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

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 ͗uЈuЈ͘, ͗wЈwЈ͘, and Ϫ͗uЈwЈ͘ 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 Ϫ5/3 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.

Estimating turbulent kinetic energy dissipation using the inertial subrange method in environmental flows

“…Hence, their idealized two-dimensional (2D) laboratory experiments (i.e., ) suggest that for boundary-induced shear flows the inertial subrange was least influenced by anisotropy in the longitudinal, followed by the vertical, and then the transverse directions. Field observations of boundary layer flows using 2D particle imagery systems in the x 1 -x 3 plane also revealed that the low wavenumber bound of the inertial subrange occurred at a larger wavenumber in compared to (Doron et al 2001;Luznik et al 2007). The Saddoughi and…”

“…Note that the lines of constant log 10 B (or log 10 I) in panel A were created with n = 1.0 × 10 -6 m 2 s -1 observed for the SS data. The NWS data have n = 1.36 × 10 -6 m mogorov scaling to nondimensionalize the spectra and included the Gargett et al (1984) universal spectra as digitized by Luznik et al (2007). In the first example (I ≈ 1000), we did not resolve the highest half decade of the inertial subrange; our sampling frequency was too slow for the observed .…”

PIV Measurements in the Atmospheric Boundary Layer within and above a Mature Corn Canopy. Part I: Statistics and Energy Flux

“…12 the dissipation spectra, 2 1 E 11 ( 1 ) and 2 1 E 33 ( 1 ), for the two components, and compare them with the universal spectrum (Gargett et al 1984;Luznik et al 2007). The spectral estimates of dissipation are used here without further refinement to match the universal spectra.…”

Ornl Adcp Post-Processing Guide and Matlab Algorithms for MHK Site Flow and Turbulence Analysis

“…ADCPs have been used to characterize mean velocity and turbulence intensity in rivers (Lemmin & Rolland 1997;Barua & Rahman 1998;Muste et al 2004a;Muste et al 2004b;Le Coz et al 2007;Stone and Hotchkiss 2007;Gunawan et al 2010a), oceans/tidal channels (Lohrmann et al 1990;Stacey et al 1999;Cheng et al 2000;Luznik et al 2007;Epler et al 2010;Thomson et al 2010) and laboratories (Nystrom et al 2007). ADCPs have also been used for measuring secondary current (Dinehart & Burau 2005a;Szupiany et al 2007;Gunawan et al 2010b;Gunawan et al 2010b), bed shear stress (Rennie et al 2002;Rennie & Church 2007;Sime et al 2007), dispersion coefficient (Carr & Rehmann 2007), sediment transports (Holmes & Garcia 2002;Dinehart & Burau 2005b;Merckelbach 2006;Klein 2003) and tidal flux (Turnipseed 2002).…”