A study in the developing region of square jet

Abstract

The developing region of a turbulent square jet is investigated using high-resolution particle image velocimetry (PIV). The mean velocity and turbulence stresses are presented in various horizontal planes, along the jet centerline covering the initial region of the jet as well as the transition to the self-similar region. To study the flow structure away from the central plane, velocity measurements in two additional horizontal planes, one located halfway from the jet central plane toward the edge and the other at the edge of the square jet, are also examined. Analysis of the instantaneous velocity fields reveal the presence of an arrow-like feature in the square jet due to the higher instability generated in the jet shear layer compared with a round jet. To elucidate the imprints of the vortex structures present in the jets, a swirling strength-based vortex identification methodology is applied on a large ensemble of instantaneous velocity fields. Statistical analysis of the number of vortex cores, and their size and rotational strength in the measurement plane is undertaken. Vortex population at the edge was found to be very different compared with that in the central plane.