Turbulence structure near a sharp density interface

Hannoun, Imad A.; Fernando, Harindra J. S.; List, E. J.

doi:10.1017/s0022112088000965

Cited by 131 publications

(140 citation statements)

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“…This agreement between the theory and the experiments, after invoking k -l / L o , suggests that this relationship might be valid, thus implying that the wavelength of the lowest-mode internal waves is determined by the large turbulence scales. This is not surprising in view of the flattening of the large eddies near a density interface as observed in oscillating-grid experiments by Dickey et al (1984) and Hannoun et al (1988). As a result of this flattening, we might anticipate that the largest eddies in the mixed layer impose the largest horizontal lengthscale of the internal waves.…”

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confidence: 59%

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Turbulent mixing at a shear-free density interface

Hannoun¹,

List

1988

J. Fluid Mech.

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The interaction of a sharp density interface with oscillating-grid-induced shear-free turbulence was experimentally investigated. A linear photodiode array was used in conjunction with laser-induced fluorescence to measure the concentration of dye that was initially only in the less dense layer. A laser-Doppler velocimeter was used to measure the vertical velocity in and above the density interface at a point where the dye concentration was also measured. Potential refractive-index-fluctuation problems were avoided using solutes that provided a homogeneous optical environment across the density interface. Internal wave spectra, amplitudes and velocities, as well as the vertical mass flux were measured. The results indicate that mixing occurs in intermittent bursts and that the gradient (local) Richardson number remains constant for a certain range of the overall Richardson number R3, defined in terms of an integral lengthscale, buoyancy jump and turbulence intensity. The spectra of the internal waves decay as f -' a t frequencies below the maximum Brunt-Vaisala frequency. These findings give support to a model for oceanic mixing proposed by Phillips (1977) in which the internal waves are limited in their spectral density by sporadic local instabilities and breakdown to turbulence. The results also indicate that, for a certain R, range, the thickness of the interfacial layer (normalized by the integral lengthscale of the turbulence) is a decreasing function of R3. At sufficiently high R, the interfacial thickness becomes limited by diffusive effects. Finally, we discuss a simple model for entrainment a t a density interface in the presence of shearfree turbulence.

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confidence: 59%

“…The bulk of the experimental procedures and equipment used in these experiments were discussed in Hannoun, Fernando & List (1988). We will confine our discussion here to the linear photodiode camera system.…”

Section: Experimental Methodsmentioning

confidence: 99%

Turbulent mixing at a shear-free density interface

Hannoun¹,

List

1988

J. Fluid Mech.

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“…The one-dimensional wavenumber spectrum of turbulence is described by a simple model similar to turbulence spectra observed in the laboratory (Hannoun et al 1988) and in the atmosphere FIG. 5.…”

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confidence: 94%

Observations of Turbulence in the Ocean Surface Boundary Layer: Energetics and Transport

Gerbi

Trowbridge

Terray

et al. 2009

Journal of Physical Oceanography

111

204

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Observations of turbulent kinetic energy (TKE) dynamics in the ocean surface boundary layer are presented here and compared with results from previous observational, numerical, and analytic studies. As in previous studies, the dissipation rate of TKE is found to be higher in the wavy ocean surface boundary layer than it would be in a flow past a rigid boundary with similar stress and buoyancy forcing. Estimates of the terms in the turbulent kinetic energy equation indicate that, unlike in a flow past a rigid boundary, the dissipation rates cannot be balanced by local production terms, suggesting that the transport of TKE is important in the ocean surface boundary layer. A simple analytic model containing parameterizations of production, dissipation, and transport reproduces key features of the vertical profile of TKE, including enhancement near the surface. The effective turbulent diffusion coefficient for heat is larger than would be expected in a rigid-boundary boundary layer. This diffusion coefficient is predicted reasonably well by a model that contains the effects of shear production, buoyancy forcing, and transport of TKE (thought to be related to wave breaking). Neglect of buoyancy forcing or wave breaking in the parameterization results in poor predictions of turbulent diffusivity. Langmuir turbulence was detected concurrently with a fraction of the turbulence quantities reported here, but these times did not stand out as having significant differences from observations when Langmuir turbulence was not detected.

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“…The attention is focused here on the unconventional SGS terms given in Eq. (27). No new models for the conventional SGS terms τ i j , ζ j , and η α j are proposed here since, as already stated in Sec.…”

Section: Resultsmentioning

confidence: 99%

“…In performing this analysis, the unclosed terms not associated with the conventional SGS fluxes are rewritten according to Eq. (27). Since in the supercritical-p realm, the ability of the typical SGS models (Smagorinsky model, the gradient model, and the scale-similarity model) to reproduce the conventional SGS fluxes has already been assessed, 12 the results described below indicate that we should focus on p(φ), q j (φ), and J α j (φ).…”

Section: B a Priori Analysismentioning

confidence: 99%

A priori and a posteriori investigations for developing large eddy simulations of multi-species turbulent mixing under high-pressure conditions

Borghesi

Bellan

2015

Physics of Fluids

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A Direct Numerical Simulation (DNS) database was created representing mixing of species under high-pressure conditions. The configuration considered is that of a temporally evolving mixing layer. The database was examined and analyzed for the purpose of modeling some of the unclosed terms that appear in the Large Eddy Simulation (LES) equations. Several metrics are used to understand the LES modeling requirements. First, a statistical analysis of the DNS-database large-scale flow structures was performed to provide a metric for probing the accuracy of the proposed LES models as the flow fields obtained from accurate LESs should contain structures of morphology statistically similar to those observed in the filtered-and-coarsened DNS (FC-DNS) fields. To characterize the morphology of the large-scales structures, the Minkowski functionals of the iso-surfaces were evaluated for two different fields: the second-invariant of the rate of deformation tensor and the irreversible entropy production rate. To remove the presence of the small flow scales, both of these fields were computed using the FC-DNS solutions. It was found that the large-scale structures of the irreversible entropy production rate exhibit higher morphological complexity than those of the second invariant of the rate of deformation tensor, indicating that the burden of modeling will be on recovering the thermodynamic fields. Second, to evaluate the physical effects which must be modeled at the subfilter scale, an a priori analysis was conducted. This a priori analysis, conducted in the coarse-grid LES regime, revealed that standard closures for the filtered pressure, the filtered heat flux, and the filtered species mass fluxes, in which a filtered function of a variable is equal to the function of the filtered variable, may no longer be valid for the high-pressure flows considered in this study. The terms requiring modeling are the filtered pressure, the filtered heat flux, the filtered pressure work, and the filtered species mass fluxes. Improved models were developed based on a scale-similarity approach and were found to perform considerably better than the classical ones. These improved models were also assessed in an a posteriori study. Different combinations of the standard models and the improved ones were tested. At the relatively small Reynolds numbers achievable in DNS and at the relatively small filter widths used here, the standard models for the filtered pressure, the filtered heat flux, and the filtered species fluxes were found to yield accurate results for the morphology of the large-scale structures present in the flow. Analysis of the temporal evolution of several volume-averaged quantities representative of the mixing layer growth, and of the cross-stream variation of homogeneous-plane averages and second-order correlations, as well as of visualizations, indicated that the models performed equivalently for the conditions of the simulations. The expectation is that at the much larger Reynolds numbers and much larger filter widths used in practical applications, the improved models will have much more accurate performance than the standard one.

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Turbulence structure near a sharp density interface

Cited by 131 publications

References 10 publications

Turbulent mixing at a shear-free density interface

Turbulent mixing at a shear-free density interface

Observations of Turbulence in the Ocean Surface Boundary Layer: Energetics and Transport

A priori and a posteriori investigations for developing large eddy simulations of multi-species turbulent mixing under high-pressure conditions

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