Experimental Analysis of Surface-Pressure–Driven Far-Field Noise in Impinging Jet Flows

This study presents an experimental investigation of the aeroacoustic characteristics of subsonic impinging jets interacting with normal and inclined plates for acoustic Mach numbers Ma=0.48, 0.67, and 0.86. Simultaneous far-field acoustic measurements and near-field surface-pressure measurements were conducted to quantify how plate inclination and axial placement modify sound generation and radiation. The far-field spectra show that the noise is dominated by turbulent mixing without evidence of screech tones or broadband shock-associated noise. The most intense radiated sound occurs when the plate is positioned near the end of the potential core at x/d = 6.33 (d denotes the nozzle outlet diameter), where geometric redirection and impingement-generated radiation combine to produce strong off-axis acoustic levels that grow systematically with increasing plate inclination. The corresponding surface-pressure measurements reveal similarly amplified fluctuations on the inclined plate at x/d = 6.33, where the stagnation point shifts from x'/d = 0 (plate center) to x'/d = 5 (toward the plate downstream edge) and the wall loading is dominated by small-scale, high-frequency shear-layer and impingement-region dynamics. These spatial and geometric conditions produce the strongest coupling between near-field pressure fluctuations and the radiated sound field. The combined measurements provide a unified description of how wall-pressure dynamics and acoustic radiation are jointly influenced by plate orientation and placement relative to the jet potential core.