Influence of diametral acoustic mode on cavity flow dynamics: Zonal large eddy simulation and proper orthogonal decomposition

The influence of a diametral acoustic mode on the flow dynamics was numerically investigated for an axisymmetric cavity system with vortex-excited acoustic resonances occurring at high Reynolds numbers and low Mach numbers. The zonal large eddy simulation (ZLES) was conducted to simulate the flow-acoustic coupling fields by the first three diametral acoustic modes at their maximum resonance intensities, respectively. First, the ZLES-simulated acoustic pressure pulsations were well validated by a preliminary acoustic modal analysis and acoustic pressure measurements in the literature. Subsequently, the acoustic-driven cavity flow dynamics were comprehensively demonstrated in terms of the time-averaged flow quantities, shear layer quantities, and high-order turbulence quantities. The results demonstrated that the shear layer momentum thickness, velocity fluctuations, and Reynolds shear stresses were remarkably intensified by the strong resonances with the first and second diametral acoustic modes. Simultaneously, large-scale helical vortex tubes were formed within the cavity, yielding an intensified flow three-dimensionality. Thereafter, the dominant flow modes behind the acoustic-driven cavity flow dynamics were extracted using the data-driven proper orthogonal decomposition from the highly noisy ZLES database. It was found that the first diametral acoustic mode significantly enhanced the dominant positions of the vertical flow-oscillation mode, yielding a large-scale flapping behavior of the mainstream flow, while the second diametral acoustic mode would modulate the cavities to synchronously absorb/release the flow streaks, resulting in the alternating expansion and compression behaviors of the mainstream flow.