Direct Measurements of Reynolds Stresses and Turbulence in the Bottom Boundary Layer

2001 ◽  
Author(s):  
Joseph Katz
Keyword(s):  
Boundary Layer ◽  
Bottom Boundary Layer ◽  
Reynolds Stresses ◽  
Bottom Boundary ◽  
Direct Measurements

Langmuir turbulence in shallow water. Part 2. Large-eddy simulation

2007 ◽  
Vol 576 ◽  
pp. 63-108 ◽  
Author(s):  
A. E. TEJADA-MARTÍNEZ ◽  
C. E. GROSCH
Keyword(s):  
Boundary Layer ◽  
Shallow Water ◽  
Reynolds Stress ◽  
Bottom Boundary Layer ◽  
Reynolds Stresses ◽  
Component Structure ◽  
Bottom Boundary ◽  
Eddy Simulation ◽  
Shear Current ◽  
Anisotropy Tensor

Results of large-eddy simulation (LES) of Langmuir circulations (LC) in a wind-driven shear current in shallow water are reported. The LC are generated via the well-known Craik–Leibovich vortex force modelling the interaction between the Stokes drift, induced by surface gravity waves, and the shear current. LC in shallow water is defined as a flow in sufficiently shallow water that the interaction between the LC and the bottom boundary layer cannot be ignored, thus requiring resolution of the bottom boundary layer. After the introduction and a description of the governing equations, major differences in the statistical equilibrium dynamics of wind-driven shear flow and the same flow with LC (both with a bottom boundary layer) are highlighted. Three flows with LC will be discussed. In the first flow, the LC were generated by intermediate-depth waves (relative to the wavelength of the waves and the water depth). The amplitude and wavelength of these waves are representative of the conditions reported in the observations of A. E. Gargett & J. R. Wells in Part 1 (J. Fluid Mech. vol .000, 2007, p. 00). In the second flow, the LC were generated by shorter waves. In the third flow, the LC were generated by intermediate waves of greater amplitude than those in the first flow. The comparison between the different flows relies on visualizations and diagnostics including (i) profiles of mean velocity, (ii) profiles of resolved Reynolds stress components, (iii) autocorrelations, (iv) invariants of the resolved Reynolds stress anisotropy tensor and (v) balances of the transport equations for mean resolved turbulent kinetic energy and resolved Reynolds stresses. Additionally, dependencies of LES results on Reynolds number, subgrid-scale closure, size of the domain and grid resolution are addressed.In the shear flow without LC, downwind (streamwise) velocity fluctuations are characterized by streaks highly elongated in the downwind direction and alternating in sign in the crosswind (spanwise) direction. Forcing this flow with the Craik–Leibovich force generating LC leads to streaks with larger characteristic crosswind length scales consistent with those recorded by observations. In the flows with LC, in the mean, positive streaks exhibit strong intensification near the bottom and near the surface leading to intensified downwind velocity ‘jets’ in these regions. In the flow without LC, such intensification is noticeably absent. A revealing diagnostic of the structure of the turbulence is the depth trajectory of the invariants of the resolved Reynolds stress anisotropy tensor, which for a realizable flow must lie within the Lumley triangle. The trajectory for the flow without LC reveals the typical structure of shear-dominated turbulence in which the downwind component of the resolved normal Reynolds stresses is greater than the crosswind and vertical components. In the near bottom and surface regions, the trajectory for the flow with LC driven by wave and wind forcing conditions representative of the field observations reveals a two-component structure in which the downwind and crosswind components are of the same order and both are much greater than the vertical component. The two-component structure of the Langmuir turbulence predicted by LES is consistent with the observations in the bottom third of the water column above the bottom boundary layer.

Distribution of Energy Spectra, Reynolds Stresses, Turbulence Production, and Dissipation in a Tidally Driven Bottom Boundary Layer

2007 ◽  
Vol 37 (6) ◽  
pp. 1527-1550 ◽  
Author(s):  
L. Luznik ◽  
W. Zhu ◽  
R. Gurka ◽  
J. Katz ◽  
W. A. M. Nimmo Smith ◽  
...  
Keyword(s):  
Boundary Layer ◽  
South Carolina ◽  
Tidal Cycle ◽  
Particle Image Velocimetry Data ◽  
Bottom Boundary Layer ◽  
Stream Velocity ◽  
Reynolds Stresses ◽  
The South ◽  
Bottom Boundary ◽  
Velocity Gradients

Abstract Seven sets of 2D particle image velocimetry data obtained in the bottom boundary layer of the coastal ocean along the South Carolina and Georgia coast [at the South Atlantic Bight Synoptic Offshore Observational Network (SABSOON) site] are examined, covering the accelerating and decelerating phases of a single tidal cycle at several heights above the seabed. Additional datasets from a previous deployment are also included in the analysis. The mean velocity profiles are logarithmic, and the vertical distribution of Reynolds stresses normalized by the square of the free stream velocity collapse well for data obtained at the same elevation but at different phases of the tidal cycle. The magnitudes of 〈u′u′〉, 〈w′w′〉, and −〈u′w′〉 decrease with height above bottom in the 25–160-cm elevation range and are consistent with the magnitudes and trends observed in laboratory turbulent boundary layers. If a constant stress layer exists, it is located below 25-cm elevation. Two methods for estimating dissipation rate are compared. The first, a direct estimate, is based on the measured in-plane instantaneous velocity gradients. The second method is based on fitting the resolved part of the dissipation spectrum to the universal dissipation spectrum available in Gargett et al. Being undervalued, the direct estimates are a factor of 2–2.5 smaller than the spectrum-based estimates. Taylor microscale Reynolds numbers for the present analysis range from 24 to 665. Anisotropy is present at all resolved scales. At the transition between inertial and dissipation range the longitudinal spectra exhibit a flatter than −5/3 slope and form spectral bumps. Second-order statistics of the velocity gradients show a tendency toward isotropy with increasing Reynolds number. Dissipation exceeds production at all measurement heights, but the difference varies with elevation. Close to the bottom, the production is 40%–70% of the dissipation, but it decreases to 10%–30% for elevations greater than 80 cm.

An approach to determine coefficients of logarithmic velocity vertical profile in the bottom boundary layer

2021 ◽  
Author(s):  
Xiaowei Wei ◽  
Yiming Zhang ◽  
Changming Dong ◽  
Meibing Jin ◽  
Changshui Xia
Keyword(s):  
Boundary Layer ◽  
Vertical Profile ◽  
Bottom Boundary Layer ◽  
Bottom Boundary

Internal solitary wave bottom boundary layer dissipation

2021 ◽  
Vol 6 (7) ◽  
Author(s):  
S. Zahedi ◽  
P. Aghsaee ◽  
L. Boegman
Keyword(s):  
Boundary Layer ◽  
Solitary Wave ◽  
Internal Solitary Wave ◽  
Bottom Boundary Layer ◽  
Bottom Boundary
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