Intermittent and stochastic characteristics of slat tones

Experiments were conducted to assess the aeroacoustic characteristics of a 30P30N three-element high-lift airfoil fitted with two different types of slat cove fillers in the Aeroacoustic Facility at the University of Bristol. The results are presented for the angle of attack α = 18° at a free-stream velocity of U∞ = 30 m/s, which corresponds to a chord-based Reynolds number of Rec = 7 × 105. Simultaneous measurements of the unsteady surface pressure were carried out at several locations in the vicinity of the slat cove and at the far-field location to gain a deeper understanding of the slat noise generation mechanism. The results were analyzed using a higher-order statistical approach to determine the nature of the broadband hump seen at low frequencies for the 30P30N high-lift airfoil observed in recent studies and also to further understand the tone generation mechanism within the slat cavity. Intermittent events induced by the resonant mechanism between the slat and its trailing edge were investigated in detail. A series of correlation and coherence analysis of the unsteady surface pressure measurements was carried out to identify and isolate the low-frequency hump. A wavelet analysis was performed to investigate the nature of the slat-wing resonant intermittent events in both time and frequency domains. Novel approaches, dynamic mode decomposition, and multi-resolution dynamic mode decomposition were applied to the wavelet coefficient moduli to determine the nature of the noise.