The thermal structure of an air–water interface at low wind
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Handler, R.; Smith, Geoffrey B.; Leighton, R. I.

doi:10.3402/tellusa.v53i2.12187

Cited by 50 publications

(42 citation statements)

References 24 publications

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“…This suggests that coherent motions associated with the low-speed and high-speed streaks have a significant relationship with the velocity shear stress. Handler et al [4] revealed that surface-temperature pattern was dominated by the streaky structure in the open-channel flows coupled with wind, and it was found that characteristic spanwise length scale is almost same as one observed in the turbulent velocity fields.…”

Section: Introductionmentioning

confidence: 93%

Turbulence structure and coherent vortices in open-channel flows with wind-induced water waves

Sanjou

Nezu

2011

Environ Fluid Mech

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When wind-induced water waves appear over the free-surface flows such as natural rivers and artificial channels, large amounts of oxygen gas and heat are transported toward the river bed through the interface between water and wind layers. In contrast, a bed region is a kind of turbulent boundary layer, in which turbulence generation and its transport is promoted by the production of bed shear stress. In particular, coherent hairpin vortices, together with strong ejection events toward the outer part of the layer, promote mass and momentum exchanges between the inner and outer layers. It is inferred that such a near-bed turbulence may be influenced significantly by these air-water interfacial fluctuations accompanied with free-surface velocity shear and wind-induced water waves. However, these wind effects on the wall-turbulence structure are less understood. To address these exciting and challenging topics, we conducted particle imagery velocimetry (PIV) measurements in openchannel flows combined with air flows, and furthermore the present measured data allows us to investigate the effects of air-water interactions on turbulence structure through the whole depth region.

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Section: Introductionmentioning

confidence: 93%

Turbulence structure and coherent vortices in open-channel flows with wind-induced water waves

Sanjou

Nezu

2011

Environ Fluid Mech

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“…The ratio of the wind surface drift to the wind velocity decreases gradually as the wind fetch increases and approaches a constant value of over 3.5% of wind speed or about a half of surface friction velocity, u * . Several recent studies by particle image velocimetry ͑PIV͒ 9-11 and infrared imaging, 6,12 as compiled in Fig. 1͑a͒, have consistently indicated 30-50% smaller surface drift values.…”

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confidence: 71%

A laboratory observation of the surface temperature and velocity distributions on a wavy and windy air–water interface

Zhang

Harrison

2004

Physics of Fluids

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Temperature and velocity distributions of the water surface are examined experimentally with infrared imaging techniques. The surface velocity is determined from the movement of the pattern of surface temperature cell. It is found that the mean wind drift is about 30%u * , much less than the widely cited measurements of 55%u * . Although many complicated thermal and dynamical processes control the surface temperature, we found that the probability distribution function ͑PDF͒ of the standardized water surface temperature does not vary significantly with wind speed. The increasing nonlinear effects of wave orbital motions and wave breaking on surface motion are shown by the similarity and trend of change in the PDFs of the water surface velocity normalized by the wave orbital velocity at different wind speeds. The standard deviation of the speed distribution increases with the wind speed while the basic skewed distribution shape remains.Wind blowing over a water surface generates waves and surface currents. It is believed that normal stress ͑pressure͒ is more important in generating long waves, and tangential stress is more efficient in producing surface currents. The momentum near the air-sea interface is then further redistributed among waves, currents and turbulence via such mechanisms as wave breaking 1-3 and Langmuir circulations. 4 In this dynamical process surface water is constantly mixed with the body water below, which is often called surface renewal and is of great importance in heat and gas exchange through air-water interface. As water evaporates, latent heat released to the air produces a thin cool skin thermal layer with temperature of a fraction of a degree less than the bulk water, ⌬TϭT surface ϪT bulk . The cool thin thermal layer and the surface viscous shear layer grow with time until broken up by surface renewal events that occur randomly in space and time. The temperature difference, ⌬T, of a local surface water element is dependent on the time that it is exposed to the air and the rate of heat exchange with the air above. There are very detailed temperature surface structures, and they can be observed with sensitive infrared ͑IR͒ cameras. Recently such cameras have been successfully used in studying surface heat flux, 5 small scale Langmuir circulations 6 and microscale breaking waves. 7 Here we present new results on surface wind drift with this new thermal imaging technology.Early wind drift measurements were made mainly by using tracers such as drifters, drogues, or dye. Wu 8 found that the current immediately below the water surface varies linearly with depth. The value at the water surface was therefore obtained by a linear interpolation. The ratio of the wind surface drift to the wind velocity decreases gradually as the wind fetch increases and approaches a constant value of over 3.5% of wind speed or about a half of surface friction velocity, u * . Several recent studies by particle image velocimetry ͑PIV͒ 9-11 and infrared imaging, 6,12 as compiled in Fig. 1͑a͒, have consistently indi...

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“…19 The interfacial cooled seawater becomes denser and produces convective motions and agitation of near-interfacial turbulent boundary layers. 20 Handler et al 9 involved the effect of surface cooling in their numerical work to observe the effect of unstable stratification on thermal streaks in the near-interface region. On the other hand, the ocean surface can absorb thermal energy from short-wave solar radiation in the daytime, forming stable density stratification.…”

Section: Introductionmentioning

confidence: 99%

“…One of the origins of the microscale structures is the instability of turbulent shear layer at the region near the interface. Handler et al 9 investigated experimentally the surface streaks in the thermal field below the wind-driven interface. They insisted that such microscale turbulence will control heat and mass exchange processes between the atmosphere and the ocean.…”

Section: Introductionmentioning

confidence: 99%

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Low shear turbulence structures beneath stress-driven interface with neutral and stable stratification

2006

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This study deals with turbulent flow below a stress-driven interface with stable density stratification, as a simplified configuration of a turbulent flow below a calm gas-liquid interface with wind forcing. A simple shear stress, which is constant in time and uniform at the interface, is enforced, hence only turbulence below the interface is studied. A flat interface is assumed to simplify transport phenomena beneath the interface by limiting the strength of the enforced wind stress and avoiding violent wave motions. A direct numerical simulation technique is employed to obtain three-dimensional turbulence structures below the interface. Results from the present study indicate two major changes of turbulence structures below the sheared interface in the presence of stable density stratification; one is a reduction of the Reynolds stress at the near-interface region, which leads to a coincidental increase of mean velocity gradient. The other effect of stable stratification is the quantitative variation of the surface-streak structures and associated microscale turbulence structures. Examination of the autocorrelation coefficients of the streamwise velocity fluctuations in the subinterface region exhibited that the surface-streak structures in the velocity field are established in both neutral and stably stratified fluid. These streak structures are, however, partially disorganized in the region very close to the interface when strong stable stratification is imposed. The spacing between the streaks tends to decrease with increasing Richardson number in the subinterfacial region −30Ͻ x 3 + Ͻ −20, where the disorganization of the streaks is not encountered. A flow visualization technique verifies the establishment of these streaks in every Richardson number case and their partial disorganization under the effect of strong density stratification. A statistical three-dimensional relation between the streaks and the vortical structures are explored by applying a two-point correlation technique to instantaneous turbulent flow realizations. The presence of a counter-rotating vortex pair below the high-momentum fluid at the interface can be found in these examinations. Such presence of the counter-rotating vortex pair are confirmed by the visualization of the vortical structures in instantaneous turbulent flow realizations, whose three-dimensional shape is rather a hairpin-like configuration than two separated vortex tubes.

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The thermal structure of an air–water interface at low wind speeds

Cited by 50 publications

References 24 publications

Turbulence structure and coherent vortices in open-channel flows with wind-induced water waves

Turbulence structure and coherent vortices in open-channel flows with wind-induced water waves

A laboratory observation of the surface temperature and velocity distributions on a wavy and windy air–water interface

Low shear turbulence structures beneath stress-driven interface with neutral and stable stratification

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