On fundamental instability mechanisms of nominally 2-D separation bubbles

Abstract

The instability of nominally laminar steady two-dimensional closed separation bubbles is investigated using direct numerical simulations and BiGlobal instability analysis. The canonical flat-plate case is studied in some detail. We demonstrate that large steady two-dimensional bubbles may become unsteady and shortened in the mean upon applying periodic forcing. Using BiGlobal instability analysis we demonstrate, for the first time, the generation of Kelvin-Helmholtz instabilities as solutions of the pertinent partial-derivative eigenvalue problem, without resorting to the simplifying assumptions on the form of the underlying basic state. Finally, we employ appropriate instability analysis to study the effect of periodic forcing as means of active control of separation on a trailing-edge geometry. © 2006 Springer.