Effects of excitation on turbulence levels in a shear layer

The first detailed study of turbulence suppression in free shear flows was due to Zaman and Hussain. They investigated the turbulence suppression due to controlled excitation (introduced acoustically or by ribbon oscillation) in a number of experimental facilities - circular jets, a plane jet, and a single-stream plane mixing layer. For high amplitudes of excitation, Strouhal number preference is lost. That is, the maximum turbulence suppression no longer occurs at the maximally unstable frequency, but occurs at a higher frequency. This paper presents experimental results of a study of turbulence suppression as a result of high amplitudes of external excitation in an axisymmetric mixing layer.