An experimental investigation of low-dimensional techniques for large scale noise source characterization in a heated jet
Date of Award
Doctor of Philosophy (PhD)
Mechanical and Aerospace Engineering
Aeroacoustic sources, Jet noise, Noise source characterization, Heated jet
Engineering | Mechanical Engineering
An investigation of the aeroacoustic sources of an 'acoustically matched' Mach 0.6 jet, at temperature ratio of T r =0.93 and T r =1.7, is conducted to identify the distinctions in contribution to the acoustic far-field spectrum. The fluctuating pressure sampled near the exit of the jet ( x/D =2, r/D ≈1), is shown to sense the dominant flow features of the velocity field. The core region in the hot jet is seen to collapse at a more rapid rate, resulting in a shorter potential core length and larger 'high-speed' shear layer thickness. The turbulence level of the hot jet are also shown to increase. The hot jet exhibits an increase in OASPL at nearly all observer angles from [straight phi]=15°-75°, largest increase of 2 dB seen at [straight phi]=15°. There is a decease of nearly a half dB seen at [straight phi]=90°, consistent with the increase in the acoustic spectrum at low frequency, and decrease at high frequency seen at all locations. Directional dependency of the acoustic spectrum with frequency is highlighted. A snapshot POD analysis reveals the presence of larger scaled, more energetic structures in the hot jet, as well as a dominant Fourier-column mode-like structure in the hot jet, and a Fourier-helical mode-like structure in the cold jet. Fourth order correlations of the self noise contributions are shown to be dominant in both jets, with the hot jet exhibiting a greater shear noise efficiency, and cold, a greater self noise contribution. The low frequency emission of the shear noise terms is linked to the increase in the acoustic spectrum at these frequency, where as the decrease at high frequency is characteristic of the self noise weighting. The pronounced effect of increased low frequency noise is not deemed likely as solely resulting from the changes in the contribution of the shear noise sources, and as such, points to the contribution of the second entropy source term.
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Hall, Andre M., "An experimental investigation of low-dimensional techniques for large scale noise source characterization in a heated jet" (2008). Mechanical and Aerospace Engineering - Dissertations. 4.