The influence of chevrons on the turbulent characteristics of jets

Abstract

To minimize the significant environmental impact of air travel a reduction in noise pollution from jet engines is required. This has led to a renewed focus on active and passive techniques which modify the turbulence characteristics and hence the noise production mechanisms in the jet. One of the most prominent technologies of this type about to be implemented on commercial aircraft are chevron nozzles. It has been shown that this technology can provide noise reductions without significant thrust penalties. However chevron nozzles suffer from a high frequency noise penalty that has been attributed to increased mixing in the near nozzle region. Current noise prediction methods can not handle the complex changes to the turbulence properties of the jet. While the effects on the far field sound and on the jet structure have been well documented more fundamental research is required on how chevrons affect the turbulence properties in order to improve the current noise prediction capabilities. A detailed investigation has been carried out comparing three chevron nozzles to a baseline single jet in which extensive measurements have been performed to determine the turbulent characteristics of the flows. The investigation is primarily concerned with the affects of chevron immersion on the flow.