Measurement of interfacial distortions at a stratified entrainment interface

A laser beam scanning technique was used to measure the rms amplitude of the largest wave (interfacial distortion) that is present at the entrainment interface of a stratified fluid. Both linearly-stratified and two-layer fluid systems, subjected to entrainment by oscillating-grid induced shear-free turbulence, are considered. The measurements were found to be in general agreement with a theory due to Long (1978), which predicts /D _e Ri ^–3/4 , where D _e is the mean thickness of the mixed layer and Ri is the appropriately defined bulk Richardson number at the interface.