Noise Prediction for Turbulent Coaxial Jets

Abstract

The aerodynamic/acoustic fields of various single and coaxial jet configurations are determined by a hybrid method to analyse the noise generation mechanisms. Three jet configurations with an artificial nozzle are considered, i.e., an isothermal single jet is compared with an unheated coaxial jet. In addition a heated coaxial jet is simulated to shed more light on the heat impact on the jet noise generation. Finally, two coaxial jet configurations with a “short cowl nozzle” are investigated to take into account more realistic jet configurations. The computational approach is based on large-eddy simulations (LES) and solutions of the acoustic perturbation equations (APE). The investigation emphasizes the core flow to have a major impact on the radiated jet noise. The analysis of the acoustic field of the coaxial jets focuses on two noise sources, the Lamb vector fluctuations and the entropy sources of the APE equations. Based on the explicit description of turbulent sources, the power spectral density (PSD) distributions evidence the Lamb vector fluctuations to represent the major acoustic sources of the isothermal jet. Furthermore, when the coaxial jet possesses a hot primary jet, the acoustic core being characterized by entropy source terms, low frequencies are amplified, i.e., the sideline acoustics is enhanced by the pronounced temperature gradient.