129 Newly-developed Compound Active Jet Noise Control Technology for Rectangular Jet Flow Noise Reduction(O.S.5 Advanced Technology for Usage of Sound and Vibration II) :

The paper describes about a compound active jet noise control (AJC) technology newly-developed for high speed jet noise reduction and about proof test results of the AJC technology performance. The AJC technology was contrived and developed as a jet noise reduction part of the active engine noise control technology. The AJC technology aims at actively reducing jet noise of large overall sound pressure level (O.A.SPL dB (A)), in response to the jet flow change. It is composed of an active jet flow mixing control technology using mobile tab mixers and an active acoustic absorption ejector technology adjusting acoustic impedance of ejector acoustic liners. For actual proof of the AJC technology, a rectangular nozzle fitted with a compound active jet noise control device and various jet flow mixers were made on a trial basis, and were examined over a wide jet flow range from subsonic to supersonic using a high speed jet test rig, without flight effect on ejector. The test result clarifies that at jet Mach number of 1.50, the rectangular nozzle with the device and mixer could achieve large overall jet noise reduction of 15 to 18dB (A) in directions from 30 to 110°to the jet axis. In response to supersonic jet velocity change, the rectangular nozzle with the device and mixer could achieve large overall jet noise reduction of 14 to 20dB (A), by controlling the insertion length of tab mixer into the jet flow and the reflective plate movement in the ejector liner. It was found that the rectangular nozzle with the device and nozzle mixer is the most efficient jet noise suppressor over the all jet flow region. The AJC technology can also be applied to adjustable expansion type mufflers for high speed exhaust gas noise reduction.