Experimental modeling of gravity underflow in a sinuous submerged channel

Abstract

[1] This paper describes the results of an experimental study involving density driven gravity underflow in a submarine sinuous channel. A single bend channel with sine generated planform was constructed inside a laboratory basin. Saline density flow was released at a constant rate at the upstream end of the channel which was submerged under fresh water. Instantaneous velocity data recorded within the body of the developed current were used to derive the vertical structures of the streamwise and cross-stream velocity. The vertical distributions of the streamwise and lateral velocity were found to vary modestly between cross sections and also within an individual cross section. The distance of the maximum velocity position from the bed was found to vary between 0.4 and 0.6 times the local current thickness. In the vicinity of the bend apex the curvature effect led to the development of two helical flow cells with one forming on top of the other. The sense of rotation of the bottom cell was similar to that observed in curved open channel flow, while the upper circulation cell had an opposite sense of rotation. Turbulent kinetic energy profiles were derived from the instantaneous velocity data. The observed turbulent kinetic energy profiles confirm some previous observations that the location of the maximum velocity in a density underflow also corresponds to significant reduction in turbulent kinetic energy.

Coriolis forces influence the secondary circulation of gravity currents flowing in large‐scale sinuous submarine channel systems

“…The velocities were averaged over an interval of Figure 1. (a) In a curved channel the velocity maximum of the gravity current is close to the base of the flow, the secondary circulation consists of a basal flow towards the outer bend and a return flow near the surface and sometimes below the velocity maxima [Keevil et al, 2006;Islam and Imran, 2008]. (b) In a straight channel Coriolis forces deflect the upper density interface and drive secondary circulations due to the presence of Ekman boundary layers.…”

“…For such velocity profiles [e.g., Corney et al, 2008;Keevil et al, 2006] the secondary flow near the base is directed towards the outer bend, with a return flow near the surface, in contrast to river flows. In some experiments using square channels there is an additional secondary flow directed towards the outside bend below the velocity maximum [Imran et al, 2007;Islam and Imran, 2008].…”

“…The dynamics of large-scale non-depositional turbidity currents are often assumed to be similar to gravity currents, so that previous experiments in sinuous channels [e.g., Keevil et al, 2006;Imran et al, 2007;Islam and Imran, 2008] have used studies of saline gravity currents to gain insight into the secondary circulation in turbidity currents. An open question is whether the secondary circulation in large-scale turbidity currents flowing down a sinuous channel will be dominated by centrifugal forces or by Coriolis forces.…”

“…Recent non-rotating experiments on channelized turbidity currents have shown that the morphological evolution and associated depositional histories of submarine channel systems are highly influenced by the secondary flow structures within the channel, which determine where erosion and deposition will occur [Keevil et al, 2006;Straub et al, 2008;Islam and Imran, 2008]. The main focus in these non-rotating experiments has been to investigate the secondary circulation due to an imbalance of centrifugal and pressure gradient forces in channel bends, which plays a major role in the formation of superelevation of levee systems at the outer bend [e.g., Straub et al, 2008;Kane et al, 2010].…”

A general model for the helical structure of geophysical flows in channel bends

“…However, the first physical experiments of helical circulation in turbidity currents showed an opposite direction of rotation -with the near-bed flow moving towards the outer bank (Corney et al, 2006;Keevil et al, 2006). To complicate matters further, both directions of helical circulation (river-like and river-reversed) have subsequently been observed in turbidity current experiments and models, depending on flow conditions and channel morphology (Imran et al, 2007;Islam and Imran, 2008;Cossu and Wells, 2010;Abad et al, 2011;Giorgio Serchi et al, 2011;Huang et al, 2012;Dorrell et al, 2013;Janocko et al, 2013;Bolla Pittaluga and Imran, 2014;Ezz and Imran, 2014).…”