Oscillatory flow across an irregular boundary

Abstract

[1] Laboratory experiments examining oscillatory flow along a coastline or isobath with a series of headlands or ridges reveal a mechanism for transfer of momentum and mass from the boundary into the interior flow through the establishment of organized residual flow patterns. Particle imaging velocimetry is used to visualize the vorticity field and to quantify large-scale residual circulations generated near the region of roughness. Two flow regimes are observed for differing ratios of alongcoast tidal excursion, L, to the length of the roughness region, D. For L/D > 1 a weak inflow is produced in the vicinity of the roughness region, with a corresponding alongshore flow away from the region. For L/D < 1 a strong outflow jet is established near the center of the roughness region. The two flow regimes result from different residual vorticity patterns and rely on eddies being longlived relative to the tidal period. Thus these results are relevant to flows in which dissipation is weak relative to the mean flow kinetic energy such as for tidal flow in deep water. Flow past a single roughness element is used as an analog to tidal flow past a headland and is represented by the high L/D limit.

Eddy Wake Generation From Broadband Currents Near Palau

“…If the tidal currents are large enough to produce flow reversals on some phases of the tide (U 0 < U 1 , lower panel), vortices of both signs are expected to form, though asymmetric in strength. Though beyond the scope of this paper to investigate, we conjecture that in either case the pairing and interaction of vortices would be quite different than that investigated for the tide-only case by studies such as Signell and Geyer (1991), Pawlak and MacCready (2002), and Callendar et al (2011).…”

Observations on the evolution of tidal vorticity at a stratified deep water headland

“…Nonetheless, using , and if we assume an eddy size of 1 km, as would be expected from flow past a sharp step and as substantiated by the bowtie observations in Figure 4, the observed vortex decay time implies a horizontal diffusivity on the order of 40 m 2 s −1 . An eddy viscosity argument based on estimates of turbulence downstream of a sharp step yields an upper bound for horizontal diffusivity of [ Pawlak and MacCready , 2001]. Using scales for TTP, we can, at best, account for roughly a third of the necessary value of horizontal diffusion.…”

“…[ Wolanski , 1986] observed formation of internal tides and enhanced mixing associated with a baroclinic island wake in deep water. Various flow regimes may also result from interactions between long‐lived vortices generated by coastal bathymetry [ Pawlak and MacCready , 2001]. Tidal flow around a headland, for example, can result in either residual flow towards (long‐lived vortices) or away from the coast (short‐lived vortices).…”

Hydrodynamic evaluation of a flood embankment in the Amazon estuary region, Brazil

“…For example, Pawlak and MacCready (2002) examined oscillatory flow along a coastline with a series of headlands or ridges, and found that the establishment of organised residual flow patterns was associated with mass and momentum transfer from the open boundary into the interior flow domain. This phenomenon is potentially important for projects involving ports, piers, groynes and land reclamation.…”