Effect of a Porous Slat Cusp on the Characteristics of Slat Noise

This paper explores the potential of porous materials in slat noise control by replacing the slat cusp with nickel–iron metal foam. Through wind tunnel tests employing a far-field microphone array and flexible thin micro-electro-mechanical-system surface microphones, the effects of the porous cusp (PC) on tonal noise and a cove flowfield are investigated. Compared to the baseline (BL) configuration, PC achieves a total noise reduction of up to 5 dB at effective angles of attack (AoA) near zero without a substantial lift loss, though it advances the airfoil’s stall AoA. PC also produces a notable shift in near- and far-field Rossiter-like tonal frequencies, implying its impact on the acoustic feedback path. Both cove wall-pressure fluctuations and acoustic integration of the cove region reveal a prominent amplitude attenuation in the fundamental mode’s frequency band. Time–frequency analysis shows that PC exhibits mode switching similar to BL, with the relative amplitudes of the primary modes, as well as the dominant mode, varying along the slat span. Higher-order spectral analysis demonstrates that PC disrupts the potential coupling of Rossiter frequencies, which contributes to the noise reduction. Coherence analysis confirms that the noise reduction is not achieved through weakening spanwise coherence.