Influence of temporal correlation function on the form of jet noise spectrum at 90°

Since Lighthill's foundational work, accurate modeling of jet noise spectra and directivity has been a central challenge in Aeroacoustics. This study investigates how the choice of the source temporal correlation function influences the predicted far-field acoustic spectrum at90° for the axisymmetric mode(m=0), within the framework of the model developed by Kopiev and Chernyshev (Acoustical Physics,58(4),442-456,2012). While based on Lighthill's analogy, this model uses the hypothesis that the dominant sound generation mechanism is associated with the sudden birth of large-scale vortices. To explore the sensitivity of the predictions to assumptions about source correlation, we replace the original Gaussian function with a Mexican-hat correlation, which permits negative values-a feature suggested by existing experimental data of pressure autocorrelation. A simple exponential decay function is also tested for comparison. The spectral predictions were obtained for the axisymmetric component of jet noise at Mach0.35 and evaluated against experimental data. Results show that the Mexican-hat correlation yields spectral shapes comparable to those obtained with the Gaussian function. The temporal width of the correlation function proved to be the dominant factor, while the amplitude of the negative lobe played a secondary role. Narrower functions and more pronounced negative lobes tended to shift the spectrum toward higher frequencies.