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SUMMARY:Jet Noise and its Reduction - Karthik Depuru-Mohan (Homerton Colle
 ge)
DTSTART:20151126T124500Z
DTEND:20151126T133000Z
UID:TALK62524@talks.cam.ac.uk
CONTACT:20337
DESCRIPTION:Jet noise is a dominant component of aircraft noise\, particul
 arly at takeoff. It is generated by turbulent mixing of the high-speed pro
 pulsive jet with ambient air. Lighthill's celebrated 8th power law showed 
 that the sound power is proportional to the 8th power of the jet velocity 
 multiplied by the jet cross-sectional area. Historically jet noise has bee
 n reduced by increasing the engine bypass ratio\, whereby the required thr
 ust is obtained by increasing the exit area of the propulsive jet and decr
 easing its speed\, resulting in a jet noise reduction. But this increases 
 the fan noise. Fan and jet noise are now appropriately equal and more subt
 le ways of reducing jet noise are required. Chevrons or corrugations aroun
 d the lip of the jet pipe have been shown experimentally to reduce the jet
  noise. Time consuming high-resolution computational fluid mechanics can p
 redict jet noise reduction due to chevrons\, but to date the development a
 nd optimisation of chevrons has required extensive large-scale empirical t
 esting. A simple theory that captures the physics of jet noise generation 
 and its reduction by chevrons will be described. The effects of the geomet
 ry of the chevrons can be calculated sufficiently quickly that the method 
 can be used in preliminary nozzle design to optimise the noise reduction. 
 The same approach can also be used to predict the effects of microjets ins
 talled around the rim of the jet pipe exit\, another technique that leads 
 to reduced noise. 
LOCATION:Drawing Room\, Homerton College
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