Transitions to chaos in the wake of an axisymmetric bluff body

Abstract

To cite this version:Yannick Bury, Thierry Jardin. Transitions to chaos in the wake of an axisymmetric bluff body. Physics Letters A, Elsevier, 2012, vol. 376, pp. 3219-3222 AbstractThis letter aims at understanding the dynamical process that leads to the onset of chaos in the flow past a blunt-based axisymmetric bluff body. On the basis of direct numerical simulations, conducted for Reynolds numbers ranging from 100 to 900, we show that the flow undergoes multiple transitions, successively giving rise to the SS, RSP a , RSP b , RSP c and RSB wake states. In particular, the RSP c state, revealed in this work via long-term computations, is characterized by intermittent vortex stretching denoting the onset of chaos before the symmetry breaking and the occurence of the RSB state.

Low-dimensional dynamics of a turbulent axisymmetric wake

“…The intensity of the axisymmetric pulsation increases as the axis of the body is approached. The frequency and shape of this mode is very close to the low frequency oscillation of the wake observed by Bohorquez et al (2011) and Bury & Jardin (2012) for a body of similar geometry in the transitional regime at low Reynolds numbers.…”

“…Beyond the second critical Reynolds number, Bury & Jardin (2012) identified a second mode with a frequency lower than the natural shedding frequency and which dominates the drag fluctuations. Bohorquez et al (2011) also reported a second peak appearing in the spectra of the axial velocity component at a frequency approximately one quarter of the shedding.…”

“…The flow past blunt-based axisymmetric bluff bodies has been considered in various direct numerical simulations (Sanmiguel-Rojas et al 2009;Bohorquez et al 2011;Bury & Jardin 2012). These studies showed that the wake undergoes two successive bifurcations at low Reynolds numbers from an axisymmetric steady state.…”

“…For larger Reynolds numbers, a Hopf bifurcation with m = ±1 leads to unsteady flow characterised by the shedding of streamwise-oriented, alternating hairpin-like vortices; the flow preserves the reflectional symmetry due to the eccentricity of the vortex shedding. The threshold of the bifurcations depends on the length-todiameter ratio of the body, L/D; for a body with L/D = 7, these regimes were observed at Reynolds numbers close to 450 and 590 (Bury & Jardin 2012).…”

“…During the chaotic regime the reflectional symmetry is broken; however, phases of reflectional symmetry whose flow topology resembles that of the reflectional symmetric state are randomly interrupted by dramatic changes of the azimuthal position of the symmetry plane (Bury & Jardin 2012). The reflectional symmetry plane exists in an instantaneous sense, but it is randomly and intermittently re-oriented on a very long time scale.…”