Analysis of a jet - Mixing layer interaction

The improvement of mixing in jets via external jets has been proven to be efficient in subsonic and supersonic flows as well. However, the hyper-mixing process is not well known. The present study deals with an experimental and a numerical approach of the interaction of an external control jet with a turbulent axisymmetric mixing layer. The main conclusion of a dual experimental/numerical study is that an intermittent penetration of the control jet occurs both in supersonic and subsonic configurations. Moreover, all results tend to show that the control jet flapping frequency and the spacing between the structures involved downstream from the interaction are respectively very close to the frequency and wavelength of the Kelvin-Helniholtz structures at the impact location. Two hypotheses are provided in order to explain the mechanism of the interaction. The first one is based upon the interaction with the passage of Kelvin-Helmholtz structures in the mixing layer, the other one deals with an intrinsic instability of such a flow configuration.