Noise of high-performance aircrafts at afterburner

The Journal of the Acoustical Society of America

et al. 2014

Near-field acoustical holography methods are used to predict sound radiation from an engine installed on a high-performance military fighter aircraft. Cylindrical holography techniques are an efficient approach to measure the large and complex sound fields produced by full-scale jets. It is shown that a ground-based, one-dimensional array of microphones can be used in conjunction with a cylindrical wave function field representation to provide a holographic reconstruction of the radiated sound field at low frequencies. In the current work, partial field decomposition methods and numerical extrapolation of data beyond the boundaries of the hologram aperture are required prior to holographic projection. Predicted jet noise source distributions and directionality are shown for four frequencies between 63 and 250 Hz. It is shown that the source distribution narrows and moves upstream, and that radiation directionality shifts toward the forward direction, with increasing frequency. A double-lobe feature of full-scale jet radiation is also demonstrated.

Section: Resultsmentioning

confidence: 86%

Cylindrical acoustical holography applied to full-scale jet noise

Wall

The Journal of the Acoustical Society of America

et al. 2014

“…Indications of the double lobe in the INTER condition support the theory that higher temperature and engine conditions at MIL and AB are not required to produce the double lobe phenomena, and the differences in radiation angle of the lobes are greatest at MIL rather than at AB. Tam et al 41 hypothesized that the double lobe phenomenon was the result of both large-scale radiation and combustion noise. However, while high engine powers exhibit strong effects due to combustion noise-which should radiate from the nozzle exit-the multilobe directivity pattern is present at lower engine powers.…”

Section: F Engine Condition Analysismentioning

confidence: 99%

Beamforming-Based Wavepacket Model for Noise Environment Predictions of Tactical Aircraft

Harker

23rd AIAA/CEAS Aeroacoustics Conference

et al. 2017

Jet noise consists of extended, partially correlated sources such that a single-wavepacket source representation is inadequate. A multiple-wavepacket (MWP) model provides an analytical framework for jet-noise-like radiation to simulate jet noise field levels as well as the corresponding spatial coherence properties within the field. Here, a beamforming method with regularization is applied to noise measured by a linear array near a high-performance military aircraft. Beamforming results are decomposed into a reduced-order MWP model and the predicted radiation is validated in terms of level and coherence properties using benchmark measurements. Sound levels and coherence lengths generated by the beamforming results show good agreement with benchmark measurements over a range of frequencies that contribute significantly to the overall radiation. The MWP model is shown to predict full-scale specific features such as multilobe directivity patterns, and the addition of an uncorrelated distribution (UD) model adequately predicts the sideline radiation that is otherwise difficult to reproduce from wavepacket radiation. The MWP model predicted radiation characteristics are an improvement over single-wavepacket models, which do not incorporate spatiotemporal features of the radiation.

“…9 In the case of the F-22A and the F-35AA-1, Neilsen et al 3,12,13 showed that the popular two-source similarity spectra 14 could not account for the double spectral peak. In an effort to explain this phenomenon for the F-22A, Tam and Parrish 15 related the different spectral peaks to combustion noise and the passage of "hot spots" through a pressure discontinuity at the nozzle throat caused by a change from the converging to the diverging nozzle portions (entropy waves). Turbulent flow and combustion data are not yet available to corroborate or refute these claims about jet acoustic source mechanisms, but several acoustic imaging techniques have shown F-22A source distributions centered on regions well downstream of the nozzle.…”

Section: Introductionmentioning

confidence: 99%

Investigation of multi-lobed fighter jet noise sources using acoustical holography and partial field decomposition methods

Wall

21st AIAA/CEAS Aeroacoustics Conference

et al. 2015

Full-scale tactical aircraft noise exhibits multiple radiation lobes not seen in laboratoryscale jets. These lobes have different radiation directions yet appear to have similar, overlapping source regions. Near-field acoustical holography (NAH) source reconstructions, in conjunction with partial field decomposition (PFD) methods that produce physically meaningful partial fields, are used in the current work to investigate the nature of these radiation patterns. First, it is shown that the two main radiation lobes are highly incoherent, suggesting independent partial sources. Second, these lobes are isolated as mutually orthogonal partial fields. In this representation, the lobes seem to be generated by independent yet spatially coincident extended partial sources. Source comparisons are made between non-afterburner and afterburner engine powers to investigate whether afterburner combustion produces any sources that are fundamentally different from those of nonafterburner operations. The current results show no qualitative changes occur due to the addition of the afterburner thrust aside from minor variations in source distribution, level, and the nature of the overlap between the multiple lobes.