The orientation of helical flow in curved channels

Abstract

The planform patterns of meandering submarine channels and subaerial fluvial bends show many similarities that have given rise to strong analogies concerning the fluid dynamics of these channel types. Existing models of helical motion in open-channel bends depict flow that is characterized by surface flow towards the outer bank, and basal flow towards the inner bank. This paper investigates and compares, through an analytical model and physical experiment, flows within fluvial meanders, and submarine channel bends that contain density-driven gravity currents. The results indicate that the sense of helical motion can be reversed in submarine bends that contain density currents when compared with fluvial bends, and that the orientation of the helical flow is dependent on the vertical distribution of downstream velocity. Specifically, the sense of helical motion is reversed in bends when the maximum downstream velocity is near the bed, resulting in near-bed flow towards the outer bank. These findings suggest that the dynamics of sediment transport and deposition in curved channels with such velocity profiles will be fundamentally different to those currently assumed from sinuous openchannels.

Flow processes and sedimentation in contourite channels on the northwestern South China Sea margin: A joint 3D seismic and oceanographic perspective

“…4 Kneller, 2009;Pyles et al, 2012), direct measurement of density flows in modern sinuous submarine channels and similar downslope analogs (e.g., Vangriesheim et al, 2009;Parsons et al, 2010;Sumner et al, 2014), physical experiments (e.g., Corney et al, 2006;Keevil et al, 2006;Peakall et al, 2007;Wells, 2010, 2013;Ezz et al, 2013;Janocko et al, 2013;Cossu et al, 2015), and numerical simulations (e.g., Corney et al, 2006;Imran et al, 2007;Giorgio Serchi et al, 2011;Dorrell et al, 2013;Janocko et al, 2013;. However, whilst there is a good understanding of the underlying flow processes in contourite channels (e.g., Faugères et al, 1993;Rebesco, 2005;Faugères and Stow, 2008;Rebesco et al, 2014), the detailed three-dimensional flow dynamics and their control on sedimentation in isobath-parallel contourite channels remain comparatively poorly studied.…”

“…Ekman boundary layers will be directed to the left (looking 14B, 14 C, and 15B). They show a vertical structure as governed by the vertical velocity profile (Corney et al, 2006(Corney et al, , 2008Dorrell et al, 2013;Peakall and Sumner, 2015), with low density stratification induced by the likely presence of fine-grained sediment, leading to the vertical position of the downstream velocity (U max ) being…”

“…14B and 15B, respectively). Centrifugal forces have a pronounced vertical structure and increase upwards away from the bed, whereas pressure-gradient forces are constant through the depth of NDPW-CCs (e.g., Corney et al, 2006Corney et al, , 2008. The interplay of upslope directed Coriolis forces versus downslope directed pressure-gradient and centrifugal forces acting on the NPDW-CCs, therefore, yields an imbalance, through the flow depth, and resultant transverse tilt of contour currents within the studied channels (e.g., Cossu et al, , 2013.…”

Experimental modeling of gravity underflow in a sinuous submerged channel

“…The experiment of Corney et al [2006] and Keevil et al [2006] involved flow that was rather deep with a flow thickness to width ratio of 0.71 and flow thickness to centerline radius of curvature ratio of 0.47. Imran et al [2008] showed that the analytical model utilized by Corney et al [2006] predicts the maximum radial velocity to be more than twice the maximum tangential velocity when the levee height of their experimental channel is used as the scale for flow depth as done by Corney et al [2006].…”

“…[6] Recently, Corney et al [2006] conducted small scale laboratory experiments on saline density flow in a curved channel with multiple bends. They measured the velocity field at the apex of a channel bend using an array of unidirectional Ultrasonic Doppler Velocity Probes (UDVP).…”