The preferred mode of incompressible jets: linear frequency response analysis

Xavier Garnaud (1) , Lutz Lesshafft (1) , Peter Schmid (1) , Patrick Huerre (1)

1 LadHyX - Laboratoire d'hydrodynamique

The linear amplification of axisymmetric external forcing in incompressible jet flows is investigated within a fully non-parallel framework. Experimental and numerical studies have shown that isothermal jets preferably amplify external perturbations for Strouhal numbers in the range 0.25 ≤ StD ≤ 0.5, depending on the operating conditions. In the present study, the optimal forcing of an incompressible jet is computed as a function of the excitation frequency. This analysis characterizes the preferred amplification as a pseudo-resonance with a dominant Strouhal number of around 0.45. The flow response at this frequency takes the form of a vortical wavepacket that peaks inside the potential core. Its global structure is characterized by the cooperation of local shear-layer and jet-column modes.

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

Xavier Garnaud, Lutz Lesshafft, Peter Schmid, Patrick Huerre. The preferred mode of incompressible jets: linear frequency response analysis. Journal of Fluid Mechanics, 2013, 716, pp. 189-202. ⟨10.1017/jfm.2012.540⟩. ⟨hal-00756811⟩