Active control of flow-induced cavity resonance

TLDR

Flow‑induced cavity resonance produces large‑amplitude tones, and while passive suppression works only at a single operating point, active control offers adaptive mitigation across varying conditions. The study investigates active control of flow‑induced cavity resonance at low Mach numbers. The authors test deep (Z/D = 0.5) and shallow (L/D = 2.0) cavities using piezoelectric actuators mounted as an active segmented flap at the upstream separation edge. Uncontrolled tones arise from the interaction between the cavity’s forced acoustic response and shear‑layer amplification, and both open‑ and closed‑loop control suppress the resonance by up to 20 dB, with closed‑loop requiring an order‑of‑magnitude less power while leaving the mean shear‑layer velocity unchanged but reducing velocity fluctuations.

Abstract

Flow-induced cavity resonance is characterized by large amplitude tones in and around the cavity. While passive suppression techniques can be optimized for a single operating condition, their performance often degrades at offdesign conditions. Active control is attractive because of its potential to adapt to different operating conditions without significant performance degradation. This paper describes an investigation of active control of flow-induced cavity resonance at low Mach numbers. Attention is focused on a deep (Z/D=0.5) and a shallow cavity (L/D=2.0). For the uncontrolled cases studied, the evidence indicates that the tones generated by low Mach number flow over a cavity are the result of an interaction between the forced acoustic response of the cavity and the amplification of feedback disturbances by the shear layer. Active control is accomplished with piezoelectric actuators implemented as an active, segmented flap at the upstream separation edge. Both open- and closed-loop control suppress the tone associated with the flow-induced resonance, resulting in SPL reductions of up to 20 dB. However, the closed-loop control requires one order-of-magnitude less power. In both cases, the mean shear-layer velocity profile is unaffected by the control input, while the velocity fluctuations undergo significant changes.