Downward propagating internal waves generated at the base of the surface layer of a stratified fluid (original) (raw)
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The pattern of attached internal waves [1] as an analogue of lee waves in the atmosphere [2] and ocean , as calculated by the source-sink method , agrees satisfactorily with observations and laboratory measurements on waves past perfectly shaped obstacles when the wake effect can be ignored. The wave field around a symmetric body dipped into a continuously stratified fluid is antisymmetric about the horizontal plane passing through the line of motion of the body center. In some flow regimes with waves interacting actively with vortices in the wake, the antisymmetric wave pattern evolves into a symmetric one at a large distance from the obstacle [6]. In a real situation, the obstacles are generally irregular in shape and, therefore, a skew in the flow can affect the field structure of radiated waves. This work is devoted to the experimental study of the internal waves generated by a vertical or inclined plate towed uniformly when not only a drag force but also a lifting force arises.
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Nonlinear Processes in Geophysics, 2015
The objective of this paper is to study the dynamics of small-scale turbulence near a pycnocline, both in the free regime and under the action of an internal gravity wave (IW) propagating along a pycnocline, using direct numerical simulation (DNS). Turbulence is initially induced in a horizontal layer at some distance above the pycnocline. The velocity and density fields of IWs propagating in the pycnocline are also prescribed as an initial condition. The IW wavelength is considered to be larger by the order of magnitude as compared to the initial turbulence integral length scale. Stratification in the pycnocline is considered to be sufficiently strong so that the effects of turbulent mixing remain negligible. The dynamics of turbulence is studied both with and without an initially induced IW. The DNS results show that, in the absence of an IW, turbulence decays, but its decay rate is reduced in the vicinity of the pycnocline, where stratification effects are significant. In this ca...
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Journal of Fluid Mechanics, 2010
Direct numerical simulations are performed to investigate the interaction between a stably stratified jet and internal gravity waves from an adjacent shear layer with mild stratification. Results from two simulations are presented: one with the jet located far from the shear layer (far jet) and the other with the shear layer right on top of the jet (near jet). The near jet problem is motivated by velocity and stratification profiles observed in equatorial undercurrents. In the far case, internal waves excited by the Kelvin-Helmholtz (K-H) rollers do not penetrate the jet. They are reflected and trapped in the region between the shear layer and the jet and lead to little dissipation. In the near case, internal waves with wavelength larger than that of the K-H rollers are found in and below the jet. Pockets of hot fluid, associated with horseshoe vortices that originate from the shear layer, penetrate into the jet region, initiate turbulence and disrupt the internal wave field. Coherent patches of enhanced dissipation moving with the mean velocity are observed. The dissipation in the stably stratified near jet is large, up to three orders of magnitude stronger than that in the propagating wave field or the jet of the far case.
Experimental study of internal waves over a slope
Journal of Fluid Mechanics, 1974
Internal waves of the fundamental mode propagating into a shoaling region have been studied experimentally in a continuously stratified fluid. The waves divide into three classes depending upon the ratio of the bottom slope γ to the wave-characteristic slope c. For γ/c < 1, the amplitude and wavenumber changes of the waves over the slope are in reasonable accord with a simple inviscid linear theory, prior to wave breakdown near the intersection of the slope and surface. Considerable mixing occurs in this corner region. When γ/c = 1, a striking instability of the bottom boundary layer is observed and the waves are heavily damped. When γ/c > 1, the waves are inhomogeneous and have complex spatial dependence.
Wave disturbances of stratified fluid due to vertical jet
The statement and solution of a new problem are presented for fluid wave motions at the injection of vertical axisymmetric jet into a stable stratified fluid, which density linearly increases with the depth. Flow in the jet is assumed to be potential, the motion of stratified fluid is described by Boussincsq's approximation. The dispersion equation is derived and analysed. The conditions of wave e:istence arc found and the analysis of phase and group velocities and wave modes is presented. It is shown that in outer medium the wave disturbances propagate along the jet as it was observed in experiments.
First stage of growth of internal waves in stably stratified fluids
Archives for Meteorology, Geophysics, and Bioclimatology Series A, 1982
A theoretical analysis of the first stage of growth of internal waves in stably stratified fluids is given. It is shown how, during the first stage, the profiles obtained by means of the lineadzed theory are maintained by the growing waves. The linearized theory seems also to model properly the mixing layers in a stably stratified fluid subject to forcing at the boundaries. The results of this work are confirmed by the analysis of the experimental data for a particular geophysical situation studied in a preceding article.