Wind wave growth in the viscous regime

Wu, Jiarong; Deike, Luc

doi:10.1103/physrevfluids.6.094801

Cited by 16 publications

(20 citation statements)

References 41 publications

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“…Overall, we are able to show directly that the pressure energy input plays a dominant role in wave growth for gravity waves of realistic wave age, especially when there is a finite amplitude established (). This is a different picture in terms of forcing mechanism from our previous 2-D study (Wu & Deike 2021), where the waves are gravity-capillary waves with , and the laminar wind has a linear velocity profile with much stronger shearing ( around 1).…”

Section: Direct Observation Of the Wind Wave Growth And The Surface S...contrasting

confidence: 66%

“…We initialise the wave shape with a given surface elevation function , in this case chosen to be a third-order Stokes wave shape similar to that used in Wu & Deike (2021). The initial steepness ranges from 0.1 to 0.3.…”

Section: The Dns Of Fully Coupled Wind and Wavesmentioning

confidence: 99%

“…After the turbulence precursor reaches a statistically steady state, the waves are released at (meaning that there is no manually setting anymore, and the initial orbital velocity is added), and travel with a phase speed given by the free surface dispersion relation where is the gravitational acceleration and is the surface tension. The orbital velocity is initialised with the corresponding velocity field of the third-order Stokes wave (see Wu & Deike 2021).…”

Section: The Dns Of Fully Coupled Wind and Wavesmentioning

confidence: 99%

“…The total energy input rate by the wind stress (into both waves and underwater drift layer) is a product of the stress and the surface water velocity: The part of that correlates with the pressure is the vertical orbital velocity , which gives (1.1); the part of that correlates with the viscous stress, however, contains both the wave horizontal orbital velocity and the drift velocity , where and denote the energy input by the viscous shear stress into the waves and the drift, respectively. The development of the drift is discussed in Wu & Deike (2021), and here we focus on the energy input into the waves Notice that the assumption means that the pressure-induced form drag contributes solely to the wave growth, while only a small variation of the viscous shear stress is correlated with and can contribute to the wave growth (Peirson & Garcia 2008). In other words, it is not the mean stresses but the correlated part of the stresses with the wave surface velocity that contributes to the wave energy growth.…”

Section: Direct Observation Of the Wind Wave Growth And The Surface S...mentioning

confidence: 99%

“…2020) and force the underlying current (Wu 1968; Lin et al. 2008; Wu & Deike 2021). With this widely adopted assumption (which we will test explicitly in this paper), the energy input rate can be written as (Grare et al.…”

Section: Introductionmentioning

confidence: 99%

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Revisiting wind wave growth with fully coupled direct numerical simulations

Popinet

Deike

2022

J. Fluid Mech.

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We investigate wind wave growth by direct numerical simulations solving for the two-phase Navier–Stokes equations. We consider the ratio of the wave speed $c$ to the wind friction velocity $u_*$ from $c/u_*= 2$ to 8, i.e. in the slow to intermediate wave regime; and initial wave steepness $ak$ from 0.1 to 0.3; the two being varied independently. The turbulent wind and the travelling, nearly monochromatic waves are fully coupled without any subgrid-scale models. The wall friction Reynolds number is 720. The novel fully coupled approach captures the simultaneous evolution of the wave amplitude and shape, together with the underwater boundary layer (drift current), up to wave breaking. The wave energy growth computed from the time-dependent surface elevation is in quantitative agreement with that computed from the surface pressure distribution, which confirms the leading role of the pressure forcing for finite amplitude gravity waves. The phase shift and the amplitude of the principal mode of surface pressure distribution are systematically reported, to provide direct evidence for possible wind wave growth theories. Intermittent and localised airflow separation is observed for steep waves with small wave age, but its effect on setting the phase-averaged pressure distribution is not drastically different from that of non-separated sheltering. We find that the wave form drag force is not a strong function of wave age but closely related to wave steepness. In addition, the history of wind wave coupling can affect the wave form drag, due to the wave crest shape and other complex coupling effects. The normalised wave growth rate we obtain agrees with previous studies. We make an effort to clarify various commonly adopted underlying assumptions, and to reconcile the scattering of the data between different previous theoretical, numerical and experimental results, as we revisit this longstanding problem with new numerical evidence.

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Section: Direct Observation Of the Wind Wave Growth And The Surface S...contrasting

confidence: 66%

Section: The Dns Of Fully Coupled Wind and Wavesmentioning

confidence: 99%