Frontal waves — tank experiment In the rotating tank, we will attempt to observe frontal waves by generating a shear layer. We immerse a disk slightly below the water surface and then rotate it at a speed δΩ relative to the tank. delta omega Omega You might expect the ﬂuid under the disk to be in solidy body rotation with a rotation rate δΩ/2 or vorticity δΩ and the ﬂuid outside to have zero vorticity (relative to the tank, of course). Find the solution with continuous velocity. This is called the Rankine vortex, and it is stable. In fact, however, you develop shear layers at the edge of the disk (c.f. Greenspan), and these can become unstable give rise to waves and vortices around the tank. Examine the structures as you vary δΩ. The wavelength for the instability should be roughly 2π times the shear layer width.