An investigation of internal gravity waves generated by a buoyantly rising fluid in a stratified medium

Abstract

Experiments have been carried out to examine the spectrum of internal gravity waves excited in a stratified incompressible fluid during stabilization following the buoyant rise of a miscible fluid. The rise time of the buoyant fluid to its stabilization height in the stratified fluid was observed to be about 0.85 of the Brunt-Väisälä period for the stratified fluid. The motion of specific fluid elements in the wave field was observed using neutrally buoyant marker particles, and the particle trajectories were found to be in close accord with theoretical predictions. Observations on the internal waves generated by the forced oscillation of a spherical body suspended in the stratified medium showed the wave pattern to be well behaved and similar to that described by Mowbray & Rarity. However, the gravity wave field generated by the motion of the buoyant fluid was observed to be inhomogeneous and transient in nature. Wave periods from one to four times the Brunt-Väisälä period were clearly observed and at later times it appeared that the motion tended towards vertical oscillations a t the Brunt- Väisälä frequency.

Internal wave generation in uniformly stratified fluids. Part 1. Green's function and point sources

“…Their decrease as l/&, consistent with the conservation of energy for conical waves, coincides with the experiments of McLaren et al (1973) again. The velocity singularity at the edges of region I11 remains integrable, and the energy flux consequently finite.…”

“…non-zero as the far field is approached. In region I11 for instance,as T >> a > lu+l,This expression makes Appleby's & Crighton's (1987) result for a pulsating sphere more explicit, and is similar to Lighthill's (1978, $4.10) result for a distributed mass source.The phase @ = wt+iarccos (u+/a) varies transversely, in agreement with the experiments ofMcLaren et al (1973). From its differentiation with respect to u+(cf.…”

“…Experiments about the generation of internal waves have involved bodies of finite dimensions, and various shapes and motions. Monochromatic oscillations of a cylinder (Mowbray & Rarity 1967;Kamachi & Honji 1988) or a sphere (McLaren et al 1973), impulsive oscillation of a cylinder (Stevenson 1973) and free motion of a displaced solid (Larsen 1969) Few theoretical studies consider the generation of internal waves by sources of finite size from a general point of view. All of them are asymptotic and rely on farfield or large-time hypotheses.…”

Internal gravity waves generated by convective plumes

“…One of the first experimental studies designed to investigate the nature of internal gravity waves generated by a thermal (an instantaneous release of a buoyant volume of fluid) was by McLaren et al (1973). The wave field was analysed by studying the trajectories of buoyant marker particles placed in the linearly stratified ambient.…”

A survey of selected aspects of stratified and rotating fluids

“…When the body remains at a fixed location and bobs up and down or " breathes fluid" in and out, these waves have been analyzed [36,37] and measured experimentally [38]. When the body is both translating and oscillating at a prescribed frequency, either greater or less than the Brunt-ViiisiiJa frequency, the internal-wave system has been analyzed [39] and the phase configuration of the waves have been observed experimentally [40] .…”