scholarly journals Gas Exchange and Bubble-Induced Supersaturation in a Wind-Wave Tank

2004 ◽  
Vol 21 (12) ◽  
pp. 1925-1935 ◽  
Author(s):  
Peter Bowyer ◽  
David Woolf
Keyword(s):  
Steady State ◽  
Gas Exchange ◽  
Wind Wave ◽  
Relative Strength ◽  
Water Interface ◽  
Wave Tank ◽  
Gas Concentration ◽  
Gas Fluxes ◽  
Air Water Interface ◽  
Series Of Experiments

Abstract Gas exchange and bubble-induced supersaturation were measured in a wind-wave tank using total gas saturation meters. The water in the tank was subjected to bubbling using a large number of frits at a depth of 0.6 m. A simple linear model of bubble-mediated gas exchange implies that this should force an equilibrium supersaturation of 3%. This is confirmed by experiment, but a small additional steady-state supersaturation is also forced by warming. The total steady-state supersaturation is approached asymptotically. When the bubblers were switched off, the total gas pressure approached a new steady state at much lower supersaturation, at a rate that depended on the state of the wind and waves in the tank. The rates of approach on the various equilibria enabled the gas flux across the surface of the bubbles or across the air–water interface to be calculated. In addition a series of experiments was conducted where the water was subjected to bubbling in the presence of wind or wind and paddle waves: in this case gas invasion from the bubbles was balanced by gas evasion near or at the surface resulting in an equilibrium at <3% and enabling the relative strength of the invasion and evasion to be estimated. Gas concentrations could be measured in a rapid, automated manner using simple apparatus. To derive gas fluxes, corrections for changes in water temperature and fluctuations in air pressure are necessary, and these are quantified. In addition, transient fluctuations in gas concentration at the start of bubbling periods allowed mixing within the tank to be observed.

Physical fitness of Arctic Indians

1960 ◽  
Vol 15 (4) ◽  
pp. 645-648 ◽  
Author(s):  
Kristian Lange Andersen ◽  
Atle Bolstad ◽  
Yngve L⊘yning ◽  
Laurence Irving
Keyword(s):  
Heart Rate ◽  
Steady State ◽  
Gas Exchange ◽  
Physical Fitness ◽  
Pulmonary Ventilation ◽  
Young Men ◽  
Exercise Load ◽  
Series Of Experiments ◽  
Sedentary Subjects ◽  
Fitness To Work

The physical fitness of healthy young men of an arctic population of Indians was studied, using two types of physiological measurements during muscular work. In one series of experiments the respiratory gas exchange and heart rate were determined during apparently ‘steady-state’ exercise on an ergometer bicycle and the maximal O2 intake was estimated. In another series the response of pulmonary ventilation to a standard exercise load was measured on the same bicycle and the time to recuperate was determined, as well as the extraventilation caused by the exercise. Comparisons were made with results observed on a group of sedentary-living young men and champion athletes drawn from the population of Norway. The Indians' fitness to work occupies a somewhat intermediate position between the sedentary subjects and the athletes. Submitted on August 3, 1959

Momentum flux across breaking air-water interface

2020 ◽  
Author(s):  
Naohisa Takagaki ◽  
Naoya Suzuki ◽  
Keigo Matsuda ◽  
Satoru Komori ◽  
Yuliya Troitskaya
Keyword(s):  
Momentum Flux ◽  
Wind Wave ◽  
Correlation Method ◽  
Eddy Correlation ◽  
Water Interface ◽  
Budget Balance ◽  
High Wind ◽  
Wind Speeds ◽  
Momentum Budget ◽  
Air Water Interface

<p>It is important to measure the momentum flux across the air–water interface in the droplet- and bubble-laden turbulent flow at extremely high-wind speeds. Generally, the momentum flux is measured by a profile method, eddy correlation method, or momentum budget (balance) method at normal wind speeds. We assessed the usage of three measurement method at extremely high wind speeds in three wind-wave tanks, Kyoto, Kindai, and Kyushu Universities, JAPAN. Here, the Kyoto tank is 15 m long, 0.8 m wide, 0.8 m high and the maximum wind speed is 68 m/s. The Kyushu tank is 64 m long and the max. speed is 40 m/s. Moreover, we will show the preliminary results for the effects of the fetch on the momentum flux.</p>

Tangential stress beneath wind-driven air–water interfaces

1998 ◽  
Vol 364 ◽  
pp. 115-145 ◽  
Author(s):  
MICHAEL L. BANNER ◽  
WILLIAM L. PEIRSON
Keyword(s):  
Tangential Stress ◽  
Wind Stress ◽  
Wind Wave ◽  
Wind Waves ◽  
Fluid Velocity ◽  
Wave Form ◽  
Water Interface ◽  
Reliable Determination ◽  
Air Water Interface ◽  
The Mean

The detailed structure of the aqueous surface sublayer flow immediately adjacent to the wind-driven air–water interface is investigated in a laboratory wind-wave flume using particle image velocimetry (PIV) techniques. The goal is to investigate quantitatively the character of the flow in this crucial, very thin region which is often disrupted by microscale breaking events. In this study, we also examine critically the conclusions of Okuda, Kawai & Toba (1977), who argued that for very short, strongly forced wind-wave conditions, shear stress is the dominant mechanism for transmitting the atmospheric wind stress into the water motion – waves and surface drift currents. In strong contrast, other authors have more recently observed very substantial normal stress contributions on the air side. The availability of PIV and associated image technology now permits a timely re-examination of the results of Okuda et al., which have been influential in shaping present perceptions of the physics of this dynamically important region. The PIV technique used in the present study overcomes many of the inherent shortcomings of the hydrogen bubble measurements, and allows reliable determination of the fluid velocity and shear within 200 μm of the instantaneous wind-driven air–water interface.The results obtained in this study are not in accord with the conclusions of Okuda et al. that the tangential stress component dominates the wind stress. It is found that prior to the formation of wind waves, the tangential stress contributes the entire wind stress, as expected. With increasing distance downwind, the mean tangential stress level decreases marginally, but as the wave field develops, the total wind stress increases significantly. Thus, the wave form drag, represented by the difference between the total wind stress and the mean tangential stress, also increases systematically with wave development and provides the major proportion of the wind stress once the waves have developed beyond their early growth stage. This scenario reconciles the question of relative importance of normal and tangential stresses at an air–water interface. Finally, consideration is given to the extrapolation of these detailed laboratory results to the field, where the present findings suggest that the sea surface is unlikely to become fully aerodynamically rough, at least for moderate to strong winds.

Growth and equilibrium of short gravity waves in a wind-wave tank

1977 ◽  
Vol 82 (4) ◽  
pp. 767-793 ◽  
Author(s):  
W. J. Plant ◽  
J. W. Wright
Keyword(s):  
Steady State ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Growth Rates ◽  
Energy Input ◽  
Wind Wave ◽  
Initial Growth ◽  
Wave Tank ◽  
Wind Speeds ◽  
Dominant Wave

Temporal and spatial development of short gravity waves in a linear wind-wave tank has been measured for wind speeds up to 15 m/s using microwave Doppler spectrometry. Surface waves of wavelength 4·1 cm, 9·8 cm, 16·5 cm and 36 cm were observed as a function of fetch, wind speed and wind duration. The waves grew exponentially from inception until they were about 10 dB smaller than their maximum height, and the temporal growth and spectral transport (spatial growth) rates were about equal when the wave amplitude was sufficiently small. The amplitude of a short gravity wave of fixed wavelength was found to decrease substantially at winds, fetches or durations greater than those at which the short gravity wave was approximately the dominant wave; such phenomena are sometimes referred to as overshoot. The dominant short gravity wave was observed to reach a maximum amplitude which depended only on wavelength, showing that wave breaking induced by an augmented wind drift cannot be the primary limitation to the wave height. Waves travelling against the wind were observed for wavelengths of 9·8 cm, 16·5 cm and 36 cm and were shown to be generated by the air flow at low wind speeds.Measured initial growth rates for 16·5 cm and 36 cm waves were greater than expected, suggesting the existence of a growth mechanism in addition to direct transfer from the wind via linear instability of the boundary-layer flow. Initial temporal growth rates and spectral transport rates were compared to yield an experimental determination of the magnitude of the sum of nonlinear interactions and dissipation in short gravity waves. If the steady-state energy input in the neighbourhood of the dominant wave occurs at the measured initial temporal growth rates, then most of the energy input is locally dissipated; relatively little is advected away. Calculated gravitycapillary nonlinear energy transfer rates match those determined from initial growth rates for 9·8 cm waves and the gravity–capillary wave interaction continues to be significant for waves as long as 16·5 cm. For longer waves the gravity–capillary interaction is too small to bring the short gravity wave to a steady state when it is the dominant wave of the wind-wave system.

scholarly journals Continuous measurement of air–water gas exchange by underwater eddy covariance

2017 ◽  
Vol 14 (23) ◽  
pp. 5595-5606 ◽  
Author(s):  
Peter Berg ◽  
Michael L. Pace
Keyword(s):  
Heat Flux ◽  
Gas Exchange ◽  
Exchange Rates ◽  
Eddy Covariance ◽  
High Speed ◽  
Heat Fluxes ◽  
Water Interface ◽  
O2 Concentration ◽  
Air Water Interface ◽  
Water Gas

Abstract. Exchange of gases, such as O2, CO2, and CH4, over the air–water interface is an important component in aquatic ecosystem studies, but exchange rates are typically measured or estimated with substantial uncertainties. This diminishes the precision of common ecosystem assessments associated with gas exchanges such as primary production, respiration, and greenhouse gas emission. Here, we used the aquatic eddy covariance technique – originally developed for benthic O2 flux measurements – right below the air–water interface (∼ 4 cm) to determine gas exchange rates and coefficients. Using an acoustic Doppler velocimeter and a fast-responding dual O2–temperature sensor mounted on a floating platform the 3-D water velocity, O2 concentration, and temperature were measured at high-speed (64 Hz). By combining these data, concurrent vertical fluxes of O2 and heat across the air–water interface were derived, and gas exchange coefficients were calculated from the former. Proof-of-concept deployments at different river sites gave standard gas exchange coefficients (k600) in the range of published values. A 40 h long deployment revealed a distinct diurnal pattern in air–water exchange of O2 that was controlled largely by physical processes (e.g., diurnal variations in air temperature and associated air–water heat fluxes) and not by biological activity (primary production and respiration). This physical control of gas exchange can be prevalent in lotic systems and adds uncertainty to assessments of biological activity that are based on measured water column O2 concentration changes. For example, in the 40 h deployment, there was near-constant river flow and insignificant winds – two main drivers of lotic gas exchange – but we found gas exchange coefficients that varied by several fold. This was presumably caused by the formation and erosion of vertical temperature–density gradients in the surface water driven by the heat flux into or out of the river that affected the turbulent mixing. This effect is unaccounted for in widely used empirical correlations for gas exchange coefficients and is another source of uncertainty in gas exchange estimates. The aquatic eddy covariance technique allows studies of air–water gas exchange processes and their controls at an unparalleled level of detail. A finding related to the new approach is that heat fluxes at the air–water interface can, contrary to those typically found in the benthic environment, be substantial and require correction of O2 sensor readings using high-speed parallel temperature measurements. Fast-responding O2 sensors are inherently sensitive to temperature changes, and if this correction is omitted, temperature fluctuations associated with the turbulent heat flux will mistakenly be recorded as O2 fluctuations and bias the O2 eddy flux calculation.

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