Seeding of helical modes in the initial region of an axisymmetric jet

Active control of fundamental two- and three-dimensional amplified modes in an axisymmetric jet is presented. This is done by introducing localized acoustic disturbances produced by an azimuthal array of miniature speakers placed in the close proximity of the jet lip on the exit face. The independent control of each speaker output allows different azimuthal amplitude and phase distributions of periodic input pressure disturbances. Coupled with this was the development and use of a circular smoke-wire for visualizing shear layer modes around the complete jet circumference.