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Which type of chevron nozzle was applied on the B787? I'm really confused about whether if it's sawtooth or sine wave.

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Strictly speaking, its neither. Chevrons don't resemble either a sawtooth wave or a sine wave in mathematical terms. The closest is that it is a smoothed (modified) saw tooth form.

Chevron

Image from compositesworld.com

Though the initial research used a serrated nozzle in saw tooth form, the final commercial application differs from it. However, the chevrons are repeatedly noted as having a saw tooth form, by NASA among others:

One of the most recent noise-reducing technologies shepherded through the research process by NASA and now making a difference on commercial jet engines is chevrons.

Chevrons are the sawtooth pattern seen on the trailing edges of some jet engine nozzles.

So, it's a choice between saw tooth and sine wave, its better to go with the former.

GE's patent for the Chevron describes the shape as triangular with qualifications:

... each of said chevrons being triangular in configuration

... said chevrons having a compound concave contour both axially between said bases and apexes and laterally between said trailing edges..

Chevron detail

Image from Chevron exhaust nozzle for a gas turbine engine

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