Wakes in Stratified Fluids

Lin, Jung-Tai; Pao, Yih-Ho

doi:10.1146/annurev.fl.11.010179.001533

Cited by 285 publications

(238 citation statements)

References 9 publications

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“…Indeed, this local Froude number decreases as 1/x and reaches unity for x I /D m = R 3 F m /6 ≈ 0.66F m . This transition distance is in good agreement with previous experimental results [6,4], where it was shown, or inferred, that the wake is 3D until N t ≈ 2, i.e. until x I /D m = F m in our units.…”

Section: A General Equationssupporting

confidence: 93%

“…until x I /D m = F m in our units. W e may also note that since the form of the reduced equations (5) and the presumed existence of self-similar solutions (6) requires that x/D is large, then the simultaneous requirement of large x/D and large local F limits this model system to flows with large initial F . Only then can a self-similar flow be imagined before the transition distance, x I .…”

Section: A General Equationsmentioning

confidence: 99%

“…In experiments on self-propelled slender bodies, Lin and Pao [6] showed that buoyancy begins to affect the flow at N t = 2, suspending the expansion of the wake in the vertical direction.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Self-preservation in stratified momentum wakes

2006

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A general model is described for drag wakes in a linearly stratified fluid, based on the selfpreservation of the flow. It is assumed that the buoyancy-controlled self-similar wake expands in the horizontal direction due to turbulent diffusion and in the vertical direction due to viscous diffusion. The mean characteristics of the wake (height, width and velocity defect) are analytically derived and show good agreement with existing data from experimental and numerical results.Moreover, the three regimes previously found in the literature that characterise different dynamical phases of the wake evolution are recovered, and two new regimes are found. The model allows for prediction of characteristic length and velocity scales at the high Reynolds numbers of large-scale applications of geophysical and naval origin.

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Section: A General Equationssupporting

confidence: 93%

Section: A General Equationsmentioning

confidence: 99%

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Self-preservation in stratified momentum wakes

2006

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“…Sufficiently strongly stratified turbulent flows are known to be highly anisotropic with relatively small characteristic velocity and length scales in the vertical direction. Lin & Pao (1979) reported observations of quasi-horizontal 'pancake' eddies, whose characteristic horizontal length scale is much bigger than its vertical scale, i.e. L h L v .…”

Section: Introductionmentioning

confidence: 99%

Robust identification of dynamically distinct regions in stratified turbulence

et al. 2016

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We present a new robust method for identifying three dynamically distinct regions in a stratified turbulent flow, which we characterise as quiescent flow, intermittent layers, and turbulent patches. The method uses the cumulative filtered distribution function of the local density gradient to identify each region. We apply it to data from direct numerical simulations of homogeneous stratified turbulence, with unity Prandtl number, resolved on up to 8192×8192×4096 grid points. In addition to classifying regions consistently with contour plots of potential enstrophy, our method identifies quiescent regions as regions where /νN 2 ∼ O(1), layers as regions where /νN 2 ∼ O(10), and patches as regions where /νN 2 ∼ O(100). Here is the dissipation rate of turbulence kinetic energy, ν is the kinematic viscosity, and N is the (overall) buoyancy frequency. By far the highest local dissipation and mixing rates, and the majority of dissipation and mixing, occur in patch regions, even when patch regions occupy only 5% of the flow volume. We conjecture that treating stratified turbulence as an instantaneous assemblage of these different regions in varying proportions may explain some of the apparently highly scattered flow dynamics and statistics previously reported in the literature.

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“…Then the size of the turbulent patch increases rapidly, even after the forcing has stopped, until a maximum vertical size is reached. During the subsequent stage of gravitational collapse, the vertical motions are suppressed and eventually the mixed region becomes fiat and the motion becomes quasi-horizontal; this final stage is characterized by the occurrence of "pancake" vortices, which have also been observed in the wakes of bodies towed through stratified fluids [Lin and Pao, 1979] or in collapsing density fronts [Liu et al, 1987] …”

Section: Paper Number 98jc01911mentioning

confidence: 99%

Evolution of an isolated turbulent region in a stratified fluid

Fonseka¹,

Fernando²,

Heijst³

1998

J. Geophys. Res.

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Abstract. This paper reports an experimental study on the evolution of an isolated turbulent region in an otherwise quiescent linearly stratified fluid. A turbulent patch was generated by pulsed horizontal injection of a small volume of fluid. It was found that the turbulent blob thus produced initially grows as in a nonstratified fluid for a nondimensional time period of Nt m 4-5 (with N the buoyancy frequency), attains a maximum height, and then physically collapses slowly to form a planar, quasi-two-dimensional dipole pattern. The timescale for the physical collapse of the blob was found to be much larger than that of the turbulence collapse. Scaling arguments are presented to explain the evolution of the turbulent region, and the experimental results are compared with the model predictions.

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Wakes in Stratified Fluids

Cited by 285 publications

References 9 publications

Self-preservation in stratified momentum wakes

Self-preservation in stratified momentum wakes

Robust identification of dynamically distinct regions in stratified turbulence

Evolution of an isolated turbulent region in a stratified fluid

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