Resolvent modelling of subsonic jet noise

When jet noise is cast in the form of a linear input–output problem, the cross-spectral-density (CSD) matrix of the sound field is forced by the CSD of nonlinear interactions via the resolvent operator. The forcing CSD is difficult to compute or measure, but its projection onto the resolvent input space can be identified from the CSD of the sound field. We performed two-point acoustic measurements in isothermal turbulent jets over a broad range of subsonic Mach numbers. The CSD matrices are used to obtain an empirical model of the forcing-projection matrix. We investigate the parametric dependence of this low-rank forcing-projection matrix on Mach number, frequency and azimuthal mode, and we propose an empirical model that captures downstream radiation with 2 dB precision for subsonic jets.