
Screech receptivity control using exit lip surface roughness for under-expanded jet noise reduction
Date29th Dec 2023
Time02:30 PM
Venue Online, Google Meet: http://meet.google.com/beg-fvyq-fyk
PAST EVENT
Details
Jet flows continue to captivate scientists with their complex physics and diverse applications. Jet noise can cause dangerous situations within the nozzle/aircraft due to resonance. This study presents a jet noise reduction technique by altering the receptivity of the screech phenomenon. The receptivity is modified by controlling the roughness on the exit lip of jet exit devices such as pipes and nozzles. First, the pipe exit lip thickness is varied to determine variations in screech staging, frequency, and amplitude. As lip thickness varies, the screech mode staging varies with minimal changes in frequency, whereas screech amplitude depends on screech mode. The jet noise reduces as lip surface roughness increases due to screech amplitude reduction or elimination because of the diffuse reflection of screech tone feedback waves by the lip surface. The coarse roughness on the exit lip eliminated the screech, while others reduced screech amplitude at high under-expansion levels. More than 50% of the maximum acoustic power is eliminated compared to the plain lip case. The surface roughness does not affect the screech tone at all the under-expansion levels or screech frequencies. The effect begins at a particular frequency (cutoff) and continues for frequencies lower than the cutoff frequency. The cutoff frequency increases with lip surface roughness and varies with lip thickness. By properly designing the surface roughness of the lip, the effect becomes a better passive technique for jet noise control. This work is under publication in "Physics of Fluids," AIP. DOI will be active soon: https://doi.org/ 10.1063/5.0175853
Speakers
Mr. Jaswanth K.K. Alapati (ME17D413)
Department of Mechanical Engineering