LES of a free annular swirling jet – Dependence of coherent structures on a pilot jet and the level of swirl

The paper presents large eddy simulation of unconfined swirling jets. In the first part, an unconfined annular jet is investigated for swirl numbers ranging from 0 to 1.2. The impact of the swirl on the mean flow and the precessing vortex structures in this flow is analysed. In the second part of the paper, a co-annular pilot jet is introduced near the axis. The investigations show that the additional swirl near the axis has a stronger effect than the pilot jet itself, leading to an almost entire removal of coherent structures.