Absolute and convective instabilities of a swirling jet/wake shear layer

Thomas Loiseleux (1) , Ivan Delbende (1) , Patrick Huerre (1)

1 LadHyX - Laboratoire d'hydrodynamique

The absolute (AI)/convective (CI) nature of the instability is determined in the family of swirling jet/wake shear layers considered by Martin and Meiburg [Phys. Fluids 6, 424 (1994)] and Lim and Redekopp [Eur. J. Mech. B/Fluids 17, 165 (1998)]. This idealized model includes as essential ingredients both the centrifugal instability associated with the swirl difference and the Kelvin-Helmholtz instability associated with the swirl and axial velocity differences between the core and the outer flow. Centrifugally stabilizing or destabilizing swirl differences are found to promote AI, but a centrifugally destabilizing configuration is more effective in triggering such a transition. For sufficiently large swirl differences, both co-flowing jets and wakes may become AI. In the case of jets, a centrifugally destabilizing swirl difference first brings about AI via the axisymmetric mode m=0 in a large range of mean swirl values. By contrast, a centrifugally stabilizing swirl difference triggers AI via the helical mode m=-8. In the case of wakes, a centrifugally destabilizing swirl difference leads to AI via the bending mode m-1 whereas a centrifugally stabilizing swirl difference triggers AI via various negative helical modes m=-1,-2, etc. © 2000 American Institute of Physics.

Domaines: Mécanique des fluides [physics.class-ph]; Mécanique des fluides [physics.class-ph]

Thomas Loiseleux, Ivan Delbende, Patrick Huerre. Absolute and convective instabilities of a swirling jet/wake shear layer. Physics of Fluids, 2000, 12 (2), pp.375-380. ⟨10.1063/1.870315⟩. ⟨hal-01025355⟩