Abstract
AbstractIntense acoustic loads from jet noise cause noise pollution and induce failures, such as the malfunctioning of electronic devices and fatigue failure of internal/external structures. Consequently, the prediction of jet noise characteristics is crucial in the development of high-speed vehicles. This study presents acoustic experiments and predictions for an under-expanded, unheated jet using a small-scale prototype. Outdoor measurements are carried out using a vertical ejection setup. Acoustic characteristics are measured using both linear and circular microphone arrays. Additionally, numerical prediction of the same jet noise is performed using a detached eddy simulation and the permeable Ffowcs-Williams and Hawkings acoustic analogy. The vertical experimental setup exhibits the typical acoustic characteristics of a supersonic jet in terms of directivity and broadband shock-associated noise. Moreover, the numerical prediction exhibits satisfactory accuracy for the jet downstream, where the large-scale turbulence structures of the directivity predominate. However, discrepancy increases in the domain of lower directivity. The presented experiment and prediction will be extended to future studies regarding the noise of various deflector duct configurations impinging on supersonic jets.
Highlights
The jet and rocket engines of a high-speed vehicle provide a significant amount of thrust, which is accompanied by excessive acoustic loads emitted from the nozzle
The envelope of the acoustic pressure is observed to stabilise within a short period of time after an initial jet ejection, and the duration corresponding to such an envelope is used for acoustical investigation using a fast Fourier transform
The acoustic measurements were conducted via outdoor tests; the results showed sufficient reproducibility, and they validated the current experimental setup
Summary
The jet and rocket engines of a high-speed vehicle provide a significant amount of thrust, which is accompanied by excessive acoustic loads emitted from the nozzle. The present authors have previously conducted investigations regarding the noisy environment surrounding high-speed vehicles via small-scale testing prototypes, such as those depicted in Fig. 1 [27,28,29] This study presents both experimental measurements and numerical predictions for the noise of an unheated, under-expanded supersonic free jet in a small-scale test. For the circular microphone array of equal distance (Fig. 9), the SPL variation approaches zero value for the large observation angle (θ > 60◦), as the omni-directional fine-scale turbulence structures become dominating. Similarity spectra and measured results was obtained for the wide variety of jet noise: unheated to heated, near- to far-field, small- to full-scale and subsonic to supersonic [33, 35, 36].
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