Direct computation of jet noise produced by large-scale axisymmetric structures

A methodology is presented for directly calculating the noise emission associated with large-scale structures in a supersonic jet. The nonlinear governing equations are solved in a computational domain that encompasses both the jet flow and the acoustic near field. A high-order discretization scheme is used along with careful boundary treatment to capture the disturbance field accurately. Nonlinear interactions among the various frequency modes of the flow structure were found to alter the development of each mode and, hence, influence its radiation pattern. Comparing the calculated radiation pattern to experimental observations indicates that the axisymmetric structure contributes preferentially in the forward direction, whereas the azimuthal structure is associated with a higher emission angle and with a stronger effect on jet spreading. Sensitivity of the radiated sound field to the type of incoming disturbances is studied.