摘要 :
The acoustic near-field of a supersonic underexpanded jet at M_j=1.34 was studied experimentally. A near-field azimuthal microphone array was utilized to study the jet oscillation dynamics and infer the geometrical pattern of the ...
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The acoustic near-field of a supersonic underexpanded jet at M_j=1.34 was studied experimentally. A near-field azimuthal microphone array was utilized to study the jet oscillation dynamics and infer the geometrical pattern of the upstream-traveling acoustic waves involved in the jet screech mechanism. Operation of the jet in isolation resulted in a lateral oscillation (mode B) with an acoustic field containing strong screech tones. Addition of a conical reflector of 60° cone half-angle changed the oscillation dynamics, with new mode E appearing prominently and coexisting with mode B. The cross-spectral densities at the distinct tone frequencies are utilized to discern the jet oscillation dynamics and screech frequency and wavelength prediction formulas are utilized to assess if mode E is an extension of previously observed screech modes.
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摘要 :
The acoustic near field of a subscale ducted fan was measured experimentally for the purpose of understanding the physics of sound generation and refining low-order models for aft-emitted tonal fan noise. The experimental rig simu...
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The acoustic near field of a subscale ducted fan was measured experimentally for the purpose of understanding the physics of sound generation and refining low-order models for aft-emitted tonal fan noise. The experimental rig simulates the fan conditions of an ultra-high-bypass turbofan. Acoustic measurements were performed with a phased array of microphones comprising fixed and scanning sensors, the combination of which offers spatial resolution sufficient to resolve detailed features of the pressure field. Partial-fields decomposition of the signals of axially-scanning sensors shows the potential of recovering the complete harmonic pressure field along the scan line. Axial space-time correlations and azimuthal correlations show trends that are in line with the predictions of a recently proposed source model that is partially informed by internal duct acoustics.
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