Noise correlation analysis between near-field fast-pressure sensitive paint and far-field microphone measurements for high-speed dual-impinging jets

This study experimentally investigated the unsteady pressure fluctuations caused by high-speed dual-jet impingement and the resulting far-field acoustic pressure, focusing on the correlation patterns between near-field and far-field pressure fluctuations and the mechanisms behind the formation of impingement tones on the obstacle. Fast-responding pressure-sensitive paint (fast PSP) measurements were performed on dual-impinging jets with varying impinging distances (h/D = 2–10, where D is the nozzle exit diameter), Mach numbers (M = 0.8–1.2), and a fixed nozzle separation distance (S/D = 3.5). Far-field acoustic signals were synchronously measured with the PSP using an array of eleven acoustic sensors. Three distinct impingement types were identified: stable impingement pattern (which can be further divided into single-frequency tone-dominated and multi-frequency tone-dominated), underdeveloped impingement pattern, and unstable impingement pattern. It was revealed that the primary distinction between these impingement patterns lies in the relative strength of pressure fluctuations in the jet core region and the dual-jet interference region. Coherent output power analysis was employed to link the near-field impinging pressure fluctuations to the far-field acoustic pressure fluctuations and to identify the sources of impingement tones on the obstacle. The direct impact of the jet core on the obstacle, the interaction between the wall-jet and the obstacle, and the interference between wall jets were found to be the three main mechanisms responsible for the formation of impingement tone sources.