Review—Self-Sustaining Oscillations of Flow Past Cavities

TLDR

Unstable flow past cavities is classified into fluid‑dynamic, fluid‑resonant, and fluid‑elastic oscillations, driven by shear‑layer instability, resonance with compressibility or free‑surface waves, and solid‑boundary elasticity, respectively, and these oscillations influence mean cavity pressure, drag, and shear‑layer characteristics. The review discusses experimental data and theoretical models for the frequencies and amplitudes of these oscillations, examines how cavity arrangements and shapes affect them, and summarizes attenuation strategies through geometry changes and mass addition.

Abstract

Unstable flow past cavities is grouped into fluid-dynamic, fluid-resonant, and fluid-elastic categories. Fluid-dynamic oscillations are attributable to instability of the cavity shear layer and are enhanced through a feedback mechanism. Fluid-resonant oscillations are governed by resonance conditions associated with compressibility or freesurface wave phenomena. Fluid-elastic oscillations are primarily controlled by the elastic displacements of a solid boundary. Experimental information and theoretical models for the frequencies and amplitudes of each of these categories of oscillations as well as a combination of them are discussed in detail. Effects of arrangements of cavities in groups and variations in cavity shape (rectangular, circular, triangular, whistle-type, Helmholtz-type) are reviewed. Means of attenuation of oscillations via geometrical modifications and mass addition are summarized. Finally, the effects of cavity oscillations on the time-mean cavity pressure, drag, and shear-layer characteristics are discussed.