the experiments. From the measurements the mass diffusivity of the liquid in the turbulent air is determined.