Measurements of a confined jet

Abstract

In this paper we study the flow characteristics of an air jet issuing from a rectangular nozzle of aspect ratio 6.0 into a confined chamber. Hot-wire measurements of mean and root mean square velocities were made in the mixing layers and interaction region of the jet, at two Reynolds numbers. The results showed that the mean velocity profiles achieved approximate self-preservation almost immediately after the end of potential core. However, the self-similarity of root mean square velocity profiles was established only after a distance of 12 nozzle widths downstream of the nozzle exit. The decay rate of the confined jet was found to be almost three times less than that of square and circular free jets but was greater than that of plane free jets by 10–30% with laminar initial conditions and similar Reynolds number (<8000). The spreading rate of the confined jet was found to be quite similar to that of the plane free jets but higher than the circular and square free jets. It is deduced from the results obtained that although the confined jet is three-dimensional flow in nature, the decay rate of the confined jet follows more closely to that of a two-dimensional type of flow rather than that for a three-dimensional flow.