The self-sustained oscillations which result from impingement of an unstable laminar mixing layer upon a solid wedge are investigated. Extensive velocity measurements using hot film anemometry, flow visualization using hydrogen bubble and dye injection techniques, and simultaneous recording of the force exerted on the wedge are employed to explore the globally organized nature of the mixing layer-wedge interaction. Special attention is given to:​ the flow dynamics in the receptive region of the mixing layer near separation;​ the region of higher harmonic activity and nonlinear amplitude saturation;​ and the region of impingement near the leading edge of the wedge.

The introduction of the wedge into the mixing layer enhances not only the fundamental mode of oscillation but also its higher harmonic modes, in a manner very similar to that caused by artificial excitation. The upstream influence of the wedge is manifested in well-organized velocity perturbations on both sides of the trailing edge of the mixing layer splitter plate;​ perturbations on the high speed side are approximately π out of phase with those at corresponding locations on the low speed side. This π phase difference across the shear layer persists along the entire stream-wise extent of the mixing layer. Moreover, the phase relation between separation and impingement, measured at the edge of the shear layer, is 2nπ for both high and low speed sides of the mixing layer. This streamwise phase criterion is maintained throughout the (four) identified stages of oscillation.

The instability characteristics of the shear layer on the high speed side dominate the instability of the mixing layerwedge system, determining the frequency, wavelength, and phase speed of oscillation. These instability characteristics are well predicted with the aid of the linear spatial stability theory together with the measured streamwise phase criterion.

Velocity perturbations at the separation location are found to be intimately related to the force exerted on the wedge. These perturbations grow exponentially downstream with growth rates in close agreement with the linear stability theory. Higher harmonics of the fundamental mode are generated near the critical layer of the mixing layer while the disturbance amplitude is still small (-2%). All harmonic modes grow at the same rate of -1.6 times the growth rate of their fundamental , which is in excellent agreement with the prediction of strong nonlinear interaction theory. Further downstream, the formed vortices, characterized in the region of nonlinear amplitude saturation, are well approximated by Stuart's vortex model.

Vortex-wedge interaction mechanisms and the amplitude of the force exerted on the wedge are a strong function of the transverse offset between the leading edge of the wedge and the center of the incident vortex. Offsets of the order of the mixing layer momentum thickness influence the scale of the vortex shed from the leading edge. The vorticity orientation of this shed vortex is opposite to that of the incident vortex. At negative values of offset, i.e. when the leading edge of the wedge is shifted from the elevation of the center of the incident vortex to the low speed side, the process of opposite vorticity shedding, though significantly retarded, is stronger than at positive values of offset.

The force exerted on the wedge drops rapidly as the offset is increased in either a positive or negative direction. However, the induced force at positive values of offset is larger than that induced at corresponding negative values of offset. Small variation in the self-induced offset as the impingement length is changed makes the induced force intimately related to the length of impingement.

The annihilation of the transverse momentum of the incident velocity field at the leading edge of the wedge is the principal parameter determining the magnitude of the induced force. However, at negative values of offset, the pronounced vortex shedding from the leading edge also contributes substantially to the exerted force, suggesting that viscous effects have to be taken into account for proper modelling and accurate force prediction.

A special case of "resonance" is also investigated. In this resonance case, the subharmonic mode is coupled with a free surface wave phenomenon, resulting in a process of consistent vortex pairing upstream of the impingement wedge. Further insight into mixing layer dynamics is gleaned from examining this selfexcitation at a frequency compatible with the unstable shear layer and a free surface effect.