TONE EXCITATION OF A SUPERSONIC BOUNDED SHEAR-LAYER

Passive acoustic excitation was employed to augment mixing in a bounde d planar supersonic shear layer. It was found that acoustically reflec tive surfaces, both downstream and below the shear layer, were essenti al for this resonance excitation to occur, and an upstream acousticall y reflective surface augmented this excitation, However, none of these surfaces directly contacted the shear layer Based on total pressure m easurements, as much as 100% augmentation in mixing layer growth rate was achieved with this passive excitation system even at pressure matc hed conditions, Shadowgraph images of the shear layer showed the prese nce of singular coherent large-scale structures, and the acoustic spec tra measured below the shear layer indicated the presence of a dominan t frequency with overall high energy for the excited flow compared wit h a lower energy broadband spectrum for the unexcited how The results indicate that a combination of streamwise and transverse modes may be responsible for the excitation.