Vorticity and Turbulent Properties in Tidal and Shelf Bottom Boundary Layers
1998
Sanford, Thomas B | Lien, Ren-Chieh
Our goal is to contribute to a better understanding of small-scale processes in shallow water and coastal flows to provide better, more physically based parameterizations for coastal models. We seek to understand how high Reynolds number coastal flows interact with boundaries to produce tangential stress, dissipation, mixing, and secondary circulation. Detailed comparison of our field observations with direct numerical simulations should improve contemporary model parameterization schemes. The approach we have taken is to measure vorticity, velocity, dissipation, and water properties within bottom boundary layers in local tidal channels with variable bottom topography. The most notable sensor is an electromagnetic vorticity detector, which determines a component of relative vorticity based on the principles of motional induction. An experimental site in Pickering Passage in the South Puget Sound was selected based on a detailed multi-beam bathymetry survey. Topographic relief is less than 0.3 m for distances of 200 m upstream of the measurement site. Other locations offer regular patterns of bedforms, such as waves with heights of 0.5-1 m and wavelengths of 20-30 m, and a prominent ridge about 500-m long, rising 10 m above a flat bottom. In addition to velocity and vorticity, observations of temperature, electrical conductivity, pressure, altitude above the bottom, and turbulent kinetic energy dissipation rate were obtained. Our instrument provides the first field measurements of turbulent vorticity and vorticity flux in a tidal turbulent boundary layer.
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