Novel chevron nozzle concepts for jet noise reduction

Abstract

Chevron nozzles are known to be excellent attenuators of jet noise. Conventional chevron nozzles use triangular serrations at the trailing edge of the nozzle. This article proposes two novel chevron concepts and evaluates their noise reduction performance. The new chevron concepts proposed are protrusions with a sinusoidal profile and chevrons with asymmetry. These nozzles are compared against the symmetric chevron nozzle with triangular profile and a baseline circular nozzle without chevrons. The results indicate that the sinusoidal profile chevron nozzle shows better noise reduction at higher pressure ratios for all emission angles. At lower pressure ratios, the acoustic benefit is marginal due to reduced turbulent mixing of jet by low-strength vortices. Shadowgraph images of the asymmetric chevron nozzle shows bevelling due to the relieving effect in the direction of the longer chevron lobes, which reduces noise in the opposite side. This asymmetry of the noise sources and the acoustic field could be advantageously exploited in the implementations of chevron nozzles for aircraft.