Shear Excitation of Internal Gravity Waves

The images show internal gravity waves being generated when a stratified. flow passes over a thin vertical barrier. The fluid near the top of the barrier is weakly stratified, and the fluid beneath is strongly stratified.

The internal waves are visualised using a recently developed "synthetic schlieren'' technique. The left image is a measure of the displacement of the waves from their initial positions, and the right image is a measure of the rate of change of the displacement. Note, the latter filters out long time-scale motions.

To illustrate the effect of large amplitude internal gravity wave generation on the shear flow numerical simulations have been performed:

The left image, showing contours of vorticity, demonstrates that negligible internal gravity wave excitation occurs if the flow is uniformly stratified. If the deep fluid is more strongly stratified (right-hand image), then large amplitude waves are generated and the evolution of the mixing region changes dramatically.