Formation of tidal starting-jet vortices through idealized barotropic inlets with finite length

Abstract

This paper presents a surface particle image velocimetry study to investigate the dynamics of shallow starting-jet dipoles formed by tidal flow through inlets and their interaction with vorticity formed at the inlet channel lateral boundaries. Vortical structure in the flow field is identified using a local swirl strength criterion evaluated from the twodimensional flow field. The starting jet dipole vortices and vortices formed as the lateral boundary layers are expelled during flow reversal are characterized by their trajectory, size, and circulation. Using these quantities, a model is developed to predict the size and strength of the expelled lateral boundary layer vortices based on the inlet velocity, channel length, and width of the lateral boundary layer. The expelled boundary layer vortices are found to disrupt the formation of the primary tidal jet dipole through two mechanisms. First, because the boundary layer vortices themselves form a dipole with each half of the starting-jet dipole, the starting-jet vortices are pulled apart and advected away from the inlet mouth early in the tidal cycle, resulting in a reduction in the spin-up time and the amount of vorticity input during starting-jet vortex formation. Second, the advection of each dipole away from the inlet disconnects each starting-jet vortex from the starting jet; hence, the vortices are not fed by fluid in the jet or energized by shear in the jet boundary layers. These influences of the lateral boundary layer on the starting-jet vortices' formation and propagation are found to be a function of the channel length L, maximum velocity U , and tidal period T , resulting in a predictive value to characterize their trajectory, strength, and evolution.

Observations and Analysis of the Horizontal Structure of a Tidal Jet at Deep Scour Holes

“…Furthermore, the tidal jets vary periodically in time in response to the tide, and a significant asymmetry between ebb and flood flow may exist (Valle-Levinson & Guo, 2009). Developing jets are typically associated with a vortex cap of two counter rotating vortices (Bryant et al, 2012;Hench et al, 2002;Wolanski et al, 1988). They form and grow directly downstream of the tidal inlet (Nicolau Del Roure et al, 2009) due to the growing intensity of the shear layer that occurs after slack tide (Wells & van Heijst, 2003).…”

Lagrangian flow measurements and observations of the 2015 Chilean tsunami in Ventura, CA

“…When the flow reversed toward offshore (negative u y ), transitional jets were expelled from the bifurcation corners, carrying three tracers that experienced surface speeds up to 1 m/s (Figure 5b). This pattern appears similar to larger tidal flows through inlets, where starting-jet and expelled boundary layer vortices form at the beginning of ebbing [Bryant et al, 2012].…”

Modeling the Dynamics of Small‐Scale River and Creek Plumes in Tidal Waters

“…Our understanding of the phenomenon is that inertia drives the central lobe offshore, while strong lateral buoyancy forcing near the mouth acts on the slow boundary‐layer outflow at the edges of the mouth channel, creating the lateral lobes. Also of interest are works by Kashiwai (1985a, 1985b) and Bryant et al (2012), who studied the influence of the lateral boundary layer and how tides may cause double dipole formation at the mouth of the channel. The supercritical flows associated with channel geometry are influenced by tidal fluctuations.…”