Experimental study of the generation of periodic internal waves by the boundary layer on a rotating disk

Abstract

The exact solution to the linearized problem of the generation of internal waves, which involves internal waves and internal boundary flows [1], allows us to estimate errors intrinsic to the well-known method of force (or mass) sources [2]. In the case of small displacements, calculations of perturbances excited by an oscillating bar satisfactorily agree with the measurement results of [3]. There exist situations when a body moving periodically in continuously stratified viscous fluid does not radiate (in the linear case) and generates only isopycnic boundary flows. This situation takes place, e.g., in the case of a horizontal disk performing torsional vibrations [4]. However, by virtue of the nonlinear nature of the hydrodynamic system of equations, various forms of motion interfere with one another. In particular, thin-layer boundary flows can be a source of periodic waves [4]. Previously, experimental studies of such internal-wave generators were not conducted. Therefore, it is of interest to investigate the practical feasibility of the principles for nonlinear generation. In the present paper, the possibility of generation of threedimensional beams of periodic internal waves by torsional vibrations of a horizontal disk are studied and the principal regularities connecting wave-field characteristics with the properties of a medium and source motion parameters are established.