Reduction of Propeller-Strut Interaction Noise by Porosity

Propeller operation in close proximity to a strut involves interactions from multiple sources, significantly contributing to noise generation. This study aims to reduce this interaction noise by employing a porous strut as a noise mitigation strategy. The paper presents experimental measurements of far-field noise for three types of rods: two solid rods with varying diameters and one porous rod. These rods were installed both upstream and downstream of the propeller flow at various distances. The porous rod proved to be an effective noise mitigation device, demonstrating reductions in Overall Acoustic Power Levels (OAPWL) of up to 3 dB when placed downstream and up to 6dB when placed upstream of the propeller. Analysis of tonal and broadband acoustic power levels revealed that while the porous rod contributed to tonal reductions, there were instances of increased broadband noise at close distances. Analytical predictions were performed for the potential field noise source for solid and porous cylinders, which is the dominant noise source at close separation distances. A generalized framework for arbitrary mean flow is also presented to predict the potential field interactions.