PIV measurements in the bottom boundary layer of the coastal ocean

Smith, W. A. M. Nimmo; Atsavapranee, Paisan; Katz, Joseph; Osborn, Thomas R.

doi:10.1007/s00348-002-0490-z

Cited by 69 publications

(14 citation statements)

References 25 publications

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“…Such measurements have been performed using profiling thermistors [ Caldwell and Chriss , ; Chriss and Caldwell , ], hot film anemometer arrays [ Foster et al ., , 2006], laser Doppler velocimeters [ Agrawal and Aubrey , ; Trowbridge and Agrawal , ], acoustic Doppler velocimeters [ Davis and Monismith , ; Feddersen et al ., ; Walter et al ., ], acoustic current meters [ Trowbridge , ; Williams et al ., ], and coherent Doppler profilers [ Lacy et al ., ; Hay , ; Zou et al ., ]. Our group has introduced the application of 2‐D particle image velocimetry (PIV) to resolve the flow in the inner part of the BBL, achieving 4–5 mm resolution over sample areas ranging from 20 × 20 cm 2 to 50 × 50 cm 2 [ Bertuccioli et al ., ; Doron et al ., ; Hackett et al ., ; Luznik et al ., ; Nimmo Smith et al ., , 2005]. Other PIV systems have been deployed recently to study turbulence structure in oceanic and fluvial environments [ Liao et al ., ; Steinbuck et al ., ; Tritico et al ., ].…”

Section: Introductionmentioning

confidence: 99%

“…Hence, a thorough understanding of the mechanisms that drive the BBL as well as small-scale processes that occur within is essential. It is commonly believed that in shallow waters, surface waves lead to the development of a 1-10 cm thin oscillating wave boundary layer (WBL) very close to the seabed, which is embedded within the few meters thick, tidally driven current BBL [Grant and Madsen, 1986;Nielsen, 1992;. The seabed itself is composed of roughness elements of various length scales, which might be misaligned with both the current and waves.…”

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: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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“…The vorticity characteristics of the extended volume are presented in Figure 3b. This is the three-dimensional equivalent of the planar evidence provided by Nimmo-Smith et al [2002 and Hackett et al [2011] that have shown the counterclockwise and clockwise rotation of cross-stream vortices within the bottom Figure 3. Visualization of coherent structures within an extended volume created using a frozen field approximation.…”

Section: Resultsmentioning

confidence: 56%

“…The vorticity characteristics of the extended volume are presented in Figure b. This is the three‐dimensional equivalent of the planar evidence provided by Nimmo‐Smith et al [, ] and Hackett et al [] that have shown the counterclockwise and clockwise rotation of cross‐stream vortices within the bottom boundary layer of the coastal ocean. The large cross‐stream vortex (labeled “vortex”) exhibits clockwise rotation (negative vorticity) consistent with a “head.”…”

Section: Resultsmentioning

confidence: 98%

“…The opposing burst/sweep motion causes a shear layer, inclined at 25–45° from the boundary [ Adrian , ]. Two‐dimensional flow visualization methods have previously shown that these coherent structures (i.e., elementary organized motions that exhibit both spatial and temporal persistence) also exist in the bottom boundary layer of tidal flows (Figure b) [ Nimmo‐Smith et al , , ; Hackett et al , ]. Conditional sampling based on vorticity revealed that these coherent structures contribute most to the Reynolds stress and, as such, are the key areas where energy is extracted from the mean flow and into turbulence [ Nimmo‐Smith et al , ].…”

Section: Introductionmentioning

confidence: 99%

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Direct measurement of hairpin‐like vortices in the bottom boundary layer of the coastal ocean

Steele

Nimmo‐Smith

Vlasenko

2016

Geophysical Research Letters

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Laboratory measurements and numerical modeling at low Reynolds numbers (Reθ<7700) indicate the energy‐containing turbulence of boundary layer flows comprises coherent packets of hairpin vortices. Here direct measurements in the bottom boundary layer of the coastal ocean at higher Reynolds numbers (Reθ = 266,150) show tidal flows also contain packets of large vortices separated by periods of more quiescent conditions. The 1452 vortices recorded within a 20 min period are typically aligned along stream (∼8.0° from the mean flow direction) and inclined to the horizontal (∼27.0° from the seabed), with a mean period of occurrence of 4.3 s. These results lend three‐dimensional, in situ support to an interpretation of the coastal ocean bottom boundary layer as comprising coherent packets of hairpin vortices. This demonstrates a direct linkage from low Reynolds number experiments to higher Reynolds number flows, permitting fine‐scale details of particle transport and pollutant dispersion to be inferred from lower Reynolds number data.

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Direct Measurements of Mean Reynolds Stress and Ripple Roughness in the Presence of Energetic Forcing by Surface Waves

et al. 2018

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Direct covariance observations of the mean flow Reynolds stress and sonar images of the seafloor collected on a wave‐exposed inner continental shelf demonstrate that the drag exerted by the seabed on the overlying flow is consistent with boundary layer models for wave‐current interaction, provided that the orientation and anisotropy of the bed roughness are appropriately quantified. Large spatial and temporal variations in drag result from nonequilibrium ripple dynamics, ripple anisotropy, and the orientation of the ripples relative to the current. At a location in coarse sand characterized by large two‐dimensional orbital ripples, the observed drag shows a strong dependence on the relative orientation of the mean current to the ripple crests. At a contrasting location in fine sand, where more isotropic sub‐orbital ripples are observed, the sensitivity of the current to the orientation of the ripples is reduced. Further, at the coarse site under conditions when the currents are parallel to the ripple crests and the wave orbital diameter is smaller than the wavelength of the relic orbital ripples, the flow becomes hydraulically smooth. This transition is not observed at the fine site, where the observed wave orbital diameter is always greater than the wavelength of the observed sub‐orbital ripples. Paradoxically, the dominant along‐shelf flows often experience lower drag at the coarse site than at the fine site, despite the larger ripples, highlighting the complex dynamics controlling drag in wave‐exposed environments with heterogeneous roughness.

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PIV measurements in the bottom boundary layer of the coastal ocean

Cited by 69 publications

References 25 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

Direct measurement of hairpin‐like vortices in the bottom boundary layer of the coastal ocean

Direct Measurements of Mean Reynolds Stress and Ripple Roughness in the Presence of Energetic Forcing by Surface Waves

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