Analysis of noise-controlled shear-layers

Despite very similar flow-structures, the uncontrolled and controlled shear-layers of Wei & Freund¹ were found to generate radically different sound fields (a difference of up to 11dB). In this work we analyse these flows-with a view to better understanding what led to this sound reduction-using two approaches: (1) we analyse the in-flow pressure fields in the K_x - ω domain, where we find that the acoustically-matched components of the controlled flow have been reduced substantially, while the global structure remains very similar; and, (2) we use causality-correlations to study the kernel of the Lighthill solution: the spatiotemporal source-correlation fields are found to have been dramatically degenerated by virtue of very subtle changes in the controlled flow's evolution.