Identification of Flap Side-Edge Two-Source Mechanism Based on Phased Arrays

The airflow past flap side edges is an important contributor to airframe noise. It has been found that the dominant features of the flow at the flap side edges are the double-vortex structures and the far-field noise features as two humps in the noise spectrum. Flap side-edge noise is commonly assumed to be linked to the double-vortex. However, whether the two humps in the noise spectrum are directly related to the double-vortex has not been fully confirmed. In this study, the flap side-edge noise sources are computed and analyzed based on phased microphone arrays. The CLEAN based on Source Coherence method is applied to the airframe noise benchmark test DLR1. It is shown that the acoustic sources have different frequencies and amplitude scaling laws in low-and high-frequency ranges. In contrast to existing studies, this study demonstrates that the high-frequency spectrum follows the Helmholtz number scaling law rather than the Strouhal number scaling law. Furthermore, the source strength distributions indicate that low-frequency noise sources are mainly located on the aft half-chord of the flap side edge, and high-frequency noise sources are located on the forward half-chord. Finally, two subregions at the flap side edge are identified as source locations for the low and high frequencies, respectively. The two-source noise mechanism revealed in this study will aid the establishment of a physics-based flap side-edge noise prediction model.