An Experimental Investigation of the 30P30N Multi-Element High-Lift Airfoil with Porous Slat Cusp

In the process of aircraft landing, the slat as a high lift device becomes an important noise source of aerodynamic noise. In this paper, the noise characteristics and reduction methods are investigated for the MD 30P30N multi-element airfoil model with the slat cusp replaced by porous metal foam. The far-field noise characteristics were measured using two microphone arrays to obtain the directivity patterns and beamforming source maps. Using hot-wire anemometer, the average flow field data in the slat cove were obtained. A synchronized measurement of both flow field and noise data was also carried out to produce the coherence between the near-and far-fields. The far-field noise spectra of a baseline slat model contains both broadband and discrete tonal components for a range of angles of attack and the directivity is dominated by the tonal noise generated from the slat cove. The porous slat cusps have significantly weakened the main tones through modifying the geometry of the slat cove. The expansion of the cusp shear layer and the development of vortex structures are hence inhibited, which in turn attenuate the vortex impingement onto the slat wall near the trailing edge. The feedback tonal noise from the slat cove is then effectively reduced as a result of the weakened excitation of sound waves along the acoustic feedback loop.