Effects of confinement, impinging shock deflection angle, and Mach number on the flow field of a supersonic open cavity

Abstract

Cavities exhibit inherent self-sustaining oscillations driven by the coupling between their hydrodynamic and acoustic properties. In practical applications, cavities are often placed within confinements that introduce compression waves, significantly influencing their primary flow characteristics. The oscillations in cavities have widespread applications, such as in fuel–air mixing, heat exchangers, and landing gears. However, when resonance occurs, these oscillations can lead to structural failures. Therefore, understanding cavity oscillations under diverse geometrical configurations and flow conditions is essential. The present study examines the impact of top wall confinement on an open cavity with a length-to-depth ratio (L/D) ratio of 3 at Mach 1.71, along with the effects of varying deflection angles on flow characteristics and the influence of an increased Mach number on configurations with the highest and lowest oscillation frequencies. A three-dimensional numerical investigation is carried out, employing large eddy simulations within the OpenFOAM framework. We analyze the flow fields through the spatial variation of density over time. Fast Fourier Transformation and Wavelet Transformation reveal the frequency content from unsteady pressure signals and illustrate its evolution over time under different conditions. Additionally, reduced-order modeling provides a better understanding of the relationship between frequencies and flow structures of the cavity. Results from these analyses demonstrate that top wall confinement increases oscillation frequency, while greater deflection angles introduce Kelvin–Helmholtz instability in the flow field, reducing the frequency. An increase in the Mach number to 2, further intensifies instability, substantially affecting oscillations.