Boeing's Noise-Reducing Chevrons Come with a Cost

The distinctive serrated engine nozzles found on Boeing jets are not just a design feature, but rather a result of years of research and collaboration between Boeing, GE Aerospace, Honeywell, and NASA to reduce aircraft noise.

The chevrons, as they're called, were introduced to tackle one of commercial aviation's biggest environmental challenges: reducing engine noise during takeoff and landing. The technology was developed in response to increasingly strict international airport noise standards without sacrificing fuel efficiency.

Modern turbofan engines produce two separate streams of air at their exhaust, with the hot core exhaust exiting through the center and a cooler bypass airflow surrounding it. When these flows meet behind the engine, they create turbulent mixing, which is a primary source of jet engine noise. Chevrons help reduce this noise by generating small vortices that encourage the hot and cold airflows to blend more gradually.

While chevrons are effective at reducing noise, they come with compromises. The serrated edges create controlled vortices that allow the hot core exhaust and cooler bypass airflow to mix more gradually, but these vortices also create additional aerodynamic losses compared with a smooth nozzle design. This results in a permanent efficiency penalty, slightly reducing thrust and increasing fuel consumption.