Sub-cavity Induced Passive Control of Confined Supersonic Cavity Flows Across Varying Freestream Mach Numbers

TL;DR

This study investigates how sub-cavities at the front and aft walls of a confined supersonic cavity flow can passively suppress oscillations across different Mach numbers, using LES simulations and spectral analysis.

Contribution

It introduces a passive control strategy using sub-cavities to effectively reduce oscillation frequencies in supersonic cavity flows at varying Mach numbers.

Findings

Aft-wall sub-cavity most effective at Mach 2.

Front-wall sub-cavity most effective at Mach 3.

Frequency suppression of 5.45% at Mach 2 and 23.4% at Mach 3.

Abstract

The self-sustaining oscillations in cavity flows enhance fluid mixing and promote energy and momentum transport. However, the associated oscillation frequencies can amplify acoustic loading, potentially damaging surrounding structures. Hence, understanding cavity dynamics across geometries and freestream conditions and developing strategies to regulate these oscillations without compromising performance are essential. This study examines the influence of sub-cavities placed at the front and aft walls of a cavity confined by a top wall with a deflection angle of 2.29 degrees, under freestream Mach numbers 2 and 3. Large eddy simulations (LES) are performed using OpenFOAM, and unsteady pressure signals are analyzed through spectral methods. Results show that the aft-wall sub-cavity most effectively suppresses the dominant oscillation at Mach number 2, while the front-wall sub-cavity achieves greater suppression at Mach number 3. Density gradient (numerical Schlieren) and vorticity fields, normalized acoustic impedance, and global wavelet power reveal the mechanisms responsible for this attenuation. At Mach number 2, the aft-wall sub-cavity entrains mass and disrupts the convective feedback loop. At Mach number 3, the front-wall sub-cavity weakens the hydrodynamic-acoustic coupling near the leading edge, disrupting the compressibility-driven feedback. These configurations suppress dominant frequencies by 5.45 and 23.4 percent for Mach numbers 2 and 3, respectively. Cross-correlation between pressure probes and Dynamic Mode Decomposition (DMD) further confirm the mechanisms behind the observed frequency suppression