Vortex dynamics in a spatially accelerating shear layer

An experimental and analytical study into the vortex dynamics of a stratifi ed shear layer subjected to a spatial acceleration is presented. The outer flow is dictated by a hydraulically controlled wedge flow which provides a spatially accelerating shear layer and baroclinic generation of vorticity a long the inclined interface. A new, finite-amplitude mechanism is observed in which the core of the growing vortex is separated from the vorticity sou rce at the interface. A secondary core develops and an altered vortex pairi ng interaction is observed. A Spatial linear stability analysis reveals tha t one of two modified Kelvin-Helmholtz modes is dominant, resulting in the centre of the instability being offset from the density interface into the slower moving stream. Digital particle imaging velocimetry (DPIV) measureme nts are presented along with flow visualization which indicate that the mec hanism is a result of the offset in the vortex core from the source of vort icity at the interface combined with the effects of spatial acceleration an d buoyancy. The mixing induced by the interfacial instabilities is such tha t a sharp density interface remains near the high-momentum stream, with a l ow-gradient region extending into the low-momentum stream.