Mixing and Noise in High Speed Axisymmetric Jets

Abstract

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searchint the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestioi AFRL-SR-AR-TR-04-.02JZS]Final Technical Report (15 Nov 99 -31 Dec 02) TITLE AND SUBTITLE Mixing and Noise in High Speed Axisymmetric Jets AUTHOR(S)M.. Samimy, J. Hileman, and E. Caraballo FUNDING NUMBERSF49620-00-1-0023 2307/AX 61102F PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)Ohio This work investigated noise sources and the effects of passive mixing and noise control schemes using vortex generating tabs on noise sources. It is believed that such information is necessary for jet noise modeling and provides guidance for active control of jets for noise mitigation that will follow. The bulk of this work attempts to correlate instantaneous large-amplitude features of the far acoustic field to the dynamic evolution and interaction of large-scale structures within the mixing-layer of ideally expanded, high-speed, high Reynolds number jets. Such mformation is essential for a better understanding of jet noise sources, and jet aeroacoustic modeling and control. ABSTRACTThis work investigated noise sources and the effects of passive mixing and noise control schemes using vortex generating tabs on noise sources. It is believed that such information is necessary for jet noise modeling and provides guidance for active control of jets for noise mitigation that will follow. The bulk of this work attempts to correlate instantaneous large-amplitude features of the far acoustic field to the dynamic evolution and interaction of large-scale structures within the mixing-layer of ideally expanded, high-speed, high Reynolds number jets. Such information is essential for a better understanding of jet noise sources, and jet aeroacoustic modeling and control.The jet under study had a nozzle exit diameter of 2.54 cm, a Mach number of 1.3, and a Reynolds number of 10*. The jet was operated with and without delta tabs to better vmderstand how these noise reduction devices (when used in a chevron configuration) modify the jet and its noise generation mechanisms. Three cases are examined: a baseline (no-tab) jet, a single delta tab jet, and a dual delta tab jet. Power spectra and average acoustic waveform measurements were made for a variety of azimuthal locations; apparent noise origins were determined with an inline microphone array as well as a 3-D microphone array; and temporally resolved flow visualization was used to examine the dynamic flow structure of the jet's mixing-layer. Both of the microphone arrays are unique in they allow for the determination of the origin of individual acoustic 'events' as opposed to obtaining a time-average soimd generation region and they were both placed at an angle of 30° relative to the downstream jet axis. The development and application of both of these novel arrays are presented. Condit...