Wavepacket Modelling of Broadband Shock-Associated Noise in Supersonic Jets

TL;DR

This paper introduces a novel two-point wavepacket model for broadband shock-associated noise in supersonic jets, leveraging LES and PIV data for improved physical accuracy and validating predictions against experimental data.

Contribution

The model uniquely integrates LES and PIV data without scaling parameters and employs reduced-order wavepacket descriptions, advancing understanding of BBSAN source mechanisms.

Findings

Good spectral shape and amplitude agreement at BBSAN-dominated angles and frequencies.

Model accurately predicts BBSAN peaks using linear wavepacket sources.

Amplitude mismatches suggest wavepacket jitter influences noise generation.

Abstract

We present a two-point model to investigate the underlying source mechanisms for broadband shock-associated noise (BBSAN) in shock-containing supersonic jets. In the model presented, the generation of BBSAN is assumed to arise from the non-linear interaction between downstream-propagating coherent structures with the quasi-periodic shock cells in the jet plume. The turbulent perturbations are represented as axially-extended wavepackets and the shock cells are modelled as a set of stationary waveguide modes. Unlike previous BBSAN models, the physical parameters describing the hydrodynamic components are not scaled using the acoustic field. Instead, the characteristics of both the turbulent and shock components are educed from large-eddy simulation and particle image velocimetry datasets. Apart from using extracted data, a reduced-order description of the wavepacket structure is obtained using parabolised stability equations (PSE). The validity of the model is tested by comparing far-field sound pressure level predictions to azimuthally-decomposed experimental acoustic data from a cold Mach 1.5 underexpanded jet. At polar angles and frequencies where BBSAN dominates, good agreement in spectral shape and sound amplitude is observed for the first three azimuthal modes. Encouraging comparisons of the radiated noise spectra, in both frequency and amplitude, reinforce the suitability of using reduced-order linear wavepacket sources for predicting BBSAN peaks. On the other hand, the mismatch in sound amplitude at interpeak frequencies reveals the role of wavepacket jitter in the underlying sound generating mechanism.