scholarly journals Horizontal Dispersion of Buoyant Materials in the Ocean Surface Boundary Layer

2018 ◽  
Vol 48 (9) ◽  
pp. 2103-2125 ◽  
Author(s):  
Jun-Hong Liang ◽  
Xiaoliang Wan ◽  
Kenneth A. Rose ◽  
Peter P. Sullivan ◽  
James C. McWilliams
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Ocean Surface ◽  
Turbulent Dispersion ◽  
Surface Boundary ◽  
Particle Trajectories ◽  
Stokes Flows ◽  
Surface Boundary Layer ◽  
Horizontal Dispersion ◽  
Shear Dispersion

ABSTRACTThe horizontal dispersion of materials with a constant rising speed under the exclusive influence of ocean surface boundary layer (OSBL) flows is investigated using both three-dimensional turbulence-resolving Lagrangian particle trajectories and the classical theory of dispersion in bounded shear currents generalized for buoyant materials. Dispersion in the OSBL is caused by the vertical shear of mean horizontal currents and by the turbulent velocity fluctuations. It reaches a diffusive regime when the equilibrium vertical material distribution is established. Diffusivity from the classical shear dispersion theory agrees reasonably well with that diagnosed using three-dimensional particle trajectories. For weakly buoyant materials that can be mixed into the boundary layer, shear dispersion dominates turbulent dispersion. For strongly buoyant materials that stay at the ocean surface, shear dispersion is negligible compared to turbulent dispersion. The effective horizontal diffusivity due to shear dispersion is controlled by multiple factors, including wind speed, wave conditions, vertical diffusivity, mixed layer depth, latitude, and buoyant rising speed. With all other meteorological and hydrographic conditions being equal, the effective horizontal diffusivity is larger in wind-driven Ekman flows than in wave-driven Ekman–Stokes flows for weakly buoyant materials and is smaller in Ekman flows than in Ekman–Stokes flows for strongly buoyant materials. The effective horizontal diffusivity is further reduced when enhanced mixing by breaking waves is included. Dispersion by OSBL flows is weaker than that by submesoscale currents at a scale larger than 100 m. The analytic framework will improve subgrid-scale modeling in realistic particle trajectory models using currents from operational ocean models.

scholarly journals A global perspective on Langmuir turbulence in the ocean surface boundary layer

2012 ◽  
Vol 39 (18) ◽  
Author(s):  
Stephen E. Belcher ◽  
Alan L. M. Grant ◽  
Kirsty E. Hanley ◽  
Baylor Fox-Kemper ◽  
Luke Van Roekel ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Ocean Surface ◽  
Global Perspective ◽  
Surface Boundary ◽  
Langmuir Turbulence ◽  
Surface Boundary Layer

LESbrary: A library of large eddy simulation data for the calibration and uncertainty quantification of ocean surface boundary layer turbulence parameterizations

2021 ◽  
Author(s):  
Gregory Wagner ◽  
Andre Souza ◽  
Adeline Hillier ◽  
Ali Ramadhan ◽  
Raffaele Ferrari
Keyword(s):  
Boundary Layer ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Ocean Surface ◽  
Limited Area ◽  
Surface Boundary ◽  
Model Errors ◽  
Surface Boundary Layer ◽  
Large Eddy ◽  
Free Parameters

<p>Parameterizations of turbulent mixing in the ocean surface boundary layer (OSBL) are key Earth System Model (ESM) components that modulate the communication of heat and carbon between the atmosphere and ocean interior. OSBL turbulence parameterizations are formulated in terms of unknown free parameters estimated from observational or synthetic data. In this work we describe the development and use of a synthetic dataset called the “LESbrary” generated by a large number of idealized, high-fidelity, limited-area large eddy simulations (LES) of OSBL turbulent mixing. We describe how the LESbrary design leverages a detailed understanding of OSBL conditions derived from observations and large scale models to span the range of realistically diverse physical scenarios. The result is a diverse library of well-characterized “synthetic observations” that can be readily assimilated for the calibration of realistic OSBL parameterizations in isolation from other ESM model components. We apply LESbrary data to calibrate free parameters, develop prior estimates of parameter uncertainty, and evaluate model errors in two OSBL parameterizations for use in predictive ESMs.</p>

scholarly journals Inner Workings of Aerodynamic Sweep

1997 ◽  
Author(s):  
A. R. Wadia ◽  
P. N. Szucs ◽  
D. W. Crall
Keyword(s):  
Boundary Layer ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Axial Flow ◽  
Tip Clearance ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Stall Margin ◽  
Design Speed ◽  
The Impact

The recent trend in using aerodynamic sweep to improve the performance of transonic blading has been one of the more significant technological evolutions for compression components in turbomachinery. This paper reports on the experimental and analytical assessment of the pay-off derived from both aft and forward sweep technology with respect to aerodynamic performance and stability. The single stage experimental investigation includes two aft-swept rotors with varying degree and type of aerodynamic sweep and one swept forward rotor. On a back-to-back test basis, the results are compared with an unswept rotor with excellent performance and adequate stall margin. Although designed to satisfy identical design speed requirements as the unswept rotor, the experimental results reveal significant variations in efficiency and stall margin with the swept rotors. At design speed, all the swept rotors demonstrated a peak stage efficiency level that was equal to that of the unswept rotor. However, the forward-swept rotor achieved the highest rotor-alone peak efficiency. At the same time, the forward-swept rotor demonstrated a significant improvement in stall margin relative to the already satisfactory level achieved by the unswept rotor. Increasing the level of aft sweep adversely affected the stall margin. A three-dimensional viscous flow analysis was used to assist in the interpretation of the data. The reduced shock/boundary layer interaction, resulting from reduced axial flow diffusion and less accumulation of centrifuged blade surface boundary layer at the up, was identified as the prime contributor to the enhanced performance with forward sweep. The impact of tip clearance on the performance and stability for one of the aft-swept rotors was also assessed.

Control of separations in a highly loaded diffusion cascade by tailored boundary layer suction

2013 ◽  
Vol 228 (8) ◽  
pp. 1363-1374 ◽  
Author(s):  
Zhiyuan Cao ◽  
Bo Liu ◽  
Ting Zhang
Keyword(s):  
Boundary Layer ◽  
Static Pressure ◽  
Three Dimensional ◽  
Flow Fields ◽  
Separated Flows ◽  
Surface Boundary ◽  
Suction Surface ◽  
Surface Boundary Layer ◽  
Boundary Layer Suction ◽  
Highly Loaded

In order to explore the control mechanism of boundary layer suction on the separated flows of highly loaded diffusion cascades, a linear compressor cascade, which has separated flows on the whole span and three-dimensional separations over the suction surface/endwall corner, was investigated by tailored boundary layer suction. Three suction surface-slotted schemes and two combined suction surface/endwall-slotted schemes were designed. The original cascade and the cascade with part blade span suction were experimentally investigated on a high-subsonic cascade wind tunnel. In addition, numerical simulation was employed to study the flow fields of different suction schemes in detail. The results shows that while tailored boundary layer suction at part blade span can effectively remove the separations at the suction span, the flow fields of other spans deteriorated. The reasons are the ‘C’ shape or reverse ‘C’ shape spanwise distribution of static pressure after part blade span boundary layer suction. Suction surface boundary layer suction over the whole span can obviously eliminate the separation at the suction surface. However, because of the endwall boundary layer, suction surface boundary layer suction cannot effectively remove the corner three-dimensional separation. The separation over the whole span and the three-dimensional separation at the corner are completely eliminated by combined suction surface/endwall boundary layer suction. After combined boundary layer suction, the static pressure distribution over the blade span just like the shape of ‘C’ is good for the transport of the low-energy fluid near the endwall to the midspan.

scholarly journals Assessing the Effects of Langmuir Turbulence on the Entrainment Buoyancy Flux in the Ocean Surface Boundary Layer

2017 ◽  
Vol 47 (12) ◽  
pp. 2863-2886 ◽  
Author(s):  
Qing Li ◽  
Baylor Fox-Kemper
Keyword(s):  
Boundary Layer ◽  
Climate Model ◽  
Ocean Surface ◽  
Buoyancy Flux ◽  
Entrainment Rate ◽  
Surface Boundary ◽  
Langmuir Turbulence ◽  
Convective Turbulence ◽  
Surface Boundary Layer ◽  
The Impact

AbstractLarge-eddy simulations (LESs) with various constant wind, wave, and surface destabilizing surface buoyancy flux forcing are conducted, with a focus on assessing the impact of Langmuir turbulence on the entrainment buoyancy flux at the base of the ocean surface boundary layer. An estimate of the entrainment buoyancy flux scaling is made to best fit the LES results. The presence of Stokes drift forcing and the resulting Langmuir turbulence enhances the entrainment rate significantly under weak surface destabilizing buoyancy flux conditions, that is, weakly convective turbulence. In contrast, Langmuir turbulence effects are moderate when convective turbulence is dominant and appear to be additive rather than multiplicative to the convection-induced mixing. The parameterized unresolved velocity scale in the K-profile parameterization (KPP) is modified to adhere to the new scaling law of the entrainment buoyancy flux and account for the effects of Langmuir turbulence. This modification is targeted on common situations in a climate model where either Langmuir turbulence or convection is important and may overestimate the entrainment when both are weak. Nevertheless, the modified KPP is tested in a global climate model and generally outperforms those tested in previous studies. Improvements in the simulated mixed layer depth are found, especially in the Southern Ocean in austral summer.

Wind- and Wave-driven Ocean Surface Boundary Layer in a Frontal Zone: Roles of Submesoscale Eddies and Ekman-Stokes Transport

2021 ◽  
Author(s):  
Jianguo Yuan ◽  
Jun-Hong Liang
Keyword(s):  
Boundary Layer ◽  
Frontal Zone ◽  
Surface Current ◽  
Ocean Surface ◽  
Buoyancy Flux ◽  
Temperature Structure ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Horizontal Mixing ◽  
The Right

AbstractLarge-eddy simulations are used to investigate the influence of a horizontal frontal zone, represented by a stationary uniform background horizontal temperature gradient, on the wind- and wave-driven ocean surface boundary layers. In a frontal zone, the temperature structure, the ageostrophic mean horizontal current, and the turbulence in the ocean surface boundary layer all change with the relative angle among the wind and the front. The net heating and cooling of the boundary layer could be explained by the depth-integrated horizontal advective buoyancy flux, called the Ekman Buoyancy Flux (or the Ekman-Stokes Buoyancy Flux if wave effects are included). However, the detailed temperature profiles are also modulated by the depth-dependent advective buoyancy flux and submesoscale eddies. The surface current is deflected less (more) to the right of the wind and wave when the depth-integrated advective buoyancy flux cools (warms) the ocean surface boundary layer. Horizontal mixing is greatly enhanced by submesoscale eddies. The eddy-induced horizontal mixing is anisotropic and is stronger to the right of the wind direction. Vertical turbulent mixing depends on the superposition of the geostrophic and ageostrophic current, the depth-dependent advective buoyancy flux, and submesoscale eddies.

A Quasi-Three-Dimensional Blade Surface Boundary Layer Analysis for Rotating Blade Rows

1982 ◽  
Vol 104 (2) ◽  
pp. 439-449 ◽  
Author(s):  
W. T. Thompkins ◽  
W. J. Usab
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Normal Vector ◽  
Surface Boundary ◽  
Nasa Lewis Research ◽  
Surface Boundary Layer ◽  
Boundary Layer Analysis ◽  
Rotating Blade ◽  
Layer Analysis ◽  
Coordinate Lines

A quasi-three-dimensional, finite difference boundary layer analysis for rotating blade rows has been developed which uses pressure distribution and streamline position data from a three-dimensional Euler equation solver. This analysis uses as coordinate lines the blade normal vector, the local inviscid streamline direction and a crossflow coordinate tine perpendicular to both normal and streamline coordinate lines. The equations solved may be determined either by assuming the crossflow velocity to be small or that its variation in the crossflow direction is small. Thus the analysis would not apply to a region where the boundary layer character changes rapidly such as a corner but could be expected to provide good results away from hub or tip casing boundary layers. Modified versions of Keller’s box scheme are used to solve the streamwise and crossflow momentum equations as well as the energy equation. Results are presented for a high-tip speed, low aspect ratio rotor designed by NASA Lewis Research Center which show that the three-dimensional boundary layer separates significantly sooner and has a much larger influence on rotor performance than would be expected from a two-dimensional analysis.

scholarly journals The Contribution of Surface and Submesoscale Processes to Turbulence in the Open Ocean Surface Boundary Layer

2019 ◽  
Vol 11 (12) ◽  
pp. 4066-4094 ◽  
Author(s):  
Christian E. Buckingham ◽  
Natasha S. Lucas ◽  
Stephen E. Belcher ◽  
Tom P. Rippeth ◽  
Alan L. M. Grant ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Ocean Surface ◽  
Open Ocean ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Submesoscale Processes

scholarly journals The Three-Dimensional Structure and Evolution of a Tornado Boundary Layer

2013 ◽  
Vol 28 (6) ◽  
pp. 1552-1561 ◽  
Author(s):  
Karen A. Kosiba ◽  
Joshua Wurman
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Flow Region ◽  
Ground Level ◽  
Dimensional Structure ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Near Surface ◽  
Three Dimensional Structure ◽  
Flow Swirl

Abstract The finescale three-dimensional structure and evolution of the near-surface boundary layer of a tornado (TBL) is mapped for the first time. The multibeam Rapid-Scan Doppler on Wheels (RSDOW) collected data at several vertical levels, as low as 4, 6, 10, 12, 14, and 17 m above ground level (AGL), contemporaneously at 7-s intervals for several minutes in a tornado near Russell, Kansas, on 25 May 2012. Additionally, a mobile mesonet anemometer measured winds at 3.5 m AGL in the core flow region. The radar, anemometer, and ground-based velocity-track display (GBVTD) analyses reveal the peak wind intensity is very near the surface at ~5 m AGL, about 15% higher than at 10 m AGL and 25% higher than at ~40 m AGL. GBVTD analyses resolve a downdraft within the radius of maximum winds (RMW), which decreased in magnitude when varying estimates for debris centrifuging are included. Much of the inflow (from −1 to −7 m s−1) is at or below 10–14 m AGL, much shallower than reported previously. Surface outflow precedes tornado dissipation. Comparisons between large-eddy simulation (LES) predictions of the corner flow swirl ratio Sc and observed tornado intensity changes are consistent.

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