Perturbation energy extraction from a fluid via a subsurface acoustic diode with sustained downstream attenuation

Abstract

Engineered subsurface structures inspired by phononic materials have shown favorable capabilities in flow control. Current efforts rely on tuning a structural resonance to the frequency of an unstable fluid mode, causing the deformations of the interfacing solid to destructively interfere with a wave-like flow instability. Although promising, the technique is most effective at targeting a single frequency mode with high-Q resonance. Additionally, several studies have shown the reduction in the perturbation energy to be spatially localized to the flow region above the subsurface strip, with a severely worsening effect downstream. Motivated by a desire to overcome these limitations, we present a different approach to methodically extract an undesirable pressure disturbance from a fluid column in a manner that capitalizes on the broad frequency range of a phononic bandgap, with the goal of permanently confining the perturbation energy within the subsurface structure. An acoustic diode (AD), i.e., a unidirectional transmitter of mechanical energy, comprised of a bi-layered phononic crystal and an auxiliary medium, interacts with a fluid cavity and provides a terminal energy sink. Two distinct ADs are presented that demonstrate active (time-variant) and passive (strain-dependent) paths to concept realization. The AD’s performance is described in terms of the time-transient energy distribution in the fluid and the interacting structure, as well as spatial wave profiles at critical time instants. The results show the system’s ability to achieve robust extraction of undesirable fluid oscillations with minimal residual energy. The concept is then tested in a fully developed plane channel flow with a superimposed perturbation, demonstrating the sustained nature of the subsurface AD’s energy trapping mechanism in addition to its ability to induce downstream attenuation.