Inertial Wave Attractors in Librating Cylinders: Axisymmetric versus Nonaxisymmetric Ends

Inertial waves in a rotating confined fluid can focus on closed trajectories, known as wave attractors. These regimes are not eigenmodes and are related only to the frequency dependence of the wave vector. This paper presents an experimental investigation of the cylindrical cavity shape’s effect on the attractor’s spatial structure. We considered three different configurations: i) a circular cylinder with both conical axisymmetric ends; ii) a cylinder with one straight end and the other end inclined to the plane of the cross-section; iii) both ends of the cylinder are inclined parallel. The major observed difference is the azimuthal flow structure. In the axisymmetric case, the shape of the wave attractor is independent of the azimuthal coordinate, and the instantaneous vorticity field represents a system of nested rings in the cross-section. If one of the cavity ends has a constant slope, wave focusing appears in the meridional plane passing near the direction specified by the geometry. The three-dimensional law of wave reflection from inclined boundaries causes meridional trapping, which is important in real geo- and astrophysical systems with complex boundary topography.