Direct numerical simulation of three-dimensional open-channel flow with zero-shear gas–liquid interface

Komori, Satoru; Nagaosa, Ryuichi; Murakámi, Yasuhiro; Chiba, Satoshi; Ishii, Katsuya; Kuwahara, Kunio

doi:10.1063/1.858797

Cited by 138 publications

(131 citation statements)

References 12 publications

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“…For simplicity, the free surface is assumed to be undeformed, an approximation good for low Froude number. In a DNS of unstratified open channel flow with a deformable free surface, Komori et al 17 found that at Re = 160, the surface is displaced by about 0.01% of the channel depth. Although we are considering a larger Reynolds number, it is expected that any displacements would remain small.…”

Section: Methodsmentioning

confidence: 99%

Large eddy simulation of stably stratified open channel flow

2005

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Large eddy simulation has been used to study flow in an open channel with stable stratification imposed at the free surface by a constant heat flux and an adiabatic bottom wall. This leads to a stable pycnocline overlying a well-mixed turbulent region near the bottom wall. The results are contrasted with studies in which the bottom heat flux is nonzero, a difference analogous to that between oceanic and atmospheric boundary layers. Increasing the friction Richardson number, a measure of the relative importance of the imposed surface stratification with respect to wall-generated turbulence, leads to a stronger, thicker pycnocline which eventually limits the impact of wall-generated turbulence on the free surface. Increasing stratification also leads to an increase in the pressure-driven mean streamwise velocity and a concomitant decrease in the skin friction coefficient, which is, however, smaller than in the previous channel flow studies where the bottom buoyancy flux was nonzero. It is found that the turbulence in any given region of the flow can be classified into three regimes ͑unstratified, buoyancy-affected, and buoyancy-dominated͒ based on the magnitude of the Ozmidov length scale relative to a vertical length characterizing the large scales of turbulence and to the Kolmogorov scale. Since stratification does not strongly influence the near-wall turbulent production in the present configuration, the behavior of the buoyancy flux, turbulent Prandtl number, and mixing efficiency is qualitatively different from that seen in stratified shear layers and in channel flow with fixed temperature walls, and, furthermore, collapse of quantities as a function of gradient Richardson number is not observed. The vertical Froude number is a better measure of stratified turbulence in the upper portion of the channel where buoyancy, by providing a potential energy barrier, primarily affects the transport of turbulent patches generated at the bottom wall. The characteristics of free-surface turbulence including the kinetic energy budget and pressure-strain correlations are examined and found to depend strongly on the surface stratification.

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Section: Methodsmentioning

confidence: 99%

Large eddy simulation of stably stratified open channel flow

2005

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“…Alternatively, there have been relatively few DNS-based studies of turbulence in problems involving two-phase flows, if one excludes earlier research focusing on freesurface turbulence with and without wind shear (Lam & Banerjee 1992;Komori et al 1993b;Lombardi, DeAngelis & Banerjee 1996). Because of its relative simplicity, stratified gas-liquid flow has been the configuration best suited to investigating the underlying physics of turbulence at the interface.…”

Section: Wave Breaking and Turbulencementioning

confidence: 99%

Turbulence structure and interaction with steep breaking waves

Lakehal

Liovic

2011

J. Fluid Mech.

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Large-eddy and interface simulation using an interface tracking-based multi-fluid flow solver is conducted to investigate the breaking of steep water waves on a beach of constant bed slope. The present investigation focuses mainly on the 'weak plunger' breaking wave type and provides a detailed analysis of the two-way interaction between the mean fluid flow and the sub-modal motions, encompassing wave dynamics and turbulence. The flow is analysed from two points of views: mean to sub-modal exchange, and wave to turbulence interaction within the sub-modal range. Wave growth and propagation are due to energy transfer from the mean flow to the waves, and transport of mean momentum by these waves. The vigorous downwellingupwelling patterns developing at the head and tail of each breaker are shown to generate both negative-and positive-signed energy exchange contributions in the thin sublayer underneath the water surface. The details of these exchange mechanisms are thoroughly discussed in this paper, together with the interplay between threedimensional small-scale breaking associated with turbulence and the dominant twodimensional wave motion. A conditional zonal analysis is proposed for the first time to understand the transient mechanisms of turbulent kinetic energy production, decay, diffusion and transport and their dependence and/or impact on surface wrinkling over the entire breaking process. The simulations provide a thorough picture of airliquid coherent structures that develop over the breaking process, and link them to the transient mechanisms responsible for their local incidence.

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“…For example, DNS and large-eddy simulation (LES) of scalar transport in turbulent free-surface flows have been performed by e.g. Komori et al (1993), Handler et al (1999), Shen, Triantafyllou & Yue (2001), Lakehal et al (2003), Nagaosa & Handler (2003), Magnaudet & Calmet (2006), Hasegawa & Kasagi (2008 and Khakpour, Shen & Yue (2011). From such numerical simulation techniques, a detailed three-dimensional description of flow and scalar fields evolving in time can be generated.…”

Section: Introductionmentioning

confidence: 99%

“…In previous numerical studies (e.g. Komori et al 1993;Handler et al 1999;Liu et al 2009), these boundary conditions have been shown to capture the salient features of gas and temperature at the water surface.…”

mentioning

confidence: 99%

Statistics of surface renewal of passive scalars in free-surface turbulence

et al. 2011

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We perform direct numerical simulation to study the transport of gas and heat as passive scalars in free-surface turbulence. Our analysis focuses on the surface age of surface fluid particles, i.e. the time elapsed since the last surface renewal they experienced. Using Lagrangian tracing of fluid particles combined with heat diffusion analysis, we are able to directly quantify surface age to illustrate scalar characteristics at different stages of interfacial transfer. Results show that at the early stage of surface renewal, vertical advection associated with upwellings greatly enhances surface gas flux; random surface renewal model does not apply at this stage when most of the interfacial gas transfer occurs. After a fluid particle leaves the upwelling region, it may enter a nearby downwelling region immediately, where the gas flux is sharply reduced but the variation in surface temperature is small; alternatively, the fluid particle may travel along the surface for some time before it is absorbed by a downwelling, where the surface temperature has changed significantly due to long duration of diffusion and the gas flux is also reduced. To gain further insight into the relationships between surface velocity and scalar quantities, we perform a statistical analysis of upwellings using clustering and nonlinear regression. With this analysis, we are able to provide qualitative and quantitative descriptions of the skewed probability density functions associated with the surface divergence, temperature and gas flux that support our physics-based investigation of surface renewal and surface age.

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Direct numerical simulation of three-dimensional open-channel flow with zero-shear gas–liquid interface

Cited by 138 publications

References 12 publications

Large eddy simulation of stably stratified open channel flow

Large eddy simulation of stably stratified open channel flow

Turbulence structure and interaction with steep breaking waves

Statistics of surface renewal of passive scalars in free-surface turbulence

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