Structure of space-time correlations of bursting phenomena in an open-channel flow

Nakagawa, Hiroji; Nezu, Iehisa

doi:10.1017/s0022112081002796

Cited by 224 publications

(129 citation statements)

References 15 publications

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“…Figure 4(b) shows that y g grows linearly with λ 0 = 2π /α 0 , at least in the range y + g 100, y g /h 0.2, which corresponds roughly to the conventional limits of the logarithmic layer in channels, 39 recalling the similar linear scaling of structures [45][46][47][48][49] and spectra in wall-bounded flows (see Figure 5(b)). The linear behavior extends farther from the wall for even perturbations than for odd ones, clearly because the latter are constrained by the requirement that they should vanish at the centerline.…”

Section: The Linear Orr Mechanism In Channelssupporting

confidence: 54%

How linear is wall-bounded turbulence?

2013

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The relevance of Orr's inviscid mechanism to the transient amplification of disturbances in shear flows is explored in the context of bursting in the logarithmic layer of wall-bounded turbulence. The linearized problem for the wall normal velocity is first solved in the limit of small viscosity for a uniform shear and for a channel with turbulent-like profile, and compared with the quasiperiodic bursting of fully turbulent simulations in boxes designed to be minimal for the logarithmic layer. Many properties, such as time and length scales, energy fluxes between components, and inclination angles, agree well between the two systems. However, once advection by the mean flow is subtracted, the directly computed linear component of the turbulent acceleration is found to be a small part of the total. The temporal correlations of the different quantities in turbulent bursts imply that the classical model, in which the wall-normal velocities are generated by the breakdown of the streamwise-velocity streaks, is a better explanation than the purely autonomous growth of linearized bursts. It is argued that the best way to reconcile both lines of evidence is that the disturbances produced by the streak breakdown are amplified by an Orr-like transient process drawing energy directly from the mean shear, rather than from the velocity gradients of the nonlinear streak. This, for example, obviates the problem of why the cross-stream velocities do not decay once the streak has broken down. C

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Section: The Linear Orr Mechanism In Channelssupporting

confidence: 54%

How linear is wall-bounded turbulence?

2013

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“…The streaky pattern observed at the water surface is very similar to the pattern of low speed streaks near no-slip walls, as described by Nakagawa and Nezu (1981) and Smith and Paxson (1983). They found the spacing between these streaks to be lognormally distributed with a mean dimensionless streak spacing of l + ¼ lu *w /ν ¼ 100, where the mean streak spacing is given by l, the friction velocity by u *w and the kinematic viscosity by ν.…”

Section: Small Scale Turbulencesupporting

confidence: 73%

Transfer Across the Air-Sea Interface

Garbe

Rutgersson

Boutin

et al. 2013

Springer Earth System Sciences

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The efficiency of transfer of gases and particles across the air-sea interface is controlled by several physical, biological and chemical processes in the atmosphere and water which are described here (including waves, large-and small-scale turbulence, bubbles, sea spray, rain and surface films). For a deeper understanding of relevant transport mechanisms, several models have been developed, ranging from conceptual models to numerical models. Most frequently the transfer is described by various functional dependencies of the wind speed, but more detailed descriptions need additional information. The study of gas transfer mechanisms uses a variety of experimental methods ranging from laboratory studies to carbon budgets, mass balance methods, micrometeorological techniques and thermographic techniques. Different methods resolve the transfer at different scales of time and space; this is important to take into account when comparing different results. Air-sea transfer is relevant in a wide range of applications, for example, local and regional fluxes, global models, remote sensing and computations of global inventories. The sensitivity of global models to the description of transfer velocity is limited; it is however likely that the formulations are more important when the resolution increases and other processes in models are improved. For global flux estimates using inventories or remote sensing products the accuracy of the transfer formulation as well as the accuracy of the wind field is crucial. IntroductionThe transfer of gases and particles across the air-sea interface depends not only on the concentration difference between the water and the air, but also on the efficiency of the transfer process. The efficiency of the transfer is controlled by complex interaction of a variety of processes in the air and in the water near the interface. Here we treat both gases and particles since the transfer, to some extent, is governed by similar mechanisms. Studies of transfer across the air-sea interface include a variety of methods and techniques ranging from laboratory studies, modeling and large-scale field studies. Various methods reach somewhat different conclusions, due to representation of different

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“…Once the fluid shear stress exceeds the local strength of the bed, surface erosion occurs initially, in the form of stripping and LENG, X., and Large instantaneous shear stresses may be associated with turbulent events (NARASIMHA et al 2007, TREVETHAN andCHANSON 2010), typically linked to coherent turbulent structures such as eddies and bursting (RAO et al 1971, NAKAGAWA andNEZU 1981). They are likely to play a major role in terms of sediment scour, transport and accretion as well as contaminant mixing and dispersion (NIELSEN 1992, NEZU andNAKAGAWA 1993).…”

Section: Discussionmentioning

confidence: 99%

Coupling between free-surface fluctuations, velocity fluctuations and turbulent Reynolds stresses during the upstream propagation of positive surges, bores and compression waves

Leng

Chanson

2015

Environ Fluid Mech

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In open channel, canals and rivers, a rapid increase in flow depth will induce a positive surge, also called bore or compression wave. The positive surge is a translating hydraulic jump. Herein new experiments were conducted in a large-size rectangular channel to characterise the unsteady turbulent properties, including the coupling between free-surface and velocity fluctuations. Experiments were repeated 25 times and the data analyses yielded the instantaneous median and instantaneous fluctuations of free-surface elevation, velocities and turbulent Reynolds stresses. The passage of the surge front was associated with large free-surface fluctuations, comparable to those observed in stationary hydraulic jumps, coupled with large instantaneous velocity fluctuations. The bore propagation was associated with large turbulent Reynolds stresses and instantaneous shear stress fluctuations, during the passage of the surge. A broad range of shear stress levels was observed underneath the bore front, with the probability density of the tangential stresses distributed normally and the normal stresses distributed in a skewed single-mode fashion. Maxima in normal and tangential stresses were observed shortly after the passage of a breaking bore roller toe. The maximum Reynolds stresses occurred after the occurrence of the maximum free-surface fluctuations, and this time lag implied some interaction between the free-surface fluctuations and shear stress fluctuations beneath the surge front, and possibly some causal effect.

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Structure of space-time correlations of bursting phenomena in an open-channel flow

Cited by 224 publications

References 15 publications

How linear is wall-bounded turbulence?

How linear is wall-bounded turbulence?

Transfer Across the Air-Sea Interface

Coupling between free-surface fluctuations, velocity fluctuations and turbulent Reynolds stresses during the upstream propagation of positive surges, bores and compression waves

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