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Self-sustained oscillations of open cavity flows: when the inner flow dynamics couple to the shear-layer oscillations
Luc Pastur, François Lusseyran, Jérémy Basley, Christelle Douay

Last modified: 2018-04-11


Flows past open cavities are known to exhibit tonal features at well-dened frequencies driven by the velocity U  and the cavity length L, following Rossiter's semi-empirical model [5]. In the incompressible regime, such striking spectral features are the result of a global instability that makes the steady base flow unstable with respect to self-sustained oscillations, via a super-critical Hopf bifurcation [2, 6]. In experiments, however, the oscillations are never perfectly monochromatic and always undergo amplitude and/or frequency modulations. Part of the modulation is due to the inner-cavity recirculation, that brings information back to the shear-layer and couple to it [7]. It has been recently discovered that the lowest broad-band frequencies that modulate the envelope find their origin in the dynamics that develop in the inner-flow [1, 3].

A closer look at the inner flow dynamics indeed reveals the spanwise formation of slowly evolving alleys of streamwise vortical structures that swirl around the main recirculating flow. Such patterns appear at Reynolds numbers much smaller than the critical values usually observed for the shear-layer self-sustained oscillations [4].

In this contribution, we present the compilation of a decade of experimental investigations on both the shear-layer oscillations and the inner-flow dynamics, together with their dynamical coupling, in incompressible open cavity flows.


cavity flows; instabilities

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