Internal waves generated by the wake of Gaussian hills

Dupont, Pascal; Kadri, Y.; Chomaz, Jean‐Marc

doi:10.1063/1.1406936

Cited by 9 publications

(7 citation statements)

References 18 publications

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“…Experimental papers report on good agreement with the linear predictions Eqs. (4) and (5) without significant influence from the object shape (Baines, 1979;Castro et al, 1983;Boyer and Tao, 1987;Kadri et al, 1996;Dupont et al, 2001). Note, however, that the dimensionless towing velocity in these experiments was restricted in the interval U/Nh ∈ [0.1, 0.8], which is much closer to an assumed linear regime than in our experiments.…”

Section: Discussionmentioning

confidence: 48%

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Stratified flow over asymmetric and double bell-shaped obstacles

Gyüre

Jánosi

2003

Dynamics of Atmospheres and Oceans

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Section: Discussionmentioning

confidence: 48%

“…Most of the data seem to collapse onto a line of slope ∼1/2, outliers are the results for obstacle "B" towed with the gentle slope leeward. Note that Dupont et al (2001) found in their experiments the same linear relationship c gz = mU, even the constant of proportionality m was found to be close to one-half.…”

Section: Initial Transientsmentioning

confidence: 68%

Stratified flow over asymmetric and double bell-shaped obstacles

Gyüre

Jánosi

2003

Dynamics of Atmospheres and Oceans

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“…Body-forced lee waves are present in all situations but tend to be the dominant IW source at low Fr. At higher Fr, turbulent wake-generated IWs dominate (Dupont et al 2001). In this regime, the turbulent eddies within the wake will result in the generation of IWs.…”

Section: Stratified Wakesmentioning

confidence: 95%

“…Also relevant are the related studies of lee wave flows over topographic obstacles (i.e. objects mounted on a fixed surface) (Castro, Snyder & Baines 1990;Vosper et al 1999;Dupont et al 2001;Dalziel et al 2011). Although many of these studies are at low Re, they exhibit the same wavefield features as objects towed in an unbounded flow.…”

mentioning

confidence: 97%

The internal wavefield generated by a towed sphere at low Froude number

Brandt

Rottier

2015

J. Fluid Mech.

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In highly stratified atmospheric and oceanic environments, a large fraction of energy input by various sources can be manifest as internal waves (IWs). The propagating nature of IWs results in the distribution of the energy over a large fraction of the air/water column. Wakes of translating bodies are one source of input energy that has been of continued interest. To further the understanding of wakes in strongly stratified environments, and particularly the near-field regime where strong coupling to the internal wavefield is evident, an extensive series of experiments on the internal wavefield generated by a towed sphere was performed, wherein the internal wavefield was measured over a Froude number range 0.1 Fr 5 (where Fr = U/ND, U is the tow speed, D the sphere diameter and N the Brunt-Väisälä (BV) frequency). In a second series of experiments, the temporal wavefield evolution was studied over two BV periods. These measurements show that the body generation (lee wave) mechanism dominates at Fr 1, while the random eddies in the turbulent wake become the dominant source at Fr 1. In the low-Fr regime, Fr 1, there is a resonant peak in the coupling of the input wake energy to the internal wavefield at a Froude number of ∼0.5, and at its maximum 70 % of the input energy is coupled into IW potential energy. In this regime it was also found that the spreading angle of the evolving wavefield was considerably broader than predicted by the classical point-source models for the wavefield further downstream, owing to the existence in the near field of a significant energy content in the higher-IW modes that deteriorate at later times. In the low-Fr regime, it was found that, while the IW potential energy increases ∝ Fr 2 , the fraction of the total energy input is a weak function of Fr, varying as Fr 1/2 .

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“…One might be tempted to correlateλ H to the size of quasi-two-dimensional coherent structures within the wake, e.g. see Dupont, Kadri & Chomaz (2001). It is known that the Strouhal number St = D/λ x scales as (X/D) −1/3 , where λ x is the horizontal length scale of the coherent structures.…”

Section: Wave Selection Mechanismmentioning

confidence: 99%

Surface manifestation of internal waves emitted by submerged localized stratified turbulence

Zhou

Diamessis

2016

J. Fluid Mech.

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The internal waves (IWs) radiated by the turbulent wake of a sphere of diameter $D$ towed at speed $U$ are investigated using three-dimensional fully nonlinear simulations performed in a linearly stratified Boussinesq fluid with buoyancy frequency $N$. The study focuses on a broad range of wave characteristics in the far field of the turbulent wave source, specifically at the sea surface (as modelled by a free-slip rigid lid) where the IWs reflect. Six simulations are performed at Reynolds number $Re\equiv UD/{\it\nu}\in \{5\times 10^{3},10^{5}\}$ and Froude number $Fr\equiv 2U/(ND)\in \{4,16,64\}$, where ${\it\nu}$ is viscosity. The wave-emitting wake is located at a fixed distance of $9D$ below the surface. As the wake evolves for up to $O(300)$ units of buoyancy time scale $1/N$, IW characteristics, such as horizontal wavelength ${\it\lambda}_{H}$ and wave period $T$, are sampled at the sea surface via wavelet transforms of horizontal divergence signals. The statistics of amplitudes and orientations of IW-induced surface strains are also reported. The mean dimensionless observable wavelength $\overline{{\it\lambda}}_{H}/D$ at the sea surface decays in time as $(Nt)^{-1}$, which is due to the waves’ dispersion. This observation is in agreement with a linear propagation model that is independent of the wake $Re$ and $Fr$. This agreement further suggests that the most energetic waves impacting the surface originate from the early-time wake that is adjusting to buoyancy. The most energetic dimensionless wavelength $\hat{{\it\lambda}}_{H}/D$ is found to scale as $Fr^{1/3}$ and decrease with $Re$, which causes the arrival time (in $Nt$ units) of the strongest waves at the surface to scale as $Fr^{-1/3}$ and increase with $Re$. This wavelength $\hat{{\it\lambda}}_{H}$ is also found to correlate with the vertical Taylor scale of the wake turbulence. IW-driven phenomena at the surface that are of interest to an observer, such as the local enrichment of surfactant and the transport of ocean surface tracers, are also examined. The local enrichment ratio of surface scalar scales linearly with the steepness of IWs that reach the surface, and the ratio often exceeds a possible visibility threshold. The Lagrangian drifts of ocean tracers, which are linked to the nonlinear interaction between incident and reflecting IW packets, create a local divergence in lateral mass transport right above the wake centreline, an effect that intensifies strongly with increasing $Fr$. The findings of this study may serve as a platform to investigate the generation and surface manifestation of IWs radiated by other canonical submerged stratified turbulent flows.

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Internal waves generated by the wake of Gaussian hills

Cited by 9 publications

References 18 publications

Stratified flow over asymmetric and double bell-shaped obstacles

Stratified flow over asymmetric and double bell-shaped obstacles

The internal wavefield generated by a towed sphere at low Froude number

Surface manifestation of internal waves emitted by submerged localized stratified turbulence

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