Modification of a Broadband Engine Noise Simulator for Enhanced Aft Fan Noise Representation

Modifications to an existing broadband noise source (BNS) model were tested in the anechoic chamber of the Structural Acoustics Loads and Transmission (SALT) facility at the NASA Langley Research Center with the goal of simulating the aft fan broadband noise produced by a high-bypass ratio turbofan engine. High geometric-resolution acoustic measurements, spanning a hemisphere in the acoustic far field, were acquired using the High Resolution Traversing Microphone Array (HiRTMA). Modifications included additively manufactured waveguides that attached to the existing BNS hardware to create a converging-diverging channel around a new plug to guide sound waves towards the desired peak radiation direction. An investigation was also performed of the isolated impinging air jet noise sources housed in the BNS to better understand the noise generation mechanisms. The optimum BNS configuration preserved the acoustic directivity observed for the isolated impinging jet and showed good agreement to published models for aft fan broadband noise.