Why do Boeing 747 and Boeing 787 engine have chevron nozzle?

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Why do Boeing 747 and Boeing 787 engine have chevron nozzle?

Boeing 747 Chevron Nozzle - Wikimedia


Queen of the sky Boeing 747 has GE's GEnx-2B engine & Boeing 787 Dreamliner has GE's GEnx-1B engine mounted on them.

Boeing 787 GEnx-2B engine Chevron Nozzle - Wikimedia



If you look at these engine's nozzle, you will see zigzag curves. Such type of nozzle is known as chevron nozzle. Those curves in chevron nozzle are not just for good looks. These curves have some purpose. Those curves in chevron nozzle reduce the noise produced due to an engine.

Before going into an explanation of chevron nozzle, let's see why aircraft engines produce such a huge noise. Nowadays, in most of the passenger aircraft, turbofan engines are used. Turbofan engines are simply a modification of turbojet engines. Just add a fan in front of turbojet engine and its turbofan engine.

Turbofan Engine

Turbofan engines have a high bypass ratio. It means most of the air simply passes through the engine without combustion. This air passes through the bypass duct of an engine. This increases the efficiency of an engine.

The air coming out of the combustion chamber has a higher temperature than the air passing through the engine bypass duct. This temperature difference causes a pressure difference between air flows.

Air passing through combustion chamber has higher pressure than the air coming out without combustion. When such two air flows suddenly meet each other shock waves are formed. Which causes the production of noise. (Remember that sound is just a simple pressure wave). Aerospace companies are trying very hard to reduce the amount of noise produced due to an aircraft engine.

So to reduce such type of noise Chevron nozzles are used. Chevron nozzle forces the air flow coming out of the bypass duct to concentrate on each pointed section of the nozzle. This prevents sudden mixing of two air flows. And reduce noise.

Pointed Section of Chevron Nozzle

Sometimes double chevron nozzles are used. In this case, for both the air flow, one coming out of combustion chamber & other coming out of bypass duct will have chevron nozzle. But in this case, both the nozzles will have a pointed section at an alternate location. So that air flows won't mix & produce noise. The Boeing 747 has double Chevron Nozzle.

But Chevron nozzle reduces the efficiency of an engine by the small amount.

Thanks for reading

Also read: - Why are most of the airplanes painted white?

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