Resonant internal waves in fluid flow

Abstract

UNDERSTANDING the flow of a stratified fluid over an uneven bed is an important problem in hydrodynamics. Previous field experiments using acoustic imagery1–3 have enhanced our understanding of internal-wave generation mechanisms. These studies have generally concentrated on isolated topographic features that show large-amplitude long internal waves and hydraulic jumps as the flow becomes critical defined in the hydraulic sense such that a long-wave speed vanishes with respect to a fixed coordinate system. We present field observations of stratified fluid flow over a nearly periodic topographic relief which show a unique series of resonant internal waves. The observations, carried out in the Rotterdam Waterway, show the presence of internal waves with wavelengths commensurate with those of the topography of the waterway bed and amplitudes that are three to four times larger than the relief of the topography generating them. Resonant internal waves may be important in understanding the flow dynamics of stratified coastal environments and may have consequences for atmospheric flows over mountain ranges.