Linear global stability of two incompressible coaxial jets. (13th July 2017)

• Record Type: Journal Article
• Authors: Canton, J.; Auteri, F.; Carini, M.
• Is Part Of: Journal of fluid mechanics. Volume 824(2017)
• Page Start: 886
• Page End: 911
• Publication Date: 2017-07-13
• Subjects: absolute/convective instability, -- wakes/jets; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2017.290
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract : The linear stability of two incompressible coaxial jets, separated by a thick duct wall, is investigated by means of both a modal and a non-modal approach within a global framework. The attention is focused on the range of unitary velocity ratios for which an alternate vortex shedding from the duct wall is known to dominate the flow. In spite of the inherent convective nature of jet flow instabilities, such behaviour is shown to originate from an unstable global mode of the dynamics linearised around the axisymmetric base flow. The corresponding wavemaker is located in the recirculating-flow region formed behind the duct wall. At the same time, the transient-growth analysis reveals that huge amplifications (up to $20$ orders of magnitude) of small flow perturbations at the nozzle exit can occur in the subcritical regime, especially for high ratios between the outer and the inner velocities.