A Free-Floating PIV System: Measurements of Small-Scale Turbulence under the Wind Wave Surface

Wang, Binbin; Qian, Lei; Xiao, Jianen; Bootsma, Harvey A.

doi:10.1175/jtech-d-12-00092.1

Cited by 11 publications

(19 citation statements)

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“…We extended the regressions describing the decrease in e with depth in the upper 10 cm [Wang et al, 2013] and find that our measured dissipations are in the range predicted for the measured wind speeds and estimated significant wave heights [Terray et al, 1996] for our study. We argue that the lower values of A, that is lower normalized dissipation, under high winds and cooling results from a larger fraction of the wind's energy working against the stable stratification found within and at the base of the actively mixing layer.…”

Section: Coefficients)supporting

confidence: 57%

Similarity scaling of turbulence in a temperate lake during fall cooling

et al. 2014

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Turbulence, quantified as the rate of dissipation of turbulent kinetic energy (e), was measured with 1400 temperature-gradient microstructure profiles obtained concurrently with time series measurements of temperature and current profiles, meteorology, and lake-atmosphere fluxes using eddy covariance in a 4 km 2 temperate lake during fall cooling. Ãw /kz, where u Ãw is the water friction velocity computed from wind shear stress, k is von Karman's constant, z is depth, and J B0 is surface buoyancy flux. Below a depth equal to |L MO | during cooling, dissipation was uniform with depth and controlled by buoyancy flux. Departures from similarity scaling enabled identification of additional processes that moderate near-surface turbulence including mixed layer deepening at the onset of cooling, high-frequency internal waves when the diurnal thermocline was adjacent to the air-water interface, and horizontal advection caused by differential cooling. The similarity scaling enables prediction of near-surface e as required for estimating the gas transfer coefficient using the surface renewal model and for understanding controls on scalar transport.

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Section: Coefficients)supporting

confidence: 57%

Similarity scaling of turbulence in a temperate lake during fall cooling

et al. 2014

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“…Typical vertical profiles of ε measured by the FPIV can be found in Wang et al . []. Generally, all profiles (with and without the chamber cover) showed higher ε close to the water surface, decaying with depth.…”

Section: Resultsmentioning

confidence: 90%

“…Wang et al . [] estimated that the platform motion‐induced artificial vorticity and dissipation rate were 2–3 orders of magnitude smaller than measured ones.…”

Section: Methodsmentioning

confidence: 88%

“…The total measurement time for each case was from 30 to 60 min. Statistics of turbulence immediately below the air‐water interface were measured by a free‐floating Particle Image Velocimetry (FPIV) system [ Wang et al ., ] with and without flux chamber cover. Cases with chamber covering are denoted with suffix “C.” CO 2 flux data were not available for case W1C due to a malfunction of the FC system.…”

Section: Methodsmentioning

confidence: 99%

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On the coefficients of small eddy and surface divergence models for the air‐water gas transfer velocity

et al. 2015

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Recent studies suggested that under low to moderate wind conditions without bubble entraining wave breaking, the air-water gas transfer velocity k 1 can be mechanistically parameterized by the nearsurface turbulence, following the small eddy model (SEM). Field measurements have supported this model in a variety of environmental forcing systems. Alternatively, surface divergence model (SDM) has also been shown to predict the gas transfer velocity across the air-water interface in laboratory settings. However, the empirically determined model coefficients (a in SEM and c 1 in SDM) scattered over a wide range. Here we present the first field measurement of the near-surface turbulence with a novel floating PIV system on Lake Michigan, which allows us to evaluate the SEM and SDM in situ in the natural environment. k 1 was derived from the CO 2 flux that was measured simultaneously with a floating gas chamber. Measured results indicate that a and c 1 are not universal constants. Regression analysis showed that a $ logðeÞ while the near-surface turbulence dissipation rate e is approximately greater than 10 26 m 2 s 23 according to data measured for this study as well as from other published results measured in similar environments or in laboratory settings. It also showed that a scales linearly with the turbulent Reynolds number. Similarly, coefficient c 1 in the SDM was found to linearly scale with the Reynolds number. These findings suggest that larger eddies are also important parameters, and the dissipation rate in the SEM or the surface divergence b 0 in the SDM alone may not be adequate to determine k 1 completely.

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“…Several self-contained, fully or partially submersible in situ PIV systems were developed and applied in natural aquatic environments [14,15]. We have recently developed a battery-powered, self-contained under water miniature PIV (UWM-PIV) system which has been successfully applied to measure smallscale hydrodynamics in the bottom boundary layer and surface streamwise mean velocity u; v; w instantaneous streamwise, spanwise, and vertical velocity u 0 , v 0 , w 0 streamwise, spanwise, and vertical fluctuating velocity component u n bottom friction velocity u 02 , w 02 Reynolds normal stress À u 0 w 0 Reynolds shear stress z height above bottom z 0 roughness height boundary layer of Lake Michigan [16,17]. A second-generation UWMPIV was also developed for high speed flow measurement with a dual-beam-dual-camera configuration [18].…”

Section: Apparatus and Experiments Setupmentioning

confidence: 99%