Leading Edge Blowing: A Targeted Approach to Reduce Three Types of Aerofoil Noise

This study investigates the use of Leading Edge Blowing to mitigate three distinct aerofoil noise sources: (1) trailing edge instability tonal noise, (2) large-scale separation (stall) noise, and (3) leading edge$–$turbulence interaction broadband noise. The control technique involves injecting air through orifices at the leading edge in a direction opposite to the incoming flow, generating shear instabilities that roll up into coherent vortices. These vortices evolve into streamwise vorticity arrays that extend from the leading to the trailing edge along the aerofoil surface. For noise source (1), the trailing edge separation bubble plays a key role in radiated tonal noise. Here, the streamwise vortices act as a disruption mechanism, weakening the amplification of incoming Tollmien–Schlichting waves and thereby reducing tonal noise radiation. For noise source (2), associated with the post-stall regime at high angles of attack, the mixing between the blowing jet and the main flow mitigate large-scale separation. Although there is no evidence of a complete suppression of flow separation, it is shown that even low-level blowing can significantly reduce stall noise. Finally, for noise source (3), the dominant control mechanism is attributed to a serration-mimicking effect, as previously demonstrated by Al-Okbi, Chong and Stalnov (2021).