Wave packets and Orr mechanism in turbulent jets

Instability waves traveling within subsonic turbulent jets have a modal linear growth until approximatively the end of the potential core. At these stations it is believed that nonlinear and/or nonmodal effects become important and a mismatch appears between experimental measurements and linear models. In this paper the response of the linearized operator to nonlinearities treated here as an external forcing is found to be consistent with a simplified model of the Orr mechanism, supporting the idea that a nonmodal growth of disturbances occurs in the downstream region of the jet in response to the modeled nonlinear forcing.