LES of bifurcation and hysteresis in confined annular swirling flows

This paper presents a LES based study of two swirling confined jet configurations corresponding to an aeronautical injection system. The objectives are to demonstrate that LES codes become sensitive to numerical parameters (grid, SGS model) in such cases and that this is due to the fact that these flows are close to bifurcating conditions because of the presence of swirl and confinement walls. To demonstrate this, in the first configuration ('full swirler'), the swirler/plenum ensemble is computed while only the swirler without plenum is computed in the second ('adjustable swirler'): this simplification allows to vary swirl continuously and explore bifurcation diagrams where the control parameter is the mean swirl number. These numerical results are compared to a similar study performed experimentally by Vanierschot and Van den Bulck (2007) [1]. They confirm that certain confined swirling flows are intrinsically submitted to bifurcations. In the context of LES this leads to a large sensitivity of the simulation results to numerical parameters, a property which is not observed in most other non swirling or non confined situations.