An investigation into the structure of a turbulent plane jet.

Abstract

An experimental investigation into the structure of the plane jet in a moving airstream has been made. The majority of the measurements have been made in a jet exhausting into a slow moving airstream providing an example of a possible self-preserving flow. The experiments showed that the flow does, in fact, become self-preserving at distances downstream from the jet nozzle of thirty jet nozzle width. The distributions of the turbulent intensities across the jet in the self-preserving region of the flow are shown to be similar to those found in the plane wake. However, the turbulent energy balance for the two flows appears to be quite different. Some measurements of the eddy structure indicate that shear carrying eddies are among the largest eddies in the flow and are also partly responsible for the intermittency phenomenon. The unsteady irrotational flow outside the jet is shown to be adequately described by the theories of Phillips (1955) and Stewart (1956). Some comments are made on the applicability of the various simple theories of turbulence to the plane jet and the interesting, though not necessarily significant, point emerges that the Prandtl Mixing Length theory gives the beat description of the flow structure. Additional measurements in jets in fast moving airstreams show that the change from a jet to a wake type of turbulence structure takes place at a very slow rate. Several simple theories were developed to account for the spread of a plane jet in a moving airstream but none of then proved wholly adequate. Apart from the main investigation, some work on the problem of measurements in a turbulent flow in discussed. Aspects of both hot wire anemometer theory and static pressure measurements are re-appraised.