Laboratory observations of shear-layer instability in a stratified fluid

Abstract

Instability and transition to turbulence is studied in a shear layer between two streams of different salinities and velocities. The viscous layer between the two streams is 15–18 times thicker than the diffusion layer. When the initial layer Richardson number is low, the instability organizes the shear-layer vorticity into discrete lumps as in the homogeneous case. Here the similarity ends. The homogeneous shear layer continues to grow by the combination of neighboring vertical lumps (vortex pairing). In the stratified shear layer, the pairing process is stopped completely, and the vorticity is redistributed along the interface. This redistribution generates interfacial waves. The interfacial waves and the residual turbulence eventually decay, and the shear flow approaches a laminar state.