Noise Sources in Single and Coaxial Jets

Abstract

The acoustic simulations of a cold single stream jet at Mach number 0.9 and Reynolds number 3,600 and two heated coaxial jets at Mach number 0.9 and Reynolds numbers 3,600 and 400,000 are performed. The computation of the acoustic field is performed by a two-step approach using a large-eddy simulation (LES) for the flow field and approximate solutions of the acoustic perturbation equations (APE) for the acoustic field. The purpose of the paper is to identify the effect by heating and the impact of the Reynolds number on the flow field and the acoustic field. The computation of the single jet is validated against the numerical and experimental findings reported in the literature. It is shown that the Lamb vector of the APE-4 formulation is the dominant source term. Compared to the cold single jet, the heated coaxial jets show an enhanced exchange and mixing of fluid due to the temperature and density gradients between the primary and secondary stream. Additional source terms such as temperature and entropy fluctuations and heat release are excited and contribute significantly to the noise radiation in the direction normal to the jet axis producing a dipole-like far field signature. The acoustic field generated by these source terms is Reynolds number dependent, while the acoustic field generated by the Lamb vector is only weakly affected.