Feedback control of vortex shedding at low Reynolds numbers

Abstract

This paper describes experiments undertaken to study in detail the control of vortex shedding from circular cylinders at low Reynolds numbers by using feedback to stabilize the wake instability. Experiments have been performed both in a wind tunnel and in an open water channel with flow visualization. It has been found that feedback control is able to delay the onset of the wake instability, rendering the wake stable at Reynolds numbers about 20% higher than otherwise. At higher flow rates, however, it was not possible to use single-channel feedback to stabilize the wake - although, deceptively, it was possible to reduce the unsteadiness recorded by a near-wake sensor. When control is applied to a long span only the region near the control sensor is controlled. The results presented in this paper generally support the analytical results of other researchers.

Drag reduction of a car model by linear genetic programming control

“…The control may be based on a local linearization of the Navier-Stokes equation. Various configurations have been studied, such as boundary layer flow (Liepmann & Nosenchuck 1982;Bagheri et al 2009), circular cylinder wake (Roussopoulos 1993) and open cavity flow (Rowley et al 2006;Samimy et al 2007). However, turbulent flow is characterized by broadband frequency dynamics with complex frequency cross-talk.…”

Active vorticity control in a shear flow using a flapping foil

“…In fact, Roussopoulos (1993) has recently presented convincing evidence that, when a single sensor is used, the flow is not observable, in the sense that unsteady patterns are present without being detected by the sensor.…”

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“…However, above this threshold, single-sensor feedback may suppress the original vortex shedding mode but destabilize other modes Roussopoulos [1993]. While this approach is relatively simple to implement experimentally, the results are very limited for the absolutely unstable cylinder wake.…”