Internal gravity waves in geophysical fluids

Staquet, Chantal

doi:10.1007/3-211-38078-7_2

Cited by 4 publications

(3 citation statements)

References 91 publications

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“…A direct consequence is that the dispersion relation of a monochromatic internal gravity wave is anisotropic, as we show now. The dispersion relation relates the wave frequency Ω to the wave vector k. It can be computed from energetic considerations in a straightforward and simple manner, without dealing with the linearized equations of motions ( [10]). According to Lighthill [1], the general expression of the dispersion relation is:…”

Section: Dispersion Relation Of Internal Gravity Wavesmentioning

confidence: 99%

Internal gravity waves: parametric instability and deep ocean mixing

Staquet¹

2007

Comptes Rendus. Mécanique

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The Boussinesq approximation provides a convenient framework to describe the dynamics of stably-stratified fluids. A fundamental motion in these fluids consists of internal gravity waves, whatever the strength of the stratification. These waves may be unstable through parametric instability, which results in turbulence and mixing. After a brief review of the main properties of internal gravity waves, we show how the parametric instability of a monochromatic internal gravity wave organizes itself in space and time, using energetics arguments and a simple kinematic model. We provide an example, in the deep ocean, where such instability is likely to occur, as estimates of mixing from in situ measurements suggest. We eventually discuss the fundamental role of internal gravity wave mixing in the maintenance of the abyssal thermal stratification. Résumé Sur les ondes internes de gravité : de l'instabilité paramétrique au mélange abyssal dans l'océan. L'approximation de Boussinesq constitue un cadre bien adapté à l'étude des fluides stablement stratifiés. Des ondes de gravité internes s'y développent, quel que soit le niveau de stratification, qui peuvent être instables par instabilité paramétrique. Turbulence et mélange en résultent. Après un bref rappel sur les propriétés des ondes de gravité internes, nous montrons comment s'organisent les transferts d'énergie, dans l'espace et dans le temps, lorsqu'une onde interne est paramétriquement instable. Un modèle cinématique simple est employé pour cela. Puis nous illustrons ce processus et ses conséquences par un exemple océanique : l'instabilité paramétique se produit très certainement dans l'océan profond, comme le suggèrent les mesures in situ. Nous discutons finalement du rôle fondamen-tal des ondes de gravité internes dans l'entretien de la stratification abyssale, par le mélange qu'elles induisent.

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Section: Dispersion Relation Of Internal Gravity Wavesmentioning

confidence: 99%

Internal gravity waves: parametric instability and deep ocean mixing

Staquet¹

2007

Comptes Rendus. Mécanique

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“…The classical book of Lighthill presents this subject with an emphasis on analogies between acoustics and internal waves (Lighthill, 1978). A general introduction to wave mean-flow interactions theories is given in (Staquet, 2005;Bühler, 2014). In the following, we will sometimes refer to the momentum flux divergence as the streaming force.…”

Section: Mean-flow Equationmentioning

confidence: 99%

On the Holton-Lindzen-Plumb model for mean flow reversals in stratified fluids

Renaud,

Venaille

2020

Preprint

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“…The flapping foil has been widely used as a simplified model for the locomotion of aquatic or aerial animals [1][2][3][4] to understand their high-efficiency mechanisms and to improve the design of artificial vehicles [5][6][7]. To our knowledge, most previous studies have focused on flapping foils operating in homogeneous fluids, or those with a constant density, while stratified fluids are found throughout nature in lakes, ponds, oceans and the atmosphere [8,9]. This density stratification (pycnoclines) can be due to temperature (thermoclines), salinity (haloclines) or both.…”

Section: Introductionmentioning

confidence: 99%

Swimming in density-stratified fluid: study on a flapping foil

Kandel

Deng

2022

Bioinspir. Biomim.

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It is of interest to investigate how a swimming animal performs in a density stratified fluid. This paper studies a simplified swimmer, a pitching NACA0015 airfoil, considering its locomotion in both homogeneous, or unstratified, and stratified fluid flows. A direct comparison is made between these two conditions, through two-dimensional numerical simulations. Our numerical results show that the stratification modifies the dynamics of the pitching foil in both its wake structures and the drag force, or thrust, as well as its propulsive performance. We suggest that the effects of stratification on the flapping performance or the propulsive efficiency can be categorized according to the Froude number, or the level of stratification. First, in the range of high Froude numbers, notable modification of the flow structure can be observed, which however does not affect much the propulsive performance. Second, at a very low Froude number, i.e., $Fr=1$, the propulsive efficiency drops markedly compared to its homogeneous counterpart, attributed to the pronounced internal waves induced by the strong stratification. Moreover, at a moderate Froude number $Fr=2$, we find an increase in the propulsive efficiency, which can be explained by the unique variation in the wake structure. At $A_D=2.50$, the propulsive efficiency peaks at $Fr=2$, with its efficiency $18.3\%$ higher than its homogeneous counterpart, exhibiting a favourable influence of the stratification on a swimmer.

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Internal gravity waves in geophysical fluids

Cited by 4 publications

References 91 publications

Internal gravity waves: parametric instability and deep ocean mixing

Internal gravity waves: parametric instability and deep ocean mixing

On the Holton-Lindzen-Plumb model for mean flow reversals in stratified fluids

Swimming in density-stratified fluid: study on a flapping foil

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