Forward Flight Effects on Chevron Noise Reduction

Jet engine exhaust nozzle chevron designs are used for reducing low frequency jet noise by enhancing the jet mixing process. The development of an empirical method to predict the effect of chevrons, based on a static engine test, can eliminate the need to flight test every engine/airplane combination and therefore would be of important practical value to future aircraft design and development activity. This study employs model-scale data to make preliminary conclusions concerning the viability of such a method. At least two effects need to be understood and modeled if such a method is to succeed. Specifically (1) the change in the relative velocity effects due to the chevrons and (2) the change in the apparent source locations of the jet noise. Based on different projections of the model-scale data, the effect of lower relative velocity on the chevrons’ impact on community noise appears to be separate from the problem of modeling the distributed source location generated by a chevron nozzle. This paper will present the analysis of the relative velocity effects.