An aircraft gas turbine engine discharges exhaust gases in a jet at high velocity for propelling the aircraft in flight. The exhaust gases expand into the ambient air upon discharge from the engine and generate considerable jet noise. Various techniques are known for reducing jet noise including specially designed exhaust nozzles for reducing noise due to shock waves; convergent-divergent (CD) nozzles to reduce noise due to shock waves; suppressor nozzles to shift generated noise to frequencies that are more readily absorbed by the atmosphere or acoustic liners; ejectors for mixing the exhaust gases with ambient airflow to reduce the mean jet velocity and, thereby, noise; and porous plug nozzles to promote mutual cancellation between expansion and compression waves.
These various noise suppression techniques operate at varying effectiveness and with varying penalties in terms of propulsion system size, weight, efficiency, performance, and cost, for example. Accordingly, improved sound suppression devices are desirable for effectively suppressing noise in a simple structural arrangement, with minimal drag losses and performance penalties while being readily manufacturable.
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