Distributions and fates of oxygen in periphyton communities

1987 ◽  
Vol 65 (5) ◽  
pp. 1031-1037 ◽  
Author(s):  
Richard G. Carlton ◽  
Robert G. Wetzel
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Environmental Conditions ◽  
Surrounding Water ◽  
Water Currents ◽  
Diffusion Characteristics ◽  
Production And Consumption ◽  
Direct Measurements ◽  
Oxygen Microelectrodes ◽  
Physical And Chemical

Direct measurements with oxygen microelectrodes demonstrated that the distribution of dissolved oxygen in periphyton communities varied on a diurnal basis and was markedly different among periphyton types. During illumination, photosynthesis in periphyton resulted in oxygen supersaturation in microzones that were subsaturated or anoxic during darkness. The fate of oxygen produced within periphyton depended on the relative rates of production and consumption, the diffusion characteristics of the periphyton, physical and chemical interactions with the substratum, and the transport rate across the boundary layer, which was affected significantly by water currents. During constant environmental conditions, steady-state oxygen distributions occurred within periphyton, but equilibrium with the surrounding water was rare.

Effect of Boundary Layers on Cutaneous Gas Exchange

1990 ◽  
Vol 154 (1) ◽  
pp. 67-80 ◽  
Author(s):  
ALAN W. PINDER ◽  
MARTIN E. FEDER
Keyword(s):  
Boundary Layer ◽  
Oxygen Uptake ◽  
Boundary Layers ◽  
Oxygen Diffusion ◽  
Water Velocity ◽  
Total Resistance ◽  
Partial Pressure Of Oxygen ◽  
Body Movements ◽  
Direct Measurements ◽  
Oxygen Microelectrodes

Boundary layers may offer significant resistance to cutaneous oxygen uptake by amphibians in water. This hypothesis was tested by measuring resistance to oxygen uptake as a function of water velocity in bullfrogs submerged at 5 °C and by direct measurements of the boundary layer with oxygen microelectrodes. The oxygen diffusion boundary layer was easily measurable with oxygen microelectrodes. The proportion of the total resistance to oxygen uptake represented by the boundary layer increased from 35 % at a water velocity of 5 cms−1 1 to over 90% at 0.1 cms−1. At water velocities below lcms−1 oxygen uptake was limited by the resistance of the boundary layer. At 0.1 cms−1, the partial pressure of oxygen immediately adjacent to the skin was only 2 kPa (15 mmHg); placing an immobilized frog in still water was tantamount to placing it in anoxic water. Body movements disrupted boundary layers efficiently; even occasional small movements by the animal (1 min−1) were sufficient to maintainoxygen uptake in still water.

An airfoil theory of bifurcating laminar separation from thin obstacles

1990 ◽  
Vol 216 ◽  
pp. 255-284 ◽  
Author(s):  
C. J. Lee ◽  
H. K. Cheng
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Steady State ◽  
Steady State Solution ◽  
Equation System ◽  
Branch Points ◽  
Laminar Separation ◽  
Kutta Condition ◽  
Numerical Studies ◽  
Steady State Solutions

Global interaction of the boundary layer separating from an obstacle with resulting open/closed wakes is studied for a thin airfoil in a steady flow. Replacing the Kutta condition of the classical theory is the breakaway criterion of the laminar triple-deck interaction (Sychev 1972; Smith 1977), which, together with the assumption of a uniform wake/eddy pressure, leads to a nonlinear equation system for the breakaway location and wake shape. The solutions depend on a Reynolds numberReand an airfoil thickness ratio or incidence τ and, in the domain$Re^{\frac{1}{16}}\tau = O(1)$considered, the separation locations are found to be far removed from the classical Brillouin–Villat point for the breakaway from a smooth shape. Bifurcations of the steady-state solution are found among examples of symmetrical and asymmetrical flows, allowing open and closed wakes, as well as symmetry breaking in an otherwise symmetrical flow. Accordingly, the influence of thickness and incidence, as well as Reynolds number is critical in the vicinity of branch points and cut-off points where steady-state solutions can/must change branches/types. The study suggests a correspondence of this bifurcation feature with the lift hysteresis and other aerodynamic anomalies observed from wind-tunnel and numerical studies in subcritical and high-subcriticalReflows.

Direct measurements of drag of ribbon-type manipulators in a turbulent boundary layer

AIAA Journal ◽  
1987 ◽  
Vol 25 (3) ◽  
pp. 388-394 ◽  
Author(s):  
S. P. Govindaraju ◽  
F. W. Chambers
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Direct Measurements

Contribution of vertical advection to supergradient wind in tropical cyclone boundary layer: A numerical study

2021 ◽  
Author(s):  
Rong Fei ◽  
Yuqing Wang ◽  
Yuanlong Li
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Wind Speed ◽  
Tropical Cyclone ◽  
Vertical Structure ◽  
Numerical Study ◽  
Substantial Reduction ◽  
Vertical Advection ◽  
Physics Model ◽  
Tropical Cyclone Boundary Layer

AbstractThe existence of supergradient wind in the interior of the boundary layer is a distinct feature of a tropical cyclone (TC). Although the vertical advection is shown to enhance supergradient wind in TC boundary layer (TCBL), how and to what extent the strength and structure of supergradient wind are modulated by vertical advection are not well understood. In this study, both a TCBL model and an axisymmetric full-physics model are used to quantify the contribution of vertical advection process to the strength and vertical structure of supergradient wind in TCBL. Results from the TCBL model show that the removal of vertical advection of radial wind reduces both the strength and height of supergradient wind by slightly more than 50%. The removal of vertical advection of agradient wind reduces the height of the supergradient wind core by ~30% but increases the strength of supergradient wind by ~10%. Results from the full-physics model show that the removal of vertical advection of radial wind or agradient wind reduces both the strength and height of supergradient wind but the removal of that of radial wind produces a more substantial reduction (52%) than the removal of that of agradient wind (35%). However, both the intensification rate and final intensity of the simulated TCs in terms of maximum 10-m wind speed show little differences in experiments with and without the vertical advection of radial or agradient wind, suggesting that supergradient wind contributes little to either the intensification rate or the steady-state intensity of the simulated TC.

EFFECT OF WATER CURRENT ON UNDERWATER GLIDER VELOCITY AND RANGE

2016 ◽  
Vol 78 (10-4) ◽  
Author(s):  
Muhammad Yasar Javaid ◽  
Mark Ovinis ◽  
Fakhruldin Mohd Hashim ◽  
Adi Maimun ◽  
Yasser M. Ahmed ◽  
...  
Keyword(s):  
Steady State ◽  
Numerical Simulations ◽  
Relative Motion ◽  
Water Current ◽  
Underwater Glider ◽  
Water Currents ◽  
Effect Of Water ◽  
Actuation System ◽  
Autonomous Underwater Glider

An autonomous underwater glider speed and range is influenced by water currents. This is compounded by a weak actuation system for controlling its movement. In this work, the effects of water currents on the speed and range of an underwater glider at steady state glide conditions are investigated. Extensive numerical simulations have been performed to determine the speed and range of a glider with and without water current at different net buoyancies. The results show that the effect of water current on the glider speed and range depends on the current relative motion and direction. In the presence of water current, for a given glide angle, glide speed can be increased by increasing the net buoyancy of the glider.

scholarly journals Effects of black carbon and boundary layer interaction on surface ozone in Nanjing, China

2018 ◽  
Author(s):  
Jinhui Gao ◽  
Bin Zhu ◽  
Hui Xiao ◽  
Hanqing Kang ◽  
Chen Pan
Keyword(s):  
Boundary Layer ◽  
Black Carbon ◽  
Physical Process ◽  
Surface Ozone ◽  
Vertical Mixing ◽  
Ozone Pollution ◽  
Model Studies ◽  
Photolysis Rate ◽  
Boundary Layer Interaction ◽  
Physical And Chemical

Abstract. As an important solar-radiation absorbing aerosol, the effect of black carbon (BC) on surface ozone, by influencing photolysis rate, has been widely discussed by offline model studies. However, BC-boundary layer (BL) interactions also influence surface ozone. Using the online model simulations and processes analysis, we demonstrate the significant impact of BC-BL interaction on surface ozone. The absorbing effect of BC heats the air above the BL and suppresses BL development, which eventually leads to changes in the contributions of ozone through chemical and physical processes (photochemistry, vertical mixing, and advection). Different from previous offline model studies, BL suppression leads large amounts of ozone precursors being confined below the BL which offsetting the influence from the reduction of photolysis rate, thus enhancing ozone photochemical formation before noon. Furthermore, the changes in physical process show a more significant influence on surface ozone. The weakened turbulence entrains much less ozone from the overlying ozone-rich air down to surface. As a result, the net contribution of ozone from physical and chemical processes leads to surface ozone reduction before noon. The maximum reduction reaches to 16.4 ppb at 12:00. In the afternoon, the changes in chemical process are small which influence inconspicuously to surface ozone. However, physical process still influences the surface ozone significantly. Due to the delayed development of the BL, less vertically mixed BL continues to show an obvious ozone gradient near the top of the BL. Therefore, more ozone aloft can be entrained down to the surface, offsetting the surface ozone reduction. Comparing all the changes in the contributions of processes, the change in the contribution of vertical mixing plays a more important role in impacting surface ozone. Our results show the great impacts of BC-BL interactions on surface ozone. And more attention should be paid on the mechanism of aerosol-BL interactions when we deal with the ozone pollution control in China.

Unsteady convective exchange flows in cavities

1998 ◽  
Vol 368 ◽  
pp. 127-153 ◽  
Author(s):  
J. J. STURMAN ◽  
G. N. IVEY
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Boundary Layer Thickness ◽  
Buoyancy Flux ◽  
Exchange Flow ◽  
Flushing Time ◽  
Exchange Flows ◽  
Buoyancy Forcing ◽  
Convective Exchange ◽  
Approach To Steady State

Horizontal exchange flows driven by spatial variation of buoyancy fluxes through the water surface are found in a variety of geophysical situations. In all examples of such flows the timescale characterizing the variability of the buoyancy fluxes is important and it can vary greatly in magnitude. In this laboratory study we focus on the effects of this unsteadiness of the buoyancy forcing and its influence on the resulting flushing and circulation processes in a cavity. The experiments described all start with destabilizing forcing of the flows, but the buoyancy fluxes are switched to stabilizing forcing at three different times spanning the major timescales characterizing the resulting cavity-scale flows. For destabilizing forcing, these timescales are the flushing time of the region of forcing, and the filling-box timescale, the time for the cavity-scale flow to reach steady state. When the forcing is stabilizing, the major timescale is the time for the fluid in the exchange flow to pass once through the forcing boundary layer. This too is a measure of the time to reach steady state, but it is generally distinct from the filling-box time. When a switch is made from destabilizing to stabilizing buoyancy flux, inertia is important and affects the approach to steady state of the subsequent flow. Velocities of the discharges from the end regions, whether forced in destabilizing or stabilizing ways, scaled as u∼(Bl)1/3 (where B is the forcing buoyancy flux and l is the length of the forcing region) in accordance with Phillips' (1966) results. Discharges with destabilizing and stabilizing forcing were, respectively, Q−∼(Bl)1/3H and Q+∼(Bl)1/3δ (where H is the depth below or above the forcing plate and δ is the boundary layer thickness). Thus Q−/Q+>O(1) provided H>O(δ), as was certainly the case in the experiments reported, demonstrating the overall importance of the flushing processes occurring during periods of cooling or destabilizing forcing.

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