Water Wave Induced Boundary Layer Flows Above a Ripple Bed

Liu, Philip L.‐F.; Al-Banaa, K.; Cowen, Edwin A.

doi:10.1142/9789812796615_0003

Cited by 6 publications

(8 citation statements)

References 3 publications

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“…However, spatially varying high levels of turbulence generated as oscillatory flows interact with complex boundaries have been observed in numerous laboratory studies, e.g., Liu et al . [] for flows over ripples, and by Canals and Pawlak [] for a flapping plate.…”

Section: Resultsmentioning

confidence: 85%

“…Except for the immediate vicinity of the ripple crest (x = 2.8–8.3 cm), the wave‐turbulence correlation terms peak at the lowest point. Furthermore, conditional sampling of

- u^{'} w_{c}

based on the phase of

w_{c}

, clearly indicates that they peak at the crest and trough of the vertical wave velocity, and are minimal around the zero crossing periods of the wave cycle (not shown), consistent with trends observed during the vortex ejection process in other studies [e.g., Liu et al ., ]. Similarly, conditional sampling of

- \overset{u_{c} w^{'}}{true}

based on the phase of

u_{c}

shows that the maximum contribution to

- \overset{u_{c} w^{'}}{true}

occurs when

u_{c}

peaks.…”

Section: Resultsmentioning

confidence: 99%

“…Our planar measurements and waves, which are largely aligned perpendicularly to the light sheet, prevent us from shedding further light on the phenomena involved. However, spatially varying high levels of turbulence generated as oscillatory flows interact with complex boundaries have been observed in numerous laboratory studies, e.g., Liu et al [2004] for flows over ripples, and by Canals and Pawlak [2011] for a flapping plate. The existence of several potentially relevant length scales for the combined wave-current BBL, such as z 0fit , z 0m , m=u Ã fit , and A b , raises questions about the proper scales for normalizing trends of Reynolds stresses and vertical scales.…”

Section: 1002/2014jc010606mentioning

confidence: 99%

“…A comparison between some of the early models has shown that the variations in the predicted mean bed shear stress values range from 30 to 40% [ Soulsby et al ., ]. A substantial number of laboratory studies of boundary layers over rippled beds have been undertaken for simplified cases of purely oscillatory flow [ Liu et al ., ; Nichols and Foster , ; Sleath , ; Van der Werf et al ., ] as well as for waves and current collinear [ Kemp and Simons , ] or perpendicular [ Faraci et al ., ; Musumeci et al ., ] to each other. Some of the important relevant findings are summarized in the next paragraph.…”

Section: Introductionmentioning

confidence: 99%

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On the wave and current interaction with a rippled seabed in the coastal ocean bottom boundary layer

Nayak

Kiani

et al. 2015

J. Geophys. Res. Oceans

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Interactions of currents and waves with a rippled seabed in the inner part of the coastal ocean bottom boundary layer are studied using particle image velocimetry, ADV, and bottom roughness measurements. Mean velocity profiles collapse with appropriate scaling in the log layer, but vary substantially in the roughness sublayer. When wave-induced motions are similar or greater than the mean current, the hydrodynamic roughness (z 0 ) determined from velocity profiles is substantially larger than directly measured values. The roughness signature in turbulent energy spectra persists with elevation when its scale falls in the dissipation range, but decays in the log layer for larger roughness elements. Reynolds shear stress profiles peak in the lower parts of the log layer, diminishing below it, and gradually decaying at higher elevations. In contrast, wave shear stresses are negligible within the log layer, but become significant within the roughness sublayer. This phenomenon is caused by an increase in the magnitude and phase lag of the vertical component of wave-induced motion. No single boundary layer length scale collapses the Reynolds stresses, but both the Prandtl mixing length and eddy viscosity profiles agree well with the classical model of linear increase with elevation, especially near the seabed. Within the log region, profiles of shear production and dissipation rates of turbulence converge. Below it, dissipation rapidly increases, peaking near the seabed. Conversely, the shear production decays near the seabed, in agreement with the eddy viscosity model, but in contrast to both laboratory and computational rough wall studies.

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Section: Resultsmentioning

confidence: 85%

“…Except for the immediate vicinity of the ripple crest (x = 2.8–8.3 cm), the wave‐turbulence correlation terms peak at the lowest point. Furthermore, conditional sampling of

- u^{'} w_{c}

based on the phase of

w_{c}

- \overset{u_{c} w^{'}}{true}

based on the phase of

u_{c}

shows that the maximum contribution to

- \overset{u_{c} w^{'}}{true}

occurs when

u_{c}

peaks.…”

Section: Resultsmentioning

confidence: 99%

Section: 1002/2014jc010606mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

On the wave and current interaction with a rippled seabed in the coastal ocean bottom boundary layer

Nayak

Kiani

et al. 2015

J. Geophys. Res. Oceans

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show abstract

“…Because this scale falls in the 16-22h range, that is, within the dissipation range of the turbulence, excessive presence of these eddies is expected to increase the dissipation rate. It seems reasonable to assume that these roughness size/scale eddies are generated due to flow separation and formation of a shear layer behind a bottom ripple [Liu et al, 2004;Fredsøe et al, 1999;Hong et al, 2011]. Accordingly, the generation rate of such eddies should correlate with the velocity above these ripples.…”

Section: Turbulent Kinetic Energy Shear Production and Dissipation Ratesmentioning

confidence: 99%

Field measurements of turbulence at an unstable interface between current and wave bottom boundary layers

Hackett¹,

Luznik²,

Nayak³

et al. 2011

J. Geophys. Res.

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[1] In situ particle image velocimetry measurements, at a resolution of 3.5 Kolmogorov scales, have been performed in the inner part of the coastal bottom boundary layer. The spatial details enable us to directly determine the vertical distributions of mean velocity, Reynolds shear stress, shear production and dissipation rates, energy spectra, and abundance of eddies. Focusing on cases with wave velocity of similar magnitude as the mean current, velocity profiles have logarithmic distributions in the upper half of the sample area. Below the log layer, but well above the bottom ripples, an inflection point appears, indicating a region of flow instability. Based on data interpretation, which includes variations in wave phase with height, this inflection occurs near the interface between current and thinner wave boundary layer (WBL) below it. Scaling of mean velocity profiles with shear velocity and characteristic roughness is effective only above the inflection point, while turbulence parameters scale reasonably well at all elevations. Instabilities associated with the inflection are manifested by a peak in turbulent shear production rate and a rapid increase in small-scale turbulence, as is evident from trends of the dissipation rate, energy spectra, and distribution of eddies with elevation. Therefore, the presence of a WBL generates a shear production peak and rapid increase in the dissipation rate at higher elevations than those found in rough-wall steady boundary layers. Transition between current and wave boundary layers is also characterized by broad Reynolds stress peaks and shear production exceeding the dissipation rate.Citation: Hackett, E. E., L. Luznik, A. R. Nayak, J. Katz, and T. R. Osborn (2011), Field measurements of turbulence at an unstable interface between current and wave bottom boundary layers,

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High-resolution PIV measurement over wind-generated waves

Abu Rowin,

Kevin,

Bhirawa

et al. 2024

Exp Fluids

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The interaction between wind and waves plays a significant role in the exchange of heat, aerosols and gases, thereby influencing our understanding of climate dynamics and air–sea interaction. Particle image velocimetry (PIV) has emerged as a valuable tool for investigating the intricate effects of small-scale waves on airflow characteristics in laboratory settings. However, previous PIV experiments have exhibited notable variability in spatial resolution, potentially affecting the accuracy of turbulence statistics, particularly in relation to small-scale waves such as capillary ripples. To systematically explore the impact of PIV spatial resolution on airflow characteristics over multi-scale wind-generated waves, we conducted high-resolution planar PIV experiments near the wave surface. We adjusted the spatial resolution of the results by modifying the spatial filter. Additionally, recognising the limitations of the high-resolution PIV system in terms of wall-normal and streamwise extent, we conducted larger field-of-view experiments to capture consecutive waveforms and achieve spatial averaging across the boundary layer. Consistent with existing literature, our findings illustrate the formation of a horizontal shear layer leading to airflow separation on the lee side of the wave, accompanied by a pronounced vorticity field and circulation region. Notably, analysis of the high-magnification dataset reveals localised airflow separation caused by small-scale capillary waves, phenomena not resolved by the large field-of-view set-up, underscoring the importance of adequate spatial resolution. Further analysis indicates that a spatial resolution larger than the size of the capillary waves leads to significant attenuation of the spanwise vorticity imposed by the small-scale waves. In this study, we also introduce a novel method relying to identify wave surfaces solely on PIV images, demonstrating its effectiveness in detecting capillary-scale waves.

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Water Wave Induced Boundary Layer Flows Above a Ripple Bed

Cited by 6 publications

References 3 publications

On the wave and current interaction with a rippled seabed in the coastal ocean bottom boundary layer

On the wave and current interaction with a rippled seabed in the coastal ocean bottom boundary layer

Field measurements of turbulence at an unstable interface between current and wave bottom boundary layers

High-resolution PIV measurement over wind-generated waves

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