Modal analysis of jet near-field pressure fluctuation

Abstract

Purpose Unstable Kelvin-Helmholtz waves are suspected to be responsible for a large part of low-frequency noise radiation in high-speed jets. The purpose of this paper is to check the coherence of numerical and experimental data concerning this phenomenon, in the particular case of a cold subsonic jet. Design/methodology/approach In the present work, a cross-investigation of the near pressure field is performed on three different data sets: large-eddy simulation (LES) computations, parabolised stability equations (PSE) semi-modal computations and microphone measurements, in order to determine the local amplitudes of unstable waves. Findings The large coherent structures are found in both LES and experimental results and they are also in good agreement with direct semi-modal computations carried out with the PSE approach. Originality/value This work confirms that the unstable wave packets can be extracted from both LES and experimental results, provided that an appropriate modal decomposition is performed.