Slat Noise Control Using a Slat Gap Filler

The leading edge slat of a high-lift system is one of the main noise contributors on many commercial aircraft during approach. This paper continues our previous studies on the gap filler for passive noise control on the 30P30N high-lift airfoil. An improved implementation of the gap filler was applied to minimize the effects of flow leakage encountered in the previous work, which resulted in spurious noise content in the far-field acoustic spectra. To evaluate the effect of passive flow control on the acoustics generated by the unsteady flow field, anechoic wind tunnel experiments are conducted on the two-dimensional, three-element high-lift airfoil with a gap filler mounted to the slat. The slat geometry modification associated with the gap filler alters the flow field in the cove region that dominates the generation of the acoustic field. A single angle of attack (훼푘=8◦) and three flow speeds corresponding to Reynolds numbersof푅푒푐=1.2푒6,1.5푒6, and1.71푒6are selected as the test conditions. Steady surface pressure measurements are conducted to assess the effect of the treatments on the overall lift. Acoustic array measurements are used to evaluate the influence of the gap filler on the radiated noise. Delay and Sum beamforming is applied to locate the noise sources on the model and to provide the integrated spectra. The gap filler is found to eliminate the narrowband peaks in the acoustic spectra and, also, to yield a 10 dB reduction in the broadband noise in comparison with the baseline case. Time-resolved Particle Image Velocimetry results show that the flow features are significantly altered with the presence of the gap filler, which leads to a more stable slat cove shear layer and, thus, to weaker pressure and velocity fluctuations.