Influence of grid resolution on the spectral characteristics of noise radiated from turbulent jets: Sound pressure fields and their decomposition

Abstract

Jet noise remains a key target for aircraft noise reduction in the foreseeable future. While being extremely challenging, the requirement of predicting both low and high frequency noise spectra is increasingly important for design purposes. Novel approaches are needed to overcome the current numerical limitations in capturing the required broad noise spectra. Once su ciently resolved, the energy contents of the numerically simulated near-and far-field sound pressure have intrinsic correlations among di↵erent levels of grid resolution. The present work explores the potential of such correlations to broaden the spectral prediction. The noise radiated from high subsonic turbulent jets is investigated using large-eddy simulation. The 3-D filtered compressible Navier-Stokes solutions are obtained for an axisymmetric and a serrated nozzle on successively refined multi-resolution grids, ranging from 5 to 80 million grid points. The radiated far-field sound is computed using the Ffowcs Williams -Hawkings (FW-H) surface integral method. Fourier decomposition for pressure near-field is applied to help identify the location of the sound source regions and the dominant directions of propagation, which provides a more thorough understanding of the e↵ect of the grid resolution on the numerical cut-o↵ frequencies of the far-field spectra. Further analysis of the far-field spectra and of their azimuthal modes confirms that a novel strategy to obtain a broadened overall sound spectrum is possible, at reduced computational cost, from a combination of multiple spectra from successively refined grids.

Propulsive jet aerodynamics and aeroacoustics

“…To illustrate the effect of grid refinement on high-frequency noise predictions, results from the LES/FWH study of Angelino et al [53] are shown for a round nozzle at M j = 0.9 and Re j = 10 6 in Fig. 27.…”

“…Naqavi et al [38] opted for a combined RANS-LES approach where the RANS equations are solved internal to and surrounding the nozzle wall and gradually blended into an LES region where 48m cells were used. Angelino et al [53] retained LES for both the internal nozzle (wall stress model) and jet flow and carried out a grid resolution study (with 5-80m cells) to explore the effect of finer meshes on flow/noise predictions. Both FWH treatments chose similarly located noise source containing surfaces and applied averaging or filtering over multiple 'end plates' to remove pseudo-sound generated by vortical structures crossing the FWH surface.…”

“…As seen below, this high-frequency issue affects all LES/FWH acoustic predictions and prompted a proposal in Ref. 53 for the need for a 'spectral broadening' approach, that is, to combine noise spectra from simulations with different spatial and temporal resolution, although this would need to be done with some care to ensure consistency in the frequency region where LES solutions overlapped. A directivity map from Ref.…”

“…A directivity map from Ref. 53 showing the Overall Sound Pressure Level (OASPL) at different polar angles compared with measurements from Refs 17 and 54 is presented in Fig. 29 (right).…”

Prediction of vibration radiation noise from shell of straw crushing machine

“…Zhao Weiguo et al 15 analyzed the transient characteristics of a centrifugal pump while pumping a sandy two-phase flow. Reviewing the literature indicates that many scholars have used CFD, sound analogy theory, and experimental methods to study the fluid-structure coupled noise of aircraft wings and nozzles 16–18 as well as the coupled noise of ship rudder bodies and fluids. 19–21 Results of these investigations are helpful to explore the acoustic characteristics of fluid–structure coupling.…”