Frequency selection in time-dependent open flows

This paper studies the process by which open flows select a global frequency of oscillation. Two model systems are presented: the canonical flow past a circular cylinder; and the flow over an open rectangular cavity. The method used is a global linear stability analysis of the time-mean flow. For both the model systems, this method is shown to very accurately capture the saturated global frequency of the flow, even at Reynolds numbers far beyond that at which the flow becomes unsteady. Additionally, the time-mean flow in both systems is shown to be close marginally stable over a wide range of Reynolds numbers, an important finding in the effort to understand the nonlinear saturation process