Reduction of Vortex-Driven Oscillations in a Choked Duct Through Active Control

Abstract

The effectiveness of active control schemes for the reduction of vortex-driven instabilities is demonstrated using an experimental setup consisting of a non-reacting primary flow of air, where both the duct exit and inlet are choked. Two plates produce the vortex-shedding phenomenon at the duct’s first longitudinal mode. The potentially damaging low-frequency instabilities that arise when vortex-shedding frequencies couple with the natural acoustic modes of a choked duct are controlled using a secondary injection method, consisting of pulsing compressed air. A dynamic pressure transducer placed near the chamber exit allows to feed back the information needed to implement a closed-loop control scheme which effectively modifies the phasing of the secondary flow. The proposed approach was proven to be an effective means of reducing the problematic instabilities providing a 66% reduction in the FFT RMS amplitude when utilizing a Proportional-Derivative controller.