Wavepacket modeling of turbulent jet noise generation using input-output analysis

We model far-field sound generated from turbulent jets using input-output analysis. We investigate small perturbations about Reynolds-averaged Navier-Stokes (RANS) solutions of M_j = 1.5 ideally expanded axisymmetric turbulent jets. We consider both isothermal and heated jets with jet-to-ambient temperature ratios T_j/T_∞ = 1 and T_j/T_∞ = 1.74, respectively. The dynamics of small perturbations are governed by the linearized Navier-Stokes (LNS) equations, accounting for the effects of eddy viscosity. We extend the system state to the acoustic far-field using the linear Ffowcs Williams-Hawkings (FW-H) equation. In this way, our hybrid input-output/FH-W method efficiently connects input uctuations embedded in the jet turbulence to pressure outputs in the far-field. By projecting acoustic far-field data extracted from a high-fidelity large eddy simulation (LES) database onto orthonormal sets of output modes, we demonstrate that a significant portion of the LES acoustic energy may be recovered using only a few output modes. From the resulting acoustic fields, we examine the role of optimal and sub-optimal input-output modes in noise generation mechanisms of high-speed turbulent jets. Finally, we repeat input-output analysis over a wide range of frequencies, and find that our analysis indicates a broadening of the far-field acoustic spectra as the radiation angle increases.