An experimental investigation of low frequency self modulation of incompressible impinging cavity shear layers

The fundamental frequency of self sustaining oscillations of impinging flows was investigated. It is shown that there exist organized low frequency components having substantial amplitudes relative to that of the fundamental. These flow frequency components are shown to be associated with the interaction of successive shear layer vortices with the downstream cavity corner. Vortices approach the corner at varying transverse locations resulting in varying degrees of severing of incident vortical structures. Organized patterns in the degree of severing of successive vortices are associated with low frequency components of the pressure fluctuation at impingement. This unsteady field at impingement modulates the upstream region of the shear layer near separation; in turn, the resultant velocity fluctuations are amplified in the free shear layer.