Characteristics of swirling and precessing flows generated by multiple confined jets

Abstract

An experimental study is reported of the interaction between multiple isothermal jets within a cylindrical chamber under conditions relevant to a wide range of engineering applications, including the confined swirl combustors, industrial mixers, and concentrated solar thermal devices. The particle image velocimetry technique was used to investigate the swirling and precessing flows generated with four rotationally symmetric inlet pipes at a fixed nozzle Reynolds number of ReD = 10 500 for two configurations of swirl angle (5° and 15°) and two alternative tilt angles (25° and 45°). The measurements reveal three distinctive rotational flow patterns within the external recirculation zone (ERZ) and the central recirculation zone (CRZ) for these configurations. It was found that the mean and root-mean-square flow characteristics of the swirl within the chamber depend strongly on the relative significance of the ERZ and CRZ, with the swirling velocity being higher in the CRZ than that in the ERZ. A precessing vortex core was identified for all experimental conditions considered here, although its significance was less for the cases with a dominant CRZ.