Aeroacoustic analysis of slat tones

Experimental measurements were carried out to assess the aeroacoustic characteristics of a 30P30N high-lift device, with particular attention to slat tonal noise. Three different types of slat modifications, namely slat cove filler, serrated slat cusp, and slat finlets have been experimentally examined. The results are presented for an angle of attack of α = 18 at a free-stream velocity of U = 30 m/s, which corresponds to a chord-based Reynolds number of Re = 7 x 10. The unsteady surface pressure near the slat region and far-field noise were made simultaneously to gain a deeper understanding of the slat noise generation mechanisms. The nature of the low-frequency broadband hump and the slat tones were investigated using higher-order statistical approaches for the baseline 30P30N and modified slat configurations. Continuous wavelet transform of the unsteady surface pressure fluctuations along with secondary wavelet transform of the broadband hump and tones were carried out to analyze the intermittent events induced by the tone generating resonant mechanisms. Stochastic analysis of the wavelet coefficient modulus of the surface pressure fluctuations was also carried out to demonstrate the inherent differences of different tonal frequencies. An understanding into the nature of the noise generated from the slat will help design the new generation of quite high-lift devices.

Three-Dimensional Simulation Analysis of the Influence of Slat Structural Parameters on Slat Aerodynamic Noise

Slat aerodynamic noise is one of important components of the frame noise. Adjusting the parameters of the slat structure can suppress the slat noise radiation effectively. Based on the typical multi-element airfoil 30P30N, firstly, by means of adjusting the parameters of slat structure, such as changing relative positions between slat and main airfoil and closing slat gap etc., a new slat profile is obtained; Then, based on the DDES simulation method, the characteristics of vortex distribution is analyzed for the new airfoil structure model, and the directivity and SPL of the far field noise are also investigated; Finally, through comparison analysis of the parameters, the physics of the generation of slat aerodynamic noise is discovered, and effects of slat parameters on the features of slat aerodynamic noise are also obtained. The results of the study show that the vortex strength of the flow around the slat has close relation to the source of slat noise. By means of adjusting slat position parameters and morphing of the slat's trailing edge, the vortex strength of the flow close to the slat cusp is reduced effectively, and further largely reducing the slat noise radiation, which can be achieved with preserving high lift coefficient of the airfoil.