Internal-wave radiation and optical measurements in stratified fluids

Abstract

In many problems of considerable geophysical and industrial interest, fluid flows are characterized by the presence of a stable vertical density gradient. Under suitable conditions such fluids can support internal waves. In many aspects internal waves are similar to surface waves. Owing to small density difference across the fluid depth the effective gravity governing the dynamics of internal waves is typically by two or three orders of magnitude smaller than the terrestrial gravity. In a continuously stratified fluid the strength of gravity and viscous effects depends on the vertical density gradient, fluid viscosity, and characteristics of a wave-emitting disturbance. In the present report we focus our attention on experiments with internal waves generated by circular and rectilinear oscillations of cylinders in a uniformly stratified fluid. Quantitative measurements of internal waves are performed with the help of ‘synthetic’ schlieren technique based on computer evaluation of optical distortions in stratified fluids. The effects of the type and amplitude of oscillations on the generation of linear and nonlinear density-gradient disturbances are discussed.