Comparison of the near-field flow structures of a triangular jet with and without the initial confinement of a chamber

This paper reports a large eddy simulation (LES) of the precession-like oscillation produced by partially confining a triangular-jet flow with a short cylindrical chamber. The present LES, which has been verified by previous experimental data, shows that there is a strong inward swirl around the jet near the inlet end of the chamber. At the center of the swirl, there is a cluster of three sink foci, where each focus is aligned midway between the corners of the triangular inlet orifice. In the time-averaged flow field, the vortices rising from the foci are helically twisted about the core of the jet. As the flow passes through the chamber, the foci merge to form a closed-loop bifurcation line which separates the inward swirl and the core flow. The core of the emerging jet is visible as a source node at the approximate centerline of the chamber. If the chamber is removed, a cluster of six counter-rotating foci is produced in the free jet. When this happens, the net swirl circulation is zero and there is no jet oscillation.